10 research outputs found

    Optimizing Porosity and Heteroatom Functionalities in Amorphous Carbon-Rich g‑C<sub>3</sub>N<sub>4</sub> for Dual-Mode Photocatalysis through Solar to Green Hydrogen and Chemical Energy Conversion

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    Herein, we have fabricated two different types of amorphous carbon-rich g-C3N4 systems with improved heteroatom functionalities and desired porosities from highly defined amorphous carbon dots and melamine. It improves the visible light absorption and effective active sites for photocatalysis compared to the pristine g-C3N4 matrix. Details of structural and elemental properties have been investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 adsorption–desorption isotherms. This was further supported by the intricate photophysical properties of the materials. Notably, the photoinduced charge separation drastically increases with increasing the amorphous C and pyrrolic N content in the g-C3N4 matrix. Photocatalytic solar H2 production also follows the same trend. The calculated external quantum efficiency for solar H2 production has reached almost 30% for the optimized material, which is one of the highest H2 production efficiencies reported to date compared to similar all-carbon-based nanomaterials. Depending on the structural insight, tunable electronic energy level alignment, and efficient charge separation, the as-synthesized C-rich g-C3N4 systems are concomitantly utilized for the selective oxidative coupling reactions of benzylamine through the simultaneous utilization of both electrons and holes. Therefore, the currently developed all-carbon-based photocatalyst will open up new possibilities for the on-demand dual mode of photocatalysis

    Photophysical Properties, Self-Assembly Behavior, and Energy Transfer of Porphyrin-Based Functional Nanoparticles

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    This paper focuses on the spectroscopic studies and self-assembly behavior of zinc octaethylporphyrin (ZnOEP) doped semiconducting [poly­(<i>N</i>-vinylcarbazole) (PVK)] polymer nanoparticles (NP) using steady state and time-resolved spectroscopy. The bathochromic shift of both Soret (by 12 nm) and Q bands (by 6–8 nm) in the absorption spectra and shortening of the porphyrin lifetime indicate the J-aggregation of porphyrin molecules in the ZnOEP doped PVK NP system. The significant quenching of fluorescence spectrum and the shortening of decay time of the PVK host unambiguously confirm an effective energy transfer (above 90%) from PVK to ZnOEP in the nanoparticles

    Stable Room-Temperature Phosphorescence from MXene-Derived Carbon Dots: Ultralong Afterglow Emission without an External Matrix

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    Herein, we synthesized highly defined carbon dots (CDs) from two-dimensional delaminated MXene through a solution-based acid etching method. The as-synthesized CDs show blue fluorescence emission in the solution phase upon neutralization with excess alkali. However, after solidification, the solid powder of CDs shows strong bright green room-temperature phosphorescence/afterglow emission for up to 5 s without using any further external matrix. The fundamental photophysical properties of the CDs are further correlated with the structural and elemental features. It suggests that the rigidity of the surface emissive states due to the slow modification of the exterior surface of CDs facilitates the afterglow emission. Temperature-dependent photoluminescence study and the systematic interconversion between room-temperature phosphorescence and prompt fluorescence depict the possible thermally activated delayed fluorescence at high temperatures. It is further correlated with the low-temperature phosphorescence studies (up to 90 K). The solid powder of CDs has been further utilized directly as a sustainable smart material for anticounterfeiting and information protection applications

    Stable Room-Temperature Phosphorescence from MXene-Derived Carbon Dots: Ultralong Afterglow Emission without an External Matrix

    No full text
    Herein, we synthesized highly defined carbon dots (CDs) from two-dimensional delaminated MXene through a solution-based acid etching method. The as-synthesized CDs show blue fluorescence emission in the solution phase upon neutralization with excess alkali. However, after solidification, the solid powder of CDs shows strong bright green room-temperature phosphorescence/afterglow emission for up to 5 s without using any further external matrix. The fundamental photophysical properties of the CDs are further correlated with the structural and elemental features. It suggests that the rigidity of the surface emissive states due to the slow modification of the exterior surface of CDs facilitates the afterglow emission. Temperature-dependent photoluminescence study and the systematic interconversion between room-temperature phosphorescence and prompt fluorescence depict the possible thermally activated delayed fluorescence at high temperatures. It is further correlated with the low-temperature phosphorescence studies (up to 90 K). The solid powder of CDs has been further utilized directly as a sustainable smart material for anticounterfeiting and information protection applications

    Photophysics and Dynamics of Dye-Doped Conjugated Polymer Nanoparticles by Time-Resolved and Fluorescence Correlation Spectroscopy

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    Fluorescent dye encapsulated conjugated polymer nanoparticles have been paid significant attention for potential applications in photonics and biophotonics due to their high brightness and better photostability. Bright, photostable, and monodispersed Nile Red (NR) dye encapsulated poly-<i>N</i>-vinylcarbazole (PVK) fluorescent polymer nanoparticles have been prepared to understand the influence of size of particles and the concentration of dye inside the particles on the photophysical properties by using steady-state, time-resolved fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS). Here, we have quantitatively analyzed the hydrodynamic diameter, particle brightness, and population of NR molecules inside the particle with varying the particle size and NR concentration by using fluorescence correlation spectroscopy (FCS). The average fluorescence intensity of a single nanoparticle, i.e., per particle brightness (PPB) value, increases from 80 to 500 kHz, and the number of NR molecules per nanoparticle increases from 5 to 22 by increasing the concentration of NR from 0.5 to 1.8 wt % at the time of nanoparticle preparation. Fluorescence anisotropy study has been undertaken to understand the rotational dynamics of encapsulated NR molecules with varying particle size and NR concentration inside the nanoparticle. The particle brightness and quantum yield are enhanced due to increasing the radiative decay rate. Higher brightness (almost one order of magnitude higher with respect to free dye) and better photostability (15-fold enhancement) of these polymer nanoparticles are found to be efficient for bioimaging purposes

    Photophysical Properties of Doped Carbon Dots (N, P, and B) and Their Influence on Electron/Hole Transfer in Carbon Dots–Nickel (II) Phthalocyanine Conjugates

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    Doping in carbon nanomaterial with various hetero atoms draws attention due to their tunable properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorus co-doped nitrogen containing carbon dots [C-dots (N, P)], and boron co-doped nitrogen containing carbon dots [C-dots (N, B)]; and detailed elemental analysis has been unveiled by X-ray photoelectron spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady-state and time-resolved spectroscopy. Nitrogen containing carbon dots have quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the nonradiative electron–hole recombination pathways due to incorporation of excess hole; as a result QY, radiative rate, and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached nickel (II) phthalocyanine on the surface of C-dots. It is seen that phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs

    Singlet Oxygen Generation from Polymer Nanoparticles–Photosensitizer Conjugates Using FRET Cascade

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    Herein, we demonstrate π-conjugated polymer nanoparticles–photosensitizer conjugates for singlet oxygen generation via FRET cascade, which would be useful for photodynamic therapy. Rose Bengal (RB) molecules are attached on the surface of coumarin 153 (C153)-dye-doped poly­[<i>N</i>-vinyl carbazole] (PVK) polymer nanoparticles, where polymer nanoparticles act as efficient light-absorbing antenna materials. The energy funneling from C153 to RB at the excitation of the PVK host (340 nm) is confirmed by shortening of decay time of C153 and disappearing of its rise time. Again, it is evident that the efficient multistep energy transfer occurs from host PVK to RB dye molecules through C153 dye molecules to generate singlet oxygen (<sup>1</sup>O<sub>2</sub>) in solution. In addition, photo-oxidation of 2-chlorophenol provides quantitative evidence of singlet oxygen generation in different systems indirectly. The estimated singlet oxygen quantum yield for RB-attached C153-dye-doped PVK polymer nanoparticles is 21%. The present investigations should pave the way for future development of different photodynamic and theranostic devices

    Single-Atom Ru Catalyst-Decorated CNF(ZnO) Nanocages for Efficient H<sub>2</sub> Evolution and CH<sub>3</sub>OH Production

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    The presence of transition-metal single-atom catalysts effectively enhances the interaction between the substrate and reactant molecules, thus exhibiting extraordinary catalytic performance. In this work, we for the first time report a facile synthetic procedure for placing highly dispersed Ru single atoms on stable CNF(ZnO) nanocages. We unravel the atomistic nature of the Ru single atoms in CNF(ZnO)/Ru systems using advanced HAADF-STEM, HRTEM, and XANES analytical methods. Density functional theory calculations further support the presence of ruthenium single-atom sites in the CNF(ZnO)/Ru system. Our work further demonstrates the excellent photocatalytic ability of the CNF(ZnO)/Ru system with respect to H2 production (5.8 mmol g–1 h–1) and reduction of CO2 to CH3OH [249 μmol (g of catalyst)−1] with apparent quantum efficiencies of 3.8% and 1.4% for H2 and CH3OH generation, respectively. Our studies unambiguously demonstrate the presence of atomically dispersed ruthenium sites in CNF(ZnO)/Ru catalysts, which greatly enhance charge transfer, thus facilitating the aforementioned photocatalytic redox reactions

    Single-Atom Ru Catalyst-Decorated CNF(ZnO) Nanocages for Efficient H<sub>2</sub> Evolution and CH<sub>3</sub>OH Production

    No full text
    The presence of transition-metal single-atom catalysts effectively enhances the interaction between the substrate and reactant molecules, thus exhibiting extraordinary catalytic performance. In this work, we for the first time report a facile synthetic procedure for placing highly dispersed Ru single atoms on stable CNF(ZnO) nanocages. We unravel the atomistic nature of the Ru single atoms in CNF(ZnO)/Ru systems using advanced HAADF-STEM, HRTEM, and XANES analytical methods. Density functional theory calculations further support the presence of ruthenium single-atom sites in the CNF(ZnO)/Ru system. Our work further demonstrates the excellent photocatalytic ability of the CNF(ZnO)/Ru system with respect to H2 production (5.8 mmol g–1 h–1) and reduction of CO2 to CH3OH [249 μmol (g of catalyst)−1] with apparent quantum efficiencies of 3.8% and 1.4% for H2 and CH3OH generation, respectively. Our studies unambiguously demonstrate the presence of atomically dispersed ruthenium sites in CNF(ZnO)/Ru catalysts, which greatly enhance charge transfer, thus facilitating the aforementioned photocatalytic redox reactions

    Excited State Features and Dynamics in a Distyrylbenzene-Based Mixed Stack Donor–Acceptor Cocrystal with Luminescent Charge Transfer Characteristics

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    Combined structural, photophysical, and quantum-chemical studies at the quantum mechanics/molecular mechanics (QM/MM) level precisely reveal the structure–property relationships in a mixed-stack donor–acceptor cocrystal, which displays vibronically structured fluorescence, strongly red-shifted against the spectra of the parent donor and acceptor, with high quantum yield despite the pronounced CT character of the emitting state. The study elucidates the reasons for this unusual combination, quantifies the ordering and nature of the collective excited singlet and triplet state manifold, and details the deactivation pathways of the initially created Franck–Condon state
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