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The development of cost-effective simple methods to fabricate nanocomposites based on metal oxide (MOX) supported noble metals with improved performance is extremely demanding, specifically in the field of nanomaterial and gas sensor. In this this work, a facile one-step hydrothermal strategy to synthesize strongly-coupled TiO2 nanosheets supported with Ag nanoparticles (Ag/TiO2 heterojunction nanocomposites) is proposed, which is proved of high effectiveness for sensor applications. The structure and morphology of synthesized nanocomposites was performed by XRD, XPS, HRTEM, UV-Vis and PL spectroscopy. Compared to pristine TiO2, the sensors based on such Ag/TiO2 heterojunction nanocomposites show excellent ethanol gas sensing properties in terms of high sensitivity (8.5 towards 100 ppm), selectivity against other gases (methanal, acetone, and methanol), short response/recover times (9/10 s), and high stability (present stable response after 30 days). Such performance demonstrates this material is promising for practical gas sensor applications. [ABSTRACT FROM AUTHOR]

The paper demonstrated cost-effective one-step hydrothermal process to synthesize TiO2 microrods modified with Cr2O3 nanoparticles. The crystal structure, microstructure and chemical composition of the obtained materials were characterized by XRD, SEM, TEM and EDS analysis. Subsequently, for gas sensor tests the sensors were fabricated onto a ceramic tube having a designed pair of Au electrodes with four Pt wires. The results indicate that the sensors based on the optimal content of Cr2O3 nanoparticles modified TiO2 microrods possess excellent gas-sensing performance to acetone. Specifically, the sensor based on optimal 3% Cr2O3 modified TiO2 microrods exhibited high response (15), fast response/recovery time (5/28 s), outstanding selectivity (against 100 ppm ethanol, methanol and formaldehyde) and good stability (1-40 days) towards 100 ppm acetone at 300 °C. Relying on the analysis, we infer that performance can be controlled by varying the Cr2O3 contents. A plausible sensing mechanism is also discussed to explain the reasons for the enhanced acetone sensing with Cr2O3-TiO2 heterostructures. [ABSTRACT FROM AUTHOR]

Owing to their unique surface adsorption characteristics, the controlled synthesis of highly ordered mesoporous materials with high adsorption traits is of utmost importance. In the present work, ordered mesoporous TiO 2 (OMT) with tunable channels was prepared via a facile soft-templet evaporation-induced self-assembly (EISA) method. The effect of phenol-formaldehyde resins (PF) and the ratio of triblock copolymer (F127) and tetrabutyl titanate (TBOT) on the OMT surface was studied by Brunauer Emmett Teller (BET) and scanning electron microscopy (SEM) analysis. The samples without PF resol did not offer any ordered mesoporous formation, while a highly ordered mesoporous structure was obtained for samples with PF resol. For the prepared samples, the specific surface area SSA∼141–254 m2/g, average pore size S P ∼5.3–9.8 nm and pore volume V P ∼0.29–0.45 cm3/g were obtained by controlling the ratio of F127 and TBOT. For 95% relative humidity (RH), the OMT with optimum specific surface area (SSA∼220 m2/g) and small pore size (S P ∼5.3 nm) showed a high response (S R ∼3.5 ×105), fast response time (26 s) and good long-term stability (over 90 days). Finally, the structure, morphology and chemical composition of the samples were determined by XRD, SEM, HRTEM, and XPS techniques to predict and authenticate the plausible sensing mechanism. [Display omitted] • Phenol as a resol with soft-template resulted controlled mesoporous features. • Phenol enhances the specific surface area and decreases the pore size. • Ordered mesoporous TiO 2 based humidity sensor exhibits excellent humidity response. • The response is 105 times with fast response (26 s) and full recovery. • High response with pore size (S P '4.1 nm) equals twice as Debye-length. [ABSTRACT FROM AUTHOR]

Metal oxides are excellent candidates for the detection of various gases; however, the issues such as the limited operating temperature and selectivity are the most important ones requiring the comprehensive understanding of gas adsorption kinetics on the sensing layer surfaces. To this context, the present study focuses mainly on the fabrication of a Pt/Cr-TiO2/Pt type sensor structure that is highly suitable in reducing the operating temperature (from 400 to 200 °C), extending the lower limit NO2 gas concentration (below 10 ppm) with fast response (37 s) and recovery (24 s) times. This illustrates that the sensor performance is not only solely dependent on the nature of sensing material, but also, it is significantly enhanced by using such a new kind of electrode geometry. Moreover, Cr doping into TiO2 culminates in altering the sensor response from n- to p-type and thus contributes to sensor performance enhancement by detecting low NO2 concentrations selectively at reduced operating temperatures. In addition, the NO2 surface adsorption kinetics are studied by fitting the obtained sensor response curves with Elovich, inter-particle diffusion, and pseudo first-order and pseudo second-order adsorption models. It is found that a pseudo first-order reaction model describes the best NO2 adsorption kinetics toward 7–170 ppm NO2 gas at 200 °C. Finally, the sensing mechanism is discussed on the basis of the obtained results. [ABSTRACT FROM AUTHOR]

Owing to their excellent gas adsorption characteristics, titanium dioxide (TiO 2) nanomaterials have been widely investigated for the detection of environmental volatile organic compounds (VOCs). In this review, we provide a summary of the recent progress in synthesis and characterization of TiO 2 nanomaterials for VOCs sensing. The basic properties of environmental VOCs and their classification, as well as the VOCs sensing principles and advantages of using TiO 2 nanomaterials are introduced. Then various synthesis methods are discussed, including sol-gel, hydrothermal, chemical vapor deposition (CVD), physical vapor deposition (PVD) and green methods. Thereafter, summary of recent studies on TiO 2 -based sensors for detecting different types of VOCs is provided. Finally, we discuss the current challenges and future prospects of using TiO 2 nanomaterials as VOCs sensing materials. This review provides valuable insights into the synthesis of TiO 2 nanomaterials for VOCs sensing applications, which can guide the design and development of high-performance sensors for environmental monitoring. [Display omitted] • This paper reviews the recent progress in the synthesis and characterization of TiO 2 nanomaterials for VOC sensing. • The research progress of titanium dioxide based sensors for the detection of different types of volatile organic compounds. • This review identifies challenges such as selectivity, stability and reproducibility, and suggests some possible solutions. [ABSTRACT FROM AUTHOR]

Abstract Owing to its high energy density and environmentally friendly nature, hydrogen has already been regarded as the ultimate energy of the 21st century and gained significant attention from the worldwide researchers. Meanwhile, there are increasing concerns about its safe use, storage and transport as, despite being colorless and odorless, after certain concentration level it becomes flammable and explosive in air. Therefore, it is imperative to develop H 2 sensors for real-time monitoring of the H 2 leakage for an early warning. This paper firstly introduces the general hydrogen gas sensing mechanism of TiO 2 -based hydrogen sensors. Then we summarize and comment on the current hydrogen gas sensor based on various TiO 2 materials, which include pristine TiO 2 , metal-assisted TiO 2 , organic-TiO 2 composites, carbon-TiO 2 composites, MOX-TiO 2 composites and novel sensor concept with effective top-bottom electrode configuration. Finally, we briefly discuss the obstacles that TiO 2 -based H 2 sensors have to overcome in the progress of the systematically practical application, possible solutions, and future research perspectives that can be focused in this area. Highlights • General hydrogen gas sensing mechanism based on TiO 2 were introduced. • Hydrogen gas sensor based on various TiO 2 materials were summarized and commented. • The obstacles that TiO 2 based hydrogen sensor have to overcome were stated briefly. • Future research perspectives of the hydrogen gas sensor are proposed and discussed. [ABSTRACT FROM AUTHOR]