Enhancing the Photoelectrocatalytic Activity of a Gr/Sb‐SnO ₂ Photoanode via Bi and Ni Co‐Doping

ABSTRACT In the current study, the photoelectrocatalytic activity of Gr/Sb‐SnO 2 photoanode was improved by doping with Bi and Ni. The effects of doping bismuth and nickel at different molar ratios on the catalytic activity of Gr/Sb‐SnO 2 photoanode were studied. SEM, XRD, and LSV techniques were utilized to identify the structure and performance of the prepared photoanodes. The best type of photoanode was applied for tetracycline (TC) removal using a photoelectrocatalytic (PEC) process, and several parameters affecting TC degradation were investigated. These are initial TC concentration, current density, and pH, which were optimized by employing a response surface methodology (RSM). It was observed that Gr/Bi‐Ni‐Sb‐SnO 2 (5:5:5:95) is an ideal photoanode for degrading TC and combining Bi and Ni with SnO 2 resulted in the formation of coherent deposits with the best photocatalytic activity when they are shared at the same doping ratio. RSM based on Box‐Behnken design was found to be efficient in clarifying the mathematical relation between TC removal efficiency and PEC variables with a correlation coefficient of 99.15%. A substantial relationship was observed between the operational variables in the PEC process and TC removal efficiency, in which the quadratic term made a significant contribution to the model. Furthermore, the main factor influencing TC degradation was the initial concentration of TC. The preferred conditions were a current density of 6.78 mA/cm 2 , an initial TC concentration of 40 mg/L, and a pH of 3, in which a TC removal of 80% was achieved, corresponding to 61.7% as COD removal during 150 min. In this case, the total energy consumption was 73.3 kWh/m 3 in terms of TC concentration and 121.72 kWh/m 3 in terms of COD removal. A significant enhancement effect was observed in the PEC system, where its rate constant was 1.26 times higher than that observed in the photocatalytic process. Moreover, the Gr/Bi‐Ni‐Sb‐SnO 2 (5:5:5:95) photoanode displayed good stability after five cycles of PEC operation. Results confirmed that Gr/Bi‐Ni‐Sb‐SnO 2 (5:5:5:95) can be utilized as a beneficial photoanode for treating pharmaceutical wastewaters.