Synthesis of Nanostructured Ni-doped ZnO Semiconductors using Hybrid Metal Organic Precursors for Gas Sensing

Abstract

The increasing concerns of industrial safety chemical control and environmental pollution are spurring demand for high performance gas sensors Growing use of gas sensors is making gas sensors on demand After decades of research and development activities semiconductorbased gas sensors are now used in a variety of applications However challenges still remain in the area of sensitivity selectivity response-recovery speeds and power consumption Therefore improvement of metal oxide gas sensors by the incorporation of different technology is important Various types of gas sensors have been developed based on different signals originated from gas interactions with either sensing materials or probing sources Among them chemiresistive sensors present unique advantages due to their simple implementation and low manufacturing cost Combined with good sensitivity selectivity and reliability for real-time monitoring semiconducting metal oxides (SMOs) represent the most popular materials to operate at high temperatures Metal-Organic Precursors (MOP) are often volatile enough to be useful as precursors of the metals in vapor phase deposition process e g chemical vapor deposition (CVD) Metal-Organic Precursor materials have been the focus in all researches for their application as molecular storage molecular sensing catalyst asymmetric synthesis and host materials These types of martials represent a promising new class of crystalline solids because they exhibit large pore volume high surface area permanent porosity high thermal stability feature open channels with tunable dimensions and topology In this study we investigated the design synthesis and structures of a new family of MOPs through their hybrid-bimetal to expand our knowledge about heterostructures of MOPs The main objective of this study is synthesis and characterization of a series of hybrid transition metal complexes as single MOP in order to enhance gas sensing and optical properties of nanocrystalline derived from ZnO thin films via hydrothermal techniques The morphology microstructure surface chemistry and photoluminescence properties of the as-grown Ni-doped ZnO nanorods (NRs) are extensively examined Optical and photocatalytic results reveal that the photodegradation of methyl orange is facilitated with Cu doping into ZnO NRs This result may facilitate the use of transition-metal ion-doped ZnO in other photo conversion such as ZnO based dye-synthesized solar cells and magnetism-assisted photocatalytic system Furthermore for Ni- doped ZnO NRs the gas sensing results are discussed in terms of doping concentration operating temperature gas type gas concentrations and relative humidity The gas sensor performance of Ni doped ZnO thin film was investigated at different operating temperatures for various reducing organic gases including CH3OH C2H5OH and inorganic gases including H2S and CH4 The enhancement of gas sensing response is attributed to increasing the number of active sites for adsorption of oxygen and target gases on the surface through incorporation of Ni3+ over Ni2+ ions The Ni doped ZnO NRs surface study results show at room temperature the sensing mechanism is related to the formation of a 7 nm-thick ZnS layer over the NRs through reactions between H2S and adsorbed oxygen Moderate amount of Humidity about 52% exhibit the highest response to gas sensing and after that decreasing trend with increasing relative humidity Adsorption and desorption of water molecule with reducing gas at room temperature has been investigated however it need further studies

Date of Award	2018 Dec 10
Original language	English
Supervisor	Chuan-Pu Liu (Supervisor)