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Identifier 000422011
Title Mesoporous assemblies from metal and metal Oxide nanoparticles for environmental applications
Alternative Title Μεσοπορώδη συσσωματώματα από νανοσωματίδια μετάλλου και οξειδίου μετάλλου για περιβαλλοντικές εφαρμογές
Author Βελεγράκη, Γεωργία
Thesis advisor Αρματάς, Γεράσιμος
Reviewer Τρικαλίτης. Παντελής
Λυκάκης, Ιωάννης
Κοπιδάκης, Γεώργιος
Κιοσέογλου, Γεώργιος
Βαμβακάκη, Μαρία
Μηλιός Κωνσταντίνος
Abstract During the last decades, the environment is ever-charged by toxic chemicals which usually are by-product of various industrial activities such as electroplating, leather tanning, paint and pigments, and are disposed uncontrollably to the environment. These by-products not only consist a threat to the environment lifecycle but also could have devastating effects to the human being. One of the prominent pollutants of groundwater is hexavalent chromium (Cr(VI)) that is a non-biodegradable contaminant of groundwater and shallow water wells and it is responsible for human carcinogen and mutagen according to the International Agency for Research on Cancer (IARC); thus, classifying it as a Group 1 carcinogen. Therefore, the effective and sustainable neutralization of Cr(VI)-bearing aqueous solutions is one of the utmost importance in terms of protecting the environment and human health. Apart from detoxification solutions, trace analysis such as part per million (ppm) level detection of toxic molecules, such as organic dyes, that may contaminate water is also of great concern. Detecting pollutants in low concentrations, however, pose a significant challenge. Surface-enhanced Raman scattering, commonly known as SERS, has become a powerful analytical technique that extends the range of Raman applications for detecting trace amounts of analytes through their vibrational signals. Assembling 3D nanoscale structures of plasmonic nanoparticles, such as copper (Cu), holds great promise for achieving enhanced optical and electronic properties. Additionally, graphite decorated Cu (Cu/G) nanoparticle assemblies can exhibit a large number of surface hot spots, while offer the possibility for synergetic effects to be achieved. This dissertation focuses on synthesis, structural characterization and environmental applications of ordered mesoporous networks of metal and metal-oxide nanoparticles. Specifically, it is studied the synthesis of high-surface-area mesoporous assemblies of CoO nanoparticles (CoO MNAs) and their potential application in the reductive detoxification of aqueous hexavalent chromium solutions, under UV and visible light irradiation. These materials indicate excellent photocatalytic performance, which is presumably a result of the combined effect of accessible pore volume, appropriate band edge positions and specific reactivity of the crystal phase. Moreover, in an effort to further improve the photocatalytic activity and chemical stability of CoO assemblies, we suggest the synthesis of high-surface-area mesoporous networks consisting of Ni and Cu-implanted cubic CoO (Co1-xNixO and Co1-xCuxO MNAs) nanoparticles as promising catalysts for detoxification of Cr(VI) aqueous solutions. Mechanistic studies with X-ray photoelectron, UV–vis/near-IR optical absorption, fluorescence and electrochemical impedance spectroscopy and theoretical (DFT) calculations indicate that the performance enhancement of these catalysts arises from the high charge transfer kinetics and oxidation efficiency of surface-reaching holes. By tuning electronic structure and chemical composition, the Co1-xNixO mesoporous catalyst at 2 wt% Ni content impart outstanding photocatalytic Cr(VI) reduction and water oxidation activity, corresponding to an apparent quantum yield (QY) of 1.5% at  = 375 nm irradiation light. The remarkable activity and durability of the CoO-based MNAs implies the great possibility of implementing these new catalysts into a realistic Cr(VI) detoxification of contaminated water. Additional subject of the present research is the fabrication of highly porous Cu nanoparticle assemblies decorated with graphite layers (denoted as Cu/G NPAs), as well as their use in SERS detection. The large surface area of the porous framework of assembled Cu/G NPAs exposes essentially a number of plasmonic sites to incoming molecules, resulting in a significant SERS enhancement for chemical analyte detection. Moreover, the network structure of these materials shows a similar SERS activity across different spot areas with high reproducibility. These findings are very promising and suggest that Cu/G nanoparticle assemblies are highly efficient, cost-effective, and stable substrates for SERS detection.
Language English
Subject Chromium reduction
Cobalt oxide
Copper oxide
Mesoporous materials
Surface Enhancement Raman Spectroscopy
Αναγωγή χρωμίου
Ενισχυμένη φασματοσκοπία Raman
Μεσοπορώδη υλικά
Οξείδιο κοβαλτίου
Οξείδιο χαλκού
Issue date 2019-03-27
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
  Type of Work
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