Synthesis of phenyl maleic anhydride polymers and the adsorption of Pb2+: effects of crosslinking agents, equilibrium, kinetics, and adsorption mechanism studies

As a new class of porous materials, hyper-crosslinked polymers can adsorb heavy metal ions from aqueous solutions. This requires them to possess good surface hydrophilicity and active functional groups that can interact with heavy metals. In this research, three polymers, namely MAH-1, MAH-2, and MAH-3, were synthesized via the Friedel-Crafts alkylation reaction using phenyl maleic anhydride (MAH) as the monomer and dimethoxymethane (FDA), 1,4-p-dichloro-benzyl (DCX), and biphenyl dichlorobenzyl (BCMBP) as cross-linkers, respectively. The effect of the molecular size of the cross-linkers on polymer yields, morphology, and Pb2+ adsorption property was investigated. The yield of MAH-1 was low, and the product was soluble in methanol. This implied that when the cross-linker molecule was short, the steric hindrance caused by the substituents on the monomer benzene ring impeded polymer formation. MAH-2 formed nanoparticles that extended into thin sheets, while MAH-3 only formed nanoparticles, exhibiting clearly different morphologies. After alkalization, the maximum Pb2+ adsorption capacities of the two polymers, determined by the Langmuir adsorption isotherm, were 216 mg g(-1) and 134 mg g(-1), respectively. Both polymers were applied to treat Pb2+ in simulated battery wastewater with a concentration of 32 mg L-1, and both reduced the concentration to below 0.55 mg L-1, meeting the requirements of the Lead and Zinc Industrial Pollutant Discharge Standard GB 25466-2010 (National Standards of the People's Republic of China). Additionally, the materials demonstrated good reusability and showed potential for treating lead-contaminated water. [GRAPHICS]