A PhD thesis was discussed at the Institute of Laser for Postgraduate Studies – University of Baghdad, presented by the researcher Nibras Nazih Mahmoud, entitled:
“Photoelectrochemical System Based on TiO₂/α-Fe₂O₃/GO Nanocomposite Photoanodes for Petroleum Refinery Wastewater Treatment”
Supervised by the late Dr. Mohammed Karim Dhahir and Dr. Zainab Fadhil Al-Bawi, the researcher obtained an Excellent grade.
The study aimed to develop an advanced photoelectrochemical (PEC) system for treating wastewater generated from oil refineries, coupled with a theoretical estimation of hydrogen generation, using nanocomposite photoanodes based on rutile phase titanium dioxide (rutile TiO₂), alpha iron oxide (α-Fe₂O₃), and graphene oxide (GO), with the aim of enhancing the efficiency of organic pollutant removal and improving the photoelectrochemical performance of the system.
The study included the preparation of three photoanodes, namely: rutile TiO₂, rutile TiO₂/α-Fe₂O₃, and rutile TiO₂/α-Fe₂O₃/GO, on fluorine-doped tin oxide (FTO) glass substrates, using a layer-by-layer drop-casting technique. The performance of these electrodes was evaluated using real wastewater collected from Al-Daura Refinery in Iraq. A set of structural, morphological, optical, and electrochemical characterizations was also conducted to evaluate the properties of the prepared electrodes.
The results showed a gradual decrease in the band gap energy from 3.03 eV for rutile TiO₂ to 2.70 eV for rutile TiO₂/α-Fe₂O₃, reaching 2.02 eV for the ternary photoanode rutile TiO₂/α-Fe₂O₃/GO, indicating improved ability to utilize visible light.
The system’s performance was also evaluated under the influence of several operational variables, including pH, temperature, irradiation time, catalyst loading, and light wavelength. The results showed that the optimal operating conditions were at pH 3, temperature 40°C, irradiation time 50 minutes, and catalyst loading of 0.4 mg cm⁻².
The ternary photoanode rutile TiO₂/α-Fe₂O₃/GO achieved the best performance in wastewater treatment, with removal efficiencies of Chemical Oxygen Demand (COD) 98.7%, Total Organic Carbon (TOC) 97.3%, and phenol 96.0%. Linear Sweep Voltammetry (LSV) measurements also showed a high photoelectrochemical response, with a photocurrent density reaching 65.23 mA cm⁻².
The study showed that the degradation of COD, TOC, and phenol followed pseudo-first-order kinetics, and the optimized system recorded a low specific energy consumption of about 0.91 kWh m⁻³. Based on the electrochemical data and the theoretical calculation method adopted in the study, the maximum theoretical amount of hydrogen generation was estimated at about 8340.33 µmol L⁻¹.
The scientific novelty of the study lies in the development of the ternary photoanode based on integrating the heterojunction rutile TiO₂/α-Fe₂O₃ with graphene oxide (GO). The synergistic effect between the components of the photoanode contributed to improving the utilization of visible light, enhancing charge separation and transfer across interfaces, reducing electron-hole recombination, and promoting surface redox reactions, which positively reflected on the photoelectrochemical performance and pollutant treatment efficiency.
The results of the study indicate the promising potential of the developed photoelectrochemical system in treating industrial wastewater generated from petroleum refineries, in addition to showing a theoretical possibility for hydrogen generation concurrently with the treatment process, supporting the development of more efficient and sustainable technologies for pollutant treatment and energy utilization.
