Metal-graphene nanostructures (NSs) as photocatalysts, prepared using simple and scalable synthesis methods, are gaining heightened attention as novel materials for water treatment and environmental remediation applications. Graphene, the unique few layers sheet-like arrangement of sp2 hybridized carbon atoms, has an inimitable two-dimensional (2D) structure. The material is highly conductive, has high electron mobility and an extremely high surface area, and can be produced on a large scale at low cost. Accordingly, it has been considered as an essential base component for producing various metal-based NSs. In particular, metal-graphene NSs as photocatalysts have attracted considerable attention because of their special surface plasmon resonance (SPR) effect that can improve their performance for the removal of toxic dyes and other pollutants. This review summarizes the recent and advanced progress for the easy fabrication and design of graphene-based NSs as photocatalysts, as a novel tool, using a range of approaches, including green and biogenic approaches.
Cerium oxide nanoparticles (CeO2 NPs) were fabricated and grown on graphene sheets using a facile, low cost hydrothermal approach and subsequently characterized using different standard characterization techniques. X-ray photoelectron spectroscopy and electron paramagnetic resonance revealed the changes in surface states, composition, changes in Ce4+ to Ce3+ ratio, and other defects. Transmission electron microscopy (TEM) and high resolution TEM revealed that the fabricated CeO2 NPs to be spherical with particle size of ~10–12 nm. Combination of defects in CeO2 NPs with optimal amount of two-dimensional graphene sheets had a significant effect on the properties of the resulting hybrid CeO2-Graphene nanostructures, such as improved optical, photocatalytic, and photocapacitive performance. The excellent photocatalytic degradation performances were examined by monitoring their ability to degrade Congo red ~94.5% and methylene blue dye ~98% under visible light irradiation. The photoelectrode performance had a maximum photocapacitance of 177.54 Fg−1 and exhibited regular capacitive behavior. Therefore, the Ce3+-ion, surface-oxygen-vacancies, and defects-induced behavior can be attributed to the suppression of the recombination of photo-generated electron–hole pairs due to the rapid charge transfer between the CeO2 NPs and graphene sheets. These findings will have a profound effect on the use of CeO2-Graphene nanostructures for future energy and environment-related applications.
Noble-metal silver (Ag) nanoparticles (NPs) anchored/decorated onto polymeric graphitic carbon nitride (g-C 3 N 4 ) as nanostructures (NSs) were prepared using modest and environment-friendly synthesis method with a developed-single-strain biofilm as a reducing implement. The as-fabricated NSs were characterized using standard characterization techniques. The nanosized and uniform AgNPs were well deposited onto the sheet-like matrix of g-C 3 N 4 and exhibited good antimicrobial activity and superior photodegradation of dyes methylene blue (MB) and rhodamine B (RhB) dyes under visible-light illumination. The Ag@g-C 3 N 4 NSs exhibited active and effective bactericidal performance and a survival test in counter to Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The as-fabricated NSs also exhibited superior visible-light photodegradation of MB and RhB in much less time as compared to other reports. Ag@g-C 3 N 4 NSs (3 mM) showed superior photocatalytic measurements under visible-light irradiation: ∼100% MB degradation and ∼89% of RhB degradation in 210 and 250 min, respectively. The obtained results indicate that the AgNPs were well deposited onto the g-C 3 N 4 structure, which decreases the charge recombination rate of photogenerated electrons and holes and extends the performance of pure g-C 3 N 4 under visible light. In conclusion, the as-fabricated Ag@g-C 3 N 4 NSs are keen nanostructured materials that can be applied as antimicrobial materials and visible-light-induced photocatalysts.
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