Synthesis of anisotropic Cu2−xS-based nanostructures by thermal oxidation

Journal of Thermal Analysis and Calorimetry - Flower-like copper sulfides nanostructures were synthesized via the solvothermal route. The structural, optical and electrochemical properties of the...     

Visible photocurrent response of TiO2 anode

The photoelectrochemical response to the electromagnetic radiation over the visible range is particularly sought for from the point of view of the efficiency of hydrogen generation by water photolysis in a photoelectrochemical solar cell, PEC. The PEC used in this work comprises thin film TiO₂ - based photoanode, Pt foil covered with Pt black as a cathode and SCE as a reference electrode, immersed in an electrolyte solution. Titanium dioxide thin films are deposited by means of rf reactive sputtering and modified, when necessary, by Au or Ag ultra-thin overcoatings. Here we show that even unmodified TiO₂ photoanode, shows a photocurrent peak over the visible range of the light spectrum (λ = 500-650 nm). The effect of the surface modification by noble metals and properties of the aqueous electrolyte on the visible photocurrent are studied. The optical spectra indicate an increased absorption due to noble metal deposits at 410 nm for Ag and at 600 nm for Au. In contrast, the photocurrent peak over the visible range (500 nm < λ < 650 nm) changes its symmetry and decreases in intensity with the increasing thickness of noble metals layers. The visible photoresponse is explained in terms of OH formation at the interface between TiO₂ electrode and aqueous electrolyte.     

From Adsorbent to Photocatalyst: The Sensitization Effect of SnO2 Surface towards Dye Photodecomposition

Semiconductor photocatalysis is considered one of the most promising technologies for water purification from toxic organic dyes. However, to reliably evaluate the possibility of using a given material as a photocatalyst, it is crucial to investigate not only the photocatalytic activity but also its affinity towards various dyes and reusability. In this work, we studied the adsorptive/photocatalytic properties of hollow-spherical raspberry-like SnO₂ and its SnO₂/SnS₂ heterostructures that were obtained via a chemical conversion method using three different concentrations of a sulfide precursor (thioacetamide). The adsorptive/photocatalytic properties of the samples towards cationic rhodamine B (RhB) and anionic indigo carmine (IC) were analyzed using uncommon wall zeta potential measurements, hydrodynamic diameter studies, and adsorption/photodecomposition tests. Moreover, after conducting cyclic experiments, we investigated the (micro)structural changes of the reused photocatalysts by scanning electron microscopy and Fourier-transform infrared spectroscopy. The obtained results revealed that the sensitization of SnO₂ resulted not only in the significantly enhanced photocatalytic performance of the heterostructures, but also completely changed their affinity towards dyes. Furthermore, despite the seemingly best photocatalytic performance, the sample with the highest SnS₂ content was unstable due to its (micro)structure. This work demonstrates that dye adsorption/desorption processes may overlap the results of cyclic photodecomposition kinetics.     

Nanocrystalline TiO2/SnO2 composites for gas sensors

TiO₂/SnO₂ nanocomposites are studied as potential candidates for gas sensors. Commercial metal oxide nanopowders milled for 1?h in ethanol are used for preparing nanocomposites with varied composition from 100?mol% TiO₂ to 100?mol% SnO₂. Brunauer?CEmmett?CTeller (BET) adsorption isotherms served to determine specific surface area, SSA. The particle size distribution is established by means of Dynamic Light Scattering, DLS technique. Differential Thermal Analysis and Thermogravimetry, DTA/TG measurements within the temperature range of 20?C900?°C indicate better stability of nanomaterials composed of bigger particles or agglomerates. The total mass loss varies from 0.9 to 8.5% for 100?mol% SnO₂ and 100?mol% TiO₂, respectively. The only gaseous products of decomposition are water and carbon dioxide. X-ray diffraction analysis of nanocomposites indicates two separate phases of different crystallite size, i.e., smaller rutile TiO₂ (9?nm) and larger cassiterite SnO₂ (28?nm). Gas sensor dynamic responses at 400?°C to the reducing gas??ammonia (NH₃) are detected in the concentration range extending from 100?ppm to ?5000?ppm. Nanosensor of 50?mol% SnO₂/50?mol% TiO₂ is stable and sensitive to the interaction with NH₃ and gives the highest response at 400?°C.     

Influence of film structure on the electron energy loss spectra of GaAs thin films

Energy loss measurements of fast electrons on GaAs yielded values for the plasma oscillation, interband transitions and the dielectric function in the region 5 — 30 ev. The results are discussed in comparison with literature statements. It is dealt especially with the influence of the degree of crystallinity of examined GaAs-films on the energy loss spectrum and the quantities derived from it.