Structural evolution, optical properties, and photocatalytic performance of copper and tungsten heterostructure materials

Abstract

Several studies reported that modifying CuO with CuWO4 can increase its photoactivity. In this study, copper and tungsten heterostructure materials were synthesized via a simple sol-gel method using ammonium paratungstate. The temperature’s influence (300, 500, 700, and 900 °C) was analyzed in the structural, morphological, microstructural, and optical properties of Cu and W materials using X-ray diffraction, infrared spectroscopy, field emission-scanning electron microcopy, transmission electron microscopy, diffuse reflectance spectroscopy, and dynamic light-scattering studies. The CuO diffraction patterns exhibited a tenorite phase formation, and the copper-tungsten materials diffractograms demonstrated the formation of CuO/CuWO4 at 300 and 500 °C and CuO/CuWO4/Cu2WO4/WO3 materials at 700 and 900 °C with crystallite sizes from 25 to 56 nm. Intense vibrational modes obtained at 300 °C for the CuWO4 phase decreased at 500 °C. Therefore, 500 °C is not a temperature that promotes CuO/CuWO4 heterostructure formation. Analyses conducted using microscopy techniques demonstrated the morphology of the CuO/CuWO4 heterostructure obtained at 300 °C, where CuWO4 nanoparticles covered the CuO polyhedral; microstructural analysis verified the heterostructure’s formation. The synthesized materials at 300 °C had an optical band gap of 2.66 eV (direct gap) and 1.35 eV and 2.11 eV (indirect gap), which were lower values than those of the CuO and CuWO4. The temperature at 300 °C proved to be optimal for the formation of the CuO/CuWO4 heterostructure. Only the material obtained at 300 °C exhibited a photocatalytic response in the rhodamine B degradation due to a possible interfacial charge transfer between the CuWO4 and CuO. The synthesis process used to obtain the CuO/CuWO4 heterostructure was novel, with a short processing time, low energy consumption and cost, and environmentally friendly properties.