In this study, the sorption behavior of Zn 2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the sorption capacity was enhanced with increasing amount of calcite in both types of mixtures. Under neutral-alkaline pH conditions and high loadings, the order of Zn 2+ retention was observed as calcite > clinoptilolite > kaolinite. The experiments on the retention of Zn 2+ by pure calcite under conditions of oversaturation showed that the uptake process proceeds via an initial adsorption mechanism (possibly ion-exchange type) followed by a slower mechanism that leads to the overgrowth of the hydrozincite phase, Zn 5 (OH) 6 (CO 3 ) 2 .
a b s t r a c tWe report a simple one-pot method to prepare organically functionalized CeO 2 nanoparticles by controlled chemical precipitation. The particles were nucleated by mixing aqueous solutions of Ce(NO 3 ) 3 ·6H 2 O and ammonia at room temperature. Different small organic molecules were chosen as capping agents and injected into the reaction medium at the beginning of the synthesis: 3-(mercaptopropyl) trimethoxy silane (MPS), hexadecyltrimethyl ammonium bromide (CTAB), 3-mercapto propionic acid (3-MPA), and thioglycolic acid (TGA). The resulting nanocrystals were quasi-spherical and had a narrow mean size distribution with an average size smaller than 10 nm. Dynamic nuclear polarization enhanced NMR (DNP-NMR) and FTIR measurements suggested a chemical grafting of the surfactant and a homogeneous surface modification. The colloidal stabilities were characterized by dynamic light scattering and zeta potential measurements. The stabilization by aliphatic groups was tested with a frequently used hydrophobic monomer, methyl methacrylate. According to the results, CTAB is the most effective of the used stabilizing surfactant. The mechanism of formation of the organophilic CeO 2 nanoparticles is discussed.
The uptake of aqueous Ba 2+ ions by abiogenic calcite and aragonite was studied over a wide range of concentration; 1.0 × 10 1 , 5.0 × 10 1 , 1.0 × 10 2 , 5.0 × 10 2 , 1.0 × 10 3 , 5.0 × 10 3 , and 1.0 × 10 4 mg/L. The uptake process was characterized using ICP-AES, XRPD, SEM/EDS, and FTIR techniques. Up to the initial concentration of 5.0 × 10 2 mg/L, the uptake of Ba 2+ ions was fast and obeyed Lagergren's kinetic model. The equilibrium data were adequately described using Freundlich isotherm model. The overgrowth of BaCO 3 (witherite) took place at higher concentrations, in a kinetically slow process and enhanced the uptake of Ba 2+ ions. Quantitative XRPD was used to evaluate the fractions of precipitated BaCO 3 on calcite and aragonite minerals and monitor their variation with time. At all the studied concentrations, aragonite showed higher removal capacity of Ba 2+ and faster uptake kinetics than did calcite. The precipitated crystals appeared to predominantly possess olivary-like morphology with an average particle size of 1-2 µm. EDS was used to reveal the elemental quantities of Ba and Ca after BaCO 3 formation on calcite and aragonite surfaces. FTIR spectroscopy was employed to analyze the vibrational modes in carbonate mixtures upon incorporation of Ba 2+ by sorption and precipitation mechanisms.
Polymerization of monomer/nanoparticle dispersion, namely in situ polymerization, has been frequently used for the fabrication of polymer nanocomposites. However, the interference of nanoparticle surface with polymerization in the course of composite formation has been tacitly neglected. In this work, surface-functionalized ceria nanoparticles were prepared using various capping agents: 3-(mercaptopropyl) trimethoxy silane, thioglycolic acid, 3-mercaptopropionic acid, and hexadecyltrimethyl ammonium bromide. Both in situ and ex situ approaches were applied for surface functionalization. The particles were dispersed into methyl methacrylate and free radical polymerization was carried out. The process of nanocomposite formation was examined in terms of conversion, molecular weight, and molecular weight distribution. The polymerization responded merely to the in situ functionalized particles. Regardless of the capping agents used, the particles function as a retarder and inhibitor. Their interaction with polymerization medium showed many complexities such that molecular weight was found to be strongly dependent on the capping agent employed.
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