Volume 7, Issue 5 - Special issue: 6th Asian Symposium on Advanced Materials: Chemistry, Physics and Biomedicine of Functional and Novel Materials (ASAM-6) / Issue editors: Thai Hoang, Tran Dai Lam and Holger Löwe

This study provides a route to prepare 4-arm star poly(methyl methacrylate) (4sPMMA)/PMMA grafted SiO 2 (PMMA-g-SiO 2 ) hybrid nanocomposites that can be used as 3D printing material and filler for dental materials. First, 4sPMMA was synthesized via atom transfer radical polymerization with low metal catalyst concentration. Modified colloidal silica nanoparticles (MCSPs) were synthesized by grafting 3-methoxypropyl trimethoxysilane (MPS) onto the surface of colloidal silica nanoparticles (CSPs) and then dispersed in the solution of methyl methacrylate monomer in dioxane. The mixture of 4sPMMA and MCSPs solutions was degassed and replaced in an oil bath at 70–75°C; the reaction was continued with α,α′-azobis(isobutyronitrile) as an initiator for 24 h to form 4sPMMA/PMMA-g-SiO 2 hybrid nanocomposites. Viscosity measurement showed that viscosity of the hybrid was increased with increasing MPS loading used in modification of CSPs, which verified that PMMA had been grafted onto MCSPs. Fourier transform infrared spectra of the hybrid nanocomposites demonstrated the strong molecular interaction between MCSPs and polymer matrix, and 1 H NMR spectra confirmed the formation of PMMA-g-SiO 2 . Field emission scanning electron microscopy and transmission electron microscopy images revealed that MCSPs were well dispersed in polymer matrix with the size of about 20–30 nm. Thermal stability of the hybrid nanocomposites was improved compared with PMMA made from free radical polymerization.

The factors influencing the green strength of commercial solid rubbers were investigated in the present study through characterization of commercial natural rubber (NR). Various solid commercial rubbers such as standard Vietnam rubber (SVR10), standard Indonesia rubber (SIR10), India standard natural rubber (ISNR10), ribbed smoked sheets (RSS3), and FNR (commercial Sumitomo Rubber) were used as a source. Purification of the samples was carried out through acetone extraction and purified samples were characterized by nuclear magnetic resonance (NMR) and Fourier-Transform infrared spectroscopy. Degradation was found for SVR10, ISNR10, and SIR10 but not for RSS3 and FNR through the assignment of 13 C-NMR signals. Acetone extraction was found to improve the green strength of commercial NR due to the removal of impurities. Linked fatty acids and proteins contributed to the upturn of stress at small strain. However, the network structure of degraded rubbers had an insignificant role in enhancing the green strength of commercial NR.

In this work, we fabricated crumpled graphite oxides (CGOs) from discharged electrodes of waste batteries by the cathodic plasma electrolysis process and applied it for arsenic (As) removal from water solutions. Several factors that affect the removal efficiency of As(III) were investigated, including pH, initial concentrations, and contact time. After 120 min of experiment [10 mg of CGO in 40 ml of 1 mg/l As(III) solution], the removal efficiency reached to as high as 98.6%. From the Langmuir isotherm model, the calculated maximum adsorption capacity (q max ) was found to be 47.39 mg/g. The results from this study showed that CGOs could be an effective adsorbent for As(III) removal from the water environment and acts as a promising adsorbent for other heavy metals from contaminated water.

Pollution of heavy metals in water can affect the health of humans and the environment; therefore, removal of heavy metal ions is getting the attention of scientists. To reduce the negative impact of heavy metals on human health and the environment, Cd 2+ ions present in water were treated using hydroxyapatite (HAp) as adsorbent. The effects of contact time, initial Cd 2+ concentration, solution pH, and adsorbent mass on the adsorption capacity and efficiency of HAp were investigated. Cd 2+ uptake was quantitatively evaluated using Langmuir and Freundlich adsorption isotherms. The maximum monolayer adsorption capacity was 119 mg/g. The experimental adsorption data were analyzed using three kinetic models: Lagergren’s pseudo-first-order law, McKay and Ho’s pseudo-second-order law, and the intra-particle diffusion model. The results showed that the Cd 2+ removal process follows the pseudo-second-order law.

Poly(lactic acid)/chitosan (PLA/CS) green nanoparticles containing hydroquinine (Hq) were prepared by emulsion method. The content of Hq was 10–50 wt% compared with the weight total of PLA and CS. The characteristics of these nanoparticles were analyzed by Fourier transform infrared (FTIR), differential scanning calorimetry, field emission scanning electron microscopy (FESEM), and particle size analysis. The wavenumbers of C=O, C=N, OH, and CH 3 groups in FTIR spectra of the PLA/CS/Hq (PCHq) nanoparticles shifted in comparision with neat PLA, CS, and Hq that proved the interaction between these components. The FESEM images and particle size analysis results showed that the basic particle size of PCHq nanoparticles ranged between 100 and 200 nm. The Hq released from PLA/CS nanoparticles in pH 2 and pH 7.4 solutions was determined by ultraviolet-visible method. The obtained results indicated that the linear regression coefficient of calibration equation of Hq in the above solutions approximates 1. The Hq release from the PCHq nanoparticles includes fast release for the eight first testing hours, and then, controlled slow release. The Hq released process was obeyed according to the Korsmeyer-Peppas kinetic model.

Green synthesis of nanoparticles (NPs) has received much attention due to biocompatibility and being facile and eco-friendly. Caesalpinia sappan Linn. (CS) is a plant found in Southeast Asia and is commonly known as sappan wood. In this research, we are the first to successfully use CS extract as reducing and stabilizing agents for the green synthesis of gold NPs (AuNPs). Colloidal solutions of AuNPs after reduction show natural red-wine and dark purple color depending on the size of AuNPs, without the interference of the orange/reddish-orange color from the CS extract. The concentration of CS was investigated for the formation and stabilization of AuNPs in colloidal solution (i.e. morphology, size and zeta potential). It was found that the optimized concentration of the reducing agent for the green synthesis of AuNPs was in the range of 0.004–0.04 wt% of CS. As the concentration of CS was increased, the sizes of AuNPs decreased due to the adsorption and stabilizing effect of CS. Transmission electron microscopy (TEM) analysis showed differences in size and shape of the NPs with earthworm and quasi-spherical characteristics. The zeta potential of AuNPs synthesized in the presence of CS was approximately in the range of −10 mV to −20 mV, indicating the stability of AuNPs synthesized by CS.

In the present study, the green chemistry approach for the biosynthesis of Ag, Au and Ag-Au bimetallic nanoparticles (NPs) was applied using lichen extract [ Cetraria islandica (L.) Ach.]. The lichen extract acts both as a reducing and stabilizing agent. The monometallic and bimetallic NPs were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results showed that NPs were successfully synthesized and the prepared structures were generally spherical. The synthesized nanostructures exhibited excellent catalytic activities towards reduction of nitrophenols (4-nitrophenol; 4-NP) to aminophenols (4-aminophenol; 4-AP) with sodium borohydride (NaBH 4 ). It was determined that bimetallic NPs exhibit more effective catalytic activity than monometallic Ag and Au nanostructures. This is the first report on 4-NP reduction with Ag, Au and Au-Ag NP catalysts prepared by lichen extract.

The kinetics of the alkali-catalyzed transesterification of sunflower oil with methanol in the presence of co-solvent (TSMPC) were investigated. The kinetics curves of the alkali-catalyzed TSMPC, in the temperature range of 26°C–55°C, were measured for conventional heating (CH) and microwave heating with controlled cooling. The results showed that for both heating modes, the kinetics of the alkali-catalyzed TSMPC reaction can be described with the kinetic model of the pseudo first-order reaction with respect to the concentration of the triglycerides. The values of apparent reaction rate constants, activation energies, and pre-exponential factors are also calculated. The existence of a linear correlation (compensation effect) between the values of apparent kinetic parameters determined for CH and microwave heating with controlled cooling conditions is established. The results confirmed that the increase in the transesterification rate in the microwave heating with controlled cooling conditions is not caused by overheating nor by the existence of hotspots. The model of mechanism of the impact of microwave heating on the kinetics of transesterification is hereby proposed.

Bi(NO 3 ) 3 ·5H 2 O/MgSO 4 was developed as an efficient and green reagent for the nitration of aromatic compounds under mechanochemistry (or ball milling) condition. While aromatics with weak activating groups such as phenyl could be nitrated by this reagent with 100% conversion, aromatics with weak deactivating groups such as chloro- or bromo- could also be nitrated but with moderate conversion and regioselectivity with big para / ortho ratios. The in situ generated N 2 O 4 or NO 2 due to the decomposition of Bi(NO 3 ) 3 ·5H 2 O promoted by MgSO 4 should be responsible for this mechanochemical nitration.

The decrease in the zinc volatilization rate is usually due to the liquid phase, which is typically generated in the rotary kiln. The response surface model was built to analyze and explore the effects of carbon content, basicity, and holding time on the zinc volatilization rate and residue state. Moreover, the model was used to optimize the experimental conditions. The results showed that the effect of basicity on zinc volatilization rate was statistically significant, whereas the effects of carbon content and holding time were relatively small. The optimized process conditions were as follows: carbon content of 32%, basicity of 3, and holding time of 30 min. Under this condition, the zinc volatilization rate was 99.65%, and the furnace residue was sintered, which proved to be beneficial to the subsequent step of iron extraction.

A green process that uses the spray pyrolysis method to prepare activated alumina is proposed in this research. The effects of spray temperature, carrier gas pressure, and AlCl 3 solution concentration are experimentally investigated using pure reagents. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and specific surface area (BET) analyses. The results indicate that the spray temperature is the most important factor on the conversion ratio of alumina during the spray pyrolysis process. The conversion ratio of alumina achieved over 99% at the following optimal conditions: temperature of 1000°C, pressure of 0.3 MPa, and AlCl 3 solution concentration of 10 wt%. The activated alumina with 8–20 nm particle size (γ-Al 2 O 3 +α-Al 2 O 3 ) was prepared using the same process, which well met the requirement of the catalyst carrier. The green utilization of high-alumina fly ash and acid recycling can be achieved by using this process.