An Insight into Carbon Nanomaterial-Based Photocatalytic Water Splitting for Green Hydrogen Production

At present, the energy shortage and environmental pollution are the burning global issues. For centuries, fossil fuels have been used to meet worldwide energy demand. However, thousands of tons of greenhouse gases are released into the atmosphere when fossil fuels are burned, contributing to global warming. Therefore, green energy must replace fossil fuels, and hydrogen is a prime choice. Photocatalytic water splitting (PWS) under solar irradiation could address energy and environmental problems. In the past decade, solar photocatalysts have been used to manufacture sustainable fuels. Scientists are working to synthesize a reliable, affordable, and light-efficient photocatalyst. Developing efficient photocatalysts for water redox reactions in suspension is a key to solar energy conversion. Semiconductor nanoparticles can be used as photocatalysts to accelerate redox reactions to generate chemical fuel or electricity. Carbon materials are substantial photocatalysts for total WS under solar irradiation due to their high activity, high stability, low cost, easy production, and structural diversity. Carbon-based materials such as graphene, graphene oxide, graphitic carbon nitride, fullerenes, carbon nanotubes, and carbon quantum dots can be used as semiconductors, photosensitizers, cocatalysts, and support materials. This review comprehensively explains how carbon-based composite materials function as photocatalytic semiconductors for hydrogen production, the water-splitting mechanism, and the chemistry of redox reactions. Also, how heteroatom doping, defects and surface functionalities, etc., can influence the efficiency of carbon photocatalysts in H2 production. The challenges faced in the PWS process and future prospects are briefly discussed.

Solar Degradation of Sulfamethazine Using rGO/Bi Composite Photocatalysts

Heterogeneous photocatalysts for water decontamination were obtained by the optimized synthesis of bismuth-functionalized reduced graphene oxide (rGO/Bi) using the Hummer method and microwave treatment. Sulfamethazine (SMZ) was used as model pollutant to evaluate the photocatalytic efficacy. Photocatalysts were characterized by VP-SEM, HRTEM, XDR, XPS, RAMAN, and FTIR analyses, which confirmed the effective reduction of GO to rGO and the presence of bismuth as a crystalline phase of Bi2O3 polydispersed on the surface. Their performance was influenced by the rGO/Bi ratio, microwave temperature, and treatment time. The as-obtained 5%rGO/Bi composite had the highest photocatalytic activity for SMZ degradation under visible light irradiation (λ > 400 nm), achieving 100% degradation after only 2 h of treatment. The degradation yield decreased with higher percentages of rGO. Accordingly, the rGO/Bi catalysts efficiently removed SMZ, showing a high photocatalytic activity, and remained unchanged after three treatment cycles; furthermore, cytotoxicity tests demonstrated the nontoxicity of the aqueous medium after SMZ degradation. These findings support the potential value of these novel composites as photocatalysts to selectively remove pollutants in water treatment plants.

Synthesis and characterization of Ag/Bi2WO6/GO composite for the fast degradation of tylosin under visible light

Ag/Bi₂WO₆/graphene oxide composite with excellent photocatalytic properties was successfully prepared by hydrothermal-photoreduction synergistic method and is applied in antibiotics degradation. The structure and properties of as-prepared photocatalysts were characterized by Fourier infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS), specific surface area analyzer (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscope (AFM). The results indicated that Ag and Bi₂WO₆ were uniformly loaded on the surface of graphene oxide. In addition, graphene oxide with conjugated carbon network structures has been applied as a photocatalyst supporter for the high electronic conductivity and the large reactive sites. Compared with the pure graphene oxide, the as-prepared Ag/Bi₂WO₆/graphene oxide catalyst exhibited excellent degradation efficiency and stability for degrading tylosin under Xe lamp irradiation. Under simulated sunlight irradiation, the photodegradation efficiency of tylosin by Ag/Bi₂WO₆/graphene oxide achieved at 98% within 2 h, compared to 50% by pure graphene oxide. The excellent photodegradation ability is caused by the synergetic effect of Ag, Bi₂WO₆, and graphene oxide nanoparticles.

Insight into the origin of photoreactivity of various well-defined Bi2WO6 crystals: exposed heterojunction-like surface and oxygen defects

Three kinds of Bi₂WO₆ with well-defined morphology were prepared. The nanosheet with exposed (020) facets was obtained. The origin of photoreactivity of Bi₂WO₆ photocatalysis was studied.

Effective charge separation and enhanced photocatalytic activity by the heterointerface in MoS2/reduced graphene oxide composites

The MoS₂/rGO exhibits enhanced photocatalytic activity for degradation of RhB due to effective separation of photo-generated electron–hole pairs by heterointerface.

Electrospinning construction of Bi2WO6/RGO composite nanofibers with significantly enhanced photocatalytic water splitting activity

Bi₂WO₆/reduced graphene oxide composite nanofibers possessing significantly enhanced photocatalytic water splitting activity have been successfully fabricated.

Graphene-based photocatalysts for oxygen evolution from water

Recent achievements of GR-based photocatalysts for oxygen evolution from water are summarized with perspectives on major challenges and opportunities.