The presence of organic micro-pollutants (OMPs) in water bodies has become a major hindrance to protecting water quality in recent years. One of the main sources of OMPs is wastewater treatment plant (WWTP) effluents. One of the most recent Advanced Oxidation Processes (AOPs) technology is photo-electrocatalysis (PEC), which can produce radicals to oxide OMPs in an aqueous medium driven by solar energy and an external bias potential. In this study, ultrasonic spray pyrolysis was determined as a proper method to fabricate the ZnO/BiVO4 heterojunction. Then, the prepared photoanodes were characterised by X-ray Photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-vis and Incident Photo-to-electron Conversion Efficiency (IPCE). The results demonstrated the ZnO/BiVO4 heterojunction was successfully fabricated on the Fluorine-Tin-Oxide (FTO) glass. Moreover, the LSV and EIS analysis were carried out in this study to analyse its photo-electrochemical properties. The PEC degradation experiments were carried out in 10 μg/L of 11 OMPs spiked in MiliQ and in real WWTP effluent under simulated solar illumination at 1 V potential bias for three hours. Nine and four of 11 OMPs had achieved more than 70 % degradation efficiency when ZnO/BiVO4 photoanode was conducted to degrade spiked MiliQ and spiked real WWTP effluent. Except for diclofenac and sotalol, the real effluent showed inhibition to the degradation efficiencies and kinetic coefficient of the other nine OMPs. The concentrations of TOC, COD and NO3-N increased after the PEC process. The increase was found to be related to the disintegration of the carbon stick cathode. To further enhance the PEC process, the ZnO@GD/BiVO4 photoanode and adding persulfate were conducted the PEC degradation experiments separately in spiked real WWTPs effluent. Both two approaches showed an enhancement of the PEC process and improved degradation efficiencies. The results obtained in the present work reveal that the PEC process has excellent potential for the removal of OMPs from WWTPs effluent.

In the recent decade, a wide range of emerging contaminants (ECs) has been regularly detected in the wastewater treatment plants (WWTPs) effluent, surface water and even groundwater. Among all these ECs, organic micropollutants (OMPs) are receiving increasing attention due to their characteristics of low concentration, difficulty in degradation and their harmful effects on humans and the environment. Nineteen OMPs have been included on the contaminant watch list of the European Union Water Framework Directive since 2015 and efficient and reliable methods to eliminate them are researched worldwide. Therefore, in this study, five of these 19 OMPs (benzotriazole (BTA), carbamazepine (CBZ), diclofenac (DIC), ketoprofen (KET) and caffeine (CAF)) were selected as target OMPs. And the research objective is to fabricate a ternary composite photoanode and to investigate its photoelectrocatalytic degradation performance for all five target OMPs. BiVO4/(TiO2/graphene oxide (GO))mix ternary composite thin films were successfully deposited on fluorine-doped tin oxide (FTO) glass substrates using ultrasonic spray paralysis (USP) method to form a ternary heterojunction structure and to improve the photoelectrocatalytic performance for degradation of the five target OMPs. The morphology, crystal phase, surface chemical composition, optical and electrochemical properties of this ternary composite photoanode were analyzed by scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, incident photon-to-electron conversion efficiency (IPCE), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), respectively. The results of these analyses showed that TiO2 P25 nanoparticles and GO sheets were distributed uniformly on the brain-shaped BiVO4 structure which indicated that the ternary heterojunction structure was formed successfully. From the UV-vis analysis, it could be estimated that the band gap energy for BiVO4/(TiO2/GO)mix ternary composite photoanodes is 2.43 eV. Further, the LSV and EIS analysis showed that the photocurrent of the ternary composite photoanodes is lower than pure BiVO4 photoanodes. The degradation experiments were divided into five stages. The optimal photoanode type was first determined in the pre-experiment stage using methylene blue (MB) as indicator organic pollutant and then the effect of initial concentrations of target OMPs and initial pH on the degradation efficiency were studied in stage II and III, respectively. The highest removal efficiency of the five target OMPs was obtained with initial OMPs concentration at 10 μg·L-1 and initial pH range of 3.5-4.0. The degradation experiments were triplicated under this optimal condition in stage IV. It was noticed from the results that the degradation efficiency of different OMPs after 3 hours of reaction time varied from 31.1 % to 99.5 %. To further confirm that there is competition between the five target OMPs during the photoelectrocatalytic degradation process, experiments were carried out in which individual OMPs were degraded independently. The reusability and stability of the photoanodes were evaluated in stage V. Trapping experiments using scavengers were also included in this stage, which showed that superoxide anions was the most active species during the degradation process.

Currently, organic micropollutants (OMPs) are continuously and uncontrollably released into the water environment worldwide, as the reason for their special properties, OMPs removal has been a global challenge. This study focuses on acetaminophen degradation by photo-electrolysis (PEC) activities, which is one of the promising advanced oxidation processes (AOP) technologies. First, we report the fabrication methods of the BiVO4/BiOI heterojunction on FTO glass, then characterised the prepared photoanodes with XPS, XRD, SEM, EDS, UV-vis and IPCE. The results demonstrated the BiVO4/BiOI p-n heterojunction had been successfully electrodeposited on the FTO glass. Further, the LSV and EIS analysis in this study showed the BiVO4/BiOI photoanode had less photocurrent density than BiVO4 when carried out in the solution of acetaminophen. Even if the heterojunction did not improve the photocurrent, it significantly enhance the acetaminophen removal efficiency in the PEC degradation process. BiVO4/BiOI photoanode achieved 99% degradation efficiency in 3 hours and obtained 0.019 mi n−1 of the reaction rate constant. Overall, these results indicate that BiVO4/BiOI heterojunction has a great application potential for the degradation of OMPs in the wastewater treatment plants secondary effluent.

As industrialization advances rapidly in pursuit of refining the quality of human life, there has been a release of organic micropollutants (OMPs) such as pharmaceuticals into various water reserves. This has endangered the ecosystem and the possibilities of water recovery. Commonly used tertiary wastewater treatment technologies have proven to, not under all conditions, be less effective in OMP removal. Hence, Advanced Oxidation Processes (AOPs) have gained attention in the recent past due to their production of reactive oxidative species (ROS) that unselectively degrade OMPs. Photocatalysis (PC), an AOP that uses solar radiation to produce ROS, has been investigated earlier, but shows low efficiency due to fast electron-hole recombination. Photoelectrocatalysis (PEC) is a modified version that additionally uses electrical energy, thereby reducing the recombination and improving the OMP removal efficiency. Bismuth vanadate (BiVO4) photocatalyst has gained importance due to its narrow band gap of 2.4 eV and hence, efficient absorption in visible light spectrum. Thus, this research focused on investigating PEC using BiVO4 electrodes for the removal of OMPs in aqueous solutions. The BiVO4 electrodes were fabricated using dip-coating from 1 to 5 layers, and electrodeposition at -0.2 V and -0.4 V, each at durations of 2, 5, 7, 10 and 15 minutes. They were then characterized using analytical techniques to investigate their structural, optical and optoelectronic properties. Subsequently, all the BiVO4 electrodes were used for the photoelectrocatalytic degradation of Acetaminophen (ACT). The electrodes fabricated by dip-coating were shown to achieve superior degradation efficiencies of ACT of over 99% in 5 hours, due to optimum surface morphology and band gap. It was seen that their varied surface structures played an important role in improving OMP degradation, and compensated for their low average quantum efficiency at 7%, as compared to that of electrodeposition at 14%. Next, the photoelectrocatalytic degradation of multiple OMPs in a solution was studied, and it was determined that although the ROS unselectively targeted all the OMPs, some were degraded quicker than others due to their chemical structure. Scavenging experiments were also carried out that affirmed the role played by ROS in the photoelectrocatalytic degradation of the OMPs. Eventually, the degradation of OMPs in secondary wastewater treatment effluent was conducted to test its usage in purification applications. Overall, PEC using BiVO4 electrodes was found to be feasible and successful in OMP degradation, and has the potential to be developed for usage in environmental remediation strategies like water treatment and recovery.