Adsorption of Pb(II) from water by treatment with an O-hydroxyphenyl thiourea-modified chitosan

An O-hydroxyphenyl thiourea-modified chitosan (OTCS) with excellent Pb(II) adsorption performance and selectivity was prepared as an adsorbent. The structure and morphology of the adsorbent were systematically investigated by SEM, BET, FTIR, EDX, zeta-potential measurements, XPS and XRD. The impacts of the initial Pb(II) concentration, reaction time, temperature, pH value, and coexisting ions were explored. At pH 7 and 303 K, the maximal adsorption capacity of OTCS for Pb(II) was 208.33 mg/g, which was greater than those of other adsorbing materials reported in the literature. The metal ion adsorption kinetics and isotherm models were found to obey pseudo-second-order kinetics and the Langmuir isothermal model, indicating that the adsorption process was monolayer chemisorption. The adsorption process could proceed spontaneously, and the thermodynamic results revealed that the adsorption mechanism was an endothermic reaction. The ion exchange and chelation between the sulfur, nitrogen and oxygen groups on the adsorbent and lead ions endowed the material with excellent adsorption properties. Significantly, OTCS showed excellent selectivity toward Pb(II). Therefore, the adsorbent OTCS is expected to promote the wider application of chitosan in the adsorption of Pb(II).