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A novelty g-C3N4/HAp composite photocatalyst was synthetized by precipitation and thermal condensation methods. The composite photocatalyst was studied by XRD technique confirming the presence of both phases in the composite. By FTIR and XPS techniques, the chemical bonds present in the photocatalyst and its components were analyzed. Electron microscopy shows a fine mixture of phases, preserving the lamellar structure of hydroxyapatite. The change in the optical properties of the photocatalyst was investigated by means of UV–vis spectroscopy and its photocatalytic behavior was evaluated for the photoreduction of Cr (VI) in presence of UV and visible light irradiation. g-C3N4/HAp composite showed an increase in its ability to reduce Cr (VI), reaching a total reduction (40 ppm solution) after 25 and 210 min for UV and visible irradiation, respectively. The increase in the photocatalytic activity can be attributed to a synergistic effect produced by the interaction between g-C3N4 and hydroxyapatite.

ZnS/MoS2 composite material was prepared by one-step solvothermal method at different molybdenum concentration. The structural properties of the composite material were analyzed by XRD, UV–vis DRS, TEM and XPS techniques, and the photocatalytic was evaluated for the hydrogen production under UV irradiation. The hydrogen yield reaches 606 μmol h−1 g−1 for the material with 10% of molybdenum, which was 30 and 50% superior than that obtained using MoS2 and ZnS as photocatalyst, respectively. The increase in the photocatalytic activity may be associated to a synergistic effect produced by the interaction between ZnS and MoS2, as well as the formation of defects in the structure of ZnS, due to sulfur vacancies produced during the synthesis, which could be observed in the TEM analysis of the composite material.

The present work comprises a study about the synthesis, characterization, and performance evaluation of four Co100-X-NiX (x = 0, 30, 70, and 100) electrocatalysts coated with Pt with potential catalytic activity towards ORR. Electrocatalysts were prepared through a two-stage process combining the versatile high-energy ball milling synthesis and the galvanic displacement method. On a first stage, high-energy ball milling was used to produce nanoparticles of non-noble transition metals, (M = Co100 and Ni100) and (BM = Co30Ni70 and Co70Ni30). On a second stage, galvanic displacement reactions via chemical reflux treatment were employed to promote a Pt coating over the milled nanoparticles. The four electrocatalysts were dispersed on Vulcan carbon maintaining a metal:carbon (wt.%) ratio of 50:50 each one. The result was two type of systems: (M-Pt/C = Co100–Pt/C and Ni100–Pt/C) and (BM-Pt/C = Co30Ni70–Pt/C and Co70Ni30–Pt/C). All the electrocatalysts presented a final composition: ~10 wt%. of Pt, ~40 wt% of Co100-xNix, and ~50 wt% of Vulcan carbon. Physical characterization of the synthesized electrocatalysts involved XRD, STEM, AAS-ICP-MS and EDS-SEM studies confirming the formation of homogeneously-distributed metallic nanoparticles on the carbon. The electrochemical evaluation, through cyclic voltammetry and steady-state polarization curves using rotating disk electrode technique, was performed for the four synthesized electrocatalysts and for a commercial platinum-loaded carbon black (Pt Etek 20 wt%) catalysts. All four synthesized electrocatalysts were electroactive for ORR. Moreover, the Ni100–Pt/C electrocatalyst presented the highest mass activity whereas Co30Ni70–Pt/C electrocatalyst showed the major stability after 3000 cycles of accelerated degradation test than the others. Two membrane electrode assemblies (MEAs) for PEM fuel cell were fabricated with the synthesized Ni100–Pt/C and Co30Ni70–Pt/C electrocatalysts used as cathodes. Results under single-fuel cell operation showed the same performance trend for those materials that observed under electrochemical glass cell conditions.

BACKGROUND: Environmental pollution and energy crisis are nowadays considered among the most important problems facing humanity. Several strategies have been proposed to solve them, being photocatalysis a very promising one because of its ease of application and low cost. In the search for active photocatalysts, those based on graphite‐like carbon nitride (g‐C₃N₄) are becoming good alternatives for various reactions. In this work, the properties of g‐C₃N₄/MoS₂/MnOOH composite material and its photocatalytic behavior for the production of hydrogen (H₂) under UV radiation were investigated. RESULTS: The composite material was synthesized by applying a combination of thermal condensation and hydrothermal methods. According to the results of X‐ray diffraction (XRD), ultraviolet diffuse reflectance spectroscopy (UV‐DRS), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), good dispersion of the phases and the formation of a heterojunction were observed. The band gap value of the composite material, calculated by the Kubelka–Munk equation using the values obtained from UV‐DRS analysis, was lower than those of the individual components, while it also had a much longer electron–hole recombination time, according to photoluminescence analysis. As a consequence of a synergistic effect, the activity of the proposed composite photocatalyst was superior in the reaction of water splitting, with a kinetic constant of 466 μmol h⁻¹ and a production rate of 1750 μmol H₂gcat−1 h⁻¹ (50 and 21% higher than those obtained with MoS₂ and g‐C₃N₄, respectively). CONCLUSION: Because of its high activity and stability, g‐C₃N₄/MoS₂/MnOOH composite photocatalyst is an excellent alternative for H₂ production by the water splitting reaction. © 2019 Society of Chemical Industry

Photocatalysts based on calcined ZnAl layered double hydroxides were obtained by coprecipitation and the subsequent thermal treatments at different temperatures. The calcined materials were characterized and its photocatalytic behavior was evaluated in the water splitting reaction in presence of UV irradiation. According to the XRD analysis, there was detected the presence of Zn as hexagonal ZnO in all the samples, as well as Al forming ZnAl2O4 and Zn6Al2O9, depending on the temperature of calcination employed. H2 yield was higher as the annealing temperature was increased due to the formation of the heterojunctions of ZnO with the Zn6Al2O9 and ZnAl2O4 oxides, reaching the maximum value in the sample annealed at 600 °C. Some decay in the activity was observed in the sample calcined at 700 °C, probably due to the higher recombination rate of the photogenerated charge carriers in that heterojunction in comparison with that obtained at 600 °C.

In this work, the obtaining of Cu7.2S4 hexapods by a hydrothermal process of two stages is reported. First, hexapods of Cu2O were obtained using copper chloride, and then in the second stage, sodium sulfite was used at different weight ratios in relation with Cu2O for the transformation into Cu7.2S4. The XRD, SEM, Raman, and XPS studies show that at 1:1 wt-ratio the conversion is not completely achieved and the presence of the two phases in the hexapod is detected. By increasing the weight-ratio to 1:2, Cu7.2S4 hexapods with smooth surface were totally transformed into Cu7.2S4 ones with modified surface completely covered by nanosheets.

Removal and photodegradation of methylene blue on the surface of three distinct carbonaceous materials, pure and nitrogen-doped multi-walled carbon nanotubes, and graphitic nanoribbons, were examined. Carbon nanostructures were characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption/desorption isotherms. Removal and photocatalytic activity were evaluated by static adsorption under UV irradiation. Photocatalytic activity on carbon nanostructure exhibited a pseudo-first-order kinetic model. The adsorption capacity and photocatalytic activity of carbon nanostructures were mainly attributed to their defective and reactive surface. Nitrogen-doped multi-walled carbon nanotubes showed the best adsorption capacity and photocatalytic activity, which can be attributed to the highly reactive sites due to nitrogen doping, also by π–π electron donor-acceptor interaction between sp2 lattice of carbon nanostructure surface and negatively charged sites at methylene blue molecules.

In this work we report the transformation of chemically deposited plumbonacrite (Pb10O(OH)6(CO3)6) films induced by thermal annealing in nitrogen atmosphere at temperatures in the 25–700 °C range. The plumbonacrite films were deposited on silicon substrates, at room temperature, by the photo-assisted chemical bath technique using lead acetate as lead precursor and sodium citrate as the complexing agent. The thermal decomposition of plumbonacrite powder was observed by TGA. The crystalline structure and surface morphology of the as-grown and annealed films were analyzed by XRD and SEM, respectively. The results show the thermal decomposition of plumbonacrite into lead oxide at lower temperature and subsequently to elemental lead at higher annealing temperature, accompanied by drastic morphology changes. The resulting Pb films are constituted by a flat, smooth layer with emerging hemispheres of micrometric variable size, in the order of 1–5 mm. These films were partially converted to PbSe by immersion in an aqueous solution containing selenium ions.

Here, the synthesis conditions involved in the obtention of magnesium hydroxide [Mg(OH) 2 ] nanoparticles by hydrothermal route are studied. The aim is to control the characteristics of the products only by setting the correct reaction conditions. In addition, they have simplified the method by using simpler equipment in the synthesis and eliminating any further purification processes to obtain pure Mg(OH) 2 particles in a scalable, safe, and economic process. They present the role of the treatment temperature by means of differential scanning calorimetry, water/magnesium oxide ratio, ageing time, and temperature increase rate and the characteristics of the resulting Mg(OH) 2 particles. Characterisation of the products was carried out by X-ray diffraction, dynamic light scattering, scanning electron microscopy, and transmission electron microscopy.

A ternary g-C3N4/NiOOH/Ag nanocomposite photocatalyst was synthesized using a combination of chemical and photoreduction methods. Physical, chemical and optical properties of the obtained material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis diffuse reflection (DRS) and X-ray photoelectron spectroscopies (XPS). The photoactivity of g-C3N4/NiOOH/Ag nanocomposite was evaluated for the H2 production from a water/methanol solution under irradiation with a low intensity UV–Vis lamp. The results showed that photoactivity obtained with the nanocomposite, measured as H2 yield, was superior than those obtained using bare g-C3N4, g-C3N4-Ag and g-C3N4-Ni as photocatalysts. This increase could be due to the effect of a lower electron-hole recombination rate, derived of an efficient charges separation, and to the synergistic effect between the compounds which integrate the material.

Catalysts have been widely used in industries and can be optimized by tuning the composition and chemical ordering of the elements involved in the nano-alloy. Among bi-metallic alloys, the Au-Cu system is of particular interest because it exhibits ordered phases at low temperatures. Nevertheless, the temperature at which these ordered structures are formed is totally unknown at the nanoscale. Consequently, to speed up the development of these catalysts, this paper theoretically predicts the structural phase transitions between ordered and disordered phases for the Au-Cu system by using nano-thermodynamics. Following the predictions, the suggested annealing temperatures have been carefully chosen and consequently, Au-Cu ordered nanocubes have been successfully synthesized through a solventless protocol. The results are fully supported by electron microscopy observations.

We report the synthesis of MWNT/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNTs with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs was covered with ZnO nanoparticles; these particles formed highly porous spherical nodules of 50-150 nm in diameter, sizes that are an order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, the self-assembled nanocomposite the ZnO exhibited a large surface-to-volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNT/ZnO nanocomposites were characterized by x-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-vis and Raman spectroscopy. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K up to -18%/K, over temperature change intervals from 10 K to 1 K. Based on these TCR results, the nanocomposite MWNT/ZnO prepared in this work is a promising material, with potential application as a bolometric sensor.