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Made available in DSpace on 2020-12-12T01:27:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-01 Volatile organic compounds (VOCs) can be associated with some diseases when found in human exhaled breath as a result of alterations in metabolic pathways. Therefore, the development of highly selective sensors to a particular VOC is required. In this paper, we used silica (SiO2) nanospheres as support for the growth of cobalt (II) oxide (CoO) nanosheets, resulting in the SiO2@CoO core-shell structure with a high specific surface area. This structure was applied as a chemoresistive VOCs sensor. The SiO2@CoO material exhibited increased sensitivity to 2-butanone in comparison with acetone, methanol, ethanol, isopropanol, acetaldehyde, benzene, toluene, and m-xylene. The response to 100 ppm of 2-butanone was ~44.7, with a response time of 27 s. The enhanced performance might be attributed to the high surface area provided by the unique core-shell structure with 2D CoO nanosheets. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265 Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265

Made available in DSpace on 2022-04-28T19:42:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-30 The chemical composition, oxidation degree, and sheet size strongly affect the properties of graphene oxide (GO). Therefore, much effort has been directed to improve the synthesis of GO and control its structure. Herein, we report the reoxidation of GO using milder conditions of a modified Hummers’ method, including shorter reaction times and a reduced proportion of chemicals to obtain the reoxidized GO (Ox-GO). The reoxidation impact was evaluated by studying the materials’ adsorption performance towards methylene blue (MB) and rhodamine B (RB). Compared to GO, Ox-GO presents a similar C/O ratio, increased interlayer spacing, smaller sheets with holes, a higher exfoliation degree, and slight differences in each oxygenated functional group. Our measurements evidence that Ox-GO has an MB adsorption capacity more than 30% higher than GO under different conditions of dye concentration and pH. Moreover, Ox-GO also shows a notable improvement in the RB removal for a high dye concentration, where the removal capacity is almost 40% higher than that of GO. The enhancements in the dyes’ removal are attributed to the increased accessible surface area of Ox-GO, which provides more sites for dyes’ adsorption. Laboratory of Materials for Sustainability (LabMatSus) São Paulo State University (UNESP), Rua Cristóvão Colombo 2265 Center for Information Technology Renato Archer (CTI), Rod. D. Pedro I, KM 143.6, 13069-901 Campinas Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85 Center for Hybrid Nanostructures (CHyN) Institute of Nanostructure and Solid State Physics University of Hamburg, Luruper Chaussee149 Laboratory of Materials for Sustainability (LabMatSus) São Paulo State University (UNESP), Rua Cristóvão Colombo 2265

Made available in DSpace on 2021-06-25T10:27:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Triethylamine (TEA), a volatile organic compound (VOC), is present in several industrial processes and is harmful to human health. Therefore, the development of highly sensitive TEA sensors is desirable. Semiconductor metal oxides (SMOx) have been widely used for VOCs detection due to their efficiency and feasibility. Herein, we report the template-free synthesis of zinc stannate nanocubes (NC-ZnSnO3) by the microwave-assisted hydrothermal method followed by a calcination step. The sample's sensing properties were investigated for different VOCs (methanol, ethanol, isopropanol, acetic acid, acetone, 2-butanone, acetaldehyde, benzene, toluene, m-xylene, and TEA). The sensor presented an improved selectivity toward TEA, showing the highest response of 57.5 to 100 ppm of TEA with a fast response time of 4 s at the optimum operating temperature of 350 °C. The NC-ZnSnO3 also showed a low detection limit for TEA of about 0.6 ppm. In summary, this work described an efficient method for producing NC-ZnSnO3 and demonstrated that this material has high selectivity and sensitivity for TEA detection. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo 2265 Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo 2265 FAPESP: 2016/25267-8 FAPESP: 2017/01267-1 FAPESP: 2018/00033-0 FAPESP: 2018/01258-5 FAPESP: 2020/05233-7 FAPESP: 2020/06421-1

Made available in DSpace on 2021-06-25T10:14:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-28 Sensors of volatile organic compounds (VOCs) are of great importance for environmental monitoring. Nevertheless, it is a great challenge to develop highly sensitive and selective sensors. In this sense, we report the synthesis of ZnO twin-rods via a combination of the ultrasonic spray nozzle and microwave-assisted hydrothermal methods, which were then loaded with platinum (Pt) nanoparticles (NPs) to obtain Pt/ZnO heterostructures. The VOC detection tests revealed that the 2% Pt/ZnO heterostructure was the best composition, which showed an improved response of 35.2 to 100 ppm of butanone at 450 °C, with high sensitivity to detect low concentrations of butanone (5 ppm) as well as high selectivity and stability. X-ray absorption spectroscopy studies revealed the presence of oxidized Pt species (PtOx) under optimal operating conditions. Thus, the enhanced sensitivity of 2% Pt/ZnO can be attributed to the p-n junction at the PtOx/ZnO interface. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo 2265 Institute of Physics Federal University of Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500 Brazilian Synchrotron Light Laboratory (LNLS) CNPEM, R. Giuseppe Máximo Scolfaro 10.000 Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo 2265

ACS applied materials & interfaces 12(15), 17745 - 17751 (2020). doi:10.1021/acsami.0c01641, Monitoring carbon dioxide (CO$_2$) levels is extremely important in a wide range of applications. Although metal oxide-based chemoresistive sensors have emerged as a promising approach for CO$_2$ detection, the development of efficient CO$_2$ sensors at low temperature remains a challenge. Herein, we report a low-temperature hollow nanostructured CeO$_2$-based sensor for CO$_2$ detection. We monitor the changes in the electrical resistance after CO$_2$ pulses in a relative humidity of 70% and show the high performance of the sensor at 100 °C. The yolk–shell nanospheres have not only 2 times higher sensitivity but also significantly increased stability and reversibility, faster response times, and greater CO$_2$ adsorption capacity than commercial ceria nanoparticles. The improvements in the CO$_2$ sensing performance are attributed to hollow and porous structure of the yolk–shell nanoparticles, allowing for enhanced gas diffusion and high specific surface area. We present an easy strategy to enhance the electrical and sensing properties of metal oxides at a low operating temperature that is desirable for practical applications of CO$_2$ sensors., Published by Soc., Washington, DC

Made available in DSpace on 2018-12-11T16:52:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-07-15 Sensors based on metal oxide semiconductors have been widely applied for the detection of several volatile organic compounds (VOCs). However, the development of sensing materials with high selectivity, improved sensitivity, low detection limit is still a challenge. In this work, bicone-like ZnO structure was synthesized by a rapid template-free microwave-assisted hydrothermal method and then applied as VOC sensor. The VOC-sensing tests revealed that ZnO structure presented a higher response toward butanone than to other VOCs, such as benzene, toluene, m-xylene, acetone, ethanol, acetaldehyde, and isopropanol. Moreover, the ZnO-based sensor showed an enhanced butanone-sensing performance at 400 °C, including a response of 29.4–100 ppm of butanone, high sensitivity to detect low butanone concentration (2 ppm), and a low detection limit of 0.41 ppm. Therefore, the unique bicone-like ZnO structure might be a promising candidate for butanone sensors. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265, S. J. Rio Preto Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265, S. J. Rio Preto

The development of highly sensitive and selective gas sensors is essential for the detection of harmful compounds. However, the gas-sensing performance presents some challenging issues such as the requirement of high operating temperatures and the negative impact of humidity. Herein, we have prepared porous CeO2 nanospheres (NS) using a simple microwave-assisted solvothermal method, followed by calcination, and demonstrated the triethylamine (TEA) sensing performance of the NS at room temperature and a relative humidity of 98%. The sensor showed enhanced sensing properties towards TEA compared to other volatile organic compounds. Significantly, the CeO2 NS exhibited a response of 4.67 to 100 ppm of TEA with a fast response time of 13 s. Furthermore, the sensor was able to detect low TEA concentrations (5 ppm) and presented excellent repeatability. The outstanding sensing properties are attributed to the high specific surface area, the porous structure of CeO2 NS (which allows a great gas diffusion), and the increased number of active sites for TEA oxidation due to the formation of hydroxyl groups on the CeO2 surface from high humidity conditions. Thus, the use of CeO2 NS is a promising approach by which to fabricate TEA sensors that operate at room temperature and high humidity levels.

Recent advances in NiO-based gas sensors have been reported, but high working temperatures and dry conditions are usually required. Herein, we report the volatile organic compound (VOC) sensing performance of flower-like (FL) NiO hierarchical structures modified with reduced graphene oxide (RGO) sheets under high humidity. RGO/FL-NiO composites were synthesized by a simple and template-free microwave-assisted hydrothermal method and subsequent calcination at 250 °C. The VOC-sensing properties were investigated for several VOCs, such as acetone, ethanol, methanol, m-xylene, and toluene, at 90% relative humidity. The RGO/FL-NiO composites exhibited a decrease in the optimal operating temperature and enhanced methanol responses compared to pure FL-NiO. In addition, the 5% RGO/FL-NiO composite exhibited the highest response of 61.51% to 100 ppm of methanol at 180 °C, which was 1.4–9.9 times superior to responses to other VOCs, indicating the sensor's great selectivity. The improved methanol sensing properties could be attributed to the NiO/RGO heterointerface.

Made available in DSpace on 2022-04-28T19:47:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Sensors of volatile organic compounds (VOCs) play a vital role in environmental monitoring. Although much progress has been made to develop new sensing materials, it remains challenging to detect a particular VOC selectively and without the interference of humidity. Herein, we report the effect of In2O3 nanoparticles on the VOC-sensing performance of ZnO twin-rods. The VOC-sensing tests were carried out in dry air and at a relative humidity (RH) of 26, 59, and 98%. The results indicated that the In2O3/ZnO heterostructure exhibited an improved sensing performance to triethylamine (TEA) compared to ZnO. In dry air, the responses to 100 ppm of TEA at 350 °C were 60.2 for the In2O3/ZnO heterostructure and 39.2 for pure ZnO. In2O3/ZnO even exhibited a high response of 6.2 to 1 ppm of TEA. Moreover, In2O3/ZnO exhibited a response to TEA up to 46.2 times higher than those of the other VOCs, indicating excellent selectivity. At 98% RH, the In2O3/ZnO heterostructure still had a high sensitivity to TEA, showing a response of 21.2 to 100 ppm of TEA with a response time of 1 s. The improved TEA-sensing performance of the In2O3/ZnO heterostructure can be attributed to the formation of the n-n heterojunction. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265 Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265 FAPESP: 2016/25267-8 FAPESP: 2017/01267-1 FAPESP: 2018/00033-0 FAPESP: 2018/01258-5 FAPESP: 2019/12345-9 FAPESP: 2020/06421-1 CNPq: 308327/2018-7

Made available in DSpace on 2018-12-11T16:44:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Graphene-based composites have emerged as gas sensor due to the possibility to obtain higher surface area with additional functional groups. In this paper, ZnO nanorods (ZnO-NR) with controlled size and morphology were grown via chemical bath deposition in mild temperature (90 °C) over gold interdigital tracks deposited on an alumina substrate. Furthermore, it was also possible to obtain by the same method composites with graphene oxide sheets below ZnO-NR structures (GO/ZnO-NR) or ZnO-NR between GO sheets (GO/ZnO-NR/GO) when GO is placed in the bath during the growth of GO/ZnO-NR. The samples were characterized by Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. These structures were tested as sensors of volatile organic compounds (VOCs), such as acetone, benzene, ethanol and methanol in the concentration range of 10–500 parts per million (ppm). It was found that the optimum working temperature of all sensors was 450 °C. The GO/ZnO-NR/GO composite showed better selectivity due to GO functional groups. In the case of our well-designed sensors, we found that the dominant oxygen species (O2-) on ZnO-NR surface were responsible for the sensors response. These findings offer a new viewpoint for further advance of the sensing performance of one-dimensional ZnO/GO nanocomposites VOCs sensors. Center for Information Technology Renato Archer CTI, Rod. D. Pedro I, KM 143.6 LabMatSus - Laboratory of Materials for Sustainability IBILCE UNESP - Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 LabMatSus - Laboratory of Materials for Sustainability IBILCE UNESP - Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 FAPESP: 2014/17343-0 FAPESP: 2015/05916-9 FAPESP: 2016/04371-1

Hierarchical WO3·0.33H2O nanocolumns were prepared by a simple combination of ultrasonic spray nozzle (USN) and microwave-assisted hydrothermal (MAH) methods. The USN step promoted a high nucleation rate of H2WO4 clusters, while glycine played an important role in the crystal growth in a preferred direction. The MAH step was responsible for the crystallization of the single orthorhombic WO3·0.33H2O phase and the self-assembly of the hierarchical structure. The as-prepared sample was tested as a volatile organic compound (VOC) sensor at room temperature (22 °C) and wet conditions. Enhanced isopropanol sensitivity and selectivity were achieved due to the high specific surface area provided by the combination of USN and MAH methods. Thus, this synthesis strategy is a promising approach for fabricating different gas sensing devices.

Made available in DSpace on 2021-06-25T10:24:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-01 Developing a device or material to detect volatile organic compounds (VOC) is no longer a challenge, despite its great interest. The difficulty is linked to developing a material that does not suffer from interferences, such as humidity, other gases, or volatiles present in the analyzes. In this sense, we present a new way to modify zinc oxide (ZnO) hollow spheres with nickel (II) sulfide (NiS) nanosheets, a barely studied material in the literature, to increase the butanone selectivity and to reduce the negative effect of humidity in the final response of the sensor. The ZnO hollow sphere (H-ZnO) was synthesized via a microwave-assisted solvothermal method followed by calcination. The NiS-H-ZnO heterostructures were produced by the deposition of NiS nanosheets on H-ZnO using thioacetamide and nickel (II) acetate tetrahydrate as NiS precursors. Under dry conditions, pure H-ZnO presents the best sensing response of 705.3 to 100 ppm of butanone followed by the 5%-NiS-H-ZnO heterostructure with a response of 123.8. However, the selectivity of 5%-NiS-H-ZnO improves and reaches a value of 12.92, which is more than four times higher than the selectivity of pure H-ZnO (3.12). Furthermore, the performance under humidity atmospheres shows that NiS heterostructures suffer less effect of the humidity. The responses to 100 ppm of butanone under 55% of relative humidity were 40.2 and 23.7 for 5%-NiS-H-ZnO and pure H-ZnO, respectively. Therefore, the developed butanone sensor demonstrated excellent response, selectivity, and a promising possibility for its practical use in sensing devices under real conditions of humidity. Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265 Laboratory of Materials for Sustainability (LabMatSus) Ibilce São Paulo State University (Unesp), R. Cristóvão Colombo, 2265

Made available in DSpace on 2018-12-11T16:45:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The interference of humidity is a key factor to be considered in metal oxide semiconductors gas sensing performance. However, an efficient gas detection under humid conditions is a challenge. Herein, we report the effect of reduced graphene oxide (RGO) on volatile organic compounds (VOCs) sensing performance of hollow SnO2nanoparticles (NPs) under wet atmosphere. For this purpose, RGO-SnO2nanocomposite was obtained by a one-pot microwave-assisted solvothermal synthesis. The sensing tests for VOCs were conducted under dry air and at a relative humidity (RH) between 24 and 98%. The samples exhibited better response toward ethanol than to other VOCs such as acetone, benzene, methanol, m-xylene, and toluene, at the optimum operating temperature of 300 °C. Furthermore, RGO-SnO2nanocomposite showed an enhanced ethanol response in comparison with pure hollow SnO2NPs. Even under 98% of RH, the RGO-SnO2nanocomposite showed a response of 43.0 toward 100 ppm of ethanol with a response time of 8 s. The excellent sensor performance is related to the hollow structure of SnO2NPs, and the heterojunction between RGO and SnO2. Therefore, the RGO content can be a promising approach to minimize the humidity effect on SnO2ethanol sensing performance. LabMatSus—Laboratory of Materials for Sustainability IBILCE UNESP—Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 LabMatSus—Laboratory of Materials for Sustainability IBILCE UNESP—Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 FAPESP: 2013/23886-4 FAPESP: 2014/17343-0 FAPESP: 2015/05916-9 FAPESP: 2016/04371-1 CNPq: 444926/2014-3

Made available in DSpace on 2018-12-11T16:44:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 Nanostructured orthorhombic WO3·0.33H2O, hexagonal h-WO3 and their RGO composites (RGO-WO3·0.33H2O and RGO-h-WO3) are reported for the purpose of efficient sensing of volatile organic compounds (VOCs) (e.g. acetone, methanol, benzene, toluene, and m-xylene). The materials were prepared at 140 °C by one-pot microwave-assisted hydrothermal (MAH) synthesis from Na2WO4·2H2O and graphite oxide (in the case of composite) suspension in acid medium, without using any reducing, organic, or capping reagent. A three-dimensional (3D) nanocolumn bundles-like morphology was obtained for WO3·0.33H2O and RGO-WO3·0.33H2O. Whereas with subsequent heat treatment at 400 °C, it was possible to obtain h-WO3 and RGO-h-WO3 composites while preserving the nanocolumn bundles-like morphology. The sensing properties of these materials were investigated by exposing them to various VOCs at room temperature and at 55% relative humidity. We found that all the materials behave as a p-type semiconductor after being exposed to reducing gases. Response to 100 ppm of acetone to the RGO-h-WO3 sensor was observed to be 20% larger than the h-WO3 sensor. LabMatSus-Laboratory of Materials for Sustainability IBILCE UNESP-Univ Estadual Paulista, Rua Cristóvão Colombo, 2265 LabMatSus-Laboratory of Materials for Sustainability IBILCE UNESP-Univ Estadual Paulista, Rua Cristóvão Colombo, 2265

The impact of humidity is a crucial factor in the sensing performance of a chemiresistive gas sensor. Therefore, strategies for developing sensors with a small humidity dependence are required. Herein, the volatile organic compound (VOC)-sensing performance of palladium-loaded hierarchical flower-like tin dioxide structures (Pd/FL-SnO2) under humid conditions is reported. To prepare the Pd/FL-SnO2 heterostructures, FL-SnO2 is first synthesized using a microwave-assisted solvothermal method, followed by calcination, and then is loaded with Pd nanoparticles (NPs). VOC-sensing studies are conducted in dry and wet air with relative humidities (RHs) between 25% and 98%. FL-SnO2 and Pd/FL-SnO2 exhibit an enhanced response toward ethanol in comparison with other VOCs, including acetone, benzene, methanol, m-xylene, and toluene. However, FL-SnO2 with Pd NPs has a substantially decreased optimal working temperature, from 340 to 140 °C, and an improved selectivity. Furthermore, the ethanol response of the Pd/FL-SnO2 heterostructures is preserved under humid conditions, whereas the response of FL-SnO2 is significantly affected by humidity. The response to 100 ppm of ethanol under 98% RH is 3.1 and 8.0 for neat FL-SnO2 and 5% Pd/FL-SnO2 heterostructure, respectively. The ethanol-sensing performance enhancement under high humidity is attributed to the Pd/SnO2 heterointerface.