Novel template synthesis and characterization of chitosan–silica composite: evaluation of sorption characteristics of cadmium(Ⅱ) and lead(Ⅱ) by mesoporous chitosan–silica composite

摘要

Template synthesis was carried out to obtain mesoporous chitosan-silica (M-CS) composite employing natural chitosan and trimethoxy(octyl) silane (TMOS) as precursor materials. Initially, TMOS was grafted with chitosan polymer to obtain a composite material and then annealed at 500 degrees C to obtain the M-CS. The Brunauer, Emmett and Teller specific surface area and pore size of the M-CS solid were found to be 371.77 m(2)/g and 3.62 nm, respectively. Energy dispersive X-ray spectroscopy analytical data confirmed the presence of silica and the X-ray diffraction analysis indicated the amorphous nature of the solid. Moreover, the Fourier-transform infrared analysis indicated the presence of Si-O-Si condensed phase network. The M-CS composite was intended to utilize in the remediation of aquatic environment contaminated with potential water pollutant cadmium(II) and lead(II) under the batch and column reactor operations. The concentration dependence data were fitted well to the Langmuir adsorption model and the Langmuir monolayer sorption capacities were found to be 5.208 and 4.587 mg/g, respectively, for the cadmium(II) and lead(II). M-CS composite was found efficient adsorbing material for the removal of cadmium(II) and lead(II) since an apparent equilibrium between solid/solution interface was achieved within 120 and 60 min, respectively. Moreover, the kinetic data are fitted well to the pseudo-second-order and fractal-like-pseudo-second-order kinetic models. The 1,000 times increase in background electrolyte concentrations (NaNO3) did not affect significantly the percentage removal of cadmium(II) by the M-CS indicated that the toxic ions are forming an inner-sphere complexes with relatively stronger chemical forces onto the solid surface. A high breakthrough volume was obtained in the fixed bed column study and the breakthrough data were fitted well to the non-linear Thomas equation. The estimated loading capacity for cadmium(II) in a column packed with M-CS composite was found to be 11.65 mg/g.