Integrated electrochemical and photocatalytic degradation using ZnO caterpillars photocatalyst: Two-step approach for textile industry based wastewater recovery

A wide range of synthetic dyes released by the textile industry endangers human and environmental health. Even trace amounts of synthetic dye in water are easily visible and toxic to human health. Therefore, there is a burgeoning need for innovative treatment techniques that can result in the destruction of dye molecules in wastewater. This work aims at developing two-step processes for treating textile wastewater before discharging them into nature waterbodies. The step includes the electrochemical processing of the real sample, followed by the real time photocatalytic degradation using novel ZnO caterpillars. A facile fabrication approach is used to produce a ZnO caterpillar over SiO2/Si wafer using a vapor–liquid-solid (VLS) method, where gold nanoparticles (Au NPs)-decorated carbon nanofibers were used as catalyst providers. These ZnO caterpillars have been well characterized using techniques such as scanning electron microscope, X-ray diffraction, Raman spectroscopy, and contact angle goniometer. The contact angle results show the shifts of contact angle from 78.85˚ to 130.35˚ for pure SiO2/Si wafer and ZnO caterpillar-SiO2/Si leading to a hydrophobic surface. It was confirmed that with ZnO caterpillars, a photocatalytic response of ∼ 240 min for completely degrading electrochemically treated textile wastewater under UV light exposure was recorded. During this study, real-time textile wastewater degradation is monitored using the IoT technique by integrating a NodeMCU microcontroller board as a control center and a pH sensor as a tool for detecting the change in pH value of the textile wastewater under UV light exposure.