Characteristics And Mechanism Of Sulfamethoxazole Removal From Aqueous Solution By Polypyrrole-Loaded Volcanic Rock

Pharmaceuticals and personal care products（PPCPs）are a novel kind of emerging micro-pollutants,which are easily bioaccumulated but hardly biodegradable.The high detection rate of PPCPs poses a huge threat to the health of plants,animals and human beings.Due to the advantages of simplicity,high efficiency,convenience,regeneration,etc.,adsorption is used to remove PPCPs from water as a common methods.Studies to date have shown that the adsorbent determines the adsorption efficiency.However,traditional adsorbents have many disadvantages such as low removal efficiency and secondary pollution.It is of great significance to develop an novel environmental friendly adsorbent with low cost and high efficiency.In this study,the volcanic rock was modified by conductive polymer to prepare a polypyrrole-loaded volcanic composite adsorbent.Sulfamethoxazole（SMX）was selected as a typical PPCPs pollutant,its adsorption process and mechanism were analyzed in depth as well.In this study,eight natural volcanic rocks were selected for raw materials.Polypyrrole-loaded volcanic rock composites were prepared by the method of chemical oxidative polymerization.Minitab was used to carry out the axial enhancement simple centroid design,and a mixture regression model was established,while the dosage ratio was also optimized according to SMX removal rate and economic cost.The adsorption performance of that new adsorbent on SMX（initial p H,SMX concentration,adsorption time,adsorbent dosage,coexisting ions,adsorbent regeneration,etc.）was investigated by batch experiments.In addition,the adsorption mechanism of SMX was studied by various characterizations（SEM,EDX,FTIR,XRD,XPS）combined with adsorption kinetics,thermodynamics and isothermal adsorption.The results show that natural volcanic rocks are porous and stratified,with the main mineral composition:disordered feldspar（Na,K）（Si₃Al）O₈.Under the condition of p H=2,the maximum removal rate of SMX was obtained,and the adsorption reached equilibrium in 4 h with a dosage of 20 g/L.The adsorption process conforms to the Langmuir isotherm model and pseudo second-order kinetics.By fitting,the maximum adsorption capacity was 0.33 mg/g.The mass ratio of the adsorbent precursor was natural volcanic rock:pyrrole:Fe Cl₃=0.10:0.28:0.62,which was optimized by the mixture regression model.Due to the interlaced connection of pyrrole,the surface of the composite is rough and clustered.Compared with natural volcanic rocks,the p H for removing SMX was extended to 5～11,and the adsorption equilibrium time is shortened to 3 h.Coexisting ions have an effect on the adsorption of SMX:SO₄^2->NO₃^->PO₄^3->HCO₃^-.The adsorption process conforms to the Freundlich isotherm model and pseudo second-order kinetics.The maximum adsorption capacity was obtained by fitting was 4.2 mg/g,which is 12.9 times that of natural volcanic rocks.△H⁰>0 means that the adsorption process is endothermic.The adsorption mechanism of polypyrrole-loaded volcanic rocks on SMX is mainly hydrogen bonding,electrostatic attraction and ion exchange.Besides,the material still had stable removal efficiency after being recycled for 5 times,which showed a good reusability.In summary,polypyrrole-loaded volcanic rocks has significant performance in the removal of PPCPs,thus it has good application effect and promising development.