Preparation of mesoporous In–Nb mixed oxides and its application in photocatalytic water splitting for hydrogen production

A series of mesoporous In–Nb mixed oxides was synthesized using NbCl₅ and In₂O₃ as the starting material and triblock copolymer P123 as template. We investigated the influence of indium content on the synthesis and characteristics of the mesoporous In–Nb mixed oxides, and their photocatalytic activities for water splitting. The materials were characterized by small angle X-ray scattering, powder X-ray diffraction, extended X-ray absorption fine structure, transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometer, N₂ sorption and UV–vis spectroscopy. The surface area of mesoporous In–Nb mixed oxides was greater than 90 m²/g with a wormhole framework. The optimization of synthesis condition of the mesoporus In–Nb oxides catalyst contained a small fraction of highly dispersed indium (In/Nb = 0.13) species intercalated into the framework of mesoporous niobium oxides and exhibited a high photocatalytic activity for water splitting reaction which was about 2.7 times as compared to mesoporous Nb₂O₅ and was about 19 times higher than commercial bulk Nb₂O₅.     

Perfluorinated sulfonic acid ionomer/poly(N-vinylpyrrolidone) nanofiber membranes: Electrospinning fabrication, water stability, and metal ion removal applications

Perfluorinated sulfonic acid ionomer/poly(N-vinylpyrrolidone) (PFSA/PVP) fibrous membranes with varying compositions were prepared by electrospinning. The morphology, physicochemical structure and water stability of these membranes were investigated by SEM, XRD, and FTIR. The crosslinking agent 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt (DAS) was added to the spinning solutions, and its effect on electrospinning behavior and PFSA/PVP membrane morphology was investigated. Thermal annealing of the DAS-containing PFSA/PVP fibrous membranes resulted in improved water stability due to PVP crosslinking. The adsorption properties of the nanofiber membranes were measured by the ability to remove Cu²⁺ and Ca²⁺ ions from water. Nanofiber membranes with higher surface area provide more exposed functional groups and thus better ion removal capability. These functional PFSA/PVP nanofiber membranes show applicability in water treatment and may find potential applications in sensors and drug delivery or as components of the catalytic layer of proton-exchange membrane fuel cells.     

First-principles study of phase-transition temperature and optical properties of alkaline earth metal (Be,Mg, Ca,Sr or Ba)-doped VO2

Vanadium dioxide (VO₂) is an attractive material for energy-saving smart windows due to its metal-to-insulator reversible phase transition near ambient temperature, accompanied by large changes in its optical properties. We conducted first-principles calculations to study the phase-transition temperature and optical properties of alkaline earth metal (Be, Mg, Ca, Sr or Ba)-doped VO₂. The results show that the Be atom prefers to locate at the octahedral interstitial site, while Mg, Ca, Sr and Ba atoms prefer to substitute for the V atom in VO₂. Be, Mg, Ca, Sr and Ba doping reduces the phase-transition temperature of VO₂ 0by 51.4, 59.7, 61.5, 58.4 and 58.3?K, respectively, when the doping concentration is set at one atomic percentage. In addition, the introduction of alkaline earth metal scales the band structures of VO₂, which enhances the ability to block the infrared light (in the order of Be > Mg > Ca > Sr > Ba) and promotes the transmission of visible light (in the order of Be > Mg ≈ Ca > Sr > Ba).     

Effects of metal doping agent on the properties of Nb2−xMxO5 (M = Mn,Fe, and Ni) system

In order to improve the behavior Niobium pentoxide on oxidation‐reductionreactions to degrade organic compounds in aqueous solutions, we developed the synthesis of Niobium pentoxide with the metal doping agents: manganese,iron, and nickel (Nb_2?xM_xO₅), respectively, and analyzing its effects on the structural and vibrational properties. The synthesis of the Nb_2?xM_xO₅ (M = Mn, Fe, and Ni; x = 0.02 and 0.05) was performed according the Pechini method, but before the annealing, the samples were submitted to Thermogravimetric analysis study showing better pre‐calcination annealing temperatures at 500 and 700°C for the materials. Then, we performed the crystal structural analysis by X‐ray Diffraction, obtaining crystallite sizes between 15 and 47 nm, the accurate size analysis was calculated by Scherrer equation. Structural analysis was also performed by IR spectroscopy to evaluate the vibrational modes of synthetized samples. The dopping effects were evaluated by UV‐Vis spectrophotometry through the energy band gap values, showing that doped samples with manganese and iron had lower values than undoped, except the sample doped with nickel. However, samples doped with iron at 2.5% showed better photocatalytic performance.     

A study of the synthesis,kinetics, and characterization of reactive graft copolymers of poly(vinyl imidazole) and cellulose for use as supports in enzyme immobilization and metal ion uptake

In continuation to our earlier work to use bioresource for developing alternate materials for use at the interface of biotechnology and polymer science, we have utilized pine needles as a renewable stock of cellulose to synthesize graft copolymers of vinyl imidazole. Kinetics of N‐VIm by simultaneous γ‐irradiation method has been investigated as a function of total dose, monomer concentration, and amount of water. Effect of water–methanol solvent composition on graft yields and polymerization kinetics has also been studied at the optimum grafting conditions of the total dose and monomer concentration. Effect of some additives such as ZnCl₂, Mohr salt, tetramethylethylene diamine, potassium persulfate, ammonium persulfate as grafting accelerators and promoters has also been studied. Graft copolymers have been characterized by elemental analysis, FTIR, and swelling studies. The graft copolymers have been used as supports for metal ions sorption, enzyme immobilization, and as potential biomimicking catalysts. Sorption behavior of Fe²⁺ ions and Cu²⁺ ions and the immobilization of bovine serum albumin and protease as a function of graft yield has been reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1522–1530, 2006     

Effect of poly(ethylene glycol) additives on the photocatalytic activity of TiO2 films prepared by sol–gel processing and low temperature treatments

Photocatalytic activity of titania with poly(ethylene glycol) (PEG) in the sample films made under different operating conditions was investigated by kinetic analysis of photodegradation tests. The sample films, composed of PEG and nano-TiO₂ particles, were prepared by sol–gel processing and then treated thermally under an atmosphere of wet and dry air at different temperatures. After the thermal treatment, photocatalytic activities of the films were evaluated by a UV-exposure test. Results showed that the photoactivity was enhanced by processing in an atmosphere of wet air at 100 °C. Moreover, the presence of poly(ethylene glycol), and the change in surface morphology in the sample films were verified to be the most influential and significant factors to affect the photoactivitic activity.     

Preparation of Au/TiO2 catalysts from Au(I)–thiosulfate complex and study of their photocatalytic activity for the degradation of methyl orange

Gold loaded on TiO₂ (Au/TiO₂) catalysts were prepared using Au(I)–thiosulfate complex (Au(S₂O₃)₂³⁻) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S₂O₃)₂³⁻ as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO₂. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO₂ catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S₂O₃)₂³⁻ precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO₂ catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO₂ and further affects the photocatalytic activity of the obtained catalysts.     

Dependence of optical properties on doping metal, crystallite size and defect concentration of M-doped ZnO nanopowders (M = Al, Mg, Ti)

ZnO, Al-, Mg- and Ti-doped ZnO nanopowders were synthesized from CTAB-assisted oxalate intermediate by thermal decomposition method at 600 °C in air. All samples presented a hexagonal wurtzite structure. The spherical nanoparticles assembled in a porous octahedron-like shape for all samples. The size of Al-doped ZnO nanopowders increased as a function of Al ion concentration whereas the size of Mg- and Ti-doped ZnO nanopowders decreased when Mg and Ti ion concentrations were increased. The increment and reduction of their sizes can be explained by the Zener pinning effect. The E_g value of Al-doped ZnO nanopowders slightly decreased when Al ions were increased due to the crystallite size and defect concentration increased. In contrast, the E_g value of Mg- and Ti-doped ZnO nanopowders increased as a function of Mg and Ti ion concentration which can be explained by the Moss-Burstein effect.     

Effects of transition metal additives on redox stability and high-temperature electrical conductivity of (Fe,Mg)3O4 spinels

Magnetite-based spinels are considered as promising oxide materials to meet the requirements for ceramic consumable anodes in molten oxide pyroelectrolysis process, a breakthrough low-CO₂ steel technology aimed to overcome the environmental impact of classical extractive metallurgy. The present work focuses on the assessment of phase relationships, redox stability and electrical conductivity of Fe_2.6Me_0.2Mg_0.2O₄ (M = Ni, Cr, Al, Mn, Ti) spinel-type materials at 300–1773 K and p(O₂) from 10⁻⁵ to 0.21 atm. The oxidation state of substituting transition metal cation, affecting the fraction of Fe²⁺ in spinel lattice, was found to be a key factor, which determines the electronic transport and tolerance against oxidative decomposition, while the impact of preferred coordination of additives on these properties was less pronounced. At T > 650 K thermal expansion of Fe_2.6Me_0.2Mg_0.2O₄ ceramics exhibited complex behaviour, and, in highly oxidizing conditions, resulted in significant volume changes, unfavourable for high-temperature electrochemical applications.     

Effects of metal phases on microstructure and mechanical properties of microwave-sintered Ti(C,N)-based cermet tool

A kind of Ti(C, N)-based cermet tool material was prepared by microwave sintering. The influence of metal phases (Ni, Co, and Mo) on densification and mechanical properties was studied by orthogonal test. The results indicated that Co was more significant in improving relative density and fracture toughness than Ni, while Ni and Co had the similar effects on increasing the hardness of Ti(C, N)-based cermet. Mo can improve fracture toughness but decrease hardness. Ti(C, N)-based cermet with 6 wt% Ni, 6 wt% Co and 6 wt% Mo (TN6C6M6) had the optimal comprehensive mechanical performances, and its fracture toughness and hardness were better than that of Ti(C, N)-based cermet prepared by conventional sintering. The increasing of sintering temperature promoted the uniformity of microstructure and significantly improved densification and hardness of the Ti(C, N)-based cermet. The highest fracture toughness of TN6C6M6 (12.41 ± 0.33 MPa·m^1/2) was achieved when sintered at 1600°C. For the microwave-sintered Ti(C, N)-based cermet, heat preservation period had little effect on densification. The relative density can reach up to 98.6% even though the heat preservation period was 0 minute.     

Preparation,characterization and antimicrobial activity of biopolymer based nanocomposite ion exchanger pectin zirconium(IV) selenotungstophosphate: Application for removal of toxic metals

A new bio-polymer based nanocomposite, pectin zirconium(IV) selenotungstophosphate (Pc/ZSWP) was prepared via sol–gel method. The material was characterized using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy. Distribution coefficient, thermal stability, elution behavior and pH titrations were investigated to explore the ion exchange behavior of nanocomposite. Pc/ZSWP exhibited higher ion exchange capacity (1.27 meq g⁻¹) than its inorganic counterpart (0.67 meq g⁻¹). To explore environmental applicability of the Pc/ZSWP, binary separation and selective separation of Cu²⁺ and Th⁴⁺ from synthetic mixtures of metal ions were achieved. Antimicrobial activity of the Pc/ZSWP was also investigated.     

The role of in situ generated nano-sized metal particles on the coulombic efficiency of MGeO3 (M = Cu, Fe, and Co) electrodes

To improve the coulombic efficiency of GeO₂ electrode, a Cu-containing ternary metal oxide (CuGeO₃) was prepared and the electrochemical behavior of Cu component was studied. The GeO₂ electrode shows a low coulombic efficiency in the first cycle (43%), which is mainly caused by a poor Ge oxidation kinetics (Ge + 2Li₂O → GeO₂ + 2Li⁺ + 2e⁻). The X-ray absorption spectroscopy (XAS) data illustrate that the Cu component in CuGeO₃ is converted to nano-sized metallic Cu in the earlier stage of lithiation but idles thereafter. In contrast, the Ge component in CuGeO₃ behaves like the GeO₂ electrode. It is converted to nano-sized Ge by a conversion reaction and further lithiated by alloying reaction. The de-lithiation proceeds in the reverse order. The CuGeO₃ electrode shows a much improved coulombic efficiency (74%) in the first cycle, which is indebted to a facilitated Ge oxidation with a much reduced electrode polarization. This feature has been explained by the favorable roles provided by the in situ generated nano-sized metallic Cu particles that make such an intimate contact with the nano-sized Ge and Li₂O that they can catalyze Li₂O decomposition and provide an electronic conductive network for Ge oxidation. A similar favorable effect was observed with the other ternary oxides (FeGeO₃ and CoGeO₃), wherein the formation of nano-sized metallic Fe and Co can be assumed.     

Removal, preconcentration and determination of trace heavy metal ions in water samples by AAS via chemically modified silica gel N-(1-carboxy-6-hydroxy) benzylidenepropylamine ion exchanger

The use of chemically modified silica gel N-(1-carboxy-6-hydroxy) benzylidenepropylamine (SiG-CHBPA), ion exchanger for removal and preconcentration of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in natural water samples collected from River Nile, Mediterranean Sea and other locations followed by their consecutive AAS determination was described. The effects on the percentage of recovered metal ions including mass change of ion exchanger, stirring time, pH of sample solutions and eluent concentration were studied. The distribution coefficient K_d, ml g^− 1 and the percentage concentration of the studied metal ions on the ion exchanger at equilibrium, C_M,_eqm ,% (Recovery, %) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficients, log K_d are 3-6.3. The interfering effects of some foreign ions on the removal, preconcentration and determination of the investigated metal ions were described. The metal-chelates formed between the ion exchanger and the studied metal ions were characterized by IR (absorption and reflectance), UV spectrometry, potentiometric titration and thermal analysis (TG and DTG). The reliability of the present method was confirmed by the comparison with a standard solvent extraction method. The present method is simple and rapidly applicable for the determination of the studied metal ions, ng ml^− 1 in different natural water samples.     

Effect of electrolyte addition on activity of (Ga1−xZnx)(N1−xOx) photocatalyst for overall water splitting under visible light

Effects of electrolyte addition on photocatalytic activity of (Ga_1−xZn_x)(N_1−xO_x) modified with either Rh_2−yCr_yO₃ or RuO₂ nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh_2−yCr_yO₃ is confirmed to selectively promote the photoreduction of H⁺, while RuO₂ functions as both H₂ evolution sites and as efficient O₂ evolution sites. The activity of Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) is found to be suppressed in the presence of Cl⁻, which undergoes oxidation by photogenerated holes in the valence band of (Ga_1−xZn_x)(N_1−xO_x). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl⁻ to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A₂SO₄ (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H₂ and O₂ is also demonstrated using Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) catalyst under visible light.     

Preparation of heterostructure g-C3N4/ZnO nanorods for high photocatalytic activity on different pollutants (MB,RhB, Cr(VI) and eosin)

The g-C₃N₄/ZnO nanorods were prepared by simple hydrothermal, grinding and calcination methods. The characterization of g-C₃N₄/ZnO nanorods was done by different analytical techniques such as SEM, TEM, XRD, XPS, FT-IR and UV–Vis. g-C₃N₄/ZnO nanorods with heterostructures have been successfully synthesized without changing the structure between the monomers, which broadens the visible light response range and improves several major pollutants in water degradation rate. Photocatalytic studies were done for the degradation of MB, RhB, Cr(VI) and eosin which are almost fully degraded. The experimental results show that the photocatalytic performance of the nanorods is much better than others. The g-C₃N₄/ZnO photocatalyst has excellent stability and repeated cycle performance. Basing on the results of comprehensive free radical trapping test and ESR tests, it is proposed that the main active substance of the catalyst for degrading dyes is ·0₂^-, and ·OH played significant roles in the degradation process. A good photocatalytic mechanism has been proven.     

Removal properties of crosslinked poly(2‐acrylamido glycolic acid) for trace heavy metal ions: Effect of pH,temperature, contact time,and salinity on the adsorption behavior

Crosslinked poly(2‐acrylamido glycolic acid) resin was synthesized by radical polymerization. This resin contains three potential ligand groups and was studied as an adsorbent of trace heavy metal ions from a saline aqueous solution and sea water by using the Batch equilibrium procedure. Adsorption characteristics of the resin toward Cu(II), Ni(II), Cd(II), and Pb(II) were studied spectrophotometrically, both in competitive and noncompetitive conditions. The effect of pH, contact time, amount of sorbent, temperature, and salinity were studied. The resin showed a high affinity particularly for Ni(II). It was possible to remove completely Ni(II) and Pb(II) from the resin by 4M HNO₃. The retention properties of the resin were also investigated for Cu(II) contained in natural sea waters. The retention behavior was similar to that of the synthetic metal ion aqueous solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2614–2621, 2003     

Effects of alkali metal ion on imprinting GRIN microstructure in GeS2-Ga2S3-MCl (M=Na,K, Cs) glasses for visible to mid-infrared microgratings

Gradient refractive index (GRIN) micro-optics present unique opportunities for control of the chromatic properties, new degrees of freedom for optical design as well as the potential for use in new optical system applications. GRIN microgratings were imprinted in GeS₂-Ga₂S₃-MCl (M = Na, K, Cs) chalcohalide glasses by microthermal poling, and the effects of the type and concentration of alkali cations on their performance were investigated. Two effective imprinting formation regions of the GRIN microstructure based on the poling saturation voltage (U_s) and glass composition are observed at fixed poling time and temperature. The U_s increases from 140 to 750 and 2600 V in accordance with the activation energy (E_a) of alkali ions (Na⁺ to K⁺ and Cs⁺) increasing from 45.15 to 58.62 and 92.58 kJ/mol for studied samples. The saturated numbers of diffraction order (N_s) of the gratings in these samples are 7, 9 and 6, respectively, the highest number being provided by the K⁺-containing sample. This is in accordance with imprinting-induced phase differences (0.14λ, 0.19λ and 0.09λ) measured in the fabricated samples containing Na⁺, K⁺ and Cs⁺ ions. Furthermore, the U_s of samples decreases from 1500 to 300 V with four concentrations of K⁺ from 10 to 30%, associated with their E_a of K⁺ decreasing from 69.62 to 53.46 kJ/mol, while N_s increases from 8 to 14, which is attributed to the increase of the phase difference in the GRIN structures. The controllable GRIN microstructures are realized by adjusting the type and concentration of alkali cations in chalcohalide glasses, which is expected to drive the design of broadband GRIN microgratings.