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Dionysios D. Dionysiou

Bio: Dionysios D. Dionysiou is an academic researcher from University of Cincinnati. The author has contributed to research in topics: Photocatalysis & Catalysis. The author has an hindex of 116, co-authored 675 publications receiving 48449 citations. Previous affiliations of Dionysios D. Dionysiou include California State University, Long Beach & Massachusetts Institute of Technology.


Papers
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TL;DR: In this paper, the development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed.
Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

3,305 citations

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TL;DR: Nine transition metals were tested for the activation of three oxidants and the generation of inorganic radical species such as sulfate, peroxymonosulfate, and hydroxyl radicals to postulate the rate-determining step of the redox reactions taking place when a metal is coupled with an oxidant in aqueous solution.
Abstract: Nine transition metals were tested for the activation of three oxidants and the generation of inorganic radical species such as sulfate, peroxymonosulfate, and hydroxyl radicals. From the 27 combinations, 14 M/Ox couples demonstrated significant reactivity toward transforming a model organic substrate such as 2,4-dichlorophenol and are further discussed here. It was found that Co(II) and Ru(III) are the best metal catalysts for the activation of peroxymonosulfate. As expected on the basis of the Fenton reagent, Fe(III) and Fe(II) were the most efficient transition metals for the activation of hydrogen peroxide. Finally, Ag(I) showed the best results toward activating persulfate. Quenching studies with specific alcohols (tert-butyl alcohol and ethanol) were also performed to identify the primary radical species formed from the reactive M/Ox interactions. The determination of these transient species allowed us to postulate the rate-determining step of the redox reactions taking place when a metal is coupled with an oxidant in aqueous solution. It was found that when Co(II), Ru(III), and Fe(II) interact with peroxymonosulfate, freely diffusible sulfate radicals are the primary species formed. The same was proven for the interaction of Ag(I) with persulfate, but in this case caged or bound to the metal sulfate radicals might be formed as well. The conjunction of Ce(III), Mn(II), and Ni(II) with peroxymonosulfate showed also to generate caged or bound to the metal sulfate radicals. A combination of sulfate and hydroxyl radicals was formed from the conjunction of V(III) with peroxymonosulfate and from Fe(II) with persulfate. Finally, the conjunction of Fe(III), Fe(II), and Ru(III) with hydrogen peroxide led primarily to the generation of hydroxyl radicals. It is also suggested here that the redox behavior of a particular metal in solution cannot be predicted based exclusively on its size and charge. Additional phenomena such as metal hydrolysis as well as complexation with other counterions present in solution might affect the thermodynamics of the overall process and are further discussed here.

2,453 citations

Journal ArticleDOI
TL;DR: The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.
Abstract: A highly efficient advanced oxidation process for the destruction of organic contaminants in water is reported. The technology is based on the cobalt-mediated decomposition of peroxymonosulfate that leads to the formation of very strong oxidizing species (sulfate radicals) in the aqueous phase. The system is a modification of the Fenton Reagent, since an oxidant is coupled with a transition metal in a similar manner. Sulfate radicals were identified with quenching studies using specific alcohols. The study was primarily focused on comparing the cobalt/peroxymonosulfate (Co/PMS) reagent with the traditional Fenton Reagent [Fe(II)/H2O2] in the dark, at the pH range 2.0-9.0 with and without the presence of buffers such as phosphate and carbonate. Three model contaminants that show diversity in structure were tested: 2,4-dichlorophenol, atrazine, and naphthalene. Cobalt/peroxymonosulfate was consistently proven to be more efficient than the Fenton Reagent for the degradation of 2,4-dichlorophenol and atrazine, at all the conditions tested. At high pH values, where the efficiency of the Fenton Reagent was diminished, the reactivity of the Co/PMS system was sustained at high values. When naphthalene was treated with the two oxidizing systems in comparison, the Fenton Reagent demonstrated higher degradation efficiencies than cobalt/peroxymonosulfate at acidic pH, but, at higher pH (neutral), the latter was proven much more effective. The extent of mineralization, as total organic carbon removed,was also monitored, and again the Co/PMS reagent demonstrated higher efficiencies than the Fenton Reagent. Cobalt showed true catalytic activity in the overall process, since extremely low concentrations (in the range of microg/L) were sufficient for the decomposition of the oxidant and thus the radical generation. The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.

1,390 citations

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TL;DR: An overview of the recent advances of ZVI and progress obtained during the groundwater remediation and wastewater treatment utilizing ZVI (including nanoscale zero-valent iron (nZVI)) for the removal of contaminants.

1,273 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of various methods for analysis of persulfate decontamination and their analysis is often prone for interference by other matrix components and hampered by the low stability of peroxydisulfate and peroxymonosulfate in aqueous systems.

1,197 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

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TL;DR: It is anticipated that this review can stimulate a new research doorway to facilitate the next generation of g-C3N4-based photocatalysts with ameliorated performances by harnessing the outstanding structural, electronic, and optical properties for the development of a sustainable future without environmental detriment.
Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

5,054 citations

Journal ArticleDOI
TL;DR: For the first time, a multi-variables optimization approach is described to determine the optimum operation parameters so as to enhance process performance and photooxidation efficiency in the photocatalytic water treatment process.

4,293 citations