Effect Of Hydrothermal Carbon On Adsorption And Retention Of Bisphenol A In Soil From Sycamore Leaf Litter

The endocrine disrupting compound bisphenol A（BPA）is widely used in modern society as a plasticizer,resulting in surface water,soil and groundwater pollution.Carbon rich adsorbents synthesized by hydrothermal carbonization（HTC）are attracting people’s research interest due to their environmental protection,economy and huge potential application value.Therefore,in order to effectively remove BPA from water environment and prevent and reduce its pollution to soil and groundwater,a high specific surface area carbon-rich adsorbent（PWAC4）was prepared by using phosphoric acid（H₃PO₄）assisted hydrothermal carbonization combined with short-term activation of sycamora leaf as raw material to remove BPA from sewage,and its adsorption mechanism was discussed.The adsorption capacity of BPA in yellow brown soil of Wuhan,Hubei Province before and after adding PWAC4 was investigated by static adsorption and soil column leaching experiments.Its main conclusions were as follows:（1）Hydrothermal carbon was prepared by three methods:hydrothermal pretreatment of deionized water-high temperature short-term activation（WC）,hydrothermal pretreatment of phosphoric acid solution（PWC）and hydrothermal pretreatment of phosphoric acid solution-high temperature short-term activation（PWAC）.PWAC had the best adsorption effect on BPA,and the optimal concentration of activator phosphoric acid was 4 mol/L（PWAC4）.PWAC4 has spherical surface structure,and its high specific surface area（994.21 m²/g）,micropore volume（0.307 cm³/g）and suitable pore size（1.91nm）promote the adsorption of BPA.（2）The adsorption capacity of PWAC4 was 237.92 mg/g in accordance with the quasi-second-order kinetic model and Sips isothermal model.The adsorption process was a spontaneous endothermic process with stable adsorption capacity over a wide range of p H（3-10）and temperature（15-35℃）.The presence of metal cations and humic acids had little effect on its adsorption capacity.After four consecutive adsorption-desorption,the adsorption capacity of BPA could still reach 81.24%of the initial adsorption capacity.Multiple physical and chemical mechanisms played an important role in PWAC4adsorption,among which pore filling,hydrogen bonding,π-πbonding and electrostatic interaction were the main ones.（3）The adsorption capacity of natural soil for BPA was weak.When the initial concentration was 50 mg/L,the saturated adsorption capacity was 0.23 mg/g.When 0.5%（mass fraction）of PWAC4 was added,the saturated adsorption capacity was 0.798 mg/g,which increased by 246%.The adsorption of BPA by soil and carbon soil mixture conforms to the quasi-second-order kinetic model.PWAC4 dominated the adsorption behavior of BPA in carbon soil mixture.With the increase of pH value,the adsorption capacity of BPA in soil decreased,but after PWAC4 was added,the adsorption capacity of BPA in carbon soil mixture was less affected by p H,temperature,oxalic acid concentration and humic acid.（4）The addition of PWAC4 significantly enhanced the retention capacity of BPA in leached sewage.When the content of PWAC4 was 0.5%and 1.0%,respectively,the retention capacity of BPA in the soil column was 5.1 and 9.3 times that without the addition of hydrothermal carbon.And the presence of humic acid and oxalic acid in the soil column had little effect on the retention capacity of BPA.Therefore,doping PWAC4in surface and shallow soil can reduce the possibility of contamination of deep soil and groundwater.