Abstract
Graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a one-step pyrolysis process using melamine, dicyandiamide, thiourea, and urea as precursors. The obtained g-C3N4 materials exhibited a significantly different performance for the photocatalytic reduction of Cr(VI) under white light irradiation, which is attributed to the altered structure and occupancies surface groups. The urea-derived g-C3N4 with nanosheet morphology, large specific surface area, and high occupancies of surface amine groups exhibited superior photocatalytic activity. The nanosheet morphology and large surface area facilitated the separation and transmission of charge, while the high occupancies of surface amine groups promoted the formation of hydrogen adsorption atomic centers which were beneficial to Cr(VI) reduction. Moreover, the possible reduction pathway of Cr(VI) to Cr(III) over the urea-derived g-C3N4 was proposed and the reduction process was mainly initiated by a direct reduction of photogenerated electrons.
Highlights
In recent years, with the rapid development of mining, electroplating, leather tanneries, and pigments, a large number of heavy metal compounds have been discharged
G-C3 N4 composites are synthesized via a facile polymerized method with four different precursors
It was found that the type of precursors has a significant impact on the morphology and structure of g-C3 N4 and further affects the performance of photocatalytic reduction of
Summary
With the rapid development of mining, electroplating, leather tanneries, and pigments, a large number of heavy metal compounds have been discharged. Because of its high toxicity, Cr(VI) has been ranked among the top 20 toxic pollutants on Superfund Priority List of Hazardous Substances [4]. Photocatalytic reduction technology is an attractive alternative technology for Cr(VI) reduction because of its acceptable cost, easy operation, and high safety. It can directly reduce high toxic Cr(VI) to less harmful Cr(III), which is a necessary trace element for human being and easy to precipitation in aqueous solution θ (Cr(OH) ) = 6.3 × 10−31 ) [5,6,7]. (Ksp. As a metal-free semiconductor photocatalyst, graphitic carbon nitride (g-C3 N4 ) has been widely studied due to its visible-light-driven, narrow bandgap, non-toxic, low cost, and excellent stability [8,9]. The conduction band of g-C3 N4 level is much more negative than that of Cr(VI)/Cr(III) (1.3 eV vs. NHE), suggesting that the photo-generated electrons in g-C3 N4 possess a large thermodynamic driving force to reduce Cr(VI) to
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