Synthesis of konjac glucomannan phthalate as a new biosorbent for copper ion removal

Konjac glucomannan (KGM) was esterified with phthalic anhydride catalyzed using pyridine, resulting in a biomass-based copolymer (PKGM), a solid biosorbent which was used for copper ion removal in aqueous. The esterification degree of substitution (DS) for KGM is a key parameter for performance of PKGM in copper ion adsorption. The DS, number average molecular weight (Mn), molecular weight distribution (D) and radium of gyration (Rg) are able to be manipulated in pretreatment of KGM and preparation reaction such as by changing swelling time, varying catalyst dosage or temperature. The effect of DS on Cu²⁺ ion adsorption efficacy (E%) was investigated and found significantly relevant to DS, pH and absorbent dosage. Langmuir isotherm model and a pseudo-second-order rate model, respectively, were applied to understanding in Cu(II) ion adsorption mechanism on PKGM and the data fitting indicated that Cu(II) ion adsorption onto PKGMs is due to chemisorption where the kinetic investigation showed that the adsorption equilibrium was established sufficiently in 120 min. Most important, at slightly acidic the maximum sorption capacity is 16.99 mg/g which is higher than those of many natural sorbents such as grape stalks wastes (11.50 mg/g dry sorbent). At pH ≥ 10 one of the PKGMs enables more than 99 % copper ion removal at its initial concentration of 100 mgL. Hence, as a biosorbent, the PKGM has shown promising potential for removal of heavy metals in the aqueous.