Ternary composites of reduced graphene oxide(GR)-CdS-Pd have been successfully synthesized via solvothermal and photodeposition methods for photocatalytic selective conversion of benzyl alcohol(BA)coupled with hydrogen(H_(2))production, which exhibit significantly improved photoactivity and selectivity than bare CdS. Mechanistic studies unveil that the cooperative effect of the close interface contact and matched energy level alignment between electrical conducting GR nanosheets(NSs) and CdS nanoparticles(NPs) in GR-CdS-Pd composite not only benefits the separation and transfer of photogenerated carriers but also improves the photocorrosion resistance of CdS. The photodeposited Pd NPs further promote the photogenerated charge separation and accelerate the formation of intermediate products(α-hydroxybenzyl radicals), thereby contributing to enhanced conversion of BA. This work would facilitate the rational design of GR as cocatalyst to construct an efficient and stable CdS-based composite photocatalyst for cooperative coupling of fine chemical synthesis and H_(2) evolution.
Graphene(GR)-CdS nanocomposites with different weight addition ratios of GR have been assembled by a facile solvothermal treatment. The GR-CdS nanocomposite photocatalyst with an appropriate ratio of GR exhibits enhanced photoactivity for selective reduction of aromatic nitro compounds to the corresponding aromatic amines in water under visible light irradiation as compared with blank-CdS. The characterization of GR-CdS nanocomposite photocatalysts by a collection of techniques discloses that: i) GR can tune the microscopic morphology of CdS nanoparticles and improve light absorption intensity in the visible light region; ii) GR scaffolds act as an electron reservoir to trap and shuttle the electrons photogenerated from CdS semiconductor under the visible light illumination; iii) the introduction of GR enhances the adsorption capacity of GR-CdS nanocomposites toward the substrates, aromatic nitro compounds. The synergistic effect of these factors should account for the photoactivity advancement of GR-CdS nanocomposites toward the probe reactions. Furthermore, because the photogenerated holes in the system are trapped by the quenching agent ammonium oxalate, the as-obtained GR-CdS photocatalyst is stable during the photocatalytic reduction reactions. A reasonable model has also been proposed to illustrate the reaction mechanism.
CdS nanowires-nitrogen doped graphene(CdS NWs-NGR) nanocomposites have been fabricated by an electrostatic self-assembly strategy followed by a hydrothermal reduction. The CdS NWs-NGR exhibits higher photoactivity for selective reduction of aromatic nitro organics in water under visible light irradiation than blank CdS nanowires(CdS NWs) and CdS nanowires-reduced graphene oxide(CdS NWs-RGO)nanocomposites. The enhanced photoactivity of CdS NWs-NGR can be attributed to the improved electronic conductivity due to the introduction of nitrogen atoms, which thus enhances the separation and transfer of charge carriers photogenerated from CdS NWs.Our work could provide a facile method to synthesize NGR based one-dimensional(1D) semiconductor composites for selective organic transformations, and broaden the potential applications for NGR as a cocatalyst.
As a new member of carbon material family, carbon quantum dots(CQDs) have attracted tremendous attentions for their potentials in the heterogeneous photocatalysis applications. Due to the unique microstructure and optical properties, the roles of CQDs played in the CQDs-based photocatalytic systems have been found to be diverse with the continuous researches in this regard. Herein, we provide a concise minireview to elaborate the multifarious roles of CQDs in photocatalysis, including photoelectron mediator and acceptor, photosensitizer, photocatalyst, reducing agent for metal salt, enhancing adsorption capacity and spectral converter. In addition, the perspectives on future research trends and challenges are proposed, which are anticipated to stimulate further research into this promising field on designing a variety of efficient CQDs-based photocatalysts for solar energy conversion.
