Tuning photocatalytic activity of g-C3N4 through Cu deposition via chemical reduction and a DBD plasma method for visible-light-driven Cr(vi) reduction

Abstract

The dispersion of metal nanoparticles (NPs) on graphitic carbon nitride, g-C₃N₄ (CN) offers a promising strategy to improve its photocatalytic efficiency. In this work, Cu deposition on CN was attempted by wet chemical reduction with NaBH₄ (Cu-CN-cr) and an atmospheric pressure dielectric barrier discharge (AP-DBD) cold plasma method (Cu-CN-pl). The samples were evaluated for Cr(VI) photocatalytic reduction under visible light at pH = 3, and compared with pristine CN and plasma-treated CN (CN-pl). FESEM, TEM, XPS and EPR showed that the Cu NPs were not formed by chemical reduction, but Cu⁺ was incorporated into the CN structure in the Cu-CN-cr sample. This caused a slight red shift of the absorption edge, reduced the PL peak intensity, and increased the photocurrent. In the Cu-CN-pl sample, Cu was deposited on the surface as Cu₂O/Cu(OH)₂ NPs, with the possibility of metallic Cu present within the core of the NPs. The plasma treatment induced remarkable structural modifications that served as binding sites for the NPs. The photogenerated electrons in the Cu-CN-cr were probably consumed for the reduction of Cu⁺ instead of Cr(VI), leading to a decrease in the photocatalytic reduction of Cr(VI). The use of plasma in the synthesis of Cu-CN-pl provided a uniform distribution and intimate contact between the deposited NPs and CN, thereby constructing an effective heterojunction. This heterojunction facilitates the separation of the carriers and enhances the photocatalytic activity compared to CN.