| 1. |
- Abdelhamid, Hani Nasser, et al.
(author)
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A Fast and Scalable Approach for Synthesis of Hierarchical Porous Zeolitic Imidazolate Frameworks and One-Pot Encapsulation of Target Molecules
- 2017
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 56:15, s. 9139-9146
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Journal article (peer-reviewed)abstract
- A trimethylamine (TEA)-assisted synthesis approach that combines the preparation of hierarchical porous zeolitic imidazolate framework ZIF-8 nanoparticles and one-pot encapsulation of target molecules is presented. Two dye molecules, rhodamine B (RhB) and methylene blue (MB), and one protein (bovine serum albumin, BSA) were tested as the target molecules. The addition of TEA into the solution of zinc nitrate promoted the formation of ZnO nanocrystals, which rapidly transformed to ZIF-8 nanoparticles after the addition of the linker 2-methylimidazole (Hmim). Hierarchical porous dye@ZIF-8 nanoparticles with high crystallinity, large BET surface areas (1300–2500 m2/g), and large pore volumes (0.5–1.0 cm3/g) could be synthesized. The synthesis procedure was fast (down to 2 min) and scalable. The Hmim/Zn ratio could be greatly reduced (down to 2:1) compared to previously reported ones. The surface areas, and the mesopore size, structure, and density could be modified by changing the TEA or dye concentrations, or by postsynthetic treatment using reflux in methanol. This synthesis and one-pot encapsulation approach is simple and can be readily scaled up. The photophysical properties such as lifetime and photostability of the dyes could be tuned via encapsulation. The lifetimes of the encapsulated dyes were increased by 3–27-fold for RhB@ZIF-8 and by 20-fold for MB@ZIF-8, compared to those of the corresponding free dyes. The synthesis approach is general, which was successfully applied for encapsulation of protein BSA. It could also be extended for the synthesis of hierarchical porous cobalt-based ZIF (dye@ZIF-67).
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| 2. |
- Abdelhamid, Hani Nasser, et al.
(author)
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Luminescence properties of a family of lanthanide metal-organic frameworks
- 2019
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In: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 279, s. 400-406
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Journal article (peer-reviewed)abstract
- Two isostructural series of lanthanide metal-organic frameworks denoted as SUMOF-7II (Ln) and SUMOF-7IIB (Ln) (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) were synthesized using4,4',4 ''-(pyridine-2,4,6-triyl)tris(benzoic acid) (H(3)L2) and a mixture of H(3)L2 and 4,4',4 ''-(benzene-1,3,5-triyl)tris(benzoic acid) (H3BTB) as linkers, respectively. Both series were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal analysis (TGA), and photoluminescence spectroscopy. Photoluminescence measurements show that Eu-MOFs demonstrate a red emission while Pr- and Nd-MOFs display an emission in the near-infrared (NIR) range. On the other hand, La-, Ce-, Sm- and Gd-MOFs exhibit only a ligand-centered emission. The average luminescence lifetimes in the SUMOF-7IIB series are 1.3-1.4-fold longer than the corresponding ones in the SUMOF-7II series. SUMOF-7IIs show a good photo- and thermal stability. Altogether, the properties of SUMOF-7II and SUMOF-7IIB render them promising materials for applications including sensing, biosensing, and telecommunications.
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| 3. |
- Abdelhamid, Hani Nasser, et al.
(author)
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Towards implementing hierarchical porous zeolitic imidazolate frameworks in dye-sensitized solar cells
- 2019
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In: Royal Society Open Science. - : Royal Society Publishing. - 2054-5703. ; 6:7
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Journal article (peer-reviewed)abstract
- A one-pot method for encapsulation of dye, which can be applied for dye-sensitized solar cells (DSSCs), and synthesis of hierarchical porous zeolitic imidazolate frameworks (ZIF-8), is reported. The size of the encapsulated dye tunes the mesoporosity and surface area of ZIF-8. The mesopore size, Langmuir surface area and pore volume are 15 nm, 960-1500 m(2). g(-1) and 0.36-0.61 cm(3). g(-1), respectively. After encapsulation into ZIF-8, the dyes show longer emission lifetimes (greater than 4-8-fold) as compared to the corresponding non-encapsulated dyes, due to suppression of aggregation, and torsional motions.
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| 4. |
- Abdellah, Mohamed, et al.
(author)
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Time-Resolved IR Spectroscopy Reveals a. Mechanism with TiO2 as a Reversible Electron Acceptor in a TiO2-Re Catalyst System for CO2 Photoreduction
- 2017
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In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 139:3, s. 1226-1232
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Journal article (peer-reviewed)abstract
- Attaching the phosphonated molecular catalyst [(ReBr)-Br-I(bpy)-(CO)(3)](0) to the wide-bandgap semiconductor TiO2 strongly enhances the rate of visible-light-driven reduction of CO2 to CO in dimethylformamide with triethanolamine (TEOA) as sacrificial electron donor. Herein, we show by transient mid-IR spectroscopy that the mechanism of catalyst photoreduction is initiated by ultrafast electron injection into TiO2, followed by rapid (ps-ns) and sequential two-electron oxidation of TEOA that is coordinated to the Re center. The injected electrons can be stored in the conduction band of TiO2 on an ms-s time scale, and we propose that they lead to further reduction of the Re catalyst and completion of the catalytic cycle. Thus, the excited Re catalyst gives away one electron and would eventually get three electrons back. The function of an electron reservoir would represent a role for TiO2 in photocatalytic CO2 reduction that has previously not been considered. We propose that the increase in photocatalytic activity upon heterogenization of the catalyst to TiO2 is due to the slow charge recombination and the high oxidative power of the Re-II species after electron injection as compared to the excited MLCT state of the unbound Re catalyst or when immobilized on ZrO2, which results in a more efficient reaction with TEOA.
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| 5. |
- Bi, Dongqin, et al.
(author)
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Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells
- 2015
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In: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:5, s. 589-594
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Journal article (peer-reviewed)abstract
- CH3NH3PbI3 perovskite solar cells have rapidly risen to the forefront of emerging photovoltaic technologies. A solution-based, two-step method was reported to enhance the reproducibility of these solar cells. In this method, first a coating of PbI2 is applied by spin-coating onto a TiO2-coated substrate, followed by a dip in a methylammonium iodide solution, leading to conversion to CH3NH3PbI3. The concentration of PbI2 in the spin-coating solution is a very important factor that affects the infiltration of the perovskite and the amount deposited. The best solar cell performance of 13.9% was obtained by devices prepared using 1.0 M of PbI2 in dimethylformamide. These devices also had the longest electron lifetime and shortest carrier transport time, yielding lowest recombination losses. Rapid quenching of the perovskite emission is found in device-like structures, suggesting reasonably good efficient carrier extraction at the TiO2 interface and quantitative extraction at the spiro-OMeTAD interface.
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| 6. |
- El-Zohry, Ahmed, et al.
(author)
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Gigantic Relevance of Twisted Intramolecular Charge Transfer for Organic Dyes Used in Solar Cells
- 2018
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:42, s. 23998-24003
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Journal article (peer-reviewed)abstract
- Within this work, we emphasis on the importance of twisted intramolecular charge transfer (TICT) process in organic dyes based on triphenyl amine moiety to achieve high performance in dye-sensitized solar cells. Through the comparison between two recent made dyes, Ll and L1Fc, on different semiconductors (TiO2, and ZrO2), we could spectrally and dynamically detect for the first time the formation of TICT state for Ll on ZrO2 after localized charge transfer (LCT) state population, and an electron injection process from TICT state on TiO2. However, for the excited L1Fc dye, the ultrafast electron transfer from ferrocene (Fc) moiety to the Ll unit quenched the formation of TICT state in L1Fc on semiconductors, leading instead to an electron injection process from the LCT state. The electron injection from TICT state in Ll associated with structural rearrangements on TiO2 leads to slow recombination process and an efficiency improvement of about 325%, compared to solar cells based on L1Fc dye, in which TICT state formation is hindered. Similar electron dynamics are obtained for Ll on TiO2 upon physically hindering the TICT process by adding polymer matrix. The presence of TICT state for Ll dye and similar triphenyl amine dyes aids to reconstruct the kinetic profile for these dyes on semiconductor surfaces, and to redesign organic dyes accordingly for higher efficiency in solar cells.
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| 7. |
- El-Zohry, Ahmed M.
(author)
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Exploring Organic Dyes for Grätzel Cells Using Time-Resolved Spectroscopy
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Grätzel cells or Dye-Sensitized Solar Cells (DSSCs) are considered one of the most promising methods to convert the sun's energy into electricity due to their low cost and simple technology of production. The Grätzel cell is based on a photosensitizer adsorbed on a low band gap semiconductor. The photosensitizer can be a metal complex or an organic dye. Organic dyes can be produced on a large scale resulting in cheaper dyes than complexes based on rare elements. However, the performance of Grätzel cells based on metal-free, organic dyes is not high enough yet. The dye's performance depends primarily on the electron dynamics. The electron dynamics in Grätzel cells includes electron injection, recombination, and regeneration. Different deactivation processes affect the electron dynamics and the cells’ performance.In this thesis, the electron dynamics was explored by various time-resolved spectroscopic techniques, namely time-correlated single photon counting, streak camera, and femtosecond transient absorption. Using these techniques, new deactivation processes for organic dyes used in DSSCs were uncovered. These processes include photoisomerization, and quenching through complexation with the electrolyte. These deactivation processes affect the performance of organic dyes in Grätzel cells, and should be avoided. For instance, the photoisomerization can compete with the electron injection and produce isomers with unknown performance. Photoisomerization as a general phenomenon in DSSC dyes has not been shown before, but is shown to occur in several organic dyes, among them D149, D102, L0 and L0Br. In addition, D149 forms ground state complexes with the standard iodide/triiodide electrolyte, which directly affect the electron dynamics on TiO2. Also, new dyes were designed with the aim of using ferrocene(s) as intramolecular regenerators, and their dynamics was studied by transient absorption.This thesis provides deeper insights into some deactivation processes of organic dyes used in DSSCs. New rules for the design of organic dyes, based on these insights, can further improve the efficiency of DSSCs.
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| 8. |
- El-Zohry, Ahmed M., et al.
(author)
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Ferrocene as a rapid charge regenerator in dye-sensitized solar cells
- 2016
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In: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 132, s. 360-368
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Journal article (peer-reviewed)abstract
- Using the reductive power of the ferrocene moiety (Fc), an ultrafast regeneration step via a covalent attachment of a Fc moiety to an organic triphenylamine-based dye (L1) when adsorbed on TiO2 is highlighted. Two modified dyes with one and two Fc moieties attached (L1Fc, and L1Fc2), respectively, were synthesized by addition to the L1 dye. These dyes have been studied spectroscopically using ultrafast transient absorption spectroscopy in the visible and the infrared (IR) regions. In acetonitrile, the results show an ultrafast excited state quenching of the modified dyes due to an expected electron transfer process from the Fc(s) to L1. Adsorbed onto TiO2, an electron transfer process is also detected from Fc to the oxidized dye (L1(+)). Despite the occurrence of an ultrafast regeneration step, the solar cell performance does not improve by the attachment of Fc(s) to the dye L1. Transient absorption measurements in the IR region revealed a fast electron recombination process to the Fc(+) moiety on an average time scale of ca. 300 ps, outcompeting the >12 ns process to L1(+). The reasons for the observed considerably faster recombination rate to Fc(+) than to L1(+) are discussed in detail. This study provides deep spectroscopic insights for such organic dyes utilized to afford ultrafast regeneration step without showing high performance in photovoltaic devices. In addition, this study will improve our understandings for the triangular relationship between the molecular design, electron kinetics, and the performance in photovoltaic devices. (C) 2016 Elsevier Ltd. All rights reserved.
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| 9. |
- El-Zohry, Ahmed M.
(author)
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The origin of slow electron injection rates for indoline dyes used in dye-sensitized solar cells
- 2019
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In: Dyes and pigments. - : ELSEVIER SCI LTD. - 0143-7208 .- 1873-3743. ; 160, s. 671-674
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Journal article (peer-reviewed)abstract
- This work highlights the direct impact of selecting acceptor moiety for organic dyes on the electron dynamics at faster time scales, in which overlooked photo-physical properties are present on semiconductor surfaces with specific acceptor moieties. Four top-performing dyes of indoline family (D131, D102, D149, and D205) sharing the same donor moiety, but through different acceptor groups, were selected and compared with respect of electron injection process, using ultrafast transient-infrared probe. The presence of rhodanine moiety at the acceptor unit in D102, D149 and D205, shows an additional slow electron injection process, of picosecond time-scale, on the low band-gap semiconductor, TiO2. This slow process is expected to be present due to a twisted intramolecular charge transfer/isomerized state of the excited dye prior to electron injection. This isomerized state reduces as well the detrimental electron recombination process rates, and results of high performance in solar cells based on these rhodanine dyes. Replacing the rhodanine moiety by a cyano-acrylic group in D131 dye shows faster electron injection and recombination processes, due to the lower dipole moment present in the excited state, hindering the formation of an isomerized state. These findings will aid to enhance the organic dyes design used in dye sensitized solar cells, in which designed photo-physical processes on semiconductor surfaces can increase the efficiencies of the solar cells.
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| 10. |
- El-Zohry, Ahmed M., et al.
(author)
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Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes : Experimental and Theoretical Studies
- 2015
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:5, s. 2249-2259
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Journal article (peer-reviewed)abstract
- Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twisting process is assumed to occur as a deactivation process for the excited molecule. This is confirmed by multireference second-order perturbation theory (CASSCF/CASPT2) calculations of the lowest-lying excited state, in which it is shown that torsion of the ethylene bond to 96° and pyramidalization to ca. 100° lead to a conical intersection with the ground state. Embedded in a plastic matrix, where double bond rotation is hindered, the decay is slowed down to nanoseconds. We have also investigated the dyes D102, D131, and D149, possessing the same indoline donor unit, by femtosecond transient absorption and found a similar decay component. The ca. 20 ps deactivation channel in D-family dyes is thus attributed to a twisting process of the donor unit. The fluorescence quantum yields of this unit and D149 were measured, and from comparison, the competition of the discovered twisting deactivation channel to the radiative decay of the excited indoline dyes could be confirmed. Blocking this deactivation channel is expected to further increase efficiency for the indoline dyes.
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| 11. |
- Gao, Jiajia, et al.
(author)
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Light-Induced Interfacial Dynamics Dramatically Improve the Photocurrent in Dye-Sensitized Solar Cells : An Electrolyte Effect
- 2018
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 10:31, s. 26241-26247
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Journal article (peer-reviewed)abstract
- A significant increase in the photocurrent generation during light soaking for solar cells sensitized by the triphenylamine-based D-pi-A organic dyes (PD2 and LEG1) and mediated by cobalt bipyridine redox complexes has been observed and investigated. The crucial role of the electrolyte has been identified in the performance improvement. Control experiments based on a pretreatment strategy reveals TBP as the origin. The increase in the current and IPCE has been interpreted by the interfacial charge-transfer kinetics studies. A slow component in the injection kinetics was exposed for this system. This change explains the increase in the electron lifetime and collection efficiency. Photoelectron spectroscopic measurements show energy shifts at the dye/TiO2 interface, leading us to formulate a hypothesis with respect to an electrolyte induced dye reorganization at the surface.
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| 12. |
- Pavliuk, Mariia V., et al.
(author)
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Magnetic Manipulation of Spontaneous Emission from Inorganic CsPbBr3 Perovskites Nanocrystals
- 2016
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In: ADVANCED OPTICAL MATERIALS. - : Wiley. - 2195-1071. ; 4:12, s. 2004-2008
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Journal article (peer-reviewed)abstract
- Metal halide perovskites have shown great potential for both light-absorbing and light-emitting devices. It is demonstrated that the presence of a low-magnetic field decreases dramatically the photoluminescence of CsPbBr3. This is found to be due to a decrease in charge separated state lifetime. The effect is fully reversible, and can be exploited for simple and remote modulation of the output of light-emitting devices.
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