Preparation Of Modified Biochar And Its Adsorption Of BPA In Aqueous Solution

Biochar is a cheap and efficient green environmental adsorbent,containing a lot of carbon elements,complex active function groups and abundant pore structures.It can efficiently remove pollutants such as ammonia nitrogen,phosphates,heavy metal ions,organic and inorganic pollutants in wastewater.In this study,Phragmites and Typha as raw materials were used to make biochar with slow pyrolysis at different carbonization temperatures（400℃,500℃）,different carbonization time（3 h,4 h,5 h,6 h）.The above biochars were treated by potassium carbonate modification,potassium phosphate modification,hydrogen peroxide modification,two-stage activation method,and then which was applied to treat BPA wastewater.Meanwhile the effect of carbonization time,carbonization temperature on the yield of biochar,the effect of different modification methods and modifier concentrations on modified biochar adsorption performance and structure were investigated.The constructs adsorption kinetic models and adsorption isotherm models were also studied to explore adsorption mechanisms of biochar.The results showed that:（1）The yield of biochar decreased with the increase of carbonization temperature and carbonization time.Phragmites and Typha biochar produced at 400℃and 3 h had the highest yields of 35.07%and 37.46%,respectively.However,the yield of Phragmites was less affected by carbonization temperature and time,which was25.54%to 35.07%stably.（2）BPA removal performance of modified Phragmites biochar made at 500℃carbonization 5 h with potassium carbonate modifier and biochar raw material quality ratio of 2:1 was best,with removal efficiency of 97.07%and adsorption capacity of1.593 mg·g^-1 on the condition of BPA initial concentration of 1.2 mg·L^-1,modified biochar dosage of 10 mg and contact time of 1440 min.BPA removal performance of modified Typha biochar made at 500℃carbonization 5 h with hydrogen peroxide modifier and biochar raw material quality ratio of 1:2 was second,with removal efficiency of 75.44%and adsorption capacity of 0.905 mg·g^-1 on the condition of BPA initial concentration of 0.8 mg·L^-1,modified biochar dosage of 10 mg and contact time of 1440 min.（3）The adsorption process of potassium carbonate modified Phragmites biochar made at 500°C carbonization for 5 h and the ratio of modifier to raw material of 2:1better fitted with quasi-second-order kinetic equation.However,the isothermal adsorption accorded with the Langmuir model,which was a single-layer adsorption mainly.The adsorption process of modified Typha biochar made at 500℃carbonization 5 h with hydrogen peroxide modifier and biochar raw material quality ratio of 1:2 fitted with quasi-first-order kinetic equations.The isothermal adsorption accorded with the Langmuir model,which was single-molecular layer adsorption.（4）The results of scanning electron microscope showed that the microporous pore structure of biochar was significantly increased by potassium carbonate modifier treatment,which provided a lot of adsorption sites for BPA and then promoted its adsorption effect.