V. Rodríguez-González

Enhancing ethylbenzene vapors degradation in a hybrid system based on photocatalytic oxidation UV/TiO2–In and a biofiltration process

The use of hybrid processes for the continuous degradation of ethylbenzene (EB) vapors has been evaluated. The hybrid system consists of an UV/TiO(2)-In photooxidation coupled with a biofiltration process. Both the photocatalytic system using P25-Degussa or indium-doped TiO(2) catalysts and the photolytic process were performed at UV-wavelengths of 254 nm and 365 nm. The experiments were carried out in an annular plug flow photoreactor packed with granular perlite previously impregnated with the catalysts, and in a glass biofilter packed with perlite and inoculated with a microbial consortium. Both reactors were operated at an inlet loading rate of 127 g m(-3)h(-1). The greatest degradation rate of EB (0.414 ng m(-2)min(-1)) was obtained with the TiO(2)-In 1%/365 nm photocatalytic system. The elimination capacity (EC) obtained in the control biofilter had values ≈ 60 g m(-3)h(-1). Consequently, the coupled system was operated for 15 days, and a maximal EC of 275 g m(-3)h(-1). Thus, the results indicate that the use of hybrid processes enhanced the EB vapor degradation and that this could be a promising technology for the abatement of recalcitrant volatile organic compounds.

Photoconversion of 4-nitrophenol in the presence of hydrazine with AgNPs-TiO2 nanoparticles prepared by the sol-gel method.

The photocatalytic properties of functionalized TiO2 with silver nanoparticles (AgNPs) for the conversion of 4-nitrophenol to 4-aminophenol in the presence of hydrazine were investigated. The TiO2 semiconductor synthesized by the sol-gel method was functionalized with AgNPs at different loadings, and their structural and optical properties were characterized by several techniques. The functionalized TiO2 with 1.5wt% AgNPs presented the highest photocatalytic activity for the conversion of 4-nitrophenol with appropriate hydrazine concentrations (0.5M). The photoefficiency enhancement under UV light irradiation was attributed to the electron transfer from the TiO2 semiconductor surface to the adsorbed acceptor reactant (4-nitrophenol) through the deposited AgNPs.

Understanding the adsorptive and photoactivity properties of Ag-graphene oxide nanocomposites

Nanocomposites of graphene oxide (GO) and silver nanoparticles (AgNPs) were synthetized using a practical photochemical silver functionalization. Their photocatalytic activities were evaluated with two dyes, Rhodamine B and Indigo Carmine, under visible-light irradiation. The prepared nanocomposites were characterized by HRTEM, FESEM, XRD, Raman, FTIR and UV-vis absorption spectroscopy. These nanocomposites present new defect domains of sp(3) type in combination with several graphitic functional groups that act as nucleation sites for anchoring AgNPs, while the sp(2)-sp(3) edge defects domains of GO generate the photoactivity. Furthermore, their photocatalytic performances are governed by their large adsorption capacity, and strong interaction with dye chromophores. A comprehensive photocatalytic way underlying the importance of adsorption is suggested to explain the low visible-light responsive photoactivity of the AgNPs-GO nanocomposites and the possible binding-site saturation. Then, the usage of H2SO4 allows the production of ionic species and helps to confirm the strong adsorption of both dyes. The ability to synthesize AgNPs-GO nanocomposites with extensive adsorptive capacity is certainly of interest for the efficient removal of hazardous materials.

Sonochemical synthesis of solar-light-driven Ag̊-PbMoO4 photocatalyst

Ag°-PbMoO4 photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO4. The synthesized powders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Diffuse Reflectance Spectroscopy (UV-vis DRS) to investigate the crystal structure, morphology, chemical composition, and optical properties of the photocatalyst. Photocatalytic activities of the Ag°-PbMoO4 samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3 mol.% of Ag showed the best photocatalytic activity as compared to other samples. The results suggest that the dispersion of Ag nanoparticles on the surface of PbMoO4 significantly enhances the photocatalytic activity of PbMoO4. Increase in photocatalytic activity of Ag°-PbMoO4 photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.

Practical microwave-induced hydrothermal synthesis of rectangular prism-like CaTiO3

The crystalline phase transition from tetragonal TiO2 anatase and rutile structures to an orthorhombic unit cell of CaTiO3 was achieved using a microwave-assisted hydrothermal process. FESEM and HRTEM Images show a well faceted CaTiO3 rectangular-prism morphology. The use of a urea solution during the hydrothermal process allows the direct transformation of TiO2 to perovskite-like with exposed (111) and (202) facets.

Gold nanoparticles supported on TiO2–Ni as catalysts for hydrogen purification via water–gas shift reaction

Gold nanoparticles deposited on TiO2–Ni prepared by sol–gel process catalyses the CO oxidation to hydrogen purification. Gold-catalysts were characterized by UV-Vis and Raman spectroscopies, X-ray diffraction, H2-TPR, N2 physisorption, HRTEM and STEM-HAADF microscopies. These catalysts were applied in the water–gas shift reaction at temperatures from 30 to 300 °C and this reaction was studied by DRIFTS to understand the catalytic surface phenomena. The best CO conversion was showed by doped Au/TiO2–Ni(1) with regard to Au/TiO2 sol–gel and Au/TiO2–P25 catalysts. DRIFTS confirm the strong and favorable effect of doping nickel ions into the reducible TiO2 framework. Nickel contents from 1 to 10% enhance the WGS reaction in contrast to the undoped catalyst. Ni-doped TiO2 support was practically inert for WGS reaction. These gold catalysts present significant activity in the water–gas shift reaction that allows purification of hydrogen from industrial sources at low-temperature.

Hydrogen-gas sensors based on graphene functionalized palladium nanoparticles: impedance response as a valuable sensor

Palladium–graphene (PdGO) nanostructures with high-quality-graphene layers and well monodispersed palladium nanoparticles (PdNPs) were synthesized by the hydrothermal microwave exfoliation method. The structural and morphological characteristics of PdGO were investigated, and the results indicate that the hydrothermal-microwave method allows both the reduction of metal precursors and their anchorage on highly exfoliated graphene layers. The synthesized PdGO nanostructures were then deposited as active layers for sensing hydrogen gas (H2). PdGO-based sensors with gas concentrations from 0.01 to 5 vol% in air exhibited a very reproducible performance with fast response times (∼30 s) and recovery behavior at room temperature. Measurement of impedance response serves as a highly sensitive feasible sensor technique. Our results show that it is feasible to obtain an efficient H2-sensor with reliable and reproducible sensing properties by means of a simple and cost-effective preparation method under real atmospheric conditions.

Green tide deactivation with layered-structure cuboids of Ag/CaTiO3 under UV light

In this work, an alternative to deactivate noxious green tide Tetraselmis suecica in the short-term is proposed by employing Perovskite-like cube-shaped, crystalline CaTiO3 semiconductors functionalized with atomic silver nanoparticles. CaTiO3 was prepared by a microwave-assisted hydrothermal method and then Ag(0)NPs (1 wt% of CaTiO3), were added by the photoreduction method. The XRD results show that crystalline CaTiO3 has an orthorhombic unit cell with a Perovskite-like structure. Images obtained by FESEM and HRTEM microscopies show well-faceted CaTiO3 rectangular prismatic morphology functionalizated with silver nanoparticles ≈ 13.5 nm. XPS and EDS-FESEM has confirmed the composition of CaTiO3 and silver occurring mainly as reduced metal. The UV inactivation of noxious T. suecica with Ag/CaTiO3 nanocomposites formed on bare materials results in complete deactivation of the algae in 12 min. The direct contact between harmful algae and Ag/CaTiO3 nanocomposite is necessary to deactivate the algae and inhibits algae viability.

Effective photoreduction of a nitroaromatic environmental endocrine disruptor by AgNPs functionalized on nanocrystalline TiO2

Unprecedented photoactivity of silver nanoparticles photodeposited on nanocrystalline TiO2 for the efficient reduction of 4-nitrophenol at room temperature is reported. The use of Na2SO3 as a harmless scavenger agent for the reduction of a nitroaromatic endocrine disruptor yields a valuable 4-aminophenol reagent.

The role of silver nanoparticles functionalized on TiO2 for photocatalytic disinfection of harmful algae

Silver loaded TiO2 samples were prepared by photodeposition of different amounts of Ag+ ions over commercial titanium dioxide (Evonik TiO2 P25) in aqueous media without the presence of sacrificial agents. The obtained photocatalysts were characterized by several techniques such as X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) in order to correlate the effect of the silver amount on the photocatalytic properties of the final nanocomposite. The effect of the silver nanoparticles on the photocatalytic behaviour of TiO2 was evaluated by means of the photodegradation of methyl orange dye and the inactivation of noxious algae Tetraselmis suecica and Amphidium carterae under continuous exposure of low power irradiation UV-light. The sample with 1.5% wt of silver nanoparticles showed the highest photocatalytic elimination of the azo dye and both algae types. According to the results, the cells were deformed during the photocatalytic process by the attack of highly reactive species such as hydroxyl radicals, H2O2 and superoxide ions generated on the TiO2 surface. The algae cells were not regenerated by themselves after the photocatalytic process due the high degree of fragmentation that they suffered during the light irradiation.