Sulfur-doped carbon nitride as a non-metal heterogeneous catalyst for sulfate radical-based advanced oxidation processes in the absence of light irradiation

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As graphene-like materials are demonstrated as non-metal catalysts to activate persulfate (PSF)/peroxymonosulfate (PMS), co-doping sulfur and nitrogen with graphene is a promising approach to improve catalytic activities. In this study, a convenient one-step approach is adopted to prepare sulfur-doped graphitic carbon nitride (SCN), which shows crumpled morphology and porosity on its surface, making SCN exhibit a much higher surface area than the common CN. Chemical analyses also confirm that a part of N atoms in CN skeleton are substituted by S. To evaluate PSF/PMS activation by SCN, decolorization of Rhodamine B (RhB) is selected as a model test. SCN showed a much higher catalytic activity than carbon nitride (CN) to activate PSF/PMS for RhB decolorization. Behaviors of PSF/PMS activation by SCN are explored by evaluating various effects on RhB decolorization, including temperature, pH, and salt. SCN-activated PSF/PMS for RhB decolorization is much favorable at elevated temperatures and neutral conditions. The presence of NaCl does not significantly inhibit the PSF/PMS activation by SCN. Several radical inhibitors on SCN-activated PMS are also evaluated and the RhB mechanism is shown to involve both sulfate and hydroxyl radicals. Potential mechanisms of PSF/PMS activation by SCN are proposed and ascribed to the more active carbon sites of SCN induced by the co-dopants of sulfur and nitrogen. SCN can be also re-used to activate PSF/PMS without catalytic activity loss. These features demonstrate that SCN is a conveniently-prepared but effective and sustainable non-metal heterogeneous catalyst for activating PSF/PMS.