Search results for: non-geometric sensitivities

Authors: Sudip Kumar Sinha, Saptarshi Ghosh

Abstract:

While there’s a perpetual buzz around zinc oxide (ZnO) superstructures for their unique optical features, the versatile material has been constantly utilized to manifest tailored electronic properties through rendition of distinct morphologies. And yet, the unorthodox approach of implementing the novel 1D nanostructures of ZnO (pristine or doped) for volatile sensing applications has ample scope to accommodate new unconventional morphologies. In the last two decades, solid-state sensors have attracted much curiosity for their relevance in identifying pollutant, toxic and other industrial gases. In particular gas sensors based on metal oxide semiconducting (wide Eg) nanomaterials have recently attracted intensive attention owing to their high sensitivity and fast response and recovery time. These materials when exposed to air, the atmospheric O2 dissociates and get absorb on the surface of the sensors by trapping the outermost shell electrons. Finally a depleted zone on the surface of the sensors is formed, that enhances the potential barrier height at grain boundary . Once a target gas is exposed to the sensor, the chemical interaction between the chemisorbed oxygen and the specific gas liberates the trapped electrons. Therefore altering the amount of adsorbate is a considerable approach to improve the sensitivity of any target gas/vapour molecule. Likewise, this study presents a spontaneous but self catalytic creation of Sn-doped ZnO hexagonal nanoprisms on Si (100) substrates through thermal evaporation-condensation method, and their subsequent deployment for volatile sensing. In particular, the sensors were utilized to detect molecules of ethanol, acetone and ammonia below their permissible exposure limits which returned sensitivities of around 85%, 80% and 50% respectively. The influence of Sn concentration on the growth, microstructural and optical properties of the nanoprisms along with its role in augmenting the sensing parameters has been detailed. The single-crystalline nanostructures have a typical diameter ranging from 300 to 500 nm and a length that extends up to few micrometers. HRTEM images confirmed the hexagonal crystallography for the nanoprisms, while SAED pattern asserted the single crystalline nature. The growth habit is along the low index <0001>directions. It has been seen that the growth mechanism of the as-deposited nanostructures are directly influenced by varying supersaturation ratio, fairly high substrate temperatures, and specified surface defects in certain crystallographic planes, all acting cooperatively decide the final product morphology. Room temperature photoluminescence (PL) spectra of this rod like structures exhibits a weak ultraviolet (UV) emission peak at around 380 nm and a broad green emission peak in the 505 nm regime. An estimate of the sensing parameters against dispensed target molecules highlighted the potential for the nanoprisms as an effective volatile sensing material. The Sn-doped ZnO nanostructures with unique prismatic morphology may find important applications in various chemical sensors as well as other potential nanodevices.

Keywords: gas sensor, HRTEM, photoluminescence, ultraviolet, zinc oxide

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Authors: Joanne Ndirangu

Abstract:

Delving into the intricate landscape of slum tourism in Kenya, this study critically evaluates its ethical implications, legal frameworks, and beneficiaries. By examining the complex interplay between tourism operators, visitors, and slum residents, it seeks to uncover the long-term consequences for the communities involved. Through an exploration of ethical considerations, legal parameters, and the distribution of benefits, this examination aims to shed light on the broader socio-economic impacts of slum tourism in Kenya, particularly on the lives of those residing in these marginalized communities. Assessing the ethical considerations surrounding slum tourism in Kenya, including the potential exploitation of residents and cultural sensitivities and examine the legal frameworks governing slum tourism in Kenya and evaluate their effectiveness in protecting the rights and well-being of slum dwellers. Identifying the primary beneficiaries of slum tourism in Kenya, including tour operators, local businesses, and residents, and analysing the distribution of economic benefits. Exploring the long-term socio-economic impacts of slum tourism on the lives of residents, including changes in living conditions, access to resources, and community development. Understanding the motivations and perceptions of tourists participating in slum tourism in Kenya and assess their role in shaping the industry's dynamics and investigate the potential for sustainable and responsible forms of slum tourism that prioritize community empowerment, cultural exchange, and mutual respect. Providing recommendations for policymakers, tourism stakeholders, and community organizations to promote ethical and sustainable practices in slum tourism in Kenya. The main contributions of researching slum tourism in Kenya would include; Ethical Awareness: By critically examining the ethical implications of slum tourism, the research can raise awareness among tourists, operators, and policymakers about the potential exploitation of marginalized communities. Beneficiary Analysis: By identifying the primary beneficiaries of slum tourism, the research can inform discussions on fair distribution of economic benefits and potential strategies for ensuring that local communities derive meaningful advantages from tourism activities. Socio-Economic Understanding: By exploring the long-term socio-economic impacts of slum tourism, the research can deepen understanding of how tourism activities affect the lives of slum residents, potentially informing policies and initiatives aimed at improving living conditions and promoting community development. Tourist Perspectives: Understanding the motivations and perceptions of tourists participating in slum tourism can provide valuable insights into consumer behaviour and preferences, informing the development of responsible tourism practices and marketing strategies. Promotion of Responsible Tourism: By providing recommendations for promoting ethical and sustainable practices in slum tourism, the research can contribute to the development of guidelines and initiatives aimed at fostering responsible tourism and minimizing negative impacts on host communities. Overall, the research can contribute to a more comprehensive understanding of slum tourism in Kenya and its broader implications, while also offering practical recommendations for promoting ethical and sustainable tourism practices.

Keywords: slum tourism, dark tourism, ethical tourism, responsible tourism

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Authors: Irmak Karaduman, Tugba Corlu, Sezin Galioglu, Burcu Akata, M. Ali Yildirim, Aytunç Ateş, Selim Acar

Abstract:

Breath analysis represents a promising non-invasive, fast and cost-effective alternative to well-established diagnostic and monitoring techniques such as blood analysis, endoscopy, ultrasonic and tomographic monitoring. Portable, non-invasive, and low-cost breath analysis devices are becoming increasingly desirable for monitoring different diseases, especially asthma. Beacuse of this, NO gas sensing at low concentrations has attracted progressive attention for clinical analysis in asthma. Recently, nanomaterials based sensors are considered to be a promising clinical and laboratory diagnostic tool, because its large surface–to–volume ratio, controllable structure, easily tailored chemical and physical properties, which bring high sensitivity, fast dynamic processand even the increasing specificity. Among various nanomaterials, semiconducting metal oxides are extensively studied gas-sensing materials and are potential sensing elements for breathanalyzer due to their high sensitivity, simple design, low cost and good stability.The sensitivities of metal oxide semiconductor gas sensors can be enhanced by adding noble metals. Doping contents, distribution, and size of metallic or metal oxide catalysts are key parameters for enhancing gas selectivity as well as sensitivity. By manufacturing doping MOS structures, it is possible to develop more efficient sensor sensing layers. Zeolites are perhaps the most widely employed group of silicon-based nanoporous solids. Their well-defined pores of sub nanometric size have earned them the name of molecular sieves, meaning that operation in the size exclusion regime is possible by selecting, among over 170 structures available, the zeolite whose pores allow the pass of the desired molecule, while keeping larger molecules outside.In fact it is selective adsorption, rather than molecular sieving, the mechanism that explains most of the successful gas separations achieved with zeolite membranes. In view of their molecular sieving and selective adsorption properties, it is not surprising that zeolites have found use in a number of works dealing with gas sensing devices. In this study, the Cu doped ZnO nanostructure film was produced by SILAR method and investigated the NO gas sensing properties. To obtain the selectivity of the sample, the gases including CO,NH3,H2 and CH4 were detected to compare with NO. The maximum response is obtained at 85 C for 20 ppb NO gas. The sensor shows high response to NO gas. However, acceptable responses are calculated for CO and NH3 gases. Therefore, there are no responses obtain for H2 and CH4 gases. Enhanced to selectivity, Cu doped ZnO nanostructure film was coated with zeolite A thin film. It is found that the sample possess an acceptable response towards NO hardly respond to CO, NH3, H2 and CH4 at room temperature. This difference in the response can be expressed in terms of differences in the molecular structure, the dipole moment, strength of the electrostatic interaction and the dielectric constant. The as-synthesized thin film is considered to be one of the extremely promising candidate materials in electronic nose applications. This work is supported by The Scientific and Technological Research Council of Turkey (TUBİTAK) under Project No, 115M658 and Gazi University Scientific Research Fund under project no 05/2016-21.

Keywords: Cu doped ZnO, electrical characterization, gas sensing, zeolite

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