The high crystallinity of graphene quantum dots-ZnO nanocomposites is considered to have a significant effect in improving the carrier lifetime for enhanced photocatalytic degradation. The graphene quantum dots-ZnO nanocomposites were synthesized by adding graphene quantum dots solution into starting precursors during the precipitation. Characterization was performed using various techniques. High crystallinity of graphene quantum dots-ZnO nanocomposites is obtained in terms of increased crystal size and decreased dislocation density. The improved crystallinity increases the carrier lifetime on the material surface for the functional improvement of photocatalytic material. Photocatalytic test of methylene blue and methyl orange was performed under UV irradiation. Degradation rate constant reaches the maximum value for both organic dyes for the appropriate preparing condition of graphene quantum dots-ZnO nanocomposites. The graphene quantum dots-ZnO nanocomposites were then applied to degrade commercial glyphosate herbicide contaminants for an agricultural wastewater treatment investigation. The investigation aims to demonstrate a facile useful way of herbicide contaminant reduction for the better health of farmers. The graphene quantum dots-ZnO nanocomposites show an enhancement of the photocatalytic process with improved degradation rate constant (23% increased) in comparison to pure ZnO. Therefore, this work demonstrates that graphene quantum dots-ZnO nanocomposites can be used as a photocatalytic material for degrading organic dyes and commercial herbicide contaminants owing to its low-cost and environmental-friendly properties.

The Ultraviolet‐shielding (UV‐shielding) and water resistance properties of graphene quantum dots/polyvinyl alcohol (GQDs/PVA) composite-based film have been investigated. The GQDs/PVA composite-based films were fabricated with different GQDs concentrations of 0, 5, 10, 15, and 20 wt%. The optical property of GQDs was carried out by utilizing fluorescence spectroscopy. Characterizations of GQDs/PVA composite-based films were performed by using FT-IR spectroscopy, and UV-vis spectroscopy. It was found that GQDs exhibited the strongest excitation wavelength in the UV range. GQDs/PVA composite-based films offered an improved UV-shielding capacity when compared to PVA films and glass. Particularly, the GQDs/PVA composite-based film containing 20 wt% GQDs exhibited a UV transmittance of 9.8%, combined with 84% optical transparency. For humidity environment application, the highest contact angle was explored for the 10 wt% GQDs contents suggesting sustainability for humidity environment application. Accordingly, GQDs played an important role in UV-shielding by considering the effect of UV absorption of GQDs and the UV absorption of GQDs can be explained in terms of the photon excitation by UV light. This GQDs/PVA composite could be potentially applied as transparent UV-protective coatings for pharmaceutical packing, food products packing, and UV-shielding or UV filter glass.

Heavy metal contamination in water is a serious issue causing adverse effects on health, ecosystem, and environment. To monitor this contamination, fluorescence quenching probe based on the graphene quantum dots (GQDs) was used for detection of metal compounds. The effect of metal compounds on the fluorescence quenching efficiency of the GQDs was investigated. A typical sample of metal compounds was selected from copper acetate, copper chloride, copper nitrate, copper sulfate, cobalt nitrate, cobalt chloride, and zinc nitrate. It was found that the GQDs exhibited high selectivity for copper acetate. The quantity of copper acetate was obtained using Stern-Volmer plot. It was found that the plot exhibited a linear behavior for the fluorescence quenching of the GQDs by copper acetate. This analytical method could be developed for the determination of copper acetate in the concentration range of 0–2.5 mM with the Stern-Volmer quenching constant of 2445 M⁻¹. To understand an occurring interaction between metal compounds and the GQDs in the system, redox characteristics of the GQDs mixed metal compounds were investigated. Noticeably, electrochemical potential gap (ΔE) of the GQDs mixed copper acetate with UV irradiation seems higher than that of the GQDs mixed copper acetate without UV irradiation, implying better electron transfer behavior from the GQDs to copper acetate. This result was in good agreement with the fluorescence quenching of the GQDs by copper acetate. Accordingly, the nonradiative recombination of the GQDs could be explained in terms of the fluorescence quenching. The fluorescence quenching efficiency was proportional to the amount of the copper acetate. These results can be further explored for a novel graphene quantum dots-based fluorescent probe and this method could be more widely applied in water resources.

This study aimed to investigate the effects of a corrosive environment on both the electrical and the water resistance properties of conductive paste based on gold/silver composites. The conductive paste was prepared by incorporating silver and gold powders, polyvinyl acetate, polyvinyl chloride as adhesive components, and methyl isobutyl ketone as a diluent. The gold/silver composite powder was prepared with different mass ratios of gold and silver. The paste was coated on a substrate and heated at 80℃ to form the conductive paste film. Characterizations of conductive paste were performed by using FT-IR spectroscopy, electrometry, cyclic voltammetry, and contact angle measurements. Thus, the conductive paste films were tested under two conditions: the absence and the presence of exposure to nitric acid vapor. The results showed that the resistance and the contact angle of the conductive paste were more stable after exposure to nitric acid vapor, particularly in samples of higher gold content. Furthermore, the electrochemical behavior of the conductive paste with gold content remains unchanged after exposure to nitric acid vapor. Results suggest that gold has properties in terms of stability, resistance to oxidation, and maintaining surface characteristics, making it a preferable component for applications requiring resistance to corrosive environments.