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The current work focused on the sunlight-driven thermo-photocatalytic reduction of carbon dioxide (CO2), the primary greenhouse gas, by ethane (C2H6), the second most abundant element in shale gas, aiming at the generation of ethanol (EtOH), a renewable fuel. To promote this process, a hybrid catalyst was prepared and properly characterized, comprising of strontium titanate (SrTiO3) co-doped with ruthenium oxide (RuO2) and nickel oxide (NiO). The photocatalytic activity towards EtOH production was assessed in batch-mode and at gas-phase, under the influence of different conditions: (i) dopant loading, (ii) temperature, (iii) optical radiation wavelength, (vi) consecutive uses, and (v) electron scavenger addition. From the results here obtained, it was found that: (i) the functionalization of the SrTiO3 with RuO2 and NiO allows the visible light harvest and narrows the band gap energy (ca. 14–20%), (ii) the selectivity towards EtOH depends on the presence of Ni and irradiation, (iii) the catalyst photoresponse is mainly due to the visible photons, (iv) the photocatalyst loses &gt, 50% efficiency right after the 2nd use, (v) the reaction mechanism is based on the photogenerated electron-hole pair charge separation, and (vi) a maximum yield of 64 μmol EtOH gcat−1 was obtained after 45-min (85 μmol EtOH gcat−1 h−1) of simulated solar irradiation (1000 W m−2) at 200 °C, using 0.4 g L−1 of SrTiO3:RuO2:NiO (0.8 wt.% Ru) with [CO2]:[C2H6] and [Ru]:[Ni] molar ratios of 1:3 and 1:1, respectively. Notwithstanding, despite its exploratory nature, this study offers an alternative route to solar fuels’ synthesis from the underutilized C2H6 and CO2.

A micro-meso-structured reactor (NETmix) was used for the first time to promote photochemical UVC/H2O2 processes. The NETmix photoreactor consists of a network of chambers and channels, where the liquid flows, sealed with a quartz slab with high UVC transparency. Due to the small size of channels and chambers, the NETmix presents a uniform irradiance through the entire reactor depth, short molecular diffusion distances and large specific interfacial areas, maximizing the pollutant/oxidant contact. In this study, the NETmix photoreactor was evaluated for As(iii) oxidation to As(v) using a photochemical UVC/H2O2 system. The effect of the UVC lamp power (4, 6 or 11 W), the number of UVC lamps (2 or 3 lamps) and the UVC lamp layout (parallel or perpendicular to the flow direction) was evaluated, in order to ensure uniform irradiation of the entire reaction mixture. The optimum H2O2 concentration for each light distribution system was also evaluated. At the best configuration, 3 lamps of 11 W positioned parallel to the flow direction, total As(iii) oxidation ([As(iii)]0 = 1.33 × 10-2 mM) was achieved in 15 min with an absorbed photon flux density of 1.9 × 10-1 einstein per m3 per s. Significant differences were highlighted between the photon flux actually received in the photoreactor and the radiant power emitted by the lamp. A kinetic model able to represent the As(iii) oxidation employing UVC radiation and H2O2 in a micro-meso-structured reactor was presented. The photochemical space time yield (PSTY) values obtained for the micro-meso-structured reactor are higher than for conventional batch reactors, showing that the NETmix technology can be a good solution for application in photochemical processes.

Despite the proven efficiency of heterogeneous photocatalysis using immobilized catalysts, this process lacks integration with the industry due to limitations on mass and photon transfer. The current study aimed to go up against this scenario by applying for the first time a Kenics® static mixer as catalyst support for heterogeneous photocatalysis in tubular reactors. Stainless steel Kenics® static mixers coated with TiO2 or Fe2O3 photocatalyst were assembled in a borosilicate tube coupled to a compound parabolic collector (CPC) and applied to the degradation of the antibiotic oxytetracycline (OTC) in aqueous solution. The use of the Kenics® static mixer provided intense mixing even under laminar flow, and, beyond that, the use of sunlight and a CPC ensured that the entire photocatalyst surface area was receiving front side illumination. Fe2O3 catalyst showed superiority over TiO2 for OTC degradation, exhibiting a pseudo-first-order kinetic constant 79% higher. However, while no TiO2 leaching occurred, up to around 0.7 mg L−1 of total dissolved iron were leachated. Thus, both homogeneous and heterogeneous photo-Fenton reactions may have contributed to the higher OTC degradation by Fe2O3 photocatalysis. The effect of various parameters on the photocatalytic efficiency was assessed: (i) photocatalyst deposition technique, (ii) photocatalyst dosage, (iii) H2O2 concentration, and (iv) number of static mixing elements. Spray coating technique showed superiority over dip coating. OTC degradation was improved by using 50 mL of TiO2 suspension together with 77 mg L−1 of H2O2, and 75 mL of Fe2O3 suspension together with 154 mg L−1 of H2O2. The increase of the number of Kenics® static mixing elements from two to six did not improve the OTC degradation rate. Furthermore, the reusability of both catalysts was proved.

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: Passalia, Claudio. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad Nacional del Litoral; Argentina

The application of electrocoagulation (EC) and electroflotation (EF) was investigated for the treatment of poultry slaughterhouse wastewater in a bench scale unit cell electrolyzer with different EC-to-EF ratios at current densities of 3, 9, and 15 mA cm−2. The EC-to-EF ratio was controlled by current reversal using aluminum and graphite electrodes. The electrochemical treatment showed satisfactory removal efficiencies for Al coagulant loads greater than 51.8 mg L−1. The 4/5 EC to EF ratio (69.1 mg L−1 Al and 32.2 NmL L−1 additional EF gas) and 3/5 (51.8 mg L−1 Al/64 NmL L−1 additional EF gas) presented the best results for the removal of COD (76–85%), color (93–99%), and turbidity (95–99%), with the additional benefit of reducing the electrode consumption and sludge disposal costs proportionally to the EC-to-EF ratio. The effects of the EC-to-EF ratio and the current density on efficiency of the electrochemical treatment for the removal of COD, apparent color, turbidity, TSS, TSD, and NH3-N were discussed in the light of the physicochemical and electrochemical processes underlying the removal mechanism for each parameter. In particular, the blow-off mechanism seems to play an important role in the NH3-N removal, whereas indirect electrooxidation mechanism accounts for a fraction of the soluble COD removal for the electrodes configuration used in the treatment.