Stability of nTiO 2 particles and their attachment to sand: Effects of humic acid at different pH

Abstract

Influence of humic acid (HA) on stability and attachment of nTiO2 particles to sand was investigated. Results showed that HA can either promote or hinder nTiO2 stability, depending on pH and HA concentration. HA can either enhance or reduce nTiO2 attachment to Fe oxyhydroxide coating at pH 5, depending on HA concentration.Results further showed that at pH 5, Fe oxyhydroxide coating reduced nTiO2 attachment to sand in the absence of HA but increased nTiO2 attachment in the presence of low concentration of HA. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was invoked to analyze particle-to-particle and particle-to-sand interactions in order to elucidate the roles of pH, HA, quartz, and Fe coating in controlling nTiO2 stability and attachment. Overall, this study showed that changes in zeta potential of nTiO2 and Fe coating due to pH changes and/or HA adsorption are the key factors that influence stability and attachment of nTiO2.iii ACKNOWLEDGEMENTS

Nanoscale Titanium Dioxide (nTiO2) Transport in Natural Sediments: Importance of Soil Organic Matter and Fe/Al Oxyhydroxides

“…Similarly, bulk density was 1.73 g/cm 3 for quartz sand, and slightly greater for mixed columns (1.77–1.83 g/cm 3 ) (Table S2). Pore space was greater in quartz sand columns due to increased uniformity compared to mixed columns with variable grain sizes, whereas specific surface area (SSA) and surface roughness of quartz sand was much less than that of the natural sediment. , Differences in physical properties between quartz sand and mixed sediment and sand columns (all of which suggest enhanced transport in quartz sand columns) needed to be considered in the interpretation of nTiO 2 transport behavior.…”

“…Zeta potential of quartz sand, sediments, and nTiO 2 at pH 5 and 9. The zeta potential of quartz sand was determined previously …”

“…Aeroxide P25 titanium­(IV) oxide powder from Arcos Organics with minimum 99.5% purity was used to prepare the nTiO 2 suspensions. Previous analysis determined the powder was 90% anatase and 10% rutile . For all experiments, 50 mg/L nTiO 2 suspensions were prepared in 1 mM NaCl in nanopure water and sonicated by Branson Digital Sonifier (Crystal Electronics) at 200W, 30% amplitude, for 30 min.…”

“…SOM is composed of both solid soil organic matter (SSOM) and dissolved organic matter (DOM) . While a large number of studies have shown that DOM enhances ENP stability and transport through adsorbing onto the ENP surface and altering surface charges through steric repulsion, − little attention has been paid to SSOM–ENP interactions. It is intuitive to hypothesize that negatively charged SSOM may attract positively charged ENPs and remove them from the aqueous phase.…”

Stability of Artificial Nano‐Hydroxyapatite in the Presence of Natural Colloids: Influence of Steric Forces and Chargeability

“…The stabilization effect of DOM in the presence of Na + was less pronounced than in the presence of Mg 2+ , likely due to effective charge screening and neutralization by divalent cations (Zhang et al, 2013). However, other observations showed that DOM may promote nanoparticle aggregation by neutralizing surface charges (Yang and Cheng, 2016). Soil inorganic colloids may facilitate, hinder, or not influence the stability and mobility of nanoparticles, depending on the physicochemical conditions and properties of the particles (Cai et al, 2014).…”