Study On The Treatment Of Organic Compounds In Oilfield Wastewater By Cu²⁺/ZnO/TiO₂ Composite Photocatalyst

Oilfield wastewater contains a large number of organic pollutants,which are toxic and harmful and difficult to degrade.The traditional water treatment process has low removal efficiency and high cost for fracturing return fluid.The photocatalytic oxidation process has good removal effect on organic matter,and is economical,green and environmental friendly.Modification study on photocatalyst can greatly improve the photocatalytic activity of photocatalyst and enhance its degradation effect,and therefore it can be used to treat actual oilfield wastewater finally.With its superior photocatalytic activity and stability,titanium dioxide has been becoming the focus of research on its performance improvement.Previous studies on the amelioration of titanium dioxide have mostly focused on single substance doping amelioration,noble metal doping or semiconductor composite amelioration for titanium dioxide,with limited photocatalytic effect and high cost.In this study,the traditional photocatalyst titanium dioxide was doped and improved by sol-gel method,and a new composite photocatalystcompound.The orthogonal test showed that the optimum doping amount was Cu²⁺:0.4%and Zn O:0.1%.Photocatalysis of methylene blue using Cu²⁺/Zn O/Ti O₂and using Ultraviolet spectrum indicates the photocatalytic degradation of methylene blue.The results showed that:the degradation rate of photocatalyst reached 99.92%after photocatalytic degradation of methylene blue solution for 2h under the irradiation of 8W ultraviolet light source.Under the same conditions,the catalytic effect is better than that of undoped titanium dioxide photocatalyst and single substance-doped photocatalyst.The catalysts Cu²⁺/Zn O/Ti O₂ were characterized by X-ray diffraction?XRD?,specific surface area?BET?,scanning electron microscopy?SEM?,infrared spectroscopy?FT-IR?,ultraviolet spectroscopy?UV-vis?and thermogravimetric analysis?TGA?.The results showed that:the XRD diffraction peak of the new composite photocatalyst Cu²⁺/Zn O/Ti O₂ after doping is the highest among the four types of composite photocatalysts,which is anatase type,with good doping effect,no impurity peak,high purity and average particle size of 16.6 nm.The BET analysis showed that the specific surface area of the catalyst Cu²⁺/Zn O/Ti O₂was 108.6 m/g,ZnO increases the specific surface area and pore number of the catalyst,enhances the adsorption capacity of the catalyst in the photocatalytic reaction,enlarges the reaction contact surface,and thus improves the photocatalytic activity of the new composite photocatalyst.SEM analysis of catalyst morphology showed that Cu²⁺/Zn O/Ti O₂ had a large number of pore structures and flocculent sponge structure.Infrared spectroscopy showed that the catalyst exhibited an obvious OH stretching vibration peak at 3500 cm^-1,which was more active than other composite photocatalysts.UV-vis spectroscopy proved that Cu²⁺/Zn O/Ti O₂had stronger light absorption ability,wider absorption range,higher light sensitivity and better photocatalytic activity.TGA analysis showed that the optimum calcination temperature of times higher than that of pure Ti O₂.After repeated use for 5 times,the reaction rate constant k remained basically unchanged with stability.Compared with the original device,the photocatalytic degradation rate of a small established and improved photocatalytic device was increased by 7%to explore the optimal photocatalytic experiment conditions of a new composite photocatalyst.The results showed that the photocatalytic efficiency was the highest when the p H was 7,the reaction temperature was 25?,the pre-reaction material concentration was 100-200 mg/L and the amount of Cu²⁺/Zn O/Ti O₂was 2.0 g/L.Under the optimal photocatalytic experimental conditions,the typical organic pollutants aniline and ethanol in oilfield wastewater were photocatalytically degraded.The results showed that:the removal rates of aniline and ethanol by the new composite photocatalyst reached 78.5%and 68.3%.Using Cu²⁺/Zn O/Ti O₂,the benzene serie?benzene,toluene,xylene?and COD were degraded in actual oilfield wastewater?oilfield fracturing reflux?.The results showed that after 7 h of photocatalytic degradation,the removal rates of p-benzene,toluene,o-xylene,m-xylene and p-xylene by the new composite photocatalyst were 93.7%,89.9%,94.3%,93.6%and 95.5%,respectively.The removal rate of COD was 80.9%.After photocatalytic treatment,the average value of the residual COD in oilfield wastewater water samples was 88.8 mg/L.The results show that the Cu²⁺/Zn O/Ti O₂ catalyst can effectively remove the organic components in the actual oilfield wastewater.The benzene serie and COD content in the treated wastewater can meet the requirements of the pollutant discharge standard of petrochemical industry?GB31571-2015?.