Removal of Cd by humic acid modified TiO2 nanoparticles from aqueous solution

In this study, removal of Cd from aqueous media by the adsorption of TiO2 nanoparticles (TNPs), with surface modification by humic acid (HA) was assessed. Results showed a linear increase of the coating percentage from 100-HA to 250-HA but no significant difference between the HA coated TNPs prepared at 250 and 350 mg L-1 due to an extremely narrow band gap. The obtained materials (HA-TNPs) were characterized by Fourier transform infrared spectroscopy and UV-visible spectrophotometer. Then, batch adsorption techniques were carried out to examine the possible adsorption mechanisms of Cd onto TNPs and HA-TNPs. It was noted that the adsorption capacity of the HATNPs for Cd enhanced considerably as compared to that of the bare TNPs, implying that HA coating might modify bioavailability of Cd in aquatic environment. Equilibrium data were best described by the Freundlich equation, and the partition distribution coefficient (k) of HA-TNPs increased by 34%, 50% and 59% for Cd at 298, 315 and 332 K respectively, as compared to the bare TNPs, suggesting that HA-TNPs had a stronger affinity of sites for Cd adsorption than that of bare TNPs.