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In this work, direct As(III) removal without pre-oxidation by the in-situ generated Fe(III) hydroxide derived from ferrous sulfate on the surface of calcium carbonate was investigated. The coagulation sediments were characterized by XPS, Zeta potential, AFM and SEM, respectively and the mechanism of the high As(III) removal efficiency was discussed and compared with the traditional neutralization of Fe 2 (SO 4) 3 at the same pH around 6. In the FeSO 4 + CaCO 3 system, Fe(II) ions dispersedly absorb on the surface of the CaCO 3 particles. Accompanied with the slowly hydrolyzed OH− from CaCO 3 and the O 2 in air, Fe(III) hydroxide is in-situ generated, which maintains nanosized particles without evident agglomeration into larger ones as usually observed with the alkali neutralization and therefore presents high activity to As(III). Although Fe arsenite has higher solubility than the arsenate, the in situ formed Fe(III) hydroxide demonstrates high reactivity to form basic Fe arsenite with Fe/As molar ratio at 4.5, resulting in almost complete arsenic precipitation. By this pathway, it is possible to remove directly arsenic at the unchanged trivalent state, without the usual requirement to oxidize As(III) to As(V), verified by the measurements of arsenic valence and hydroxyl radicals (OH) formation during the conversion of Fe(II) into Fe(III). Unlabelled Image • In-situ generated Fe(III) hydroxide achieves great As(III) removal effect. • Fe(II) ions dispersedly absorb on the surface of the CaCO 3 particles. • Fe(III) hydroxide maintains a nanosized state without evident agglomeration. • As(III) directly removed as basic iron arsenite without usual oxidization to As(V). [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of inorganic cations (Na+, Ca2+, and Al3+) with different valences and concentrations on the stability of Na-montmorillonite (Na-MMT) suspension. The stability was studied by turbidity and zeta potential measurements and adsorption thermodynamics. The results showed that the Na-MMT particles coagulated at pH 3-4.8, the stability of which was much inhibited by cations with higher concentration and higher valence. This was caused by the adsorption of cations and the reduction of electrostatic repulsion. Adsorption of Ca2+ on Na-MMT surface fits the Freundlich curve model well. Furthermore, the adsorption reduced the zeta potential of Na-MMT and then the energy barrier between the particles which well obeyed the classic DLVO theory. [ABSTRACT FROM AUTHOR]

Air lime mortar is an important material for restoring ancient buildings, but its application is limited because of its low compressive strength, high shrinkage, and high porosity. In this work, improvement of the compressive strength of lime mortar by adding carboxymethyl cellulose (CMC) solution has been investigated. We characterized fine particles of Ca(OH) and lime mortars by scanning electron microscopy, infrared spectroscopy, the adsorption capacity, and the zeta potential. The experimental results show that the addition of CMC improves the compressive strength of lime mortar. Chemisorption of CMC to Ca(OH) particles leads to CMC bridging Ca(OH) particles, which is the key to form a more compact structure according to the porosity of the lime mortar. It was found that CMC acts as a skeleton in lime mortar because of the bridging effect of the molecules and the extended conformation of the molecules at high pH, which contributes to improvement of the compressive strength of lime mortar. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of inorganic cations (Na+, Ca2+, Ba2+, Fe3+, Al3+) with different valence and concentration on the swelling behaviors of montmorillonite. Na-montmorillonite, obtained from China, was chosen as experimental objective. It was first characterized through the measurements of swelling capacity and zeta potential. Then, swelling properties of Na-montmorillonite influenced by cation concentration, valence, and hydration analyzed were studied. The results showed that the swelling capacity was much inhibited by cations of higher concentrations, higher valences, or weaker hydration. This work also verified the conclusion that the decreased degree of potential is more significant caused by cations of higher valence. [ABSTRACT FROM PUBLISHER]

Montmorillonite (MMT) is easily exfoliated into two-dimensional(2D) nanosheets, which are widely used to prepare functional composites. However, there are few studies on the differences in the performance of MMT nanosheets (MMTNS) with different exfoliation degrees, which seriously limits the further breakthrough in the preparation of high-performance MMTNS based materials. In this work, some representative performance of MMTNS with different exfoliation degrees was investigated, and the performance was closely related with making functional composites. The exfoliation degrees of MMTNS were controlled by different ultrasonic exfoliation powers. The performance of MMTNS was studied by the measurements of atomic force microscopy (AFM), Zeta potential, turbidity, viscosity, scanning electron microscopy (SEM) and molecular dynamics simulation. The results show that MMTNS with high exfoliation degree had more negative electrical sites exposed and stronger repulsive potential energy between particles, which exhibited high surface negative electricity and excellent dispersion stability. Moreover, the MMTNS with high exfoliation degree had better gelling property. It can be seen that the "house-of-cards" structure in the structure after gelation of MMTNS with high exfoliation degree was more intensive. Also, with the increase of MMTNS exfoliation degree, its adsorption capacity for organic matter was better and its reaction with organic was more active. These findings might be helpful to select the suitable MMTNS for making functional composites by controlling its exfoliation degree. [Display omitted] • MMTNS with different exfoliation degree had different properties for making materials. • Highly exfoliated MMTNS had high surface electrical property and dispersion stability. • High exfoliation degree helps MMTNS show excellent gelling property. • The reaction of highly exfoliated MMTNS with organic was more active. [ABSTRACT FROM AUTHOR]

In this work, the exfoliation of montmorillonite related with electric charges on the layers in aqueous solutions were investigated through the measurements of zeta potential, turbidity and atomic force microscopy, as well as molecular dynamics simulation. The charge amount on montmorillonite layers was adjusted by blocking or neutralizing the layer charges with tetraethylenepentaminecopper (II) ([Cu(tetren)] 2+ ) through cation exchange reaction. The experimental results have shown that the exfoliation closely correlated to the amount of the layer charges. The larger are the charge amount on montmorillonite layers, the more easily the montmorillonite is exfoliated. This observation might be attributed to the repulsive energy (electrostatic and hydration repulsion) was stronger between the high charged montmorillonite layers than low charged ones. [ABSTRACT FROM AUTHOR]

The adsorption of Pb 2+ at the rutile/water interface has been studied for the activation of rutile flotation with salicyl hydroxamic acid (SHA) as a collector in this work. This study was performed through measurement of the zeta potential, adsorption capacity, calorimetry and X-ray photoelectron spectroscopy. The experimental results showed that the adsorption of SHA on rutile and the flotability of rutile were significantly improved by the addition of Pb 2+ . This improvement was attributed to the specific adsorption of Pb 2+ in the form of PbOH + , which interacted with the Ti-OH at the rutile surface and formed a surface Ti-O-Pb + complex. This adsorption followed the Langmuir model. It reversed the zeta potential sign of rutile at pH 5.5–6.8 and had a heat of adsorption of −46.71 kJ/mol, suggesting the occurrence of a chemiosorptive process. [ABSTRACT FROM AUTHOR]

[Display omitted] Montmorillonite (MMT), having special property of hydration expansion, can be easily exfoliated into two-dimensional (2D) nanosheets, which are the promising blocks for making multifunctional nanocomposites. In this work, the exfoliation performances of MMTs from different region including Inner Mongolia (IM), Zhejiang (ZJ) and Liaoning (LN) were investigated from the perspective of layer charge density. All the MMTs were prepared as Na-MMTs first to avoid the effect of the interlaminar ion. Atomic force microscope (AFM) measurements indicated that the exfoliation performance increased as: IM-MMT < ZJ-MMT < LN-MMT. Alkyl ammonium ion exchanged method was applied to study the layer charge density of the MMTs. It was found that the exfoliation performance decreased with the layer charge density of MMT increased. The characterizations of zeta potential, swelling index and BET specific surface area were used to reveal the effects of layer charge density on the exfoliation performance of MMT. The results showed that with increasing the layer charge density, MMT was with more negative zeta potential, thus leading to the stronger binding forces between the layers. The swelling index of LN-MMT was the highest who had the lowest layer charge density, demonstrated by the largest specific surface area and pore diameter after hydration swelling, which explained the best exfoliation behavior of LN-MMT. This study correlates the exfoliation performances with the layer charge density of MMT, and it will provide a guidance to prepare much thinner and larger MMT nanosheets. [ABSTRACT FROM AUTHOR]