Morphological, optical and photocatalytic properties of TiO2–Fe2O3 multilayers

Morphological, optical and photocatalytic properties of TiO₂, Fe₂O₃ and TiO₂–Fe₂O₃ samples (formed by 1, 3 and 5 coatings) were studied. The layers were deposited on glass substrate by the sol–gel method. The catalytic activity of the samples was studied by the photodecomposition of methylene blue (MB) under visible light illumination. The FTIR results indicate that all samples present surface OH radicals that are bound either to the Ti or Fe atoms. This effect is better visualized at larger number of coatings in the TiO₂–Fe₂O₃/glass systems. Also, two mechanisms are observed during the photodecomposition of the MB.     

Cathodic shift and improved photocurrent performance of cost-effective Fe2O3 photoanodes

We successfully fabricated cost-effective and efficient pulse electrodeposited Fe₂O₃ photoanodes for PEC water splitting application. Surface modifications of Fe₂O₃ by oxygen evolution catalysts like cobalt phosphate (Co–Pi), a monoclinic BiVO₄ or both showed cathodic/anodic shift in photocurrent with significantly improved photo-response.     

Improved separation efficiency of photogenerated carriers for Fe2O3/SrTiO3 heterojunction semiconductor

To investigate the mechanisms of the improvement on separation efficiency of photogenerated carriers, a Fe₂O₃/SrTiO₃ heterojunction semiconductor with an improved separation efficiency was successfully prepared. The heterojunction semiconductor was characterized with X-ray diffraction (XRD), UV–vis absorption spectrum, scanning electron microscope (SEM) and surface photovoltage (SPV) spectroscopy. The energy band diagrams of Fe₂O₃ and SrTiO₃ were determined with X-ray photoelectron spectroscopy (XPS), based on which the conduction band offset (CBO) between Fe₂O₃ and SrTiO₃ was quantified to be 1.26 ± 0.03 eV. The recombination of photogenerated carriers was investigated with photoluminescence (PL) spectrum, which indicates that the formation of Fe₂O₃/SrTiO₃ decreases the recombination. Thus the improved separation efficiency is mainly due to the energy difference between the conduction band edges of Fe₂O₃ and SrTiO₃, and the decreased electron-hole recombination for Fe₂O₃/SrTiO₃.     

Study on photocurrent of bilayers photoanodes using different combination of WO3 and Fe2O3

Bilayer photoanodes were prepared onto glass substrates (FTO) in order to improve generated photocurrents using UV-vis light by water splitting process. A comparative study of photocatalytic was performed over the films surface using Fe₂O_3, WO₃ and mixture of bicomponents (Fe₂O₃:WO₃). Different types of films were prepared using Fe₂O_3, WO₃ and bicomponents (mixture) on FTO substrates. The films were grown by sol gel method with the PEG-300 as the structure-directing agent. The photo-generated of the samples were determined by measuring the currents and voltages under illumination of UV-vis light. The morphology, structure and related composition distribution of the films have been characterized by SEM, XRD and EDX respectively. Photocurrent measurements indicated surface roughness as the effective parameter in this study. The deposited surfaces by bicomponents or mixture are flat without any feature on the surface while the deposited surfaces by WO₃ appears rough surface as small round (egg-shaped particles) and cauliflower-like. The surface deposited by Fe₂O₃ show rough no as well as WO₃ surface. The deposited surfaces by WO₃ reveal the higher value of photocurrent measurement due to surface roughness. Indeed, the roughness can be effective in increasing contact surface area between film and electrolyte and diffuse reflection (light scattering effect). The solution (Fe₂O₃:WO₃) shows the low photocurrent value in compare to WO₃ and Fe₂O₃ hat it may be due to decomposition the compound at 450 ± 1 °C to iron-tungstate Fe₂(WO₄)₃.     

Photoelectrochemical behavior of In2S3 formed on sintered In2O3 pellets

Microcrystals of In₂S₃ were formed on sintered In₂O₃ pellets by sulfurizing in H₂S atmosphere. The flat band potential of compound In₂S₃|In₂O₃ electrodes was evaluated as −1.0 V vs Ag|AgCl in 1 M KOH, 1 M Na₂S, 10⁻² M S. Significantly enhanced photocurrent was observed on compound In₂S₃|In₂O₃ electrodes with a lower degree of sulfurization to that of compound In₂S₃|In₂O₃ electrodes with higher degree of sulfurization. Photocurrent generation of compound In₂S₃|In₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization.     

Influence of surfactants on Fe2O3 nanostructure photoanode

Fe₂O₃ nanostructures photoanodes were prepared via sol–gel spin-coating method onto fluorine-doped tin oxide glass substrates using six different surfactants: polyethylene glycol (PEG-300), Triton X-100, pluronic F127, cetyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium bromide (OTAB) and tetradecyltrimethylammonium bromide (TTAB). The resulting films have thickness from 520 ± 10 to 980 ± 10 nm after calcinations at 450 °C in the air. A comparative study of photocatalytic activity of thin films was performed. The photo-generated samples were determined by measuring the currents and voltages under illumination of UV–vis light. The highest photocurrent density of 1.77 mA/cm² at 1 V/SCE, under illumination intensity of 100 mW cm⁻² from a solar simulator with a global AM 1.5 filter, were produced by TTAB treated sample. The optical properties, morphology, surface roughness and structure of the films were also characterized by UV–visible spectroscopy, SEM, AFM and XRD. The results are consistent with photocatalytic performance: TTAB treated sample has the highest grain size and optical absorption. The improved performance of this sample can be attributed to the crystallinity process of TTAB, which leads to the larger grain size and highest photocatalytic activity. The study demonstrates that photoelectrochemical performance of metal oxide can be improved by simply changing surfactant. The results highlighted the superior performance of cationic surfactants over non-ionic surfactants in preparing Fe₂O₃ photoanodes by sol–gel method. Moreover, the study showed that decreasing hydrocarbon tail of cationic surfactants can increase the crystallite size and improve photocatalytic activity.     

Catalytic effect of Gd2O3 and Nd2O3 on hydrogen desorption behavior of NaAlH4

This study investigated the effect of Nd₂O₃ and Gd₂O₃ as catalyst on hydrogen desorption behavior of NaAlH₄. Pressure-content-temperature (PCT) equipment measurement proved that both two oxides enhanced the dehydrogenation kinetics distinctly and increasing Nd₂O₃ and Gd₂O₃ from 0.5 mol% to 5 mol% caused a similar effect trend that the dehydrogenation amount and average dehydrogenation rate increased firstly and then decreased under the same conditions. 1 mol% Gd₂O₃–NaAlH₄ presented the largest hydrogen desorption amount of 5.94 wt% while 1 mol% Nd₂O₃–NaAlH₄ exerted the fastest dehydrogenation rate. Scanning Electron microscopy (SEM) analysis revealed that Gd₂O₃–NaAlH₄ samples displayed uniform surface morphology that was bulky, uneven and flocculent. The difference of Nd₂O₃–NaAlH₄ was that with the increasing of Nd₂O₃ content, the particles turned more and more big. Compared to dehydrogenation behavior, this phenomenon demonstrated that small particles structure were beneficial to hydrogen desorption. Besides, the further study found that different catalysts and addition amounts had different effects on the microstructure of NaAlH_4.     

Preparation and photoelectrochemical properties of functional carbon nanotubes and Ti co-doped Fe2O3 thin films

Functional carbon nanotubes (CNTs) were incorporated into Ti-doped Fe₂O₃ thin films by a facile, one-step co-electrodeposition method. The films were characterized by X-ray diffraction, scanning electron microscopy, UV–visible absorption, and X-ray photoelectron spectroscopy. The introduction of CNTs results in a better absorption in visible region and greatly enhances the photoelectrochemical properties of the Ti–Fe₂O₃ films. The improved photoelectrochemical properties of the CNTs and Ti co-doped Fe₂O₃ films are due to the charge equilibration which interplays between the Ti–Fe₂O₃ and CNTs. The effect of CNTs to mediate fast charge transfer and to retard charge recombination rate in the composites is also demonstrated by kinetics analysis and electrochemical impedance spectroscopy. The influence of different groups-modified CNTs and different content of CNTs was also studied. The highest photocurrent is 4.5 mA/cm² at 1.23 V (vs. RHE) obtained by incorporating 0.10 mg/mL amino-group modified CNTs in the Ti–Fe₂O₃ film. The amino-functionalized CNTs doped film exhibits the highest photoelectric response compared with those doped by the pristine and acid-treated CNTs under the same conditions, which can be ascribed to the better hydrophilicity and dispersibility of the amino-functionalized CNTs.     

Magnetic field effects on selective catalytic reduction of NO by NH3 over Fe2O3 catalyst in a magnetically fluidized bed

Selective catalytic reduction (SCR) of NO from simulated flue gas by ammonia with Fe₂O₃ particles as the catalyst was performed using a magnetically fluidized bed (MFB). X-ray diffraction (XRD) spectroscopy and Brunauer–Emmett–Teller (BET) method were used to analyze Fe₂O₃ catalyst. Important effects of magnetic fields were observed in the SCR of NO by ammonia over Fe₂O₃ catalyst. The apparent activation energies of SCR were reduced by external magnetic fields, and the SCR activity of Fe₂O₃ catalyst was improved with the magnetic fields at low temperatures. Thus the scope of temperature with high efficiency of NO removal was extended from 493–523 K to 453–523 K by magnetic fields. Magnetic fields of 0.01–0.015 T were suggested for NO removal on Fe₂O₃ catalyst with MFB. The results suggested that the magnetoadsorption of NO onto Fe₂O₃ surface together with NH₂ and NO free radicals effects induced by the external magnetic fields both acted to improve the rate of SCR of NO on Fe₂O₃ catalyst. On the other hand, magnetic field effects were also attributed to improved gas–solid contact in MFB.     

Visible light induced hydrogen evolution on new hetero-system ZnFe2O4/SrTiO3

The physical properties and photoelectrochemical characterization of the spinel ZnFe₂O₄, elaborated by chemical route, have been investigated for the hydrogen production under visible light. The forbidden band is found to be 1.92 eV and the transition is indirectly allowed. The electrical conduction occurs by small polaron hopping with activation energy of 0.20 eV. p-type conductivity is evidenced from positive thermopower and cathodic photocurrent. The flat band potential (0.18 V_SCE) determined from the capacitance measurements is suitably positioned with respect to H₂O/H₂ level (−0.85 V_SCE). Hence, ZnFe₂O₄ is found to be an efficient photocatalyst for hydrogen generation under visible light. The photoactivity increases significantly when the spinel is combined with a wide band gap semiconductor. The best performance with a hydrogen rate evolution of 9.2 cm³ h⁻¹ (mg catalyst)⁻¹ occurs over the new hetero-system ZnFe₂O₄/SrTiO₃ in Na₂S₂O₃ (0.025 M) solution.     

Effect of carbonaceous materials on electrochemical properties of nano-sized Fe2O3-loaded carbon as a lithium battery negative electrode

Nano-sized Fe₂O₃-loaded carbon material was prepared by loading Fe₂O₃ on carbon using various carbonaceous materials. Carbonaceous materials strongly affected the electrochemical behavior of nano-sized Fe₂O₃-loaded carbon. Among the carbons used, nano-carbons such as acetylene black (AB), tubular carbon nanofibers (CNF), and platelet CNF provided larger capacities than other carbons. This may be due to the greater surface area of nano-carbon, which gives a greater distribution of nano-sized Fe₂O₃ particles than other carbons and delivers a greater capacity than other carbons. Investigation of the first-cycle materials by X-ray photoelectron spectroscopy (XPS) revealed that Fe₂O₃ was reduced to Fe metal in the charge process (reduction of Fe₂O₃), and, conversely, Fe metal was not completely oxidized to Fe₂O₃ during discharge (oxidation of Fe). This result may be due to the covering of non-conductive Li₂O formed during charging.     

Photo-catalytic hydrogen production over Fe2O3 based catalysts

The hydrogen photo-evolution was successfully achieved in aqueous (Fe_1−xCr_x)₂O₃ suspensions (0 ≤ x ≤ 1). The solid solution has been prepared by incipient wetness impregnation and characterized by X-ray diffraction, BET, transport properties and photo-electrochemistry. The oxides crystallize in the corundum structure, they exhibit n-type conductivity with activation energy of ∼0.1 eV and the conduction occurs via adiabatic polaron hops. The characterization of the band edges has been studied by the Mott Schottky plots. The onset potential of the photo-current is ∼0.2 V cathodic with respect to the flat band potential, implying a small existence of surface states within the gap region. The absorption of visible light promotes electrons into (Fe_1−xCr_x)₂O₃-CB with a potential (∼−0.5 V_SCE) sufficient to reduce water into hydrogen. As expected, the quantum yield increases with decreasing the electro affinity through the substitution of iron by the more electropositive chromium which increases the band bending at the interface and favours the charge separation. The generated photo-voltage was sufficient to promote simultaneously H₂O reduction and SO₃²⁻ oxidation in the energetically downhill reaction (H₂O + SO₃²⁻ → H₂ + SO₄²⁻, ΔG = −17.68 kJ mol⁻¹). The best activity occurs over Fe_1.2Cr_0.8O₃ in SO₃²⁻ (0.1 M) solution with H₂ liberation rate of 21.7 μmol g⁻¹ min⁻¹ and a quantum yield 0.06% under polychromatic light. Over time, a pronounced deceleration occurs, due to the competitive reduction of the end product S₂O₆²⁻.     

Reduction characteristics of CuFe2O4 and Fe3O4 by methane; CuFe2O4 as an oxidant for two-step thermochemical methane reforming

The reduction characteristics of CuFe₂O₄ and Fe₃O₄ by methane at 600–900 °C were determined in a thermogravimetric analyzer for the purpose of using CuFe₂O₄ as an oxidant of two-step thermochemical methane reforming. It was found that the addition of Cu to Fe₃O₄ largely affected the reduction kinetics and carbon formation in methane reduction. In the case of CuFe₂O₄, the reduction kinetics was found to be faster than that of Fe₃O₄. Furthermore, carbon deposition and carbide formation from methane decomposition were effectively inhibited. In case of Fe₃O₄, Fe metal formed from Fe₃O₄ decomposed methane catalytically, that lead to the formation of graphite and Fe₃C phases. It is deduced that Cu in CuFe₂O₄ enhanced reduction kinetics, decreased reduction temperature and prevented carbide and graphite formation. Additionally, methane conversion and CO selectivity in the syngas production step with CuFe₂O₄ were in the range of 33.5–55.6% and 54.9–59.6%, respectively.     

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY₂O₃–Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al₂O₃ catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH₄ conversion increased with elevating levels of Y₂O₃ from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY₂O₃–Al₂O₃ catalysts maintained high activity after 24 h on stream, while Ni/Al₂O₃ had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.     

g-C3N4/TiO2可见光催化降解磺胺甲恶唑的研究

以TiO₂颗粒和三聚氰胺为原料,采用高温煅烧法制备g-C₃N₄/TiO₂复合光催化材料,研究其对仿生生态系统中磺胺类抗生素的去除效果。利用扫描电子显微镜（SEM）、X射线衍射仪(XRD)、傅里叶变换红外光谱仪（FTIR）、紫外可见分光光度计（UV-vis DRS）对g-C₃N₄/TiO₂进行表征,并研究在可见光条件下g-C₃N₄/TiO₂对溶液中磺胺甲恶唑（SMX）的光催化降解效果。结果表明,g-C₃N₄/TiO₂具有良好的光催化活性,在可见光照射下,当g-C₃N₄/TiO₂投加量为0.2 g·L^-1时,对初始质量浓度为200 μg·L^-1的SMX的去除率可达84.3%。在相同条件下,而g-C₃N₄和TiO₂只能分别去除21.0%和16.0%的SMX,同时在仿生系统中12.37 g·m^-2 g-C₃N₄/TiO₂可以去除95.35%的SMX。通过质谱分析推测,SMX可能的降解路径分别为S—N键断裂、C—N键断裂、S—C键断裂、SMX的羟基化和SMX上氨基的硝化反应,两种可能的中间产物分别为对氨基苯磺酰胺和3-氨基-5-甲基异恶唑。     

Influence of the method of synthesis on hydrogen adsorption properties of mesoporous binary B2O3/Al2O3 gel systems

Three series of binary oxide systems B₂O₃/Al₂O₃ were prepared and the effect of alumina on dispersion of boron (B₂O₃) component was investigated. The aim of the study was to achieve a maximum dispersion of B₂O₃ in the Al₂O₃ a gel matrix that would lead to increased sorption capacity on boron oxide. Many attempts were made to establish the preparation conditions that would lead to a maximum dispersion of B₂O₃ in the Al₂O₃ gel matrix needed to increase the hydrogen sorption capacity on boron oxide. The systems were characterized by X-ray diffraction, SEM, TEM and low temperature nitrogen adsorption. Hydrogen adsorption was tested in the volumetric system.Results of the study showed that the amount of hydrogen adsorbed on B₂O₃ depended not only on the surface area of the system but also on the separation of B₂O₃ domains in Al₂O₃ gel network. Irrespective of the method of synthesis of the binary oxide system, the dispersion of B₂O₃ phase reflected in the amount of hydrogen adsorbed was the highest for the systems of the lowest B/Al molar ratios studied, i.e. for B/Al = 0.25.     

Photoelectrochemical study on charge separation mechanisms of Bi2WO6 quantum dots decorated g-C3N4

In this paper, the Bi₂WO₆ quantum dots (QDs) decorated g-C₃N₄ nanoplates were successfully synthesized via a one-step hydrothermal method. The morphology of the Bi₂WO₆ could be tuned from regular nanoplates to quantum dots. Remarkably, the Bi₂WO₆ QDs coupled with g-C₃N₄ not only prevented the aggregation, but also decreased the size of Bi₂WO₆ QDs about 3.5 nm. Meanwhile, the charge separation mechanisms of Bi₂WO₆ QDs/g-C₃N₄ photocatalyst were investigated by electrochemical impedance spectra, Mott-Schottky and linear voltammetry scans. As a result, the photoelectrochemical (PEC) experiments provided forceful evidence for the charge separation mechanism of the Bi₂WO₆ QDs/g-C₃N₄ Z-scheme. The Z-scheme system not only accelerated the separation efficiency of charge, but also improved the ability of PEC water splitting at measured 1.23 V vs. RHE.     

Iron oxide (n-Fe2O3) nanowire films and carbon modified (CM)-n-Fe2O3 thin films for hydrogen production by photosplitting of water

Iron oxide n-Fe₂O₃ nanowire photoelectrodes were synthesized by thermal oxidation of Fe metal sheet (Alfa Co. 0.25 mm thick) in an electric oven then tested for their photoactivity. The photoresponse of the n-Fe₂O₃ nanowires was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which is proportional to photocurrent density, J_p. The optimized electric oven-made n-Fe₂O₃ nanowire photoelectrodes showed photocurrent densities of 1.46 mA cm⁻² at measured potential of 0.1 V/SCE at illumination intensity of 100 mW cm⁻² from a Solar simulator with a global AM 1.5 filter. For the optimized carbon modified (CM)-n-TiO₂ synthesized by thermal flame oxidation the photocurrent density for water splitting was found to increase by two fold to 3.0 mA cm⁻² measured at the same measured potential and the illumination intensity. The carbon modified (CM)-n-Fe₂O₃ electrode showed a shift of the open circuit potential by −100 mV/SCE compared to undoped n-Fe₂O₃ nanowires. A maximum photoconversion efficiency of 2.3% at applied potential of 0.5 V/E_aoc was found for CM-n-Fe₂O₃ compared to 1.69% for n-Fe₂O₃ nanowires at higher applied potential of 0.7 V/E_aoc. These CM-n- Fe₂O₃ and n- Fe₂O₃ nanowires thin films were characterized using photocurrent density measurements under monochromatic light illumination, UV-Vis spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Improvement of hydrogen storage characteristics of Mg by planetary ball milling under H2 with metallic element(s) and/or Fe2O3

Among samples of Mg-Ni, Mg-Ni-5Fe₂O₃, and Mg-Ni-5Fe, Mg-Ni-5Fe had the highest hydriding and dehydriding rates. For the as-milled Mg-Ni-5Fe alloy and the hydrided Mg-Ni-5Fe alloy after activation, the weight percentages of the constituent phases were calculated using the FullProf program. The creation of defects and the diminution of Mg particle size through reactive mechanical grinding and hydriding-dehydriding cycling, and the formation of the Mg₂Ni phase are considered to increase the hydriding and dehydriding rates. Mg-14Ni-2Fe-2Ti-2Mo had higher hydriding and dehydriding rates than did any of the other samples (Mg-Ni, Mg-Ni-5Fe₂O₃, Mg-Ni-5Fe, and Mg-14Ni-6Fe₂O₃) prepared in this work.     

Synthesis of g-C3N4/TiO2 with enhanced photocatalytic activity for H2 evolution by a simple method

A photocatalyst composed of graphite-like carbon nitride (g-C₃N₄) and TiO₂ was fabricated by a simple method to calcine the mixture of melamine and TiO₂ precursor. The photocatalyst has enhanced photoactivity for hydrogen evolution from water. Characterization by XRD, FTIR, SEM and elemental analysis showed that the crystal structure and morphologies of composites were affected by the amount of melamine in the composite. The UV–Vis characterization displayed that the optical absorption range of g-C₃N₄/TiO₂ hybrid was broadened with a synergistic effect. The photoactivity for H₂ evolution was shown that the best result obtained from the composite with 67 wt% melamine has about 5 times improvement compared with bare TiO₂ or pure g-C₃N₄. The enhanced photoactivity might be related with the favorable structure resulted from heat-treatment temperature, and the content of g-C₃N₄ participating in wide optical absorption, separation and transportation of electronic-holes, as well as morphology of composite.