Synthesis of a novel, ternary AgI/CeO2@g-C3N4 nanocomposite with exceptional stability and reusability for visible light-assisted photocatalytic reduction of hexavalent chromium

Abstract

This work demonstrates a highly efficient photocatalytic reduction of Cr(VI) to Cr(III) by using a AgI/CeO2@g-C3N4 nanocomposite, under visible light (Vis) irradiation. The as-prepared samples were characterized by FT-IR, XRD, FE-SEM, TEM, XPS, DRS, PL, PC, and BET. Optimization of the treatment conditions included systematic parameterization, such as initial solution pH, photocatalyst dosage, and Cr(VI) concentration were investigated in the reaction. Compared with pure g-C3N4, CeO2, AgI, and CeO2@g-C3N4 binary nanocomposite, the as-made AgI/CeO2@g-C3N4 ternary nanocomposite showed significantly higher photo-reduction efficiency. The ternary photocatalyst shows a 99.6% reduction efficiency for Cr(VI) (15 mg/L) within 75 min at pH = 3.0. The highest rate constant value (0.058 min−1) was calculated for ternary photocatalyst that is 2.1 times higher than CeO2@g-C3N4/Vis process. The improved activity could be related to the effective electron/hole (e-/h+) pairs separation by forming a hetero-junction structure. The XPS analysis of recovered photocatalyst shows the presence only of Cr(III), which indicated a complete photo-reduction of Cr(VI) over AgI/CeO2@g-C3N4 nanocomposite. Moreover, the as-made photocatalyst exhibited more than 91% reduction efficiency after four cycles under the optimum reaction conditions. Based on the radical trapping experiments, photo-generated electrons (e−), and superoxide radicals O2∙- were the dominant active species in photo-catalytic Cr(VI) removal.