Tailored nanostructures for CO2 gas sensing applications

Carbon dioxide (CO2) is a thermodynamically stable gas owing to its inherent colourless, odourless and inflammable nature. At low concentrations (~1000 ppm) it is considered harmless, however at higher concentrations (>20000 ppm), it significantly affects the respiratory system. In recent years, the health hazards of CO2 have forced government and environmental safety bodies around the world to introduce stern rules to curb CO2 emission from major anthropogenic sources. In this context, efficient and selective detection of CO2 gas has gained considerable interest as it is the first step to emission reduction of this greenhouse pollutant. To date, metal oxide based sensors have shown promising potential in gas sensing applications as they can be easily miniaturized, has defect tuned facile synthesis and high structural stability necessary in harsh testing conditions. However, the major issue of using them for CO2 sensing applications is their lack of sensitivity and selectivity towards the gas at the desired operating temperatures. This doctoral project centres around the development of metal oxides based CO2 gas sensors that can detect low concentrations (<1000 ppm) in the presence of oxidising co-interfering gases such as NO2, SO2, CO and NO at various operating temperatures. The initial stage of this doctoral work deals with comprehensive literature review that revealed challenging inadequacies in the existing sensor materials synthesis and fabrication techniques. Furthermore, important semiconductor materials that have not yet been explored towards CO2 but have shown sensing capabilities towards similar oxidising gases were studied for the first time. In an attempt to address the research questions developed during the course of study, potentiometric and chemo-resistive micro-sensors were fabricated as a case study to successfully develop a set of sensitive and selective CO2 gas sensors operating from 100 to 500oC for range of potential applications. Among the CO2 sensors, potentiometric sensors are extensively tried in sectors requiring sensors operating efficiently at temperature above 400oC. Unlike the conventional potentiometric sensors using commercially procured sensitive materials, the sensor developed in this work was fabricated out of nanomaterials in a bid to improve its electrochemical stability. In case of chemo-resistive gas sensors, various hierarchical n-type metal oxide semiconductors (ZnO, SnO2 and BaTiO3) were synthesized and decorated with Ag@CuO to target CO2 application, where an operating temperature less than 300oC is required. The chosen n-type metal oxides were selected based on their band-gap, work function, and charge carrier concentration. Carbonising ability of CuO in the presence of CO2 and catalytic role of Ag in expediting the CO2 sensing phenomenon were the sole reasons for the decoration of n-type MOS with Ag@CuO. Plausible formation mechanism in each case was proposed based on the nucleation and crystal growth supported by physicochemical characterizations techniques. Both types of the developed sensors were tested towards CO2 gas concentrations (100-10000 ppm) as a function of operating temperature (40-700°C) and their influence on sensor performance (i.e. sensitivity, selectivity, long-term stability, response/recovery times, dynamic range, repeatability and reusability) were thoroughly investigated. The probable CO2 sensing mechanism has also been attempted by corroborating sensing performance with in-situ spectroscopic techniques. The results demonstrated in this work were found to be encouraging and is anticipated to pave way for intensified research efforts in CO2 sensor development for real industrial applications. For example, the nanostructured potentiometric CO2 composing of Li4Ti5O12 octahedra showed enhanced response compared to commercial sensor, thus standing strong chance as real-time sensor. Among the n-type MOS tested, Ag@CuO/BaTiO3 showed exceptional sensing performance and the sensing mechanism were determined by employing in-situ DRIFTS technique. The sensors developed in this doctoral work are anticipated to be suitable for industrial applications requiring low operating temperatures and detection limits. The methods, materials and devices presented in this thesis have potential to be explored further, not only for CO2 based sensing but also many other applications such as visible light driven dye degradation, supercapacitors and so on

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties. Of late, graphene and graphene-related derivatives have been proven as the most versatile two-dimensional nanomaterials with superb mechanical, electrical, electronic, optical, and magnetic properties. To understand the in-depth technology, an effort has been made to explain the basics of nano dimensional materials. The importance of nano particles in various aspects of nano technology is clearly indicated. There is more than one chapter describing the use of nanomaterials as sensors. In this volume, an effort has been made to clarify the use of such materials from non-conductor to highly conducting species. It is expected that this book will be useful to the postgraduate and research students as this is a multidisciplinary subject

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties

Biomimetic Based Applications

The interaction between cells, tissues and biomaterial surfaces are the highlights of the book "Biomimetic Based Applications". In this regard the effect of nanostructures and nanotopographies and their effect on the development of a new generation of biomaterials including advanced multifunctional scaffolds for tissue engineering are discussed. The 2 volumes contain articles that cover a wide spectrum of subject matter such as different aspects of the development of scaffolds and coatings with enhanced performance and bioactivity, including investigations of material surface-cell interactions