Impact of Nanoparticles and Natural Organic Matter on the Removal of Organic Pollutants by Activated Carbon Adsorption

Abstract

Isotherm experiments evaluating trichloroethylene (TCE) adsorption onto powdered-activated carbon (PAC) were conducted in the presence and absence of three commercially available nanomaterials: iron oxide (Fe₂O₃), titanium dioxide (TiO₂), and silicon dioxide (SiO₂). Isotherm experiments were also conducted in the presence and absence of natural organic matter (NOM), in the form of humic acid, to more closely model natural water conditions. Nanoparticles at two concentration levels (0.5 and 1.0 mg/L for Fe₂O₃ and TiO₂, and 5.0 and 10 mg/L for SiO₂) were considered. Zeta potential and pH of point of zero charge (pH_pzc) of the nanoparticles and the PAC were measured. Particle size distribution (PSD) of the nanoparticle dispersions was analyzed as a function of time to determine the nanoparticle size range of each dispersion. Aggregation of Fe₂O₃ and TiO₂ nanoparticles was observed but not for SiO₂ nanoparticles. Adsorption isotherm experiments were conducted at three initial TCE concentrations, two nanoparticle concentrations, and with varying amounts of PAC. Isotherm data showed a higher degree of adsorption in the presence of Fe₂O₃ and TiO₂ nanoparticles, regardless of concentration. In activated carbon-free experiments both Fe₂O₃ and TiO₂ nanoparticles alone were observed to act as adsorption sites for TCE by removing up to 60% of TCE from the aqueous phase. Silica appeared to have no impact on TCE adsorption at either of the concentrations evaluated, except in the presence of humic acid. This study provides important information related to the use of nanoparticles in water treatment and their impact on the performance of a commonly used adsorbent used to remove organic pollutants. No studies to date have attempted to quantitatively describe the adsorption behavior of TCE to PAC in the presence of TiO₂, SiO₂, and Fe₂O₃ nanoparticles.