Preparation of poly ethyleneimine (PEI))/nano titania (TiO2) multilayer film on quartz tube by layer-by-layer self-assembly and its applications for petroleum refinery wastewater treatment

•PEI/TiO2 multilayer film on quartz tubes was successfully fabricated.•The PEI/TiO2 multilayer film exhibited higher photocatalytic activity under UV.•More than 98% of COD removed from the PRW in the optimum condition.•RSM was used to evaluate the effects of process variables on the PRW treatment.•Immobilization is inexpensive and catalysts can be reused making it a cost effective method.

Poly ethyleneimine (PEI)/titania (TiO2) multilayer film on quartz tubes have been successfully fabricated via a layer-by-layer (LbL) self-assembly method. scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area analysis were carried out for characterization and determination of the morphology and roughness of the prepared thin films on quartz tube. AFM and SEM images indicated that the film surface is smooth and uniform, and thickness of the film was estimated to be around 120 nm. The BET characterization proved the formation of multilayer thin film. The photocatalytic activity of the PEI/TiO2 multilayer deposited on the quartz tubes was evaluated in the treatment of raw petroleum refinery wastewater (PRW) under UV light irradiation in three annular photocatalytic reactors. Our preliminary study showed that the most significant variables on the PRW treatment in these photoreactores are initial chemical oxygen demand (COD) concentration, H2O2 concentration, pH and reaction time. Thus, further experiments and optimization were performed using response surface methodology (RSM) based on three-level central composite design to evaluate process conditions. Maximum COD removal (98%) was achieved at the optimum conditions (initial COD concentration of 200 mg/L, Hydrogen peroxide concentration of 8.8 mM, pH of 6 and reaction time of 120 min).