Study On The Adsorption Effect Of Nano-manganese Dioxide Modified Biochar On Phthalate In Water And Soil

Phthalates are often used as plasticizers to improve plasticity and toughness and are widely used in many fields.Because they do not degrade easily in the environment and accumulate through the food chain,they pollute the environment and threaten human health.In this study,we used corn straw as the raw material to prepare biochar（BC）,and used BC as the carrier to prepare Nano-manganese Dioxide modified Biochar（Mn-BC）by co-precipitation method,and used dibutyl phthalate（DBP）and diethyl phthalate（DEP）as the carrier,The target pollutants were dibutyl phthalate（DBP）and diethyl phthalate（DEP）,and the adsorption of Mn-BC on the target pollutants was investigated.Firstly,we investigated the optimal conditions for the preparation of biochar;compared the differences in physicochemical properties of biochar before and after modification by SEM,BET,FTIR and XPS characterization;explored the adsorption behaviors of DBP and DEP under different influencing factors（p H,dosage and temperature）through single-factor experiments;investigated the adsorption kinetics of DBP and DEP removal by Mn-BC in aqueous solution,adsorption isotherm of The adsorption mechanism was studied by the adsorption kinetics and adsorption isotherm model of DBP and DEP removal by Mn-BC in aqueous solution;followed by the leaching experiment to analyze the effect of Mn-BC on DBP fixation in soil.The main contents and results of the study are as follows:（1）In this study,corn straw biochar was used as a carrier and loaded with Nano manganese dioxide by chemical co-precipitation method to successfully prepare Nano manganese dioxide modified biochar.The optimal conditions for the preparation of Mn-BC were analyzed using orthogonal tests:calcination temperature of 500°C,calcination time of 2 h,and modification mass ratio of 1:10.（2）The BC and Mn-BC were characterized using SEM,BET,FTIR and XPS.The SEM results showed that the basic carbon skeleton structure of Mn-BC was retained,and uniformly distributed agglomerated particles appeared on the surface and in the pores.The surface area results showed that BET showed that it possessed larger pores and pore size compared to BC,with a surface area of 179.25 m²/g.FTIR showed that-OH and Mn-O played an important role in the adsorption and removal of DBP and DEP,and Mn O₂ modification,which significantly enhanced the adsorption of DBP and DEP.The agglomerated particles were confirmed to be Mn O₂ by XPS,and the characteristic peak of Mn was detected on the surface of Mn-BC,which also indicated the presence of Mn in the form of Mn-O chemical bond.（3）Single-factor experiments were used to explore the optimal adsorption conditions.The initial concentration of DBP and DEP was 10 mg/L.The results showed that the adsorption of DBP and DEP was better at lower p H;the optimal dosage of DBP and DEP was 2 g/L and 4g/L,respectively;in the range of experimental temperature（288～308 K）,the higher the temperature,the better the adsorption effect.The results of adsorption experiments showed that the adsorption process of Mn-BC on DBP and DEP could be better described by using quasi-secondary kinetic model.The maximum adsorption capacities of Mn-BC on DBP and DEP were 4.61 mg/g and 1.96 mg/g,the adsorption was monolayer adsorption and chemisorption was dominant.The thermodynamic results showed that the adsorption of Mn-BC on DBP and DEP belonged to the heat absorption process could be carried out spontaneously,and the higher temperature was favorable for the adsorption.（4）Soil column leaching experiment was conducted to investigate the effect of biochar on DBP fixation in soil,and the addition of biochar could enhance the fixation of DBP in soil,and the amount of fixation by Mn-BC was better than that by BC.The fixation amount of Mn-BC at 3%was 9.10 mg/kg,which was 73%higher than that of blank.