Synthesis Of Crop Biomass-based Hydrogels And Their Adsorption Properties For Heavy Metal Ions

In contemporary society,resources and environmental problems have become increasingly prominent.Energy crisis,resource depletion and environmental pollution have been the focus of the whole world.Because biomass resources are renewable and rich,their development and utilization are beneficial for solving the problem of resource shortages.Waste agricultural biomass resources such as plant stalks,waste nameko mushroom substrate,soybean dregs and maize bran etc.,are rich in production.At present,the low utilization,handling trouble and high cost,improper handling cause pollution of the environment and waste of resources.So the efficient utilization of such biomass has become the urgent need to study the subject.Hydrogel is a functional polymer material with a three-dimensional network structure,which has soft structure,good hydrophilic,liquid permeability,biocompatibility,optical transparency and mechanical strength,and it can maintain a certain degree of flexibility Shape.The hydrogel can be used in the fields of industry,agriculture,health,biomedical and drug delivery.The main components of these waste agricultural biomasses are cellulose or starch.Cellulose and starch,as two important renewable resources,contain rich hydroxyl.They are considered as the ideal raw materials in the preparation of polymers.In this work,the composite hydrogels were synthesized using waste agricultural biomass waste nameko mushroom substrate,soybean dregs and maize bran via UV radiation.The prepared hydrogels were characterized by elemental analysis,FTIR,SEM,EDS,TG/DTG,XRD and XPS.The water absorption and water retention capacity of the composite hydrogels were studied.Besides,the adsorption of Pb(?),Cd(?),Zn(?),Fe(?),Cu(?)and Cr(?)ions in liquid solution were discussed.The specific contents are as follows:1.In this part,maize bran(MB)and acrylic acid were used to synthesize a novel salt sensitive hydrogel MB–PAA via UV radiation,with benzoic dicarboxylate and ammonium persulfate as initiator,N,N'-methylenebisacrylamide as crosslinking agent.Effects of synthesis conditions such as neutralization degree of acrylic acid,the amount of crosslinking agent,initiator and MB and reaction time on the water absorption of MB–PAA were investigated.The optimum synthesis conditions were determined.The structure and properties of the hydrogels synthesized under the optimum conditions were characterized by elemental analysis,FTIR,TG/DTG,SEM and XRD.Effects of the particle size,the concentration of the salt solution,the cation and the anion on the water absorption were discussed.The swelling kinetics and diffusion mechanism of the water absorption process were analyzed.The adsorption of Pb(?)and Cd(?)ions on MB–PAA from liquid solution were studied.The effects of adsorption time,ion initial concentration,p H value and temperature on the adsorption of Pb(?)and Cd(?)ions were studied.The synthesis mechanism of the hydrogels and the metal ions adsorption mechanism were discussed.2.A low-cost,environment-friendly composite hydrogel WNMS–PAA was synthesized by chemical modification of waste nameko mushroom substrate(WNMS)using acrylic acid.The water absorption properties of the composite hydrogels,the water retention capacity under high temperature and high pressure were measured.The adsorption properties of Pb(?)and Cd(?)ions on WNMS–PAA from liquid solutions were also measured.The effects of adsorption time,Pb(?)and Cd(?)ion concentration,p H value and temperature on of Pb(?)and Cd(?)adsorption were studied.The kinetic and thermodynamic analysises of WNMS–PAA adsorbed metal ions were discussed.The results showed that the metal ions adsorption process was an exothermic process,following the pseudo-second-order swelling kinetic model.The XPS and EDS analysis showed that the Pb(?)and Cd(?)ions were successfully adsorbed by WNMS–PAA.The removal of metal ions by the hydrogels was mainly due to the ion exchange and chelation of metal ions and polymers.3.A novel composite hydrogel(SESD–PAA)was synthesized using UV irradiation method using waste biomass soybean dregs(SESD),in the presence of AA as monomer,BDK and APS as initiator,N,N'-methylene bisacrylamide as cross linker agent.The SESD–PAA hydrogel was characterized by FTIR,TG/DTG,SEM and XRD.It was proved that SESD was successfully involved in the polymerization reaction,and the synthesis mechanism of SESD–PAA was analyzed.It was proved that the synthesis was typical radical polymerization reaction.The adsorption properties of Zn(?),Fe(?),Cu(?)and Cr(?)ions SESD–PAA from liquid solution were studied.The effects of adsorption time,metal ion concentration,p H value and temperature on metal ions adsorption were discussed.The competitive adsorption was also studied,competitive adsorption order of SESD–PAA to metal ions is Fe(?)> Cu(?)> Cr(?)> Zn(?).It was proved that the metal ions were successfully adsorbed on SESD–PAA by XPS and EDS analysis.The metal ions adsorption mechanism of hydrogels was studied.The adsorption was mainly chemical adsorption,exactly,ion exchange and coordination between the carboxylate,hydroxyl and amine in the polymer network structure and metal ions in the solution.The kinetic and thermodynamic analysis of the metal ions adsorption by SESD–PAA was also discussed.The results proved that the process was consistent with pseudo-second-order kinetics and Freundlich adsorption isotherm model.Intra-particle diffusion mechanism analysis showed that the removal of metal ions by the polymer mainly included two stages: surface adsorption and diffusion of metal ions into the network.In addition,the desorption properties and repeated metal ions adsorption properties of SESD–PAA were also studied.Compared with the existing adsorbents reported,SESD–PAA has a faster adsorption rate and higher adsorption of metal ions.4.An inorganic-organic composite hydrogel Na-Bentonite/MB–PAA with strong water absorption was synthesized by UV irradiation.The chemical modification of MB was completed by using acrylic acid / sodium acrylate and Na-Bentonite.The adsorption properties of the hydrogels,water retention capacity and Cd(?)and Pb(?)ions adsorption from liquid solution were studied.The effects of p H value,the adsorption temperature,the initial concentration of the metal ions and the adsorption time on Cd(?)and Pb(?)ions adsorption were discussed.After the chemical modification,the hydrogel has a higher adsorption capacity and a faster adsorption rate for the metal ions.The kinetic analysis showed that the metal ions adsorption process was in accordance with the pseudo-second-order kinetics model.In addition,the adsorption mechanism of metal ions on Na-Bentonite/MB–PAA was also discussed by XPS analysis.