The adsorption of calcium ions on the surface of precipitated calcium carbonate (calcite, prismatic, 0.7 pm diameter) has been studied in 20 w t 94 aqueous slurries by calcium chloride addition. The adsorption of the calcium ions was found to follow the Langmuir adsorption isotherm, and the adsorbed calcium ions were the {-potential-determining ions. The monolayer coverage was determined to be 1.58 X l V mol of Ca2+/m2 (105 A2/Ca2+). Experimentally, this coverage was closely approached at the Ca2+ concentration of 7.51 mM in the bulk solution after adsorption equilibrium and was about one-fifth of the lattice Ca2+ density. The cpotential, as determined in the high-solids slurries by a Matec ESA-8000 instrument, varied with increasing Ca2+ concentration from +3.8 to +18.7 mV. As the {potential increased and the interparticle repulsion became greater, the sedimentation volume decreased, and the dispersion was slower to flocculate, a typical response to improved dispersion. The standard-state Gibbs free energy change for the adsorption process was calculated to be -28.3 kJ/mol (-6.8 kcal/mol) by using the experimentally determined adsorption equilibrium constant. The heat of adsorption measured by direct solution microcalorimetry was -6.9 kcal/mol of Ca2+, indicating that the adsorption is enthalpically driven.

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Over the past several decades, the design and development of nanomaterials with intrinsic enzyme-mimicking activities (nanozymes) have attracted increasing attention. Herein, we present a simple strategy for the construction of graphene−gold nanoparticle (Graphene/Au-NPs) nanozymes via a one-step hydrothermal reaction, which can act as a highly efficient dye scavenger with the synergetic effect of adsorption and degradation. The asprepared nanocomposites can overcome the intrinsic drawbacks of singlecomponent Au-NPs, such as ease of aggregation and cannot capture substrates effectively. In our catalytic system, Graphene/Au-NPs can readily adsorb organic dyes onto their surfaces, catalyze H 2 O 2 to generate • OH radicals, and then exhibit outstanding removal performance toward different organic dyes. Their catalytic mechanism is analogous to that of natural enzymes, in which the specific high catalytic efficiency depends mainly on their capacity to keep the substrate close to the active site of the enzyme. Collectively, our work may pave the way to apply multifunctional nanozymes in different research areas, such as environmental treatment, sensing, and biotechnology.

The objective of this study was to find an indigenous Cr(VI)-reducing bacterium that can effectively be used for Cr(VI) remediation in the contaminated soils. The results showed that one isolate from soil under a chromium-containing slag heap at a steel-alloy factory in China had a strong ability of reducing Cr(VI). It can completely reduce 500 mg L(-1) Cr (VI) within 24 h. Based on 16S rRNA gene sequence and similarity analysis, this isolate was identified as Pannonibacter phragmitetus and assigned as strain BB. Images of scanning electron microscopy (SEM) indicated that the cell surface of P. phragmitetus BB remained intact without cell rupture under 500 mg L(-1) Cr (VI) stress. The transmission electron microscopy (TEM) patterns showed that the Cr(VI) reduction products were both bound to the outer surface of the cells and dispersed in the culture medium, thereby suggesting that the reduction of Cr (VI) occurred extracellularly. Elemental analysis by energy dispersive X-ray (EDX) revealed that Cr was the major element comprising the reduction product. Furthermore, X-ray photoelectron spectroscope (XPS) verified that the Cr(VI) reduction product was Cr(III) compounds.