Solar photocatalytic reduction of Cr(VI) over Fe(III) in the presence of organic sacrificial agents

Toxic hexavalent chromium reduction to less toxic trivalent chromium was evaluated using a solar driven photocatalytic system, Fe(III)/UV, in the presence of organic sacrificial agents. The photocatalytic reduction experiments were conducted in a lab-scale tubular photoreactor with compound parabolic collectors under simulated solar radiation. The effect of parameters such as iron (1-12 mg L-1) and citric acid (0.058-3.840 mM) concentrations, pH value (3.0-8.0), temperature (15-40 degrees C), UVA irradiation source and initial Cr(VI) concentration (1, 10, 20, 40 mg L-1) on the process efficiency was analyzed, and also the addition of other organic ligands like oxalic acid, maleic acid and EDTA. The presence of citric acid proved to enhance the Cr(VI) reduction by Fe(III)/UV due to the formation of Fe(III)-Citrate complexes, providing a quicker pathway for ferric iron regeneration in the presence of UV-vis light. The organic ligands proved to act also as sacrificial agents of reactive oxygen species formed, avoiding the Cr(III) re-oxidation. The catalytic activity of the organic ligands in the Cr(VI) reduction by Fe(III)/UV followed this order: citric acid > oxalic acid > EDTA > maleic acid. The best Cr(VI) reduction (99% in 15 min) was achieved with citric acid in a Cr(VI):Citric acid molar ratio of 1:3 at pH 5 and 25 degrees C. Finally, the photocatalytic reduction of Cr(VI) present in a real effluent was achieved after 30 min, demonstrating the potential of the Fe(III)/UVA-vis/citric acid system for the treatment of Cr(VI) containing wastewaters

Photocatalytic reduction of Cr(VI) over TiO2-coated cellulose acetate monolithic structures using solar light

The major drawback of TiO2 based advanced oxidation processes (AOPs) is the use of massive amounts of dispersed nanoparticles that are hard to recover after the water treatment and potentially harmful for humans due to their very small size. The stabilization of the nanoparticles in an adequate inert support is a good strategy to overcome such limitations. In the present work, the photoreduction of Cr(VI) to Cr(III), using citric acid as a hole scavenger, was performed in a tubular photoreactor packed with cellulose acetate monolithic (CAM) structures coated with TiO2-P25 thin films by a simple dip coating method and irradiated by simulated or natural solar light. Firstly, the effect of TiO2 coating layers number on the Cr(VI) photoreduction was analysed. At the optimal amount, the photoreactor provides 0.10 g of TiO2 per liter of liquid inside the reactor. The support geometry allowed a high surface-area-to-volume ratio, offering an illuminated catalyst surface area per unit of volume inside the reactor of 212 m(2) m(-3). Following, operating conditions such as pH value, citric acid concentration, irradiation source and initial Cr(VI) concentration were analysed. Several. organic species were also tested as hole scavengers. Results indicate reduction rates of 0.07 mmol(cr(VI)) m(illuminatedvolume)(-3) S-1 and a photonic efficiency of 1.9% during the reduction of 0.02 mM of Cr(VI) with 6 P25 layers and 6.9 mM of citric acid at pH 2.5 and 25 degrees C. Furthermore, the catalytic bed was reused for 10 consecutive cycles with almost no efficiency decrease after the second cycle, achieving near 100% Cr(VI) removal after 90 min

A step forward on NETmix reactor for heterogeneous photocatalysis: Kinetic modeling of As(III) oxidation

This study focuses on the kinetic modeling of As(III) oxidation by heterogeneous TiO2 photocatalysis, assisted by ultraviolet light emitting diodes, using a static mixer ? NETmix reactor ? in two different configurations: back-side illumination and front-side illumination. First, preliminary experimental assays were performed varying the load of TiO2-P25 and the incident radiation flux for each configuration, and the observed pseudo-first-order kinetic constants were obtained. A model was built based on a mechanistic reaction pathway for As(III) oxidation, taking into account the radiation absorption by the catalytic surface. Three kinetic parameters were estimated considering the solution of the material balance for the existing chemical species and the evaluation of the radiation field inside the reactor by solving the Radiative Transfer Equation. The incident radiation flux was determined at every point on the catalyst surface. It was concluded that the initial reaction rate per unit area is similar in both reactor configurations. However, when compared per unit volume, front-side illumination exhibits twice the reaction rate as the back-side illumination. Moreover, according to the obtained parameters, the front-side configuration showed higher As(V) adsorptivity when compared to the back-side. In addition, the dependence of the reaction rate upon the incident radiation level proved to be the same regardless of the illumination mechanism. Nevertheless, considering that the radiation field is not uniform, the complete expression of the dependence with the local incident radiation flux in the reaction rate equations must be used. The results obtained with the model predictions were contrasted with the experimental data regarding As(III) concentrations and showed a good agreement for both reactor configurations.Fil: Santos, Sara G.S.. Universidad de Porto; PortugalFil: Paulista, Larissa O.. Universidad de Porto; PortugalFil: Marinho, Belisa A.. Universidade Federal de Santa Catarina; BrasilFil: Passalia, Claudio. Universidad Nacional del Litoral; ArgentinaFil: Flores, Marina Judith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Labas, Marisol Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Brandi, Rodolfo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Vilar, Vítor. Universidad de Porto; Portuga