Effect of light-active nanomaterials on the behavior of cadmium(II) in the presence of humic acid: the case of titanium dioxide

Abstract

The influence of photoactive nano-TiO2 on metal behavior in the presence of humic acid (HA) in aqueous system was investigated. Our study showed that the attachment of HA onto nano-TiO2 enhanced the adsorption ability for Cd(II). The functional groups of HA could then coordinate with Cd(II), thus enhanced Cd(II) adsorption. We found that Cd(II) adsorption by HA-TiO2 followed pseudo-second-order kinetics. The FTIR spectra confirmed that Cd(II) adsorption was mainly ascribed to the presence of hydroxyl groups and polysaccharides/polysaccharide-like substances. The hydrogen-binding mechanism therefore accounted for the observations relating to the combination of HA and nano-TiO2 in our study. Solar light irradiation was found to weaken Cd(II) adsorption because of the photoactive properties of titania. The photoactive TiO2 in the aqueous system induced the degradation of the adsorbed HA, thus decreased the functional groups for the complexation of Cd(II). The results illustrated that the presence of photoactive nanomaterials (such as TiO2) would change the bioavailability of heavy metals in aquatic environments under solar irradiation.