Abstract: Developing a photocatalysis system to generate hydrogen from water is a topic of great interest for fundamental and practical importance. In this study, hydrogen production by a new Z-scheme photocatalysis water splitting system was examined over Rh modified K4Nb6O17 nanosheets and Pt/WO3 photocatalysts for H2 evolution and O2 evolution with I-/IO3- electron mediator under UV light irradiation. The H2 evolution photocatalyst, Rh/K4Nb6O17 nanosheets with a slit like framework, was prepared by exfoliation of and proton exchange reaction. Pt/WO3 prepared by incipient-wetness impregnation method was used as O2 evolution photocatalyst. The catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy analysis (XPS), and ultraviolet-visible spectroscopy (UV-vis). These catalysts characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV-Vis). In this study, we developed a facile method of preparing K4Nb6O17 nanosheets containing Rh nanoparticles. Our results show that I- concentration and pH of reaction solution significantly influenced the photocatalytic activity. The combination of Rh modified K4Nb6O17 nanosheets with Pt/WO3 achieves a very high photoactivity (H2: 4240 O2: 1622 (μmol g-1 h-1)).
Abstract: The main aim of this study was to electrochemically synthesize and characterise bismuth vanadate (BiVO4) photoelectrodes for photoelectrochemical (PEC) water splitting. The influence of annealing temperature on the nanostructured semiconductor BiVO4 thin film structure was studied systematically. This was followed by advanced characterisation of the BiVO4 photoelectrodes by using field emission-scanning electron microscopy (FE-SEM), Raman spectroscopy, photoluminescence and PEC properties measurements. When the electrochemically synthesized BiVO4 thin films were subjected to different annealing temperatures, phase transitions occurred for tetragonal BiVO4 at 300 °C and monoclinic BiVO4 at 400 °C. Through this study, it was found that the annealing treatment at 400 °C resulted in the highest photocurrent density (i.e. photoactivity) of 1.23 mA/cm2 at 0.6 V vs. Ag/AgCl. Finally, the BiVO4/CuO heterojunction photoelectrode was also fabricated in order to further enhance its photoactivity under visible light irradiation.
Abstract: Grafting TiO2 on PMMA was studied by atom-transfer radical-polymerization (ATRP). Each step in grafting process was monitored by fourier transform infrared spectroscopy (FT-IR), 1H NMR and 13C NMR spectra. The glass temperature of grafted-PMMA film was determined by using differential scanning calorimetry (DSC). The morphology and bulk composition were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The surface composition was characterized by X-ray photoelectron spectroscopy (XPS). As results, a novel method of grafting TiO2 on PMMA was successfully grafted and confirmed in various techniques. The photocatlytic activity was evaluated under UV and visible light irradiation. The reusability of TiO2-g-PMMA films was studied in details.
Abstract: TiO2 films of varying mineralogical and microstructural characteristics were fabricated on sand-blasted Ti6Al4V plates by anodisation in 2 M sulphuric acid (H2SO4) and 2 M phosphoric acid (H3PO4) at 120 V and 300 mA/cm2 for 10 min and 15 min, respectively. The film formed by anodisation in H2SO4 consisted of both anatase and rutile while the film formed by anodisation in H3PO4 consisted only of rutile. This inconsistency is attributed to the presence of anatase below the level of detection in the sample anodised in the H3PO4, which consisted of a thinner TiO2 anodised film. SEM images demonstrated that H2SO4 resulted in arcing and resultant porosity while H3PO4 did not. Profilometry revealed that the former was rougher than the latter and that the latter was nearly the same roughness as the sand-blasted plate. These observations are consistent with the conclusion that H3PO4 formed a thinner anodised film and that the greater thickness from H2SO4 resulted in asperity formation, which enhanced arcing and densification. Although the anatase-rutile mixture and the greater roughness of the sample anodised in H2SO4 could be expected to have yielded superior performance, the fact that it did not is attributed to the greater bulk density and associated lower surface area of the TiO2 matrix. Preliminary cell culture tests showed that human osteoblast-like cells (MG63) were attached effectively on smooth anodised films (on polished plates) after 4 h of incubation while cell proliferation was confluent after 2 days. The major finding of the present work is that X-radiation in clinical doses (<200 cGy) is sufficient to cause degradation of organic species via photocatalysis.
Abstract: This contribution revisits recent results regarding the selective detection of the trace gases hydrogen sulfide, nitrogen oxide, and nitrogen dioxide using cupric oxide (CuO). It demonstrates how the variation of the surface temperature may be used to learn about basic material parameters as well as control the surface reactions. In contrast to commonly employed modulation schemes that continuously vary the temperature we use a steady-state approach in order to extract information about gas matrices. Our results highlight the potential for incorporating laboratory results regarding surface processes in pattern recognition schemes to improve the performance of these algorithms. We propose to implement the findings into temperature modulation schemes in order to allow for adding highly gas specific elements to the algorithms deployed.
Abstract: SnO2-based sensor has many advantages such as low cost, small size, high reliability, and long operating life, but selectivity has been a major obstacle on the application for discriminating gas species in mixture of multi-reduction gases. To resolve the problem in this work, the pure SnO2 and NiO-, CuO- and Pt-modifying SnO2 as sensing materials were prepared by sol-gel method, the sensor cells were fabricated and characteristics of sensitivity and selectivity of the sensor cells to CO and H2 at 400°C were investigated. The results showed that the response of CO was improved obviously by doping 20mol%NiO or 5mol%CuO into the SnO2, while the response of H2 was changed no more, and the responses of CO and H2 both were enhanced dramatically by bearing 1mol%Pt into the SnO2. On the basis of empirical equation (R=1+kCn), two sensor cells with different selectivity were introduced to assemble a novel SnO2-based sensor, and proposed a potential method to detect the concentrations of CO and H2 in multi-component gases, in which the parameters of k and n for sensor cells were obtained and feasibility of the method was demonstrated.
Abstract: Six different ZnO nanomorphologies were synthesized trough wet chemical routes starting from a water solution of zinc nitrate hexahydrate, obtaining two types of morphologies: bidimensional nanocrystals and nanoparticles aggregates. Powders and films characterizations have been carried out by means of TG–DTA, SEM, and X-ray diffraction analysis. Finally, electrical measurements were performed with the aim to compare conductive properties of the thick films, surface barrier heights and gas sensing features, mainly versus acetone and other VOCs related to the breath gas analysis. Among the different morphologies tested, it turned out that the samples constituted by nanoparticle aggregates exhibited the best performances versus all gases, but especially toward acetone at sub-ppm level.
Abstract: In this research work, a very simple, low cost eco-friendly method is presented for the synthesis of silver nanoparticles to be used in colorimetric optical sensors based on localized SPR (LSPR) measurement for gas ammonia. Silver nitrate salts are reduced using gaur gum which acts as a capping and reducing agent. Commonly used reducing agents such as trisodium citrate or sodium borohydride are replaced by a more environmental friendly natural polysaccharide. Nanocomposite films of ~ 1.5 μm thicknesses were fabricated using Gaur Gum and silver nanoparticles. The uniformity of nanoparticles size was measured by SEM and TEM, while face centred cubic structure of crystalline silver nanoparticles was characterized using the X-ray diffraction technique. The optical properties of the composite film were tested by UV-VIS Spectroscopy. The formation of Gaur Gum/silver nanocomposite films was confirmed using SEM images. Also the resistivity of nanocomposite thin film was measured which could be then used for gas sensing application.
Abstract: Several approaches to improve H2 sensing properties of TiO2-based diode-types sensors have been investigated. Those include the adoption of a Pd-Pt alloy electrode instead of using a pure Pd electrode, formation of a polymer coating atop the Pd-Pt alloy electrode and an Au coating on the Pd-Pt alloy electrode. The advantages of the using of the Pd-Pt alloy electrode, the polymer or Au coatings are demonstrated.