Synthesis, Characterization And Photocatalytic Properties Of Sulfur And Metal Sulfides-Graphitic Carbon Nitride Nanocomposites

Environment pollution and energy crisis are the two problems for the humanity in the 21 st century. Semiconductor-based photocatalysis is an emerging technology which belongings to green chemistry. The traditional photocatalyst can only utilize the ultraviolet light and its practical application is limited due to its low quantum efficiency as well as the difficulty in separation and reuse of the powder catalysts. To overcome this problem, the exploration of novel, highly efficient visible-light-responded photocatalysts has become one of the most important research areas for environmental pollution control and renewable energy. Meanwhile, a challenge of the pristine semiconductor faced before its practical application is the poor quantum yield, resulting from the rapid recombination of photogenerated electrons and holes. In this study, we focus on the synthesis, characterization and visible light photocatalytic activity of sulfur and metal sulfides-modifiedg-C3N4-based photocatalysts and study their photocatalytic performance towards the degradation of dyes and antibiotics.The details are summarized briefly as follows:(1) Composite photocatalysts consisting of different ratios of sulfur and graphitic carbon nitride(S/g-C3N4) were prepared by chemical reduction. The resulted S/g-C3N4 composite photocatalysts were characterized and their photocatalytic activity was evaluated using Rh B as a probe. The S/g-C3N4 exhibits obviously enhanced photocatalytic activity under visible light irradiation, which is much higher than that of pure sulfur and g-C3N4. The S/g-C3N4 composite was very stable during the reaction and can be used repeatedly. The synergistic effect between sulfur and g-C3N4 was found to be responsible for the improvement of the separation of photogenerated electrons and holes. The holes(h+) and superoxide(·O2-) were the main active species in the photocatalytic degradation of rhodamine B. The study provides new insight to develop high performance composite photocatalysts without any metal oxide or metal sulfide for environmental remediation.(2) Novel composite photocatalysts consisting of Cd S and graphitic carbon nitride(Cd S/g-C3N4) with different ratios of Cd S were prepared. The Cd S/g-C3N4 composite photocatalysts were characterized in detail and their photocatalytic activity was evaluated by using rhodamine B and colorless metronidazole as probes. Compared with pure g-C3N4, the Cd S/g-C3N4 composite exhibits significantly enhanced photocatalytic activity under visible-light irradiation. More importantly, g-C3N4 substantially reinforces the photostability of Cd S nanowires even in a non-sacrificial system. The synergistic effect between Cd S and g-C3N4 is found to be primarily responsible for enhancement of the separation of photogenerated electrons and holes, which helps improve the photocatalytic performance. A probable photodegradation process of metronidazole was proposed based on the analysis of the degradation products. This study provides new insightinto the preparation of highly efficient and stable sulfide based composite photocatalysts and facilitates their application in a number of environmental sensitive areas.(3) Novel composite photocatalysts consisting of Zn In2S4 and graphitic carbon nitride(Zn In2S4/g-C3N4) with differentratios of Zn In2S4 were prepared by an in-situ controlled growth process. The resulted Zn In2S4/g-C3N4(EG) composite photocatalysts were characterized by XRD, SEM, HRTEM and UV-vis DRS. Their photocatalytic activity was evaluated using colourless antibiotic metronidazole as a probe. The Zn In2S4/g-C3N4(EG) photocatalysts exhibit enhanced photocatalytic activity obviously under visible light irradiation. More importantly, by compounding with g-C3N4, photostability of the Zn In2S4 nanoparticlesis substantially reinforced even in a non-sacrificial system. The as-obtained Zn In2S4/g-C3N4(EG) composites showed excellent photocatalytic performance and the synergistic effect between Zn In2S4 and g-C3N4(EG) was found to be responsible for the improvement of the separation of photogenerated electrons and holes.(4) Novel composite photocatalysts consisting of Cd S, S and graphitic carbon nitride(Cd S/S/g-C3N4) with different ratios of Cd S were prepared by an in-situ process method. The resulted Cd S/S/g-C3N4(EG) composite photocatalysts were characterized by XRD, SEM, TGA, HRTEM and UV-vis DRS. Their photocatalytic activity was evaluated using antibiotic metronidazole as a probe. The Cd S/S/g-C3N4(EG) photocatalysts exhibit enhanced photocatalytic performance obviously under visible light irradiation and the MTZ was degraded completely in 3 h. More prominently, the incorporation of g-C3N4(EG) and S with Cd S nanoparticles substantially reinforcedits photostability even in a non-sacrificial system. The as-obtained Cd S/S/g-C3N4(EG) catalystsshowed excellent photocatalytic performance and the synergistic effect between Cd S, S and g-C3N4(EG) was found to be responsible for the improvement of the separation of photogenerated electrons and holes. The Cd S/S/g-C3N4(EG) composites withhigh photocatalytic performance, low photocorrosion and environmentally friendly, hold great potential for practical applications.