| ZnO is emerged as a promising material in recent years because of its excellent electrical and optical properties depends on its wide band gap of 3.37 eV and large exciton binding energy of 60 meV.Due to its excellent properties,ZnO has come forward as an appealing candidate in a variety of optoelectronic devices such as solar cells,light emitting diodes,gas sensors and so on.As a gas detector,it has gained much attention because of its ease of synthesis,high thermal and chemical stability.Moreover,ZnO has become an important material and taken much consideration of the researchers,as most of its properties and applications that rely upon doping.Also,this promising material can be grown in to different morphologies and shape i.e.nanoparticles,nanorods,nanotubes,nanowires,nanoflowers etc.Due to its surface modification,the tunable band gap of ZnO can be used in numerous novel devices.Besides that,the development of alternative energy sources is a hot area of research nowadays.Hydrogen is emerged as a most suitable candidate to get rid of fossil fuels in the future energy market due to its environment friendly nature.The hydrogen evolution reaction(HER)has been regarded as the most economical and effective method to produce clean hydrogen energy.In the first chapter,general introduction about gas sensor,gas sensing mechanism,semiconducting gas sensor,the importance of ZnO gas sensor,general properties of ZnO,quantum confinement effect,doping and coding in ZnO,electrocatalytic hydrogen evolution reaction,HER mechanism,significant parameters of HER and aim and obj ectives of this thesis are briefly discussed.In the second chapter,the synthesis,characterization and applications of ZnO nanoparticles and nanorods in acetone gas detection are discussed.ZnO nanoparticles and nanorods are prepared by cost effective wet chemical method.Then,the structural and morphology characterization are done by X-ray diffraction and transmission electron microscopy.However,the optical properties are examined by UV-visible near infrared and PL spectroscopies.All the characteristics peaks in the XRD spectrum confirm the hexagonal wurtzite structure of ZnO.Moreover,an obvious blue shift is well noted for ZnO nanoparticles as compared to ZnO nanorods in UV-Visible and PL spectroscopies due to its lower dimension size.Finally,our dynamic response recovery characterization for ZnO nanoparticles and nanorods gas sensor reveals that ZnO nanoparticles exhibit better acetone gas sensing performance as compared to its counterpart under an optimum operating temperature of 250 ?.In the third chapter,we have reported the tunable band gap engineering of single phase Ni/Co codoped ZnO nanoparticles by changing the dopant concentrations.The as synthesized undoped and codoped ZnO nanoparticles are characterized by UV-visible near infrared spectroscopy,PL spectroscopy,Transmission electron microscopy,X-ray diffraction,Fourier-transform infrared spectroscopy,and X-ray photoelectron spectroscopy.A clear blue shift of 15 nm for the codoped Ni/Co ZnO nanoparticles is well noted in the absorption spectrum.Moreover,the energy band structure of ZnO nanoparticles is tuned(i.e.3.55 eV to 3.71 eV)by varying the dopant concentration.In PL spectrum,the intensity of green emission PL peak is significantly reduced for the codoped samples attributed to the decrease in intrinsic defects.Our results not only improve the structural and optical properties of Ni and Co codoped ZnO nanoparticles but also these nanostructures could be used as the potential candidate for future optoelectronic devices.In the fourth chapter,we have reported the synthesis of Fe2O3 nanoparticles by hydrothermal method by adjusting the value of pH at 12 and 14 during the reaction.The as-prepared pH dependent samples are then subjected to structural and morphology characterization by X-ray diffraction and Transmission electron microscopy.However,the characterization of the present chemical components has done by X-ray photoelectron spectroscopy.Finally,electrochemical measurements are used to evaluate the catalytic performance of Fe2O3 nanoparticles.Linear sweep voltammetry experiment depicts the enhanced HER performance at pH 12 and pH 14,including a low value of overpotential i.e.321 mV and 423 mV at 10 mAcm-2 and Tafel slope values of 140 mV/dec and 144 mV/dec in basic medium.Moreover,cyclic voltammetry cycles reveal the excellent stability of our as synthesized material before and after 1000 cycles.Our work provides a new route to develop inexpensive non-noble electrocatalysts for driving electrocatalytic hydrogen evolution reaction. |
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