Synthesis, characterization, and photocatalytic study of Bi-doped CuS nanoparticles

Pure CuS and Bi-doped CuS nanoparticles (NPs) with varying concentrations (2.5, 5, 7.5, and 10 wt%) of Bi were synthesized using a facile chemical co-precipitation method. Various characterization techniques, including spectroscopy, microscopy, and diffraction analysis, were used to study the prepared samples. XRD confirmed the formation of a hexagonal CuS phase, and Scherrer calculations revealed that crystallite size increased from 15.15 nm (undoped) to 16.22 nm (10% Bi-doped). HRTEM images indicated mixed shapes with an increase in the size of CuS nanostructures due to the incorporation of Bi dopant atoms (16.27-17.16 nm). The presence of dopants was determined using XRF. UV-vis diffuse reflectance spectroscopy (DRS) indicated a band gap narrowing from 1.38 eV (pure CuS) to 1.23 eV (10% Bi-doped), enhancing visible-light absorption. The low band gap of CuS NPs in the current work indicates their significance for use in optoelectronic devices. The absorption coefficient, extinction coefficient, and refractive index have been widely studied. Photoluminescence (PL) spectra showed suppressed recombination in doped samples. Under direct sunlight irradiation, methylene blue (MB) dye was photocatalytically degraded using pure CuS and Bi-doped CuS NPs. The 10% Bi-doped CuS NPs exhibited the highest degradation efficiency (75.77%) and a pseudo-first-order rate constant (k = 0.006 min^-1), attributed to improved charge separation and band structure modulation. These findings highlight Bi-doped CuS as a promising candidate for cost-effective, sunlight-driven environmental remediation technologies.