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[Display omitted] • CoCr 2 O 4 was prepared by co-precipitation method. • CoCr 2 O 4 was used for Congo red dye degradation under solar irradiation. • CoCr 2 O 4 has a direct transition and a band gap (E g) of 1.74 eV. • The degradation of Congo red (15 mg/L) is quasi total after 180 min. • The mechanism and the potential band diagram are suggested. The aim of this study was to examine the potential of CoCr 2 O 4 , produced by co-precipitation method to degrade the hazardous dye Congo red (CR) when exposed to solar light irradiation. The as-prepared spinel was characterized by X-ray diffraction, attenuated total reflectance-Fourier transform, BET, X-ray photoelectron spectroscopy, scanning electron-microscopy with integrated EDX, and UV–Vis Diffuse Reflectance Spectroscopy. The experimental tests found that CoCr 2 O 4 has a direct transition with a band gap (E g) of 1.74 eV. Curiously, the normal spinel crystallizing in a cubic symmetry exhibits n -type conduction and to confirm such type behavior of CoCr 2 O 4 , electrochemical characterization was undertaken to determine the flat band potential using the Mott-Schottky plot of the interfacial capacitance. The pseudo-second order model was used to fit the kinetic data of CR adsorption. The results of the photodegradation tests showed that n- CoCr 2 O 4 nanoparticles facilitated the separation of photogenerated electrons/holes (e-/h+) pairs by decreasing the recombination process. This increased the overall efficiency of the photocatalytic process, up to be 94% in oxidizing the CR molecules after 180 min with a low catalyst dose of 0.2 g/L. A reaction mechanism is suggested based on a potential band diagram to explain the photocatalytic degradation of the dye onto CoCr 2 O 4 surface. [ABSTRACT FROM AUTHOR]

The present work focuses on the effect of Cu substitution on the crystal structure and photocatalytic activity of nano-spinel oxides Ni (1−x) Cu x Al 2 O 4 (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 Ni 0.2 Cu 0.8 Al 2 O 4 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 Ni 0.2 Cu 0.8 Al 2 O 4 can be attributed to the valence band of the catalyst which enhances the mobility of the photoexcited charge carriers. [ABSTRACT FROM AUTHOR]

• New hetero-system CuCr 2 O 4 /SnO 2 was 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 CuCr 2 O 4 and its photoactive effect with the hetero-system CuCr 2 O 4 /SnO 2. The spinel CuCr 2 O 4 presents a direct gap (E g) 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 (V fb = −0.27 V SCE) was determined from the capacitance measurement. At natural pH, the degradation of CV (15 mg/L) is quasi total with CuCr 2 O 4 /SnO 2 under sunlight after 90 min. CV degradation obeys pseudo-first-order kinetics with an apparent constant 0.012 min−1. [ABSTRACT FROM AUTHOR]