Suitable energy platform significantly improves charge separation of g-C_3N_4 for CO_2 reduction and pollutant oxidation under visible-light

The photocatalytic activities of g-C_3N_4 can be significantly improved by increasing life time of the photogenerated charges. Here, in this work we introduced TiO_2 as proper energy platform to accept the photogenerated electrons from g-C_3N_4 during photocatalysis. The nanophotocatalysts formed from the combination of a suitable amount of TiO_2 nanoparticles and g-C_3N_4 nanosheets showed 8.75 and 4.22% enhancement in photocatalytic activities for CO_2 reduction and 2-chlorophenol(2-CP) degradation under visible light illumination as compared to bare g-C_3N_4. Based on the surface photovoltage spectra, photoluminescence spectra and examination of formed hydroxyl radicals, it was confirmed that these enhanced photoactivities were attributed to the much-improved charge separation via the electron transfer from g-C_3N_4 to TiO_2. From trapping experiments,it was found that hydroxyl radicals were the major species involved in the photocatalytic degradation of 2-CP.This study is helpful to synthesize efficient photocatalysts to cope with energy and environmental issues.     

Earth-abundant photovoltaic semiconductor NaSbS_2 in the rocksalt-derived structure:A first-principles study

NaSbS_2 was recently proposed as a novel photovoltaic semiconductor with earth-abundant component elements,but its fundamental material properties have not been well studied.The systematical first-principles calculations for its electronic,optical and defect properties were carried out in the present study,and the results show that:i)NaSbS_2 in the rocksalt-derived structure has a quasi-direct band gap and thus may have long minority carrier lifetime;ii) its absorption coefficients are as high as 10~4～10~5 cm~(-1) for the visible light and almost isotropic despite that the structure is distorted relative to the high-symmetry rocksalt structure;iii) the effective masses of the electron and hole carriers are anisotropic with much larger values along the z direction than in the x-y plane,and hence the orientational control of thin films should be important for enhancing the photovoltaic performance;iv) the valence and conduction band edges of NaSbS_2 are close to those of CuGaSe_2) so the n-CdS/pCuGaSe_2 device structure can be inherited to form the n-CdS/p-NaSbS_2 solar cells;v) the acceptor defects (Na_(Sb)antisites and Na vacancies) have very high concentration,making the synthesized NaSbS_2 always be p-type;vi)the S-rich condition can suppress the formation of deep-level donor defects (S vacancies and Sb_(Na) antisites) and therefore should be adopted for fabricating high-efficiency NaSbS_2 solar cells.     

Room-temperature facile synthesis of MnO2on carbon film via UV-photolysis for supercapacitor

A facile UV-photolysis method has been developed to synthesize birnessite-type MnO_2 nanosheets on carbon film at room temperature for supercapacitor electrode materials. The results clearly demonstrated that the specific capacitance of carbon/MnO_2 composite electrodes was controlled by the adjustable UV-photolysis reaction time in KMnO_4 solution. For the optimized composite electrode obtained after 2 h reaction, a superior specific capacitance of 277 Fg~(-1) was achieved at current density of 0.2 Ag~(-1). This finding suggests that UV-photolysis is a potential method to fabricate MnO_2 on carbon film for supercapacitor.