Ethylenediamine-assisted solvothermal synthesis of ZnS/ZnO photocatalytic heterojunction for high-efficiency hydrogen production.

Organic-inorganic hybrid materials have emerged as a class of novel materials over the last two decades, as they combine functional organic components and inorganic building blocks into unique materials through various chemical or physical interactions. In the present work, the importance of the use of ethylenediamine in sulfided materials applied to photocatalytic processes in the H2 production is demonstrated. The ZnS/ZnO heterojunction was prepared by the solvothermal synthesis in the presence and absence of ethylenediamine. The photocatalytic behavior showed that the addition of ethylenediamine increases the photocatalytic efficiency up to eight times compared to the photocatalyst without the organic agent. The materials were characterized by X-ray diffraction, scanning electron microscopy, infrared and UV-visible spectroscopies of solids, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and photoelectrochemical characterization. The ethylenediamine plays a double role: to stabilize the cubic phase of zinc sulfide and to act as a promoter molecule of charge transfer on the surface of ZnS/ZnO/en heterojunction, slowing down the rate of recombination of the electron-hole pair, which is reflected in a decrease in the resistance to transfer of charge carriers, improving the H2 production rate until 1564 µmol h-1 g-1.

Synthesis and characterization of V2O5-Ga2O3 photocatalysts and their application on the photocatalytic reduction of CO2.

The photocatalytic reduction of carbon dioxide (CO2) to produce methanol (CH3OH) is a promising strategy for producing clean energy. The catalyst, the aqueous medium, and the UV light are key parameters for the formation of the most relevant pair (e-/h+) and the specific selectivity towards the desired product (methanol). The use of Ga2O3 and V2O5 in the photocatalytic reduction of CO2 to produce methanol has been little studied. However, the combination of these oxides is important to generate synergies and decrease the band energy, enhancing the photocatalytic activity in CO2 reduction. In this work, V2O5-Ga2O3 combined photocatalysts have been prepared and investigated for the photocatalytic reduction of CO2. These photocatalysts were characterized by spectroscopic and microscopic techniques. The results showed that textural properties such as surface area and morphology do not influence the photocatalytic activity. However, species such as Ga2p3/2 and Ga2p1/2 identified by XPS enhanced the photocatalytic activity, most likely due to the formation of vacancies and the reduction of the bandgap in the combined oxides, as compared to single oxides. The contribution of these factors in pair interactions (e-/h+) with CO2 to generate methanol is demonstrated.

Photocatalytic Degradation of Diclofenac Using Al2O3-Nd2O3 Binary Oxides Prepared by the Sol-Gel Method.

This paper reports the sol-gel synthesis of Al2O3-Nd2O3 (Al-Nd-x; x = 5%, 10%, 15% and 25% of Nd2O3) binary oxides and the photodegradation of diclofenac activated by UV light. Al-Nd-based catalysts were analyzed by N2 physisorption, XRD, TEM, SEM, UV-Vis and PL spectroscopies. The inclusion of Nd2O3 in the aluminum oxide matrix in the 10-25% range reduced the band gap energies from 3.35 eV for the γ-Al2O3 to values as low as 3.13-3.20 eV, which are typical of semiconductor materials absorbing in the UV region. γ-Al2O3 and Al-Nd-x binary oxides reached more than 92.0% of photoconverted diclofenac after 40 min of reaction. However, the photocatalytic activity in the diclofenac degradation using Al-Nd-x with Nd2O3 contents in the range 10-25% was improved with respect to that of γ-Al2O3 at short reaction times. The diclofenac photoconversion using γ-Al2O3 was 63.0% at 10 min of UV light exposure, whereas Al-Nd-15 binary oxide reached 82.0% at this reaction time. The rate constants determined from the kinetic experiments revealed that the highest activities in the aqueous medium were reached with the catalysts with 15% and 25% of Nd2O3, and these compounds presented the lowest band gap energies. The experimental results also demonstrated that Nd2O3 acts as a separator of charges favoring the decrease in the recombination rate of electron-hole pairs.

Pt-Ni/ZnO-rod catalysts for hydrogen production by steam reforming of methanol with oxygen.

Ni, Pt and a mixture of Ni and Pt supported on ZnO-rods were evaluated in autothermal steam reforming of methanol (ASRM) for hydrogen production as a function of the reaction temperature. The catalytic materials were characterized by SEM-EDS, XRD, TEM, HRTEM, TPR and BET. Analysis by SEM and TEM showed structural modifications on the surface of the ZnO rods after Ni impregnation. The reactivity of the catalytic materials in the range of 200-500 °C showed that the bimetallic sample had better catalytic activity among all the catalysts studied. This finding could be associated to PtZn and NiZn alloys present in this catalyst, which were identified by XRD and HRTEM analyses. Catalyst characterization by XRD after the catalytic testing showed that the intermetallic PtZn phase was stable during the reaction in the Pt/ZnO-rod sample. The cubic Ni0.75-Zn0.25 structure identified in the Ni/ZnO-rod sample was transformed to Zn0.1-Ni0.9-O and metallic Ni phases, respectively. On the bimetallic PtNi/ZnO-rod sample, the cubic Ni0.75-Zn0.25 structure remained, although the tetragonal NiZn structure is unstable and was destroyed during the ASRM reaction and then a new phase of Ni0.7Pt0.3 emerged. The promotion effect of Pt and/or Ni on the ZnO-rod was clearly shown.

Al2O3-Phosphated Green Catalysts with High Selectivity to Ecological Gasoline C8= by Dimerization of Isobutene.

In this paper, phosphated-alumina prepared from boehmite and phosphoric acid (1, 4, and 6 mmol of PO4(3-)) is proposed as a good alternative catalyst to obtain ecological gasoline by the reaction of dimerization of butenes in gas phase using a flow reactor and mild conditions (60 degrees C and a C4/C4= molar ratio = 1). XRD spectra of the samples showed the formation of the gamma-alumina phase in the solids. BET specific surface area values of the bare alumina were not notably modified when these materials were phosphate, from 180-m2/g to 170 m2/g. All the solids are mesoporous structured materials. FTIR pyridine-adsorption spectra showed the formation of strong Lewis acid sites, which remains stable even at desorption temperatures above 300 degrees C. Brönsted acid sites were not observed on the materials. The phosphated-alumina catalysts were active for the dimerization of isobutene in mild conditions and 100% selectivitiy to C8= olefins was reached without the presence of olefinic compounds with higher molecular weight (trimers, tetramers).

Effect of the Method of Synthesis in the Photoactivity of TiO2-Co and TiO2-CoCe Materials.

Cobalt modified TiO2 and cobalt-cerium modified TiO2 were synthesized by sol gel technique using two different routes. In the first case the material was prepared by adding directly the precursor of metal (Co) during the sol-gel synthesis (In situ). The second one consisted in the impregnation of the supports of TiO2 and Ce-TiO2 prepared by sol-gel with a cobalt solution (Impregnated). The materials obtained were characterized by XRD and their textural properties were determined. The effect of the technique of synthesis as well as the presence of cerium in the photocatalytic properties of the material was evaluated in the photodegradation of phenol in aqueous phase. According to the results obtained in this study, it can be concluded that both, the integration of the metals during the sol-gel synthesis and the presence of cerium significantly improves the photocatalytic activity of TiO2.

Room temperature olefins oligomerization over sulfated titania.

Oligomerization reaction was carried out at room temperature using sulfated titania as catalyst. Total isobutene conversion was obtained with high stability for a long period of time. In case of deactivation, total reactivation of the catalyst was reached.