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Wastewater treatment targeting reuse may limit water scarcity. Photocatalysis is an advanced oxidation process that may be employed in the removal of traces of organic pollutants, where the material choice is important. Titanium dioxide (TiO2) is a highly efficient photocatalyst with good aqueous stability. TiO2 powder has a high surface area, thus allowing good pollutant adsorption, but it is difficult to filter for reuse. Thin films have a significantly lower surface area but are easier to regenerate and reuse. In this paper, we report on obtaining sol-gel TiO2 thin films on spherical beads (2 mm diameter) with high surface area and easy recovery from wastewater. The complex influence of the substrate morphology (etched up to 48 h in concentrated H2SO4), of the sol dilution with ethanol (1:0 or 1:1), and the number of layers (1 or 2) on the structure, morphology, chemical composition, and photocatalytic performance of the TiO2 thin films is investigated. Etching the substrate for 2 h in H2SO4 leads to uniform, smooth surfaces on which crystalline, homogeneous TiO2 thin films are grown. Films deposited using an undiluted sol are stable in water, with some surface reorganization of the TiO2 aggregates occurring, while the films obtained using diluted sol are partially washed out. By increasing the film thickness through the deposition of a second layer, the roughness increases (from ~50 nm to ~100 nm), but this increase is not high enough to promote higher adsorption or overall photocatalytic efficiency in methylene blue photodegradation (both about 40% after 8 h of UV-Vis irradiation at 55 W/m2). The most promising thin film, deposited on spherical bead substrates (etched for 2 h in H2SO4) using the undiluted sol, with one layer, is highly crystalline, uniform, water-stable, and proves to have good photocatalytic activity.

A facile, green synthesis methodology to obtain zinc oxide nanoparticles using three polysaccharide gums (Acacia gum, Guar gum and Xanthan gum) of biological origin was developed. Subsequently, biosynthesized zinc oxide nanoparticles were incorporated into a sustainable chitosan hydrogel matrix functionalized with propolis extract. This study has revealed that the selected polysaccharides as chelates represents a suitable approach to synthesize ZnO nanoparticles of particular interest with controlled morphology. The formation of ZnO nanoparticles using polysaccharide gums was confirmed by FTIR, XRD, UV-Vis spectroscopy, thermal analysis, SEM, Raman and photoluminescence spectroscopies. The rheological behaviour of obtained hydrogels was evaluated. The AFM studies demonstrate that all synthesized chitosan incorporated ZnO composites hydrogels functionalized with propolis extract exhibit corrugated topographies. The present study highlights the possible incorporation of various guest molecules into hydrogel matrix due to its tuneable morphologies. The obtained hydrogel composites were cytocompatible in L929 fibroblast cell culture, in a range of concentrations between 50 and 1000 μg/mL, as assessed by MTT, LDH and Live/Dead double staining assays. By enhancing the biological properties, these novel green hydrogels show attractive superior performance in a wide concentration range to develop future in vivo suitable natural platforms as effective delivery systems of pharmacologic agents for biomedical applications.

New bimetallic LnTi-SBA-15 (where Ln is Eu or Pr) photocatalysts were obtained by immobilization of the lanthanide ions on Ti-SBA-15 supports synthesized by direct- and post-synthesis methods. The obtained materials were characterized by X-ray diffraction, SEM microscopy, N2 adsorption-desorption and UV-Vis spectroscopy. The obtained results evidenced an insignificant effect of Eu and Pr on support ordered mesoporous structure and optical properties of titania dispersed species. The activity of these photocatalysts was evaluated in the photocatalytic degradation, under UV light (254 nm), of Brilliant blue FCF from aqueous solutions. A higher activity was obtained for samples with lower loading of lanthanide. The best results were obtained for samples with lowest Eu oxide loading (2.5%).

The research focuses on a few key points concerning the light-driven processes taking place on TiO2 anatase and sodium titanates with tubular morphology, such as the relationship between the morphology and activity for H2 and CO2 production, density of surface hydroxyl groups, ROS ( OH and O2−) production and photocatalytic activity, and charge separation at the interface of semiconducting domains and enhancement of activity. One key point discussed is whether the materials with peculiar morphologies (i.e. tubular) are superior to the conventional ones. The experimental evidences show that the main advantage of the tubular morphology of sodium titanate is given by its significantly higher surface area compared to parental anatase. FTIR and XPS progressive analyses evidence that the density of surface hydroxyl groups decreases with the development of the tubular morphology. The radical trapping experiments show that the variation of surface hydroxyl density is, generally, followed by activities for OH and O2− generation, as well as by the photocatalytic production of H2 and CO2 from water/methanol mixture. Consequently, the ROS, formed by action of photogenerated electrons and holes on adsorbed O2 and hydroxyl groups, respectively, play an important role in determining the photocatalytic activity of titania-based materials. The other major aspect revealed by this research is that the charge separation at the interfaces formed between anatase and sodium titanate crystalline phases has remarkable effect on the activity formation rates of H2 and CO2.

Studies on the nitrate reduction reaction have shown that the bimetallic catalysts may be more efficient compared to the monometallic ones. To reduce nitrate, it is necessary to activate the precious metal by addition of a promoting second metal. Some studies have pointed out the relevance of the structure and geometry of the metal particles in the final mechanism of nitrate reduction. Well-defined nanoparticles could be used to catalyze structure-sensitive reactions with practical importance (pollution control). Our investigation aimed to make deeper insight into NO3- catalytic reduction and photocatalytic reduction mechanisms. Two types of Pt-Cu supported on TiO2 materials were employed in order to study the nitrate removal from aqueous phase and the ability of obtaining and using the in situ generated solar H2 as reducing agent. The prepared catalysts were characterized and tested in photocatalytic/catalytic reduction of nitrate in aqueous solution in water splitting reaction. A correlation between the catalytic/photocatalytic performances of the supported Pt-Cu catalysts and their associated physicochemical and adsorption properties has been made. The catalysts activity for the nitrate reduction can be directly related to the interactions between platinum and copper. Deposition with Pt nanoparticles was found to contribute to enhance the photocatalytic activity toward H2 production from aqueous solution. Our future research aims at optimizing the photocatalytic system having as future possible applications for hydrogen production using sunlight and water as the hydrogen source.

Titanium dioxide, TiO2, plays an important role due to its catalytic properties and high chemical [...]

A series of Pt-VOx/γ-Al2O3 catalysts with vanadium loading corresponding to 5 and 20 wt% V2O5 was prepared by impregnation method. The catalytic performance of the obtained materials was investigated in propene deep oxidation reaction. The catalysts were characterized by N2 physisorption, chemical analysis, X-ray diffraction (XRD), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, and UV–Vis diffuse reflectance spectroscopy. Alternating current (AC) electrical conductivity measurements (differential steps technique) were performed in situ during propene oxidation, using an own design reactivity cell. The variation in the measured electrical conductance brings information about the relative oxidation state of the catalyst's surface during reaction. It was found by TPR, EPR, and UV–Vis that the presence of platinum facilitates the reduction of V5+ to V4+ species. The catalytic performance of the investigated catalysts was discussed in relation to their structure, reducibility, and conductance.

Thin films of GexSb40-xSe60 (x = 15, 20, 25, 27, 32 and 35 at.%) were deposited on quartz by vacuum thermal evaporation of the pre-synthesized parental glasses powders. By spectroscopic ellipsometry the complex refractive index values are determined in the 0.20–33 μm spectral range. The optical band gap and single oscillator energies are established as a function of the Ge content and average coordination number Z. In the (0.85–3.5) μm spectral range the GexSb40-xSe60 films possess about 80% transmission. Infrared ellipsometric and Raman studies identified Se Se and Ge Ge homopolar bonds, oxygen and hydrogen related impurity bonds and heteropolar Ge Se and Sb Se chemical bonds. Neutron- and X-ray Diffraction data coupled with Reverse Monte Carlo simulations support the optical results reproducing the Ge Se and Sb Se cell units and cross-linked Ge Ge bonds. Atomic force microscopic imaging confirmed smooth surfaces with low RMS roughness values (

Iron (III) doped TiO2 nanopowders were synthesized by solgel method starting from the concentrated alcoholic solutions of tetraethyl (TET) and tetraisopropyl (TIP) orthotitanate precursors. TET precursor leads to gel formation while TIP precursor conducted to powder generation. The optimized thermal treatments, derived from TG/DTA analysis, allowed the transformation of precursor powders and gels into crystalline powders with anatase structure, as determined by X-ray diffraction (XRD). Corroboration of XRD, FT-IR and Raman investigations lead to the conclusion that Fe3+ was introduced substitutionally into TiO2 matrix. TEM analysis revealed similar morphology for all prepared samples, consisting of nanometric particles. UV–vis spectroscopy evidenced that Fe3+ dispersed into TiO2 matrix shifts the optical bandgap to the visible range. The photocatalytic mineralization of oxalic acid over Iron (III) doped TiO2 nanopowders under simulated solar irradiation was studied to assess the application potential of these materials in depollution field. CO2 production was identified as main product of photocatalytic reaction. The CO2 output was proportional to the surface area of the photocatalysts. In mean time, the lower was the optical band-gap of tested materials the higher was the photocatalytic activity for mineralization of oxalic acid. Introduction of Fe3+ into TiO2 lattice leads to creation of optically active redox sites, able to absorb the visible component of solar light. A reaction mechanism was advanced based on experimental facts. The role of substitutional Fe3+ in mechanism of oxalic acid photomineralization was examined in relationship with generation of e− and h+ charges and O2− and OH radicals. The optimized preparation method, requiring lower amounts of reagents and milder synthesis conditions, lead to homogeneous Fe3+/TiO2 materials with promising potential for depollution applications.

In the present study we report on a low cost synthesis of amorphous ZnO modified anatase TiO2 (40 and 20 mol% ZnO) thin films deposited via sol-gel spin coating technique on glass substrate. The effects of the composition on the structural, morphological and surface chemistry properties were discussed and correlated with the electrical behavior. Thus, by X-ray diffraction and Raman spectroscopy only TiO2 indexed in the anatase crystalline structure was identified without any ZnO characteristic crystalline phase. The surface chemistry assessed by X-ray Photoelectron spectroscopy highlighted the presence of Ti4+ in TiO2 as well as the presence of Zn2+ coordinated in the amorphous ZnO proved by the Auger ZnLMM transition shifted toward lower binding energies. The films are continuous, homogeneous with grain size below 20 nm and exhibit an intergranular porosity, as it was displayed by Scanning Electron Microscopy. The sensor signal towards CO exposure is strongly related to the amount of the ZnO amorphous phase formation. Thus, we found that a higher content of the ZnO amorphous phase leads to a lower sensitivity. The electrical and sensing measurements were performed in the temperature range (room temperature 400 °C), over the range of CO concentrations (0-2000 ppm). The sensor containing 20 mol.% amorphous ZnO exhibits a good sensitivity at ~300 °C for a low CO concentration .

In this paper, the CO oxidation on Pd/TiO 2 and Pd/SnO 2 /TiO 2 catalysts was studied using a non-conventional tool: AC electrical measurements in operando conditions. The structural and textural properties of the obtained powders have been characterized using BET, XRD, SEM, and CO chemisorption. Their redox properties were tested using the TPR technique. The surface dynamics was studied by electrical conductivity measurements under similar conditions with those encountered in the practical use in catalysis and correlated with their performances in CO oxidation.

The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO 2 . High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 °C) and by optimizing the ratios between reactants. The calcined tubular SiO 2 is characterized by intense and broad absorption band centered at ≈320 nm, spanning from deep UV to green. The formation of Si 3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320–380 nm. The photocatalytic generation of H 2 and CO 2 from water-methanol mixture under solar (AM 1.5) and visible (λ>390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO 2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO 2 are highlighted by employing [Ru(bpy) 3 ]Cl 2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO 2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields.

The aim of this paper is the replacing of the expensive sputtering method with the low cost sol–gel one in TCO applications. To this end two sets of indium tin oxide (ITO) thin films are compared and discussed in this paper: one obtained by r.f. sputtering and one by the sol–gel technique and dip-coating. For each of these sets of samples, a series of deposition parameters have been varied in an effort to obtain the most promising optical and electrical properties. Comparative structural, morphological and opto-electrical characterization of sol–gel and sputtered ITO-based films was performed by X-ray diffraction, Scanning electron microscopy, Atomic force microscopy, Spectroellipsometry, UV–VIS Spectroscopy and Hall Effect measurements in order to establish whether the chemical deposition method could lead to thin films with competitive properties as those obtained through the physical method. Comparable, high transmittance (85–90 %) in the VIS–NIR range (250–1050 nm) and carrier concentration values (1020–1021 cm−3) were obtained between sputtered and sol–gel ITO films. The sputtered ITO film in 75 % N2, annealed at 500 °C and the sol–gel 0.1 M ITO film with 10 layers deposited on SiO2/glass exhibit degenerate semiconductor behavior.

CuOx nanorods grown by calcination on a Cu plate and TiO2 successive layers were assembled by chemical means to obtain a broad band light captor. The synthesis of composite with complex architecture aimed at maximization of light absorption and at improvement of electron–holes separation of via the multiple n–p heterojunctions created at TiO2–CuOx boundaries, formed mostly by filling the pore network composite material with CuOx. Au nanoparticles were embedded into TiO2 matrix to enhance the light harvesting ability in visible domain via surface plasmon resonance (SPR) phenomenon and to help the photo-generated charge separation through the formation of Schottky barriers. Dual p–n semiconducting character of the composite was clearly evidenced by photoelectrochemical measurements. The composite material exhibited photoresponse even at wavelengths higher than 420 nm (in visible domain), both in cathodic and anodic regions. The enhanced light adsorption characteristics, the advancement in synthesis procedure of CuOx–Au_TiO2 composite material provide rationale for further development of novel light captor composites for photoenergy conversion. Other applications such electronics and gas sensors are envisaged.

We have explored an efficient strategy to enhance the overall photocatalytic performances of layered perovskites by increasing the density of hydroxyl group by protonation. The experimental procedure consisted of the slow replacement of interlayer Rb+ cation of RbLaTa2O7 Dion-Jacobson (DJ) perovskite by H+ via acid treatment. Two layered perovskites synthesized by mild (1200 &deg, C for 18 h) and harsh (950 and 1200 &deg, C, for 36 h) annealing treatment routes were used as starting materials. The successful intercalation of proton into D-J interlayer galleries was confirmed by FTIR spectroscopy, thermal analyses, ion chromatography and XPS results. In addition, the ion-exchange route was effective to enlarge the specific surface area, thus enhancing the supply of photocharges able to participate in redox processes involved in the degradation of organic pollutants. HLaTa_01 protonated layered perovskite is reported as a efficient photocatalyst for photomineralization of trichloroethylene (TCE) to Cl&minus, and CO2 under simulated solar light. The enhanced activity is attributed to combined beneficial roles played by the increased specific surface area and high density of hydroxyl groups, leading to an efficiency of TCE mineralization of 68% moles after 5 h of irradiation.

Two TiB2:(Na2B4O7–Al2O3)=3:5 and TiB2:(1.28Na2B4O7–Al2O3)=6:7 compositions, named 5DB and 7DB respectively, were prepared by combustion synthesis in simultaneous mode at 800, 900 and 1000 °C. X-ray diffraction, differential scanning calorimetry (DSC), UV–vis and room and high temperature Raman measurements were carried out to investigate the combustion products. The crystalline phase of the 5DB composite yielded at 1000 °C (5DB_1000), which represents 62 wt%, mostly consists of TiB2 (93 wt%) while Ti2O3 accounts for only 7 wt%. Also, the Na2Al2B2O7 compound was found to crystallize in the borate glassy matrix of the (5/7) DB composites obtained at the lower combustion temperatures. Proportion of the tetrahedral boron atoms, N4, in the blank and embedding sodium aluminium borate matrices was found from the high frequency Raman spectra using a constrained-width model in order to agree with the literature NMR data. The oxidation stability below 600 °C of the TiB2 crystallites in the (5/7) DB composites was proved by in-situ Raman measurements in air.

CO oxidation on TiO2 was studied in order to obtain detailed information about the reaction mechanism. Simultaneous kinetic and electrical measurements were performed at 400 °C. Experimental data have indicated that the oxidation occurs through a Langmuir–Hinshelwood mechanism, with the oxygen dissociation as rate-determining step.

AC electrical conductivity of CeO2 catalyst samples containing 5, 10 and 20 wt% SnO2 prepared by co-precipitation and of SnO2 and CeO2 pure oxides (prepared under the same conditions) was measured in operando conditions. The measurements were carried out at a frequency of 1592 Hz in the temperature range from room temperature up to 400 °C, using successively programmed heating–cooling cycles under various atmospheres. The catalyst samples were tested in the catalytic oxidation of CO in presence and in absence of oxygen in the same temperature range (30–400 °C). An improved deep oxidation of carbon monoxide has been found with these co-precipitated mixed oxides compared to pure components, leading to a better catalytic activity at lower temperature. The band gap energies were estimated based on the UV–Vis spectra and correlated with XRD results and AC electrical conductivity data. These results show the influence of the tin oxide on the electrical properties and oxygen mobility of the catalytic systems studied and on the surface behaviour of ceria.

A series of SnO2–CeO2 powder mixed oxides (with 5, 10, and 20 % wt SnO2) was prepared, characterized and used to study the sensing properties for CO, in absence of oxygen, using a CO-helium mixture. The results have shown that the SnO2–CeO2 powder has good response and recovery characteristics. This powder has better sensitivity to CO than pure SnO2 at the working temperature of 400–450 °C. A sensing mechanism was proposed and discussed in this paper. The results have indicated that the SnO2–CeO2 mixed oxides can be used as CO sensors, in absence of oxygen.

The surface behavior of a series of SnO2 (5, 10 and 20 wt.%) - CeO2 catalyst samples prepared by impregnation method and also pure SnO2, CeO2, was studied based on the response of the ac electrical conductivity. The electrical measurements were carried out in operando conditions in order to obtain information about the surface interaction with reactants during CO/hydrocarbon oxidation over these catalysts. The apparent activation energies of conduction in presence of CO:O2 and C3H6:air mixtures were presented. The catalyst samples were tested in catalytic oxidation of CO and C3H6 at temperature range of room temperature up to 400 C. The catalytic activity in both oxidation reactions and selectivity towards CO2 in propylene oxidation at 400 C exhibited by the SnO2-CeO2 systems were significantly higher to those exhibited by the pure ceria catalyst.

Newly prepared SnO2-CeO2 catalyst samples used as depollution catalysts were characterized applying low-temperature nitrogen adsorption (BET), X-ray diffraction (XRD), thermo-gravimetry (TG-dTG) and temperature-programmed reduction (TPR) methods. Pure SnO2 has higher surface area (17 m2/g) than the pure CeO2 (8 m2/g). Addition of organic tin oxide precursor to ceria in amount of 5 wt% slightly decreases the surface area of CeO2 (SSn5-Ce= 7 m2/g). The increase of tin oxide content to 10 and 20 wt% increases the surface area of the catalyst (SSn10-Ce= 9 m2/g; SSn20-Ce= 10 m2/g). A similar effect was observed for pores of 1.7-300nm size. Catalyst sample Sn5-Ce exhibited the lowest pore volume, which increases with increasing the amount of tin oxide. Tin dioxide in Sn-Ce samples with lower loadings of SnO2 (.10 wt%) were well dispersed showing amorphous structure. High loading (20 wt%) of tin dioxide in Sn-Ce showed XRD lines of formation of cassiterate crystalline structure of SnO2 without evidence of solid solution formation. In case of SnO2 the TPR profile exhibits a major peak at about 545 C with much greater intensity than in case of CeO2, revealing that SnO2 was more easily reducible than CeO2. Sn-Ce samples exhibit reducibility at lower temperatures (between 545-635 C) compared to the single tin dioxide (750 C).

The electrical conductivity and the catalytic activity of SnO2 loaded TiO2 (anatase) particles were investigated in operando conditions. SnO2 depositions over commercial TiO2 samples (Sigma Aldrich and Rhone Poulenc) were obtained by the impregnation method. The samples were characterized by XRD, SEM/EDX and BET–N2 adsorption techniques. The AC electrical conductivity of the samples were measured between 25 and 400 °C under various atmospheres. The effect of the reactant mixture on the electrical conductivity and the catalytic performances of the samples were tested in propene oxidation. The results showed that the conductivity of SnO2/TiO2 samples depends strongly on the surface area of TiO2 support. The reducing effect of propene is more evident for higher surface area catalysts, these one showing also higher activity. On the other hand, the SnO2 deposition results in an increase of catalytic performances.

The changes of the electrical properties of semiconductor oxide catalysts, when measured in situ provide useful information about surface processes as adsorption/desorption/reaction occur with charge transfer. The electrical properties of polycrystalline powders, mainly controlled by inter-grain Schottky-type barriers, are sensible to the “quality” of the surface/inter-grain domains, to sample morphology and to changes in charge and coverage of the surface due to operating conditions. This can be exploited to study oxide catalysts dispersed on supports at nanoscale levels for answering questions like: (i) adsorption ability of the surface layer and (ii) the influence of the active phase and of the support. It is demonstrated that for low loading supported SnO 2 or V 2 O 5 catalysts (also important as sensor materials), the conductivity plots show the “fingertip” of the support, which controls the behavior of the supported phase. As an example, the lower propylene combustion activity of SnO 2 when dispersed on γ-Al 2 O 3 is explained by hydrophile/proton conductor properties of the support; γ-Al 2 O 3 diminishes the oxygen adsorption ability of SnO 2 by providing a higher concentration of molecularly adsorbed water and surface OH groups towards its surface. It is proposed that by selecting appropriate n-type semiconductor oxide supports (as TiO 2 ), and by increasing the surface conductivity one can increase the oxygen adsorption ability of the supported phase, with increased activity for combustion/chemical sensing. This suggests the possibility of tuning the surface properties of the supported oxide by inter-phase charge (electron or ion) transfer.

Oxide ion conductors have been increasingly studied for many years because of their application in devices with high economical impact such as solid oxide fuel cells (SOFC), oxygen sensors, and dense ceramic membranes for oxygen separation, and membrane reactors for oxidative catalysis. New fast oxide ion conductors for low temperature applications (400–600 °C) have been proposed during recent years. The influence of Sb2O3 and Ta2O5 as on the Bi2O3 structures and the corresponding electrical behavior were investigated. The powder products, obtained by solid state reactions, were characterized by XRD and SEM. They were sintered at different temperatures and the bulk ceramics were characterized and their electrical behavior versus temperature were recorded. This investigation underlines the influence of the nature of dopants on the structures and electrical performances bismuth based oxides. For microstructure analysis the theory of fractals was used.

Changes of electrical conductance and capacity of γ-Al 2 O 3 were studied in situ during dehydration/rehydration in gas flow. The measurements were performed at atmospheric pressure by following a standard protocol of experiments, and were coupled with simultaneous monitoring of the composition of the inlet/effluent gas. The electrical properties are dominated by the protonic conduction. It was shown that at low temperature this occurs by vehicle mechanism, being facilitated by the presence of water molecule adsorbed on γ-Al 2 O 3 surface; the decrease of electrical conductance on heating is obviously connected with dehydration. At higher temperature ( t >200°C) conduction is dominated by proton hopping between OH groups (Grotthuss mechanism). It is suggested that in current operating conditions in catalysis, γ-Al 2 O 3 is only partially dehydrated/dehydroxylated, the bulk acting as a source of water/OH groups for the surface; this process controls the acidity of alumina and alumina-supported catalysts.