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Removal of antiviral favipiravir from wastewater using biochar produced from hazelnut shells

  • Ayşegül Türk Baydır ORCID logo EMAIL logo
Published/Copyright: April 15, 2025
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Open Chemistry
From the journal Open Chemistry Volume 23 Issue 1

Abstract

Increasing drug pollution represents a substantial risk to the safeguarding of water resources. Favipiravir, a commonly used antiviral medication, is one of the pharmaceutical residues found in wastewater and poses a threat to the ecosystem. Favipiravir is classified as Category 2 for germ cell mutagenicity and reproductive toxicity and is a drug suspected of leading to genetic abnormalities and adverse effects on the developing fetus. In this study, hazelnut shell-derived activated carbon was utilized as an adsorbent for the removal of favipiravir from aqueous solutions. First, the produced activated carbon was characterized through various analyses. Then, during the adsorption process, key parameters such as initial favipiravir concentration, adsorbent dosage, solution pH, contact time, and temperature were optimized. The process was analyzed based on equilibrium, kinetics, and thermodynamics. Optimum conditions (30 μg/mL initial concentration, 15 mg adsorbent dose, 90 min contact time, pH 2) were determined, and the highest adsorption efficiency of 94.60% was obtained under these conditions. The adsorption mechanism was most accurately by the pseudo-second-order rate model (R²: 0.9998) and the Langmuir adsorption model (R 2: 0.9942). Moreover, thermodynamic studies have shown that the mechanism is spontaneous since the free energy change (ΔG < 0), exothermic since the enthalpy change (ΔH < 0), and the entropy change (ΔS < 0) reduce the disorder in the system. This study emphasizes the adsorbent’s potential as a green and economical treatment solution.

Keywords: biochar; favipiravir; hazelnut shells; adsorption

1 Introduction

Pharmaceuticals are increasingly used to improve wellness and prolong life [1,2]. However, the intensive use of pharmaceutical compounds has led to a serious environmental problem on a global scale [3]. Therefore, water resources need to be continuously monitored for pollution [2]. Antiviral drugs play a critical role in controlling viral infections by inhibiting the spread of pathogens [4]. These drugs, which are widely used for cure and prevention of illnesses such as influenza, human immunodeficiency virus, herpes, and hepatitis [5,6,7], pollute the environment and threaten water quality by entering wastewater [8,9]. After being metabolized in the body, antiviral drugs are usually excreted through urine or feces and enter the sewage system. Studies show that up to 60% of the administered dose is excreted [4,7]. These compounds, which are released into the environment due to inadequate removal in wastewater treatment plants [7,10], cause adverse effects such as toxicity, genotoxicity, resistance development, and endocrine system disorders in aquatic ecosystems [1,11]. Furthermore, the presence of antiviral drugs in the same water body as the target virus can lead to the development of resistance in susceptible organisms and the emergence of new forms of resistance [12,13]. Favipiravir is one of the most widely used antiviral medicines.

Favipiravir, a chemically synthesized broad-spectrum antiviral, has been widely used in the treatment of severe cases, especially during the COVID-19 pandemic [14,15,16,17,18,19]. However, due to low absorption in the body and insufficient waste disposal practices, favipiravir and its metabolites can enter the sewage system through medical and household waste [10]. Current treatment processes cannot effectively remove pharmaceutical components such as favipiravir from wastewater, which causes favipiravir to spread into the environment through treated wastewater [5,20,21]. Favipiravir has been detected in groundwater at nanograms per liter levels [22,23]. Favipiravir, which can be toxic even at low concentrations, poses significant risks to human health and ecosystems due to its resistance to degradation, high solubility, and semi-permanence [13,24,25].

Various treatment techniques have been developed for the elimination of antiviral drugs from wastewater, such as ozonation [26,27], photolysis [28,29,30] electrochemical advanced oxidation, photocatalysis [29], activated sludge systems [31,32,33,34], and membrane bioreactors [30,35,36,37]. Nevertheless, these technologies come with drawbacks, including significant costs, high energy usage, secondary pollution, and the generation of harmful side products. There is a need to develop alternative and economical methods to address the effects of antiviral compounds in the environment.

Adsorption is an economical and applicable method based on the binding of dissolved substances to a solid surface [38,39]. Activated carbon is frequently utilized because of its extensive surface area and porous nature. However, the high costs of activated carbon production limit the large-scale use of this material [40,41]. Therefore, it is important to discover cost-effective alternatives. Low-cost adsorbents include animal bones [42], bamboo waste [43], waste tires [44], sewage sludge [45], rice husks [46,47], coconut shells [48], sugar cane bagasse [49], orange peels [50], and almond shells [51].

Hazelnut shells are an easily accessible waste material originating from agricultural production. However, they are usually disposed of in landfills or burned, which leads to both resource wastage and environmental problems [52]. In this study, activated carbon from hazelnut shells was produced and characterized, and the potential of this material for favipiravir removal from wastewater was investigated. The kinetics of the adsorption mechanism were examined using pseudo-first-order (PFO) and pseudo-second-order (PSO) models, while equilibrium states were assessed through Freundlich and Langmuir adsorption models. In addition, adsorption thermodynamics was studied at temperatures of 300, 308, 318, and 328 K to elucidate the energy requirements and mechanisms of the process. These temperatures are the temperatures that can be encountered in summer and winter under natural conditions.

2 Materials and methods

2.1 Chemicals, materials, instruments

An Agilent 1260 high-performance liquid chromatography (HPLC) system, equipped with an ultraviolet detector and ChemStation software, was used to quantify favipiravir concentrations in aqueous solutions.

pH values were measured with a Mettler Toledo pH meter featuring glass electrodes, calibrated daily before use. Ultra-pure water for all experiments was obtained using the Merck Millipore Milli-Q water purification system. Adsorption tests were carried out in a WITEG WSB 30 shaking water bath.

Hydrochloric acid (37%), sodium hydroxide (98%), orthophosphoric acid (85%), and potassium dihydrogen phosphate (≥99%) were supplied by Sigma-Aldrich. Favipiravir (CAS No. 259793-96-9, C5H4FN3O2, 99%) was obtained from Sigma-Aldrich, and favipiravir tablets (200 mg RAVIRAN) were sourced from a nearby pharmacy in Afyonkarahisar. Ultrapure water (0,055 µS/cm) was used to prepare all aqueous solutions, and HCl and NaOH solutions were utilized for pH adjustments.

2.2 Preparation of hazelnut shell activated carbon (HSAC)

Hazelnut shells were gathered from a hazelnut garden in Zonguldak/Alaplı in August (2024). The collected shells were first cleaned completely with normal water and then with ultrapure water and dried for 24 h in an oven at 80°C. The dried shells were milled into powder in a blender to a size of 0.10–0.50 mm. Hazelnut shell powder was pyrolyzed at 550°C for 30 min under an N₂(g) atmosphere with a flow rate of 200 mL/min in a Carbolite CTF 12/65/550 tube furnace, using a heating rate of 10°C/min. The obtained coal was ground to 80 mesh, then combined with a KOH solution in an Erlenmeyer flask. The Erlenmeyer flask was closed and shaken at 120 rpm and 30°C for 12 h, then incubated at 105°C. It was subsequently heated at 600°C for 1.5 h under a pure N₂ flow rate of 200 mL/min, with a heating rate of 10°C/min. In the final step, the activated product was cooled under pure N2(g), then sequentially washed with water and 0.1 M HCl solution, followed by pure water until the filtrate’s pH stabilized. then dried at 105°C for 3 h, and preserved in a glass flask to be used in adsorption studies [53,54].

2.3 Characterization methods

Fourier transform infrared spectroscopy (FTIR, Perkin Elmer) was utilized to analyze the functional groups attached to the surface of HSAC. The surface characteristics and pore structure of HSAC were determined using a Micromeritics Gemini VII 5.03 Brunauer Emmett Teller (BET) device. For surface morphology imaging, a scanning electron microscope (SEM, Zeiss Sigma 300) was used, and energy-dispersive X-ray (EDX) spectroscopy was utilized for elemental analysis.

2.4 Determination of zero load point (pHpzc) of HSAC adsorbent

pHpzc of HSAC adsorbent was determined by the salt addition method with some modifications. For this purpose, 0.1 M NaCl solution was prepared and transferred to six separate 250 mL Erlenmeyer flasks in 50 mL portions. The initial pH value (pHi) of every solution was set to 2, 4, 6, 8, 10, and 12 by adding different concentrations of HCl or NaOH solution. Then, 0.050 g of HSAC was added to each Erlenmeyer flask, and all solutions were shaken for 24 h in a device capable of shaking at 170 rpm at 25°C. After the shaking process was completed, the solutions were filtered through white band filter paper and the final pH (pHf) values were measured with a pH meter. The relationship between the pHi and pHf value was plotted on a graph, and the point where pHi and pHf intersect was determined as the pHpzc value of the HSAC adsorbent [55].

2.5 Batch adsorption experiments

In this research, the adsorption efficiency of favipiravir from aqueous solutions was investigated using HSAC adsorbent. To prepare the 500 ppm stock solution, 50 mg favipiravir was exactly weighed and placed to a 100 mL volumetric flask. Nearly 30 mL of ultrapure water was added and shaken on a shaker for 30 min to make sure of total dissolution. The volume was made up to 100 ml with ultrapure water. The mixture was ultrasonicated for 5 min. Sample solutions were prepared by diluting the stock sample solution with ultrapure water. Adsorption experiments were carried out using 50 mL favipiravir solutions in 250 mL capped Erlenmeyer flasks.

The adsorption experiments assessed the impact of pH, adsorbent dosage, initial concentration, and temperature on the efficiency of favipiravir removal. To prepare the experimental series, the stock solution was diluted to the required concentrations. Following pH adjustment, the determined amount of HSAC adsorbent was added to the solutions and then shaken at 180 rpm in a thermostatic water bath. The samples were filtered using a 0.22 µm membrane syringe filter, and the concentrations of favipiravir in the filtrates were measured with an HPLC system. The impact of pH on the efficiency of favipiravir removal was examined by changing the pH between 2 and 12 while keeping the other parameters constant. pH adjustments were made using HCl or NaOH solutions. Then, the effect of different HSAC dosages ranging from 5 to 20 mg on the adsorption efficiency was evaluated at the pH that provided optimum removal. In addition, the effect of the initial favipiravir concentration (20–100 mg/L) and temperature (298–328 K) on the removal efficiency was investigated while keeping the other variables constant. The ranges of the variables used were selected (pH 2–12, adsorbent dose 5–20 mg, initial concentration 20–100 mg/L, temperature 298–328 K). The temperature range is the temperature encountered in atmospheric conditions when summer and winter months are considered. Adsorbent dose was kept at a minimum level since it directly affects the treatment cost. Since pH directly affects the adsorbent–adsorbate interaction, its effect on adsorption in acidic, basic, and neutral environments was determined. The initial concentration range was determined as 20–100 mg/L to be able to observe the removal. In real wastewater, concentrations lower than this range may be encountered, but this range was selected in order to observe the removal efficiency. All experiments were performed in triplicate, and the average results were reported, allowing systematic evaluation of the factors affecting adsorption efficiency. The amount of favipiravir adsorbed per unit mass of HSAC at a given time t (q t ) and equilibrium (q e) was calculated using the following equations:

(1) q t = ( C 0 − C t ) V / w ,

(2) q e = ( C 0 − C e ) V / w .

Additionally, the percentage of favipiravir adsorbed was calculated using the following formula:

(3) Adsorption ( % ) = ( ( C 0 – C e ) / C 0 ) 100 ,

where C e (mg/L) is the equilibrium concentration, C t (mg/L) is the concentration at time t, C 0 (mg/L) is the initial concentration, w (g) is the mass of HSAC, and V (L) is the volume of the solution.

2.6 Equilibrium modeling of favipiravir removal process

Adsorption isotherms describe the correlation between the concentration of the solution and the amount of adsorbate accumulated on the adsorbent surface at a certain temperature. They also provide an idea about the nature of the interactions between the solute and the surface. Properly constructed adsorption equilibrium curves allow the design of an effective adsorption system by showing the correlation between the favipiravir remaining in the solution and the favipiravir adsorbed on the surface.

In this study, the adsorption of favipiravir to HSAC was modeled using the Langmuir and Freundlich isotherm models. There are other isotherm models, but these two are the most commonly used. Excel software was used to fit the data to isotherm models.

The Langmuir isotherm assumes that adsorbate molecules interact physically or chemically with vacant sites on the adsorbent surface. Its linear form is expressed by the following equation [56,57]:

(4) C e q e = 1 q m K L + C e q m ,

where K L represents the adsorption constant in the Langmuir model (L mg−1), and qm represents the single-layer activated carbon’s adsorption capacity (mg/g). The relationship between the adsorbate and the adsorbent can be evaluated using the dimensionless separation factor (R L), which reflects the suitability of the adsorption process. R L is determined using the following equation:

(5) R L = 1 ( 1 + K L C 0 ) ,

where C 0 represents the adsorbate’s initial concentration in solution (mg L−1). The R L value helps in interpreting the adsorption isotherm: if R L = 0, the adsorption is irreversible; if 0 < R L < 1, the isotherm is favorable for adsorption; if R L = 1, the isotherm is linear; and if R L > 1, the isotherm is unfavorable. Unlike the Langmuir model, the Freundlich model assumes that the adsorbate molecules form multiple layers on the adsorbent surface instead of a single homogeneous layer. This model is particularly suitable for describing adsorption on heterogeneous surfaces with varying affinities for the adsorbate. The linearized form of the Freundlich isotherm model is expressed as follows [52]:

(6) ln ( q e ) = ln ( K F ) + ( 1 / n ) ln ( C e ) ,

where K F is the Freundlich constant (L/mg) and n is a parameter indicating the favorability of the adsorption process. If n > 1, higher concentrations should facilitate the adsorbate adsorption on the adsorbent.

2.7 Kinetic modeling of favipiravir removal process

The discrete adsorption data were interpreted using PFO and PSO kinetic models, and the relevant kinetic parameters were calculated. Excel software was used to fit the data to kinetic models. The PFO model assumes that each molecule of the adsorbate adheres to a specific site on the adsorbent, and the adsorption rate is determined by the sorption capacity of the solid surface. The linear form of this model is expressed as follows [56,57]:

(7) ln ( q e − q t ) = ln ( q e ) − k 1 t ,

where qe and qt represent the adsorption capacities at equilibrium and at a given time t (mg/g), and k 1 is the pseudo-first-order rate constant (min−1). In contrast, the PSO model describes the adsorption kinetics in relation to the capacity of the adsorbent and is defined by the following equation:

(8) t q t = 1 ( k 2 q e 2 ) + ( 1 / q e ) t ,

where q e and q t are the adsorption capacities at equilibrium (mg/g), and at given time t, k 2 is the rate constant for the (g/(mg min)), and t is the elapsed time.

2.8 Thermodynamic modeling of favipiravir removal process

Thermodynamic parameters, including enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°) changes, were determined to evaluate the spontaneity of the adsorption process and the effect of temperature on the adsorption performance. Gibbs free energy change (ΔG°) was calculated using the following equation [56,57]:

(9) Δ G ° = − RT   ln ( K e ) ,

where T denotes the absolute temperature (K), R stands for the universal gas constant (8.314 J/(mol K)), and K e represents the equilibrium constant, defined as follows:

(10) K e = ( q e / C e ) .

The Gibbs free energy change (ΔG°) is expressed in terms of enthalpy change (ΔH°) and entropy change (ΔS°) using the following equation:

(11) Δ G ° = Δ H ° − T Δ S ° .

By rearranging this expression, a linear equation is derived that allows for the calculation of thermodynamic parameters:

(12) ln ( K e ) = ( Δ S ° / R ) − ( Δ H ° / R T ) .

2.9 Determination of favipiravir

The concentration of favipiravir in solutions was measured using HPLC on a 1260 Infinity LC system (Agilent, USA). ODS 3-C18 chromatographic column (250 × 4.6 mm, 5 μm) was used, and detection was performed at a wavelength of 227 nm. The analysis was performed under isocratic conditions using a mobile phase consisting of 0.01 M KH2PO4 solution (pH:2, adjusted with phosphoric acid) and acetonitrile at a ratio of 70:30 (v/v). The column temperature was kept at 30°C, the flow rate was 1.0 mL/min, and the injection volume was 5 μL. The analytical method was validated for parameters such as linearity, system suitability, specificity, precision, accuracy, robustness, and sensitivity, in accordance with international conference on harmonisation Q2 (R1) guidelines [56,57].

3 Results and discussion

3.1 Characterization of HSAC

HSAC samples were characterized using SEM and FTIR analyses. SEM was used to examine the surface morphology of the adsorbent. SEM images of HSAC in the form of polycrystalline bonds are given in Figure 1a and b. It exhibited a porous structure with different dimensions. The finding regarding significantly porous material corresponds well with the findings of earlier studies on HSAC [58].

Figure 1 (a) and (b) HSAC’s SEM images at different magnification levels (A: 2 µm, B: 10 µm); (c) EDX image and elemental composition of HSAC; and (d) FTIR spectrum of HSAC.
Figure 1

(a) and (b) HSAC’s SEM images at different magnification levels (A: 2 µm, B: 10 µm); (c) EDX image and elemental composition of HSAC; and (d) FTIR spectrum of HSAC.

FTIR spectral measurement was performed to identify the structure of HSAC, and the spectrum obtained is given in Figure 1c. The spectral bands observed at 2,977 and 2,891 cm−1 in the FT–IR spectrum can be attributed to the C–H stretching vibration of alkyl groups and aromatic C═C stretching in the lignin structure. The spectrum bands observed at 1,568 cm−1 may match to C–O stretching, and the peak at 1,391 cm−1 may match to aromatic C–C functional group and/or C–H asymmetric deformation. The spectrum bands observed at 1,242, 1,166, and 1,066 cm−1 are thought to be related to C–O stretching vibration in carboxylic groups, esters, or phenolic groups [58].

The surface area of the HSAC samples was measured using BET analysis, and the results are shown in Table 1. Based on the IUPAC classification, the results indicated that the activated carbon follows a type II isotherm. This type II isotherm suggests that the activated carbon possesses exceptional surface properties and pore structures, making it highly suitable for applications such as wastewater treatment, gas purification, and solvent recovery [59].

Table 1

Properties of HSAC related to its pore structure

S BET (m2/g) S micro (m2/g) S out (m2/g) V total (cm3/g) V micro (cm3/g) V cumulatif (cm3/g) D p (nm)
1045.25 621.18 421.08 0.5875 0.3032 0.2658 2.2243

3.2 Determination of pHpzc of HSAC

pHpzc refers to the pH at which the surface of the adsorbent has a neutral charge. Determining this parameter is essential to understand the electrostatic interactions between the adsorbate and the adsorbent surface at different pH levels. The pHpzc value of HSAC was determined as 7.69. At pH levels lower than this, a positive charge is present on the adsorbent surface, increasing anion adsorption. On the contrary, when the pH is higher than pHpzc, a negative charge forms on the surface and enhances its suitability for cation adsorption. This behavior corresponds to a negative surface charge for activated carbon at pH levels higher than 7.69.

3.3 Impact of pH on favipiravir removal efficiency

To examine the effect of pH on adsorption efficiency, six solutions with a concentration of 30 mg/L, spanning pH values from 2 to 12, were prepared. A 15 mg amount of adsorbent was measured and added to each sample. The samples were then placed in a mixer set to 180 rpm at an ambient temperature of 25°C and stirred for 90 min. After the designated time, the samples were analyzed using the HPLC system. The results are shown in Figure 2a. As seen in the figure, favipiravir adsorption consistently decreased with increasing pH. The removal efficiency decreased from 94.55% at pH 2 to 64.77% at pH 12. Based on these findings, the optimum pH value for the adsorption process was determined to be 2.00.

Figure 2 (a): Impact of pH on favipiravir efficiency of removal, (b) impact of adsorbent dosage on favipiravir efficiency of removal, (c) impact of mixing time on favipiravir efficiency of removal, and (d) impact of initial concentration on favipiravir efficiency of removal.
Figure 2

(a): Impact of pH on favipiravir efficiency of removal, (b) impact of adsorbent dosage on favipiravir efficiency of removal, (c) impact of mixing time on favipiravir efficiency of removal, and (d) impact of initial concentration on favipiravir efficiency of removal.

3.4 Impact of HSAC dose on favipiravir removal efficiency

To assess the effect of HSAC quantity on adsorption efficiency, the concentration of 30 mg/L six solutions, at pH 2, was prepared. Varying amounts of adsorbent (5, 10, 15, and 20 mg) were carefully weighed and added to the solutions. The samples were then placed on a shaker at 180 rpm and stirred for 90 min at 25°C. After the specified time, 2 mL of each sample was drawn into a syringe, filtered through a syringe tip filter into a vial, and analyzed using the HPLC system. Figure 2b illustrates the correlation between adsorbent dosage and adsorption efficiency.

As illustrated in Figure 2b, the favipiravir removal efficiency increased with rising adsorbent dosage, reaching its peak at 15 mg. The initial experiment with a 5 mg dose achieved an efficiency of 48.04%. As the adsorbent amount was increased, the efficiency improved, reaching approximately 94.57% at 15 mg. Up to this dosage, the efficiency increase followed a linear trend. Based on Figure 2b, since saturation occurred at 15 mg with a 94.57% removal rate, this dosage was selected as the optimal amount to minimize adsorbent usage while ensuring over 90% adsorption efficiency.

3.5 Impact of mixing time on the efficiency of favipiravir removal

To evaluate the impact of mixing time on adsorption efficiency, 15 mg of adsorbent was added to a favipiravir solution with an initial concentration of 30 mg/L, at pH 2, and at 25°C.

The solution was then shaken at 180 rpm for 150 min. At specific time intervals, 1 mL of the sample was withdrawn using a syringe, filtered through a syringe tip filter into a vial, and analyzed using the HPLC system. The variation in adsorption efficiency with mixing time is shown in Figure 2c.

The adsorption efficiency showed a linear increase for the first 5 min as the mixing time increased, followed by a slight rise in removal efficiency between 5 and 90 min, after which it nearly stabilized. In the study, at the end of 5 min contact time, the efficiency was 68.67%. Equilibrium was achieved with an efficiency of 94.60% after 90 min and 94.93% after 150 min. Therefore, 90 min was selected as the optimal time for equilibrium adsorption kinetic modeling in the subsequent study. The results showed that equilibrium continued for 150 min, reaching an efficiency of 94.93%. Based on these findings, the optimal mixing time was determined to be 90 min.

3.6 Impact of initial favipiravir concentration on removal efficiency

To investigate the effect of initial concentration on favipiravir removal, experiments were conducted at pH 2, temperature 25°C, mixing time 150 min, adsorbent amount 15 mg in 50 mL, and initial concentration values between 20–100 mg/L. In accordance with the results, analyses showed that favipiravir adsorption depends on the initial concentration. Figure 2a–d shows the effect of initial favipiravir concentration on removal efficiency.

As seen in Figure 2d, favipiravir removal varies depending on the increase in concentration. The study initiated at a concentration of 20 mg L mg/L resulted in an efficiency of 96.53% and 30 mg/L resulted in an efficiency of 95.83%. However, a significant decrease in removal efficiency was observed at concentrations after the initial concentration of 30 mg/L. The removal efficiency was 91.58% at a concentration of 40 mg/L, 85.50% at 50 mg/L, and 59.99% at 100 mg/L. This is an anticipated outcome, as the adsorbent’s ability to retain favipiravir diminishes once it reaches saturation. Consistent with these findings, the optimal initial concentration was identified as 30 mg/L.

3.7 Impact of ambient temperature on the efficiency of favipiravir removal

In order to investigate the effect of ambient temperature on adsorption, experiments were carried out at pH 2, temperature 25°C, mixing time 150 min, adsorbent dose 15 mg for 50 mL, and initial concentration 30 mg/L. Values of temperature 25, 35, 45 and 55°C were selected for analysis. The effect of temperature on favipiravir removal efficiency is given in Figure 3.

Figure 3 Effect of temperature on favipiravir removal effectiveness.
Figure 3

Effect of temperature on favipiravir removal effectiveness.

As seen in Figure 3, 94.93% efficiency was obtained at 25°C. As the temperature increased, this efficiency tended to decrease and was determined as 89.30% at 55°C. This situation shows that the adsorption process has a negative enthalpy. Increasing temperature values will cause a decrease in the viscosity of the solution. This will reduce diffusion in adsorption. This situation is consistent with similar studies in the literature [13]. As a result, changing the temperature affects the equilibrium capacity in adsorption.

3.8 Thermodynamic behavior of adsorption

The thermodynamic evaluation of adsorption was performed by calculating the entropy, enthalpy, Gibbs free energy change (∆G), and equilibrium constant throughout the adsorption process. Temperature had a significant impact in this investigation. In the experimental study, equilibrium was achieved at five varying temperatures (25, 35, 45, 55°C), using 30 mg L−1 favipiravir solutions with 15 mg of adsorbent. The effect of varying temperatures on favipiravir adsorption was examined. K equilibrium constants and ∆G values of the adsorption solutions studied at different temperatures were obtained. The ∆H values were determined from the slope of the plot between 1/T and lnK, whereas the ∆S values were calculated from the intercept. The thermodynamic variables for favipiravir adsorption are presented in Table 2.

Table 2

Thermodynamic variables for favipiravir adsorption

Temperature ΔG ΔH ΔS
K J/mol J/mol J/mol
298 −9.749 −23.599 −46
308 −9.284
318 −8.819
328 −8.355

The standard of Gibbs free energy change (∆G) was consistently negative across all temperatures. This negative value suggests that the adsorption process occurs spontaneously [60]. When examining the data in Table 2, it is seen that as the temperature increases, the Gibbs free energy change becomes less negative. This situation shows that adsorption is more effective at lower temperatures. We can say that the adsorption process is exothermic due to the negative ∆H value and that the disorder decreases due to the negative ∆S value.

3.9 Adsorption isotherms

The adsorption mechanism of favipiravir onto HSAC was investigated using the Langmuir and Freundlich isotherm models. The results from these models are summarized in Table 3. To assess the fit of the models, the correlation coefficients (R 2) were considered, and it was found that the Langmuir model best represented the experimental data. The high correlation coefficient (R 2 = 0.9942) obtained from the Langmuir model indicates that favipiravir adsorption onto HSAC occurred in a monolayer, with uniformly distributed active sites on the adsorbent and appropriate binding [61]. The maximum theoretical adsorption capacity (q max) calculated using the Langmuir model is an important parameter in designing efficient adsorption systems for specific pollutants and is very similar to the equilibrium capacity values obtained experimentally in this study (Table 3). While the Freundlich model yielded slightly lower R 2 values, the heterogeneity factor (n) exceeding 1 suggests that the adsorption process is favorable [62]. In addition, the R L constant was calculated as 0.7673, and the process is in good agreement with this isotherm, as R L values between 0 and 1 indicate favorable adsorption. Furthermore, the high K L value reflecting the affinity of favipiravir for HSAC further supports the agreement of the Langmuir isotherm with the data [63].

Table 3

Important variables of the Langmuir and Freundlich isotherm models

Langmuir isotherm model data Freundlich isotherm model data
q max (mg/g) K L (mg/L) R 2 K F (mg/g) n R 2
212.77 0.3032 0.9942 73.00 3.55 0.9940

3.10 Adsorption kinetics

The kinetics of the adsorption process was investigated using PFO and PSO models; the relevant kinetic parameters and correlation coefficients are given in Table 4. According to the PFO model, adsorption takes place through diffusion across a limiting layer on the surface. In contrast, the PSO model indicates that chemical adsorption is the primary mechanism [64]. When the table data are evaluated, it is seen that the adsorption of favipiravir fits the PSO model better because the correlation coefficient calculated for this model (R 2 = 0.9998) is higher than that of the PFO model (R 2 = 0.9839). Kinetic graphs were created to visualize the data, and these graphs are presented in Figure 4. In addition, the experimentally determined adsorption capacity (q e = 94.93 mg/g) is quite close to the capacity calculated from the PSO model (q e = 97.09 mg/g), further supporting the PSO model. In line with these results, it can be said that chemical adsorption is the dominant mechanism for favipiravir adsorption on the adsorbent surface.

Table 4

Important parameters of PFO and PSO models

PFO kinetic model data PSO kinetic model data
k 1 (min−1) q e (mg/g) R 2 k 2 (g/(mg min)) q e (mg/g) R 2
0.0227 19.68 0.9839 0.0312 97.09 0.9998
Figure 4 Kinetic graphs of PFO (a) and PSO (b) models.
Figure 4

Kinetic graphs of PFO (a) and PSO (b) models.

4 Discussion

The data from this study confirm that activated carbon sourced from hazelnut shell waste (HSAC) work as a powerful adsorbent for the removal of favipiravir from synthetic wastewater. The optimized conditions obtained (30 μg/mL initial concentration, 25°C temperature, pH 2, 15 mg HSAC dose per 50 mL solution, and 90 min of contact time) resulted in a high removal efficiency of 94.60%. These findings highlight HSAC’s potential as a budget and environmentally friendly alternative for pharmaceutical wastewater treatment.

Compared to previous studies utilizing various bio-based adsorbents for pharmaceutical removal, HSAC exhibits a notably high adsorption capacity. While other agricultural waste-derived adsorbents, such as rice husk, coconut shell, and almond shell-based activated carbons, have been investigated for pharmaceutical adsorption, their efficiency in removing favipiravir or structurally similar compounds has generally been lower. Furthermore, many reported adsorbents require extensive chemical activation processes involving harsh reagents, whereas HSAC was produced using a relatively simple and sustainable activation method. This makes HSAC not only an effective but also a more sustainable option for pharmaceutical wastewater treatment.

Additionally, most adsorption studies focus on commonly detected pharmaceuticals such as antibiotics (e.g., tetracycline, ciprofloxacin) or analgesics (e.g., ibuprofen, diclofenac), whereas favipiravir has received limited attention. Given the increasing use of favipiravir during viral outbreaks and its subsequent release into aquatic environments, this study addresses a critical research gap by systematically evaluating its adsorption behavior.

The importance of low pH levels (such as pH 2) in real wastewater conditions should be particularly emphasized. Pharmaceutical industry effluents and hospital wastewater can exhibit acidic characteristics due to the presence of various pharmaceutical compounds and processing chemicals. The strong adsorption performance of HSAC under acidic conditions suggests that it may be highly effective in treating favipiravir-contaminated wastewater streams originating from these sources. Additionally, at low pH, the protonation of favipiravir molecules increases, enhancing electrostatic interactions with HSAC’s functional groups, which contributes to the high removal efficiency observed.

The necessity of removing favipiravir from wastewater is reinforced by its toxicity and potential environmental risks. Studies have shown that favipiravir and its metabolites can persist in aquatic environments, posing potential risks to aquatic organisms. Research indicates that chronic exposure to favipiravir can disrupt enzymatic activity in fish, affect microbial communities essential for aquatic ecosystem balance, and contribute to the development of antibiotic resistance. Given its antiviral properties, favipiravir may also interfere with the virome of natural water bodies, potentially impacting microbial populations that play a role in nutrient cycling and water purification.

While current environmental regulations do not yet specifically limit favipiravir concentrations in effluents, the increasing detection of pharmaceutical residues in water sources underscores the urgency of effective removal strategies. The high adsorption efficiency of HSAC suggests that it could be a practical solution for mitigating favipiravir contamination and its associated environmental risks.

The robustness of the obtained results is supported by thorough experimental validation, including repeatability tests and error analysis. The strong agreement between the experimental data and the Langmuir isotherm model (R 2: 0.9942) confirms monolayer adsorption on a homogeneous surface. The high fit of the PSO kinetic model (R 2: 0.9998) suggests that chemical interactions, such as hydrogen bonding, π–π interactions, and electrostatic attractions, play a dominant role. These findings enhance the credibility of the adsorption mechanism proposed in this study.

Despite its promising findings, this study has some limitations for future research. While this study was conducted using synthetic wastewater, real wastewater matrices contain complex mixtures of organic and inorganic substances that may influence adsorption efficiency. Future studies should investigate HSAC’s performance in real hospital or pharmaceutical industry wastewater to validate its practical applicability. The economic viability of HSAC as an adsorbent relies on its capacity to be regenerated and reused several times without a substantial decrease in adsorption efficiency. Further studies should assess different regeneration techniques, such as thermal or chemical desorption, to determine the sustainability of HSAC in long-term applications. Most laboratory-scale studies, including this one, are conducted in batch systems, which may not fully replicate real-world wastewater treatment conditions. Evaluating HSAC in continuous-flow adsorption columns or pilot-scale treatment systems would provide valuable insights into its industrial applicability. Although the adsorption behavior of favipiravir onto HSAC has been well characterized through isotherm and kinetic models, more detailed molecular-level investigations, such as spectroscopic analysis (FTIR) before and after adsorption, could further elucidate the exact nature of the interactions involved.

The superior performance of HSAC in favipiravir removal highlights its potential as an effective adsorbent for pharmaceutical wastewater treatment. Its high adsorption capacity, simple preparation process, and environmentally friendly nature make it a promising alternative to conventional treatment methods. Given the increasing environmental concerns surrounding pharmaceutical contamination, further research into HSAC’s application in real wastewater treatment, regeneration potential, and large-scale implementation will be crucial for optimizing its use in industrial settings.

  1. Funding information: The author states no finding involved.

  2. Author contribution: The author confirms sole responsibility for the following: study conception and design, data collection, analysis and interpretation of results, and manuscript preparation.

  3. Conflict of interest: The author states no conflict of interest.

  4. Ethical approval: The conducted research is not related to either human or animal use.

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

References

[1] Couto CF, Lange LC, Amaral MCS. Occurrence, fate and removal of pharmaceutically active compounds (PhACs) in water and wastewater treatment plants—A review. J Water Process Eng. 2019;32:100927. 10.1016/j.jwpe.2019.100927.Search in Google Scholar

[2] Bilal M, Rizwan K, Adeel M, Iqbal HMN. Hydrogen-based catalyst-assisted advanced oxidation processes to mitigate emerging pharmaceutical contaminants. Int J Hydrog Energy. 2022;47:19555–69. 10.1016/j.ijhydene.2021.11.018.Search in Google Scholar

[3] Krasucka P, Rombel A, Yang XJ, Rakowska M, Xing B, Oleszczuk P. Adsorption and desorption of antiviral drugs (ritonavir and lopinavir) on sewage sludges as a potential environmental risk. J Hazard Mater. 2022;425:127901. 10.1016/j.jhazmat.2021.127901.Search in Google Scholar PubMed

[4] Yao L, Dou WY, Ma YF, Liu YS. Development and validation of sensitive methods for simultaneous determination of 9 antiviral drugs in different various environmental matrices by UPLC-MS/MS. Chemosphere. 2021;282:131047. 10.1016/j.chemosphere.2021.131047.Search in Google Scholar PubMed

[5] Nannou C, Ofrydopoulou A, Evgenidou E, Heath D, Heath E, Lambropoulou D. Antiviral drugs in aquatic environment and wastewater treatment plants: A review on occurrence, fate, removal and ecotoxicity. Sci Total Env. 2020;699:134322. 10.1016/j.scitotenv.2019.134322.Search in Google Scholar PubMed

[6] De Clercq E, Li G. Approved antiviral drugs over the past 50 years. Clin Microbiol Rev. 2016;29:695–747. 10.1128/CMR.00102-15.Search in Google Scholar PubMed PubMed Central

[7] Yao L, Chen ZY, Dou WY, Yao ZK, Duan XC, Chen ZF, et al. Occurrence, removal and mass loads of antiviral drugs in seven wastewater treatment plants with various treatment processes. Water Res. 2021;207:117803. 10.1016/j.watres.2021.117803.Search in Google Scholar PubMed

[8] Silva M, Baltrus JP, Williams C, Knopf A, Zhang L, Baltrusaitis J. Heterogeneous photo-Fenton-like degradation of emerging pharmaceutical contaminants in wastewater using Cu-doped MgO nanoparticles. Appl Catal A Gen. 2022;630:118468. 10.1016/j.apcata.2021.118468.Search in Google Scholar

[9] Nippes RP, Macruz PD, da Silva GN, Neves Olsen Scaliante MH. A critical review on environmental presence of pharmaceutical drugs tested for the covid-19 treatment. Process Saf Env Prot. 2021;152:568–82. 10.1016/j.psep.2021.06.040.Search in Google Scholar PubMed PubMed Central

[10] Jain S, Kumar P, Vyas RK, Pandit P, Dalai AK. Occurrence and removal of antiviral drugs in environment: A review. Water Air Soil Pollut. 2013;224:1410. 10.1007/s11270-012-1410-3.Search in Google Scholar

[11] Kumari M, Kumar A. Environmental and human health risk assessment of mixture of Covid-19 treating pharmaceutical drugs in environmental waters. Sci Total Env. 2022;812:152485. 10.1016/j.scitotenv.2021.152485.Search in Google Scholar PubMed PubMed Central

[12] Nannou C, Ofrydopoulou A, Evgenidou E, Heath D, Heath E, Lambropoulou D. Analytical strategies for the determination of antiviral drugs in the aquatic environment. Trends Env Anal Chem. 2019;24:e00071. 10.1016/j.teac.2019.e00071.Search in Google Scholar

[13] Bulduk İ, Demir İ, Enginar H, Çifci C, Mahammadiev J. Removal of antiviral ribavirin from aqueous solutions by activated carbon prepared from tobacco stems. Acta Chromatogr. 2025;3–12. 10.1556/1326.2025.01311.Search in Google Scholar

[14] Biswas P, Hasan MM, Dey D, dos Santos Costa AC, Polash SA, Bibi S, et al. Candidate antiviral drugs for COVID-19 and their environmental implications: A comprehensive analysis. Env Sci Pollut Res. 2021;28:59570–93. 10.1007/s11356-021-16096-3.Search in Google Scholar PubMed PubMed Central

[15] Frediansyah A, Tiwari R, Sharun K, Dhama K. Antivirals for COVID-19: A critical review. Clin Epidemiol Glob Heal. 2021;9:90–8.10.1016/j.cegh.2020.07.006Search in Google Scholar PubMed PubMed Central

[16] Gong WJ, Zhou T, Wu SL, Ye JL, Xu JQ, Zeng F, et al. A retrospective analysis of clinical efficacy of ribavirin in adults hospitalized with severe COVID-19. J Infect Chemother. 2021;27:876–81. 10.1016/j.jiac.2021.02.018.Search in Google Scholar PubMed PubMed Central

[17] Khalili JS, Zhu H, Mak NSA, Yan Y, Zhu Y. Novel coronavirus treatment with ribavirin: Groundwork for an evaluation concerning COVID-19. J Med Virol. 2020;92:740–6. 10.1002/jmv.25798.Search in Google Scholar PubMed PubMed Central

[18] Li H, Xiong N, Li C, Gong Y, Liu L, Yang H, et al. Efficacy of ribavirin and interferon-α therapy for hospitalized patients with COVID-19: A multicenter, retrospective cohort study. Int J Infect Dis. 2021;104:641–8. 10.1016/j.ijid.2021.01.055.Search in Google Scholar PubMed PubMed Central

[19] Liu L, Guo S, Che C, Su Q, Zhu D, Hai X. Improved HPLC method for the determination of ribavirin concentration in red blood cells and its application in patients with COVID-19. Biomed Chromatogr. 2022;36:1–7. 10.1002/bmc.5370.Search in Google Scholar PubMed PubMed Central

[20] Chen X, Lei L, Liu S, Han J, Li R, Men J, et al. Occurrence and risk assessment of pharmaceuticals and personal care products (PPCPs) against COVID-19 in lakes and WWTP-river-estuary system in Wuhan, China. Sci Total Env. 2021;792:148352. 10.1016/j.scitotenv.2021.148352.Search in Google Scholar PubMed PubMed Central

[21] Liu Q, Feng X, Chen N, Shen F, Zhang H, Wang S, et al. Occurrence and risk assessment of typical PPCPs and biodegradation pathway of ribavirin in wastewater treatment plants. Env Sci Ecotechnol. 2022;11:1–9. 10.1016/j.ese.2022.100184.Search in Google Scholar PubMed PubMed Central

[22] Prasse C, Schlüsener MP, Schulz R, Ternes TA. Antiviral drugs in wastewater and surface waters: A new pharmaceutical class of environmental relevance? Env Sci Technol. 2010;44:1728–35. 10.1021/es903216p.Search in Google Scholar PubMed

[23] Xu WH, Zhang G, Zou SC, Li XD, Liu YC. Determination of selected antibiotics in the Victoria Harbour and the Pearl River, South China using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry. Env Pollut. 2007;145:672–9. 10.1016/j.envpol.2006.05.038.Search in Google Scholar PubMed

[24] Kumar M, Mazumder P, Mohapatra S, Kumar Thakur A, Dhangar K, Taki K, et al. A chronicle of SARS-CoV-2: Seasonality, environmental fate, transport, inactivation, and antiviral drug resistance. J Hazard Mater. 2021;405:1–18. 10.1016/j.jhazmat.2020.124043.Search in Google Scholar PubMed PubMed Central

[25] Kuroda K, Li C, Dhangar K, Kumar M. Predicted occurrence, ecotoxicological risk and environmentally acquired resistance of antiviral drugs associated with COVID-19 in environmental waters. Sci Total Env. 2021;776:145740. 10.1016/j.scitotenv.2021.145740.Search in Google Scholar PubMed PubMed Central

[26] Prasse C, Wagner M, Schulz R, Ternes TA. Oxidation of the antiviral drug acyclovir and its biodegradation product carboxy-acyclovir with ozone: Kinetics and identification of oxidation products. Env Sci Technol. 2012;46:2169–78. 10.1021/es203712z.Search in Google Scholar PubMed

[27] Mascolo G, Laera G, Pollice A, Cassano D, Pinto A, Salerno C, et al. Effective organics degradation from pharmaceutical wastewater by an integrated process including membrane bioreactor and ozonation. Chemosphere. 2010;78:1100–9. 10.1016/j.chemosphere.2009.12.042.Search in Google Scholar PubMed

[28] Ngumba E, Gachanja A, Tuhkanen T. Removal of selected antibiotics and antiretroviral drugs during post-treatment of municipal wastewater with UV, UV/chlorine and UV/hydrogen peroxide. Water Env J. 2020;34:692–703. 10.1111/wej.12612.Search in Google Scholar

[29] Mestankova H, Schirmer K, Escher BI, Von Gunten U, Canonica S. Removal of the antiviral agent oseltamivir and its biological activity by oxidative processes. Env Pollut. 2012;161:30–5. 10.1016/j.envpol.2011.09.018.Search in Google Scholar PubMed

[30] Zhou Y, Li WB, Kumar V, Necibi MC, Mu YJ, Shi CZ, et al. Synthetic organic antibiotics residues as emerging contaminants waste-to-resources processing for a circular economy in China: Challenges and perspective. Env Res. 2022;211:1–18. 10.1016/j.envres.2022.113075.Search in Google Scholar PubMed

[31] Tang S, Xu L, Yu X, Chen S, Li H, Huang Y, et al. Degradation of anticancer drug capecitabine in aquatic media by three advanced oxidation processes: Mechanisms, toxicity changes and energy cost evaluation. Chem Eng J. 2021;413:127489. 10.1016/j.cej.2020.127489.Search in Google Scholar

[32] Mareai BM, Fayed M, Aly SA, Elbarki WI. Performance comparison of phenol removal in pharmaceutical wastewater by activated sludge and extended aeration augmented with activated carbon. Alex Eng J. 2020;59:5187–96. 10.1016/j.aej.2020.09.048.Search in Google Scholar

[33] Yan X, Zheng S, Huo Z, Shi B, Huang J, Yang J, et al. Effects of exogenous N-acyl-homoserine lactones on nutrient removal, sludge properties and microbial community structures during activated sludge process. Chemosphere. 2020;255:126945. 10.1016/j.chemosphere.2020.126945.Search in Google Scholar PubMed

[34] Shao Y, Liu GH, Wang Y, Zhang Y, Wang H, Qi L, et al. Sludge characteristics, system performance and microbial kinetics of ultra-short-SRT activated sludge processes. Env Int. 2020;143:105973. 10.1016/j.envint.2020.105973.Search in Google Scholar PubMed

[35] Judd S. The status of membrane bioreactor technology. Trends Biotechnol. 2008;26:109–16. 10.1016/j.tibtech.2007.11.005.Search in Google Scholar PubMed

[36] González-Hernández Y, Jáuregui-Haza UJ. Improved integrated dynamic model for the simulation of submerged membrane bioreactors for urban and hospital wastewater treatment. J Memb Sci. 2021;624:1–16. 10.1016/j.memsci.2021.119053.Search in Google Scholar

[37] Jang Y, Kim HS, Ham SY, Park JH, Park HD. Investigation of critical sludge characteristics for membrane fouling in a submerged membrane bioreactor: Role of soluble microbial products and extracted extracellular polymeric substances. Chemosphere. 2021;271:129879. 10.1016/j.chemosphere.2021.129879.Search in Google Scholar PubMed

[38] Dobe N, Abia D, Tcheka C, Tejeogue JPN, Harouna M. Removal of amaranth dye by modified Ngassa clay: Linear and non-linear equilibrium, kinetics and statistical study. Chem Phys Lett. 2022;801:139707. 10.1016/j.cplett.2022.139707.Search in Google Scholar

[39] Ebrahimi P, Kumar A. Diatomite chemical activation for effective adsorption of methylene blue dye from model textile wastewater. Int J Env Sci Dev. 2021;12:23–8. 10.18178/ijesd.2021.12.1.1313.Search in Google Scholar

[40] Maingi FM, Mbuvi HM, Ng’ang’ MM, Mwangi H. Adsorption of cadmium ions on geopolymers derived from ordinary clay and rice husk ash. Int J Mater Chem. 2018;8:1–9. 10.5923/j.ijmc.20180801.01.Search in Google Scholar

[41] Onutai S, Kobayashi T, Thavorniti P, Jiemsirilers S. Porous fly ash-based geopolymer composite fiber as an adsorbent for removal of heavy metal ions from wastewater. Mater Lett. 2019;236:30–3. 10.1016/j.matlet.2018.10.035.Search in Google Scholar

[42] Cechinel MAP, Ulson De Souza SMAG, Ulson De Souza AA. Study of lead (II) adsorption onto activated carbon originating from cow bone. J Clean Prod. 2014;65:342–9. 10.1016/j.jclepro.2013.08.020.Search in Google Scholar

[43] Wang L. Application of activated carbon derived from “waste” bamboo culms for the adsorption of azo disperse dye: Kinetic, equilibrium and thermodynamic studies. J Env Manage. 2012;102:79–87. 10.1016/j.jenvman.2012.02.019.Search in Google Scholar PubMed

[44] Betancur M, Martínez JD, Murillo R. Production of activated carbon by waste tire thermochemical degradation with CO2. J Hazard Mater. 2009;168:882–7. 10.1016/j.jhazmat.2009.02.167.Search in Google Scholar PubMed

[45] Björklund K, Li LY. Adsorption of organic stormwater pollutants onto activated carbon from sewage sludge. J Env Manage. 2017;197:490–7. 10.1016/j.jenvman.2017.04.011.Search in Google Scholar PubMed

[46] Chen Y, Zhu Y, Wang Z, Li Y, Wang L, Ding L, et al. Application studies of activated carbon derived from rice husks produced by chemical-thermal process – A review. Adv Colloid Interface Sci. 2011;163:39–52. 10.1016/j.cis.2011.01.006.Search in Google Scholar PubMed

[47] Foo KY, Hameed BH. Utilization of rice husks as a feedstock for preparation of activated carbon by microwave induced KOH and K2CO3 activation. Bioresour Technol. 2011;102:9814–7. 10.1016/j.biortech.2011.07.102.Search in Google Scholar PubMed

[48] Iriarte-Velasco U, Álvarez-Uriarte JI, Chimeno-Alaníc N, González-Velasco JR. Natural organic matter adsorption onto granular activated carbons: Implications in the molecular weight and disinfection byproducts formation. Ind Eng Chem Res. 2008;47:7868–76. 10.1021/ie800912y.Search in Google Scholar

[49] Gonçalves G, da C, Pereira NC, Veit MT. Production of bio-oil and activated carbon from sugarcane bagasse and molasses. Biomass Bioenergy. 2016;85:178–86. 10.1016/j.biombioe.2015.12.013.Search in Google Scholar

[50] Hashemian S, Salari K, Yazdi ZA. Preparation of activated carbon from agricultural wastes (almond shell and orange peel) for adsorption of 2-pic from aqueous solution. J Ind Eng Chem. 2014;20:1892–900. 10.1016/j.jiec.2013.09.009.Search in Google Scholar

[51] Omri A, Lambert SD, Geens J, Bennour F, Benzina M. Synthesis, surface characterization and photocatalytic activity of TiO2 supported on almond shell activated carbon. J Mater Sci Technol. 2014;30:894–902.10.1016/j.jmst.2014.04.007Search in Google Scholar

[52] Mumba PP, Phiri R. Environmental impact assessment of tobacco waste disposal. Int J Env Res. 2008;2:225–30.Search in Google Scholar

[53] Lupul I, Yperman J, Carleer R, Gryglewicz G. Tailoring of porous texture of hemp stem-based activated carbon produced by phosphoric acid activation in steam atmosphere. J Porous Mater. 2015;22:283–9. 10.1007/s10934-014-9894-4.Search in Google Scholar

[54] Wang X, Feng X, Ma Y. Activated carbon from chili straw: K2CO3 activation mechanism, adsorption of dyes, and thermal regeneration. Biomass Convers Biorefin. 2024;14:19563–80. 10.1007/S13399-023-04173-1/FIGURES/17.Search in Google Scholar

[55] Cuerda-Correa EM, Domínguez-Vargas JR, Olivares-Marín FJ, de Heredia JB. On the use of carbon blacks as potential low-cost adsorbents for the removal of non-steroidal anti-inflammatory drugs from river water. J Hazard Mater. 2010;177:1046–53. 10.1016/j.jhazmat.2010.01.026.Search in Google Scholar PubMed

[56] Mehdizadeh A, Najafi Moghadam P, Ehsanimehr S, Fareghi AR. Preparation of a new magnetic nanocomposite for the removal of dye pollutions from aqueous solutions: Synthesis and characterization. Mater Chem Horiz. 2022;1:23–34.Search in Google Scholar

[57] Imanipoor J, Mohammadi M, Dinari M, Ehsani MR. Adsorption and desorption of amoxicillin antibiotic from water matrices using an effective and recyclable MIL-53(Al) metal-organic framework adsorbent. J Chem Eng Data. 2021;66:389–403. 10.1021/acs.jced.0c00736.Search in Google Scholar

[58] Kaya N, Yıldız Z, Ceylan S. Preparation and characterisation of biochar from hazelnut shell and its adsorption properties for methylene blue dye. J Polytech. 2018;0900:765–76. 10.2339/politeknik.386963.Search in Google Scholar

[59] Chen R, Li L, Liu Z, Lu M, Wang C, Li H, et al. Preparation and characterization of activated carbons from tobacco stem by chemical activation. J Air Waste Manag Assoc. 2017;67:713–24. 10.1080/10962247.2017.1280560.Search in Google Scholar PubMed

[60] Kausar A, Iqbal M, Javed A, Aftab K, Nazli ZIH, Bhatti HN, et al. Dyes adsorption using clay and modified clay: A review. J Mol Liq. 2018;256:395–407. 10.1016/j.molliq.2018.02.034.Search in Google Scholar

[61] Abu Rumman G, Al-Musawi TJ, Sillanpaa M, Balarak D. Adsorption performance of an amine-functionalized MCM–41 mesoporous silica nanoparticle system for ciprofloxacin removal. Env Nanotechnol Monit Manag. 2021;16:100536. 10.1016/j.enmm.2021.100536.Search in Google Scholar

[62] Nassar MY, Ahmed IS, Raya MA. A facile and tunable approach for synthesis of pure silica nanostructures from rice husk for the removal of ciprofloxacin drug from polluted aqueous solutions. J Mol Liq. 2019;282:251–63. 10.1016/j.molliq.2019.03.017.Search in Google Scholar

[63] Zaidi R, Khan SU, Farooqi IH, Azam A. Investigation of kinetics and adsorption isotherm for fluoride removal from aqueous solutions using mesoporous cerium-aluminum binary oxide nanomaterials. RSC Adv. 2021;11:28744–60. 10.1039/d1ra00598g.Search in Google Scholar PubMed PubMed Central

[64] Bullen JC, Saleesongsom S, Gallagher K, Weiss DJ. A revised pseudo-second-order kinetic model for adsorption, sensitive to changes in adsorbate and adsorbent concentrations. Langmuir. 2021;37:3189–201. 10.1021/acs.langmuir.1c00142.Search in Google Scholar PubMed

Received: 2024-12-12
Revised: 2025-03-11
Accepted: 2025-03-17
Published Online: 2025-04-15

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

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

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https://doi.org/10.1515/chem-2025-0149
Keywords for this article
biochar; favipiravir; hazelnut shells; adsorption
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BY 4.0

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  4. Discovery of the bacterial HslV protease activators as lead molecules with novel mode of action
  5. Characterization of volatile flavor compounds of cigar with different aging conditions by headspace–gas chromatography–ion mobility spectrometry
  6. Effective remediation of organic pollutant using Musa acuminata peel extract-assisted iron oxide nanoparticles
  7. Analysis and health risk assessment of toxic elements in traditional herbal tea infusions
  8. Cadmium exposure in marine crabs from Jiaxing City, China: Insights into health risk assessment
  9. Green-synthesized silver nanoparticles of Cinnamomum zeylanicum and their biological activities
  10. Tetraclinis articulata (Vahl) Mast., Mentha pulegium L., and Thymus zygis L. essential oils: Chemical composition, antioxidant and antifungal properties against postharvest fungal diseases of apple, and in vitro, in vivo, and in silico investigation
  11. Exploration of plant alkaloids as potential inhibitors of HIV–CD4 binding: Insight into comprehensive in silico approaches
  12. Recovery of phenylethyl alcohol from aqueous solution by batch adsorption
  13. Electrochemical approach for monitoring the catalytic action of immobilized catalase
  14. Green synthesis of ZIF-8 for selective adsorption of dyes in water purification
  15. Optimization of the conditions for the preparation of povidone iodine using the response surface methodology
  16. A case study on the influence of soil amendment on ginger oil’s physicochemical properties, mineral contents, microbial load, and HPLC determination of its vitamin level
  17. Removal of antiviral favipiravir from wastewater using biochar produced from hazelnut shells
  18. Effect of biochar and soil amendment on bacterial community composition in the root soil and fruit of tomato under greenhouse conditions
  19. Bioremediation of malachite green dye using Sargassum wightii seaweed and its biological and physicochemical characterization
  20. Evaluation of natural compounds as folate biosynthesis inhibitors in Mycobacterium leprae using docking, ADMET analysis, and molecular dynamics simulation
  21. Novel insecticidal properties of bioactive zoochemicals extracted from sea urchin Salmacis virgulata
  22. Elevational gradients shape total phenolic content and bioactive potential of sweet marjoram (Origanum majorana L.): A comparative study across altitudinal zones
  23. Study on the CO2 absorption performance of deep eutectic solvents formed by superbase DBN and weak acid diethylene glycol
  24. Preparation and wastewater treatment performance of zeolite-modified ecological concrete
  25. Multifunctional chitosan nanoparticles: Zn2+ adsorption, antimicrobial activity, and promotion of aquatic health
  26. Comparative analysis of nutritional composition and bioactive properties of Chlorella vulgaris and Arthrospira platensis: Implications for functional foods and dietary supplements
  27. Growth kinetics and mechanical characterization of boride layers formed on Ti6Al4V
  28. Enhancement of water absorption properties of potassium polyacrylate-based hydrogels in CaCl2-rich soils using potassium di- and tri-carboxylate salts
  29. Electrochemical and microbiological effects of dumpsite leachates on soil and air quality
  30. Modeling benzene physicochemical properties using Zagreb upsilon indices
  31. Characterization and ecological risk assessment of toxic metals in mangrove sediments near Langen Village in Tieshan Bay of Beibu Gulf, China
  32. Protective effect of Helicteres isora, an efficient candidate on hepatorenal toxicity and management of diabetes in animal models
  33. Valorization of Juglans regia L. (Walnut) green husk from Jordan: Analysis of fatty acids, phenolics, antioxidant, and cytotoxic activities
  34. Molecular docking and dynamics simulations of bioactive terpenes from Catharanthus roseus essential oil targeting breast cancer
  35. Selection of a dam site by using AHP and VIKOR: The Sakarya Basin
  36. Characterization and modeling of kidney bean shell biochar as adsorbent for caffeine removal from aquatic environments
  37. The effects of short-term and long-term 2100 MHz radiofrequency radiation on adult rat auditory brainstem response
  38. Biochemical insights into the anthelmintic and anti-inflammatory potential of sea cucumber extract: In vitro and in silico approaches
  39. Resveratrol-derived MDM2 inhibitors: Synthesis, characterization, and biological evaluation against MDM2 and HCT-116 cells
  40. Phytochemical constituents, in vitro antibacterial activity, and computational studies of Sudanese Musa acuminate Colla fruit peel hydro-ethanol extract
  41. Chemical composition of essential oils reviewed from the height of Cajuput (Melaleuca leucadendron) plantations in Buru Island and Seram Island, Maluku, Indonesia
  42. Phytochemical analysis and antioxidant activity of Azadirachta indica A. Juss from the Republic of Chad: in vitro and in silico studies
  43. Stability studies of titanium–carboxylate complexes: A multi-method computational approach
  44. Efficient adsorption performance of an alginate-based dental material for uranium(vi) removal
  45. Synthesis and characterization of the Co(ii), Ni(ii), and Cu(ii) complexes with a 1,2,4-triazine derivative ligand
  46. Evaluation of the impact of music on antioxidant mechanisms and survival in salt-stressed goldfish
  47. Optimization and validation of UPLC method for dapagliflozin and candesartan cilexetil in an on-demand formulation: Analytical quality by design approach
  48. Biomass-based cellulose hydroxyapatite nanocomposites for the efficient sequestration of dyes: Kinetics, response surface methodology optimization, and reusability
  49. Multifunctional nitrogen and boron co-doped carbon dots: A fluorescent probe for Hg2+ and biothiol detection with bioimaging and antifungal applications
  50. Separation of sulphonamides on a C12-diol mixed-mode HPLC column and investigation of their retention mechanism
  51. Characterization and antioxidant activity of pectin from lemon peels
  52. Fast PFAS determination in honey by direct probe electrospray ionization tandem mass spectrometry: A health risk assessment insight
  53. Correlation study between GC–MS analysis of cigarette aroma compounds and sensory evaluation
  54. Synthesis, biological evaluation, and molecular docking studies of substituted chromone-2-carboxamide derivatives as anti-breast cancer agents
  55. The influence of feed space velocity and pressure on the cold flow properties of diesel fuel
  56. Acid etching behavior and mechanism in acid solution of iron components in basalt fibers
  57. Protective effect of green synthesized nanoceria on retinal oxidative stress and inflammation in streptozotocin-induced diabetic rat
  58. Evaluation of the antianxiety activity of green zinc nanoparticles mediated by Boswellia thurifera in albino mice by following the plus maze and light and dark exploration tests
  59. Yeast as an efficient and eco-friendly bifunctional porogen for biomass-derived nitrogen-doped carbon catalysts in the oxygen reduction reaction
  60. Novel descriptors for the prediction of molecular properties
  61. Special Issue on Advancing Sustainable Chemistry for a Greener Future
  62. One-pot fabrication of highly porous morphology of ferric oxide-ferric oxychloride/poly-O-chloroaniline nanocomposite seeded on poly-1H pyrrole: Photocathode for green hydrogen generation from natural and artificial seawater
  63. High-efficiency photocathode for green hydrogen generation from sanitation water using bismuthyl chloride/poly-o-chlorobenzeneamine nanocomposite
  64. Special Issue on Phytochemicals, Biological and Toxicological Analysis of Plants
  65. Comparative analysis of fruit quality parameters and volatile compounds in commercially grown citrus cultivars
  66. Total phenolic, flavonoid, flavonol, and tannin contents as well as antioxidant and antiparasitic activities of aqueous methanol extract of Alhagi graecorum plant used in traditional medicine: Collected in Riyadh, Saudi Arabia
  67. Study on the pharmacological effects and active compounds of Apocynum venetum L.
  68. Chemical profile of Senna italica and Senna velutina seed and their pharmacological properties
  69. Essential oils from Brazilian plants: A literature analysis of anti-inflammatory and antimalarial properties and in silico validation
  70. Toxicological effects of green tea catechin extract on rat liver: Delineating safe and harmful doses
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