Ternary chalcogenides and their composites with titanium dioxide for photocatalytic applications /

Abstract

This thesis addresses the preparation of semiconductor nanomaterials and their composites with ternary chalcogenides (TC) for photocatalytic applications. Rapid depletion and ever-increasing demand for fossil fuels have posed some grave challenges. Rising global temperature and population are the key elements of concern to the energy shortage and environmental pollution. Heterogeneous photocatalysis, in the past decade, has deemed to be an effective route for producing greener energy and environmental remediation. Ternary chalcogenides (TC) with remarkable visible light absorption, are identified as an ideal candidate to form heterostructure with classical semiconductors such as TiO2. In the present investigation, heterostructure nanocomposite of AgBiS2-TiO2, AgInS2-TiO2, AgBiSe2- TiO2 and AgInSe2-TiO2 composites are synthesised utilising two-step calcination and solvothermal technique. The study also contributes to the process optimisation of the TC nanoparticles synthesis. Computational analysis was utilised to study the structural, electronic and optical properties of the pristine parent samples. This aided in validating the results obtained experimentally as well as to understand the charge transfer mechanism within the heterojunction creation. The XRD results confirm the formation of the parent TC nanoparticles of different crystal structure and anatase phase of titania. The minor shift in binding energies in XPS, red shift observed in Raman spectra, and the TEM results illustrate the successful heterostructure formation. The UV-DRS pattern for all the composites shows enhanced visible light absorption due to the coupling of TC. The band gap of the composites decreased with increased doping levels. Moreover, these materials were studied for their photocatalytic efficiency, by photocatalytic degradation of Doxycycline, photocatalytic hydrogen generation and photocatalytic antimicrobial disinfection. The composite samples illustrated more than 95% degradation results within 180 minutes and showed about 5 log reductions of bacterial strains (E. coli and S. aureus) within 30 minutes of irradiation. 10 The hydrogen production results were promising as all the composites samples displayed higher efficiencies compared to their parent samples. The PL measurement also validated the enhanced activity exhibited by the composite structures, as the intensity of the composite samples gets dampened compared to pristine TiO2, which suggests the decreased rate of recombination. A mechanism for the enhanced photocatalytic activity is proposed based on scavenging experiments and theoretical analysis