Study On Degradation Of Organic Pollutants In Printing Wastewater By TiO₂ Based Composite Photocatalyst

The main source of printing wastewater refers to the ink wastewater during the printing process,organic solvents,organic pigments and equipment cleaning wastewater.The wastewater has complex compositions,high content of organic pollutants,difficulty in biodegradation,high chroma and high COD value.It has become one of the primary tasks to solve the environmental pollution problem in the printing industry.Therefore,it is of great practical significance to develop an efficient wastewater treatment technology.In recent years,a new type of green water treatment technology-photocatalytic oxidation has been rapidly developed.The method can degrade the organic pollutants of wastewater into CO₂ and H₂O by the light.Nano-TiO₂ is a photocatalyst with high catalytic activity,strong oxidizing ability,stable chemical properties,non-toxicity.However,in practical applications,nano-TiO₂ still has other defects such as low oxidation efficiency,poor adsorption capacity and easy to reunite.GO has the advantages of large specific surface area,good dispersion and superior adsorption,SiO₂ aerogels has the advantages of high porosity,high specific surface area and strong adsorption,etc.They can be used as an excellent photocatalyst composite matrix.In this thesis,the preparation of nano-TiO₂ based composite photocatalysts and the photocatalytic degradation of printing ink wastewater were studied.The main contents as follows:?1?Degradation of methyl orange by graphene oxide/nano-TiO₂ blending photocatalyst.The effect of factors such as the mass ratio of graphene oxide and nano-TiO₂,the amount of catalyst and the pH value on the degradation of methyl orange were investigated.The photocatalyst degredation results showed,the mass ratio of graphene oxide and nano-TiO₂ was 1?5,the amount of catalyst was0.3 g/L,the initial mass concentration of methyl orange was 20 mg/L,the pH was 4,the photocatalytic degradation rate effect was the best.After 2 hour of light irradiation,the degredation rate of methyl orange was 99.64%.?2?In order to further reduce the degredation time and improve the degredation efficiency,SiO₂ aerogels with TEOS as the silicon source were prepared by sol-gel method.The optimal reaction parameters were determined by controlling the dosage of acid catalyst and base catalyst,reaction time and temperature,etc.The Si O₂ aerogels/nano-TiO₂ blending photocatalyst was prepared by mechanical grinding method.The results showed that the specific surface ares of SiO₂ aerogels was 624.54 m²/g,when the nano-TiO₂ particles were evenly distributed in SiO₂ aerogels,the specific surface area can reach600.84 m²/g,the structure of the blending photocatalyst was loose,there was small amount of pores between the particles,thereby facilitating the enhancement of the adsorption capacity of organic substances.To obtain the best experimental conditions of photocatalytic degradation technology,methyl orange was used to simulate single printing wastewater,the effects of the mass ratio of the various components of the photocatalyst,the dosage of the catalyst,the initial mass concentration of methyl orange and pH value on the degradation of methyl orange was discussed.The results showed that the mass ratio of the SiO₂aerogels and nano-TiO₂ was 4?1,the amount of the catalyst was 0.2 g/L,the initial mass concentration of methyl orange was 10 mg/L,the degradation rate of methyl orange was the highest and the degradation rate can reach 99.85%.?3?Owing to further explore the degradation of printing ink wastewater by SiO₂ aerogels/nano-TiO₂ blending catalyst and obtain the best experimental conditions for photocatalytic degradation of printing ink wastewater.Firstly,the printing ink wastewater was subjected to coagulation pretreatment and impurities were removed to reduce the turbidity,then use photocatalytic oxidation to treat the printing ink wastewater.The results showed that the mass ratio of SiO₂aerogels and nano-TiO₂ was 4?1,the amount of the catalyst was 0.2 g/L,the pH was 4,after 30 minutes of dark adsorption and the light was irradiated for 40minutes,COD value and color removal rate of printing ink wastewater can reach95.83%and 96.62%,respectively.In addition,SiO₂ aerogels/nano-Ti O₂ blending catalyst was reusable,after 6 times,it still has good reproducibility on photocatalytic degradation effect of the printing ink wastewater.From the above,this study deals with printing ink wastewater through photocatalytic oxidation process,TiO₂ was supported on different carriers to prepare the blending photocatalyst,which can degrade printing ink wastewater.Finally meet national wastewater discharge requirements,it has important significance for the implementation of green printing.