Author
Gugu H. Mhlongo
Other affiliations: Council for Scientific and Industrial Research, Council of Scientific and Industrial Research
Bio: Gugu H. Mhlongo is an academic researcher from University of the Free State. The author has contributed to research in topics: Photoluminescence & Scanning electron microscope. The author has an hindex of 22, co-authored 49 publications receiving 1305 citations. Previous affiliations of Gugu H. Mhlongo include Council for Scientific and Industrial Research & Council of Scientific and Industrial Research.
Papers
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TL;DR: In this paper, the authors reported on the ultra-high sensitive and selective hydrogen gas sensing using CeO2-SnO2 mixed oxide heterostructure synthesized by a simple hydrothermal method.
Abstract: Detection of toxic and explosive gases in a selective manner and with higher sensitivity in industries and homes remains very challenging. Therefore, herein, we report on the ultra-high sensitive and selective hydrogen gas sensing using CeO2-SnO2 mixed oxide heterostructure synthesized by a simple hydrothermal method. The BET, photoluminescence, X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses demonstrated that the CeO2-SnO2 heterostructure comprehends a high surface area and a large number of defects related to oxygen vacancies. The formation of heterojunction in CeO2-SnO2 nanostructures was confirmed by the non-linear behaviour I–V curve. The gas-sensing characteristics of the CeO2-SnO2 heterostructure showed shorter response and recovery times of approximately 17 and 24 s, respectively, together with high sensitivity (19.23 ppm−1) to 40.00 ppm H2 gas at 300 °C. The improved H2 gas sensing response of 1323 at 60 ppm H2 gas is correlated with the higher surface area, pore diameter, surface defects and CeO2-SnO2 heterojunction emerging at the interfaces between the CeO2 and SnO2 serves as additional reaction sites and as well as exposed facets creating the surface to be extremely reactive for the adsorption of oxygen species. The high H2 gas selectivity observed for the CeO2-SnO2 makes them possible candidates for monitoring H2 gas at low concentrations (ppm levels).
162 citations
TL;DR: Structural analyses showed that the ZnO nanostructures are polycrystalline and wurtzite in structure, without any secondary phases, and an intense structure- and shape-dependent ferromagnetic signal with an effective g-value of >2.0 and a sextet hyperfine structure was shown.
Abstract: We report on the room temperature ferromagnetism of various highly crystalline zinc oxide (ZnO) nanostructures, such as hexagonally shaped nanorods, nanocups, nanosamoosas, nanoplatelets, and hierarchical nano “flower-like” structures. These materials were synthesized in a shape-selective manner using simple microwave assisted hydrothermal synthesis. Thermogravimetric analyses demonstrated the as-synthesized ZnO nanostructures to be stable and of high purity. Structural analyses showed that the ZnO nanostructures are polycrystalline and wurtzite in structure, without any secondary phases. Combination of electron paramagnetic resonance, photoluminescence, and X-ray photoelectron spectroscopy studies revealed that the zinc vacancies (VZn) and singly ionized oxygen vacancies (VO+) located mainly on the ZnO surface are the primary defects in ZnO structures. A direct link between ferromagnetism and the relative occupancy of the VZn and VO+ was established, suggesting that both VZn and VO+ on the ZnO surface pl...
124 citations
TL;DR: In this paper, a combination of defect structure analysis based on photoluminescence (PL) and electron paramagnetic resonance (EPR) was employed to detect coexisting oxygen vacancies (V O ) and zinc interstitials (Zn i ) defects in undoped and transition metal doped ZnO systems.
115 citations
TL;DR: It was confirmed that Au form nanoparticles loaded on the surface of ZnO, and it was demonstrated that Au/ZnO based sensors were highly selective to NH3 gas at room temperature.
108 citations
TL;DR: In this article, the violet-blue emitting ZnO nanostructures were synthesized by a microwave-assisted hydrothermal method followed by post-synthesis annealing at different temperatures.
82 citations
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01 Aug 2001
TL;DR: The study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence, is concentrated on in this work.
Abstract: With digital equipment becoming increasingly networked, either on wired or wireless networks, for personal and professional use alike, distributed software systems have become a crucial element in information and communications technologies. The study of these systems forms the core of the ARLES' work, which is specifically concerned with defining new system software architectures, based on the use of emerging networking technologies. In this context, we concentrate on the study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence.
2,774 citations
TL;DR: In this paper, the room-temperature gas sensing properties of ZnO-based gas sensors are comprehensively reviewed, and more attention is particularly paid to the effective strategies that create room temperature gas sensing, mainly including surface modification, additive doping and light activation.
Abstract: Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.
756 citations
TL;DR: This review organizes and introduces several common gas sensing mechanisms of metal oxide semiconductors in detail and classifies them into two categories, the scope and relationship of these mechanisms are clarified and some perspectives for future investigations on the gas sensing mechanism are discussed.
Abstract: In recent years, gas sensors have been increasingly used in industrial production and daily life. Metal oxide semiconductor gas sensing materials are favoured for their outstanding physical and chemical properties, low cost and simple preparation methods. However, the gas sensing mechanisms of metal oxide semiconductors have not been considered by researchers, resulting in omissions and errors in the interpretation of gas sensing mechanisms in many articles. This review organizes and introduces several common gas sensing mechanisms of metal oxide semiconductors in detail and classifies them into two categories. The scope and relationship of these mechanisms are clarified. In addition, this review selects four strategies for enhancing the gas sensing properties of metal oxide semiconductors and analyses the gas sensing mechanisms to highlight the importance of the gas sensing mechanism. Finally, some perspectives for future investigations on the gas sensing mechanisms of metal oxide semiconductors are discussed as well.
488 citations
TL;DR: In this paper, the authors highlight 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.
Abstract: 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.
434 citations
TL;DR: In this article, the synergistic effect achieved by combining these two mechanisms are examined, and the authors connect experimental evidence to conceptual mechanistic descriptions by examining adsorption processes, charge transfer, reaction mechanisms, morphology, and ambient gas interactions.
Abstract: Metal oxide resistive-type nano-scale gas sensors have been investigated for their low cost, high sensitivity, and environmentally friendly fabrication. In these sensors, electrical resistance measurements are used to detect the presence of gas. In n-type metal oxides, resistance is increased by coverage of adsorbed oxygen and lowered by removal of adsorbed oxygen through reactions with reducing gasses. The sensitivity and selectivity of these sensors have been improved by incorporation of heterostructures. Heterostructures may improve sensor performance through facilitating catalytic activity, increasing adsorption, and creating a charge carrier depletion layer that produces a larger modulation in resistance. Synergistic effects in these gas sensors describe the improved sensor signal due to these combined effects which act to amplify the reception and transduction of the sensor signal. Receptive mechanisms may be improved by increasing adsorption and reactivity. Transduction mechanisms may be improved by restriction of the major charge conduction channels which helps to maximize resistance modulation. In this review, the synergistic effect achieved by combining these two mechanisms are examined. Fundamental properties of the metal oxide surface are used to provide insight for the large body of experimental evidence available for metal oxide resistive-type gas sensors. This review aims to connect experimental evidence to conceptual mechanistic descriptions by examining adsorption processes, charge transfer, reaction mechanisms, morphology, and ambient gas interactions.
371 citations