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In this work, we proposed to combine oxalic acid and ferric ions in very low concentrations to create new, economic, and effective homogeneous photo-Fenton catalytic systems for the degradation of methylene blue. The effects of ferric concentration, H2C2O4 concentration, pH, and tert-butanol on the catalytic activity were also investigated. According to the experimental results, Fe3+ ions exhibited impressive catalytic performances in the presence of H2C2O4 at concentrations below type B (5.0 mg.l–1) from the Vietnam National Technical Regulation on Industrial Wastewater. Specifically, a ferric concentration of 3.0 mg.l–1, H2C2O4 concentration of 10–3 mol.l–1, and pH value of 3 were found to be the best conditions for MB degradation under UVA light. Furthermore, owing to a very low concentration of ferric ions, iron sludge formation can be avoided after wastewater treatment, which makes the photo-Fenton process suitable for practical applications.

In this work, we proposed to synthesize CuFe2O4/Fe2O3 core-shell materials with different Fe2O3 contents in order to create new and efficient photo-Fenton-like catalysts for the degradation of methylene blue with oxalic acid as a radical-producing source. The catalysts were prepared through two stages: first, CuFe2O4 was prepared by a hydroxide coprecipitation – annealing method and then, Fe2O3 was immobilized on CuFe2O4 surface by a simple impregnation – annealing procedure. According to the experimental results, our CuFe2O4/Fe2O3 core-shell materials exhibit high photo-Fenton-like catalytic activity for the degradation of methylene blue under both UVA light and visible light, as well as good ferromagnetic properties, which allows them to be easily separated from the solution by a magnet. Among them, the catalyst prepared with the molar CuFe2O4/Fe2O3 ratio of 1:2 showed the best catalytic performance with the rate constant of 2.103 h–1 under UVA light and 0.542 h–1 under visible light, which were 2 times higher than CuFe2O4 sample. The enhanced catalytic activities of our core-shell materials can be attributed to the high content of surface Fe3+ species, high specific surface area and the presence of rod-like Fe2O3 particles on their surface.

Metal–organic frameworks have been extensively studied in catalysis owing to their unique physicochemical properties. However, this class of materials has not yet been directly applied to the catal...

A facile approach is demonstrated for the fabrication of Cu-ZnO-based hybrid nanostructures for the catalytic CO2 conversion to methanol. The method combines colloid stabilization of Al2O3 nanoparticles (as support material) and controlled co-precipitation of Cu (active metal) and ZnO (promoter) onto the Al2O3 nanoparticles. Complementary approaches, including X-ray diffractometry, Brunauer-Emmett-Teller surface area analysis, N2O pulse chemisorption, CO2-based temperature-programmed desorption, transmission electron microscopy coupled with energy dispersive spectroscopy, inductively coupled plasma optical emission spectrometry and thermal gravimetric analysis are employed for the characterization of catalyst materials. The results show a successful synthesis of ultrafine Cu-ZnO nanocrystallites deposited on the Al2O3 nanoparticle clusters (Cu-ZnO@Al2O3). Hybridization with Al2O3 nanoparticles enhanced metal dispersion and number of basic sites of the Cu-ZnO-based nanocatalyst. Aminosilane-based surface functionalization on the Al2O3 nanoparticle increased metal surface area in the hybrid nanostructure. The CO2 conversion catalyzed by the synthesized Cu-ZnO@Al2O3 was shown to be proportional to active surface area of the hybrid nanostructure. An optimum selectivity of the synthesized catalyst was identified (≈47–49%) when the mass fraction of Al2O3 was (35–36) %, in correspondence to the highest moderate basicity of the synthesized hybrid nanostructures. The highest yield of methanol achieved 12989 ± 2007 µmolg−1 h−1 by the developed Cu-ZnO@Al2O3. Our work demonstrates a prototype study of fabricating high-performance hybrid nanocatalyst with the support of mechanistic understanding in material synthesis for the synergistic catalysis of CO2 hydrogenation to methanol.

ZnO nanoparticles were modified with KF using thermal shock method at various temperatures in order to improve the photocatalytic activity of ZnO under both UVA and visible light irradiation. The influences of KF-modification on the crystal structure, morphology, UV–visible absorption, specific surface area as well as surface structure of ZnO were respectively characterized by XRD, FE-SEM, UV–Visible diffuse reflectance, N2 adsorption and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA irradiation. According to the results, the thermal shock process with KF did not modify the structure, the particle size and the optical properties of ZnO nanoparticles but successfully increase their UVA and visible light induced photocatalytic activity. This enhancement of activity may be attributed to the increase of surface hydroxyl groups and zinc vacancies of modified ZnO samples. Keywords: ZnO nanoparticles, Thermal shock, KF, Methylene blue, Photocatalytic activity

Ag-modified ZnO, F-modified ZnO and (Ag, F)-modified ZnO nanoparticles were prepared by thermal shock method in order to study the effects of doping agents on their crystal structure, morphology, optical properties, surface structure and photocatalytic activity. The catalysts were characterized by XRD, FE-SEM, TEM, FTIR, UV–Visible diffuse reflectance and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA and visible light irradiation. According to the results, the thermal shock process with AgNO3 did not modify the morphology but successfully created silver species on the surface of ZnO, which induces the visible light absorption and then increases the photocatalytic activity. The enhanced phototcatalytic performance was also observed in F-modified ZnO sample owing to the increase of surface hydroxyl groups and the formation of zinc vacancies. Among three modified ZnO samples, (Ag, F)-modified ZnO was found to be the best sample with the photocatalytic activity enhanced by the factor of 3 under both UVA and visible light, which may be attributed to the synergic effects of AgNO3 and KF used in thermal shock process. Keywords: ZnO nanoparticles, Ag-doping, F-doping, Thermal shock method, Photocatalytic activity

N-doped ZnO photocatalysts with enhanced UVA-light and visible-light-driven activities were prepared by hydrothermal treatment of various zinc-containing precursors, including zinc oxide, zinc hydr...

In this work, Al-doped ZnO nanoparticles were prepared with different Al contents by a simple co-precipitation method in order to suppress the photocatalytic activity without modifying their UV lig...

Controlled synthesis of metal–organic framework (MOF)-derived Mg-Zn hybrid nanostructure was demonstrated for the development of basic catalysts applied in biodiesel production from soybean oil. Two types of Mg-Zn hybrid nanostructures were successfully fabricated under different atmospheres (Ar, air), (1) MgO nanoparticles encapsulated in Zn-based MOF (MgO@Zn-MOF) and (2) MgO nanoparticles uniformly decorated on ZnO nanoparticles derived from Zn-MOF (MgO@ZnO), respectively. Ultrafine MgO nanoparticles (

The aim of the study was to prepare magnetic photo-Fenton catalysts based on CoFe2O4 by polyethylene glycol-assisted sol-gel method for the degradation of methylene blue under UVA and visible light irradiation with H2C2O4 as a radical producing source. The catalysts were synthesized at different annealing temperatures in order to investigate the influence of annealing temperature on their crystal structure, morphology, surface functional groups, magnetic properties, and their photo-Fenton catalytic activity. According to the results, when the annealing temperature increased from 600 to 800 °C, the content of CoFe2O4 cubic spinel phase was significantly enhanced, the amount of Fe3+ ions in the tetrahedral sites also increased on the surface of samples, which improved the magnetic properties as well as the photo-Fenton catalytic performance under both UVA and visible light. However, at the annealing temperature of 900 °C, the photo-Fenton activity was declined, which can be attributed to the growth of catalytic particles and the decrease of Fe3+ ions on their surface.

Magnetic Mn2O3/CuFe2O4 catalysts for the synthesis of p-hydroxybenzaldehyde were prepared by a facile in-situ growth method at different annealing temperatures in order to study the influences of annealing temperatures on their structure, atomic composition, morphology, surface functional groups, magnetic and catalytic properties. The catalytic performance was evaluated via the aerobic oxidation of p-hydroxybenzyl alcohol to p-hydroxybenzaldehyde. All Mn2O3/CuFe2O4 catalysts exhibited the activity for the synthesis of p-hydroxybenzaldehyde with the selectivity of 100% and ferromagnetic properties, which allows them to be easily separated from the solution by a magnet. When the annealing temperature increased from 300 to 500 °C, the atomic manganese content on the surface and the particle size were not modified, but highly crystalline α-Mn2O3 was formed on the surface of CuFe2O4 nanoparticles, leading to the enhanced conversion of p-hydroxybenzyl alcohol. It was also observed that the elemental composition and the core–shell structure of this catalyst remained unchanged after the synthesis of p-hydroxybenzaldehyde, which ensures its magnetic separation. However, when the annealing temperature rose up to 700 °C, the catalytic activity was reduced, due to the increase of Mn–O bonding strength and the growth of particles.

In this work, we proposed to immobilize Fe2O3 nanoparticles on the surface of magnetic CuFe2O4 particles by a facile impregnation – annealing method at different annealing temperatures (200, 300, 400 and 500°C) in order to create new heterogeneous photo-Fenton catalysts with enhanced catalytic performance for the oxidation of organic dyes. The influences of annealing temperatures used in the synthesis procedure on the phase composition, the morphology, the particle size and the surface functional groups of our catalysts were investigated by XRD, FE-SEM and FTIR techniques, respectively. The photo-Fenton catalytic performance was evaluated by the degradation of methylene blue under both UVA and visible light illumination in the presence of H2C2O4 as radical-producing source. According to the experimental results, Fe2O3 nanoparticles were successfully coated on CuFe2O4 surface, which successfully formed the α-Fe2O3 phase in the phase composition and also increased the Fe3+ content on the surface. As a consequence, the rate constant of photo-Fenton catalytic degradation of methylene blue over these samples were clearly improved. More especially, owing to the good magnetic property of CuFe2O4 component, our CuFe2O4/Fe2O3 samples were easy to be separated from the solution by a magnet, making them more feasible in practical applications of environmental treatment. Among our catalytic samples, the CuFe2O4/Fe2O3 sample annealed at 300°C showed the best performance with the highest rate constants under both UVA light and visible light. Its catalytic activities was found to be 6.8 times higher than CuFe2O4 under UVA light and 2.1 times higher than CuFe2O4 under visible light. However, when the annealing temperature was up to 500°C, the catalytic activity was reduced, which can be explained by the growth of particles and the stabilization of surface Fe-O bonds.

The fluorination of perlite granules and the immobilization of ZnO nanoparticles on the perlite surface were carried out at the same time by a simple impregnation method to create new highly photocatalytic materials which are easily separated from reaction solutions after treatment. The influence of perlite fluorination on the crystal structure, morphology, UV-visible absorption, and surface functional groups of ZnO, as well as on the ZnO content on perlite, was respectively characterized by XRD, FE-SEM, UV-Visible diffuse reflectance, FTIR and atomic absorption spectrometry. The photocatalytic activity was evaluated via the extent of degradation of methylene blue under UVA irradiation. According to the results, the fluorination of perlite leads to numerous effects on ZnO, such as the decline of ZnO cell parameters, the increase of ZnO content on perlite granules (resulting in the enhancement of light absorption in UVA range), and the decrease of ZnO particle size, which can effectively improve its photocatalytic performance. The photocatalysts were also found to be able to stay afloat on water, allowing for easy separation from the reaction solution.

Magnetic photo-Fenton catalysts based on spinel CuFe2O4 were successfully prepared by the starch-assisted sol–gel method. Various synthetic conditions such as annealing temperatures (700, 800 and 900 °C) and molar ratios of Cu2+/Fe3+/C6H10O5 in the precursor solution (from 1:2:2 to 1:2:4) were, respectively, used in order to study the influences of annealing temperatures and precursor starch contents on the magnetic and catalytic properties of CuFe2O4 powders. The photo-Fenton catalytic activity was evaluated via the degradation of methylene blue under ultraviolet and visible irradiation with H2C2O4 as a new oxidizing agent. According to the results, when the annealing temperature increased to 800 °C, the spinel CuFe2O4 phase amount was increased, which strongly enhances the photo-Fenton catalytic performance. However, above 800 °C, the catalytic activity was reduced, due to the increase in particle size. The starch content also affected the surface Cu2+ content and the particle size of catalysts. The catalyst prepared at 800 °C with the molar Cu2+/Fe3+/C6H10O5 ratio of 1:2:3 presented the best photo-Fenton performance, owing to its highest surface Cu2+ content. This catalyst also exhibits ferromagnetic properties (saturation magnetization of 25.836 emu/g and coercivity of 1010.23 Oe), which allows them to be easily separated from the solution by a magnet.

In this work, ZnO nanoparticles were surface-modified by thermal shock method with HAuCl4 and KF as precursors at different temperatures. The impacts of our modification process on the crystal structure, morphology, surface functional groups and surface composition of catalysts were characterized by XRD, TEM, FTIR and XPS spectra, respectively. Their photocatalytic activity was investigated through the degradation of methylene blue under UVA light and visible light irradiation. According to the results, our modification method successfully improved the photocatalytic activity of ZnO. Among all catalysts, the sample co-modified with Au and F at thermal shock temperature of 400 °C showed the best performance which was three times greater than that of unmodified ZnO sample under both UVA light and visible light. The enhanced photocatalytic activity of our modified catalysts can be attributed to the synergic effect of HAuCl4 and KF precursors which are able to produce Au(0) nanoparticles, Au+ ions and zinc vacancies on the oxide surface.

The heterogeneous Fenton-like catalysts based on CuFe2O4 were prepared by polymeric precursor method at several annealing temperatures. The obtained catalysts were respectively characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, point of zero charge measurement, and vibrating sample magnetometer. The Fenton-like catalytic activity was evaluated via the oxidation of methylene blue with H2O2. The results show that the CuFe2O4 phase content and the particle size increase with the annealing temperatures whereas the surface OH groups and the surface acidity decrease. The prepared powders possess typical ferromagnetic properties which allow them to be easily recovered and reused. These catalysts also present highly catalytic activities for the oxidation of methylene blue, which is principally attributed to the catalysis of the CuFe2O4 phase. When the annealing temperature increased, the catalytic performance was reduced, corresponding to the increase of par...

Heterogeneous Fenton-like catalysts based on CuFe2O4 were prepared by polymeric precursor method, using various polyhydroxy alcohols as polymeric agents: ethylene glycol, diethylene glycol and triethylene glycol. These catalysts were, respectively, characterized by XRD, SEM, pHPZC and VSM measurements. All catalysts showed typical ferromagnetic properties and highly catalytic activities for the degradation of methylene blue. When the chain length of polyhydroxy alcohols increased, the pHPZC value and particle size of these catalysts were not significantly modified, whereas the percentage of CuFe2O4 tetragonal spinel phase decreased, leading to the decline of catalytic activity and the reduction in coercive field.

The synthesis and characterization of ZnO nanoparticles doped with different metals (Al, Fe, Cu) were studied in order to reduce the photocatalytic activity of ZnO without modifying its optical properties for application in sunscreen. The metal doped ZnO materials were prepared by a simple co-precipitation method from corresponding metal precursors. The effect of metal ion doping on the crystal structure, morphology and optical properties of ZnO was respectively characterized by XRD, SEM and UV–visible diffuse reflectance. The photocatalytic activity was evaluated via the bleaching of methylene blue under UV irradiation. According to the results, the metal ion doping modified the cell volume, reduced the crystallinity and decreased the particle size of ZnO, which induces the increase of structural defects and then the suppression of its photocatalytic activity. The metal doped ZnO materials exhibited the UV absorption capacity comparable to the undoped ZnO. However, the optical properties in the visible region of ZnO were influenced by the nature of metal dopant. The Fe and Cu doping strongly enhanced the visible light absorption whereas the Al doped ZnO sample showed the visible light transparency, which make this material a promising constituent of sunscreen.

We have investigated the binding of two electrolyte additives, 4-tert-butylpyridine (4-TBP) and 2,2′-bipyridine (bipy), to the surface of TiO2 photo-anode by attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR); X-ray photoelectron spectroscopy (XPS); zeta potential; cyclic voltammetry analyses, and explained how the adsorption affects photovoltaic performance of dye-sensitized solar cell (DSC). To clarify whether the adsorption of 4-TBP/bipy on TiO2 surface affects the DSC performance, DSC devices were fabricated with non-grafted and 4-TBP or bipy grafted TiO2 photo-anodes, with application of two types of electrolytes with and without the nitrogen additives. Furthermore, the interaction between 4-TBP or bipy with the electrolyte mediator I−/I3− was investigated by cyclic voltammetry. The results showed that 4-TBP and bipy were able to bind chemically to TiO2 surface at elevated temperatures. DSC prepared with N-additive grafted TiO2 photo-anodes had lower short current and efficiencies than non-grafted cells. The open circuit voltage (Voc) was, however, increased 110 mV for 4-TBP grafted cells with 0.5 M 4-TBP in the electrolyte. One third of the overall increase in Voc was estimated to be due to the adsorption of the 4-TBP to the TiO2 surface. The remaining Voc increase was due to effects of 4-TBP on the electrolyte mediator.

Cu-modified ZnO photocatalysts were prepared using a thermal shock method with different copper-containing precursors (Cu(NO3)2, Cu(CH3COO)2, CuSO4) in order to study the impacts of the thermal shock method on the photocatalytic activity of ZnO under both UVA light and visible light irradiation. The influences of copper-containing precursors on the crystal structure, morphology, surface structure and surface composition were investigated by X-ray diffraction, transmission electron microscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. The UVA-light and visible-light-induced photocatalytic activities were evaluated through the degradation of methylene blue. According to the experimental results, ZnO catalysts modified with Cu(NO3)2 and Cu(CH3COO)2 exhibited higher performance than unmodified ZnO, which may be explained by the formation of oxygen vacancies and Cu(I) species on the surface of modified oxides. However, when ZnO was modified by CuSO4, the absence of oxygen vacancies and the presence of large sulphate ions on the ZnO surface were supposed to be the factors decreasing its photocatalytic activity.

International audience; In this study, we have modified TiO2 P25 photocatalyst by thermal shock method at different temperatures in order to study the effects of thermal shock process on the crystal structure, surface properties and photocatalytic activity. The thermal-shock-modified catalysts were respectively characterized by X ray diffraction (XRD), scanning electronic microscopy (SEM), X ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra and compared with thermal-shock-fluorinated TiO2 catalysts. The photocatalytic activity was evaluated via the degradation of methylene blue under UV and visible light irradiation. The results show that the deficiency of oxygen on the surface of catalysts created by thermal shock at 500°C can enhance the photocatalysis under both UV and visible light. Moreover, when the thermal shock was combined with the fluorination of TiO2, the photocatalytic performance was further improved. However, the thermal shock from 700°C promoted the growth of particles and the phase transition from anatase to rutile, which resulted in two different effects: inhibit the photocatalysis under UV irradiation but improve it under visible irradiation. © 2014 Elsevier B.V.

Our research aimed to improve the overall energy conversion efficiency of DSCs by applying nitrogen-doped TiO 2 nano-tubes ( N -TNT) for the preparation of DSCs photo-anodes. The none-doped TiO 2 nano-tubes (TNTs) were synthesized by alkaline hydrothermal treatment of Degussa P25 TiO 2 particles in 10 M NaOH. The nano-tubes were N -doped by reflux in various concentrations of NH 4 NO 3 . The effects of nitrogen doping on the structure, morphology, and crystallography of N -TNT were analyzed by transmission electron microscopy (TEM), infrared spectroscopy (IR), Raman spectroscopy, and X-ray photoelectron spectra (XPS). DSCs fabricated with doped N -TNT and TNT was characterized by J-V measurements. Results showed that nitrogen doping significantly enhanced the efficiency of N-TNT cells, reaching the optimum value ( η = 7.36%) with 2 M nitrogen dopant, compared to η = 4.75% of TNT cells. The high efficiency of the N -TNT cells was attributed to increased current density due to the reduction of dark current in the DSCs.

Fluorinated TiO 2 was prepared from anatase and rutile monophasic TiO 2 nanopowders by thermal shock method at different temperatures (400–950 °C), then characterized by XRD, SEM, XPS in order to elucidate the influences of thermal shock fluorination on the crystallite structure, morphologies and surface structure of TiO 2 in different phases. Their photocatalytic activities were evaluated via the degradation of methylene blue. According to the results, the fluorination below 600 °C did not change the crystallite structure or the particle size. However, the surface hydroxyl groups content is increased with the creation of fluoride ions and oxygen/titanium vacancies on the surface of anatase/rutile TiO 2 which are all involved in the improvement of the photocatalytic activity. The TiO 2 anatase fluorinated at 500 °C showed the best photocatalytic behaviour under UV light whereas the TiO 2 rutile fluorinated at 500 °C is the best photocatalyst under visible light. At higher thermal shock temperatures, the photocatalytic activity decreased, which was assigned to the decrease of the surface hydroxyl groups and vacancies content and the formation of the K 2 Ti 6 O 13 phase.

International audience; Surface fluorinated TiO 2 powders were prepared by thermal shock method and an overall comparative study was achieved on the basis of XRD, SEM, UVvis and XPS analyses. The main objective was to elucidate the influences of surface fluorination on the crystallite structures, morphologies, optical properties and surface chemistry with the temperature. According to the results, the surface fluorination under thermal shock method below 600 °C did not change the crystallite structure and the particles size, but successfully created chemisorbed fluoride ions, oxygen vacancies and increased the hydroxyl groups on the surface of TiO 2. The presence of oxygen vacancies was assigned to the red shift of TiO 2 optical absorption edge, which was the origin of visible-light-induced photocatalytic activity of these samples. For the thermal shock temperatures over 600 °C, the K 2Ti 6O 13-like phase was formed, resulting from the decrease of surface hydroxyl groups and the blue shift in absorption edge which reduced the photocatalytic activity.

International audience; A detailed X-ray photoelectron spectroscopy study has been performed for the CuRh1-xMgxO2 (x=0, 0.04 and 0.10) series for a better understanding of the role of the Mg2 substitution on the electrical properties and the value of the Seebeck coefficient. This study is based on an analysis of different compounds such as Rh2O3, Sr2RhO4 and CuCrO2 in order to characterize different oxidation states (Rh3 and Rh4 in octahedral oxygen environment and Cu in a dumbbell OCuO coordination). The Cu2p signal of copper in the non-doped compounds CuCrO2 and CuRhO2 reveals different electronic structures. An evolution of the Cu2p core signal with the increase of Mg2 content in the CuRh1-xMg xO2 is highlighted by XPS. The differences observed, especially for the Cu2p core peaks are discussed for the non-doped compounds CuCrO2 and CuRhO2 as for the CuRh1-xMg xO2 series upon Mg2 substitution. © 2011 Elsevier Inc.