Desorption and regeneration of metal oxide nanoparticles for aquatic metal removal
The adsorption-desorption of toxic compounds onto engineered nanoparticles is an important process that governs their potential as sorbents for treatment applications. In order for sorption to be cost-effective and sustainable, engineered nanoparticles need to be able to be regenerated. This study investigated the desorption of Pb (II), Cu (II), Zn (II) and Cd (II) from commercially prepared nano-Fe2O3 (hematite) and nano-TiO2 (anatase), along with the regeneration of nano-TiO2. Experiments were conducted using batch techniques. Desorption was evaluated for isothermal, kinetic and thermodynamic properties. Regeneration was conducted by determining the best solution for regeneration, evaluating the effects of consecutive regeneration cycles and coexisting metals, and testing the ability to treat synthetic metal polluted water.
Adsorption studies showed that adsorption capacities of both nanoparticles had a trend of Pb > Zn > Cd > Cu, while nano-TiO2 had larger adsorption capacities than nano-Fe2O3. Desorption of metals from both nanoparticles was pH dependent and fast; more than 98% of metals desorbed from nano-TiO2 at pH 2. Metals desorption from nano-TiO2 was exothermic and non-spontaneous. Pb desorption was due to inner-sphere surface complexation while Cu and Zn showed physical interaction. pH 2 and EDTA solutions were determined to be the most effective method for regenerating nano-TiO2. Nano-TiO2 was able to treat simulated metal polluted water with greater than 94% adsorption and greater than 92% desorption after 4 cycles of regeneration. This study improved the capabilities of researchers to develop practical methods for the application of nanoparticles as sorbents with simple and low-cost regeneration technologies.