Photocatalytic reduction of Cr(VI) via surface modified g-C3N4 by acid-base regulation

Abstract

Cr(VI) is a class of highly toxic heavy metals. In this study, alkali-modified g-C3N4 (cOH-CN) and acid-modified g-C3N4 (cH-CN) materials were successfully synthesized, and their photocatalytic activities for Cr(VI) reduction under visible light irradiation were tested. Owing to defect structures by cH-CN and –OH group introduction by cOH-CN, the modified materials exhibited a larger surface area, more abundant pore structures, a wider visible light absorption range, higher energy gap values, and a stronger capacity for electron-hole pair separation. As a result, satisfactory Cr(VI) reduction performance was gained by these two photocatalysts. Almost all Cr(VI) was converted to Cr(III) after 60 min of treatment in the presence of these two catalysts, while it was only 30% for the pristine g-C3N4 materials. Relatively higher dosages of cH-CN and cOH-CN and acidic conditions both improved Cr(VI) reduction in the cH-CN and cOH-CN photocatalytic systems. Cr(VI) reduction was mainly initiated by free electrons in the photocatalytic system of the modified materials. Finally, Cr(VI) in the photocatalytic system was almost completely converted to Cr(III). Furthermore, the stability and recycling of the cH-CN and cOH-CN catalysts were evaluated.