{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/109619"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/109619","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Tracking the evolution of photoexcitations in strongly light absorbing systems","abstract":"Author requested closed access (OA after 2yrs) in Vireo ETD system","abstract_html":"Author requested closed access (OA after 2yrs) in Vireo ETD system","abstract_has_math":false,"creators":["Mohan, Varun"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Materials Science & Engr","degree_department":null,"school":null,"contributors":["Jain, Prashant K","Shim, Moonsub","Braun, Paul V","Chen, Qian"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2021,"date_issued":"2021-03-05T21:47:26Z","date_published":"2021-03-05T21:47:26Z","updated_at":"2026-07-22T22:24:50Z","subjects":["Photocatalysis","Light-Matter interactions","Natural Gas Upgradation","Nanoparticles"],"languages":["en"],"rights":["© 2020 VARUN MOHAN"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/109619","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Jain, Prashant K","Shim, Moonsub","Braun, Paul V","Chen, Qian"]},{"key":"dc:creator","label":"Author","values":["Mohan, Varun"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2021-03-05T21:47:26Z","2023-03-05T21:47:41Z","2020-12-04","2020-12"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science & Engr"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Photocatalysis","Light-Matter interactions","Natural Gas Upgradation","Nanoparticles"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["© 2020 VARUN MOHAN"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/109619"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Author requested closed access (OA after 2yrs) in Vireo ETD system","Limited","This dissertation consists of the work done towards a Ph.D. degree in the research group of Professor Prashant K. Jain at the University of Illinois at Urbana-Champaign. Here, I describe the study of the conversion of light energy using hybrid perovskite and noble metal-based semiconductor nanoparticles. The large surface-area-to-volume ratios and superlative ability to absorb visible light make these materials worthy candidates for solar energy harvesting. The primary questions I have asked in my research are: what is the fate of photoexcitation in a nanostructured material and how can we channel such photo-excitations in an efficient and selective manner? Chapter 1 of this dissertation introduces some of the theoretical backdrops to my studies of strongly light-absorbing plasmonic nanoparticulate systems. This chapter elucidates what follows and introduces the concepts and terms used. Chapter 2 presents my investigation of hybrid organic-inorganic perovskite materials for potential uses towards light trapping and emission. We discovered that commonly observed luminescence from microcrystals of these materials showed a spectrum that varied with sample morphology and location on the sample. The origin of this spectral heterogeneity was then traced to the phenomenon of luminescence self-absorption, which is prevalent due to the overlapping absorption and emission, i.e., small Stokes-shift, in these materials. Then we explored light-to-chemical-energy conversion in perovskite materials, but they proved to be photochemically unstable; so, we turned our attention to noble metal nanoparticles, which have strong plasmon resonance absorption and high photostability. Chapter 3 describes the investigation of light-to-chemical energy conversion in colloidal gold (Au) nanoparticles In particular, we studied the effect of visible-light excitation of Au nanoparticles in the presence of an electron acceptor (HAuCl4) and a hole acceptor (short-chain alcohol). This led to the discovery of a hitherto unknown photoreaction, which involves the splitting and chlorination of the alcohol generating a chloroalkane and an aldehyde. This reaction was found to take place with several alcohols, which led us to a general reaction mechanism that is catalyzed synergistically by the photoexcited nanoparticle and the Lewis acidic HAuCl4. In the specific case of 2-butanol as the hole acceptor, we found a substantial difference between the product distributions of the light-driven reaction as compared to a thermal reaction. This finding represents an example of light-driven-control of catalytic selectivity. Finally, as presented in Chapter 4, the insights gained from the study described in Chapter 3 led me to a new, simple chemical process for low-temperature chlorination of methane in a non-corrosive aqueous environment. The kinetics and mechanism of this reaction were studied. Methane chlorination is at the heart of natural-gas upgradation, so this new finding represents an ideal culmination of my dissertation. An outlook and potential future directions are presented in Chapter 5.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-12-01","The student, Varun Mohan, accepted the attached license on 2020-12-01 at 18:31.","The student, Varun Mohan, submitted this Dissertation for approval on 2020-12-01 at 18:50.","This Dissertation was approved for publication on 2020-12-04 at 10:01.","DSpace SAF Submission Ingestion Package generated from Vireo submission #16022 on 2021-03-04 at 16:33:11","Made available in DSpace on 2021-03-05T21:47:26Z (GMT). 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Jain at the University of Illinois at Urbana-Champaign. Here, I describe the study of the conversion of light energy using hybrid perovskite and noble metal-based semiconductor nanoparticles. The large surface-area-to-volume ratios and superlative ability to absorb visible light make these materials worthy candidates for solar energy harvesting. The primary questions I have asked in my research are: what is the fate of photoexcitation in a nanostructured material and how can we channel such photo-excitations in an efficient and selective manner? Chapter 1 of this dissertation introduces some of the theoretical backdrops to my studies of strongly light-absorbing plasmonic nanoparticulate systems. This chapter elucidates what follows and introduces the concepts and terms used. Chapter 2 presents my investigation of hybrid organic-inorganic perovskite materials for potential uses towards light trapping and emission. We discovered that commonly observed luminescence from microcrystals of these materials showed a spectrum that varied with sample morphology and location on the sample. The origin of this spectral heterogeneity was then traced to the phenomenon of luminescence self-absorption, which is prevalent due to the overlapping absorption and emission, i.e., small Stokes-shift, in these materials. Then we explored light-to-chemical-energy conversion in perovskite materials, but they proved to be photochemically unstable; so, we turned our attention to noble metal nanoparticles, which have strong plasmon resonance absorption and high photostability. Chapter 3 describes the investigation of light-to-chemical energy conversion in colloidal gold (Au) nanoparticles In particular, we studied the effect of visible-light excitation of Au nanoparticles in the presence of an electron acceptor (HAuCl4) and a hole acceptor (short-chain alcohol). This led to the discovery of a hitherto unknown photoreaction, which involves the splitting and chlorination of the alcohol generating a chloroalkane and an aldehyde. This reaction was found to take place with several alcohols, which led us to a general reaction mechanism that is catalyzed synergistically by the photoexcited nanoparticle and the Lewis acidic HAuCl4. In the specific case of 2-butanol as the hole acceptor, we found a substantial difference between the product distributions of the light-driven reaction as compared to a thermal reaction. This finding represents an example of light-driven-control of catalytic selectivity. Finally, as presented in Chapter 4, the insights gained from the study described in Chapter 3 led me to a new, simple chemical process for low-temperature chlorination of methane in a non-corrosive aqueous environment. The kinetics and mechanism of this reaction were studied. Methane chlorination is at the heart of natural-gas upgradation, so this new finding represents an ideal culmination of my dissertation. An outlook and potential future directions are presented in Chapter 5.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-12-01","The student, Varun Mohan, accepted the attached license on 2020-12-01 at 18:31.","The student, Varun Mohan, submitted this Dissertation for approval on 2020-12-01 at 18:50.","This Dissertation was approved for publication on 2020-12-04 at 10:01.","DSpace SAF Submission Ingestion Package generated from Vireo submission #16022 on 2021-03-04 at 16:33:11","Made available in DSpace on 2021-03-05T21:47:26Z (GMT). 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