Startseite Naturwissenschaften Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass
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Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass

  • Mageswari Manimaran , Mohd Nurazzi Norizan EMAIL logo , Mohamad Haafiz Mohamad Kassim , Mohd Ridhwan Adam , Norli Abdullah und Mohd Nor Faiz Norrrahim EMAIL logo
Veröffentlicht/Copyright: 16. April 2025
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Nanotechnology Reviews
Aus der Zeitschrift Nanotechnology Reviews Band 14 Heft 1

Abstract

Recent advancements in nanotechnology have expanded the applications of cellulose nanoparticles (CNPs) isolated from various types of biomass waste like oil palm empty fruit bunches. These applications are particularly enhanced by incorporating nanoparticles or polymers. However, a significant challenge in synthesizing CNP-based nanocomposites lies in the selection of appropriate synthesis methods, as ineffective techniques can result in poor compatibility between nanoparticles. To overcome this issue, surface modification through carboxymethylation has emerged as an effective strategy. This process introduces anionic groups (−CH2COONa+) onto the CNP surface, producing anionic nanocellulose particles (ACNPs) that act as capping agents to enhance nanoparticle incorporation. Despite these advancements, the optimum reaction time for isolating ACNPs from CNPs, particularly nanocrystalline cellulose, remains underexplored. This study investigates the effect of varying carboxymethylation reaction times (30 min, 2, 4, 6, and 8 h) on the synthesis of ACNPs. Characterization techniques, including Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, transmission electron microscopy, zeta potential analysis, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), were employed. The results indicate that a reaction time of 4 h is optimal for carboxymethylation. ACNPs synthesized at this duration exhibit good dispersion, improved thermal stability, and a high zeta potential value (−41 mV) compared to CNPs (−25 mV). FTIR analysis reveals new peaks at 1,564, 1,432, and 1,321 cm⁻¹, corresponding to the carboxyl, methyl (−CH2), and hydroxyl groups of the carboxymethyl group (−CH2–COONa), respectively. Additionally, XPS results show a high concentration of Na⁺ ions in ACNPs synthesized at 4 h. Beyond this reaction time, Na⁺ concentration decreases.

Keyword: nanocellulose; oil palm empty fruit bunch; carboxymethylation reaction

1 Introduction

Oil palm is the most cultivated plant in Malaysia with approximately 5.65 million hectares of planted area and also with annual production of crude palm oil production around 18.55 million metric tons according to the 2023 statistic [1]. At the same time, there has been a significant increase in biomass waste from plantations and milling activities, as illustrated in Figure 1. Oil palm biomass produced from plantations includes oil palm trunks and oil palm fronds, while milling operations generate additional biomass such as oil palm empty fruit bunches (OPEFB), mesocarp fibre, and palm kernel shells. Annually, approximately 127 million tons of oil palm biomass are generated, presenting substantial environmental and economic challenges that require immediate attention [2]. If left unmanaged, this enormous volume of biomass could contribute to deforestation, air pollution, and greenhouse gas emissions, further exacerbating climate change.

Figure 1 The statistics of oil palm biomass generated in Malaysia annually.
Figure 1

The statistics of oil palm biomass generated in Malaysia annually.

Therefore, it is crucial to implement efficient and eco-friendly solutions to mitigate potential harm and unlock the full potential of these resources for renewable energy, waste reduction, and other beneficial uses. Hence, the development of advanced materials with superior properties has led to the significant interest of researchers in utilizing oil palm biomass in various applications in order to produce a valuable product from oil palm biomass. One of the valuable products from the oil palm biomass is the nano-scaled sized materials known as nanocellulose, which has superior properties such as high reinforcing strength and stiffness, which is often times comparable to Kevlar and steel, large surface area, remarkable optical properties, tailored crystallinity, and easy surface functionalization due to abundance of hydroxyl groups (−OH) [3]. Not only that, due to its high surface area and biocompatibility, nanocellulose from oil palm biomass has become particularly promising materials as a bio-reinforcing filler or in the production of biopolymer composites [4,5]. The incorporation of the cellulose nanoparticles (CNPs) with different types of nanoparticles can improve mechanical, thermal, and electrical properties, which exhibit unique characteristics that differ from the bulk counterparts [4].

However, very limited studies are conducted by researchers on the incorporation of different types of nanoparticles such as metal oxide or carbon-based with oil palm-based CNPs to produce nanocomposite rather than film and polymer-nanocomposite. This is mainly due to the −OH group on the CNP surface, which resulting issues of agglomeration, poor dispersion, and compatibility, which should be addressed in order to produce a high-quality nanocomposite [6]. Metal oxide nanoparticles may be separately synthesized and added to nanocellulose (ex situ processes), or they can be synthesized using nanocellulose as a template (in situ processes) [7]. In the latter case, the precursor is trapped inside the CNP network and then reduced to metal oxide.

As a result, concern about the synthesis and functionalization method of nanocomposite is crucial as it can help overcoming the issue mentioned above. There are four ways to synthesize the nanocomposite: (1) simple blending, (2) by the external reducing agent, (3) surface modification, and lastly, (4) without an external reducing agent, as shown in Figure 2 [8]. The most widely used method based on recent studies is surface modification for film production and bio-composite synthesis. The surface chemical modification methods of CNPs can be divided into two, which are (a) chemical modification (esterification, silylation, cationization, treatment with isocyanates, and so on) or (b) grafting macromolecules on the CNPs surface [9].

Figure 2 Four methods to synthesize nanocomposite: (1) simple blending, (2) by using an external reducing agent, (3) surface modification, and lastly (4) using without external reducing agent. Reproduced from ref. [8].
Figure 2

Four methods to synthesize nanocomposite: (1) simple blending, (2) by using an external reducing agent, (3) surface modification, and lastly (4) using without external reducing agent. Reproduced from ref. [8].

In addition, there is a surface modification that aims to introduce charged or hydrophobic moieties on the CNP surface such as esterification, etherification (carboxymethylation), silylation, amidation, carbamation, sulfonation, and phosphorylation. Hence, the presence of an abundance of the −OH group on CNPs offers a unique platform for anchoring a wide spectrum of functional molecules such as aldehydes, carboxylic acids, and amines as well as macromolecule groups using these modifications [10]. Moreover, there are some surface modifications that can generate the anionic charges on the surface of the CNPs to produce anionic nanocellulose (ACNPs), such as carboxymethylation, sulfation, and phosphorylation. The anionic charge plays a crucial role and can act as a capping agent for the incorporation of the nanoparticles and also in enhancing compatibility, dispersion, and stability of the nanoparticles within the composite materials by preventing agglomeration. In that, the anionic charge from the nanocellulose will create repulsive forces that can reduce or prevent nanoparticles from clumping together, ensuring uniform dispersion in the matrix. The reported effective used method of surface modification for the ACNPs isolation is the carboxymethylation process [11].

Reaction time is a critical factor in the carboxymethylation process, as it directly influences the degree of substitution (DS) of anionic groups (−CH2COONa+) on the CNP surface. The DS represents the average number of hydroxyl groups per glucose unit of cellulose replaced by anionic groups. This study explores the use of OPEFB as a sustainable biomass source for synthesizing ACNPs by varying the carboxymethylation reaction times (30 min, 2, 4, 6, and 8 h). While significant research has focused on synthesizing anionic carboxymethyl cellulose using cellulose as the starting material, studies on synthesizing anionic nanocellulose – especially from nanocrystalline cellulose – remain limited. Moreover, the optimum reaction time for the carboxymethylation of nanocellulose has not been fully explored. For carboxymethyl cellulose, the optimum reaction time typically ranges from 3 to 4 h, as shown in Table 1. However, it is unclear if this range applies to anionic nanocellulose synthesis, necessitating further investigation into the ideal reaction conditions. Given the nano-sized nature and high surface area of nanocellulose compared to cellulose, a shorter reaction time might be sufficient. Consequently, reaction times of 30 min and 2 h were included in this study, along with longer times (6 and 8 h), to determine the optimal reaction duration and identify when the overall properties of ACNPs begin to decline or indication of the optimization parameter for the formation of anionic charge.

Table 1

The reaction time of carboxymethyl cellulose from various types of biomass waste

Type of biomass waste Starting materials Reaction time (h) Ref.
Sago waste Cellulose 3 [12]
Banana peel Cellulose 4 [13]
OPEFB Cellulose 3 [14]
Agricultural wastes Cellulose 8 [15]
OPEFB (stalk fibre) Cellulose 3 [16]
Coconut fibre Cellulose 1 [17]
OPEFB Cellulose 4 [18]
OPEFB Cellulose nanofibre 3 [19]
— Cellulose acetate nanofibres 6 [20]

To address this gap, the present study aims to determine the optimum reaction time for synthesizing ACNPs. A range of reaction times was selected to ensure a comprehensive evaluation and to identify the most effective duration for achieving optimal ACNP synthesis. These ACNPs have potential applications across various fields, particularly when combined with different types of nanoparticles, such as bismuth ferrite for anionic dye degradation [21] or graphene to produce composite aerogel [22] or as an electrochemical working electrode [23] and as a stabilizer in nanofluids in thermal applications. Additionally, ACNPs can be combined with polymers like PVA to produce films suitable for optoelectronic applications, energy storage [24], and numerous other uses.

2 Materials

Sodium hydroxide (NaOH), sodium chlorite (NaClO2, 80% w/w), and sodium chloroacetate (ClCH2COONa) were supplied by Sigma Aldrich. Sulfuric acid (H2SO4, 95–97%) and glacial acetic acid (CH3COOH, AR grade) were purchased from Quality Reagent Chemicals (QRec). OPEFB was taken from Oriental Rubber & Palm Oil Sdn. Bhd, Johol, Negeri Sembilan. All reagents were of analytical grade and were used without further purification. All aqueous solutions were prepared with deionized (DI) water.

3 Methodology

3.1 Nanocellulose isolation

3.1.1 Sample preparation

OPEFB was first ground using a rotor mill to fibre length around 3 mm, then sieved with 35-mesh sieves to obtain the constant fibre diameter between 2.5 and 5 mm. Then, the raw OPEFB fibres were washed with warm water (50°C) for 20 min to eliminate water-soluble impurities, as shown in Figure 3(a), and then dried in an oven at 60°C until a constant weight was attained.

Figure 3 The three important steps in the isolation of CNPs: (a) washing and grinding of OPEFB fibre, (b) bleaching process, (c) alkaline treatment, and lastly, (d) acid hydrolysis.
Figure 3

The three important steps in the isolation of CNPs: (a) washing and grinding of OPEFB fibre, (b) bleaching process, (c) alkaline treatment, and lastly, (d) acid hydrolysis.

3.1.2 Bleaching process

Then, the dried raw OPEFB fibre was added with 2% w/v NaClO2 for the bleaching process, which was prepared by mixing equal volumes of acetate buffer (a mixture of NaOH and CH3COOH) at pH 4, consisting of 27 g NaOH and 75 mL glacial acetic acid, diluted to 1 L with DI water as demonstrated in Figure 3(b). The bleaching process was conducted in triplicate with constant stirring for 2 h at a temperature of 80°C, utilizing an overhead stirrer at 300–400 rpm in a water bath. The treated fibre underwent a washing process with DI water until a neutral pH (6–7) was attained, and subsequently, it was dried in an oven at 60°C until a constant weight was achieved. Now, the product is referred to as bleached OPEFB fibre.

3.1.3 Alkaline treatment on bleached OPEFB fibre

After that, the bleached OPEFB fibre was treated with 4% (1.5M) NaOH solution to completely remove non-cellulosic substances (hemicellulose and lignin). This alkaline treatment was repeated three times under continuous stirring for 2 h at 80°C under constant stirring using an overhead stirrer (300–400 rpm) in a water bath, as shown in Figure 3(c). After the treatment, the resulting pulp was filtered using Whatman filter paper (pore size = 11 μm) and washed with DI water until the pulp reached pH 6–7. The retentive was collected and kept in the freezer for 24 h for freeze drying. After the freeze dry the sample is known as cellulose.

3.1.4 Acid hydrolysis on cellulose

Next, acid hydrolysis was performed using 58 wt% of H2SO4, with an acid-to-pulp ratio of 20 mL/g for 60 min, as illustrated in Figure 2(d). The reaction was conducted under constant stirring using an overhead stirrer (120–230 rpm) at 45°C using a water bath. Upon completion, 10 times the volume of cold water (4°C) was added to the hydrolysed mixture to stop the reaction. The mixture was then centrifuged at 7,500 rpm for 15 min to collect the sediment. The collected sediment was then dialyzed using a dialysis membrane with a molecular weight cut-off of 12,000–14,000 Da against DI water for 3–4 days until pH to 6–7. The DI water is changed every hour or daily to expedite the neutralization process. Then, the sample was subjected to ultrasonication using a ½ in. sonication probe at 60% amplitude for 5 min in an ice bath to disperse the sample. The well-dispersed samples were frozen for 24 h before freeze-dried at −95°C for 48 h to obtain the nanocellulose, which will be denoted as CNPs.

3.2 Anionic nanocellulose isolation

The oil palm-based CNPs were first added into the 1.5 M NaOH solution and stirred constantly using the magnetic stirrer for 15 for a constant dispersion as shown in Figure 4. After 15 min, the solution was filtered using the filter paper and then washed with 0.05 M NaOH to remove the unreacted NaOH. After this process, the resultant residue will be known as sodium CNPs (NaCNPs), which will further react with 1.0 M ClCH2COONa at different reaction times starting with 30 min, then 2, 4, 6, and 8 h with constant stirring using a magnetic stirrer. Finally, the obtained anionic CNPs (ACNPs) will be washed thoroughly with DI water until pH around 6–7 and dried in air for 24 h. All this step was carried out at 25°C or room temperature.

Figure 4 The steps to produce ACNPs.
Figure 4

The steps to produce ACNPs.

4 Sample analysis and characterizations

Seven types of characterization were conducted to determine the optimum reaction time for the ACNPs. Structural characterization was performed using Fourier transform infrared (FTIR) (Shimadzu) and RAMAN spectroscopy (Renishaw). The chemical state and binding energy of ACNPs were analyzed by X-ray photoelectron spectroscopy (XPS) using the Axis Ultra DLD XPS (Kratos). Physical characterization included zeta potential measurement using MALVERN and particle size analysis based on transmission electron microscopy (TEM) images (ImageJ) obtained with a Zeiss Libra 120 (Germany). Finally, the crystallinity and thermal stability of the sample were evaluated using X-ray diffraction (XRD) (Bruker) and thermogravimetric analysis (TGA) analysis.

5 Result and discussion

5.1 FTIR analysis of ACNPs

The chemical characteristics of cellulose are influenced by the sensitivity of the β-1,4-glycosidic linkages to hydrolytic attack and by the presence of three hydroxyl groups: the primary OH on C(6) and the secondary OH groups on C(2) and C(3) in the anhydroglucose units [25]. The surface modification of CNPs occurs in two phases: mercerization and carboxymethylation. During this process, some of the OH groups in the CNPs are etherified with sodium carboxymethyl groups (−CH2COONa), as shown in Figure 5.

Figure 5 The synthesis of ACNPs from the CNPs via the carboxymethylation of the OH group.
Figure 5

The synthesis of ACNPs from the CNPs via the carboxymethylation of the OH group.

The initial stage, mercerization, serves as a swelling and impregnation phase, allowing NaOH to penetrate the cellulose matrix, forming alkaline cellulose (Na-CNPs). Na-CNPs exhibit significant reactivity with salt named sodium chloroacetate (C2H2ClNaO2), which is then used in the subsequent carboxymethylation phase. Sodium chloroacetate is a chemical compound that contains an acetate group (CH2COO−) that bonded to a chlorine atom (Cl) and the sodium ion (Na+).

Figure 6 shows the FTIR results of the ACNPs at varying reactions. It is obvious one prominent narrow absorption peak was observed in the range of 3,348 cm−1, which refers to the stretching vibration of the hydroxyl (−OH) group [26,27]. This peak refers to the intermolecular hydrogen bonding network within the CNPs chain. Another notable peak can be observed at the peak around 2,904 cm−1 in both CNPs and ACNPs, at all reaction times representing the stretching vibration of the C–H stretching of −CH2 and −CH3 groups [19]. These two peaks refer to the main polysaccharide nature, which is composed of glucose units [27]. However, −OH stretching vibration for ACNPs at different reaction times shows a wide and weak absorption band with low intensity at 3,415 cm−1 compared to CNPs. This is due to the low number of −OH groups in ACNPs, which can be due to the substitution of the bulky functional group (−CH2−COOH) in ACNPs or the high density of the functional group [28]. In other words, the functionalization can alter the hydrogen bonding network and molecular conformation of cellulose, potentially leading to a reduction in the number of available −OH groups or changes in their accessibility. Among the functionalized samples, ACNPs-30 min, ACNPs-2 h, and ACNPs-4 h show weaker and wider band (high-intensity changes compared to CNPs (70–40%), whereas ACNPs-6 h and ACNPs-8 h (exhibit lower intensity changes compared to CNPs (55–40%). This indicates that the OH groups in ACNPs-30 min, ACNPs-2 h, and ACNPs-4 h underwent more substantial functionalization than those in ACNPs-6 h and ACNPs-8 h. The same applies to the peak around 2,904 cm⁻¹, where ACNPs exhibit lower intensity compared to CNPs. This reduction is attributed to surface modification, which alters the number of methyl and methylene groups present on the surface of the CNPs. The replacement of some −OH groups by anionic groups or changes in the accessibility of these C–H groups leads to the observed decrease in intensity in this region. Next, the peak from 1,700 to 1,300 cm⁻¹ is presented in Table 2 by comparing the peak that is present in this work with the previous study.

Figure 6 FTIR spectra CNPs and ACNPs at different reaction times.
Figure 6

FTIR spectra CNPs and ACNPs at different reaction times.

Table 2

Comparison between the present and previous studies on the functional group that is presented according to the peak

Obtain peak (present work) cm⁻¹ Peak (wavelength) cm⁻¹ Functional group Justification Ref.
1,700–1,500 cm −1
1,637, 1,564 1,640 Water absorption The presence of the carbonyl group is confirmed [29]
1,585 C═O stretching
1,590 Asymmetric stretching vibrations of carboxylate ions (−COO−) [19]
1,600–1,640 Carbonyl group (C═O) [30]
1,572 Carboxyl group (COO−) and (C–CH2) indicating the presence of the sodium carboxymethyl (−CH2–COONa) group [20]
1,611
1,610 represents CH₂COONa [31]
1,606 Carbonyl group (C═O) of acetyl or carboxymethyl [11]
1,600 and 1,400–1,450 Carboxyl salt groups
1,589 Asymmetrical −COO group [27]
1,640 Water absorption [17]
1,589 Carboxylate [18]
1,414
1,565 Carboxyl group (COO−) [32]
1,500–1,300 cm −1
1,431, 1,379, 1,321 1,423 Symmetric stretching of the −COO group Conforming the presence of the C–O and −CH2 functional group [27]
1,415 Symmetric stretching vibration of carboxylate ion (−COO), stretching vibration of C−O [19]
1,320
1,426 CH2 scissoring and –OH bending vibration [28]
1,370
1,416 Symmetric stretching in the NaCOO group [29]
1,314
1,418 COO− group two symmetric carboxylate stretches [32]
1,416 [33]
1,324
1,424 −CH2 bonding [12]
1,322 −OH plane bending
1,315 C–O stretch in the carboxylate functional group [18]
1,100–1,000 cm −1
1,064 1,061 >CH–O–CH2 stretching, which indicates C–O–C ether linkage Proving the presence of the ether linkage [25]
1,060 >CH–O–CH2 stretching [12]
1,032 Ether linkages [34]

Next, in the range of 2,000–500 cm⁻¹, both CNPs and ACNPs exhibit similar peaks with some new peaks and changes in intensity. A sharp peak is present at 1,636 cm⁻¹ in CNPs, while the ACNP spectra show peaks at 1,641–1,651 cm⁻¹, with slight intensity variations. These peaks likely correspond to the bending vibration of water molecules (H−O−H bending) [29]. Furthermore, peaks at 1,568–1,571 cm⁻¹ corresponding to the asymmetric stretching vibrations of carboxylate ions (−COO⁻) are present only in ACNPs 30 min, ACNPs-2 h, and ACNPs-4 h [19]. This observation aligns with findings from Adinugraha and Marseno [30], who noted that wavenumbers between 1,600 and 1,640 cm⁻¹ represent carbonyl groups, confirming the introduction of carboxymethyl groups in CNPs during carboxymethylation. Zheng et al. [31] also agreed that the peak at 1,610 cm⁻¹ represents CH2COONa. Carboxyl salt groups typically appear around 1,600 cm⁻¹ and between 1,400 and 1,450 cm⁻¹ [11] or within the 1,500–1,700 cm⁻¹ range [27]. Moreover, based on the study by Ndruru et al., they point out that the peak around 1,685–1,537 cm−1 represents the −C═O functional group [17].

Besides that, peaks at 1,430, 1,369, 1,325 and 1,465, 1,431, 1,379, 1,321 cm−1 can be observed in CNP and ACNP spectra, respectively. The bending at 1,430 and 1,431 cm−1 for CNPs and ACNPs, respectively, represent similar functional groups, which are C–H bending vibrations in a cellulose structure. This is a common feature for cellulose and lignocellulosic materials. Furthermore, the peak at 1,379 cm−1 for the ACNPs corresponds to the C–H bending of CH2 groups similar to 1,369 cm−1 in CNPs. Next, the peak at 1,321 cm−1 in ACNPs is also similar to the peak at 1,325 cm−1 at CNPs, which indicates the C–H bending or C–O–C stretching vibration. Those slight shifts at those peaks may be due to the effect of the anionic modification. An additional peak at ACNPs at 1,465 cm−1 is often associated with the CH2 bending vibration. This additional intensity can also be influenced by the carboxylate group present. According to Suman et al. [28], the peak around 1,426 and 1,370 cm−1 in ACNPs are assigned to –CH2 scissoring and –OH bending vibration, respectively. Moreover, based on the studies of Devi et al. [32], the band at 1,418 and 1,325 cm−1 is referred to COO− group and −OH bending vibrations, respectively, whereas Zhang et al. [33] report that the peak around 1,416 and 1,324 cm−1 in the ACNPs spectrum is representing the two symmetric carboxylate stretches. Furthermore, Pushpamalar et al. [12] highlight that the band around 1,420 and 1,320 cm−1 are assigned to −CH2 scissoring and −OH bending vibration, respectively.

Furthermore, peaks around 1,163, 1,114, and 1,060 and also 1,163, 1,114, and 1,064 cm−1 are present in the CNPs and ACNPs spectrum, respectively. Those peaks represent C–O stretching in ether. Mohamed et al. [19] agreed that the range group at 1,112 cm−1 is referring C–O–C bond stretching present along the functionalization process. Finally, the band at 1,059 cm−1 is due to the >CH–O–CH2 stretching, which indicates C–O–C ether linkage [12,25]. This peak intensity in the ACNPs spectra is higher or stronger than at CNPs. This result was the same as discussed by Xu et al. [34], who synthesized the carboxymethyl cellulose nanocrystals from skimmed cotton and reported that the absorption peak of the ether band increased on functionalized CNPs. Moreover, the width of the absorption peak of ACNPs is narrower than CNPs, indicating the involvement of the hydroxyl group in the nucleophilic substitution reaction [34]. Table 2 shows the list of the peaks and corresponding functional groups.

5.1.1 Degree of substitution

From FTIR results, the calculated DS of carboxymethyl groups on the ACNPs provided insights into the optimum reaction time. The DS value represents the average number of hydroxyl groups replaced by other molecules in the polymer chain [13]. In cellulose chemistry, the reactivity of cellulose is primarily determined by its reactive groups. Specifically, the three hydroxyl groups in the anhydroglucose units of cellulose participate in substitution reactions, with the DS ranging from zero to three for each unit [35]. In the synthesis from CNPs to ACNPs, the DS refers to the number of carboxymethyl groups attached to each anhydroglucose unit [36]. Since the peak around 3,400 cm⁻¹ corresponds to the −OH group, it can be compared with the C═O peak to assess the extent of carboxymethyl substitution [21]. The DS of the carboxyl group in ACNPs is determined using the following equation:

(1) DS = T B − T 1,564 T B − T 3,400 ,

where T 3,400 represents the −OH stretching, T 1,600 are related to the carboxymethyl group, and T B is the baseline of the FTIR spectrum (100) [37]. Based on Figure 7, it is obvious that the optimum reaction time of carboxymethylation for the CNPs is 4 h due to the high DS of around 0.43, and the reaction time after the 4 h (6 and 8 h) shows low DS of around 0.26 and 0.23, respectively. This indicates that there are fewer available sites for substitution after 4 h or due to the degradation of the CNPs or the carboxymethylation agent, which can reduce the effective substitution with metal oxide.

Figure 7 Degree of substitution of ACNPs at different reaction times.
Figure 7

Degree of substitution of ACNPs at different reaction times.

5.2 Morphology analysis of ACNPs

Figure 8 shows the morphology of the CNPs and ACNPs at different reaction times. The morphology of the CNPs and ACNPs was similar, which is a needle-like shape as demonstrated in Figure 8(e). This indicates that the functionalization process did not affect the shape of the sample. The TEM image in Figure 8 reveals that the functionalization helps to improve the agglomeration of the CNPS, where the least agglomeration was observed in the ACNPs sample after 2 h of reaction time compared to the CNPs due to the presence of the anionic charge on the CNPs. However, after 6 h of reaction time, the ACNPs begin to agglomerate. It can be concluded that based on the TEM image, ACNPs-4 h (Figure 8(d)) and ACNPs-6 h (Figure 8(e)) show better distribution with the least agglomeration compared with ACNPs-30 min (Figure 8(b)), 2 h (Figure 8(c)), and 8 h (Figure 8(f)). This observation aligns with the findings of Li et al., who synthesized cationically modified cellulose nanocrystals. They reported that surface modification of cellulose nanocrystals enhances homogeneous dispersion due to electrostatic repulsion forces, while samples with low DS tend to aggregate and form bundles [38].

Figure 8 The TEM image at 20 KX magnification of the (a) CNPs and functionalized CNPs at different reaction times, (b) ACNPs-30 min, (c) ACNPs-2 h, (d) ACNPs-4 h, (e) ACNPs-6 h, and (f) ACNPs-8 h.
Figure 8

The TEM image at 20 KX magnification of the (a) CNPs and functionalized CNPs at different reaction times, (b) ACNPs-30 min, (c) ACNPs-2 h, (d) ACNPs-4 h, (e) ACNPs-6 h, and (f) ACNPs-8 h.

Particle diameters of the ACNPs at different reaction times were measured using ImageJ (Figure 9). The diameter of the CNPs is in the range of 10−40 nm, with an average diameter of 24.46 nm. After the functionalization, the sample at reaction time 30 min and 2 h shows a similar diameter ranging from 10 to 40 nm, with average diameters of 21.95 nm and 23.81 nm, respectively. After 2 h of reaction time, the diameter of the ACNPs started to decrease with the range from 14 to 30 nm, where ACNPs-4 h, ACNPs-6 h, and ACNPs-8 h showing the average diameter of 20.90, 18.80, and 20.01 nm, respectively. This indicates that the prolonged reaction time and excessive carboxymethylation may lead to fragmentation of the CNPs, which can decrease the average diameter size of the ACNPs. Based on Figure 9, the ACNPs-4 h show the constant particle size compared to the ACNPs-6 h and ACNPs-8 h.

Figure 9 Particle diameter of the (a) CNPs and functionalized CNPs at different reaction times, (b) ACNPs-30 min, (c) ACNPs-2 h, (d) ACNPs-4 h, (e) ACNPs-6 h, and (f) ACNPs-8 h.
Figure 9

Particle diameter of the (a) CNPs and functionalized CNPs at different reaction times, (b) ACNPs-30 min, (c) ACNPs-2 h, (d) ACNPs-4 h, (e) ACNPs-6 h, and (f) ACNPs-8 h.

5.3 Zeta potential of ACNPs

The zeta potential reflects the surface charge characteristics of particles and is closely associated with the stability of the particle system. The stability of functionalized CNPs can be assessed through their zeta potential values, as shown in Table 3. A zeta potential above 30 mV is generally considered stable with minimal agglomeration. This is due to the presence of sufficient carboxylic group charges (CH₂COO− Na⁺) among ACNPs, which create repulsive forces that prevent aggregation and enhance stability. According to the zeta potential values, ACNPs-6 h exhibit the highest zeta potential at −42.8 mV, followed by ACNPs-4 h at −41.8 mV, while CNPs show the lowest value at −23.9 mV. This indicates that functionalization significantly enhances the stability of CNPs. The zeta potential findings are consistent with the TEM images, where ACNPs-4 h and ACNPs-6 h demonstrate minimal agglomeration compared to other functionalized CNPs at varying reaction times. The functionalization increases the charge density on the nanocellulose due to the introduction of carboxyl groups, resulting in a more negative zeta potential, which enhances stability by increasing repulsive forces between particles. In other words, a higher DS strengthens steric hindrance, leading to better dispersibility and stability for ACNPs [39].

Table 3

The zeta potential value of each sample

Sample name Zeta potential (mV)
CNPs −23.9
ACNPs-30 min −28.1
ACNPs-2 h −34.4
ACNs-4 h −41.8
ACNPs-6 h −42.8
ACNPs-8 h −35.2

5.4 TGA and DTG of ACNPs

The TGA and DTG analysis presented in Figures 10 and 11 illustrate the thermal stability and weight changes of the samples under inert conditions as a function of temperature. The TGA curve reveals three main stages of decomposition: the first stage occurs between 30 and 50°C, followed by the second and third stages at 250–340°C and above 400°C, respectively. Figure 11 indicates that ACNPs at different reaction times exhibit higher water/moisture content compared to CNPs. This suggests that the surface modification of CNPs increased their hydrophilicity [17]. Among the ACNPs sample, ACNPs-4 h have higher moisture content, as it has a high maximum degradation temperature (44.56°C) compared to other ACNPs.

Figure 10 The TGA curve of the CNPs and the ACNPs at different reaction times.
Figure 10

The TGA curve of the CNPs and the ACNPs at different reaction times.

Figure 11 The DTG curve of the CNPs and the ACNPs at different reaction times.
Figure 11

The DTG curve of the CNPs and the ACNPs at different reaction times.

The decomposition temperature of the CNPs started at 251.12–329.11°C, while ACNPs sample at different reaction times started decomposition at temperatures ranging from 260 to 340°C. This temperature range decomposition of ACNPs is probably owing to depolymerization, with the formation of H2O, CO, CO2, and CH4 [40]. Due to the presence of COO− groups in ACNPs, decarboxylation occurs within this temperature range. This observation aligns with the findings of Mohamed et al. [19], who synthesized carboxymethyl cellulose nanofibres from OPEFB. They also reported that major thermal decomposition occurs above 220°C, primarily due to various degradation processes, including dehydration, decarboxylation, depolymerization, decomposition of the glycosyl units of cellulose, and the breakdown of cross-linked structures, as well as the decomposition of hydroxyl and carboxymethyl groups within the material.

In addition, the temperature at which the maximum degradation rate occurs can be used as an indicator of sample’s stability in comparative studies. Based on Figure 11, the maximum decomposition temperature of the ACNPs sample is higher (around 300°C) than that of CNPs (271. 54°C), indicating that the thermal stability of CNPs improves after functionalization. Besides that, relative weight (RW) refers to the weight of a sample remaining after heating to a specified temperature, expressed as a percentage of the initial weight of the sample. The information obtained from the RW in Table 4 provides insight into the thermal stability and decomposition characteristics of the materials. Higher RW% suggests better thermal stability; conversely, a lower RW% indicates a higher weight loss, suggesting more significant decomposition or degradation of the ACNPs.

Table 4

The summary of thermal stability of the CNPs and the ACNPs at different reaction times

Type of sample T onset (°C) DTG T max (°C) T end (°C) T 10% (°C) T 20% (°C) RW (%) at 800°C
CNPs 251.12 271.54 329.11 238.58 260.53 6.21
ACNPs-30 min 265.86 295.97 327.36 254.95 279.87 13.51
ACNPs-2 h 277.55 300.01 338.54 267.78 287.04 6.55
ACNPs-4 h 266.66 297.97 328.70 251.04 273.96 13.86
ACNPs-6 h 275.85 299.76 339.49 265.07 286.04 8.31
ACNPs-8 h 282.63 298.35 336.89 276.59 289.70 7.65

Among the ACNPs, the highest RW%, around 13%, is owned by the ACNPs-30 min and ACNPs-4 h, and the rest ACNP shows low RW%, around 6–8%. Based on the RW result, it can be concluded that the ACNPs-30 min and the ACNPs-4 h have higher thermal stability than other ACNPs at different reaction times. However ACNPs-4hrs and ACNPs-30 showing the lowest value of T onset, T max, T end, T 10%, and T 20%. This indicates that a significant portion of the materials remain after heating which is thermally stable even if the initial degradation starts at low temperature (low T onset). Moreover, the lower T onset and T end might indicate that the materials begin to decompose at a lower temperature, but the remaining substance contributes to the high RW and is more resistant to further degradation. Another reason could be due to the DS and char. Higher DS may lead to greater distribution of the crystalline structure, potentially reducing thermal stability. This finding is in good agreement with XRD and DS data, where the ACNPs-4 h have a high DS value (around −40 mV) and also a low crystallinity index of around 77% compared to other ACNP samples. Moreover, another possibility is that the significant amount of the materials has thermally stabilized into char, indicating that some of the components including the carboxymethyl group may contribute to the formation of stable char rather than fully decomposing. This stability can be beneficial in applications where thermal resistance is desired. The reduction in the thermal stability observed could be associated with the reduction in crystallinity upon carboxymethylation [41].

5.5 Crystallinity analysis of ACNPs

The crystallinity of ACNPs from XRD is presented in Figure 12 and Table 5. According to Figure 12, the crystallinity index of the ACNPs-2 h and ACNPs-4 h is obviously lower than CNPs, from 78.22 to around 77% due to the functionalization, which broadens the cleavage of hydrogen bonds at the −OH group of cellulose and reduced the crystallinity [11]. Moreover, the main step of carboxymethylation is the formation of alkali cellulose, which can also affect the crystalline structure of cellulose. The loss of crystallinity results from the opening of the glucopyranose rings; therefore, the higher the level of oxidation, the lower the degree of crystallinity [42]. Among the functionalized CNPs, the ACNPs-4 h have the lowest crystallinity intensity than other samples (Table 4). This indicates that there is high cleavage of the hydrogen bonds occurs at the −OH group, which was substituted with the carboxymethylation group into cellulose structure [43], which leads to a more amorphous structure. Moreover, the bulky carboxymethyl group on the surface of the cellulose can also reduce the ability of the cellulose chain to pack closely together.

Figure 12 The XRD result of the CNPs and functionalized CNPs at different reaction times.
Figure 12

The XRD result of the CNPs and functionalized CNPs at different reaction times.

Table 5

The crystallinity index of CNPs and functionalized CNPs at different reaction times

Sample Peak Intensity of crystallinity ( I cry ) Peak Intensity of amorphous ( I am ) Crystallinity index (%)
CNPs 23.15282 2,594 18.92516 565 78.22
ACNPs-30 min 22.72392 993 18.68007 182 81.67
ACNPs-2 h 22.47884 685 18.21034 151 77.96
ACNPs-4 h 22.60138 731 18.45542 168 77.01
ACNPs-6 h 22.64223 1,046 18.63923 224 78.59
ACNPs-8 h 22.7035 981 18.57796 208 78.80

Furthermore, high DS can further decrease crystallinity due to the increased steric hindrance, which can be absorbed in the ACNPs-4 h, indicating the optimum reaction time. Besides that, ACNPs-30 min had the high crystallinity index among the other ACNPs sample, followed by the ACNPs-6 and 8 h. This shows that, at low reaction time, the inherent structure of the cellulose, which has high and well-ordered cellulose, could be contributing to maintaining crystallinity despite the short reaction time. However, after increasing the reaction time, the crystallinity of the ACNPs started to reduce, indicating substitution of the hydroxyl group was increased and 4 h is the optimum reaction time. This is because, beyond the 4 h of reaction time of carboxymethylation, the crystallinity index of the ACNPs was almost the same as CNPs, indicating no further substitution occurred at the −OH group. The high crystallinity index of the ACNPs-6 h and ACNPs-8 h also would be the reaction for high maximum decomposition temperature.

5.6 RAMAN analysis of ACNPs

Figure 13 shows the RAMAN spectra of the CNPs and functionalized CNPs at different reaction times. The peak around 2,800–3,000 cm−1 represents CH stretching, and the peak around 1,430–1,480 cm−1 refers to vibrational modes associated with deformation or bending motions of the molecules structure, which intensities relative to the backbone around 1,100 cm−1 [44]. Here, the backbone refers to the primary structure framework of the molecules, where peaks around 1,066, 1,096, 1,119, and 1,155 cm−1 are signals of C–O stretching or C–C bonds. The region around 1,480 cm−1 is assigned to the CH2 deformation from the substitution [45], and finally peak around 2,965 cm−1 represents the methyl and methylene stretching.

Figure 13 The RAMAN spectra of the CNPs and functionalized CNPs at different reaction times.
Figure 13

The RAMAN spectra of the CNPs and functionalized CNPs at different reaction times.

Based on Figure 13, ACNPs-4 h is the only sample exhibiting a higher intensity than CNPs. Raman spectra display two important bands: the disorder band (D band) at approximately 1,350 cm⁻¹ and the graphitic band (G band) at around 1,580 cm⁻¹ [46]. The D/G ratio provides information about the DS of carboxymethyl groups on the CNPs. A high D band intensity indicates increased disorder or defects introduced into the CNPs, correlating with a higher DS of carboxymethyl groups.

In other words, the higher the D/G ratio, the greater the DS of carboxymethyl groups, and vice versa. According to Table 6, the lowest D band intensity is observed in ACNPs-8 h (3891.86), while the highest D band intensity is found in ACNPs-4 h (939,820.28). This suggests that ACNPs-4 h has the highest level of structural disorder among the ACNP samples. Furthermore, ACNPs-4 h also exhibits the highest D/G ratio, confirming that it has the highest DS of carboxymethyl groups.

Table 6

The ratio of band D and band G of CNPs and ACNPs at different reaction times

Sample Band D (1,379) Band G (1,480) Ratio D/G
CNPs 75801.74 76634.34 0.9891
ACNPs-30 min 49283.80 47597.38 1.0354
ACNPs-2 h 48709.27 47458.91 1.0263
ACNPs-4 h 93982.28 89481.51 1.0503
ACNPs-6 h 47987.71 46135.14 1.0402
ACNPs-8 h 38917.86 37832.53 1.0287

5.7 XPS analysis of ACNPs

In functionalized CNPs, there are three primary elements, which are C 1s, O 1s, and Na 1s, as shown in Figure 14. The C 1s is around 284.8–286.5 eV, O 1s around 532–533 eV, and lastly, Na 1s around 1,071 eV.

Figure 14 The three important key elements in the functionalized CNPs.
Figure 14

The three important key elements in the functionalized CNPs.

From the XPS results, the type of C 1s and O 1s functional groups was plotted as shown in Figure 15(a)–(c) for the C 1s, O 1s, and Na 1s, respectively. By referring to the binding energy of the C–C/C–H assigned at 284.7 and the peak at 286.1 and 287.5 eV are attributed to C–O and C═O groups, respectively [47,48]. Next, based on O 1s spectra, binding energies at 531.5 and 532.4 eV are assigned to the C–OH and C═O, respectively [20,48]. In addition, a new peak at 1070.1 eV was observed, which corresponds to the photoemission from Na+ [28]. Based on Figure 15(c), XPS results of Na 1 s clearly confirmed the successful functionalization of CNPs, occurring in the ACNPs-4 h, ACNPs-6 h, and ACNPs-8 h, due to the presence of the peak. However, ACNPs-4 h and ACNPs 6 h had the peak at 1,071 eV, but ACNPs-8 h had Na 1s peak at 1,068 eV. The shift in Na 1s binding energy from 1,071 eV in ACNPs-4 h and ACNPs-6 h to 1,068 eV in ACNPs-8 h suggests that the sodium ions (Na⁺) in ACNPs experience a change in their chemical environment with increasing reaction time. At 4 and 6 h, the sodium ions may be more strongly coordinated or bound to the CNPs backbone, resulting in higher binding energy, as more energy is required to remove an electron from a tightly bound ion. In contrast, at ACNPs-8 h, where the ions are less tightly bound, it becomes easier to remove an electron, resulting in a lower binding energy. Furthermore, the 0% atomic mass of Na 1s, as shown in Table 7, indicates the absence of Na⁺ in ACNPs-30 min and ACNPs-2 h. Among ACNPs-4 h, ACNPs-6 h, and ACNPs-8 h, ACNPs-4 h has the highest Na atomic concentration, suggesting that 4 h may be the optimal reaction time for carboxymethylation, as supported by the Raman and DS results.

Figure 15 The (a) C 1s, (b) O 1s, and (c) Na 1s binding energy versus intensity spectra of CNP and ACNPs at different reaction times.
Figure 15

The (a) C 1s, (b) O 1s, and (c) Na 1s binding energy versus intensity spectra of CNP and ACNPs at different reaction times.

Table 7

The binding energy and the atomic mass concentration of C 1s, O 1s, and Na 1s

Type of sample C 1s O 1s Na 1s
Atomic concentration (%) Atomic concentration (%) Atomic concentration (%)
CNPs 49.98 49.17 —
ACNPs-30 min 67.27 30.73 —
ACNPs-2 h 72.13 25.43 —
ACNPs-4 h 78.07 17.80 0.50
ACNPs-6 h 65.29 30.82 0.16
ACNPs-8 h 48.87 48.68 0.21

According to Table 6, the atomic concentration of O 1 s in CNPs is 49.17%. After carboxymethylation, however, the atomic concentration of O 1s decreases. Among the samples, ACNPs-4 h has the lowest O 1s concentration (17.80%), while ACNPs-8 h remains nearly unchanged at 48.68%. Because in ACNPs, the −CH₂COONa group attaches to the cellulose backbone by replacing the OH groups. When the DS of −CH₂COONa groups in CNPs is high, there are more −COONa groups and fewer OH groups, leading to reduced oxygen intensity. This results in a lower O 1s signal, as fewer hydroxyl groups are available to contribute to the oxygen peak. Additionally, the low O 1s concentration may be due to the substitution of cellulose’s −OH groups with ether linkages in ACNPs, decreasing the number of oxygen atoms directly associated with the cellulose structure. These changes confirm the successful functionalization of the CNPs. This result aligns with FTIR findings, where the −OH peak shows weaker intensity in ACNPs compared to CNPs, indicating a reduced number of OH groups.

The atomic concentration of C 1s in ACNPs was higher than in CNPs. However, at ACNPs-8 h, the atomic concentration was similar to that in CNPs, with ACNPs-4 h showing the highest concentration (78.01%). This increase is likely due to the substitution of −OH groups with ether linkages, which contributes additional carbon atoms to the structure. Additionally, based on Na 1s data, it is evident that carboxymethylation begins after 2 h of reaction time. Consequently, ACNPs-4 h, ACNPs-6 h, and ACNPs-8 h show varying Na atomic concentrations, with ACNPs-4 h having the highest concentration (0.50%), followed by ACNPs-8 h (0.21%) and ACNPs-6 h (0.16%). While extended reaction time can optimize certain transformations, it may also reduce Na 1s atomic concentration due to possible decomposition or side reactions. Longer reaction times might promote unwanted reactions or decomposition, altering the sample’s composition and ultimately decreasing sodium concentration.

6 Conclusion

In conclusion, FTIR characterization reveals a decrease in the intensity of the −OH and C–H peaks in the ACNP samples compared to CNPs, indicating successful surface modification. This reduction is attributed to the extended carboxymethylation time, enhancing the interaction between chloroacetic acid and cellulose hydroxyl groups. Additional peaks around 1,600 and 1,400–1,450 cm⁻¹ in the FTIR spectra confirm the carboxymethylation of CNPs, corresponding to the carboxylate group (COO−) and the stretching and deformation vibrations of methyl (–CH3) groups. Among the samples, ACNPs-4 h exhibits the highest DS at 0.43, indicating the most significant substitution of –OH groups with anionic groups during the 4-h reaction time. TEM analysis shows that the needle-like shape of CNPs is retained after functionalization, demonstrating that surface modification does not alter the morphology of the particles. While surface modification improves particle distribution for up to 2 h, ACNPs begin to agglomerate beyond 4 h. ACNPs-4 h demonstrates the best particle distribution and uniform particle diameter, confirming it as the optimum reaction time. Thermal stability analysis using TGA and DTG shows improved stability in ACNPs after functionalization. XRD analysis reveals a lower crystallinity index for ACNPs compared to CNPs due to structural modifications, with ACNPs-4 h exhibiting the lowest crystallinity index among all samples. Raman spectroscopy further supports these findings, with ACNPs-4 h displaying the highest D/G band ratio (1.0503), reflecting greater substitution of carboxymethyl groups. This aligns with zeta potential measurements, where ACNPs-4 h achieves a value of −41.8 mV, indicating excellent dispersion and uniform particle size. Finally, XPS analysis confirms ACNPs-4 h as the optimum reaction time, evidenced by the highest concentration of sodium ions (Na⁺) in the Na 1s spectra (0.50%), compared to ACNPs-6 h (0.16%) and ACNPs-8 h (0.21%). Based on these results, ACNPs-4 h is identified as the optimal sample that offers superior substitution, distribution, thermal stability, and structural properties for further hybridization with metal oxide that has cationic characteristics.

Acknowledgments

Special thanks to the Ministry of Higher Education (MOHE) for funding under the Fundamental Research Grant Scheme (FRGS) (FRGS/1/2023/STG05/USM/02/3). The authors would like to express gratitude for the financial support received from the Universiti Pertahanan Nasional Malaysia.

  1. Funding information: Fundamental Research Grant Scheme (FRGS) (FRGS/1/2023/STG05/USM/02/3).

  2. Author contributions: Conceptualization, writing-original draft preparation, review, and editing: Mageswari Manimaran, Mohd Nurazzi Norizan, Mohd Nor Faiz Norrrahim; conceptualization: Mohamad Haafiz Mohamad Kassim, Mohd Ridhwan Adam, Norli Abdullah. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Data availability statement: All data generated or analyzed during this study are included in this published article.

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Received: 2024-12-08
Revised: 2024-12-31
Accepted: 2025-03-02
Published Online: 2025-04-16

© 2025 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

  1. Research Articles
  2. MHD radiative mixed convective flow of a sodium alginate-based hybrid nanofluid over a convectively heated extending sheet with Joule heating
  3. Experimental study of mortar incorporating nano-magnetite on engineering performance and radiation shielding
  4. Multicriteria-based optimization and multi-variable non-linear regression analysis of concrete containing blends of nano date palm ash and eggshell powder as cementitious materials
  5. A promising Ag2S/poly-2-amino-1-mercaptobenzene open-top spherical core–shell nanocomposite for optoelectronic devices: A one-pot technique
  6. Biogenic synthesized selenium nanoparticles combined chitosan nanoparticles controlled lung cancer growth via ROS generation and mitochondrial damage pathway
  7. Fabrication of PDMS nano-mold by deposition casting method
  8. Stimulus-responsive gradient hydrogel micro-actuators fabricated by two-photon polymerization-based 4D printing
  9. Physical aspects of radiative Carreau nanofluid flow with motile microorganisms movement under yield stress via oblique penetrable wedge
  10. Effect of polar functional groups on the hydrophobicity of carbon nanotubes-bacterial cellulose nanocomposite
  11. Review in green synthesis mechanisms, application, and future prospects for Garcinia mangostana L. (mangosteen)-derived nanoparticles
  12. Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy
  13. Green synthesis of silver nanoparticles using Ginkgo biloba seed extract: Evaluation of antioxidant, anticancer, antifungal, and antibacterial activities
  14. A numerical analysis of heat and mass transfer in water-based hybrid nanofluid flow containing copper and alumina nanoparticles over an extending sheet
  15. Investigating the behaviour of electro-magneto-hydrodynamic Carreau nanofluid flow with slip effects over a stretching cylinder
  16. Electrospun thermoplastic polyurethane/nano-Ag-coated clear aligners for the inhibition of Streptococcus mutans and oral biofilm
  17. Investigation of the optoelectronic properties of a novel polypyrrole-multi-well carbon nanotubes/titanium oxide/aluminum oxide/p-silicon heterojunction
  18. Novel photothermal magnetic Janus membranes suitable for solar water desalination
  19. Green synthesis of silver nanoparticles using Ageratum conyzoides for activated carbon compositing to prepare antimicrobial cotton fabric
  20. Activation energy and Coriolis force impact on three-dimensional dusty nanofluid flow containing gyrotactic microorganisms: Machine learning and numerical approach
  21. Machine learning analysis of thermo-bioconvection in a micropolar hybrid nanofluid-filled square cavity with oxytactic microorganisms
  22. Research and improvement of mechanical properties of cement nanocomposites for well cementing
  23. Thermal and stability analysis of silver–water nanofluid flow over unsteady stretching sheet under the influence of heat generation/absorption at the boundary
  24. Cobalt iron oxide-infused silicone nanocomposites: Magnetoactive materials for remote actuation and sensing
  25. Magnesium-reinforced PMMA composite scaffolds: Synthesis, characterization, and 3D printing via stereolithography
  26. Bayesian inference-based physics-informed neural network for performance study of hybrid nanofluids
  27. Numerical simulation of non-Newtonian hybrid nanofluid flow subject to a heterogeneous/homogeneous chemical reaction over a Riga surface
  28. Enhancing the superhydrophobicity, UV-resistance, and antifungal properties of natural wood surfaces via in situ formation of ZnO, TiO2, and SiO2 particles
  29. Synthesis and electrochemical characterization of iron oxide/poly(2-methylaniline) nanohybrids for supercapacitor application
  30. Impacts of double stratification on thermally radiative third-grade nanofluid flow on elongating cylinder with homogeneous/heterogeneous reactions by implementing machine learning approach
  31. Synthesis of Cu4O3 nanoparticles using pumpkin seed extract: Optimization, antimicrobial, and cytotoxicity studies
  32. Cationic charge influence on the magnetic response of the Fe3O4–[Me2+ 1−y Me3+ y (OH2)] y+(Co3 2−) y/2·mH2O hydrotalcite system
  33. Pressure sensing intelligent martial arts short soldier combat protection system based on conjugated polymer nanocomposite materials
  34. Magnetohydrodynamics heat transfer rate under inclined buoyancy force for nano and dusty fluids: Response surface optimization for the thermal transport
  35. Fly ash and nano-graphene enhanced stabilization of engine oil-contaminated soils
  36. Enhancing natural fiber-reinforced biopolymer composites with graphene nanoplatelets: Mechanical, morphological, and thermal properties
  37. Performance evaluation of dual-scale strengthened co-bonded single-lap joints using carbon nanotubes and Z-pins with ANN
  38. Computational works of blood flow with dust particles and partially ionized containing tiny particles on a moving wedge: Applications of nanotechnology
  39. Hybridization of biocomposites with oil palm cellulose nanofibrils/graphene nanoplatelets reinforcement in green epoxy: A study of physical, thermal, mechanical, and morphological properties
  40. Design and preparation of micro-nano dual-scale particle-reinforced Cu–Al–V alloy: Research on the aluminothermic reduction process
  41. Spectral quasi-linearization and response optimization on magnetohydrodynamic flow via stenosed artery with hybrid and ternary solid nanoparticles: Support vector machine learning
  42. Ferrite/curcumin hybrid nanocomposite formulation: Physicochemical characterization, anticancer activity, and apoptotic and cell cycle analyses in skin cancer cells
  43. Enhanced therapeutic efficacy of Tamoxifen against breast cancer using extra virgin olive oil-based nanoemulsion delivery system
  44. A titanium oxide- and silver-based hybrid nanofluid flow between two Riga walls that converge and diverge through a machine-learning approach
  45. Enhancing convective heat transfer mechanisms through the rheological analysis of Casson nanofluid flow towards a stagnation point over an electro-magnetized surface
  46. Intrinsic self-sensing cementitious composites with hybrid nanofillers exhibiting excellent piezoresistivity
  47. Research on mechanical properties and sulfate erosion resistance of nano-reinforced coal gangue based geopolymer concrete
  48. Impact of surface and configurational features of chemically synthesized chains of Ni nanostars on the magnetization reversal process
  49. Porous sponge-like AsOI/poly(2-aminobenzene-1-thiol) nanocomposite photocathode for hydrogen production from artificial and natural seawater
  50. Multifaceted insights into WO3 nanoparticle-coupled antibiotics to modulate resistance in enteric pathogens of Houbara bustard birds
  51. Synthesis of sericin-coated silver nanoparticles and their applications for the anti-bacterial finishing of cotton fabric
  52. Enhancing chloride resistance of freeze–thaw affected concrete through innovative nanomaterial–polymer hybrid cementitious coating
  53. Development and performance evaluation of green aluminium metal matrix composites reinforced with graphene nanopowder and marble dust
  54. Morphological, physical, thermal, and mechanical properties of carbon nanotubes reinforced arrowroot starch composites
  55. Influence of the graphene oxide nanosheet on tensile behavior and failure characteristics of the cement composites after high-temperature treatment
  56. Central composite design modeling in optimizing heat transfer rate in the dissipative and reactive dynamics of viscoplastic nanomaterials deploying Joule and heat generation aspects
  57. Double diffusion of nano-enhanced phase change materials in connected porous channels: A hybrid ISPH-XGBoost approach
  58. Synergistic impacts of Thompson–Troian slip, Stefan blowing, and nonuniform heat generation on Casson nanofluid dynamics through a porous medium
  59. Optimization of abrasive water jet machining parameters for basalt fiber/SiO2 nanofiller reinforced composites
  60. Enhancing aesthetic durability of Zisha teapots via TiO2 nanoparticle surface modification: A study on self-cleaning, antimicrobial, and mechanical properties
  61. Nanocellulose solution based on iron(iii) sodium tartrate complexes
  62. Combating multidrug-resistant infections: Gold nanoparticles–chitosan–papain-integrated dual-action nanoplatform for enhanced antibacterial activity
  63. Novel royal jelly-mediated green synthesis of selenium nanoparticles and their multifunctional biological activities
  64. Direct bandgap transition for emission in GeSn nanowires
  65. Synthesis of ZnO nanoparticles with different morphologies using a microwave-based method and their antimicrobial activity
  66. Numerical investigation of convective heat and mass transfer in a trapezoidal cavity filled with ternary hybrid nanofluid and a central obstacle
  67. Halloysite nanotube enhanced polyurethane nanocomposites for advanced electroinsulating applications
  68. Low molar mass ionic liquid’s modified carbon nanotubes and its role in PVDF crystalline stress generation
  69. Green synthesis of polydopamine-functionalized silver nanoparticles conjugated with Ceftazidime: in silico and experimental approach for combating antibiotic-resistant bacteria and reducing toxicity
  70. Evaluating the influence of graphene nano powder inclusion on mechanical, vibrational and water absorption behaviour of ramie/abaca hybrid composites
  71. Dynamic-behavior of Casson-type hybrid nanofluids due to a stretching sheet under the coupled impacts of boundary slip and reaction-diffusion processes
  72. Influence of polyvinyl alcohol on the physicochemical and self-sensing properties of nano carbon black reinforced cement mortar
  73. Advanced machine learning approaches for predicting compressive and flexural strength of carbon nanotube–reinforced cement composites: a comparative study and model interpretability analysis
  74. Review Articles
  75. A comprehensive review on hybrid plasmonic waveguides: Structures, applications, challenges, and future perspectives
  76. Nanoparticles in low-temperature preservation of biological systems of animal origin
  77. Fluorescent sulfur quantum dots for environmental monitoring
  78. Nanoscience systematic review methodology standardization
  79. Nanotechnology revolutionizing osteosarcoma treatment: Advances in targeted kinase inhibitors
  80. AFM: An important enabling technology for 2D materials and devices
  81. Carbon and 2D nanomaterial smart hydrogels for therapeutic applications
  82. Principles, applications and future prospects in photodegradation systems
  83. Do gold nanoparticles consistently benefit crop plants under both non-stressed and abiotic stress conditions?
  84. An updated overview of nanoparticle-induced cardiovascular toxicity
  85. Arginine as a promising amino acid for functionalized nanosystems: Innovations, challenges, and future directions
  86. Advancements in the use of cancer nanovaccines: Comprehensive insights with focus on lung and colon cancer
  87. Membrane-based biomimetic delivery systems for glioblastoma multiforme therapy
  88. The drug delivery systems based on nanoparticles for spinal cord injury repair
  89. Green synthesis, biomedical effects, and future trends of Ag/ZnO bimetallic nanoparticles: An update
  90. Application of magnesium and its compounds in biomaterials for nerve injury repair
  91. Micro/nanomotors in biomedicine: Construction and applications
  92. Hydrothermal synthesis of biomass-derived CQDs: Advances and applications
  93. Research progress in 3D bioprinting of skin: Challenges and opportunities
  94. Review on bio-selenium nanoparticles: Synthesis, protocols, and applications in biomedical processes
  95. Gold nanocrystals and nanorods functionalized with protein and polymeric ligands for environmental, energy storage, and diagnostic applications: A review
  96. An in-depth analysis of rotational and non-rotational piezoelectric energy harvesting beams: A comprehensive review
  97. Advancements in perovskite/CIGS tandem solar cells: Material synergies, device configurations, and economic viability for sustainable energy
  98. Deep learning in-depth analysis of crystal graph convolutional neural networks: A new era in materials discovery and its applications
  99. Review of recent nano TiO2 film coating methods, assessment techniques, and key problems for scaleup
  100. Antioxidant quantum dots for spinal cord injuries: A review on advancing neuroprotection and regeneration in neurological disorders
  101. Rise of polycatecholamine ultrathin films: From synthesis to smart applications
  102. Advancing microencapsulation strategies for bioactive compounds: Enhancing stability, bioavailability, and controlled release in food applications
  103. Advances in the design and manipulation of self-assembling peptide and protein nanostructures for biomedical applications
  104. Photocatalytic pervious concrete systems: from classic photocatalysis to luminescent photocatalysis
  105. Corrigendum
  106. Corrigendum to “Synthesis and characterization of smart stimuli-responsive herbal drug-encapsulated nanoniosome particles for efficient treatment of breast cancer”
  107. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part III
  108. Efficiency optimization of quantum dot photovoltaic cell by solar thermophotovoltaic system
  109. Exploring the diverse nanomaterials employed in dental prosthesis and implant techniques: An overview
  110. Electrochemical investigation of bismuth-doped anode materials for low‑temperature solid oxide fuel cells with boosted voltage using a DC-DC voltage converter
  111. Synthesis of HfSe2 and CuHfSe2 crystalline materials using the chemical vapor transport method and their applications in supercapacitor energy storage devices
  112. Special Issue on Green Nanotechnology and Nano-materials for Environment Sustainability
  113. Influence of nano-silica and nano-ferrite particles on mechanical and durability of sustainable concrete: A review
  114. Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass
  115. Processing and effective utilization of lignocellulosic biomass: Nanocellulose, nanolignin, and nanoxylan for wastewater treatment
  116. Retraction
  117. Retraction of “Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation”
https://doi.org/10.1515/ntrev-2025-0152
Schlagwörter für diesen Artikel
nanocellulose; oil palm empty fruit bunch; carboxymethylation reaction
Creative Commons
BY 4.0

Artikel in diesem Heft

  1. Research Articles
  2. MHD radiative mixed convective flow of a sodium alginate-based hybrid nanofluid over a convectively heated extending sheet with Joule heating
  3. Experimental study of mortar incorporating nano-magnetite on engineering performance and radiation shielding
  4. Multicriteria-based optimization and multi-variable non-linear regression analysis of concrete containing blends of nano date palm ash and eggshell powder as cementitious materials
  5. A promising Ag2S/poly-2-amino-1-mercaptobenzene open-top spherical core–shell nanocomposite for optoelectronic devices: A one-pot technique
  6. Biogenic synthesized selenium nanoparticles combined chitosan nanoparticles controlled lung cancer growth via ROS generation and mitochondrial damage pathway
  7. Fabrication of PDMS nano-mold by deposition casting method
  8. Stimulus-responsive gradient hydrogel micro-actuators fabricated by two-photon polymerization-based 4D printing
  9. Physical aspects of radiative Carreau nanofluid flow with motile microorganisms movement under yield stress via oblique penetrable wedge
  10. Effect of polar functional groups on the hydrophobicity of carbon nanotubes-bacterial cellulose nanocomposite
  11. Review in green synthesis mechanisms, application, and future prospects for Garcinia mangostana L. (mangosteen)-derived nanoparticles
  12. Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy
  13. Green synthesis of silver nanoparticles using Ginkgo biloba seed extract: Evaluation of antioxidant, anticancer, antifungal, and antibacterial activities
  14. A numerical analysis of heat and mass transfer in water-based hybrid nanofluid flow containing copper and alumina nanoparticles over an extending sheet
  15. Investigating the behaviour of electro-magneto-hydrodynamic Carreau nanofluid flow with slip effects over a stretching cylinder
  16. Electrospun thermoplastic polyurethane/nano-Ag-coated clear aligners for the inhibition of Streptococcus mutans and oral biofilm
  17. Investigation of the optoelectronic properties of a novel polypyrrole-multi-well carbon nanotubes/titanium oxide/aluminum oxide/p-silicon heterojunction
  18. Novel photothermal magnetic Janus membranes suitable for solar water desalination
  19. Green synthesis of silver nanoparticles using Ageratum conyzoides for activated carbon compositing to prepare antimicrobial cotton fabric
  20. Activation energy and Coriolis force impact on three-dimensional dusty nanofluid flow containing gyrotactic microorganisms: Machine learning and numerical approach
  21. Machine learning analysis of thermo-bioconvection in a micropolar hybrid nanofluid-filled square cavity with oxytactic microorganisms
  22. Research and improvement of mechanical properties of cement nanocomposites for well cementing
  23. Thermal and stability analysis of silver–water nanofluid flow over unsteady stretching sheet under the influence of heat generation/absorption at the boundary
  24. Cobalt iron oxide-infused silicone nanocomposites: Magnetoactive materials for remote actuation and sensing
  25. Magnesium-reinforced PMMA composite scaffolds: Synthesis, characterization, and 3D printing via stereolithography
  26. Bayesian inference-based physics-informed neural network for performance study of hybrid nanofluids
  27. Numerical simulation of non-Newtonian hybrid nanofluid flow subject to a heterogeneous/homogeneous chemical reaction over a Riga surface
  28. Enhancing the superhydrophobicity, UV-resistance, and antifungal properties of natural wood surfaces via in situ formation of ZnO, TiO2, and SiO2 particles
  29. Synthesis and electrochemical characterization of iron oxide/poly(2-methylaniline) nanohybrids for supercapacitor application
  30. Impacts of double stratification on thermally radiative third-grade nanofluid flow on elongating cylinder with homogeneous/heterogeneous reactions by implementing machine learning approach
  31. Synthesis of Cu4O3 nanoparticles using pumpkin seed extract: Optimization, antimicrobial, and cytotoxicity studies
  32. Cationic charge influence on the magnetic response of the Fe3O4–[Me2+ 1−y Me3+ y (OH2)] y+(Co3 2−) y/2·mH2O hydrotalcite system
  33. Pressure sensing intelligent martial arts short soldier combat protection system based on conjugated polymer nanocomposite materials
  34. Magnetohydrodynamics heat transfer rate under inclined buoyancy force for nano and dusty fluids: Response surface optimization for the thermal transport
  35. Fly ash and nano-graphene enhanced stabilization of engine oil-contaminated soils
  36. Enhancing natural fiber-reinforced biopolymer composites with graphene nanoplatelets: Mechanical, morphological, and thermal properties
  37. Performance evaluation of dual-scale strengthened co-bonded single-lap joints using carbon nanotubes and Z-pins with ANN
  38. Computational works of blood flow with dust particles and partially ionized containing tiny particles on a moving wedge: Applications of nanotechnology
  39. Hybridization of biocomposites with oil palm cellulose nanofibrils/graphene nanoplatelets reinforcement in green epoxy: A study of physical, thermal, mechanical, and morphological properties
  40. Design and preparation of micro-nano dual-scale particle-reinforced Cu–Al–V alloy: Research on the aluminothermic reduction process
  41. Spectral quasi-linearization and response optimization on magnetohydrodynamic flow via stenosed artery with hybrid and ternary solid nanoparticles: Support vector machine learning
  42. Ferrite/curcumin hybrid nanocomposite formulation: Physicochemical characterization, anticancer activity, and apoptotic and cell cycle analyses in skin cancer cells
  43. Enhanced therapeutic efficacy of Tamoxifen against breast cancer using extra virgin olive oil-based nanoemulsion delivery system
  44. A titanium oxide- and silver-based hybrid nanofluid flow between two Riga walls that converge and diverge through a machine-learning approach
  45. Enhancing convective heat transfer mechanisms through the rheological analysis of Casson nanofluid flow towards a stagnation point over an electro-magnetized surface
  46. Intrinsic self-sensing cementitious composites with hybrid nanofillers exhibiting excellent piezoresistivity
  47. Research on mechanical properties and sulfate erosion resistance of nano-reinforced coal gangue based geopolymer concrete
  48. Impact of surface and configurational features of chemically synthesized chains of Ni nanostars on the magnetization reversal process
  49. Porous sponge-like AsOI/poly(2-aminobenzene-1-thiol) nanocomposite photocathode for hydrogen production from artificial and natural seawater
  50. Multifaceted insights into WO3 nanoparticle-coupled antibiotics to modulate resistance in enteric pathogens of Houbara bustard birds
  51. Synthesis of sericin-coated silver nanoparticles and their applications for the anti-bacterial finishing of cotton fabric
  52. Enhancing chloride resistance of freeze–thaw affected concrete through innovative nanomaterial–polymer hybrid cementitious coating
  53. Development and performance evaluation of green aluminium metal matrix composites reinforced with graphene nanopowder and marble dust
  54. Morphological, physical, thermal, and mechanical properties of carbon nanotubes reinforced arrowroot starch composites
  55. Influence of the graphene oxide nanosheet on tensile behavior and failure characteristics of the cement composites after high-temperature treatment
  56. Central composite design modeling in optimizing heat transfer rate in the dissipative and reactive dynamics of viscoplastic nanomaterials deploying Joule and heat generation aspects
  57. Double diffusion of nano-enhanced phase change materials in connected porous channels: A hybrid ISPH-XGBoost approach
  58. Synergistic impacts of Thompson–Troian slip, Stefan blowing, and nonuniform heat generation on Casson nanofluid dynamics through a porous medium
  59. Optimization of abrasive water jet machining parameters for basalt fiber/SiO2 nanofiller reinforced composites
  60. Enhancing aesthetic durability of Zisha teapots via TiO2 nanoparticle surface modification: A study on self-cleaning, antimicrobial, and mechanical properties
  61. Nanocellulose solution based on iron(iii) sodium tartrate complexes
  62. Combating multidrug-resistant infections: Gold nanoparticles–chitosan–papain-integrated dual-action nanoplatform for enhanced antibacterial activity
  63. Novel royal jelly-mediated green synthesis of selenium nanoparticles and their multifunctional biological activities
  64. Direct bandgap transition for emission in GeSn nanowires
  65. Synthesis of ZnO nanoparticles with different morphologies using a microwave-based method and their antimicrobial activity
  66. Numerical investigation of convective heat and mass transfer in a trapezoidal cavity filled with ternary hybrid nanofluid and a central obstacle
  67. Halloysite nanotube enhanced polyurethane nanocomposites for advanced electroinsulating applications
  68. Low molar mass ionic liquid’s modified carbon nanotubes and its role in PVDF crystalline stress generation
  69. Green synthesis of polydopamine-functionalized silver nanoparticles conjugated with Ceftazidime: in silico and experimental approach for combating antibiotic-resistant bacteria and reducing toxicity
  70. Evaluating the influence of graphene nano powder inclusion on mechanical, vibrational and water absorption behaviour of ramie/abaca hybrid composites
  71. Dynamic-behavior of Casson-type hybrid nanofluids due to a stretching sheet under the coupled impacts of boundary slip and reaction-diffusion processes
  72. Influence of polyvinyl alcohol on the physicochemical and self-sensing properties of nano carbon black reinforced cement mortar
  73. Advanced machine learning approaches for predicting compressive and flexural strength of carbon nanotube–reinforced cement composites: a comparative study and model interpretability analysis
  74. Review Articles
  75. A comprehensive review on hybrid plasmonic waveguides: Structures, applications, challenges, and future perspectives
  76. Nanoparticles in low-temperature preservation of biological systems of animal origin
  77. Fluorescent sulfur quantum dots for environmental monitoring
  78. Nanoscience systematic review methodology standardization
  79. Nanotechnology revolutionizing osteosarcoma treatment: Advances in targeted kinase inhibitors
  80. AFM: An important enabling technology for 2D materials and devices
  81. Carbon and 2D nanomaterial smart hydrogels for therapeutic applications
  82. Principles, applications and future prospects in photodegradation systems
  83. Do gold nanoparticles consistently benefit crop plants under both non-stressed and abiotic stress conditions?
  84. An updated overview of nanoparticle-induced cardiovascular toxicity
  85. Arginine as a promising amino acid for functionalized nanosystems: Innovations, challenges, and future directions
  86. Advancements in the use of cancer nanovaccines: Comprehensive insights with focus on lung and colon cancer
  87. Membrane-based biomimetic delivery systems for glioblastoma multiforme therapy
  88. The drug delivery systems based on nanoparticles for spinal cord injury repair
  89. Green synthesis, biomedical effects, and future trends of Ag/ZnO bimetallic nanoparticles: An update
  90. Application of magnesium and its compounds in biomaterials for nerve injury repair
  91. Micro/nanomotors in biomedicine: Construction and applications
  92. Hydrothermal synthesis of biomass-derived CQDs: Advances and applications
  93. Research progress in 3D bioprinting of skin: Challenges and opportunities
  94. Review on bio-selenium nanoparticles: Synthesis, protocols, and applications in biomedical processes
  95. Gold nanocrystals and nanorods functionalized with protein and polymeric ligands for environmental, energy storage, and diagnostic applications: A review
  96. An in-depth analysis of rotational and non-rotational piezoelectric energy harvesting beams: A comprehensive review
  97. Advancements in perovskite/CIGS tandem solar cells: Material synergies, device configurations, and economic viability for sustainable energy
  98. Deep learning in-depth analysis of crystal graph convolutional neural networks: A new era in materials discovery and its applications
  99. Review of recent nano TiO2 film coating methods, assessment techniques, and key problems for scaleup
  100. Antioxidant quantum dots for spinal cord injuries: A review on advancing neuroprotection and regeneration in neurological disorders
  101. Rise of polycatecholamine ultrathin films: From synthesis to smart applications
  102. Advancing microencapsulation strategies for bioactive compounds: Enhancing stability, bioavailability, and controlled release in food applications
  103. Advances in the design and manipulation of self-assembling peptide and protein nanostructures for biomedical applications
  104. Photocatalytic pervious concrete systems: from classic photocatalysis to luminescent photocatalysis
  105. Corrigendum
  106. Corrigendum to “Synthesis and characterization of smart stimuli-responsive herbal drug-encapsulated nanoniosome particles for efficient treatment of breast cancer”
  107. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part III
  108. Efficiency optimization of quantum dot photovoltaic cell by solar thermophotovoltaic system
  109. Exploring the diverse nanomaterials employed in dental prosthesis and implant techniques: An overview
  110. Electrochemical investigation of bismuth-doped anode materials for low‑temperature solid oxide fuel cells with boosted voltage using a DC-DC voltage converter
  111. Synthesis of HfSe2 and CuHfSe2 crystalline materials using the chemical vapor transport method and their applications in supercapacitor energy storage devices
  112. Special Issue on Green Nanotechnology and Nano-materials for Environment Sustainability
  113. Influence of nano-silica and nano-ferrite particles on mechanical and durability of sustainable concrete: A review
  114. Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass
  115. Processing and effective utilization of lignocellulosic biomass: Nanocellulose, nanolignin, and nanoxylan for wastewater treatment
  116. Retraction
  117. Retraction of “Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation”
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