Adsorption Of SMZ And BPA From Water By Chitosan Hydrogel

In recent years,the frequent detection of emerging contaminants?ECs?in water bodies and their potential hazards have already threatened the ecological environment and human health.ECs in the water have low concentration and are rich in variety,complex in physical and chemical properties.The adsorption method,which is easily operated,low cost,no by-products and can be recycled,was proved to be efficient for the removal of ECs.A good adsorbent is supposed to adsorb ECs with different properties.The adsorption efficiency depends mainly on the adsorption force between adsorbents and adsorbates,and the design of the adsorbent should also be based on this.The disadvantage of conventional adsorbent materials is that the process of grafting functional groups is complicated,difficult to control,or energy intensive.However,the preparation conditions of the hydrogel are mild and easy to control,which can effectively solve the problem.Chitosan?CS?is an environmentally friendly material that is low-cost and widely available.In addition,chitosan is rich in hydroxyl and amino groups,and it has good adsorption potential for ECs through functional design.Two typical ECs,sulfamethoxazole?SMZ?and bisphenol A?BPA?,were selected as representative of hydrophilic and hydrophobic ECs in order to design high efficient adsorbents to simultaneously adsorb different types of ECs.To this end,two chitosan-based hydrogel adsorbents were designed,synthesized and characterized.The separate adsorption and simultaneous adsorption performance of SMZ and BPA on each adsorbent,as well as the adsorption capacity in simulating actual water bodies were explored.Finally,the adsorbents were desorbed and regenerated to evaluate their practical application.The main results are as follows:?1?A magnetic PNIPAM/CS@Fe₃O₄ interpenetrating network hydrogel was prepared using N-isopropyl acrylamide?NIPAM?and CS as functional materials.The adsorption amount of SMZ and BPA both reached the maximum at equilibrium pH=6.However,the effects of pH on the adsoption of SMZ and BPA were different.It was speculated that the adsorption forces were electrostatic attraction and hydrogen bond for SMZ,hydrophobic forces and hydrogen bonds for BPA based on the effects of pH,temperature and coexisting anions.The adsorption kinetics showed that the adsorption amount reached 90%within 5min,and the data fitted better to pseudo-second-order model.For adsorption isotherm,the Freundlich model fitted well for SMZ at 25,35 and 45?,indicating that multiple-layer adsorption on the heterogeneous surface occurred.However,the adsorption of BPA exhibited the sigmoidally shaped isotherm at 25?with the Slips model fitting well,and both the Freundlich isotherm and the Slips isotherm fitted the data well at 35?and 45?,suggesting that the adsorption force was initially weak but enhanced with an increase in adsorbate concentration or ambient temperature.?2?When the PNIPAM/CS@Fe₃O₄ interpenetrating network hydrogel was applied to the simultaneous adsorption of SMZ and BPA,the adsorption properties were same as that of the separate adsorption,which indicated that the adsorption forces of SMZ and BPA would not interfere with each other.When the hydrogel was applied for the adsorption of simulating actual polluted water,various coexisting substances inhibited the adsorption fo SMZ,but had no effect on the adsorption of BPA.The adsorbent was regenerated with methanol,and the adsorption capacities of SMZ and BPA were 55%and 94%of the initial one after 5 adsorption desorption cycles,separately.?3?The PAC/CS/PVA hydrogel was synthesized by using powdered activated carbon?PAC?and CS as functional materials and adding polyvinyl alcohol?PVA?to enhance mechanical properties.The adsorption amount of SMZ and BPA reached the maximum at initial pH=4,and the adsorption forces were assumed to be electrostatic attraction,hydrogen bonding and?-?interaction for SMZ,as well as hydrophobic interaction,?-?interaction and hydrogen bonding for BPA according to the effects of pH,temperature and coexisting anions.The pseudo-second-order model fitted better to the adsorption kinetics.The adsorption isotherms were more consistent with the Langmuir model,which indicated that the adsorptive process was monolayer adsorption.Adsorption thermodynamics indicate that adsorption was a spontaneous,endothermic process.?4?When the PAC/CS/PVA hydrogel was applied to the simultaneous adsorption of SMZ and BPA,the adsorption properties were almost the same as that of the separate adsorption.This indicated that the adsorbent could be used for simultaneous adsorption of hydrophilic and hydrophobic organic pollutants.When the hydrogel was applied to the adsorption of simulated actual polluted water,the effects of the separate coexisting substances on the adsorption of SMZ and BPA were different,and the mixure of them showed an inhibition effect on the adsorption.The adsorbent was regenerated with methanol,and the adsorption capacities of SMZ and BPA were 97%and 113%of the initial one after 5 adsorption-desorption cycles,separately,indicating that the reusability was good.