Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid by electrospun TiO2 nanofibres synthesised from two different titanium molecular precursors.

The evaluation of the photocatalytic properties of electrospun TiO2 nanofibres (TiO2-NFs) synthesised in the same experimental conditions using two distinct precursors, tetraisopropyl orthotitanate (TTIP) and tetrabutyl orthotitanate (TNBT), with morphology and crystalline structure controlled by annealing at 460 °C for 3 h is presented. The presence of circular-shaped TiO2-NFs was corroborated by scanning electron microscopy (SEM). By using X-ray photoelectron spectroscopy (XPS), the chemical binding energies and their interactions of the TiO2 with the different incorporated impurities were determined; the most intense photoelectronic transitions of Ti 2p3/2 (458.39 eV), O 1 s (529.65 eV) and C 1 s (284.51 eV) were detected for TTIP and slightly blue-shifted for TNBT. By using energy-dispersive X-ray spectroscopy (EDS), the chemical element percentages in TiO2 were determined. Using X-ray diffraction, it was found that the annealed electrospun TiO2-NFs presented the anatase crystalline phase and confirmed by Raman scattering. Bandgap energies were determined by diffuse reflectance spectroscopy at room temperature. The photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide under exposure to ultraviolet light was studied using the TiO2-NFs obtained with the two molecular precursors. The results showed that the catalyst, prepared with the TTIP precursor, turned out to be the one that presented the highest photocatalytic activity with a half-life time (t1/2) of 28 min and a degradation percentage of 93%. The total organic carbon (TOC) in the solutions resulting from the 2,4-D degradation by the TiO2-NFs was measured, which showed a TOC removal of 50.67% for the TTIP sample and 36.14% for the TNBT sample. Finally, by using FTIR spectroscopy, the final chemical compounds of the degradation were identified as H2O and CO2.

Photocatalytic Evaluation and Application as a Sensor for the Toxic Atmospheres (Propane and Carbon Monoxide) of Nickel Antimonate (NiSb2O6) Powders.

Nickel antimonate (NiSb2O6) powders were synthesized using a wet chemistry process assisted by microwave radiation and calcination from 600 to 700 °C to evaluate their photocatalytic and gas-sensing properties. The crystalline phase obtained at 800 °C of trirutile-type nickel antimonate was confirmed with powder X-ray diffraction. The morphology and size of the nanostructures were analyzed employing electron microscopy (SEM and TEM), identifying irregular particles and microrods (~277 nm, made up of polyhedral shapes of size ~65 nm), nanorods with an average length of ~77 nm, and nanostructures of polyhedral type of different sizes. UV-vis analysis determined that the bandgap of the powders obtained at 800 °C was ~3.2 eV. The gas sensing tests obtained a maximum response of ~5 for CO (300 ppm) at 300 °C and ~10 for C3H8 (500 ppm) at 300 °C. According to these results, we consider that NiSb2O6 can be applied as a gas sensor. On the other hand, the photocatalytic properties of the antimonate were examined by monitoring the discoloration of malachite green (MG) at five ppm. MG concentration monitoring was carried out using UV-visible spectroscopy, and 85% discoloration was achieved after 200 min of photocatalytic reaction.

Preliminary study of the photodegradation of dyes using amorphous films of ZnO-CuO obtained by photochemical deposition in solid phase.

Here, we propose an original method of photochemical deposition for the synthesis of metal oxides from coordination complexes sensitive to UV light. The method consists of the synthesis of zinc oxide amorphous films doped with different concentrations of copper oxide followed by annealing at 600 °C. The photo-reactivity of the samples was evaluated by the decrease of the FT-IR spectroscopy bands. The films were analyzed by scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD) to study their morphology and structures, respectively. The results show an amorphous characteristic in the photo-deposits. The optical properties show a gradual decrease of both the optical band gap and the luminescent emissions of the ZnO photo-deposits when CuO doping increases. Both properties allow a shift in absorption towards the visible and a decrease in the rate of recombination of charge carriers. The photocatalytic activity was analyzed using methyl orange and methylene blue as pollutants under a lamp that emulates solar energy. The results show that the photocatalytic activity is favored by the insertion of CuO; 46.6 and 93.0% efficiency in the photodegradation of methyl orange and methylene blue, respectively, were reached at 1.0 mol % of CuO with respect to pure ZnO. These differences in degradation efficiency respond to the chemical stability of the dyes. Finally, the use of appropriate scavengers suggests an oxidative route in the dye degradation mechanism.

ZnO Nanoparticles for Photocatalytic Application in Alkali-Activated Materials.

This paper reports an Alkali-Activated Materials (AAM) using two different precursors, metakaolin and a metallurgical slag with photocatalytic zinc oxide nanoparticles, as novel photocatalytic composites. The photodegradation performance of the composites using methylene blue (MB) dye as a wastewater model was investigated by ultraviolet radiations (UV-vis) spectroscopy. Adsorption in dark conditions and photodegradation under UV irradiation are the mechanisms for removing MB dye. The pseudo-first-order kinetic and pseudo-second-order kinetic models were employed, and the experimental data agreed with the pseudo-second-order model in both cases with UV and without UV irradiations. As new photocatalytic materials, these composites offer an alternative for environmental applications.