Removal of carbamazepine, diclofenac and trimethoprim by solar driven advanced oxidation processes in a compound triangular collector based reactor: A comparison between homogeneous and heterogeneous processes.

Contaminants of emerging concern (including pharmaceuticals) are not effectively removed by municipal wastewater treatment plants (WWTPs), so particular concern is related to agricultural wastewater reuse due to their possible uptake in crops irrigated with WWTPs effluents. Advanced oxidation processes (AOPs) and solar AOPs have been demonstrated to effectively remove pharmaceuticals from different aqueous matrices. In this study, an heterogeneous photocatalytic process using powdered nitrogen-doped TiO2 immobilized on polystyrene spheres (sunlight/N-TiO2) was compared to the benchmark homogenous AOP sunlight/H2O2 in a compound triangular collector reactor, to evaluate the degradation of three pharmaceuticals (carbamazepine (CBZ), diclofenac (DCF), trimethoprim (TMP)) in water. The degradation of the contaminants by sunlight and sunlight-AOPs well fit the pseudo-first order kinetic model (but for TMP under sunlight). High removal efficiency by solar photolysis was observed for DCF (up to 100%, half-life sunlight cumulative energy QS,1/2 = 2 kJ L-1, half-life time t1/2 = 32 min), while CBZ (32%, QS,1/2 = 28 kJ L-1, t1/2 = 385 min) and TMP (5% removal after 300 min) removal was poor. The degradation rate of CBZ, TMP and DCF was found to be slower during sunlight/H2O2 (QS,1/2 = 5 kJ L-1, t1/2 = 77 min; QS,1/2 = 20 kJ L-1, t1/2 = 128 min; QS,1/2 = 4 kJ L-1, t1/2 = 27 min, respectively) compared to sunlight/N-TiO2 (QS,1/2 = 4 kJ L-1, t1/2 = 55 min; QS,1/2 = 3 kJ L-1, t1/2 = 42 min; QS,1/2 = 2 kJ L-1, t1/2 = 25 min, respectively). These results are promising in terms of solar technology upscale because the faster degradation kinetics observed for sunlight/N-TiO2 process would result in smaller treatment volume, thus possibly perspective compensating the cost of the photocatalyst.

Ag modified ZnS for photocatalytic water pollutants degradation: Influence of metal loading and preparation method.

In this paper, the photocatalytic degradation of organic pollutants was investigated using Ag/ZnS nanoparticles at different noble metal loadings. The photocatalysts were prepared at room temperature by two different methods: photodeposition and chemical reduction. The obtained samples were characterized by Specific surface area measurement, X-ray photoelectron spectroscopy, X-ray Powder diffraction, ultraviolet-visible diffuse reflectance and Raman spectroscopy. The X-ray photoelectron spectroscopy spectra showed that Ag is present on ZnS surface as intermediate state between nanostructured Ag0 and Ag2O. Moreover, the addition of silver caused a significant change of the absorption spectrum of bare ZnS, resulting in higher absorbance in the visible region, due to the Ag surface plasmon band. Methylene blue (MB) was used to evaluate the photocatalytic activity of the prepared samples. The best photocatalytic activity was observed using the sample at 0.1 wt% Ag loading prepared by chemical reduction method. In particular, the almost complete MB degradation was achieved using UV-LEDs as light sources and 6 g L-1 of catalyst dosage. Finally, the optimized photocatalyst was also effective in the degradation of phenol in aqueous solution under UV irradiation.

Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials.

The photocatalytic reduction of CO2 with H2O to produce CH4 in the gas phase was carried out in the presence of two Bi2WO6-based materials. For this purpose, single Bi2WO6 and a coupled Bi2WO6-TiO2 system were synthesised and metallised with Pt, through a Pt photodeposition method. Then, the samples were characterised and the photocatalytic activity was evaluated in a continuous fluidised-bed reactor irradiated with UV light. Single Bi2WO6 presents an interesting behaviour under H2O rich conditions. In particular, the metallisation improves the material's performance for CH4 formation, while the TiO2 addition to Bi2WO6 increases the CH4 yield only at low H2O/CO2 ratio. The Bi2WO6-TiO2 system metallised with a Pt photocatalyst displayed the highest CH4 yield among all the prepared photocatalysts. The stability of the system can be enhanced through the addition of a blue phosphor to the reactant mixture, especially under H2O rich conditions.

Steam reduction of CO2 on Pd/TiO2 catalysts: a comparison between thermal and photocatalytic reactions.

The aim of this work was to compare traditional catalysis, which drives chemical reactions by thermal energy, with a photocatalytic process that can induce chemical reactions by light activation. Taking apart the obvious economic advantage to operate under mild conditions, a closer view of the characteristic behaviours of the thermal and light activation can give new insights for the selection of the more appropriate process. The performances of Pd/TiO2 catalysts in the steam reduction of CO2 were analyzed in a photocatalytic and in a thermo-catalytic system. The comparison in the range 140 °C-600 °C showed, for this reaction, the superiority of the photocatalytic route, since at any temperature level, no relevant products or higher selectivities towards the formation of methane and CO were observed. The CH4 photo-formation rate achieved a value of about 64 µmol g(-1) h(-1) at Pd loading equal to 1 wt%.

Intensification of gas-phase photoxidative dehydrogenation of ethanol to acetaldehyde by using phosphors as light carriers.

In this work a significant improvement of VO(x)/TiO(2) photocatalytic activity in the selective partial oxidation of ethanol to acetaldehyde was achieved by the simultaneous irradiation with light emitting phosphorescent particles and UVA-LEDs as external light source. Photocatalytic tests were carried out in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency, in which the bed is constituted by VO(x)/TiO(2) photocatalyst at nominal V(2)O(5) content of 5 wt% and suitable selected phosphors, diluted with glass spheres. In this way, phosphors were fluidized together with the catalyst, excited by external UVA-LEDs, emitting their stored energy in close proximity to the catalyst. In the absence of phosphors the ethanol consumption rate initially grows linearly with initial alcohol concentration, then bends towards an asymptotic value for initial ethanol concentration higher than 0.5 vol%. By contrast, when phosphors are present, the ethanol consumption rate increased linearly in the overall range. In all cases acetaldehyde was the main product detected in gas phase with a selectivity of about 97%, ethylene and carbon dioxide the by-products. The results evidenced that the presence of phosphors allowed improved photon transfer, increasing the apparent quantum yield from 2 to 30% together with a high photoreactivity.

A step forwards in ethanol selective photo-oxidation.

This work focuses on the optimization of a photocatalyst formulation for the selective oxidation of ethanol to acetaldehyde. VO(x)/TiO(2) catalysts at different vanadium loading were studied in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency, in which the bed is constituted by photocatalyst diluted with alpha-Al(2)O(3) or silica gel. Photocatalytic tests showed the selective formation of acetaldehyde, with ethylene and carbon dioxide as by-products. Selectivity is influenced by the vanadium loading. For ethanol inlet concentration of 0.2 vol%, maximum conversion and acetaldehyde selectivity of 73% and 97%, respectively, were obtained at 100 degrees C on catalyst at nominal 5 wt% V(2)O(5) content (53% of surface monolayer) mixed with alpha-Al(2)O(3). Selective sites were related to surface polymeric vanadates possessing Ti-O-V and V-O-V functionalities while the photoactivity appeared correlated with the catalyst equivalent band gap energy. Increasing the ethanol inlet concentration to 1 vol% and diluting the catalyst with silica gel, total ethanol conversion with about 97% selectivity to acetaldehyde was achieved with a photoreactivity of 0.34 mol m(irradiated)(-3) s(-1). This is three times higher than reported for other photoreactors.