1-Hexyl-3-methylimidazole-2-thione (HMImT), a low-viscosity extractant, was firstly synthesized and used to extract rhodium(I). The negligible solubility of HMImT in solution was measured by HPLC to be about 0.015%. In the extraction process, rhodium(III) in solution was activated into rhodium(I) by SnCl2 to improve extraction percentage, which was confirmed by XPS spectra. Under optimum conditions, the extraction percentage reached 99.6%. The neutral complexing mechanism was confirmed by UV-vis spectra, 1H NMR spectra, titration method and FT-IR spectra. Quantum chemical calculations based on density functional theory (DFT) were also performed to support the results from a theoretical perspective. The extraction process was modeled by Langmuir (R2 = 0.998), Freundlich (R2 = 0.972) and Dubinin–Radushkevich isotherms (R2 = 0.990). According to the model results, the monolayer absorption capacity was 2.82 mmol g−1, and the mean free energy was obtained as 9.8 kJ mol−1. The thermodynamic parameters of ΔG, ΔH and ΔS showed that the extraction process was spontaneous and exothermic. Pseudo-second-order kinetics well fitted the experimental data (R2 = 0.996). In addition, HMImT possesses high selectivity to Rh(I) rather than other base metals during extraction. In summary, HMImT with low dissipation, excellent extractability and high selectivity for rhodium(I) extraction will hold great promise and potential in the separation field.

•Pd (II), Pt (IV), Rh (III) and Ir (IV) were separated with low-viscosity HMImT by microextraction.•Ion association mechanism of Pt (IV) was proved by theoretical calculation and experiments.•Novel precipitating-calcining method was designed to obtain Rh2O3, Pd and Pt2O.•The separation process was simple and economical.In this study, palladium (II), platinum (IV), rhodium (III) and iridium (IV) were sequentially separated with 1-hexyl-3-methylimidazole-2-thione (HMImT) from aqueous hydrochloric acid media by adjustment of hydrochloric acid concentration or in the presence of tin (II) chloride using environmental-friendly microextraction method. It is the first time to use sole extractant to selectively separate four platinum group metals from aqueous solution. Through condition optimization, HMImT shows outstanding extraction capacity (Pd 0.54 mmol/g, Pt 0.14 mmol/g, Rh 0.82 mmol/g) and high extraction percentage to palladium (99.4%), platinum (99.8%), rhodium (99.6%) respectively. The separation coefficient exceeds 10,000 and obtained metals purity reaches 99%. Based on Job's method, FT-IR spectra, UV–vis spectra, 1H NMR spectra and theoretical natural population analysis (NPA), the anion exchange mechanism of HMImT on Pt (IV) extraction was confirmed. By precipitating-calcining method palladium (II), platinum (IV) and rhodium (III) could be recycled in the form of Rh2O3, Pd and Pt2O.Download high-res image (146KB)Download full-size image

A simple protocol has been reported here to successfully perform a controllable conversion between Ce(OH)4 nanorods [Ce(OH)4-NR] and Ce(OH)4 nanoflowers [Ce(OH)4-NF] based on a prolonged mechanical force-driven stirring process. Results show that the Ce(OH)4 nanostructures undergo a morphology transformation from the initial nanorods to irregular nanoflowers, then to nanoflowers emanating from one center only, by varying the stirring time before solvothermal reaction. The detailed study confirmed that the mechanical force significantly improved the mass transport of the solution and drove the seeds of Ce(OH)4-NR [seeds-NR] to generate the seeds of Ce(OH)4-NF [seeds-NF]. The final CeO2 products (CeO2 nanorods [CeO2-NR] and CeO2 nanoflowers [CeO2-NF]) that inherited the original morphology were obtained by annealing Ce(OH)4-NR and Ce(OH)4-NF, respectively. To further optimize the performance of the final products, Au/CeO2-NR and Au/CeO2-NF were synthesized by a simple oxidation–reduction process, which led to increased surface areas and promising potential in CO oxidation.

In this work, a facile one-step solvothermal method with the assistance of hydrochloric acid has been developed to prepare well-dispersed CeO2 hollow nanospheres with high surface areas. The effects of hydrochloric acid on the growth mechanism and the size distribution are investigated in detail. It is found that the hydrogen ions expedite the nucleation rate of the CeO2 nuclei in the nucleation course, while the chloride ions accelerate the Ostwald ripening in the acidic environment. Both the hydrogen ion (H+) and the chloride ion (Cl−) are confirmed to play a key role in the formation of hollow morphology. Based on our experiments, a HCl-assisted oxidation–nucleation with an Ostwald ripening process mechanism was proposed. Furthermore, Au nanoparticles with a size of 2.5–6 nm were uniformly deposited on the surface of the ceria support by a simplified reduction process with sodium borohydride (NaBH4). The synthesized Au/CeO2 nanospheres exhibit a higher catalytic activity in CO oxidation than pure ceria nanospheres due to the existence of different Au species (metallic Au0 and positively charged Auδ+) and the strengthened interfacial interactions between the Au NPs and the ceria support.

In this paper, novel hierarchically mesoporous CeO2 nanoparticles assembled by hollow nanocones were prepared through a facile solvothermal strategy using Ce(HCOO)3 as the precursor. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and thermal gravimetric analysis (TGA) were utilized to characterize the products and research the formation mechanism. The whole synthesis process involves two steps: formation of Ce(HCOO)3 nanoparticles constructed with nanocones at room temperature in an alkaline environment and oxidation induced phase transformation from Ce(HCOO)3 to CeO2 with formation of hollow nanocones assembled by nanocrystals in a solvothermal process at 150 °C. The as-prepared mesoporous CeO2 nanoparticles with an average diameter of 500 nm displayed a high surface area of 147.6 m2 g−1 using N2 adsorption and desorption measurement. The H2-TPR test showed its great reduction behavior in a low temperature zone. By comparing the T100 temperature of CO conversion with a commercial sample (above 350 °C) and other reported samples (above 300 °C) in the literature, the mesoporous CeO2 nanoparticles (270 °C) presented an excellent catalytic activity for CO oxidation.

The extraction of cobalt by Winsor II microemulsion system was studied. In the bis (2-ethylhexyl) sulfosuccinate sodium salt (AOT)/n-pentanol/n-heptane/NaCl system, AOT was used as a anionic surfactant to form microemulsion in n-heptane, n-pentanol was injected in the microemulsion as a cosurfactant. Co(II) was found to be extracted into the microemulsion phase due to ion pair formation such as Co2+(R–SO3−)Cl. The influence of different parameters such as the volume ratio of aqueous phase to microemulsion, surfactant concentration, pH of the feed solutions, cosurfactant concentration as well as temperature on the extraction yield (E%) were investigated. The results showed that it was possible to extract 95% of cobalt by the AOT Winsor II microemulsion.