The significance of photocatalysts is unquestionable, and scientists are devoted to improving their photocatalytic efficiency. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions-type-II and Z-scheme heterojunctionshave been widely acknowledged. However, we soberly reflect the charge-transfer mechanism from many perspectives and are finally aware of the fundamental challenges they face. To ensure a correct understanding, it is necessary to share our analysis with others. Moreover, step-scheme (S-scheme) heterojunctions, consisting of a reduction photocatalyst and an oxidation photocatalyst with staggered band structure, are introduced to avoid misinterpretation. The differences in the charge-transfer mechanism between S-scheme, type-II, and Z-scheme heterojunctions are highlighted. Finally, limitations and the future research direction of S-scheme photocatalysts are discussed.

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Sunlight‐driven photocatalytic water splitting to generate hydrogen (H2) is a promising approach for utilizing solar energy. Herein, direct Z‐scheme Fe2O3/g‐C3N4 photocatalysts are rationally fabricated for H2 evolution under visible light. The graphitic carbon nitride (g‐C3N4) nanosheets obtained by solvent exfoliation of bulk g‐C3N4 display modest photocatalytic activity. Strikingly, its photocatalytic performance can be greatly improved by electrostatically assembling with hematite α‐Fe2O3 nanoplates. With platinum (Pt) as co‐catalyst and triethanolamine (TEOA) as hole scavenger, the H2 generation rate of optimized Fe2O3/g‐C3N4 composite with Fe2O3 weight percentage of 10% is about 13‐fold that of g‐C3N4. Based on the enhanced photocatalytic performance and slower time‐resolved photoluminescence decay, Z‐scheme charge transfer process is accepted for running this photocatalytic system, which is further evidenced by selective photo‐deposition of Pt nanoparticles on the g‐C3N4 surface. This rationally synthesized Fe2O3/g‐C3N4 composite is expected to have great potentials in solar energy conversation.

Z-scheme heterojunction photocatalysts have received considerable attention for solar energy conversion and environmental purification due to their spatially separated reduction and oxidation sites, effective separation and transportation of photo-excited charge carriers and strong redox ability. With their wide visible-light responsive range and high photocatalytic activity, metal sulphide is an important material in developing photocatalysts. This review summarizes and highlights recent research progress in sulphide-based direct Z-scheme photocatalysts, followed by analysis on the limitations over all-solid-state Z-scheme photocatalyst. Furthermore, the applications and characterization methods of sulphidebased direct Z-scheme photocatalyst are summarized. Finally, the challenges and perspectives of sulphide-based Z-scheme photocatalyst are discussed.[a] T.

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Gold (Au) nanoparticles (NPs) supported on well-defined ceria (CeO2) nanorods with exposed {110} and {100} facets were prepared by a deposition-precipitation method and characterized by powder X-ray diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption, transmission electron microscopy, high-resolution transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy. Both nanometer and subnanometer gold particles were found to coexist on ceria supports with various Au contents (0.01-5.4 wt %). The catalytic performance of Au/CeO2 catalysts was examined for formaldehyde (HCHO) oxidation into CO2 and H2O at room temperature and shown to be Au content dependent, with 1.8 wt % Au/CeO2 displaying the best performance. On the basis of the results from hydrogen temperature-programmed reduction and in situ Fourier transform infrared spectroscopy observations, the high reactivity and stability of Au/CeO2 catalysts is mainly attributed to the well-defined ceria nanorods with {110} and {100} facets which present a relatively low energy for oxygen vacancy formation. Furthermore, gold NPs could induce the weakened Ce-O bond which in turn promotes HCHO oxidation.