The Pr2NiO4/SnO2 heterojunction with a mass ratio equal to unity was tested with success for the hydrogen production under visible light irradiation. Pr2NiO4, prepared by nitrate route, crystallizes ...in a tetragonal symmetry with K2NiF4 type structure. The physical, electrical and photo-electrochemical characterizations are correlated to show the feasibility of Pr2NiO4 for the hydrogen formation under visible light. The enhanced hydrogen production activity is due to electron injection of activated conduction band Pr2NiO4-CB (−1.53 VSCE) into SnO2-CB (−0.87 VSCE) which acts as an electron pump, resulting in better water reduction. The band gap of the semiconductor Pr2NiO4 is 1.81 eV with a direct optical transition. Pr2NiO4 acquired p type conductivity, due to oxygen insertion in the layered lattice with an activation energy of 0.09 eV. The flat band potential (Efb, 0.18 VSCE), very close to the photocurrent onset potential (0.13 VSCE) and the density of the holes (NA, 1.85 1020 cm−3) were obtained from the Mott-Schottky characteristic. H2 production rate of 24.3 μmol g−1 min−1 is obtained with a quantum yield of 1.45% within 30 min under optimal conditions (1 mg of catalyst/mL, pH ~12 and 50 °C) in presence of S2O2−3 as hole scavenger under visible light flux of 29 mW cm−2.
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•New hetero-system Pr2NiO4/SnO2 was used for H2 production.•Pr2NiO4 crystallizes in a K2NiF4-type structure with space Bmab.•The optical band gap of Pr2NiO4 is directly allowed with a value of 1.81 eV.•The insertion of oxygen into the layered crystal lattice induces p-conductivity.•The photocurrent and Mott-Schottky characterizations indicate p-type conductivity.
The CuBi2O4/TiO2 heterojunction was tested with success for the photo-catalytic reduction of chromate ions under sunlight. CuBi2O4, prepared by nitrate process, was characterised ...photo-electrochemically. The oxide is stable against photo corrosion by consumption of holes in presence of oxalic acid. The light absorption promotes electrons in the conduction band of the sensitizer (CuBi2O4) with a very negative potential (−1.74 VSCE) to participate in the exchange of the electron with HCrO4−. The enhanced activity is due to electron injection of activated CuBi2O4 into TiO2-CB (−0.97 VSCE). The band gap of the semiconductor CuBi2O4 is 1.50 eV with a direct optical transition. This compound is a p-type semiconductor with a flat band potential of −0.39 VSCE and activation energy of 0.18 eV. The electrochemical impedance spectroscopy was undertaken to study the semiconductor/electrolyte interfacial phenomena. The photoactivity on the heterojunction is strongly enhanced. A remarkable performance is obtained in less than 4 h for a concentration of 30 mg in (Cr (VI)) at pH ∼ 4 and a dose of 1 mg/mL; a 98% reduction has been obtained. The kinetic of chromate photoreduction is well described by the Langmuir-Hinshelwood model. The chromate elimination obeys to a pseudo-first order kinetic with an apparent rate constant of 0.014 min−1.
•In this work, the photocatalytic reduction of chromate using a new hetero-system CuBi2O4/TiO2 was studied.•The cathodic photocurrent is characteristic of p-type semiconductor. The flat band potential was determined from the Mott-Schottky characteristic.•The photocatalytic activity of the p-n hetero-system is much better than those of TiO2 or CuBi2O4 under the same conditions.•In less than 4 h and at pH∼ 4, 98% reduction was obtained for a concentration of 30 mg/L.•The experimental data fit adequately the Langmuir-Hinshelwood model. The reduction obeys to a first order kinetics.
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•The structural and photo-electrochemical properties of the new heterostructure of NiAl2O4 supported on Kaolin (10:90) prepared by the impregnation method were studied.•The adsorption ...was carried for methyl green dye solution (C0 = 50 mg/L) and the process was well described by Langmuir isotherm model.•The photocatalytic activity under the solar light irradiation was successfully tested for the degradation of methyl green dye.•The photocatalytic reaction mechanism of NiAl2O4/Kaolin was established regarding to the different characterizations carried out.
Nanosized spinel NiAl2O4 was successfully supported on kaolin, natural support, by impregnation method; then tested as photocatalyst towards organic pollutant. The catalyst was characterized by IR spectroscopy, XR diffraction, BET, reflectance and XPS techniques. The photocatalytic tests were followed by UV–Vis spectroscopy for degradation of Methyl Green (MG) solution (C0 = 50 mg/L) under sunlight irradiation. The maximum adsorption (91.56 mg/g) of MG dye solution was observed for NiAl2O4 at an equilibrium time of 240 min; nevertheless, for NiAl2O4/kaolin, the equilibrium time was only 150 min for an adsorbed quantity equal to 45.78 mg/g. Some parameters influencing the dye adsorption were optimized. The fitting of the adsorption data for the Methyl green follows the Langmuir isotherm model. This new nanocomposite of NiAl2O4/kaolin exhibited excellent photocatalytic activity, which can degrade MG dye; mainly after adding the hole sensors (H2O2), within 90 min under sunlight irradiation.
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•The structural and photoelectrochemical properties of Ni1-xCuxAl2O4 prepared by the co-precipitation method were studied.•The photocatalytic activity under the solar light ...irradiation was tested for the degradation of Congo Red dye.•The adsorption kinetic of the Congo red followed well the Langmuir isotherm model.•The energy diagram of Ni0.2Cu0.8Al2O4 was established regarding to the different characterizations carried out.
The present work focuses on the effect of Cu substitution on the crystal structure and photocatalytic activity of nano-spinel oxides Ni(1−x)CuxAl2O4 (x = 0.0–1.0). The synthesized compounds by co-precipitation route are characterized by X-ray diffraction, FT-IR, X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and UV–vis diffuse reflectance. The photocatalytic activity is followed by UV–vis spectroscopy and Electrochemical Impedance Spectroscopy in order to confirm the good performance of the catalyst and the charge separation of photogenerated (e−/h+) pairs. The photocatalytic efficiency of the synthesized catalysts is investigated through the decomposition of Congo Red dye under solar light irradiation. The efficient catalyst is Ni0.2Cu0.8Al2O4 with a removal conversion of 90.55% of the dye after 180 min. The parameters influencing the dye degradation like initial concentration are studied for the optimum degradation and the results have been discussed. This study shows that the adsorption kinetic of the Congo red has well followed the Langmuir isotherm model. The high photocatalytic activity of Ni0.2Cu0.8Al2O4 can be attributed to the valence band of the catalyst which enhances the mobility of the photoexcited charge carriers.
•New hetero-system CuCr2O4/SnO2was used for Crystal Violet dye degradation under solar irradiation.•The degradation of CV (15 mg/L) is quasi total after 90 min.•The mechanism for the enhanced ...photocatalytic performance was investigated.•CV degradation obeys a pseudo-first-order kinetics.
We report the study of the physicochemical properties of the spinel CuCr2O4 and its photoactive effect with the hetero-system CuCr2O4/SnO2. The spinel CuCr2O4 presents a direct gap (Eg) of 1.39 eV, a stable behavior against photo-corrosion and a cathodic photocurrent which characteristic of type p conduction in conformity with the chrono-amperometric profile. The flat band potential (Vfb = −0.27 VSCE) was determined from the capacitance measurement. At natural pH, the degradation of CV (15 mg/L) is quasi total with CuCr2O4/SnO2 under sunlight after 90 min. CV degradation obeys pseudo-first-order kinetics with an apparent constant 0.012 min−1.
Cu-doped ZnAl2O4 spinel oxides (Zn(1-x)CuxAl2O4, 0.0 ≤ x ≤ 1.0) were synthesized by co-precipitation method at 800 °C. The X-ray diffraction analysis of the as-prepared powders confirmed a spinel ...structure with a space group Fd-3 m. XPS was used to investigate the state of the material surface and the elemental composition. The SEM image confirmed the presence of nano spherical particles. The optical properties were characterized by UV–Vis diffuse reflectance and all band gap values, in the range of 1.71 to 3.54 eV, indicate a semiconductor character of our compounds. The energy bandgap (Eg) values of Zn(1-x)CuxAl2O4 decreased with increasing of the copper content. The photocatalytic activity was evaluated for Cr(VI) reduction under sunlight irradiation. The highest photoreduction efficiency was obtained for Zn0.2Cu0.8Al2O4 with a removal ratio of 75% after 150 min. The increase of surface area increases the photocatalytic activity as it implies larger contact surfaces exposed to Cr(VI). High surface area and pore volume are useful in the formation of photogenerated electron and hole pairs. The kinetics of photoreduction follow the modified Langmuir-Hinshelwood model. The obtained results indicate a good photocatalytic activity, in particular for compounds with a high content of Cu.
This work deals with the synthesis of the spinel CdFe2O4 by co-precipitation and its physico-chemical and electrochemical properties. The X-ray diffraction (XRD) attests the formation of single phase ...with a cubic symmetry with a lattice constant of 8.709 Ǻ nm and the ferrite was characterized by X-ray photoelectron spectroscopy (XPS) analysis and Fourier-transform infrared (FTIR) spectroscopy. The diffuse reflectance gives a band gap of 1.71 eV, assigned to the crystal field splitting of Fe3+: 3d orbital, octahedrally coordinated. A specific surface area of 39 m2/g was obtained from the Brunauer-Emmett-Teller (BET) analysis. The chrono-amperometry of CdFe2O4 indicates p-type conductivity, a result supported by the Mott-Schottky characteristic and a flat band potential (Efb) of 0.27 VSCE was computed. CdFe2O4 has an activation energy of 0.21 eV. It has been evaluated for the photocatalytic degradation of Methyl Green Dye (MGD), a hazardous dye under solar light. The charge separation of photogenerated electron-hole (e-/h+) pairs by solar excitation of CdFe2O4 within a depletion width, extended up 15 nm. The photoactivity was confirmed by chemical oxygen demand (COD), a total MGD degradation was observed within 3 h for an initial concentration of 10 mg/L and a dose of 1 mg CdFe2O4/1 mL MGD at pH ∼ 8, close to the natural aquatic environment.
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•CdFe2O4 nanoparticles was used for photodegradation of Methyl Green.•The chrono-amperometry of CdFe2O4 indicates p-type conductivity•The photoactivity was confirmed with the chemical oxygen demand (COD).•Total MGD degradation was observed within 3 h for an initial concentration of 10 mg/L.
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•New heterosystem CuFe2O4/α Fe2O3 was used for Methyl green dye degradation under solar irradiation.•The degradation of RPS (10 mg/L) is quasi total after 120 min.•The mechanism for ...the enhanced photocatalytic performance was investigated.•Kinetic data was well fitted by pseudo-second order model.
The purpose of this work was to investigate the photocatalytic activity of CuFe2O4/α Fe2O3 heterojunction toward Methyl green (MG) under sun light irradiation. Structural and textural properties were characterized using X ray diffraction (XRD), Fourier Transform infrared (FTIR) spectroscopy, Scanning electronic microscopy (SEM) and Brunauer, Emmet and Teller (BET) methods. UV–vis diffuse reflectance was used to evaluate the optical band gap energy (Eg = 1.83 eV) which confirmed the semiconductor character of the prepared material. To construct the energy band diagram, conducting and valence bands positions were determined using the predicted flat band potential (Vfb) of CuFe2O4 (0.51 V/SCE) and α-Fe2O3 (- 0.18 V/SCE) from Mott-Schottky plots. The adsorption study of Methyl green was carried out using kinetic models and adsorption isotherms. The kinetic data were well fitted by pseudo-second order model and Langmuir isotherm was used as the best model to describe the adsorption of MG dye. The photocatalytic activity of the catalyst under solar light irradiation was followed by UV–vis spectroscopy. The photodegradation results showed the efficient of the CuFe2O4/α Fe2O3 heterojunction toward Methyl green with a yield of 91 % within 120 min.
The present work focuses on the effect of Cu substitution on the crystal structure and photocatalytic activity of nano-spinel oxides Ni(1−x)CuxAl2O4 (x = 0.0–1.0). The synthesized compounds by ...co-precipitation route are characterized by X-ray diffraction, FT-IR, X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and UV–vis diffuse reflectance. The photocatalytic activity is followed by UV–vis spectroscopy and Electrochemical Impedance Spectroscopy in order to confirm the good performance of the catalyst and the charge separation of photogenerated (e−/h+) pairs. The photocatalytic efficiency of the synthesized catalysts is investigated through the decomposition of Congo Red dye under solar light irradiation. The efficient catalyst is Ni0.2Cu0.8Al2O4 with a removal conversion of 90.55% of the dye after 180 min. The parameters influencing the dye degradation like initial concentration are studied for the optimum degradation and the results have been discussed. This study shows that the adsorption kinetic of the Congo red has well followed the Langmuir isotherm model. The high photocatalytic activity of Ni0.2Cu0.8Al2O4 can be attributed to the valence band of the catalyst which enhances the mobility of the photoexcited charge carriers.
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