| 1. |
- Bora, Tanujjal, et al.
(författare)
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Modulation of defect-mediated energy transfer from ZnO nanoparticles for the photocatalytic degradation of bilirubin
- 2013
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Ingår i: Beilstein Journal of Nanotechnology. - : BEILSTEIN-INSTITUT. - 2190-4286. ; 4:1, s. 714-725
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, nanotechnology has gained significant interest for applications in the medical field. In this regard, a utilization of the ZnO nanoparticles for the efficient degradation of bilirubin (BR) through photocatalysis was explored. BR is a water insoluble byproduct of the heme catabolism that can cause jaundice when its excretion is impaired. The photocatalytic degradation of BR activated by ZnO nanoparticles through a non-radiative energy transfer pathway can be influenced by the surface defect-states (mainly the oxygen vacancies) of the catalyst nanoparticles. These were modulated by applying a simple annealing in an oxygen-rich atmosphere. The mechanism of the energy transfer process between the ZnO nanoparticles and the BR molecules adsorbed at the surface was studied by using steady-state and picosecond-resolved fluorescence spectroscopy. A correlation of photocatalytic degradation and time-correlated single photon counting studies revealed that the defect-engineered ZnO nanoparticles that were obtained through post-annealing treatments led to an efficient decomposition of BR molecules that was enabled by Forster resonance energy transfer.
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| 2. |
- Favereau, Ludovic, et al.
(författare)
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A Molecular Tetrad That Generates a High-Energy Charge-Separated State by Mimicking the Photosynthetic Z-Scheme
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:11, s. 3752-3760
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Tidskriftsartikel (refereegranskat)abstract
- The oxygenic photosynthesis of green plants, green algae, and cyanobacteria is the major provider of energy rich compounds in the biosphere. The so-called "Z-scheme" is at the heart of this "engine of life". Two photosystems (photo system I and II) work in series to build up a higher redox ability than each photosystem alone can provide, which is necessary to drive water oxidation into oxygen and NADP(+) reduction into NADPH with visible light. Here we show a mimic of the Z-scheme with a molecular tetrad. The "tetrad Bodipy-NDI-TAPD-Ru is composed of two different dyes-4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethy1-4-bora-3a,4a-diaza-s-indacene (Bodipy) and a Ru-II(bipyridine), (Ru) derivative-which are connected to a naphthalene diimide (NDI) electron acceptor and tetraalkylphenyldiamine (TAPD) playing the role of electron donor. A strong laser pulse excitation of visible light where the two dye molecules (Ru and Bodipy) absorb with equal probability leads to the cooperative formation of a highly energetic charge-separated state composed of an oxidized Bodipy and a reduced Ru. The latter state cannot be reached by one single photon absorption. The energy of the final charge-separated state (oxidized Bodipy/reduced Ru) in the tetrad lies higher than that in the reference dyads (Bodipy-NDI and TAPD-Ru), leading to the energy efficiency of the tetrad being 47% of the sum of the photon threshold energies. Its lifetime was increased by several orders of magnitude compared to that in the reference dyads Bodipy-NDI and TAPD-Ru, as it passes from about 3 ns in each dyad to 850 ns in the tetrad. The overall quantum yield formation of this extended charge-separated state is estimated to be 24%. Our proof-of-concept result demonstrates the capability to translate a crucial photosynthetic energy conversion principle into man-made molecular systems for solar fuel formation, to obtain products of higher energy content than those produced by a single photon absorption.
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| 3. |
- Favereau, Ludovic, et al.
(författare)
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Tris-bipyridine based dinuclear ruthenium(II)--osmium(III) complex dyads grafted onto TiO2 nanoparticles for mimicking the artificial photosynthetic Z-scheme
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:6, s. 4778-4786
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Tidskriftsartikel (refereegranskat)abstract
- The Z-Scheme function within molecular systems has been rarely reported for solar energy conversion although it offers the possibility to achieve higher efficiency than single photon absorber photosystems due to the use of a wider range of visible light. In this study, we synthesized and investigated the electrochemical and spectroscopic properties of two new dyads based on ruthenium and osmium tris-bipyridine complexes covalently linked via a butane bridge to explore their ability to realize the Z-scheme function once immobilized on TiO2. These dyads can be grafted onto a nanocrystalline TiO2 film via the osmium complex bearing two dicarboxylic acid bipyridine ligands, while the ruthenium complex contains either two unsubstituted bipyridine ancillary ligands (RuH-Os) or two (4,4'-bis-trifluoro-methyl-bipyridine) ancillary ligands (RuCF3-Os). Transient absorption spectroscopy studies of the Ru(II)-Os(III) dyads with femtosecond and nanosecond lasers were conducted both in solution and on TiO2. For both conditions, the photophysical studies revealed that the MLCT excited state of the ruthenium complex is strongly quenched and predominantly decays by energy transfer to the LMCT of the adjacent Os(III) complex, in spite of the high driving force for electron transfer. This unexpected result, which is in sharp contrast to previously reported Ru(II)-Os(III) dyads, precluded us to achieve the expected Z-scheme function. However, the above results may be a guide for designing new artificial molecular systems reproducing the complex function of a Z-scheme with molecular systems grafted onto a TiO2 mesoporous film.
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| 4. |
- Makhal, Abhinandan, et al.
(författare)
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Dynamics of light harvesting in ZnO nanoparticles
- 2010
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Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 21:26, s. 265703-1
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Tidskriftsartikel (refereegranskat)abstract
- We have explored light harvesting of the complex of ZnO nanoparticles with the biological probe Oxazine 1 in the near-infrared region using picosecond-time-resolved fluorescence decay studies. We have used ZnO nanoparticles and Oxazine 1 as a model donor and acceptor, respectively, to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle–dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO nanoparticles can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the nanoparticles (contributing to visible emission at λ≈550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorods has also been explored in this study and they were found to have much less efficiency (~40%) for energy transfer compared to the nanoparticles. The possibility of an electron transfer reaction has been ruled out from the picosecond-resolved fluorescence decay of the acceptor dye at the ZnO surface.
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| 5. |
- Sarkar, Soumik, et al.
(författare)
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Engineering FRET-based solar cells : Manipulation of energy and electron transfer processes in a light harvesting assembly
- 2014
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Ingår i: High-Efficiency Solar Cells. - Cham : American Chemical Society (ACS). ; , s. 267-318
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Bokkapitel (refereegranskat)abstract
- From the prevalent interest in the advancement of renewable energy sources, dye-sensitized solar cells (DSSCs) have emerged as one of the front running prospects due mainly to a constructive balance between cost and efficiency. In this chapter, we will review our works on the utility of using Fo¨rster resonance energy transfer (FRET) in the light harvesting dynamics of zinc oxide (ZnO)-based nanomaterials, which has recently shown promise for significant improvement in various aspects of photoelectrochemical cells. Firstly, we have used ZnO nanoparticles (NPs) and Oxazine 1 as model donor and acceptor, respectively, to investigate the key ultrafast process of FRET in the NP–dye system. The consequence of the energy transfer on the performance of a model ZnO NP-based DSSC has also been explored by using well-known Ruthenium-based sensitizers N719 attached to ZnO NPs offering as an intrinsic co-sensitizer. By using a picosecondresolved FRET technique, we have also demonstrated the role of the gold layer in promoting photoinduced charge transfer from ZnO–Au nanocomposite to a model contaminant methylene blue (MB). Due to the formation of the Schottky barrier at the ZnO–Au interface and the higher optical absorptions of the ZnO–Au photoelectrodes arising from the surface plasmon absorption of the Au NPs, enhanced power-conversion efficiency was achieved compared to bare ZnO-based DSSCs. Finally, potential co-sensitization of extrinsic sensitizer CdTe quantum dots (QDs) in ZnO nanorod (NR)-based DSSCs has been established where we have shown two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs to ZnO semiconductor via photoinduced electron transfer (PET) and (2) an indirect excitation of the sensitizing dye N719 molecules by funneling harvested light via FRET. Based on these advantages, the short-circuit current density and the photoconductivity of the QD-assembled DSSCs with distinct architectures are found to be much higher than DSSCs fabricated with N719 sensitizer only. As demonstrated, the multipath enhancement offered in this device architecture results in an increased and extended photo-response with respect to the individual materials employed. Further engineering of suitable donor acceptor pairs and optimization of charge separation in conjugated molecular blends has the potential to become a continuing avenue toward enhancing hybrid DSSC efficiencies.
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| 6. |
- Sarkar, Soumik, et al.
(författare)
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Nanoparticle-Sensitized Photodegradation of Bilirubin and Potential Therapeutic Application
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:17, s. 9608-9615
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Tidskriftsartikel (refereegranskat)abstract
- Bilirubin (BR) is a protective antioxidant; however, when its conjugation and excretion are impaired, as in neonatal and hereditary jaundice, BR accumulates and may cause severe neurotoxicity. Here, we report a novel mechanism for ZnO nanoparticle (NP)-sensitized BR degradation via defect-mediated nonradiative energy transfer pathway. Among different sizes and shapes, ZnO particles with diameter of 5 nm having very high concentration of defect states are found to be the most effective catalyst, which particularly follows a pseudofirst-order kinetics validating the Langmuir–Hinshelwood model of surface catalysis. The nontoxic wide band gap ZnO NPs essentially transmit defect-mediated visible optical radiation, which is not supposed to interfere with the conventional phototherapy process. Therefore, the recyclable ZnO nanocatalysts essentially invite an added advantage in potential therapeutic applications and/or in a flow-device that has been explored in the present study.
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| 7. |
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