Efficent removal of nickel(II) salts from aqueous solution using carboxymethylchitosan-coated silica particles as adsorbent

Three types of organo-mineral composites have been probed as adsorbents for the removal of Ni(II) ions from aqueous solution. Native Aerosil 200 silica particles have been encapsulated with carboxymethylchitosan (CM-CS) providing SiO2 + CM − CS, surface-silanized silica particles SiO2NH2 + CM − CS were obtained by treatment with APTES and subsequent encapsulation by CM-CS. Alternatively, surface-carboxylated Aerosil 200 was coated by CM-CS affording SiO2CO2H + CM − CS. The materials have been characterized by various techniques. The effects of counter ions (Cl−, Br−, CH3COO−, NO3− and SO42−), pH and initial Ni(II) concentration on the adsorption capacities have been systematically investigated. The maximum adsorption capacity qm of CM-CS-coated silica was determined using the Langmuir adsorption isotherm. For SiO2CO2H + CM − CS, SiO2 + CM − CS and SiO2NH2 + CM − CS, they decrease at pH 7 in the order 256 mg/g > 140 mg/g > 105 mg/g. The adsorption kinetic fits well with a pseudo-second order model. These carbohydrate-derived biosorbents are excellent adsorbents with capacities superior to most other adsorbents reported in the literature.