Qianhong Yu

Characterizations of Nb-doped WO3 nanomaterials and their enhanced photocatalytic performance

In this paper, Nb-doped WO3 nanowires were successfully prepared using a low-temperature, hydrothermal method. The physicochemical properties of pristine and Nb-doped WO3 were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy (UV-vis). The photocatalytic properties of those Nb-doped WO3 nanomaterials are evaluated on the basis of their ability to degrade methylene blue (MB) in an aqueous solution under simulated sunlight irradiation. It is demonstrated that the pristine nanowires tend to aggregate, whereas the energy band gap of those nanomaterials narrows as more niobium ions are doped. The photocatalytic experimental results indicated that the Nb-doped WO3 exhibited superior photocatalytic activities to that of the undoped WO3. The Nb-doped WO3 nanowires synthesized with an Nb/W molar ratio of 0.03 possessed the most effective photocatalytic activity among the tested samples.

Thermodynamic Study on the Protonation Reactions of Glyphosate in Aqueous Solution: Potentiometry, Calorimetry and NMR spectroscopy

Glyphosate [N-(phosphonomethyl)glycine] has been described as the ideal herbicide because of its unique properties. There is some conflicting information concerning the structures and conformations involved in the protonation process of glyphosate. Protonation may influence the chemical and physical properties of glyphosate, modifying its structure and the chemical processes in which it is involved. To better understand the species in solution associated with changes in pH, thermodynamic study (potentiometry, calorimetry and NMR spectroscopy) about the protonation pathway of glyphosate is performed. Experimental results confirmed that the order of successive protonation sites of totally deprotonated glyphosate is phosphonate oxygen, amino nitrogen, and finally carboxylate oxygen. This trend is in agreement with the most recent theoretical work in the literature on the subject (J. Phys. Chem. A 2015, 119, 5241-5249). The result is important because it confirms that the protonated site of glyphosate in pH range 7-8, is not on the amino but on the phosphonate group instead. This corrected information can improve the understanding of the glyphosate chemical and biochemical action.

Complexation of Manganese with Glutarimidedioxime: Implication for Extraction Uranium from Seawater

The molecule of glutaroimidedioxime, a cyclic imidedioxime moiety that can form during the synthesis of the poly(amidoxime)sorbent and is reputedly responsible for the extraction of uranium from seawater. Complexation of manganese (II) with glutarimidedioxime in aqueous solutions was investigated with potentiometry, calorimetry, ESI-mass spectrometry, electrochemical measurements and quantum chemical calculations. Results show that complexation reactions of manganese with glutarimidedioxime are both enthalpy and entropy driven processes, implying that the sorption of manganese on the glutarimidedioxime-functionalized sorbent would be enhanced at higher temperatures. Complex formation of manganese with glutarimidedioxime can assist redox of Mn(II/III). There are about ~15% of equilibrium manganese complex with the ligand in seawater pH(8.3), indicating that manganese could compete to some degree with uranium for sorption sites.

Adsorption of radioactive iodine on surfactant-modified sodium niobate

Iodine radioisotopes have been released into the environment both by the nuclear industry and as a result of medical treatment using radioactive materials, potentially posing a serious threat to human health. Thus, when developing applications of radioactive iodine, emergency procedures for dealing with it, and preventing its leakage, are constant concerns. In this study, nanofibers and cubes of Ag2O anchored sodium niobate composites were synthesized by a wet chemical process, and characterized by means of XRD, SEM, TEM and BET techniques. It was found that the well-dispersed Ag2O nanocrystals (3–5 nm) were firmly anchored on the external surface of sodium niobate along the planes with crystallographic similarity to those of Ag2O. These composites can efficiently capture I− anions by precipitating AgI, firmly attaching it to the substrate and allowing it to be recovered easily for safe disposal. Variations in the iodine removal abilities with differing pH value, adsorption time, adsorption temperature, initial I− concentration, and in the presence of competing ions, were studied. The maximum monolayer adsorption capacities of I− anions for Ag2O anchored sodium niobate nanofibers and cubes were found to be 296 and 193 m2 g−1 respectively. TEM, XRD, XPS and Raman results indicated that I− anion adsorption was mainly due to the Ag2O nanocrystals on the sodium niobate surfaces. We conclude that Ag2O deposited on sodium niobate hass a great potential for removal of radioactive iodine from waste water.

Characterization of Li-doped WO3 nanowires and their enhanced electrocatalytic oxidation of ascorbic acid

Li-doped WO3 nanowires have been hydrothermally prepared and characterized mainly via spectroscopic methods. Both the hexagonal structure distortion and morphology evolution induced by Li doping reveal a lattice expansion of about 0.07 A. Also, the residence of oxygen vacancy and the enlargement of external surface areas positively correlate with the narrowing of energy band. Subsequently, the electrocatalytic oxidation of ascorbic acid using a Li-doped WO3 film-coated electrode performs a 13% and 21% negative shift of the oxidation overpotential compared with a WO3 film-coated electrode and a bare glassy carbon electrode, respectively. A preliminary mechanism has been proposed on the basis of relevant model analyses.

Thermodynamics of the Protonation of an Analogue of Glyphosate, N -(phosphonomethyl)- l -proline, in Aqueous Solutions

N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, 31P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.

Pyrochlore Ta-doped antimony oxide as a novel adsorbent for efficient strontium removal

Hydrous antimony oxide Sb2O5·4H2O with a pyrochlore structure is an ion exchanger that is selective toward Sr2+ in mild solutions. The present study aims to improve the Sr2+ adsorption capacity of antimony oxide. Cubic pyrochlore non-doped and Ta-doped antimony oxide nanoparticles were prepared by a hydrothermal method. The particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 gas sorption, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Incorporation of Ta5+ into the sorbent led to an expansion of the pyrochlore structure, and increases in the surface hydroxyl group content and surface area of the sorbent, consequently improving the Sr2+ adsorption capacity considerably. A satisfactory correlation coefficient and a relatively low normalized standard deviation of the fit of the experimental data using the Freundlich model demonstrate that Sr2+ adsorption onto Ta-doped antimony oxide proceeds via a multilayer chemical adsorption process. Thermodynamic studies were conducted under different reaction temperatures. The results indicate that Sr2+ adsorption onto Ta-doped antimony oxide is an endothermic and a spontaneous process. Under the current experimental conditions, the maximal Sr2+ adsorption capacity of 26.37 mg g−1 was obtained at pH 4.

Crystal structure stability of simulated Sr 1–1.5 x Y x TiO 3 ( x = 0–0.12) waste forms

A series of Sr1–1.5xYxTiO3 (x = 0–12) solid solutions were synthesized by a solid state reaction process. The effects of reaction temperature and dopant on the crystallinity, microstructure and morphology of Sr1–1.5xYxTiO3 (x=0–0.12) were investigated. Pure and single-phase perovskite-type Sr1–1.5xYxTiO3 (x<0.08) solid solutions were obtained at 1 400 °C for 6 h. The perovskite-type SrTiO3 and pyrochlore-phase Y2Ti2O7 coexisted for x = 0.08–0.12, leading to an unstable and unfavourable solid solution structure for long-term immobilization of the 90Sr. The X-ray diffraction patterns for Rietveld refinement analysis confirmed the formation of a Sr1–1.5xYxTiO3 (x = 0–0.12) continuous solid solution. Stretching and bending vibrations were assigned in the infrared region. The SrTiO3 grain size increased with Y content. The leaching behavior of Y3+ from the waste forms of Sr1–1.5xYxTiO3 was controlled by its structural change.

Hydrothermal synthesis of WO3 nanowires in the presence of guanidine sulfate and its photocatalytic activity

WO3 nanowires were fabricated by a hydrothermal method, which proceeded at 170 °C for 48 h in a solution containing C2H10N6H2SO4 as a dispersant and Na2WO4 as a starting material. The nanowires exhibit a well crystallized one-dimensional structure with 20 nm in diameter and several microns in length. The physicochemical properties of WO3 were compared using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and UV-vis spectroscopy (UV-Vis). The photoactivity of the as-perpared WO3 nanowires was evaluated through the photodegradation of methylene blue (MB) in aqueous solution. The experimental results demonstrate that addition of C2H10N6H2SO4 salt in the WO3 nanowires synthesis process can enhance its photocatalytic activity obviously.