The MoS 2 /g-C 3 N 4 heterojunction composite (marked as MoS 2 /g-C 3 N 4 -H) was successfully prepared via calcining the melamine coated MoS 2 nano-sphere, where the thin g-C 3 N 4 nano-sheets were tightly grown on the surface of MoS 2 nano-sphere to form MoS 2 inlaying in g-C 3 N 4 heterostructure. The detailed charge transfer mechanism was discussed by combining theoretical calculation and experiments, in which the intrinsic cause of photo-generated charge separation and transfer was determined as the directional built-in electric field driven by different Fermi levels of MoS 2 and g-C 3 N 4 . Comparatively, the enhanced photo-catalytic performance and stability of the sample were assessed by degrading the Rhodamine (RhB) and reducing the Dichromate (Cr 6+ ) solutions under the irradiation of the simulated sunlight, which could be attributed to the widened spectral absorption range and improved electron-hole separation rate. Based on above results, the photo-catalytic mechanism involving redox reactions was also clearly proposed.
The photocatalytic hydrogen production has become one of the most promising strategies to solve the energy crisis and environmental pollution. Novel CdSe/SrTiO 3 nanocomposites (average diameter ≈ 114.6 nm) with high photocatalytic activity are synthesized and used for visible light photocatalytic water splitting for hydrogen production . Through optimizing the concentration of CdSe QDs, CdSe/SrTiO 3 nanocomposites exhibit increased visible light absorption and enhanced photocatalytic hydrogen evolution efficiency compared to SrTiO 3 nanoparticles. The maximum H 2 evolution amount reaches to 3350.53 μmol in 8 h by using CdSe/SrTiO 3 -3 as catalyst. Owing to the formation of heterojunction at the interface between CdSe and SrTiO 3 , the electrochemical impedance spectrum of CdSe/SrTiO 3 -3 exhibits the smallest arc radius and the photocurrent density of CdSe/SrTiO 3 -3 reaches to 0.26 μA cm −2 . The photogenerated electrons are effectively separated and transferred and the recombination of electron-hole pairs is avoided, thus significantly improving the photocatalytic hydrogen production performance of CdSe/SrTiO 3 nanocomposites.
The two-stage removal process of tetracycline (TC) in aqueous solutions using a novel photocatalyst based on nano-zero-valent iron (NZVI), g-C3N4 and expanded graphite by carbon layer (EGC) is reported for the first time. The composite (NZVI/g-C3N4@EGC) exhibits remarkable adsorption, reduction ability and visible light activity over the reaction course. Compared with pristine g-C3N4 (25.9%) and pure NZVI (45.9%), NZVI/g-C3N4@EGC achieves high degradation efficiency of TC (98.5%) due to the formation of a heterogeneous photo-Fenton system. This study shows that synergistic effects are achieved in the reaction system, including maintaining the reduction ability of NZVI and enhancing the photocatalytic activity of g-C3N4 by facilitating the separation of photogenerated electrons (e−) and holes (h+). TC removal involved a two-stage process of adsorption–reduction and photo-degradation. The quencher experiments determined that holes (h+) and superoxide radicals (˙O2−) are the major reactive species in the degradation of TC. The degradation pathways of TC were proposed based on the analysis of the intermediates. In addition, NZVI/g-C3N4@EGC revealed a high stability in a five-cycle test and good magnetic properties for facile separation from aqueous solutions. From an application viewpoint, NZVI/g-C3N4@EGC has favorable prospects in the direction of the photocatalytic degradation of antibiotic wastewater.
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