Aggregation Kinetics of Manganese Dioxide Colloids in Aqueous Solution: Influence of Humic Substances and Biomacromolecules

Abstract

In this work, the early stage aggregation kinetics of manganese dioxide (MnO2) colloids in aqueous solution and the effects of constituents of natural organic matter (i.e., Suwannee River fulvic acid (SRFA), Suwannee River humic acid (SRHA), alginate, and bovine serum albumin (BSA)) were investigated by time-resolved dynamic light scattering. MnO2 colloids were significantly aggregated in the presence of monovalent and divalent cations. The critical coagulation concentrations were 28, 0.8, and 0.45 mM for NaNO3, Mg(NO3)2, and Ca(NO3)2, respectively. The Hamaker constant of MnO2 colloids in aqueous solution was 7.84 × 10(-20) J. All the macromolecules tested slowed MnO2 colloidal aggregation rates greatly. The steric repulsive forces, originated from organic layers adsorbed on MnO2 colloidal surfaces, may be mainly responsible for their stabilizing effects. However, the complexes formed by alginate and Ca(2+) (>5 mM) might play a bridging role and thus enhanced MnO2 colloidal aggregation instead. These results may be important for assessing the fate and transport of MnO2 colloids and associated contaminants.

Assessment of Key Environmental Factors Influencing the Sedimentation and Aggregation Behavior of Zinc Oxide Nanoparticles in Aquatic Environment

“…Interestingly, the citric acid sample shows a significant shift of 83 cm −1 i.e., 1722 to 1639 cm −1 in carboxylate (-COO-) group ( Figure 3C), indicating strong inner sphere complexation with the ZnO surface [38,42]. In addition, the strong adsorption may be either via polynuclear-polydentate linkage or mononuclear-polydentate linkage between citrate and ZnO, thus resulting in weakened bonds in the metal-oxygen surface due to polarization [48,49]. Similar observations were reported in earlier studies [35,36], that enhanced release of Zn +2 may be expected due to ligand-promoted dissolution.…”

“…The amount of organic matter adsorbed on the metal surface may vary among types, concentration and their adsorption capacities on NP [40,43]. Different functional groups of organic matter have a tendency to attach on ZnO NPs surface and undergo ligand exchange through weakening Zinc-Oxygen bond [49,50]. Hence the affinity of organic matter towards the metal surface and amount adsorbed may directly or indirectly relate to NPs aggregation, which may affect the overall sedimentation behavior of ZnO NPs in the system [30].…”

“…Furthermore, the concentration of the counter-ions exceeds the CCC value for inverting the surface potential, and the dosage effect of the electrolyte would be mitigated. Consequently, the concentration of the Cl -and SO 4 −2 ions in the DWW was much higher than other waters, which might have neutralized or reversed the surface potential of NPs and therefore slow down the aggregation rate [49]. In the case of IWW, high TOC content and possible interference of metal ions such as arsenic (As) and antimony (Sb) may have contributed to the stability of NPs.…”

Effect of alginate on the aggregation kinetics of copper oxide nanoparticles (CuO NPs): bridging interaction and hetero-aggregation induced by Ca2+

“…The concentration of CuO NPs in the DLS vial was maintained at 100 mg/L. Then, the tested suspensions were vortexed (WH-2, Huxi Analysis Instrument Factory, Shanghai) for 1 s immediately after mixing and then placed in the Zetasizer (Huangfu et al 2013). At the initial stage of aggregation, the aggregation rate constant is directly proportional to the initial aggregation rate for Rh with time.…”

“…For the sample preparation, several drops of the CuO NP suspension were deposited onto a 300-mesh carbon-coated copper grid (Nanjing Zhongjing Technology Co., China) in a dust-free condition (Huangfu et al 2013). The excess water was then removed with filter papers and the grid was air-dried for 30 min.…”