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Made available in DSpace on 2021-06-25T11:44:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-12-07 LNLS, Campinas, SP, Brazil Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this study, we report the potential of ethylenediamine (En) in the modification of the morphological, structural, optical and catalytic properties of alpha-Ag2WO4 crystals decorated with Ag nanoparticles (Ag NPs). Experimental techniques were used to characterize the as-synthesized samples such as X-ray diffraction, Raman, electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and photoluminescence spectroscopy. The results confirmed the efficiency of En in the decoration with the formation of Ag/alpha-Ag2WO4 crystals and also the modification of alpha-Ag2WO4 morphology that indicated its influence on the crystal growth mechanism via self-assembly and Ostwald ripening. En affects the degree of order/disorder of the crystalline structures in long and short-ranges. In addition, photoluminescence measurements revealed a blue shift of the optical emission caused by a reduction of oxygen vacancies and an increase in structural disorder due to the En concentration used in the synthesis processes. Regarding the photocatalysis experiments, the reduction in oxygen vacancies also caused a decrease in the photoactivity of alpha-Ag2WO4 against the rhodamine B dye, thus confirming the relevance of oxygen vacancies for the development of alpha-Ag2WO4 photocatalysts. Univ Fed Sao Carlos, Ctr Dev Funct Mat, Rod Washington Luiz,Km 235, BR-13565904 Sao Carlos, SP, Brazil Sao Paulo State Univ, Interdisciplinary Lab Ceram Studies, BR-14800900 Araraquara, SP, Brazil Univ Estadual Campinas, Inst Chem, Dept Phys Chem, BR-13083970 Campinas, SP, Brazil Univ Fed Sao Carlos, Dept Phys, Rod Washington Luiz,Km 235, BR-13565905 Sao Carlos, SP, Brazil Sao Paulo State Univ, Interdisciplinary Lab Ceram Studies, BR-14800900 Araraquara, SP, Brazil LNLS, Campinas, SP, Brazil: XAFS2-20180338 CNPq: 443733/2018-0 FAPESP: 2013/07296-2 FAPESP: 2017/12437-5 CAPES: 001

International audience; Chemiresistors are highly important for monitoring and detection of harmful gases produced from industrial processes and vehicle emissions. We report herein an experimental investigation of the gas-sensing properties of Zn0.95Co0.05O thin film deposited by spray pyrolysis technique. The X-ray photoelectron spectroscopy indicated the presence of Co2+ ions into de ZnO lattice. The gas-sensing measurements revealed the sensitivity of Zn0.95Co0.05O film towards ozone gas in a wide range of concentrations from 20 to 1040 ppb, exhibiting good repeatability and total reversibility after consecutive exposures. Selectivity towards ozone is observed in comparison to NO2, NH3, and CO gases even at low levels. This manuscript reports the effectiveness of spray-pyrolysis method for obtaining nanostructured Zn1-xCoxO thin films for practical applications as an ozone gas sensor.

CO2 electrochemical reduction reaction (CO2RR) is an attractive strategy for closing the anthropogenic carbon cycle and storing intermittent renewable energy. Tin-based electrocatalysts exhibit remarkable properties for reducing CO2 into HCOOH. However, the effects of morphology and oxidation state of tin-based electrocatalysts on the performance of CO2 reduction have not been well-described. We evaluate the oxidation state and particle size of SnOx for CO2 reduction. SnOx was effective for converting CO2 into formic acid, reaching a maximum selectivity of 69%. The SnO exhibited high activity for CO2RR compared to SnO2 electrocatalysts. A pre-reduction step of a SnO2 electrocatalyst increased its CO2 reduction performance, confirming that Sn2+ is more active than Sn4+ sites. The microsized SnO2 is more effective for converting CO2 into formic acid than nanosized SnO2, likely due to the impurities of nanosized SnO2. We illuminated the role played by both SnOx particle size and oxidation state on CO2RR performance. Graphic abstract

Made available in DSpace on 2018-11-29T12:10:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-06-05 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Brazilian Nanotechnology National Laboratory Brazilian Laboratory of Synchrotron Radiation (LNLS) Generalitat Valenciana, Ministerio de Economia y Competitividad Programa de Cooperacion Cientifica con Iberoamerica (Brazil), Ministerio de Educacion This paper consists of an experimental investigation on the effects of annealing temperature on the structural, surface and ozone gas-sensing properties of CuWO4 nanoparticles prepared via a sono-chemical route. X-ray diffraction patterns and X-ray absorption near-edge structure spectroscopy revealed that both long-and short-order structures increase with the annealing temperature. Electrical resistance measurements indicated that CuWO4 samples were sensitive in the range of 15-1400 ppb, exhibiting a good reversibility and repeatability. The enhancement of the ozone gas-sensing properties was attributed to the reduction of hydroxyl species and the improvement of the crystallization degree. This study provides a versatile strategy for obtaining CuWO4 nanoparticles for practical applications as an ozone gas sensor. (C) 2018 Elsevier B.V. All rights reserved. Sao Paulo State Univ, Inst Chem, POB 355, BR-14801907 Araraquara, SP, Brazil Aix Marseille Univ, CNRS UMR 7334 IM2NP, FS St Jerome S152, F-13397 Marseille, France Univ Estadual Piaui, PPGQ CCN, POB 381, BR-64002150 Teresina, PI, Brazil Univ Fed Sao Carlos, Dept Phys, Lab Nanostruct Multifunct Mat, BR-13565905 Sao Carlos, SP, Brazil Jaume I Univ, Dept Chem & Phys, Castellon De La Plana, Spain Sao Paulo State Univ, Inst Chem, POB 355, BR-14801907 Araraquara, SP, Brazil FAPESP: 2013/07296-2 FAPESP: 2017/10313-7 FAPESP: 2017/12437-5 CNPq: 310863/ 2014-7 CNPq: 434266/2016-7 Brazilian Nanotechnology National Laboratory: LMF-18580 Brazilian Laboratory of Synchrotron Radiation (LNLS): D04B-XAFS111883

Made available in DSpace on 2018-11-26T17:44:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The need to improve the sensitivity, selectivity and stability of ozone gas sensors capable of monitoring the environment to prevent hazard to humans has sparked research on binary metal oxides. Here we report on a novel ozone gas sensor made with ca. 0.5 mu m yolk-shelled ZnCo2O4 microstructures synthesized via an eco-friendly, co-precipitation method and subsequent annealing. With these ZnCo2O4 microspheres, ozone concentrations down to 80 parts per billion (ppb) could be detected with a.c. and d.c. electrical measurements. The sensor worked within a wide range of ozone concentrations, from 80 to 890 ppb, being also selective to ozone compared to CO, NH3 and NO2. The high performance could be attributed to the large surface area to volume ratio inherent in yolk-shell structures. Indeed, ozone molecules adsorbed on the ZnCo2O4 surface create a layer of holes that affect the conductivity, as in a p-type semiconductor. Since this mechanism of detection is generic, ZnCo2O4 microspheres can be further used in other environment monitoring devices. (c) 2017 Elsevier B.V. All rights reserved. Univ Sao Paulo, Sao Carlos Inst Phys, CP 369, BR-13560970 Sao Carlos, SP, Brazil Univ Calif Berkeley, Dept Mech Engn, Berkeley, CA 94720 USA Univ Fed Sao Carlos, Dept Phys, Rodovia Washington Luis Km 235, BR-13565905 Sao Carlos, SP, Brazil Myongji Univ, Dept Energy Sci & Technol, Yongin, South Korea Sao Paulo State Univ, Inst Chem, Dept Phys Chem, POB 355, BR-14800900 Araraquara, SP, Brazil Sao Paulo State Univ, Inst Chem, Dept Phys Chem, POB 355, BR-14800900 Araraquara, SP, Brazil FAPESP: 2012/15543-7 FAPESP: 2013/14262-7 FAPESP: 2013/07296-2 FAPESP: 2014/23546-1 FAPESP: 2016/23474-6

This manuscript addresses an experimental and theoretical investigation regarding the ozone (O3) gas-sensing properties of hematite microrhombuses obtained via the hydrothermal method. Gas-sensing experiments showed the sensitivity of the microrhombuses towards O3 gas from 12 ppb (parts-per-billion), presenting total recovery and a long-term stability of 4 months. Theoretical calculations revealed that the surfaces play an important role in the adsorption/desorption processes. Moreover, it was found that the presence of (1 0 4) surfaces is favorable to the high sensitivity towards O3 molecules, confirming the experimental results. These results allowed us to better understand the morphological changes and directly relate the sensing performance of hematite microcrystals at different exposed surfaces.

Made available in DSpace on 2018-11-26T15:44:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-11-30 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Financiadora de Estudos e Projetos (FINEP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposites were successfully synthesized using a facile microwave-hydrothermal method under mild conditions, and their electrocatalytic properties towards O-2 evolution were investigated. The microwave radiation played an important role in obtainment of well dispersed ZnO nanoparticles directly on reduced graphene oxide sheets without any additional reducing reagents or passivation agent. X-ray diffraction (XRD), Raman and infrared spectroscopies indicated the reduction of GO as well as the successful synthesis of rGO-ZnO nanocomposites. The chemical states of the samples were shown by XPS analyses. Due to the synergic effect, the resulting nanocomposites exhibited high electronic interaction between ZnO and rGO sheets, which improved the electrocatalytic oxidation of water with low onset potential of 0.48 V (vs. Ag/AgCl) in neutral pH and long-term stability, with high current density during electrolysis. The overpotential for water oxidation decreased in alkaline pH, suggesting useful insight on the catalytic mechanism for O-2 evolution. (C) 2017 Elsevier B.V. All rights reserved. Univ Fed Uberlandia, Inst Quim, BR-38400902 Uberlandia, MG, Brazil Univ Estadual Paulista, LIEC, Inst Quim, BR-14800900 Araraquara, SP, Brazil Univ Fed Sao Carlos, Dept Fis, BR-13565905 Sao Carlos, SP, Brazil Univ Fed Sao Carlos, Dept Quim, LIEC, BR-13565905 Sao Carlos, SP, Brazil Univ Estadual Paulista, LIEC, Inst Quim, BR-14800900 Araraquara, SP, Brazil FAPEMIG: APQ-00988-13 FAPEMIG: CEX-RED-00010-14 FAPEMIG: APQ-00330-14

In this contribution, we present an experimental and theoretical investigation of the role of counter-ions in the crystal morphology, surface structure, and photocatalytic activity of hierarchical ZnO nanostructures. The effect of zinc precursor (nitrate, acetate and, sulfate) along the synthesis of ZnO nanostructures grown directly onto a substrate by means of a simple hydrothermal method was analyzed in detail. Scanning electron microscopy images showed a preferential growth of ZnO nanostructures along the c-axis, with a slight reduction in the orientation depending on the choice of the Zn source. Theoretical calculations based on the Wulff theory allowed us to better understand the morphological changes and directly relate the photocatalytic performance at the different exposed surfaces of the as-observed crystal shapes. Our results showed that photocatalytic activities in the discoloration of organic dyes became superior for hierarchical ZnO nanostructures obtained from zinc nitrate. This finding was explained by X-ray photoelectron and photoluminescence spectroscopies, which revealed that in addition to, the attached counter-ions and the abundance of carboxylate groups and organic residuals on ZnO surfaces, the presence of surface defects are determinant to enhance the photocatalytic performance of the material.

Over the last decades, there has been considerable interest in the synthesis of one-dimensional (1D) metal oxide nanostructures that can be used in gas sensor devices. Heterostructures, obtained by a combination of different semiconductor nanomaterials with different band energies, have been extensively studied in order to enhance their gas-sensing performance. In this context, our present study focuses on the investigation of chemiresistive-sensing capabilities of a combination of TiO2 nanoparticles and V2O5 nanowires obtained via hydrothermal treatment of the peroxo-metal complex. The formation of V2O5/TiO2 heterostructures was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) measurements. This study also proposes an efficient approach to produce 1D V2O5/TiO2 heterostructures with a good range of detection (0.09–1.25 ppm) and remarkable ozone-sensing properties related to repeatability and selectivity., The authors gratefully acknowledge the financial support of the Brazilian research funding agencies FAPESP (under grant number FAPEP 2013/17639-4, 2013/07296-2, 17/18649-4, and 2017/12437-5), CNPq (311463/2017-7), and CAPES (Financial Code 001). Transmission electron microscopy (TEM-21464) and X-ray photoelectron spectroscopy (XPS20607 and XPS-21082) were performed at the LME/ LNNano/CNPEM. The electrodes used for the gas-sensing experiments were fabricated in the Laboratory of Microfabrication at the LNNano/CNPEM (Projects LMF-18580). The STEM-EELS and HRTEM measurements were performed in the Advanced Microscopy Laboratory (LMA) at the Institute of Nanoscience of Aragon (INA), University of Zaragoza (Spain). R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MAT2016-79776-P) and the Government of Aragon through projct DGA E13_17R (FEDER, EU).

Two kinds of flexible ozone (O3) sensors were obtained by placing pristine ZnO nanorods and gold-modified ZnO nanorods (NRs) on a bi-axially oriented poly(ethylene terephthalate) substrate. The chemiresistive sensor is operated at typically 1 V at room temperature under the UV-light illumination. The ZnO nanorods were prepared via a hydrothermal route and have a highly crystalline wurtzite structure, with diameters ranging between 70 and 300 nm and a length varying from 1 to 3 μm. The ZnO NRs were then coated with a ca. 10 nm gold layer whose presence was confirmed with microscopy analysis. This sensor is found to be superior to detect ozone at a room temperature. Typical figures of merit include (a) a sensor response of 108 at 30 ppb ozone for gold-modified ZnO NRs, and (b) a linear range that extends from 30 to 570 ppb. The sensor is stable, reproducible and selective for O3 compared to other oxidizing and reducing gases. The enhanced performance induced by the modification of ZnO nanorods with thin layer of gold is attributed to the increased reaction kinetics compared to pristine ZnO NRs. The sensing mechanism is assumed to be based on the formation of a nano-Schottky type barrier junction at the interface between gold and ZnO.

Made available in DSpace on 2019-10-06T15:22:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Zinc sulfide (ZnS) is a II–VI inorganic semiconductor material and has received remarkable attention because of fundamental physical properties, versatility, nontoxicity, chemical stability and has been widely applied to make numerous optical devices as phosphor material. As a wide band gap semiconductor, ZnS can easily host different metal ions as luminescent center to improve or modify its structural and optical performances such as Cu atoms. In this paper, ZnS:Cu nanoparticles were synthesized by solvothermal method and the photoluminescence and the structural at long- and local-range properties were characterized. According to X-ray diffraction results, ZnS sample crystallizes with the cubic zinc blende structure (F-43m space group) without spurious phases. Images from transmission electron microscope depict the morphology of ZnS particles as round shape and average size value lower than 5 nm. Theoretical and experimental X-ray absorption near edge structure (XANES) spectra at Zn K-edge suggest the incorporation of Cu atoms into the ZnS host and indicate the occurrence of Zn and S vacancies, which are confirmed by extended X-ray absorption fine structure (EXAFS) fit results. These native defects are related to a red-shift observed in the peak emission of photoluminescence (PL) spectrum for ZnS sample, which is centered at ~ 504 nm. An emission in orange-red region is observed as Cu is incorporated in the ZnS host matrix that is attributed to the transition from the 4T1 level to the 6A1 level. Moreover, the intensity of the emissions due to zinc vacancies and interstitial zinc in the deconvoluted PL spectrum is in accordance with results determined in X-ray absorption spectroscopy characterization. Institute of Geosciences and Exact Sciences São Paulo State University Unesp Department of Physics Federal University of São Carlos UFSCar São Carlos Institute of Physics University of São Paulo USP LIEC Department of Chemistry Federal University of São Carlos UFSCar Institute of Geosciences and Exact Sciences São Paulo State University Unesp FAPESP: 2013/07296-2 FAPESP: 2013/12993-4 FAPESP: 2017/12437-5 CNPq: 473568/2013-6

Metal molybdate compounds have attracted considerable attention due to their technological applications. Herein, we demonstrate the controllable synthesis of cerium molybdate (Ce2(MoO4)3) nanocrystals via the co-precipitation method followed by microwave-assisted hydrothermal (MAH) treatment at 150 C during different times (15, 30 and 60 min). The effect of MAH treatment time on the microstructural, optical, and ozone gas-sensing properties of these nanocrystals was investigated. X-ray diffraction (XRD) and Raman spectroscopy measurements revealed that the samples presented a single-crystalline phase with scheelite-type tetragonal structure. Field emission gun scanning electron microscopy (FEG-SEM) images showed that the MAH conditions favored changes in the Ce2(MoO4)3 nano crystal morphology. Photoluminescence (PL) measurements indicated a significant enhancement of PL emission with MAH time, suggesting an increase in the intrinsic defects formed during the MAH treatment. The gas-sensing performance of cerium molybdate nanocrystals towards sub-ppm ozone levels was also investigated. The experiments revealed complete recovery and good repeatability as well as good sensor response, which was improved in the sample synthesized at longer MAH time

Strontium titanate nanoparticles have attracted much attention due to their physical and chemical properties, especially as photocatalysts under ultraviolet irradiation. In this paper, we analyze the effect of heating rate during the crystallization process of SrTiO3 nanoparticles in the degradation of organic pollutants. The relationship between structural, morphological and photocatalytic properties of the SrTiO3 nanoparticles was investigated using different techniques. Transmission electron microscopy and N2 adsorption results show that particle size and surface properties are tuned by the heating rate of the SrTiO3 crystallization process. The SrTiO3 nanoparticles showed good photoactivity for the degradation of methylene blue, rhodamine B and methyl orange dyes, driven by a nonselective process. The SrTiO3 sample with the largest particle size exhibited higher photoactivity per unit area, independent of the molecule to be degraded. The results pointed out that the photodegradation of methylene blue dye catalyzed by SrTiO3 is caused by the action of valence band holes (direct pathway), and the indirect mechanism has a negligible effect, i.e. degradation by O2 (-•) and (•) OH radicals attack.

We report on the chemiresistive gas sensing characteristics of ZnO nanorods (NRs) modified by a thin layer of nickel phthalocyanine (NiPc). Ozone detection was carried out through electrical measurements with an optimized performance at 250°C, good reproducibility and suitable concentration range (from 80 to 890 ppb) for technological applications. The hybrid NiPc:ZnO films had superior performance to pure ZnO nanorods in terms of response time and sensitivity. The response times were 22 s and 26 s, respectively, whereas the ratio of resistances under ozone and air was 3.27 for NiPc:ZnO films and 2.56 for the pure ZnO NRs. The improvement in response time is attributed to the large surface area generated with the coating of the ZnO nanorods with the NiPc layer. Significantly, images taken with field-emission scanning electron microscopy (FE-SEM) indicated that the ZnO nanorods were fully covered with NiPc. X-ray diffraction measurements (XRD) revealed a preferential growth of the nanorod-like structures along the [100] direction. In summary, a successful approach has been developed to functionalize ZnO nanorods, which is promising for detection of ppb levels of ozone gas.

Made available in DSpace on 2018-11-26T17:55:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-10-25 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Brazilian Nanotechnology National Laboratory (LNNano), Microfabrication laboratory, Campinas, SP, Brazil Generalitat Valenciana Ministerio de Ciencia e Innovacion Programa de Cooperacion Cientifica con Iberoamerica (Brazil) Ministerio de Educacion This manuscript addresses the synthesis of one-dimensional (1D) alpha-Ag2WO4 nanorod-like structures via a microwave-assisted hydrothermal method to be used as an acetone gas sensor. The nanorods showed excellent gas-sensing performance, evidenced by their sensor response and repeatability, as well as a good range of detection (0.5-20.0 ppm). The manuscript also proposes an easy and efficient way of obtaining 1-D alpha-Ag2WO4 nanorods that exhibit remarkable acetone sensing properties. (C) 2016 Elsevier B.V. All rights reserved. Univ Estadual Paulista, Inst Quim, LIEC, POB 355, BR-14800900 Araraquara, SP, Brazil Univ Sao Paulo, Inst Fis Sao Carlos, Ave Trabalhador Sao Carlense 400, BR-13566590 Sao Carlos, SP, Brazil Univ Fed Sao Paulo, Dept Fis, Rodovia Washington Luiz, Sao Carlos, SP, Brazil DQ GERATEC Univ Estadual Piaui, BR-64002150 Teresina, PI, Brazil Univ Jaume 1, Dept Quim Fis & Analit, Campus Riu Sec, E-12080 Castellon de La Plana, Spain Aix Marseille Univ, CNRS UMR 7334 IM2NP, FS St Jerome S152, F-13397 Marseille, France Univ Estadual Paulista, Inst Quim, LIEC, POB 355, BR-14800900 Araraquara, SP, Brazil FAPESP: 2013/09573-3 FAPESP: 2013/07296-2 FAPESP: 2012/15170-6 FAPESP: 479644/2012-8 FAPESP: 442076/2014-2 FAPESP: 304531/2013-8 Brazilian Nanotechnology National Laboratory (LNNano), Microfabrication laboratory, Campinas, SP, Brazil: 17168 Generalitat Valenciana: Prometeo/2009/053 Ministerio de Ciencia e Innovacion Programa de Cooperacion Cientifica con Iberoamerica (Brazil): CTO2009-14541-C02 Ministerio de Educacion: PHB2009-0065-PC

Made available in DSpace on 2018-12-11T16:59:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-15 Small-angle X-ray scattering (SAXS) and nitrogen adsorption were used to study ambient pressure drying (APD) silica aerogels prepared from hydrolysis of tetraethoxysilane (TEOS) with additions of sodium dodecyl sulfate (SDS). The surfactant-extracted precursor wet gels have presented mass-fractal structure with typical fractal dimension 2.25 in a SAXS characteristic length scale from ∼10 nm to ∼0.35 nm. Hydrophobic APD aerogels with typical specific surface of 800 m2/g and bulk density of 0.20 g/cm3 were obtained after silylation of the precursor wet gels with a mixture of hexamethyldisiloxane (HMDSO) and trimethylchlorosilane (TMCS). The pore volume and the mean pore size of the APD aerogels increased with increasing the SDS quantity. APD aerogels presented most of the mass-fractal characteristics of the precursor wet gels at large length scales. The radius of gyration of the clusters of the APD aerogels (typically 17 nm) increased with increasing the SDS quantity, while the radius of the silica primary particles (typically 2.0 nm) increased at first with the addition of SDS (with respect to the sample without SDS) and decreased regularly afterward with increasing the SDS quantity. The primary particles presented yet some internal inhomogeneity and a diffuse-boundary interface with thickness of about 0.7 nm, according to a linear-gradient model for the diffuse boundary. Unesp-Univ Estadual Paulista IGCE Departamento de Física, Cx.P. 178 Unesp-Univ Estadual Paulista IQ Departamento de Bioquímica e Tecnologia, Rua Prof. Francisco Degni, 55 Unesp-Univ Estadual Paulista IGCE Departamento de Física, Cx.P. 178 Unesp-Univ Estadual Paulista IQ Departamento de Bioquímica e Tecnologia, Rua Prof. Francisco Degni, 55

Made available in DSpace on 2018-11-26T15:31:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Nanostructured semiconducting oxides have been used as resistive gas sensors of toxic and non-toxic gases, but little emphasis has been placed on ozone sensing. Here we present a new ozone gas sensor based on hierarchical NiCo2O4 cubic structures synthesized via a facile urea-assisted co-precipitation method and annealed at 450 degrees C, which showed a low detection level. Ozone detection was carried out through electrical measurements with an optimized performance at 200 degrees C, with fast response (similar to 32 s) and recovery (similar to 60 s) time with suitable concentration range (from 28 to 165 ppb) for technological applications. Furthermore, NiCO2O4 platelets are selective to ozone compared to other oxidizing and reducing gases. The low detection level can be attributed to the coexistence of 3D structures based on hexagonal platelet-like and porous flower-like shape, which were revealed by field emission scanning electron microscopy (FE-SEM). In summary, NiCo2O4 is promising for detection of sub-ppb levels of ozone gas. Univ Sao Paulo, Sao Carlos Inst Phys, CP 369, BR-13560970 Sao Carlos, SP, Brazil Sao Paulo State Univ, Inst Chem, LIEC, POB 355, BR-14800900 Araraquara, SP, Brazil Myongji Univ, Dept Energy Sci & Technol, Yongin, South Korea Aix Marseille Univ, CNRS IM2NP, UMR 7334, FS St Jerome S152, F-13397 Marseille, France Sao Paulo State Univ, Inst Chem, LIEC, POB 355, BR-14800900 Araraquara, SP, Brazil FAPESP: 2014/23546-1

In this manuscript, we report an investigation into the sensitivity of two oxidizing gases (ozone and nitrogen dioxide) for nanocrystalline SrTi 0.85 Fe 0.15 O 3 thin films deposited by the electron beam physical vapor deposition technique. Annealing treatment at 500 °C enhanced the crystallization and surface roughness of the thin film. Electrical measurements revealed that the thin film was sensitive to oxidizing gases, especially to low ozone gas levels, exhibiting a fast response time, a short recovery time as well as good reproducibility and reversibility. These findings demonstrate the great potential of the SrTi 0.85 Fe 0.15 O 3 compound to be applied as a selective ozone gas sensor.

A novel and promising ozone gas sensor based on α-Ag2WO4 rod-like structures is obtained via a microwave-assisted hydrothermal method. The electrical resistance measurements show a good gas sensor performance of nanorods at an operating temperature of 300 °C, especially a fast response and a short recovery time.