Deposition kinetics of zinc oxide nanoparticles on natural organic matter coated silica surfaces

The deposition kinetics of ZnO nanoparticles on silica surfaces and surfaces that pre-coated with Suwannee River humic acid (SRHA) were examined over a wide range of environmentally relevant ionic strengths in both monovalent and divalent solutions by employing a quartz crystal microbalance with dissipation (QCM-D). Deposition efficiencies of ZnO nanoparticles on bare silica surfaces increased with increasing ionic strength in both NaCl and CaCl2 solutions, which agreed with the trends of interaction forces between nanoparticle and silica surface and thus was consistent with classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The presence of divalent cation Ca2+ in solutions greatly enhanced the deposition kinetics of ZnO nanoparticles on silica surfaces. Pre-coated SRHA on silica surfaces hindered the deposition of ZnO nanoparticles in both monovalent and divalent solutions, which was not consistent with classic DLVO theory. Steric repulsion, a non-DLVO interaction, was found to be a major mechanism controlling the deposition of ZnO nanoparticle on SRHA-coated silica surfaces.

Graphical abstractPre-coating SRHA on silica surfaces hindered ZnO nanoparticle deposition in both monovalent and divalent solutions. Steric repulsion was responsible for the decreased deposition of ZnO particles on SRHA-coated surfaces.Figure optionsDownload full-size imageDownload high-quality image (54 K)Download as PowerPoint slideResearch highlights► Deposition of ZnO nanoparticles on silica surfaces is controlled by DLVO theory ► Ca2+ enhances the deposition kinetics of ZnO nanoparticles on silica surfaces ► NOM present on silica surfaces hinders the deposition of ZnO nanoparticles ► Steric repulsion controls ZnO nanoparticle deposition on SRHA-coated surfaces