A sorbent containing pH-responsive chelating residues of aspartic and maleic acids for mitigation of toxic metal ions, cationic, and anionic dyes

t-Butyl hydroperoxide-initiated cycloterpolymerization of diallylaminoaspartic acid hydrochloride [(CH2=CHCH2)(2)NH+CH(CO2H)CH2CO2H Cl-] (I), maleic acid (HO2CH=CHCO2H) (II) and cross-linker tetraallylhexane-1,6-diamine dihydrochloride [(CH2=CHCH2)(2)NH+(CH2)(6)NH+ (CH2CH=CH2)(2) 2Cl(-)] (III) afforded a new pH-responsive resin (IV), loaded with four CO2H and a chelating motif of NH+center dot center dot center dot CO2- in each repeating unit. The removal of cationic methylene blue (MB) (3000 ppm) at pH 7.25 and Pb(II) (200 ppm) at pH 6 by IV at 298, 313, and 328 K followed second-order kinetics with E-a of 33.4 and 40.7 kJ mol(-1), respectively. Both MB and Pb(II) were removed fast, accounting for 97.7% removal of MB within 15 min at 313 K and 94% of Pb(II) removal within 1 min. The super-adsorbent resin gave respective q(max) values of 2609 mg g(-1) and 873 mg g(-1) for MB and Pb(II). IV was also found to trap anionic dyes; it removed 91% Eriochrome Black T (EBT) from its 50 ppm solutions at pH 2. The resin was found to be effective in reducing priority metal contaminants (like Cr, Hg, Pb) in industrial wastewater to sub-ppb levels. The synthesis of the recyclable resin can be easily scaled up from inexpensive starting materials. The resin has been found to be better than many recently reported sorbents.

Automated summary

A new pH-responsive resin was prepared by t-Butyl hydroperoxide-initiated cycloterpolymerization, which showed fast removal of both cationic and anionic contaminants and had excellent adsorption performance. The resin can be widely applied in industrial wastewater treatment.