LAUSR

Designing highly efficient and stable photocatalysts is of vital importance for solar-to-fuel conversion, as a potential strategy to address the concerns of global energy crisis and environmental deterioration. The development of novel photocatalytic materials is desirable to overcome those shortcomings of traditional semiconductor photocatalysts. Feng and colleagues report in Nature Communications that two-dimensional gersiloxenes have great potential for photocatalytic H2 evolution and CO2 photoreduction. An ideal semiconductor photocatalyst is qualified by a narrow band gap for harvesting abundant photons in a wide range of solar spectrum, a high electron mobility to migrate photoelectrons from the bulk to the surface active sites and sufficient adsorption/catalytic centers to activate reactant molecules [1]. Moreover, a negative enough conduction band (CB) position is required to satisfy the redox potentials of water reduction and CO2 reduction reactions [2]. Well-studied semiconductors have already included metal oxides, metal sulfides, carbon nitrides, etc. However, these semiconductors are still facing challenges toward photocatalytic H2 evolution and CO2 photoreduction. In particular, TiO2, ZnO, WO3, etc., are only active in the UV region; Cu2O, CdS, CdSe, etc., easily suffer from photocorrosion; carbon nitrides are poor in electron mobility; BiVO4, Fe2O3, etc., could not drive the relevant reduction reactions due to their less negative CB potentials [3, 4]. In the past years, two-dimensional (2D) materials such as graphene, graphdiyne and MoS2 have been recognized as efficient co-catalysts in photocatalysis because of their advanced merits such as large specific surface areas, excellent conductivity and good electron mobility [5, 6]. However, these 2D materials alone could not drive the photocatalytic reactions as they are more close to conductors rather than semiconductors. Apart from them, it is noteworthy that silicene, germanene and their derivatives have been theoretically and experimentally demonstrated with great potential in photocatalysis [7, 8]. Recently, in Nature Communications, Feng and colleagues for the first time reported the 2D –H/–OH terminalsubstituted siligenes (gersiloxenes) with tunable band gap [9]. Two-dimensional Ge1–xSixH1–y(OH)y (x = 0.1–0.9) were synthesized by the typical topotactic deintercalation of the Zintl-phase precursor CaGe2–2xSi2x (x = 0.1, 0.3, 0.5, 0.7 and 0.9), in aqueous HCl at 30 C (Fig. 1a). The authors elucidated the chemical structural features of the synthesized 2D honeycomb GeSi alloys and their morphology, finding that the thickness of the nanosheets was * 3 to 6 nm, and when x B 0.5, only hydroxyl groups are bonded to Si, while when x[ 0.5, either hydrogen atoms or hydroxyl groups are bonded to Si. Benefiting from the tunable composition, the gersiloxenes showed gradual shift of absorption edge in ultraviolet–visible (UV–Vis) diffuse reflectance spectra from long wavelength to short wavelength with x increasing, corresponding to the color change form dark red to light green (Fig. 1b). The 2D gersiloxenes thus exhibited adjustable band gap from 1.80 eV (x = 0.1) to 2.57 eV (x = 0.9), in between that of GeH (1.53 eV) and Si6H3(OH)3 (2.45 eV). The authors determined the valence-band (VB) positions of gersiloxenes using valence-band X-ray photoelectron spectroscopy (XPS) and thus demonstrated the electronic band structures, as shown in Fig. 1c. The authors also calculated the adsorption energies of H2O and CO2 molecules on the S.-W. Cao* State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China e-mail: [email protected]