Adsorption of arsenic(V) from aqueous solutions by goethite/silica nanocomposite

Silica nanoparticles were synthesized and coated with goethite, creating a nanocomposite. The nanocomposite was tested for removal of arsenic, As(V), from aqueous solutions. We used scanning electron microscopy (SEM), Fourier transform infrared spectrometry, and a Zetasizer to characterize particle size, surface morphology, functional groups, and surface charge of the nanocomposite. SEM results showed that the size of the synthesized silica nanoparticles ranged from 150 to 250 nm. Batch sorption studies were carried out on the adsorption of As(V) as a function of pH, contact time, initial concentration, and ionic strength. Maximum adsorption occurred at pH 3.0. The adsorption capacity did not change significantly with increasing ionic strength. A kinetics study revealed that adsorption of As(V) by the goethite/silica nanocomposite was rapid: Equilibrium was reached within 120 min. Adsorption kinetics followed a pseudo-second-order kinetic model. The adsorption data were analyzed by both the Langmuir and Freundlich isotherm models. The maximum adsorption capacity of goethite/silica nanocomposite for As(V) from the Langmuir isotherm was 17.64 mg g−1, which is larger than that of several other adsorbents. The nanocomposite adsorbent showed high efficiency in removing arsenic from aqueous solutions, even at low initial concentrations.