Investigation On Removal Of Antibiotics And Dyes Onto Polydopamine Microspheres From Aqueous Solution

With the rapid growth of population and the acceleration of urbanization,as well as the rapid development of industry and the modernization of agriculture,water pollution has become the primary problem that threatens life and health.Organic pollutant is especially harmful because of its complex type,difficult degradation and high biological toxicity.Micro-nano polymer materials possess large specific surface area,contain a large number of active groups,anti-acid and alkali,which has become a hotspot in recent years.It has shown a wide application prospect in the fields of catalysis industry,electronic industry,biomedicine,environmental protection and so on.Polydopamine microspheres(PDMPs)have a large surface area,a large number of active groups on the surface,and low biological toxicity.PDMPs have been adopted as a potential adsorbent for the removal of Norfloxacin(NOR),Ciprofloxacin(CIP)and Malachite Green(MG)from aqueous solution.The adsorption mechanisms have been investigated.(1)PDMPs were synthesized by a facile solution oxidation method via the self-polymerization of dopamine monomer in alkaline solution and characterized by SEM,TEM,particle size distribution,pHPZC and FTIR.The results showed that the well dispersibility PDMPs has an average diameter of 200 nm.There were a large number of reactive functional groups such as amino groups,phenolic hydroxyl groups,and imino groups on the surface of PDMPs.(2)To maximize NOR and CIP removal from liquid phase,Box–Behnken experimental design(BBD)combined with response surface modeling(RSM)was employed based on the 17 preliminary experiments.The results showed that the predicted regression equations fitted the experimental data well.For NOR,optimum contact time,initial NOR concentration and initial pH value were found to be 97 min,303 mg/L,and 6.6,respectively,the corresponding NOR removal capacity was found to be 0.964 mmol/g.For CIP,optimum contact time,initial CIP concentration and initial pH value were found to be 89 min,290 mg/L and 6.9,respectively,the corresponding CIP removal capacity was found to be 0.777 mmol/g.(3)Parameters effects such as initial solution concentration,adsorption time,solution pH,salt ion concentration,and temperature on the adsorption capacity of NOR?CIP and MG onto PDMPs were studied by a series of static tests.It was found that the adsorption amount was positively correlated with the adsorption time and concentration.Conversely,the addition of salt ions was not conducive to the adsorption process.The obtained kinetic and adsorption isothermal data points were fitted with kinetic models and adsorption isotherm models,respectively,and error analysis was performed.Kinetic analysis confirmed that the kinetic data were well described by Pseudo-second order model and the Intraparticle diffusion was not the only rate-control step for the adsorption of the three adsorbates by PDMPs.The experimental equilibrium data were well fitted by Langmuir,Redlich-Peterson and Dubinin-Radushkevich models.The calculated maximum monolayer adsorption amounts of NOR,CIP and MG onto PDMPs by Langmuir model were 0.953,0.855 and 0.743 mmol/g at 298 K,respectively.The calculated activation energies of three adsorption processes by Dubinin-Radushkevich model were less than 8 kJ/mol,indicated that the adsorption processes are mainly physical adsorption.Thermodynamic parameters such as Gibbs free energy,enthalpy and entropy were calculated,the results indicated that the NOR,CIP and MG adsorption onto PDMPs were spontaneous and endothermic.(4)Combine the results of the infrared analysis the effects of pH values on the adsorption capacity,the adsorption mechanisms of NOR and CIP onto PDMPs were assumed to be electrostatic interaction,hydrogen bonding and ?-? stacking,and the adsorption process may be attributed to the electrostatic interaction and ?-? stacking interactions among the PDMPs and MG.