RESEARCH ARTICLE Adsorption of Pb, Cd, Cu, Zn, and Ni to titanium dioxide nanoparticles: effect of particle size, solid concentration, and exhaustion Karen E. Engates & Heather J. Shipley Received: 5 March 2010 / Accepted: 20 July 2010 / Published online: 9 August 2010 # Springer-Verlag 2010 Abstract Purpose Adsorption of metals (Pb, Cd, Cu, Ni, Zn) to TiO 2 nanoparticles and bulk particles was examined for use as a contaminant removal substrate as a function of particle size, sorbent concentration, and exhaustion. Methods Adsorption experiments were conducted with 0.01, 0.1, and 0.5 g/L nanoparticles in a pH 8 solution and in spiked San Antonio tap water. Results When results were normalized by mass, nanoparticles adsorbed more than the bulk particles but when results were surface-area normalized, the opposite was observed. The adsorption data shows the ability of the TiO 2 nanoparticles to remove Pb, Cd, and Ni from solution with similar adsorption at 0.1 and 0.5 g/L. Adsorption kinetics for all metals tested was described by a modified first order rate equation with the nanoparticles having a faster rate of adsorption than the bulk particles. The nanoparticles were able to simultaneously removal multiple metals (Zn, Cd, Pb, Ni, Cu) from both pH 8 solution and spiked San Antonio tap water. Exhaustion experiments showed that both the nanoparticles and bulk particles were exhausted at pH 6 but at pH 8, exhaustion did not occur for the nanoparticles. Conclusion Comparison of K d , distribution coefficient, with other literature showed that the nanoparticles were better sorbents than other metal oxide nanoparticles and a commercial activated carbon. Keywords Adsorption . Titanium dioxide nanoparticles . Particle size 1 Introduction Researchers in science and engineering continue to have increased interest in the use of nanoparticles due to their unique physical and chemical properties. One area of particular interest focuses on environmental clean-up (Liu 2006; Shipley et al. 2009; Tratnyek and Johnson 2006), especially in regard to public health and drinking water quality. Electronic waste (e-waste, i.e., waste generated from cell phones, computers, toys, and other electronics) has become the most rapidly growing waste stream in the industrialized world, growing 4% annually (UNEPDEWA/ GRID-Europe 2005). Considerable attention has been raised over the amount of e-waste that is improperly disposed of each year since it contains several metals which eventually may find their way into potential sources of drinking water. While naturally distributed levels of metals found in rocks and soils are usually not cause for concern, anthropogenic activities (e.g., industrial, agricul- tural, and military sources and incorrect disposal of e- waste) often disperse metal pollution throughout the environment, which may pose human health risks at high levels (USEPA 2006). Currently, the US Environmental Protection Agency regulates at least ten metals, including Pb, Cd, and Cu, which are found in e-waste and other sources, as primary contaminants in drinking water. More unregulated metals like Ni and Zn, which are also e-waste contaminants, might be monitored in the future due to their comparable detrimental health effects (WHO 2005). Numerous methods for metal removal from water exist, including but not limited to chemical precipitation, electro- chemical methods, or adsorbent substrates (Rebhun and Galil 1990). Nanoparticles could be an additional alterna- tive option as a metal contaminant sorbent. Larger surface area may translate into greater sorption capacities allowing Responsible editor: Hailong Wang K. E. Engates : H. J. Shipley (*) Department of Civil and Environmental Engineering, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA e-mail: heather.shipley@utsa.edu Environ Sci Pollut Res (2011) 18:386–395 DOI 10.1007/s11356-010-0382-3