Preparation Of Porous Hydrogel Containing Thiol And Carboxyl Groups And Their Adsorption For Copper,Lead And Cadmium

Heavy metal pollution in water and soil has always been a very serious problem.Heavy metals have attracted extensive attention because of their great harm and transmission through the food chain.The treatment of heavy metal pollution has become a key problem.Adsorption is considered to be an ideal method for the treatment of heavy metals because of wide source of adsorbents,simple operation,no secondary pollution and most of them can be recycled.Polyacrylamide(PAM)is often used to synthesize polymer materials due to its strong mechanics and low cost.However,owing to its single functional group,its adsorption effect on heavy metals is general.Acrylic acid(AA)and 2,4-dimercapto-6-mercaptopropyl-1,3,5-triazine monomer(DMTM)contain many active sites such as carboxyl and thiol groups.If they are used to treat heavy metals,the effect will be very good.Therefore,acrylamide(AM),acrylic acid and 2,4-dimercapto-6-mercaptopropenyl-1,3,5-triazine monomers were selected to polymerize to prepare a new porous hydrogel adsorbent containing carboxyl and thiol groups.In this study,a new porous hydrogel adsorbent containing thiol and carboxyl groups,namely polyacrylamide/polyacrylic acid/poly(2,4-dimercapto-6-mercaptopropenyl-1,3,5-triazine monomer)hydrogel adsorbent(PAM/PAA/PDMTM gel),was prepared and used to remove heavy metals from water and soil.Through a series of characterization techniques,it is found that PAM/PAA/PDMTM gel has macroporous structure,high swelling,good thermal stability and rich active functional groups.By studying the adsorption properties of PAM/PAA/PDMTM gel in the solution under different conditions,it was found that when the initial pH value of the solution was 5,the removal effect of gel on Cu2+and Pb2+was the best.Nevertheless,the removal rate of Cd2+was the highest at pH=6.In addition,it is also found that the material has good selectivity for Cu2+and Pb2+.Under the condition of the coexistence of sodium,potassium,calcium and magnesium ions,the adsorption of Pb2+by the material is hardly affected,and the adsorption of Cu2+and Cd2+will be affected.It is greatly affected by Ca2+and Mg2+and less affected by K+and Na+.When the pH value was 5.0 and the temperature was 298 K,the maximum adsorption capacities of PAM/PAA/PDMTM gel for Cu2+,Cd2+and Pb2+were 92.33,110.08 and 200.97 mg/g,respectively.By fitting the experimental data,it is found that the pseudo second-order kinetic and Langmuir isothermal model have good adaptability to adsorption.At the same time,PAM/PAA/PDMTM gel shows excellent regeneration ability and the removal efficiencies of Cu2+,Cd2+and Pb2+are still above 85%after five cycles.Mechanism analysis reveals that coordination is the key adsorption mechanism of the material.It is worth noting that the application test of adsorbent also shows that the adsorbent has a good adsorption effect on Pb in soil.The results show that the PAM/PAA/PDMTM gel has great potential in removing heavy metals from actual water and soil.