Research

17 pages, 8945 KiB

Open AccessEditor’s ChoiceArticle

Metallic Effects on p-Hydroxyphenyl Porphyrin Thin-Film-Based Planar Optical Waveguide Gas Sensor: Experimental and Computational Studies

by Nuerguli Kari, Marco Zannotti, Rita Giovannetti, David Řeha, Babak Minofar, Shawket Abliz and Abliz Yimit

Nanomaterials 2022, 12(6), 944; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12060944 - 13 Mar 2022

Cited by 8 | Viewed by 2378

Abstract

Metal effects on the gas sensing behavior of metal complexes of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (THPP) thin film was investigated in terms of detecting NO₂ gas by the planar optical waveguide. For this purpose, several THPP and metal complexes were synthesized with different central metal [...] Read more.

Metal effects on the gas sensing behavior of metal complexes of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (THPP) thin film was investigated in terms of detecting NO₂ gas by the planar optical waveguide. For this purpose, several THPP and metal complexes were synthesized with different central metal ions: Co(II), Ni(II), Cu(II), and Zn(II). Planar optical gas sensors were fabricated with the metalloporphyrins deposited on K⁺ ion-exchanged soda-lime glass substrate with the spin coating method serving as host matrices for gas interaction. All of the THPP complex’s films were fully characterized by UV-Vis, IR and XPS spectroscopy, and the laser light source wavelength was selected at 520 and 670 nm. The results of the planar optical waveguide sensor show that the Zn–THPP complex exhibits the strongest response with the lowest detectable gas concentration of NO₂ gas for both 520 nm and 670 nm. The Ni–THPP and Co–THPP complexes display good efficiency in the detection of NO₂, while, on the other hand, Cu–THPP shows a very low interaction with NO₂ gas, with only 50 ppm and 200 ppm detectable gas concentration for 520 nm and 670 nm, respectively. In addition, molecular dynamic simulations and quantum mechanical calculations were performed, proving to be coherent with the experimental results. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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16 pages, 5683 KiB

Open AccessArticle

Three-Layer PdO/CuWO₄/CuO System for Hydrogen Gas Sensing with Reduced Humidity Interference

by Nirmal Kumar, Stanislav Haviar and Petr Zeman

Nanomaterials 2021, 11(12), 3456; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11123456 - 20 Dec 2021

Cited by 7 | Viewed by 2468

Abstract

The growing hydrogen industry is stimulating an ongoing search for new materials not only for hydrogen production or storage but also for hydrogen sensing. These materials have to be sensitive to hydrogen, but additionally, their synthesis should be compatible with the microcircuit industry [...] Read more.

The growing hydrogen industry is stimulating an ongoing search for new materials not only for hydrogen production or storage but also for hydrogen sensing. These materials have to be sensitive to hydrogen, but additionally, their synthesis should be compatible with the microcircuit industry to enable seamless integration into various devices. In addition, the interference of air humidity remains an issue for hydrogen sensing materials. We approach these challenges using conventional reactive sputter deposition. Using three consequential processes, we synthesized multilayer structures. A basic two-layer system composed of a base layer of cupric oxide (CuO) overlayered with a nanostructured copper tungstate (CuWO₄) exhibits higher sensitivity than individual materials. This is explained by the formation of microscopic heterojunctions. The addition of a third layer of palladium oxide (PdO) in forms of thin film and particles resulted in a reduction in humidity interference. As a result, a sensing three-layer system working at 150 °C with an equalized response in dry/humid air was developed. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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14 pages, 4903 KiB

Open AccessArticle

Light-Excited Ag-Doped TiO₂−CoFe₂O₄ Heterojunction Applied to Toluene Gas Detection

by Wenhao Wang, Lu Zhang, Yanli Kang and Feng Yu

Nanomaterials 2021, 11(12), 3261; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11123261 - 30 Nov 2021

Cited by 3 | Viewed by 1590

Abstract

(1) Background: Toluene gas is widely used in indoor decoration and industrial production, and it not only pollutes the environment but also poses serious health risks. (2) Methods: In this work, TiO₂−CoFe₂O₄−Ag quaternary composite gas-sensing material was [...] Read more.

(1) Background: Toluene gas is widely used in indoor decoration and industrial production, and it not only pollutes the environment but also poses serious health risks. (2) Methods: In this work, TiO₂−CoFe₂O₄−Ag quaternary composite gas-sensing material was prepared using a hydrothermal method to detect toluene. (3) Results: The recombination of electron–hole pairs was suppressed, and the light absorption range was expanded after constructing a heterojunction and doping with Ag, according to ultraviolet–visible (UV–vis) diffuse reflectance spectra and photoluminescence spectroscopy. Moreover, in the detection range of toluene gas (3 ppm–50 ppm), the response value of TiO₂−CoFe₂O₄−Ag increased from 2 to 15, which was much higher than that of TiO₂−Ag (1.7) and CoFe₂O₄−Ag (1.7). In addition, the working temperature was reduced from 360 °C to 263 °C. Furthermore, its response/recovery time was 40 s/51 s, its limit of detection was as low as 10 ppb, and its response value to toluene gas was 3–7 times greater than that of other interfering gases under the same test conditions. In addition, the response value to 5 ppm toluene was increased from 3 to 5.5 with the UV wavelength of 395 nm–405 nm. (4) Conclusions: This is primarily due to charge flow caused by heterojunction construction, as well as metal sensitization and chemical sensitization of novel metal doping. This work is a good starting point for improving gas-sensing capabilities for the detection of toluene gas. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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17 pages, 5260 KiB

Open AccessArticle

Sensing Behavior of Metal-Free Porphyrin and Zinc Phthalocyanine Thin Film towards Xylene-Styrene and HCl Vapors in Planar Optical Waveguide

by Nuerguli Kari, Marco Zannotti, Rita Giovannetti, Patigu Maimaiti, Patima Nizamidin, Shawket Abliz and Abliz Yimit

Nanomaterials 2021, 11(7), 1634; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11071634 - 22 Jun 2021

Cited by 7 | Viewed by 2041

Abstract

The sensing behavior of a thin film composed of metal-free 5, 10, 15, 20-tetrakis (p-hydroxy phenyl) porphyrin and zinc phthalocyanine complex towards m-xylene, styrene, and HCl vapors in a homemade planar optical waveguide (POWG), was studied at room temperature. The thin film was [...] Read more.

The sensing behavior of a thin film composed of metal-free 5, 10, 15, 20-tetrakis (p-hydroxy phenyl) porphyrin and zinc phthalocyanine complex towards m-xylene, styrene, and HCl vapors in a homemade planar optical waveguide (POWG), was studied at room temperature. The thin film was deposited on the surface of potassium ion-exchanged glass substrate, using vacuum spin-coating method, and a semiconductor laser light (532 nm) as the guiding light. Opto-chemical changes of the film exposing with hydrochloric gas, m-xylene, and styrene vapor, were analyzed firstly with UV-Vis spectroscopy. The fabricated POWG shows good correlation between gas exposure response and absorbance change within the gas concentration range 10–1500 ppm. The limit of detection calculated from the logarithmic calibration curve was proved to be 11.47, 21.08, and 14.07 ppm, for HCl gas, m-xylene, and styrene vapors, respectively. It is interesting to find that the film can be recovered to the initial state with trimethylamine vapors after m-xylene, styrene exposures as well as HCl exposure. The gas-film interaction mechanism was discussed considering protonation and π-π stacking with planar aromatic analyte molecules. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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11 pages, 2935 KiB

Open AccessArticle

Quantitative Assessment of Trout Fish Spoilage with a Single Nanowire Gas Sensor in a Thermal Gradient

by Matteo Tonezzer, Nguyen Xuan Thai, Flavia Gasperi, Nguyen Van Duy and Franco Biasioli

Nanomaterials 2021, 11(6), 1604; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11061604 - 18 Jun 2021

Cited by 16 | Viewed by 2936

Abstract

The response of a single tin oxide nanowire was collected at different temperatures to create a virtual array of sensors working as a nano-electronic nose. The single nanowire, acting as a chemiresistor, was first tested with pure ammonia and then used to determine [...] Read more.

The response of a single tin oxide nanowire was collected at different temperatures to create a virtual array of sensors working as a nano-electronic nose. The single nanowire, acting as a chemiresistor, was first tested with pure ammonia and then used to determine the freshness status of trout fish (Oncorhynchus mykiss) in a rapid and non-invasive way. The gas sensor reacts to total volatile basic nitrogen, detecting the freshness status of the fish samples in less than 30 s. The sensor response at different temperatures correlates well with the total viable count (TVC), demonstrating that it is a good (albeit indirect) way of measuring the bacterial population in the sample. The nano-electronic nose is not only able to classify the samples according to their degree of freshness but also to quantitatively estimate the concentration of microorganisms present. The system was tested with samples stored at different temperatures and classified them perfectly (100%), estimating their log(TVC) with an error lower than 5%. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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21 pages, 45629 KiB

Open AccessArticle

Structure–Activity Relationships between the State of Silver on Different Supports and Their I₂ and CH₃I Adsorption Properties

by Bruno Azambre, Mouheb Chebbi and Nagham Ibrahim

Nanomaterials 2021, 11(5), 1300; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11051300 - 14 May 2021

Cited by 13 | Viewed by 2338

Abstract

In this study, the performances of silver-impregnated adsorbents prepared from different host supports (SBA-15, alumina, ceria, and faujasite Y zeolite) and calcined or not at 500 °C (1 h) were compared for the capture of I₂ and CH₃I. By keeping [...] Read more.

In this study, the performances of silver-impregnated adsorbents prepared from different host supports (SBA-15, alumina, ceria, and faujasite Y zeolite) and calcined or not at 500 °C (1 h) were compared for the capture of I₂ and CH₃I. By keeping the silver content rather similar (about 15–17 wt %) among the sorbents, it was possible to assess the effect of silver dispersion and speciation on the adsorption capacities measured for both adsorbates. In a first part, several characterization techniques (XRD, DRS-UV-Vis, TEM, etc.) were used to probe the state of silver in the calcined and non-calcined materials. It was found that the characteristics of silver species are strongly influenced by the thermal treatment, the presence or absence of exchange sites, and the stability of the supports. Silver agglomeration was enhanced after calcination at 500 °C especially for supports bearing no exchange sites (SBA-15) or no ordered pores (alumina and ceria). Then, the adsorption performances of the studied silver sorbents were discussed in relation with their physicochemical characteristics. After-test characterizations were useful to assess the proportion of silver species that have reacted with CH₃I and I₂ to yield AgI precipitates. Depending on the adsorbate, different trends were obtained. I₂ adsorption/reaction with silver sites was found to be quantitative (I/Ag ≈1), whatever the silver speciation and dispersion on the support. By contrast, a high proportion of cationic silver species was found essential to increase CH₃I adsorption (I/Ag about 0.6–0.7 against 0.2–0.3 for Ag agglomerated species). Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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9 pages, 23631 KiB

Open AccessArticle

Room-Temperature Hydrogen-Sensing Capabilities of Pt-SnO₂ and Pt-ZnO Composite Nanoceramics Occur via Two Different Mechanisms

by Ming Liu, Pengcheng Li, Yong Huang, Liang Cheng, Yongming Hu, Zilong Tang and Wanping Chen

Nanomaterials 2021, 11(2), 504; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11020504 - 17 Feb 2021

Cited by 8 | Viewed by 2337

Abstract

Impressive room-temperature gas-sensing capabilities have been reported for nanomaterials of many metal oxides, including SnO₂, ZnO, TiO₂, WO₃, and Fe₂O₃, while little attention has been paid to the intrinsic difference among them. Pt-SnO [...] Read more.

Impressive room-temperature gas-sensing capabilities have been reported for nanomaterials of many metal oxides, including SnO₂, ZnO, TiO₂, WO₃, and Fe₂O₃, while little attention has been paid to the intrinsic difference among them. Pt-SnO₂ and Pt-ZnO composite nanoceramics have been prepared through convenient pressing and sintering. The former shows strong and stable responses to hydrogen in 20% O₂-N₂ (synthetic air) at room temperature, while the responses to hydrogen in N₂ cannot be stabilized in limited times; the latter shows strong and stable responses to hydrogen in N₂, while the responses to hydrogen in synthetic air are greatly depressed. Further analyses reveal that for Pt-ZnO, the responses result from the reaction between hydrogen and oxygen chemisorbed on ZnO; while for Pt-SnO₂, the responses result from two reactions of hydrogen, one is that with oxygen chemisorbed on SnO₂ and the other is hydrogen chemisorption on SnO₂. These results reveal two different room-temperature hydrogen-sensing mechanisms among MOXs, which results in highly contrasting room-temperature hydrogen-sensing capabilities attractive for sensing hydrogen in oxygen-contained and oxygen-free environments, separately. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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8 pages, 1883 KiB

Open AccessCommunication

Surface Structure Engineering of Nanosheet-Assembled NiFe₂O₄ Fluffy Flowers for Gas Sensing

by Xiaofeng Wang, Xu Li, Guozheng Zhang, Zihao Wang, Xue-Zhi Song and Zhenquan Tan

Nanomaterials 2021, 11(2), 297; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11020297 - 24 Jan 2021

Cited by 4 | Viewed by 1716

Abstract

In this work, we present a strategy to improve the gas-sensing performance of NiFe₂O₄ via a controllable annealing Ni/Fe precursor to fluffy NiFe₂O₄ nanosheet flowers. X-ray diffraction (XRD), a scanning electron microscope (SEM), nitrogen adsorption–desorption measurements and [...] Read more.

In this work, we present a strategy to improve the gas-sensing performance of NiFe₂O₄ via a controllable annealing Ni/Fe precursor to fluffy NiFe₂O₄ nanosheet flowers. X-ray diffraction (XRD), a scanning electron microscope (SEM), nitrogen adsorption–desorption measurements and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure, morphology, specific surface area and surface structure. The gas-sensing performance was tested and the results demonstrate that the response was strongly influenced by the specific surface area and surface structure. The resultant NiFe₂O₄ nanosheet flowers with a heating rate of 8 °C min⁻¹, which have a fluffier morphology and more oxygen vacancies in the surface, exhibited enhanced response and shortened response time toward ethanol. The easy approach facilitates the mass production of gas sensors based on bimetallic ferrites with high sensing performance via controlling the morphology and surface structure. Full article

(This article belongs to the Special Issue Nanostructured Materials for Gas Sensor Applications)

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