Search

Shiftsof the critical coagulation concentration (CCC) in particlesuspensions in salt solutions containing multivalent co-ions and monovalentcounterions are rationalized. One observes that the CCC is inverselyproportional to the valence, and this behavior is referred to as theinverse Schulze–Hardy rule. This dependence is establishedby means of measurements of the stability ratio for positively andnegatively charged latex particles with time-resolved light scattering.The same dependence is equally suggested by calculations of the CCCwith the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, wherebythe full Poisson–Boltzmann equation for the asymmetric electrolyteshas to be used. The latter aspect is essential, since in the caseof multivalent co-ions the surface charge is principally neutralizedby monovalent counterions. This rule complements the classical Schulze–Hardyrule, which applies in the case of multivalent counterions, and statesthat the CCC is inversely proportional to the sixth power of the valence. [ABSTRACT FROM AUTHOR]

In situ contaminant degradation and detoxification mediated by microbes and minerals is an important element of green remediation. Improved understanding of microbe-mineral interactions on the nanoscale offers promising opportunities to further minimize the environmental and energy footprints of site remediation. In this Perspective, we describe new methodologies that take advantage of an array of multidisciplinary tools─including multiomics-based analysis, bioinformatics, machine learning, gene editing, real-time spectroscopic and microscopic analysis, and computational simulations─to identify the key microbial drivers in the real environments, and to characterize in situ the dynamic interplay between minerals and microbes with high spatiotemporal resolutions. We then reflect on how the knowledge gained can be exploited to modulate the binding, electron transfer, and metabolic activities at the microbe-mineral interfaces, to develop new in situ contaminant degradation and detoxication technologies with combined merits of high efficacy, material longevity, and low environmental impacts. Two main strategies are proposed to maximize the synergy between minerals and microbes, including using mineral nanoparticles to enhance the versatility of microorganisms (e.g., tolerance to environmental stresses, growth and metabolism, directed migration, selectivity, and electron transfer), and using microbes to synthesize and regenerate highly dispersed nanostructures with desired structural/surface properties and reactivity.

Experimentally determined heteroaggregation rates between charged and neutral colloidal particles are reported for the first time. Different positively and negatively charged polystyrene latex particles are investigated. The neutral particles are obtained through adsorption of an appropriate amount of oppositely charged additives, such as aliphatic oligoamines, iron cyanide complexes, or alkyl sulfates. Heteroaggregation rates were measured with time-resolved multiangle light scattering. One observes that heteroaggregation between charged and neutral particles is always fast and diffusion controlled. These experimental values are compared with calculations of the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, whereby one finds that this heteroaggregation process is highly sensitive to charge regulation conditions. The comparison with experiments shows unambiguously that the surface of the neutral particles regulates strongly and probably behaves close to a constant potential surface. This observation is in line with direct force measurements on similar systems and further agrees with the fact that for neutral surfaces the capacitance of the diffuse layer is expected to be much smaller than the one of the inner layer.

Aqueous suspensions of amidine latex (AL) and sulfate latex (SL) particles containing sodium tetraphenylborate and NaCl are studied with electrokinetic and time-resolved light-scattering techniques. In monovalent salt solutions, AL is positively charged, whereas SL is negatively charged. Electrophoretic mobility measurements demonstrate that adsorption of tetraphenylborate anions leads to a charge reversal of AL particles. At higher concentrations, both types of particles accumulate negative charge. For AL particles, the charge reversal leads to a narrow fast aggregation region and an intermediate regime of slow aggregation. For SL particles, the intermediate slow regime is also observed. These aspects can be explained with classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Another regime of fast aggregation is observed at intermediate concentrations, and the existence of this regime can be rationalized by an additional attractive non-DLVO force. We suspect that this additional force is caused by surface charge heterogeneities.