Construction of direct solid-state Z-scheme g-C 3 N 4 /BiOI with improved photocatalytic activity for microcystin-LR deg
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The novel visible-light-responsive direct solid-state Z-scheme g-C3N4/BiOI heterojunction has been synthesized successfully by means of a solid phase calcination method and used for the degradation of microcystin-LR (MC-LR). The layered g-C3N4 disperses on the surface of BiOI microspheres. The samples are characterized by FESEM, HRTEM, XRD, FT-IR, UV-vis spectroscopy, XPS, BET, PL, and Mott–Sckottky. The photocatalytic activity and photodegradation mechanism of the as-prepared g-C3N4/BiOI microsphere photocatalysts are conducted under visible light irradiation using MC-LR as the target pollutant. The g-C3N4/BiOI material exhibits superior photocatalytic performance when compared with pure BiOI, the possible reason is the efficient separation of photogenerated carriers at the interface between g-C3N4 and BiOI. The heterostructure is responsible for the improved separation efficiency of photogenerated electron–hole pairs and thus the higher photocatalytic activity. The possible photocatalytic mechanism is proposed based on relative band positions of these two semiconductors.
I. INTRODUCTION
Industrial and agricultural wastewaters as well as domestic waste water contain a lot of organic matters, nitrogen and phosphorus, and many other nutrients. It is easy to result in eutrophication, and the overgrowth of cyanobacteria leads to microcystins (MCs) pollution which calls for an efficient remediation solution.1–3 MCs are a class of naturally produced cyclic heptapeptide toxins released by cyanobacteria during algal blooms in eutrophic waters. They have been shown to have toxic effects on the liver, nerves, kidney, and reproductive organs. Wang et al. and his colleagues studied the distribution of MCs in various tissues of Wistar rats under laboratory conditions, and they observed the highest concentration of MCs in the lungs after the kidney.4 Until now, more than 60 microcystin variants have been found, and among which, Microcystin-LR (MC-LR) possesses the most toxic effect and widely distributes in natural waters.5 As a result, the threshold value of 1 lg/L for MC-LR in drinking water has been issued by the World Health Organization.5 However, the concentrations of MCs in many water bodies are far beyond that guideline. One study showed that the level in the Poyang Lake, the largest freshwater lake in China, was 7.97 mg/L.6 MC-LR is chemically stable and has a very slow natural degradation process. The stability of the cyclic peptide
Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.434
structure hinders the degradation of MC-LR efficaciously by traditional water or waste water treatments. Thus, various water treatments have been tried for MC-LR removal, such as UV/H2O2,7 UV/O3,8 and biotreatment5 et al. The development of an efficient, safe, and low-cost method for removing MC-LR in water has become one of the important problems to be solved urgently in environmental science research. Advanced oxidation processes including chlorination, ozonation,
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