Solar photo degradation of the Rose Bengal (RB), a recalcitrant dye in water is carried out in the presence of the spinel CaFe2O4 synthetized by sol-gel route. Its structural characterization and ...FTIR spectroscopy were undertaken. The BET analysis measured is A specific surface area of 29.5 m2 g−1 is determined from the BET analysis. The diffuse reflectance of the normal spinel CaFe2O4 is used to determine a band gap of 1.83 eV. This optical transition directly allowed, is assigned to the crystal field splitting of Fe3+ octahedrally coordinated. The oxide is characterized photo-electrochemically. The absorption of solar light increases the presence of electrons in the conduction band (ECB = −1.45 VSCE). The chrono-amperometry curve indicates that CaFe2O4 exhibits p-type semiconductor. A flat band potential of 0.24 VSCE is determined from the capacitance measurement. The p-type character is corroborated by chrono-photo amperometry. The values of the conductivity increases with raising temperature attesting a semi-conducting character of CaFe2O4 with an activation energy (Ea) of 0.14 eV. As application, CaFe2O4 was successfully used as an efficient photocatalyst for the RB photo-degradation. Due to the good charge separation of photogenerated electron-hole pairs, a quasi-complete degradation of RB occurred within 2 h under sunlight for an initial concentration of 10 mg/L, a CaFe2O4 dose of 1 mg/mL of catalyst and an environmental pH ~ 8. The degradation kinetics are well illustrated by the Langmuir-Hinshelwood (L-H) model, follows pseudo-first order with an apparent constant of 0.016 min−1, corresponding to a half photocatalytic life of 43 min.
•CaFe2O4 was used for Rose Bengal (RB) dye degradation under solar light irradiation.•The degradation of RB is quasi total after 120 min for an initial concentration of 10 mg/L.•The mechanism for the enhanced photocatalytic performance was investigated.•RB degradation obeys a pseudo-first-order kinetics
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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.
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•New hetero-system MgCr2O4/WO3 was used for photoreduction of the hexavalent chromate.•MgCr2O4 and WO3 were prepared by the sol–gel and chemical precipitation methods.•Hexavalent ...chromium (30 mg/L) is totally photo-reduced within 120 min at (pH 4) under sunlight.•The kinetics of the photocatalytic reaction of Cr (VI) reduction to Cr (III) followed a first order model.
MgCr2O4 produced by the sol–gel route is active under the visible range. The spinel is characterized structurally, physically and photo electrochemically. From the diffuse reflectance measurement, its optical gap (1.69 eV) is suitable for the solar spectrum. Using the Mott Schottky method, the flat band potential is −0.15 VSCE. A BET area value of 30 m2/g was found. In a heterogeneous MgCr2O4/WO3/Cr (VI) system, the photoreduction of the hexavalent chromate is successfully achieved; WO3 is synthesized by chemical precipitation. The electrons of the conduction band (CB, −1.66 VSCE) of MgCr2O4 excited by solar light are injected into CB-WO3 (-0.21 VSCE). After 120 min, a rate of 100% conversion of 30 mg/L of Cr (VI) into Cr (III) was obtained under optimal conditions (pH ∼ 4, 25 °C, C7H6O3 = 10−5 mol/L, MgCr2O4/WO3 (1/1) and a dose of 1 mg/mL). The C7H6O3 scavenger used in the chromate solution Cr(VI) is advantage for avoiding the photocorrosion of MgCr2O4/WO3 hetero-system and improving the photoactivity. The kinetic of the photocatalytic reaction of Cr (VI) reduction to Cr (III) follows a first order model with an apparent constant of 0.02 min−1 (t1/2 = 35 min).
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•The Zn1-xCoxO system (x = 0 and 0.1) were prepared by nitrate route.•the capacitance-2-potential curve showed n-type conduction with a flat band potentials equal to −0.55 and −0.57 ...VSCE respectively for x = 0 and 0.1.•Orange II was oxidized on Zn0.9Co0.1O by•OH radicals under 93 mW cm−2 solar light.
The Zn1-xCoxO system (x = 0 and 0.1) were prepared by nitrate route. The diffractogram are indexed in the hexagonal Wurtzite structure. The scanning electron microscopy exhibits well-developed nano-particles homogeneously dispersed. The electrical conductivity (σ300K = 1.43 × 10−4 and 2.08 × 10-4 Ω−1 m−1 for x = 0 and 0.1 resp.) increases the photo oxidation of Orange II (OII) upon sunlight through the extension of the depletion width. At pH ∼ 7, the capacitance-2 - potential (Csc-2 - E) graph indicated n type conduction due to vacancies with a flat band potentials (Efb) equal to −0.55 and −0.57 VSCE respectively for x = 0 and 0.1. The semicircle in the complex impedance, measured between 1 mHz and 105 Hz, is due mainly to the bulk material with a depletion, assigned to a deviation from a capacitive character. The improved photoactivity of Zn1-xCoxO for the Orange II degradation under sunlight demonstrates the electrical energy consumption. The elaborated oxides remain stable after five cycles. Zn1-xCoxO was found to remove OII (10 ppm), efficiently on Zn0.9Co0.1O under sunlight with an abatement of 80 %.
•ZnMn2O4 was synthesized by the sol-gel auto-combustion method.•Hetero-junction ZnMn2O4/TiO2 was used as photocatalyst for Rhodamine B.•Kinetic data of RhB adsorption were fitted using the ...pseudo-second order model.•p-ZnMn2O4/n-TiO2 demonstrated a significant pollutant degradation rate.•Dynamic behavior of Rhodamine B adsorption on ZnMn2O4 (211) and TiO2 (101) surfaces was studied.
This study focuses on the application of the hetero-junction ZnMn2O4/TiO2 as an efficient photocatalyst for the degradation of Rhodamine B (RhB), a cationic dye. ZnMn2O4 was synthesized by sol-gel auto-combustion, employing citric acid as fuel. The photocatalysts underwent characterization by X-ray diffraction, Fourier Transform infrared spectroscopy, Scanning Electronic Microscopy with integrated EDX and UV–Vis Diffuse Reflectance. Creating a p-n heterojunction could significantly boost photocatalytic efficiency. In this work, we use TiO2 as a n-type co-catalyst to enhance electron transfer efficiency. The ZnMn2O4 spinel exhibits direct optical transition at 1.97 eV, while TiO2 displays an indirectly allowed transition at 3.24 eV. Mott-Schottky plots revealed flat band potentials of -0.121 and +0.3 V/SCE for ZnMn2O4 and TiO2, respectively. Kinetic data of RhB adsorption were fitted using the pseudo-second order model. The heterojunction p-ZnMn2O4/n-TiO2 demonstrates a significant pollutant degradation rate, with 95% removal within 180 min under sunlight irradiation, surpassing the effectiveness of ZnMn2O4. To validate the experimental results, a theoretical investigation was conducted using density functional theory (DFT) and molecular dynamics (MD) simulations. Geometry optimization of the Rhodamine B molecule was studied in both gas and liquid phases, and various quantum chemical parameters were computed. Molecular dynamics simulations were additionally employed to examine the dynamic behavior of Rhodamine B adsorption on ZnMn2O4 (211) and TiO2 (101) surfaces in an aqueous environment.
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•CuAl2O4 is synthetized by co-precipitation route.•CuAl2O4 is used as photocatalyst for the degradation of Eriochrome Black T (EBT).•Chrono-amperometry indicated n-type conductivity ...of CuAl2O4.•A quasi-complete degradation of EBT was observed within 180 min under sunlight.
This work focuses on the use of the spinel CuAl2O4 as photocatalyst for the degradation of Eriochrome Black T (EBT), a potentially hazardous dye. CuAl2O4 is synthetized by co-precipitation and studied by physic-chemical and electrochemical properties. X-ray diffraction revealed the formation of a single phase with cubic symmetry with a homogeneous morphology. X-ray Photoelectron Spectroscopy (XPS) and FTIR spectroscopy provide a better understanding of the chemical composition and surface structure of CuAl2O4. Diffuse reflectance (DR) gave a band gap of 1.94 eV, attributed to Al3+ in octahedral configuration. The BET analysis led to a specific surface area of 37 m2/g with the availability of an appreciable surface for photochemical reactions. Chrono-amperometry indicated n-type conductivity of CuAl2O4, with electrons as dominant charges and an activation energy (Ea) of 0.17 eV. A flat band potential of 0.26 VSCE (Volt vs. Saturated Calomel Electrode) was calculated from the interfacial capacitance in Na2SO4 solution. The photoactivity of EBT degradation was assessed by using chemical oxygen demand (COD). A quasi-complete degradation of EBT was observed within 180 min under sunlight. The mineralization was carried out with an initial EBT concentration of 10 mg/L, a dose of 1 g/L at pH ∼ 8, similar to that of an aquatic environment. These experimental conditions are important to assess the applicability of this method in a real environment.
•New hetero-system La2NiO4/SnO2 was used for H2 production under visible light irradiation.•Photoactivity of the hetero-system is significantly improved compared to La2NiO4.•H2 evolution rate reaches ...15.1 μmol g−1 min−1.•Best performance occurs at pH 13 in the presence of S2O3−3 as a hole scavenger.•La2NiO4 is p-type semiconductor.
La2NiO4 elaborated by nitrate route gives a positive result when used as a catalyst for the hydrogen photo-evolution. The prepared oxide crystallizes in the tetragonal K2NiF4 structure I4/mmm. The BET method was used to determine the specific surface area (4.91 m2/g); such value could suggest an interesting catalytic activity. Optical, electrical and photo-electrochemical properties have been studied to elaborate the energy diagram, a preamble for the photocatalysis. The band gap (Eg) has been evaluated at 1.51 eV and the transition is directly allowed. La2NiO4 is p-type semiconductor assigned to O2− intercalation in the two-dimensional crystal lattice; activation energy of 0.13 eV in the heating direction from the Arrhenius type law. The flat band potential Efb (−0.45 VSCE) and the density of the holes NA (1.13 × 1021 cm-3) were computed from the capacitance measurement. The conduction band illustrated in the energetic diagram for La2NiO4 (−1.77 VSCE) offers the possibility of H2 generation upon visible light. The best performance occurs at pH 13 in the presence of S2O3-3 as a hole scavenger. The H2 generation of the hetero-system (La2NiO4/SnO2) is significantly improved compared to La2NiO4. The higher photoactivity is ascribed to the electrons injection from the conduction band (La2NiO4-CB = −1.77 V/SCE), acting as generator and electrons pump, to (SnO2-CB = 0.35 V/SCE) inducing a better water reduction. The H2 evolution rate reaches 15.1 μmol g−1 min−1.
Using the hetero-junction Fe
2
O
3
/WO
3
, a significant rate of photocatalytic activity was obtained for the degradation of Ponceau S Red dye (PSR) under solar irradiation. The mass ratio of Fe
2
O
...3
/ WO
3
was studied. Similarly, the experimental conditions leading to the total degradation of Ponceau S Red dye were optimized. The physical and optical properties of both semiconductors Fe
2
O
3
and WO
3
were correlated with the photo-electrochemical characterization to establish the energy diagram of the hetero-junction Fe
2
O
3
/WO
3
/electrolyte. The XRD, UV–visible and BET analyses were performed for both prepared compounds. Fe
2
O
3
and WO
3
have the band gap values of 2.18 and 2.66 eV, respectively and their optical transition is directly allowed. The flat band potentials, determined from the capacitance
−2
– potential (C
−2
–E) plots are found to be − 0.16 and 0.47 V
SCE
,
respectively. The absorption of visible light produces a transfer of electrons from the conduction band of Fe
2
O
3
(− 0.61 V
SCE
) toward low trapping of WO
3
–CB energy sites (0.04 V
SCE
), which promotes the separation of charge carriers and therefore accelerates the PSR degradation. Under solar light illumination and the following conditions: pH ∼ 8, T ∼ 25 °C, and a catalyst dose of 1 mg/mL, total degradation of 10 mg/L of PSR is obtained. The chemical oxygen demand test confirms that most of Ponceau S Red dye was completely mineralized by photocatalytic process.
•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.
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