Abstract:The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume phase transition found for PNIPAM-co-AAc particles in the bulk disappears after the adsorption at the surface and only a one step transition was identified. The transition temperature increased strongly with increasing the co-monomer content. The dependence of the Young's modulus of the adsorbed microgel particles on the temperature and the co-monomer content was discussed. The investigations were performed via DLS and SFM.
In this study, nZVI prepared by borohydride reduction was applied for the removal of Cu 2+ ions under a variety of experimental conditions. The uptake experiments investigated the effects of initial concentration, contact time, pH, and repetitive loading on the extent of retardation of Cu 2+ ions. Within the applied conditions, the sorbent demonstrated fast uptake kinetics and outstanding fixation abilities up to an initial Cu per g of nZVI. According to X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results, Cu 2+ ions were sorbed primarily via a redox mechanism that resulted in the formation of Cu 2 O and Cu 0 . The contact of iron nanoparticles with aqueous media caused extensive formation of iron oxide. However, the material did not completely lose its removal capacity and was repeatedly applied at low concentrations for further uptake trials.
Recently, iron nanoparticles are increasingly being tested as adsorbents for various types of organic and inorganic pollutants. In this study, nanoparticles of zero-valent iron (NZVI) synthesized under atmospheric conditions were employed for the removal of Ba 2+ ions in a concentration range 10 −3 to 10 −6 M. Throughout the study, 133 Ba was used as a tracer to study the effects of time, concentration, and temperature. The obtained data was analyzed using various kinetic models and adsorption isotherms. Pseudo-second-order kinetics and Dubinin-Radushkevich isotherm model provided the best correlation with the obtained data. Observed thermodynamic parameters showed that the process is exothermic and hence enthalpy-driven.
Co
2+This study reports the synthesis and characterization of nano-scale zero-valent iron in the presence of kaolinite clay (nZVI-kaol). The adsorbent, nZVI-kaol, was produced at initial Fe:kaolinite mass ratios of 1:1, 0.5:1, and 0.2:1. The presence of kaolinite resulted in decreased aggregation of iron nanoparticles, yielding composites with iso-electric points (IEPs) around 6.7-7.0. The reduction in Fe 2+ precursor concentration appeared to decrease further the extent of aggregation and the size of individual nZVI particles. The synthesized nZVI-kaol materials were then tested for the removal of aqueous Cu 2+ and Co 2+ ions. The investigated parameters in the uptake experiments included volume/mass (V/M) ratio, initial concentrations of Cu 2+ and Co 2+ ions, contact time, pH, and repetitive application of the adsorbent. The adsorbents demonstrated high removal abilities towards both cations under the investigated conditions. Repetitive loading tests showed that significant removal could still be achieved at small concentrations by samples reused several times. X-ray photoelectron spectroscopy (XPS) analysis showed that while Co 2+ was mainly fixed by the oxyhydroxyl groups of iron nanoparticles, Cu 2+ ions were fixed by a redox mechanism, leading to the formation of Cu 2 O and Cu 0 .
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