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[Display omitted] • Need for economic growth led to the development of fiber optic-based sensors. • Coupling of metal oxides permits redox reactions supporting sensing property. • TiO 2 -ZnO composites (S1) and annealed 500 °C (S2) & 1200 °C (S3) in sensing study. • Enhanced sensitivity and selectivity in S3 sensor for ammonia at room temperature. • The rise and fall time of the S3 sensor were 18 sec and 15 sec respectively. Fiber optic sensors, promising for their compactness and remote sensing abilities, are explored in this study as a platform for detecting volatile organic compounds (VOCs) using nanocrystalline metal oxide composites like TiO 2 -doped ZnO. Hydrothermally synthesized (S1 sample)and annealed composites (500 °C (S2 sample) and 1200 °C (S3 sample) annealing) were investigated for their gas-sensing properties towards inorganic gas like ammonia and VOCs like acetone, and isopropyl alcohol. Remarkably, annealing at 1200 °C yielded S3 sample with higher response (7.5 %) towards ammonia at room temperature for 500 ppm concentration. This superior performance is attributed to increased surface area, narrowed bandgap, and faster response/recovery times (18/15 s) compared to other samples. The proposed sensing mechanism involves the adsorption and desorption of oxygen molecules on the sensor surface, altering refractive index and light scattering, ultimately modulating the transmitted light intensity. X-ray diffraction, SEM imaging, and UV–Vis absorption techniques confirmed the structure and morphology of the nanocomposites. [ABSTRACT FROM AUTHOR]

Highlights • Gas sensing property of magnesium tetraborate glasses, a radiation dosimetry material, was revealed. • Gamma irradiated Cerium doped glass shows good sensitivity towards ammonia gas. • Gas sensitivity of Magnesium tetraborate in polycrystalline and glassy form were compared. Abstract Gamma irradiated MTB has been explored as a chemical gas sensor. For this purpose, MTB is used as the cladding in the sensing area of a multimode optical fiber in a home made fiber optic gas sensor. Solid state sintering and melting-quenching methods were followed for the synthesis of polycrystalline and glassy magnesium tetraborate (MTB). The structural and morphological studies were carried out using powder XRD and FESEM analysis. XRD peaks matched well with the Joint committee on powder diffraction standards(JCPDS) data. From EDAX analysis, the elemental composition of the sample showed the presence of cerium in MTB. Samples were irradiated in a 60Co gamma chamber and the dose of 20 Gy was given to the samples. UV–vis spectra of the as-prepared and gamma irradiated MTBs showed a marked variation in the absorbance. The sensor was used for the detection of ammonia gas at various concentrations. The gamma irradiated MTB showed a highly improved response for gas detection compared to as prepared MTB. In this paper, the experimental results and analysis are presented for ammonia detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gadolinium doped CeO 2 has superior sensitivity. • The response, and recovery rate towards ammonia gas at room temperature than methanol and ethanol test gases. • Detection of VOC's such as ammonia, methanol and ethanol gases. • Clad modified fiber optic gas sensor coated with Gadolinium doped CeO 2 was employed at normal atmospheric temperature. A Plastic PMMA optical fiber with a small portion of the clad being replaced by Gadolinium (Gd) doped CeO 2 sensing material has been proposed in this work for VOC gas sensing. Gadolinium doped CeO 2 has superior sensitivity, descent response, and recovery rate towards ammonia gas at room temperature than methanol and ethanol test gases. The number of oxygen species present on the surface after adsorption was found to be responsible for the enhanced sensitivity of Gadolinium doped CeO 2 towards the VOC gases. [ABSTRACT FROM AUTHOR]

Abstract: A clad-modified fiber optic sensor with nanocrystalline CeO2 is proposed for gas detection. As-prepared and annealed CeO2 (500 °C) samples have been used as gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia, ethanol and methanol gases (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the gas concentration. The characteristics of the sensor are also studied for gas selectivity. The time response characteristics of the sensor are reported. [Copyright &y& Elsevier]

Abstract: A cladding modified fiber optic sensor coated with nanocrystalline ZnO is proposed for ammonia gas detection. As-prepared and annealed zinc oxide (500 and 1200°C) samples are used as the gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia (0–500ppm). The sensor exhibits linear variation in the spectral peak intensity with the ammonia concentration. The characteristics of the sensor when exposed to ethanol and methanol gases are also studied for gas selectivity. The time response characteristics of the sensor are reported. [Copyright &y& Elsevier]

Abstract: Spectral characteristics of a clad modified fiber optic gas sensor are studied for various concentrations (0–500ppm) of ammonia, methanol and ethanol at room temperature. Cerium, aluminum and lithium doped (6at.%) nanocrystalline zinc oxides are replaced with a clad and used as gas sensing materials. The study shows that the spectral intensity increases linearly with concentration for ammonia whereas it decreases for methanol and ethanol. The Ce doped ZnO exhibits higher gas sensitivity compared to Al and Li doped zinc oxides. The time response of the sensor is presented for a Ce doped ZnO with ammonia gas. A model is proposed for understanding the spectral intensity variations. [Copyright &y& Elsevier]

A novel one-pot microwave irradiation method has been adapted to synthesize cubic spinel cobalt oxide/multi-walled carbon nanotube composite. X-ray diffraction and scanning electron microscope results reveal that cubic spinel structure of Co3O4 with nanodimensional and well implanted over the multi walled carbon nanotubes (MWCNTs) metrics. The N2 adsorption–desorption results exhibit that Co3O4/MWCNT composite confirms the highest specific area (135 m2 g−1) and lower pore size 7.8 nm compared with pure Co3O4 (surface area 88 = m2 g−1 and pore size = 10.5 nm). The XPS result demonstrates that Co is 2+ in state in the spinel Co3O4. The gas-detecting test displayed that Co3O4/MWCNT composite indicated high sensitivity toward ethanol (35 counts/ppm) and ammonia (51 counts/ppm) gases as compared with pure Co3O4 (24 counts/ppm and 43 counts/ppm for ethanol and ammonia gases, respectively). It also exhibits excellent long-term stability with small deviations (less than 5%) for the evaluation of a 2-month period. The enhanced gas-sensing mechanism of Co3O4/MWCNT was also discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: The micro structured plate-like lithium tetraborate, Li2B4O7 (1 μm in diameter) has been prepared by sol–gel method and characterized structurally by X-ray diffraction and morphologically by scanning electron microscopy. UV–Vis spectrum shows about 60% transparency in the visible region and the optical energy band gap is found to be 3.5 eV which is also confirmed by strong near band edge emission from luminescence spectrum. The spectral characteristics of the cladding modified fiber optic sensor coated with microcrystalline Li2B4O7 are studied for various concentrations of ethanol, methanol and ammonia (50–500 ppm). At 298 K, the sensitivity for ethanol is −10 counts/ppm which is relatively higher than ammonia (−4 counts/ppm) and methanol (−3 counts/ppm). The time response of the sensor is presented for pure Li2B4O7 with ethanol gas. [Copyright &y& Elsevier]

Abstract: Part of the outer layer of a commercial two-layer poly-methyl methacrylate optical fiber was mechanically removed and replaced with a coating of single-walled carbon nanotubes (SWCNT) by a dip-coating technique. The resulting fiber was used as a fiber optic sensor for the detection of ammonia, methanol and ethanol vapors in the concentration range 0–500ppm at room temperature. Different thicknesses of the SWCNT layer on the fiber were prepared by repeated dip coating. All the sensors were found to show good response for all three vapors used even at lower vapor concentrations (<50ppm). The results show that a lower SWCNT thickness is good for ammonia sensing whereas a higher thickness is good for alcohol sensing. The interaction between the analyte and SWCNT is responsible for the sensing of the volatile organic compounds. [Copyright &y& Elsevier]