Improved Solar-Driven Photocatalytic Activity of Hybrid Graphene Quantum Dots/ZnO Nanowires: A Direct Z-Scheme Mechanism

Abstract

Herein, an electrochemical technique as a cost-effective and one-step approach was utilized to fabricate graphene quantum dots (GQDs). Different amounts of GQDs (0, 0.2, 0.4, 0.8, and 1.2 wt %) were decorated uniformly on the surface of anodized ZnO nanowires (NWs) forming GQD/ZnO NWs. Transmission electron microscopy and atomic force microscopy confirmed formation of GQDs on the ZnO NWs, 12–22 nm in width and 1–3 graphene layers thick. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were employed to verify the functional groups on the surface of GQDs, and the results indicated that GQDs readily anchored on the surface of ZnO NWs. The GQD/ZnO NWs exhibited a considerable improvement on the photocatalytic degradation of methylene blue under solar irradiation, due to efficient light absorption. In addition, the results indicated that the optimized GQD (0.4 wt %)/ZnO NWs showed the highest photoactivity with about 3-fold enhancement as compared to pure ZnO NWs. Finally, a mechanism of charge carrier generation, transport, and separation was proposed using different scavengers to probe the potential reaction pathway following a direct Z-scheme approach.

Chemical Interaction in Nitrogen‐Doped Graphene Quantum Dots/Graphitic Carbon Nitride Heterostructures with Enhanced Photocatalytic H2 Evolution

“…The measured highest occupied molecular orbital (HOMO) energy level of the NGQDs was 2.51 eV (vs NHE). The NGQDs possess a bandgap energy of ≈2.64 eV obtained from the UV–vis absorption spectrum of its solution (Figure S2a, Supporting Information) . Thus, the lowest unoccupied molecular orbital (LUMO) position was located at −0.13 eV (vs NHE).…”

Sunlight-Driven Combustion Synthesis of Defective Metal Oxide Nanostructures with Enhanced Photocatalytic Activity

“…Thus, the MO degradation was enhanced due to the increase in the photogenerated electron concentration. 60…”

Enhancement Photocatalytic Activity of the Heterojunction of Two-Dimensional Hybrid Semiconductors ZnO/V2O5

“…In these systems, the main absorber is the secondary semiconductor while the role of ZnO is principally limited to the charge curriers transport. That notwithstanding, some interesting approaches to directly improve ZnO visible-light absorption have been also attempted; namely by creating electronic levels within the ZnO band gap, by metal or non-metal doping, or surface modification via organic materials grafting [22][23][24][25]. Most attempts to improve the photocatalysis of organic contaminants by optimizing the adsorption of the substrates upon the photocatalyst mainly concern the increment of its specific surface area, so the utilization of 2D layered materials that have larger specific surface areas-a great number of active sites on the surface and superior electron mobility that facilitates the transfer and separation of photogenerated electrons and holes-is a good strategy for constructing effective photocatalyst [26,27].…”