High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

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Advances in designs and mechanisms of semiconducting metal oxide nanostructures for high-precision gas sensors operated at room temperature

Ultrasensitive ppb-level NO 2 gas sensor based on WO 3 hollow nanosphers doped with Fe

https://iopscience.iop.org/article/10.1149/1945-7111/ab64bc/pdf

Review—Metal Oxides: Application in Exhaled Breath Acetone Chemiresistive Sensors

Photocatalytic activity of nitrogen and copper doped TiO2 nanoparticles prepared by microwave-assisted sol-gel process

In the present work, Ni2+ and Cu2+ ions are doped with TiO2 using sol–gel technique. The effects of Ni and Cu doping in TiO2 matrix are characterized by XRD, Micro-Raman, FTIR, UV–DRS, PL, and FESEM with EDS. Furthermore, it is analyzed for photocatalytic activity and magnetic applications. From XRD analysis, it is observed that the peaks corresponding to the planes match with the JCPDS data [anatase: 89-4203] of TiO2. The crystallite size of the doped samples is found to be greater than that of TiO2. Micro-Raman analysis shows the confirmation of anatase phase of TiO2. FTIR analysis confirms the presence of functional groups which are presented in the prepared samples. From UV–DRS, the band-gap values of TiO2 and doped TiO2 (Ni2+, Cu2+) are found to be 3.25, 2.48, and 1.25 eV. Photoluminescence (PL) results show an emission edge of Ni- and Cu-doped TiO2 is red shifted which is due to the vacancies of titanium and oxygen imported subsequently during doping. The surface morphology and the elemental composition of Ni- and Cu-doped TiO2 nanoparticles are also analyzed. The photocatalytic activity of all the prepared samples are assessed by methylene blue dye as testing pollutant and visible radiation. The test reveals that Cu–TiO2, Ni–TiO2, and TiO2 show the degradation efficiency of 68.14, 61.04, and 33.32%, thereby showing that the doped TiO2 are more efficient in degrading the pollutant and can be applied for future photocatalytic applications. From VSM analysis, the saturation magnetization of Ni–TiO2 and Cu–TiO2 is found to be weak and can be improved by the synthesis process and the proportion of dopant.

Synthesis and analysing the structural, optical, morphological, photocatalytic and magnetic properties of TiO 2 and doped (Ni and Cu) TiO 2 nanoparticles by sol–gel technique

In this work, we report the influence of oxygen vacancy related defects on the magnetism and gas sensing of TiO2 nanoparticles doped with different concentrations of cobalt (1, 3 and 5 at.%) prepared by sol–gel method at room temperature. XRD and Raman studies confirmed the formation of anatase tetragonal TiO2 nanoparticles and the studies also clearly supported that the Co atoms go into the Ti site in TiO2. The obtained nanoparticles of size 6–20 nm was identified by HRTEM. The distribution of particles and the elemental composition present in the sample were determined by SEM with EDS. UV–Vis absorption spectra showed that the incorporation of Co into the TiO2 lattice leads to redshift in the optical response as well as lowering of band gap energy. The defect oriented emissions were seen from photoluminescence study. Functional groups of the samples were identified by FTIR. The magnetic result demonstrated that the prepared Co-doped TiO2 nanoparticles exhibit room temperature ferromagnetism due to oxygen vacancy related defects on the surface of the sample. The ethanol sensing studies conducted at room temperature showed that Co-doped (5 at.%) TiO2 with higher oxygen vacancies is more sensitive to ethanol compared with pure TiO2, and the results reveal that oxygen vacancies play a significant role in both magnetism and sensing properties.

Oxygen vacancies induced room temperature ferromagnetism and gas sensing properties of Co-doped TiO 2 nanoparticles

A diluted magnetic semiconductor (DMS) Co-doped TiO2 is studied here for dielectric properties Undoped and Co-doped TiO2 samples were prepared by sol-gel method The formation of anatase phase has been investigated by X-ray diffraction (XRD) UV-Vis absorption spectra show that the incorporation of Co into the TiO2 lattice leads to redshift in the optical response, as well as lowering the band gap energy The defect oriented emissions were seen from photoluminescence (PL) study The dielectric properties of pure and Co-doped TiO2 samples were studied in the frequency range of 10 Hz to 10 MHz at different temperatures Doped sample exhibit low dielectric constant when compared with host system Both dielectric constant and ac conductivity increases with temperature

Diva Prabhakar

Papers

Oxygen vacancies induced room temperature ferromagnetism and gas sensing properties of Co-doped TiO 2 nanoparticles

Effect of cobalt doping on structural, optical and dielectric properties of TiO2