Soon Wei Chook

Antibacterial performance of Ag nanoparticles and AgGO nanocomposites prepared via rapid microwave-assisted synthesis method

Silver nanoparticles and silver-graphene oxide nanocomposites were fabricated using a rapid and green microwave irradiation synthesis method. Silver nanoparticles with narrow size distribution were formed under microwave irradiation for both samples. The silver nanoparticles were distributed randomly on the surface of graphene oxide. The Fourier transform infrared and thermogravimetry analysis results showed that the graphene oxide for the AgNP-graphene oxide (AgGO) sample was partially reduced during the in situ synthesis of silver nanoparticles. Both silver nanoparticles and AgGO nanocomposites exhibited stronger antibacterial properties against Gram-negative bacteria (Salmonella typhi and Escherichia coli) than against Gram-positive bacteria (Staphyloccocus aureus and Staphyloccocus epidermidis). The AgGO nanocomposites consisting of approximately 40 wt.% silver can achieve antibacterial performance comparable to that of neat silver nanoparticles.

Bifunctional graphene oxide–cellulose nanofibril aerogel loaded with Fe(III) for the removal of cationic dye via simultaneous adsorption and Fenton oxidation

A highly porous cellulose nanofibril (CNF) aerogel loaded with graphene oxide–iron(III) (GO–Fe) nanocomposites was produced and used for the treatment of methylene blue (MB) in aqueous solution. The CNF aerogel serves as an adsorbent for the dye, while the GO–Fe nanocomposites play a role in the decomposition of the dye via the Fenton oxidation reaction. The aerogel exhibits rapid adsorption performance (less than 10 min) for removing MB, with a maximum adsorption capacity of 142.3 mg g−1. On the side of enhancing the MB removal, the GO in the GO–CNF nanocomposite aerogel was loaded with 1 wt% of Fe(III) to perform as a catalyst for the Fenton oxidation reaction. The MB continues to decolorize by 30.4% more after 24 h of the reaction process. Moreover, by performing Fenton oxidation for adsorbent regeneration, the adsorption capacity for nanocomposite adsorption was reduced by 52.2% after five cycles of adsorption–oxidation.

A porous aerogel nanocomposite of silver nanoparticles-functionalized cellulose nanofibrils for SERS detection and catalytic degradation of rhodamine B

Herein, cellulose nanofibrils (CNFs) were functionalised with silver nanoparticles (AgNPs) via a green in situ hydrothermal synthesis approach. The presence of active functional groups on the CNFs favours the direct synthesis and growth of AgNPs on the nanofibrils without the use of an external reducing agent. The freeze-dried CNF–AgNPs aerogel nanocomposite exhibited a highly porous structure, as revealed by FESEM. An organic dye, rhodamine B (RhB), was chosen to investigate the characteristics of the produced nanocomposite. Detection of the dye via Raman spectroscopy and analysis of catalytic capabilities by degradation of the dye were used to define the nanocomposites properties. The nanocomposite showed significant enhancement in detection of signal for RhB in aqueous solution, as compared to the neat CNF, which is attributed to the surface-enhanced Raman scattering effect (SERS) of the immobilized AgNPs. Moreover, the CNF–AgNPs nanocomposite also showed sensitivity for detecting RhB at different concentrations, ranging from 5 × 10−3 M to 5 × 10−7 M. In addition, the nanocomposite exhibited a notable catalytic effect on the degradation of RhB in the presence of sodium borohydride.

A graphene oxide facilitated a highly porous and effective antibacterial regenerated cellulose membrane containing stabilized silver nanoparticles

Abstract Regenerated nanocomposite cellulose membranes embedded with silver nanoparticles (AgNP) and AgNP-graphene oxide (AgGO) were prepared in this study. The as-synthesized AgNP and AgGO were added respectively to a cellulose solution that was prepared by dissolving cellulose in a precooled NaOH/urea (NU) solvent. The solution mixtures were further regenerated into nanocomposite membranes through coagulation in an acidic solution. UV-Vis and TEM results revealed the improved stability of the AgGO compared to that of the AgNP in NU solutions. As revealed by FESEM, the AgGO nanocomposite membrane possessed a more porous structure than a membrane containing AgNP. Antibacterial tests demonstrated that the cellulose membrane of AgGO inhibited the growth of both Staphylococcus aureus and Escherichia coli more effectively than the AgNP nanocomposite membrane, with a lower concentration of AgGO. This work provides a proven and effective method to prepare novel functional cellulose membranes with antibacterial properties, thus broadening the applications of cellulose.

Silver Nanoparticles - Graphene Oxide Nanocomposite for Antibacterial Purpose

Graphene oxide (GO) sheets, a single layer of carbon atoms which can be served as substrates for fabricating metallic nanoparticles-GO nanocomposites. In this study, the nanocomposite of silver nanoparticles and graphene oxide were produced via in-situ synthesis and with the addition of chitosan to investigate the formation of silver nanoparticles on the graphene oxide sheets. XRD and UV-Vis studies confirmed the formation of silver nanoparticles on GO sheets, while TEM and FESEM images presented the loading of silver nanoparticles on the GO sheets. The degree of loading and distribution of the silver nanoparticles on the graphene oxide were depend on the method during the formation of silver nanoparticles. The nanocomposites can be potentially used in food packaging and biomedical applications.

Effective immobilization of silver nanoparticles on a regenerated cellulose-chitosan composite membrane and its antibacterial activity

An antibacterial chitosan–cellulose composite membrane, containing silver nanoparticles (AgNPs), was fabricated by coagulating a cellulose solution in a chitosan solution, followed by the in situ synthesis of AgNPs on the produced membrane. By adjusting the concentration of chitosan (0–2.5%, w/v) in acetic acid coagulating solution, various cellulose–chitosan membranes with different chitosan contents were produced, which then served as substrates for the in situ synthesis and immobilization of AgNPs via a microwave-assisted approach. The amount of AgNPs deposited on the membrane was measured and found to increase with an increasing in the chitosan content on the membrane. Electron micrographs of the membranes revealed entanglement of chitosan on the membranes structure, whereas AgNPs were deposited on the membrane surfaces. In addition, the surface roughness of the membrane increased as a result of the increase of chitosan and AgNPs on the membrane surfaces. Consequently, the membranes exhibited an improved antibacterial activity against Staphylococcus aureus and Escherichia coli as the AgNPs content increased. In conclusion, this study demonstrated a successful green approach for preparing a nanocomposite membrane of cellulose–chitosan–AgNPs with strong antibacterial activities.

Conversion of glucose into lactic acid using silica-supported zinc oxide as solid acid catalyst

Abstract Zinc oxide (ZnO) has been proven to be highly effective in converting biomass into fine chemicals. It possesses several limitations, such as leaching in hydrothermal reactions and difficulty with regard to its recovery. Supporting ZnO on silica improves its recovery, stability and recyclability. In this study, we produced silica-supported ZnO by incipient wetness impregnation (IWI) method for the conversion of glucose into lactic acid. The presence of the ZnO provided active sites for isomerization to occur. The highest yield of lactic acid was 39.2% at 180 °C for 60 min. Prolonged reaction time and higher reaction temperature promoted further degradation of lactic acid into acetic acid. The yield of lactic acid decreased after the first cycle and decreased slightly for the nine consecutive cycles.

Simplified production of graphene oxide assisted by high shear exfoliation of graphite with controlled oxidation

In this work, a scalable method was developed to produce graphene oxide (GO) via high-shearing of pre-oxidized graphite. Various oxidation states of pre-oxidized graphite were obtained following different oxidation periods through a modified Hummers’ method. The oxidized graphite flakes were investigated by X-ray diffractometry, Fourier transform infrared spectroscopy, and Raman spectroscopy. Instead of a prolonged oxidation period of more than 24 hours, the graphite sample that underwent 6 hours of oxidation was selected for the high-shearing process to obtain exfoliated GO. The transmission electron microscopy and atomic force microscopy results confirmed that large-area and single-layer GO can be produced by the high-shear exfoliation method with pre-oxidized graphite flakes. This modified procedure enables the remarkably simple, fast, and effective production of high-quality GO.