| 1. |
- Elsayed, Mohamed Hammad, et al.
(författare)
-
Overcoming small-bandgap charge recombination in visible and NIR-light-driven hydrogen evolution by engineering the polymer photocatalyst structure
- 2024
-
Ingår i: Nature Communications. - 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- Designing an organic polymer photocatalyst for efficient hydrogen evolution with visible and near-infrared (NIR) light activity is still a major challenge. Unlike the common behavior of gradually increasing the charge recombination while shrinking the bandgap, we present here a series of polymer nanoparticles (Pdots) based on ITIC and BTIC units with different π-linkers between the acceptor-donor-acceptor (A-D-A) repeated moieties of the polymer. These polymers act as an efficient single polymer photocatalyst for H2 evolution under both visible and NIR light, without combining or hybridizing with other materials. Importantly, the difluorothiophene (ThF) π-linker facilitates the charge transfer between acceptors of different repeated moieties (A-D-A-(π-Linker)-A-D-A), leading to the enhancement of charge separation between D and A. As a result, the PITIC-ThF Pdots exhibit superior hydrogen evolution rates of 279 µmol/h and 20.5 µmol/h with visible (>420 nm) and NIR (>780 nm) light irradiation, respectively. Furthermore, PITIC-ThF Pdots exhibit a promising apparent quantum yield (AQY) at 700 nm (4.76%).
|
|
| 2. |
- Jlassi, Khouloud, et al.
(författare)
-
Highly sensitive humidity sensor based on cadmium selenide quantum dots-polymer composites : synthesis, characterization, and effect of UV/ozone treatment
- 2023
-
Ingår i: Journal of Materials Science: Materials in Electronics. - 0957-4522. ; 34:21
-
Tidskriftsartikel (refereegranskat)abstract
- This work describes the rational design of thin film-based cadmium selenide quantum dots (CdSe) mixed with conductive polyvinylidene fluoride (PVDF), inducing PVDF-CdSe composite for potential resistive humidity-sensing applications. The effect of UV/ozone treatment on surface hydrophilicity and sensing properties was investigated. AFM has been performed to examine the prepared films' texture, distribution over the surface, and size. Overall, the hydrophilicity of the developed films increases with UV radiation exposure time, leading to enhanced water vapor absorption without deforming the film surface. The sensor's sensitivity is improved with increasing UV radiation exposure. The electrical response of the PVDF-CdSe humidity sensors after 30 min of UV/ozone treatment reveals that at higher humidity levels (i.e., > 80% RH), the sensors exhibit an irregular response. However, at 20 min, treatment increases sensitivity and a linear change in impedance response concerning humidity level change compared to other samples. The hysteresis response was divided into two regions: the lower region, between 30 and 60% RH—where the maximum hysteresis loss was calculated to be 3%. While the higher area between 60 and 90% RH, where the maximum estimated hysteresis loss of the PVDF-CdSe sensor is around 14%, the UV/ozone treatment of the PVDF-CdSe nanocomposite film was found to enhance the sensing film's hydrophilicity without deforming the surface of the as-prepared PVDF-CdSe as well as the UV-treated films validates a potential for novel humidity sensors.
|
|
| 3. |
- Elsayed, Mohamed Hammad, et al.
(författare)
-
Hydrophobic and Hydrophilic Conjugated Polymer Dots as Binary Photocatalysts for Enhanced Visible-Light-Driven Hydrogen Evolution through Forster Resonance Energy Transfer
- 2021
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:47, s. 56554-56565
-
Tidskriftsartikel (refereegranskat)abstract
- Organic semiconducting polymers exhibited promising photocatalytic behavior for hydrogen (H-2) evolution, especially when prepared in the form of polymer dots (Pdots). However, the Pdot structures were formed using common nonconjugated amphiphilic polymers, which have a negative effect on charge transfer between photocatalysts and reactants and are unable to participate in the photocatalytic reaction. This study presents a new strategy for constructing binary Pdot photocatalysts by replacing the nonconjugated amphiphilic polymer typically employed in the preparation of polymer nanoparticles (Pdots) with a low-molecular-weight conjugated polyelectrolyte. The as-prepared polyelectrolyte/hydrophobic polymer-based binary Pdots truly enhance the electron transfer between the Pt cocatalyst and the polymer photocatalyst with good water dispersibility. Moreover, unlike the nonconjugated amphiphilic polymer, the photophysics and mechanism of this photocatalytic system through time-correlated single-photon counting (TCSPC) and transient absorption (TA) measurements confirmed the Forster resonance energy transfer (FRET) between the polyelectrolyte as a donor and the hydrophobic polymer as an acceptor. As a result, the designated binary Pdot photocatalysts significantly enhanced the hydrogen evolution rate (HER) of 43 900 mu mol g(-1) h(-1) (63.5 mu mol h(-1), at 420 nm) for PTTPA/PFTBTA Pdots under visible-light irradiation.
|
|
| 4. |
- Elsayed, Mohamed Hammad, et al.
(författare)
-
Visible-light-driven hydrogen evolution using nitrogen-doped carbon quantum dot-implanted polymer dots as metal-free photocatalysts
- 2021
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 283
-
Tidskriftsartikel (refereegranskat)abstract
- Given the photocatalytic properties of semiconducting polymers and carbon quantum dots (CQDs), we report a new structure for a metal-free photocatalytic system with a promising efficiency for hydrogen production through the combination of an organic semiconducting polymer (PFTBTA) and N-doped carbon quantum dots (NCQDs) covered by PS-PEGCOOH to produce heterostructured photocatalysts in the form of polymer dots (Pdots). This design could provide strong interactions between the two materials owing to the space confinement effect in nanometer-sized Pdots. Small particle size NCQDs are easy to insert inside the Pdot, which leads to an increase in the stability of the Pdot structure and enhances the hydrogen evolution rate by approximately 5-fold over that of pure PFTBTA Pdots. The photophysics and the mechanism behind the catalytic activity of our design are investigated by transient absorption measurement, demonstrating the role of NCQDs to enhance the charge separation and the photocatalytic efficiency of the PFTBTA Pdot.
|
|
| 5. |
- Kamel, Mohamed, et al.
(författare)
-
Synthesis, Optical, Magnetic and Thermodynamic Properties of Rocksalt Li1.3Nb0.3Mn0.4O2 Cathode Material for Li-Ion Batteries
- 2021
-
Ingår i: Crystals. - : MDPI. - 2073-4352. ; 11:7
-
Tidskriftsartikel (refereegranskat)abstract
- Since the discovery of the reversible intercalation of lithium-ion materials associated with promising electrochemical properties, lithium-containing materials have attracted attention in the research and development of effective cathode materials for lithium-ion batteries. Despite various studies on synthesis, and electrochemical properties of lithium-based materials, fairly little fundamental optical and thermodynamic studies are available in the literature. Here, we report on the structure, optical, magnetic, and thermodynamic properties of Li-excess disordered rocksalt, Li1.3Nb0.3Mn0.4O2 (LNMO) which was comprehensively studied using powder X-ray diffraction, transient absorption spectroscopy, magnetic susceptibility, and low-temperature heat capacity measurements. Charge carrier dynamics and electron-phonon coupling in LNMO were studied using ultra-fast laser spectroscopy. Magnetic susceptibility and specific heat data are consistent with the onset of long-range antiferromagnetic order at the Neel temperatures of 6.5 (1.5) K. The effective magnetic moment of LNMO is found to be 3.60 mu B. The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows negative values of the Weiss temperature 52 K (3), confirming the strong AFM interactions.
|
|
| 6. |
- Lin, Wei Cheng, et al.
(författare)
-
Effect of energy bandgap and sacrificial agents of cyclopentadithiophene-based polymers for enhanced photocatalytic hydrogen evolution
- 2021
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 298
-
Tidskriftsartikel (refereegranskat)abstract
- A library of donor-acceptor system consisting of cyclopentadithiophene-based polymer photocatalysts have been designed and synthesized. Among all photocatalysts, the active PCPDTBSO achieved hydrogen evolution rates of 24.6 mmol h–1 g–1 with apparent quantum yields of 8.7 % at 500 nm. More importantly, combined the results of photocatalytic efficiency, apparent quantum yield, the time-resolved fluorescence decay spectra, the steady-state photoluminescence spectra, and the transient absorption spectroscopy, and the oxidation potentials of sacrificial donors and protons reduction potentials in different pH values, we confirmed the concept that ascorbic acid is a suitable sacrificial donor for narrow bandgap polymers and triethylamine is a suitable sacrificial donor for wide bandgap polymers owing to the existence of the optimal thermodynamic driving force. We believed this study would be advantageous for the selection of photocatalysts and sacrificial donors for hydrogen production.
|
|
| 7. |
- Taibi, Mohamed, et al.
(författare)
-
Phytochemical characterization and multifaceted bioactivity assessment of essential oil from Ptychotis verticillata Duby: Anti-diabetic, anti-tyrosinase, and anti-inflammatory activity
- 2024
-
Ingår i: Heliyon. - : CELL PRESS. - 2405-8440. ; 10:8
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to explore the pharmacological properties of the essential oil derived from Ptychotis verticillata Duby (PVEO), a medicinal plant native to Morocco, focusing on its antidiabetic, anti-tyrosinase, and anti-inflammatory effects. Additionally, the study aims to characterize the phytochemical composition of PVEO and evaluate its potential as a natural therapeutic alternative for various health conditions. To achieve this, phytochemical analysis was conducted using gas chromatography-mass spectrometry (GC-MS). Furthermore, in vitro assessments were conducted to investigate PVEO's antidiabetic activity by inhibiting alpha-amylase, xanthine oxidase, and alpha-glucosidase. Tests were also undertaken to evaluate the anti-inflammatory effect of PVEO on RAW 264.7 cells stimulated by lipopolysaccharide (LPS), as well as its efficacy as an antityrosinase agent and its lipoxygenase inhibition activity. The results of the phytochemical analysis revealed that PVEO is rich in terpene compounds, with percentages of 40.35 % gamma-terpinene, 22.40 % carvacrol, and 19.77 % beta-cymene. Moreover, in vitro evaluations demonstrated that PVEO exhibits significant inhibitory activity against alpha-amylase, xanthine oxidase, and alpha-glucosidase, indicating promising antidiabetic, and anti-gout potential. Furthermore, PVEO showed significant anti-tyrosinase activity, with an IC50 of 27.39 +/- 0.44 mu g/mL, and remarkable lipoxygenase inhibition (87.33 +/- 2.6 %), suggesting its candidacy for dermatoprotection. Additionally, PVEO displayed a dose-dependent capacity to attenuate the production of NO and PGE2, two inflammatory mediators implicated in various pathologies, without compromising cellular viability. The findings of this study provide a solid foundation for future research on natural therapies and the development of new drugs, highlighting the therapeutic potential of PVEO in the treatment of gout, diabetes, pigmentation disorders, and inflammation.
|
|
| 8. |
- Zheng, Kaibo, et al.
(författare)
-
Fast Monolayer Adsorption and Slow Energy Transfer in CdSe Quantum Dot Sensitized ZnO Nanowires
- 2013
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society. - 1089-5639 .- 1520-5215. ; 117:29, s. 5919-5925
-
Tidskriftsartikel (refereegranskat)abstract
- A method for CdSe quantum dot (QD) sensitization of ZnO nanowires (NW) with fast adsorption rate is applied. Photoinduced excited state dynamics of the quantum dots in the case of more than monolayer coverage of the nanowires is studied. Transient absorption kinetics reveals an excitation depopulation process of indirectly attached quantum dots with a lifetime of similar to 4 ns. Photoluminescence and incident photon-to-electron conversion efficiency show that this process consists of both radiative e-h recombination and nonradiative excitation-to-charge conversion. We argue that the latter occurs via interdot energy transfer from the indirectly attached QDs to the dots with direct contact to the nanowires. From the latter, fast electron injection into ZnO occurs. The energy transfer time constant is found to be around 5 ns.
|
|
| 9. |
- Abdellah, Mohamed, et al.
(författare)
-
Competitive Hole Transfer from CdSe Quantum Dots to Thiol Ligands in CdSe-Cobaloxime Sensitized NiO Films Used as Photocathodes for H-2 Evolution
- 2017
-
Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 2:11, s. 2576-2580
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum dot (QD) sensitized NiO photocathodes rely on efficient photoinduced hole injection into the NiO valence band. A system of a mesoporous NiO film co-sensitized with CdSe QDs and a molecular proton reduction catalyst was studied. While successful electron transfer from the excited QDs to the catalyst is observed, most of the photogenerated holes are instead quenched very rapidly (ps) by hole trapping at the surface thiols of the capping agent used as linker molecules. We confirmed our conclusion by first using a thiol free capping agent and second varying the thiol concentration on the QD's surface. The later resulted in faster hole trapping as the thiol concentration increased. We suggest that this hole trapping by the linker limits the H-2 yield for this photocathode in a device.
|
|
| 10. |
- Abdellah, Mohamed, et al.
(författare)
-
Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1−xS1−y quantum dots
- 2017
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 9:34, s. 12503-12508
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrafast fluorescence spectroscopy was used to investigate the hole injection in CdxSeyZn1-xS1-y gradient core-shell quantum dot (CSQD) sensitized p-type NiO photocathodes. A series of CSQDs with a wide range of shell thicknesses was studied. Complementary photoelectrochemical cell measurements were carried out to confirm that the hole injection from the active core through the gradient shell to NiO takes place. The hole injection from the valence band of the QDs to NiO depends much less on the shell thickness when compared to the corresponding electron injection to n-type semiconductor (ZnO). We simulate the charge carrier tunneling through the potential barrier due to the gradient shell by numerically solving the Schrodinger equation. The details of the band alignment determining the potential barrier are obtained from X-ray spectroscopy measurements. The observed drastic differences between the hole and electron injection are consistent with a model where the hole effective mass decreases, while the gradient shell thickness increases.
|
|
