Studies On The Removal Potential And Mechanism Of Phragmites Australis Biomass Functional Materials For Phenolic Pollutants

Phenolic pollutants have attracted more attention in the environmental protection field due to their high environmental hazards,difficult degradation and easy bioaccumulation.The adsorption method has the advantages of low cost,simple design,convenient operation,etc.,especially in the case of sudden environmental hazards,which can treat pollutants in time.It is considered to be one of the best choices for removing phenolic pollutants.However,some adsorbents are expensive,the preparation process is complicated,and the adsorption process is determined by varieties factors,which have become the practical reasons for limiting the application of adsorption technology.Therefore,the preparation of the adsorbent and the optimization of the adsorption process are very important.Plant–derived biomass materials have huge reserves and low cost.The preparation of them into adsorbents can not only be used for pollutant treatment but also can achieve the resource utilization of waste biomass.It has great application potential in the field of water pollution control and treatment.Based on the above,this study uses Phragmites australis biomass as raw materials and to optimize the preparation of P.australis biochar(PAAC),bifunctional P.australis biochar(MnO₂–PAAC).The removal ability and mechanism of phenol,2,4–dichlorophenol,hydroquinone and bisphenol A were evaluated and analyzed.The main research results are as follows:(1)The adsorption capacity of P.australis biomass materials for four phenolic pollutants was evaluated.The results show that,the maximum monolayer adsorption capacity of phenol,2,4–dichlorophenol,hydroquinone and bisphenol A were 19.48,18.81,19.94 and 19.44 mg/g,respectively.P.australis biomass materials structure and surface morphology have been characterized.Environmental factors such as adsorbate concentration,p H,contact time,dosage and size will affect the adsorption effect.Pseudo–second order and Langmuir isotherm can fit the adsorption process well of phenol,2,4–dichlorophenol,hydroquinone and bisphenol A on the surface of P.australis biomass materials.The adsorption process is controled by physical adsorption,and the adsorption mechanism is the key factor of the adsorption process.(2)In order to improve the adsorption capacity and efficiency of P.australis biomass materials,the response surface method(RSM)was used to optimize the process of preparing P.australis biochar(PAAC)by microwave radiation.The best conditions for preparing PAAC were obtained:Microwave radiation power is 617 W,Microwave radiation time is 17.34 min,and Liquid–to–Material ratio is 3:1.Meanwhile,the PAAC iodine adsorption value is 667.68 mg/g,the methylene blue adsorption value is 128 mg/g,and the yield is 36.30%.The characterization results show that the surface of PAAC has a network structure formed by a large number of uneven and abundant pores intertwined with each other.The formation of bulk and surface structural features dominated by carbonyl groups,carboxyl groups,other acidic oxygen–containing functional groups and nitrogen–containing functional groups.These features will be beneficial to improve the physical adsorption capacity of PAAC.(3)The adsorption capacity of PAAC to four phenolic pollutants was evaluated.The results show that,the maximum monolayer adsorption capacity of phenol,2,4–dichlorophenol,hydroquinone and bisphenol A on PAAC were 79.37,144.93,158.73 and 204.08 mg/g,respectively.Different environmental factors such as contact time,initial concentration,dosage,environment temperature and p H will affect the adsorption capacities of the four phenolic pollutants by affecting the driving force of the solute,the contact area,the thermodynamic process and the state of the solute in the solution.The established kinetic models and mass transfer model simulation found that the adsorption process on PAAC is from the bulk solution transferred to the outer surface of the adsorbent through the liquid membrane.And then,it diffuses into the pores of the adsorbent through the process of surface diffusion and pore volume diffusion.Finally,the adsorption is completed on the inner surface of the pore.Among them,the surface diffusion plays a major role in the intra–particle diffusion.Freundlich isotherm indicates that the adsorption of PAAC surface is a multi–molecular adsorption process.The adsorption of PAAC may be contributed by pore filling,?–?interactions,electrostatic interactions,hydrophobic interactions,H–bond and ion exchange interactions.(4)Bifunctional P.australis biochar material MnO₂–PAAC was successfully prepared by co–precipitation method.In the MnO₂–PAAC and permonosulfate(PMS)system,the removal of phenol,2,4–dichlorophenol,hydroquinone and bisphenol A can reach equilibrium in a short time.Compared with PAAC,the MnO₂–PAAC removal efficiency of the four phenolic pollutants is greatly improved(the removal rates of phenol,2,4–dichlorophenol and bisphenol A are 7,6.69,and 15.08 times that of PAAC,hydroquinone are completely removed within 3 min).The product toxicity is significantly reduced after degradation.Different environmental factors(dosing,environmental temperature and p H)will affect the removal efficiency in MnO₂–PAAC and PMS system.In the MnO₂–PAAC and PMS system,the removal mechanism of phenolic pollutants is determined by adsorption and oxidation.Among them,high–valence Mn ions and the generated SO₄^·–and·OH by the reaction of PMS to participate in the oxidation reaction process of phenolic pollutants.In summary,plant–derived P.australis biomass,PAAC and MnO₂–PAAC can effectively remove four typical phenolic pollutants in water,while realizing the resource utilization of waste P.australis biomass.The research provides a reference for promoting the application of waste biomass materials in water pollution control.