Characterization of the hetero-system ZnCo 2 O 4 /ZnO prepared by sol gel: application to the degradation of Ponceau 4R
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Characterization of the hetero‑system ZnCo2O4/ZnO prepared by sol gel: application to the degradation of Ponceau 4R under solar light G. Rekhila1 · A. Saidani1 · F. Hocine1 · S. Habi Ben Hariz1 · M. Trari1 Received: 24 March 2020 / Accepted: 26 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Ponceau 4R is successfully oxidized on the hetero-system ZnCo2O4/ZnO under the solar light. The spinel with a nano-morphology is elaborated by the sol gel method at ~ 850 °C. The X-ray diffraction pattern exhibits narrow peak characteristics that reveals a good crystallization. The c apacitance−2–potential (C−2–E) plot of the semiconductor Z nCo2O4 indicates p type behavior from which a flat band potential of + 0.30 V SCE is determined. The energy band diagram, built from the physicchemical properties, clearly predicts the electron transfer from the conduction band of ZnCo2O4 toward dissolved oxygen via ZnO. Indeed, the Z nCo2O4/ZnO composite improves the photocatalytic performance, where the colloidal photochemical hetero-system is successfully used for the light induced Ponceau 4R oxidation. The spinel dose and Ponceau 4R concentration are optimized. The conversion rate is controlled by UV–Visible spectrophotometry and, under the ideal conditions, the oxidation of 70% of Ponceau 4R (15 ppm) is obtained in aerated solution for less than 4 h when exposed to the solar light. The oxidation obeys a first order kinetic with a half-photocatalytic life of 130 min (k ~ 52 × 10−4 min−1). Keywords Ponceau 4R · Hetero-system ZnCo2O4/ZnO · Photocatalytic degradation · Kinetic · Solar light
1 Introduction The water contaminated by heavy metals, dyes drugs and pesticides are traditionally treated by biological and/ or physical methods which decreases the pollution level, but not enough to reach the limit required by the World Health Organization (WHO) [1–4]. Indeed, the classical techniques are expensive and inefficient at low concentrations (10–150 mg L −1). Respectively, the advanced oxidation process (PDO) is a promising alternative for the treatment of effluent water from different industries [5–7] and the batch-process solar decontamination is found to be an effective treatment for the potable water. In this regard, the semiconductor/liquid junction, assimilated to a photoelectrochemical system to remediate the aquatic pollution [8–10]. Among the oxides, the spinels MMʹ2O4, where M * G. Rekhila [email protected] * M. Trari [email protected] 1
Laboratory of Storage and Valorization of Renewable Energies, Faculty of Chemistry (USTHB), BP 32 16111, Algiers, Algeria
and M′ are commonly 3d metals, start to gain a growing popularity in photocatalysis owing to their chemical stability, non-toxicity, easy synthesis and absorption over a wide range of the solar spectrum [11, 12]. The potential of their conduction bands (~ − 1 V) [13] is below the O2/O·2 couple, leading to spontaneous oxidation of organic molecules [14, 15]. They were used in the hydrogen production from water [16, 17] a
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