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1.
Nanomaterials (Basel) ; 10(7)2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32679795

RESUMO

Plasmonics nanoparticles gained prominence in the last decade in fields of photonics, solar energy conversion and catalysis. It has been shown that anchoring the plasmonics nanoparticles on semiconductors via a molecular linker reduces band bending and increases hot carriers' lifetime, which is essential for the development of efficient photovoltaic devices and photocatalytic systems. Aminobenzoic acid is a commonly used linker to connect the plasmonic metal to an oxide-based semiconductor. The coordination to the oxide was established to occur via the carboxylic functional group, however, it remains unclear what type of coordination that is established with the metal site. Herein, it is demonstrated that metal is covalently bonded to the linker via the amino group, as supported by Surface-Enhanced Resonant Raman and infrared spectroscopies. The covalent linkage increases significantly the amount of silver grafted, resulting in an improvement of the system catalytic proficiency in the 4-nitrophenol (4-NP) photoreduction.

2.
Nat Mater ; 2020 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-32719510

RESUMO

A fundamental understanding of hot-carrier dynamics in photo-excited metal nanostructures is needed to unlock their potential for photodetection and photocatalysis. Despite numerous studies on the ultrafast dynamics of hot electrons, so far, the temporal evolution of hot holes in metal-semiconductor heterostructures remains unknown. Here, we report ultrafast (t < 200 fs) hot-hole injection from Au nanoparticles into the valence band of p-type GaN. The removal of hot holes from below the Au Fermi level is observed to substantially alter the thermalization dynamics of hot electrons, reducing the peak electronic temperature and the electron-phonon coupling time of the Au nanoparticles. First-principles calculations reveal that hot-hole injection modifies the relaxation dynamics of hot electrons in Au nanoparticles by modulating the electronic structure of the metal on timescales commensurate with electron-electron scattering. These results advance our understanding of hot-hole dynamics in metal-semiconductor heterostructures and offer additional strategies for manipulating the dynamics of hot carriers on ultrafast timescales.

3.
Harmful Algae ; 96: 101819, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32560833

RESUMO

Studies on phytoplankton and in particular Harmful Algal Blooms (HABs) species in southern Mediterranean waters are scarce. We performed from April 2008 to June 2009 weekly investigations on microphytoplankton community structure and abundance in two contrasted marine ecosystems located in the western Moroccan Mediterranean coast, M'diq Bay and Oued Laou Estuary. Simultaneously, we measured the main physico-chemical parameters. Globally, the two studied areas showed comparable values of the assessed abiotic environmental factors. Temperature and salinity followed seasonal variation with values ranging from 13.5 °C to 21.4 °C and 31 to 36.8, respectively. Average nutrient values in surface water ranged from 0.7 to 45.76 µM for dissolved inorganic nitrogen, 0.02-2.10 µM for PO4 and 0.23-17.46 µM for SiO4 in the study areas. A total of 92 taxa belonging to 8 taxonomic classes were found. The highest number of microphytoplankton abundance reached 1.2 × 106 cells L-1 with diatoms being the most abundant taxa. Factorial Discriminant Analysis (FDA) and Spearman correlation test showed a significant seasonal discrimination of dominant microphytoplankton species. These micro-organisms were associated with different environmental variables, in particular temperature and salinity. Numerous HABs species were encountered regularly along the year. Although Dinophysis species and Prorocentrum lima were present in both sites, no Lipophilic Shellfish Poisoning was detected for the analyzed bivalve mollusks. Domoic acid (DA), produced by toxic species of Pseudo-nitzschia was found with concentrations up to 18 µg DA g-1 in the smooth clam Callista chione. Data showed that the observed persistent and dramatic Paralytic Shellfish Poisoning (PSP) intoxication of mollusks resulted probably of Gymnodinium catenatum proliferations in both studied areas. Contrary to C. chione, the cockle Achanthocardia tuberculatum showed a permanent and extremely high toxicity level during the 15 months survey with up to 7545 µg Equivalent Saxitoxin kg-1 flesh (ten times higher than the sanitary threshold of 800 µg eqSTX Kg-1flesh). The present work highlights for the first time the dynamic of microphytoplankton including HABs species and their associated toxin accumulation in the commercially exploited shellfish in the southern western Mediterranean waters of Morocco. Furthermore, the acquired data will help us to improve the monitoring of HABs species and related toxins in these coastal marine systems.

4.
J Phys Chem Lett ; : 3705-3711, 2020 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-32329350

RESUMO

Transition-metal ion doping has been demonstrated to be effective for tuning the photoluminescence properties of perovskite quantum dots (QDs). However, it would inevitably introduce defects in the lattice. As the Mn concentration increases, the Mn dopant photoluminescence quantum yield (PLQY) first increases and then decreases. Herein the influence of the dopant and the defect states on the photophysics in Mn-doped CsPbCl3 QDs was studied by time-resolved spectroscopies, whereas the energy levels of the possible defect states were analyzed by density functional theory calculations. We reveal the formation of deep interstitials defects (Cli) by Mn2+ doping. The depopulation of initial QD exciton states is a competition between exciton-dopant energy transfer and defect trapping on an early time scale (<100 ps), which determines the final PLQY of the QDs. The present work establishes a robust material optimization guideline for all of the emerging applications where a high PLQY is essential.

5.
ChemSusChem ; 2020 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-32149460

RESUMO

Photocatalytic water splitting has become a promising strategy for converting solar energy into clean and carbon-neutral solar fuels in a low-cost and environmentally benign way. Hydrogen gas is such a potential solar fuel/energy carrier. In a classical artificial photosynthetic system, a photosensitizer is generally associated with a co-catalyst to convert photogenerated charge into (a) chemical bond(s). In the present study, assemblies consisting of CdSe quantum dots that are coupled with one of two molecular complexes/catalysts, that is, [Fe2 S2 (CO)6 ] or [Fe3 Te2 (CO)9 ], using an interface-directed approach, have been tested as catalytic systems for hydrogen production in aqueous solution/organic solution. In the presence of ascorbic acid as a sacrificial electron donor and proton source, these assemblies exhibit enhanced activities for the rate of hydrogen production under visible light irradiation for 8 h in aqueous solution at pH 4.0 with up to 110 µmol of H2 per mg of assembly, almost 8.5 times that of pure CdSe quantum dots under the same conditions. Transient absorption and time-resolved photoluminescence spectroscopies have been used to investigate the charge carrier transfer dynamics in the quantum dot/iron carbonyl cluster assemblies. The spectroscopic results indicate that effective electron transfer from the molecular iron complex to the valence band of the excited CdSe quantum dots significantly inhibits the recombination of photogenerated charge carriers, boosting the photocatalytic activity for hydrogen generation; that is, the iron clusters function as effective intermediaries for electron transfer from the sacrificial electron donor to the valence band of the quantum dots.

6.
J Phys Chem Lett ; 11(6): 2133-2141, 2020 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-32069410

RESUMO

An atomistic understanding of the photoinduced spin-state switching (PSS) within polynuclear systems of d4-d7 transition metal ion complexes is required for their rational integration into light-driven reactions of chemical and biological interest. However, in contrast to mononuclear systems, the multidimensional dynamics of the PSS in solvated molecular arrays have not yet been elucidated due to the expected complications associated with the connectivity between the metal centers and the strong interactions with the surroundings. In this work, the PSS in a solvated triiron(II) metallogrid complex is characterized using transient optical absorption and X-ray emission spectroscopies on the femtosecond time scale. The complementary measurements reveal the photoinduced creation of energy-rich (hot) and long-lived quintet states, whose dynamics differ critically from their mononuclear congeners. This finding opens major prospects for developing novel schemes in solution-phase spin chemistry that are driven by the dynamic PSS process in compact oligometallic arrays.

7.
ACS Appl Mater Interfaces ; 12(1): 858-867, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31820629

RESUMO

Recently, metal-halide perovskites have emerged as a candidate for optoelectronic applications such as photodetectors. However, the poor device performance and instability have limited their future commercialization. Herein, we report the spontaneous growth of perovskite/N-rGO hybrid structures using a facile solution method and their applications for photodetectors. In the hybrid structures, perovskites were homogeneously wrapped by N-rGO sheets through strong hydrogen bonding. The strongly coupled N-rGOs facilitate the charge carrier transportation across the perovskite crystals but also distort the surface lattice of the perovskite creating a potential barrier for charge transfer. We optimize the addition of N-rGO in the hybrid structures to balance interfacial structural distortion and the intercrystal conductivity. High-performance photodetection up to 3 × 104 A/W, external quantum efficiency exceeding 105%, and detectivity up to 1012 Jones were achieved in the optimal device with the weight ratio between perovskites and N-rGO to be 8:1.5. The underlying mechanism behind the optimal N-rGO addition ratio in the hybrids has also been rationalized via time-resolved spectroscopic studies as a reference for future applications.

8.
Small ; 15(49): e1905081, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31639286

RESUMO

Dion-Jacobson (DJ) type 2D perovskites with a single organic cation layer exhibit a narrower distance between two adjacent inorganic layers compared to the corresponding Ruddlesden-Popper perovskites, which facilitates interlayer charge transport. However, the internal crystal structures in 2D DJ perovskites remain elusive. Herein, in a p-xylylenediamine (PDMA)-based DJ perovskite bearing bifunctional NH3 + spacer, the compression from confinement structure (inorganic layer number, n = 1, 2) to nonconfinement structure (n > 3) with the decrease of PDMA molar ratio is unraveled. Remarkably, the nonconfined perovskite displays shorter spacing between 2D quantum wells, which results in a lower exciton binding energy and hence promotes exciton dissociation. The significantly diminishing quantum confinement promotes interlayer charge transport leading to a maximum photovoltaic efficiency of ≈11%. Additionally, the tighter interlayer packing arising from the squeezing of inorganic octahedra gives rise to enhanced ambient stability.

9.
Turk J Gastroenterol ; 30(8): 708-713, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31418415

RESUMO

BACKGROUND/AIMS: There is less data regarding the changes in body mass index (BMI) after treating hepatitis C virus (HCV) patients with new direct-acting antiviral agents (DAAs). This study aimed to assess the changes in BMI in chronic HCV patients treated with DAAs in Egypt and to explore other factors influencing this change. MATERIALS AND METHODS: The data of chronic HCV patients who received antiviral therapy with new DAAs in one of Egypt's specialized viral hepatitis treatment centers were retrospectively analyzed. In addition to the routine clinical and laboratory workup, changes in body weight during and after treatment were monitored and BMI was calculated. Viral load was measured at 12 weeks post-treatment to assess a sustained virological response. Patients with documented thyroid abnormalities, bariatric surgery, or ensuing special diets were excluded. BMI of >30 was taken as the cutoff for pa¬tients with obesity. RESULTS: The study included 162 patients with a mean age of 48.56±11.49 years, of whom 61.1% were males, 16% were treatment-experienced, 12% were diabetic, and 29% were obese. Treatment duration was 12 weeks in 84% of patients and 24 weeks in 16% of patients. There was a significant increase in BMI post-treatment as compared to pretreatment measures (28.68±5.35 vs 28.18±4.55) (p=0.03). BMI changes were constant regardless of cirrhosis or previous treatment experience. CONCLUSION: Treatment of chronic HCV with DAAs was associated with increased body mass index. Further studies are needed to explore if this effect is secondary to treatment with DAAs or is an improvement in the liver function and lifestyle of treated patients.


Assuntos
Antivirais/efeitos adversos , Índice de Massa Corporal , Peso Corporal/efeitos dos fármacos , Hepacivirus , Hepatite C Crônica/tratamento farmacológico , Adulto , Feminino , Hepatite C Crônica/fisiopatologia , Hepatite C Crônica/virologia , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Resposta Viral Sustentada
10.
Arab J Gastroenterol ; 20(2): 109-113, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31175077

RESUMO

Liver diseases are among the most challenging health care problems worldwide. In Egypt, we established different care programs to combat liver diseases including schistosomiasis and viral hepatitides. A lot of research work addressing liver diseases in Egypt have been published with special focus on these two major fields. Other liver disease seems to be neglected although present and contributing to the liver disease burden in Egypt. In this report we reviewed the available evidence published from Egypt and elucidate areas of weakness and future research needs. Our search for Egyptian liver disease evidence retrieved 4683 articles, 67% of them were relevant to the topic. Out of the relevant articles; 1646/3265 (50.4%) were discussing clinical science, 1131 (34.7%) were discussing basic science and 488 (14.9%) were discussing both basic and clinical sciences. Cairo university (16.8%, n = 513) and Mansoura university (9.3%, n = 285) had the largest number of publications related to liver disease in Egypt respectively. The most commonly reported diseases were hepatitis C in 719/3361 articles (21.4%), parasitic liver infestations in 663 articles (19.7%), hepatocellular carcinoma in 544 articles (16.2%), liver fibrosis or cirrhosis in 537 articles (16%), and drug induced liver injury in 516 articles (15.4%). Most of the reviewed articles (36%) were discussing treatment of chronic liver diseases (n = 1201) followed by diagnostics (28%, n = 940), pathogenesis and pathophysiology (21%, n = 706). This review will direct attention to areas with less research like hepatitis B related liver disease, HIV/HCV co-infections, and non-alcoholic fatty liver disease (NAFLD) to encourage future research in these topics. In conclusion; our results ring a bell inviting the development of a roadmap for liver research in Egypt targeting to put future policies to cover areas of weakness in liver research with an ultimate goal of tackling liver disease and its overwhelming socioeconomic burden in our developing country.


Assuntos
Bibliometria , Pesquisa Biomédica , Hepatopatias/diagnóstico , Hepatopatias/terapia , Egito , Humanos , Hepatopatias/etiologia
11.
Catal Sci Technol ; 9(6): 1365-1371, 2019 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-31131076

RESUMO

The use of enzymes for synthetic applications is a powerful and environmentally-benign approach to increase molecular complexity. Oxidoreductases selectively introduce oxygen and hydrogen atoms into myriad substrates, catalyzing the synthesis of chemical and pharmaceutical building blocks for chemical production. However, broader application of this class of enzymes is limited by the requirements of expensive cofactors and low operational stability. Herein, we show that morpholine-based buffers, especially 3-(N-morpholino)propanesulfonic acid (MOPS), promote photoinduced flavoenzyme-catalyzed asymmetric redox transformations by regenerating the flavin cofactor via sacrificial electron donation and by increasing the operational stability of flavin-dependent oxidoreductases. The stabilization of the active forms of flavin by MOPS via formation of the spin correlated ion pair 3[flavin˙--MOPS˙+] ensemble reduces the formation of hydrogen peroxide, circumventing the oxygen dilemma under aerobic conditions detrimental to fragile enzymes.

12.
J Phys Chem Lett ; 10(11): 3140-3146, 2019 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-31117685

RESUMO

We have successfully investigated the simultaneous injection of hot electrons and holes upon excitation of gold localized surface plasmon resonance (LSPR). The studies were performed on all-solid-state plasmonic system composed of titanium dioxide (TiO2)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) p-n junctions with gold nanoparticles (Au NPs). The study revealed that both charge carriers are transferred within 200 fs to the respective charge acceptors, exhibiting a free carrier transport behavior. We also confirmed that the transfer of charge carriers are accompanied by change in the initial relaxation dynamics of Au NPs.

13.
J Phys Chem Lett ; 10(8): 1743-1749, 2019 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-30920838

RESUMO

Hydrated electrons are important in radiation chemistry and charge-transfer reactions, with applications that include chemical damage of DNA, catalysis, and signaling. Conventionally, hydrated electrons are produced by pulsed radiolysis, sonolysis, two-ultraviolet-photon laser excitation of liquid water, or photodetachment of suitable electron donors. Here we report a method for the generation of hydrated electrons via single-visible-photon excitation of localized surface plasmon resonances (LSPRs) of supported sub-3 nm copper nanoparticles in contact with water. Only excitations at the LSPR maximum resulted in the formation of hydrated electrons, suggesting that plasmon excitation plays a crucial role in promoting electron transfer from the nanoparticle into the solution. The reactivity of the hydrated electrons was confirmed via proton reduction and concomitant H2 evolution in the presence of a Ru/TiO2 catalyst.

14.
World J Gastroenterol ; 24(38): 4330-4340, 2018 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-30344418

RESUMO

Worldwide, more than one million people die each year from hepatitis C virus (HCV) related diseases, and over 300 million people are chronically infected with hepatitis B or C. Egypt used to be on the top of the countries with heavy HCV burden. Some countries are making advances in elimination of HCV, yet multiple factors preventing progress; remain for the majority. These factors include lack of global funding sources for treatment, late diagnosis, poor data, and inadequate screening. Treatment of HCV in Egypt has become one of the top national priorities since 2007. Egypt started a national treatment program intending to provide cure for Egyptian HCV-infected patients. Mass HCV treatment program had started using Pegylated interferon and ribavirin between 2007 and 2014. Yet, with the development of highly-effective direct acting antivirals (DAAs) for HCV, elimination of viral hepatitis has become a real possibility. The Egyptian National Committee for the Control of Viral Hepatitis did its best to provide Egyptian HCV patients with DAAs. Egypt adopted a strategy that represents a model of care that could help other countries with high HCV prevalence rate in their battle against HCV. This review covers the effects of HCV management in Egyptian real life settings and the outcome of different treatment protocols. Also, it deals with the current and future strategies for HCV prevention and screening as well as the challenges facing HCV elimination and the prospect of future eradication of HCV.


Assuntos
Antivirais/uso terapêutico , Erradicação de Doenças/organização & administração , Hepacivirus/isolamento & purificação , Hepatite C Crônica/prevenção & controle , Programas Nacionais de Saúde/organização & administração , Erradicação de Doenças/métodos , Erradicação de Doenças/estatística & dados numéricos , Quimioterapia Combinada/métodos , Egito/epidemiologia , Hepatite C Crônica/diagnóstico , Hepatite C Crônica/epidemiologia , Hepatite C Crônica/virologia , Humanos , Programas de Rastreamento/métodos , Programas de Rastreamento/organização & administração , Programas de Rastreamento/estatística & dados numéricos , Programas Nacionais de Saúde/estatística & dados numéricos , Prevalência
15.
J Am Chem Soc ; 140(43): 14042-14045, 2018 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-30296074

RESUMO

The dynamics of photopromoted electrons in BiVO4, WO3, and WO3/BiVO4 heterojunction electrodes has been directly probed by transient absorption (TA) midinfrared (mid-IR) spectroscopy in the picosecond to microsecond time range. By comparison of the dynamics recorded with the two individual oxides at 2050 cm-1 with that of the heterojunction system after excitation at different wavelengths, electron-transfer processes between selectively excited BiVO4 and WO3 have been directly tracked for the first time. These results support the charge carrier interactions which were previously hypothesized by probing the BiVO4 hole dynamics through TA spectroscopy in the visible range. Nanosecond mid-IR TA experiments confirmed that charge carrier separation occurs in WO3/BiVO4 electrodes under visible-light excitation, persisting up to the microsecond time scale.

16.
ACS Appl Mater Interfaces ; 10(35): 29574-29582, 2018 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-30088920

RESUMO

All-inorganic halide perovskite nanowires (NWs) exhibit improved thermal and hydrolysis stability and could thus play a vital role in nanoscale optoelectronics. Among them, blue-light-based devices are extremely limited because of the lack of a facile method to obtain high-purity CsPbCl3 NWs. Herein, we report a direct and facile method for the synthesis of CsPbCl3 NWs assisted by inorganic ions that served both as a morphology controlling agent for the anisotropic growth of nanomaterials and a surface passivation species modulating the surface of nanomaterials. This new approach allows us to obtain high-purity and size-uniform NWs as long as 500 nm in length and 20 nm in diameter with high reproducibility. X-ray photoelectron spectroscopy and ultrafast spectroscopic measurements confirmed that a reduced band gap caused by the surface species of NWs relative to nanocubes (NCs) was achieved at the photon energy of 160 eV because of the hybrid surface passivation contributed by adsorbed inorganic ions. The resulting NWs demonstrate significantly enhanced photoelectrochemical performances, 3.5-fold increase in the photocurrent generation, and notably improved stability compared to their NC counterparts. Our results suggest that the newly designed NWs could be a promising material for the development of nanoscale optoelectronic devices.

17.
Sci Rep ; 7(1): 8670, 2017 08 17.
Artigo em Inglês | MEDLINE | ID: mdl-28819324

RESUMO

The efficient conversion of light energy into chemical energy is key for sustainable human development. Several photocatalytic systems based on photovoltaic electrolysis have been used to produce hydrogen via water reduction. However, in such devices, light harvesting and proton reduction are carried separately, showing quantum efficiency of about 10-12%. Here, we report a nano-hybrid photocatalytic assembly that enables concomitant reductive hydrogen production and pollutant oxidation with solar-to-fuel efficiencies up to 20%. The modular architecture of this plasmonic material allows the fine-tuning of its photocatalytic properties by simple manipulation of a reduced number of basic components.

18.
Nanoscale ; 9(34): 12503-12508, 2017 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-28819669

RESUMO

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 Schrödinger 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.

19.
Phys Chem Chem Phys ; 19(8): 6006-6012, 2017 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-28182179

RESUMO

Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO. We conclude that the motion of injected electrons in ZnO nanoparticles is strongly influenced by their interaction with positive charges left in the sensitizing quantum dots.

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