Visible light driven efficient photocatalytic degradation of Congo red dye catalyzed by hierarchical CuS–Bi2CuxW1−xO6−2x nanocomposite system

Abstract

A series of CuS–Bi₂Cu_xW_1−xO_6−2x nanocomposite materials were prepared and evaluated as photocatalyst for degradation of Congo red dye from aqueous sources. The Bi₂WO₆ (BT) nanoparticles were synthesized by amorphous citrate process. The CuS nanomaterials were dispersed over the BT matrix using hydrothermal route. The composite materials (CuSBT) were characterized using XRD, FESEM, TEM, XPS, UV-Vis-DRS, PL, sorptometric and FTIR techniques. XRD study indicated the existence of hexagonal covellite CuS and orthorhombic Russellite BT phase. During hydrothermal treatment, the Cu²⁺ ions substituted for the W⁶⁺ ions in the BT lattice to form a substitutional solid solution (Bi₂Cu_xW_1−xO_6−2x). The composite materials contain CuS nanorods and BT nanosheets. During hydrothermal treatment, significant morphological reorganization of the BT phase took place leading to the formation of flower like hierarchical nanostructures. The CuSBT materials possess characteristic features of a type-II heterojunction exhibiting narrow band gap, enhanced visible light absorption and efficient charge separation properties. The CuSBT materials were evaluated as visible light active photocatalyst for complete degradation of Congo red dye using H₂O₂ as oxidant. The CuSBT materials exhibited higher apparent rate constant (K_app) and greater efficiency for Congo red degradation compared to pure BT material. The photocatalytic protocol developed in this work was significant in terms of minimum and efficient use of catalyst and oxidant, less irradiation time and its applicability for aqueous effluents containing higher concentration of the dye.