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.
ZnO and Ti-doped ZnO (Ti-ZnO) nanoparticles were synthesized using rapid combustion. The morphology of ZnO and Ti-ZnO featured nanoparticles within cluster-like structures. The ZnO and Ti-ZnO structures exhibited similar hexagonal wurtzite structures and crystal sizes. This behavior occurred because Zn2+ sites of the ZnO lattice were substituted by Ti4+ ions. The chemical structure characterization implied the major vibration of the ZnO structure. The physisorption analysis showed similar mesoporous and non-rigid aggregation structures for ZnO and Ti-ZnO using N2 adsorption–desorption. However, Ti-ZnO demonstrated a specific surface area two times higher than that of ZnO. This was a major factor in improving the photocatalytic degradation of methylene blue (MB). The photocatalytic degradation analysis showed a kinetic degradation rate constant of 2.54 × 10−3 min−1 for Ti-ZnO, which was almost 80% higher than that of ZnO (1.40 × 10−3 min−1). The transformation mechanism of MB molecules into other products, including carbon dioxide, aldehyde, and sulfate ions, was also examined.
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.
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