Chapter 6 Thesis Highlights and Scope for Future

Chapter 6 Thesis Highlights and Scope for Future

Summary: Chapter 6 Developing intelligent or smart nanomaterials with multiple functions and tailoring their properties at the molecular level is one of the major challenges in materials science. The large surface-to-volume ratios and unique functionalities of nanomaterials have given immense scope and opportunities to develop technologies that are aimed at alleviating the problems of environmental pollution and addressing energy issues. The main objective of this thesis work has been to develop novel nanostructured functional materials with desired properties and explore their potential applications in energy and environmental sector. In this perspective, simple and low cost routes has been developed to fabricate TiO 2, ZnO nanocrystals with significant control on crystallite size, phase, morphology. The applications in photocatalysis and dye sensitized solar cells with improved performance characteristics demonstrated. First and foremost, a phase induced enhanced photoactivity of biphasic TiO 2 nanocrystals developed by a simple hydrolysis method in aqueous-ethanol mixed solvent media was established. The synthesized TiO 2 nanocrystals predominantly comprised of brookite phase and the phase ratio of rutile to brookite and brookite to anatase composition was conveniently tailored by tuning the water to ethanol volume ratio. The visible light photoactivity of synthesized samples was explained by interfacial charge transfer from one phase to the other phase resulting in increased charge separation. Similarly, shape induced, enhanced photocatalytic activity of ZnO microcrystals with preferentially exposed polar facets was revealed. Hierarchical structures including hexagonal twin discs, 3D-trapezoids, self-assembled rings, doughnuts, and hemisphere morphologies was achieved by simple hydrothermal route without the use of any additives/templates. The superior photoactivity of hexagonal discs was attributed to their exotic structural 143

Chapter 6 features with predominantly exposed active polar facets. Finally, a versatile approach for the large scale synthesis of hierarchical spherical rutile TiO 2 aggregates with a wide size distribution has been demonstrated. These hierarchical rutile TiO 2 aggregates have been used as a scattering layer of the working electrodes for DSSCs and the light scattering effect was examined. The aggregates were formed by nanosized crystallites and, therefore, were able to contribute both to a large specific surface area and strong light scattering ability, which enhanced the light harvesting efficiency. The overall conversion efficiency of 8.4% was achieved using the hierarchical rutile TiO 2 aggregates as scattering over layer of photoelectrodes. Various characterization techniques were used to confirm the structure, morphology, ascertain their physical and electronic properties and to propose the mechanistic pathway for the obtained nanostructures. Scope for Future Work: The work initiated and accomplished as a part of the PhD program has paved the way to frame and outline new programs in the areas of energy devices both generation and storage. Most photocatalysts available to date are active only in the ultraviolet (UV) or near UV regime with limited efficiency due to its energy mismatch to the visible solar spectrum. This defines a challenge, opening up an interesting area for future work towards developing of new and superior photocatalyst materials with improvement in the light trapping capability by bandgap engineering. The expertise gained and the processes established could also be utilized for developing materials suitable for application in supercapacitors, lithium ion batteries, hybrid solar cells etc. The efficiencies in the DSSCs and the photocatalytic reaction could be further improved by fine tuning the materials studied. The scope of the future work would be follows: 144

Chapter 6 Exploration of above strategies to synthesize other photo-functional materials like for example SnO 2, WO 3 and pervoskite materials. The synthesized materials could be extended to other applications, including photocatalytic reduction of CO 2, water splitting and Quantum dot solar cells. Efforts will be continued to find newer materials with multifunctional properties, suitable crystal and band structure which can produce higher efficiencies in the appropriate devices. 145

Publications, Trainings, Symposia, Presentations and Awards

Publications: 1. Ramireddy Boppella, Pratyay Basak and Sunkara V Manorama,* A viable method for the synthesis of biphasic TiO 2 nanocrystals with tunable phase composition and enabled visible-light photocatalytic performance (ACS Appl. Mater. Interfaces 2012, 4, 1239 1246 ) 2. P Manjula, Ramireddy Boppella, Sunkara V Manorama,* A Facile Green Synthetic Approach for Controlled Synthesis of Porous SnO 2 Nano Spheres: Application as an Efficient Photocatalyst and an Excellent Gas Sensing Material (ACS Appl. Mater. Interfaces, 2012, 4 (11), 6252 6260) 3. Ramireddy Boppella, k. Anjaneyulu, Pratyay Basak and Sunkara V Manorama,* Facile Synthesis of Face Oriented ZnO Crystals: Tunable Polar Facets and Shape Induced Enhanced Photocatalytic Performance (J. Phys. Chem. C 2013, 117, 4597 4605) 4. Ramireddy Boppella, P. Manjula, S. Arunkumar and Sunkara V Manorama* Advances in synthesis of nanostructured metal oxides for chemical sensors: Chemical sensors ( Accepted Feature Review article) 5. Ramireddy Boppella, Pratyay Basak and Sunkara V Manorama, Hierarchical Rutile TiO 2 Aggregates: An efficient light scattering Materials for Dye Sensitized Solar Cells (DSSCs) ( Manuscript submitted) 6. Arunkumar Shanmugasundaram, Ramireddy Boppella, S. Srinath, Pratyay Basak* and Sunkara V. Manorama*, Hierarchical In(OH) 3 as a Precursor to Mesoporous In 2 O 3 Nanocubes: A Facile Synthesis Route, Mechanism of Self-Assembly and Enhanced Sensing Response towards Hydrogen (Manuscript submitted to J. Phys. Chem. C)

7. Ramireddy Boppella, Pratyay Basak and Sunkara V. Manorama*, Hallow Porous TiO 2 Hierarchitectures for efficient Dye Sensitized Solar Cells (manuscript under preparations) Presentations: 1. Ramireddy Boppella, Pratyay Basak and Sunkara V Manorama, Hierarchical Rutile TiO 2 photoanode: An efficient light scatterer for Dye Sensitised Solar Cells (DSSCs) presented in Advanced nanomaterials and Nanotechnology (ICANN-2013) held at IIT Guwahathi, December -2013. 2. Ramireddy Boppella, P Manjula, Pratyay Basak and Sunkara V Manorama: "Facile Green synthetic Approaches for Porous SnO 2 and TiO 2 Nanospheres for environmentally benign photocatalysis" poster presentation at the 2nd International Indo German Symposium on Green Chemistry and Catalysis for Sustainable Development to be held on October -2012. 3. Ramireddy Boppella, Pratyay Basak and Sunkara V Manorama, Hierarchical TiO 2 nanospheres fabricated by environmentally benign method for high efficiency photoanode in DSSCs poster present in Materials Challenges in Alternative & Renewable Energy organised by American ceramic society held at Clearwater, Florida., USA, Feb-2012. 4. Ramireddy Boppella, Pratyay Basak and Sunkara V Manorama, Designing Nanoarchitectures by Low Temperature and Green Synthetic Methods for Photocatalytic and Solar Cell applications Poster presented at Indo-German Nachkontakt associations (IGNA), IICT-India, Dec-2011.

5. Ramireddy Boppella, P.Manjula, S. Arunkumar, Pratyay Basak and Sunkara V Manorama, Nano/Micro structured Multifunctional Metal Oxides for Energy and Environmental Applications. Poster presented at APEX Excitonic cell symposium under the DST (India) EPSRC (UK) held at Imperial College London UK. July 2011. 6. Participated in the seminar on Recent Trends in Renewable Energy Resources organized by Indo-German Nachkonatakt Assosiation (IGNA), Hyderabad, Jan-2011. Trainings: Attended orientation program on "Pre-School on Photocatalysis" organised by national centre for catalysis IIT-Madras, India, Dec-2011 Awards and Honours: Awarded short term Canadian Commonwealth Research Fellowship: Host: Dr. Karthik Shankar, Assistant Professor, Department of Electrical & Computational Engineering, University of Alberta, Edmonton, Canada; November-2012 to April-2013 Awarded UGC-Senior Research Fellowship at IICT, 2011-2014. Qualified Council of Scientific and Industrial Research-National Eligibility Test (CSIR-NET) in 2009, and awarded UGC-Junior Research Fellowship at IICT, India; 2009-2011.