No abstract

Hierarchical CeO2 nanocrystal microspheres were synthesized with a nonaqueous sol−gel method at a low temperature of 120 °C. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and nitrogen sorption measurements. The adsorption performances of hierarchical CeO2 nanocrystal microspheres were tested with the batch removals of typical pollutants of Cr(VI) and rhodamine B from simulated wastewater. It was found that the nanostructured CeO2 could effectively remove Cr(VI) without pH preadjustment. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Cr(VI) removal was found to follow pseudosecond-order rate equation. Furthermore, the as-prepared and Cr(VI)-adsorbed hierarchical CeO2 nanocrystal microspheres were carefully analyzed by X-ray photoelectron spectroscopy (XPS). On the basis of the XPS results, a possible mechanism of Cr(VI) removal with hierarchical CeO2 nanocrystal microspheres was proposed. Moreover, these nonaqueous sol−gel synthesized hierarchical CeO2 nanocrystal microspheres also exhibited remarkable ability to remove rhodamine B, suggesting they are promising absorbents for wastewater treatment.

No abstract

A novel adsorbent of Li−Al layered double hydroxides (LDHs) was prepared through the precipitation of metal nitrates and further applied to remove excessive fluoride ions from water. The physical and chemical properties of synthesized materials were examined by powder transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, N 2 adsorption/ desorption analysis, and thermogravimetric analysis (TGA). The TEM results indicated that the materials synthesized via coprecipitation present a preferential orientation of the nanoscale LDH platelets. The XRD analysis confirmed that the synthesized products have a highly crystalline nature and a well-ordered layer structure. The high specific surface areas (37.24− 51.27 m 2 /g) of calcined products were demonstrated to be beneficial for the adsorption of fluoride. For the adsorption experiment, the effects of the adsorption conditions including pH, coanions and adsorbent dose were investigated at initial fluoride concentration of 20 mg/L. The kinetics and isotherms of fluoride adsorption by calcined Li−Al LDHs were studied. The results indicated that the Li−Al LDHs can be effectively used to remove fluoride from water, where the maximum percentage removal (97.36%) could be reached and the adsorption equilibrium could be attained within 1 h. The kinetic data were well-fitted to the pseudo-second-order model, while the Freundlich isotherm model provided the better correlation of the equilibrium data. Based on FT-IR and kinetic analysis, the "memory effect" may play an important role in the early adsorption stage, while the ionexchange process may control the adsorption rate at the second adsorption stage. Since the Li−Al LDHs show excellent fluoride removal efficiency, they are expected to separate fluoride from water in pollution control.

Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion-oxygen bond formation destabilizes the transition-metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and Mx O (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.