The intensive development of the petrochemical industry globally reflects the necessity of an efficient approach for oily sludge and wastewater. Hence, for the first time, the current study utilized magnetic waxy diesel sludge (MWOPS) to synthesize activated carbon coated with TiO2 particles for the removal of total petroleum hydrocarbons (TPH) and COD from oily petroleum wastewater (OPW). The photocatalyst was characterized using CHNOS, elemental analysis was performed using X-ray fluorescence spectroscopy (XRF), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HR-TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectrometer (FTIR), Raman, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), MAP thermo-gravimetric analysis/ differential thermo-gravimetric (TGA–DTG), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM). The optimization of synthesized highly porous AC/Fe3O4/TiO2 photocatalyst was conducted considering the impacts of pH, temperature, photocatalyst dosage, and UVA6W exposure time. The results demonstrated the high capacity of the MWOPS with inherent magnetic potential and desired carbon content for the removal of 91% and 93% of TPH and COD, respectively. The optimum conditions for the OPW treatment were obtained at pH 6.5, photocatalyst dosage of 250 mg, temperature of 35 °C, and UVA6W exposure time of 67.5 min. Moreover, the isotherm/kinetic modeling illustrated simultaneous physisorption and chemisorption on heterogeneous and multilayer surfaces. Notably, the adsorption efficiency of the AC/Fe3O4/TiO2 decreased by 4% after five adsorption/desorption cycles. Accordingly, the application of a well-designed pioneering photocatalyst from the MWOPS provides a cost-effective approach for industry manufacturers for oily wastewater treatment.

Preparation of superparamagnetic ACFe3O4TiO2 nanoparticles from magnetic waste oily petroleum sludge (MWOPS): comprehensive characterization, H2 production, design batch photoreactor, and treatment of oily petroleum wastewater (OPW) under UVA light
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Synthesis of ACFe3O4
        2.2 Synthesis of ACFe3O4TiO2
        2.3 Characterization of the ACFe3O4TiO2
        2.4 Photoreactor system
        2.5 Experimental design
        2.6 Characteristics of diesel tank wastewater
    3 Results
        3.1 Characterization
        3.2 Experimental design
            3.2.1 Interaction effects
        3.3 Optimization process
        3.4 Isotherm model
        3.5 Kinetics, thermodynamic, and reusability of the ACFe3O4TiO2
    4 Discussion
        4.1 Characterization
        4.2 COD and TPH removal
        4.3 Optimization process and reusability of the ACFe3O4TiO2
        4.4 Isotherm, kinetics, and thermodynamics model
        4.5 Necessity of managing oil sludge
    5 Conclusion
    References

• Saeedeh Rastgar(Department of Environmental Sciences, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan 49189‑43464, Iran) Corresponding author
• Hassan Rezaei(Department of Environmental Sciences, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan 49189‑43464, Iran)
• Habibollah Younesi(Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, Noor 46414‑356, Iran)
• Hajar Abyar(Department of Environmental Sciences, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan 49189‑43464, Iran)