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.
In this work, Y-doped ZnO nanoparticles were precipitately synthesized for various yttrium molar percentage values ranging from 0 to 5%, and then utilized as photocatalysts to demonstrate methylene blue degradation. Morphology shows that the particle size of pure ZnO is 113.7733.26 nm, which is reduced to the minimum value less than one-third for the Y-doped ZnO samples. As a result, surface-to-volume ratios of Y-doped ZnO samples have successfully increased due to their decreased size. This decrease in particle size is consistent with the small crystalline size, primarily due to low crystallization in the presence of yttrium doping. However, the expansion of the crystal structure is observed. Chemical surface structures point to the major vibration of ZnO. However, some carbon-relating groups remain to appear. Optical property reveals similar trends for all Y-doped ZnO samples. The estimated band gap energy (Eg) was reduced to the minimum value for the 4 mol% condition. For use as a photocatalyst, the appropriate Y-doped ZnO for 4 mol% yttrium doping presents the maximum degradation efficiency of 61.19%. The improvement in photocatalytic degradation is caused by the synergy of decreased particle size and reduced Eg. Therefore, yttrium plays a role to decrease particle size and reduce Eg of Y-doped ZnO materials, thus leading to enhance photocatalytic performance.
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