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1.
J Nanosci Nanotechnol ; 20(5): 2971-2978, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-31635635

RESUMO

Crystalline fullerene C70 microtubes (FMTs) were produced employing ultrasound-assisted liquid- liquid interfacial precipitation (ULLIP) technique at the interface between fullerene C70 solution in 1,2 dichlorobenzene (DCB) and isopropanol (IPA) at 15 °C. Using the vortex-flow motion of the subphase water (also called Vortex-Langmuir-Blodgett technique), the FMTs were aligned and homogeneous films were prepared at the air-water interface. The aligned FMTs film exhibited enhanced photoluminescence (PL) with PL intensity ~5 times higher than that of the pristine C70. Moreover, the aligned FMT film showed better photovoltaics properties compared with randomly oriented FMTs and pristine C70 film obtained from the spin coating. The compact, directional orientation and proper surface coverage of the FMT film enhanced the charge transport properties in the photovoltaic device.

2.
Chemistry ; 24(21): 5591-5600, 2018 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-29411906

RESUMO

Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π-π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern-Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10-11 m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PAx with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques.


Assuntos
Aminas/química , Géis/química , Picratos/análise , Colorimetria , Corantes/química , Elétrons , Fluorescência , Fluorometria
3.
ACS Appl Mater Interfaces ; 9(51): 44458-44465, 2017 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-29210263

RESUMO

Fullerene C60 microbelts were fabricated using the liquid-liquid interfacial precipitation method and converted into quasi 2D mesoporous carbon microbelts by heat treatment at elevated temperatures of 900 and 2000 °C. The carbon microbelts obtained by heat treatment of fullerene C60 microbelts at 900 °C showed excellent electrochemical supercapacitive performance, exhibiting high specific capacitances ca. 360 F g-1 (at 5 mV s-1) and 290 F g-1 (at 1 A g-1) because of the enhanced surface area and the robust mesoporous framework structure. Additionally, the heat-treated carbon microbelt showed good rate performance, retaining 49% of capacitance at a high scan rate of 10 A g-1. The carbon belts exhibit super cyclic stability. Capacity loss was not observed even after 10 000 charge/discharge cycles. These results demonstrate that the quasi 2D mesoporous carbon microbelts derived from a π-electron-rich carbon source, fullerene C60 crystals, could be used as a new candidate material for electrochemical supercapacitor applications.

4.
ACS Nano ; 11(8): 7790-7796, 2017 08 22.
Artigo em Inglês | MEDLINE | ID: mdl-28742325

RESUMO

We report production of highly crystalline fullerene C70 cubes possessing an open-hole structure at the center of each of their faces using a solution-based self-assembly strategy. The holes are isolated with a solid core at the interiors of the cubes. The open-hole structure of the cubes can be intentionally closed by introducing additional C70 and reopened by applying electron beam irradiation. The open-hole cubes exhibit preferential recognition of graphitic carbon particles over polymeric resin particles of similar dimensions due to the cubes' sp2-rich carboniferous nature.

5.
Spectrochim Acta A Mol Biomol Spectrosc ; 184: 128-133, 2017 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-28494374

RESUMO

The present work compares the dissimilarity and covariance based unsupervised chemometric classification approaches by taking the total synchronous fluorescence spectroscopy data sets acquired for the cumin and non-cumin based herbal preparations. The conventional decomposition method involves eigenvalue-eigenvector analysis of the covariance of the data set and finds the factors that can explain the overall major sources of variation present in the data set. The conventional approach does this irrespective of the fact that the samples belong to intrinsically different groups and hence leads to poor class separation. The present work shows that classification of such samples can be optimized by performing the eigenvalue-eigenvector decomposition on the pair-wise dissimilarity matrix.


Assuntos
Algoritmos , Preparações de Plantas/análise , Preparações de Plantas/química , Espectrometria de Fluorescência/métodos , Bases de Dados de Compostos Químicos
6.
ACS Nano ; 10(9): 8796-802, 2016 09 27.
Artigo em Inglês | MEDLINE | ID: mdl-27541964

RESUMO

Supramolecular assembly can be used to construct a wide variety of ordered structures by exploiting the cumulative effects of multiple noncovalent interactions. However, the construction of anisotropic nanostructures remains subject to some limitations. Here, we demonstrate the preparation of anisotropic fullerene-based nanostructures by supramolecular differentiation, which is the programmed control of multiple assembly strategies. We have carefully combined interfacial assembly and local phase separation phenomena. Two fullerene derivatives, PhH and C12H, were together formed into self-assembled anisotropic nanostructures by using this approach. This technique is applicable for the construction of anisotropic nanostructures without requiring complex molecular design or complicated methodology.

7.
ACS Nano ; 10(7): 6631-7, 2016 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-27341124

RESUMO

We report the preparation of hierarchically structured fullerene C70 cubes (HFC) composed of mesoporous C70 nanorods with crystalline pore walls. Highly crystalline cubic shape C70 crystals (FC) were grown at a liquid-liquid interface formed between tert-butyl alcohol and C70 solution in mesitylene. HFCs were then prepared by washing with isopropanol of the FC at 25 °C. The growth directions and diameters of C70 nanorods could be controlled by varying washing conditions. HFCs perform as an excellent sensing system for vapor-phase aromatic solvents due to their easy diffusion through the mesoporous architecture and strong π-π interactions with the sp(2) carbon-rich pore walls. Moreover, HFCs offer an enhanced electrochemically active surface area resulting in an energy storage capacity 1 order of magnitude greater than pristine C70 and fullerene C70 cubes not containing mesoporous nanorods.

8.
Langmuir ; 32(21): 5373-82, 2016 05 31.
Artigo em Inglês | MEDLINE | ID: mdl-27159227

RESUMO

The organogel of (E)-N'-(anthracene-10-ylmethylene)-3,4,5-tris(dodecyloxy)benzohydrazide (I) in methyl cyclohexane having a fibrillar network structure exhibits excellent fluorescence, which decreases sharply with time upon photoirradiation at λ = 365 nm. It has been attributed to the transformation of the E isomer of I to the Z isomer, and the kinetics of E-Z isomerization are compared for the sol, gel, xerogel, and powder states. The rate constants at different temperatures are measured from Avrami plots and its increase with an increase in temperature, indicating temperature acts as a promoter for photoirradiated E-Z isomeization along the imine (C═N) bond. In the powder form, the rate constant values are the lowest compared to those of other states for all temperatures and the xerogels exhibit the highest rate of E-Z isomerization. The rate constants of sol and gel states mostly lie between the two. The wide-angle X-ray scattering pattern changes after ultraviolet (UV) irradiation with the generation of new sharp peaks whose intensities increase with an increase in irradiation time. A polarized optical microscopic study indicates formation of small crystalline dots on the fibers in the gels, dendritic morphology on the xerogel fibers, and large needlelike morphology at the surface boundary of the solid. The dried I gel exhibits a melting peak at 96.7 °C, but upon irradiation, two peaks are observed at 98.5 and 152.7 °C; the latter has been attributed to the melting of crystals of Z isomers. Similar higher melting peaks are observed both for the xerogel and for powders after UV irradiation; the powders exhibit the highest meting peak at 159.4 °C. Possible reasons for the variation of rate constant values in the four different states and the difference in morphology and melting points of crystals of Z isomers of I are discussed.

9.
Langmuir ; 32(7): 1871-80, 2016 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-26836971

RESUMO

In the quest to engineer the nanofibrillar morphology of folic acid (F) gel, poly(4-vinylpyridine-co-styrene) (PVPS) is judiciously integrated as a polymeric additive because of its potential to form H-bonding and π-stacking with F. The hybrid gels are designated as F-PVPSx gels, where x denotes the amount of PVPS (mg) added in 2 mL of F gel (0.3%, w/v). The assistance of PVPS in the gelation of F is manifested from the drop in critical gelation concentration and increased fiber diameter and branching of F-PVPSx gels compared to that of F gel. PVPS induces a magnificent improvement of mechanical properties: a 500 times increase of storage modulus and ∼62 times increase of yield stress in the F-PVPS5 gel compared to the F gel. The complex modulus also increases with increasing PVPS concentration with a maximum in F-PVPS5 gel. Creep recovery experiments suggest PVPS induced elasticity in the otherwise viscous F gel. The fluorescence intensity of F-PVPSx gels at first increases with increasing PVPS concentration showing maxima at F-PVPS5 gel and then slowly decreases. Gelation is monitored by time-dependent fluorescence spectroscopy, and it is observed that F and F-PVPSx gels exhibit perfectly opposite trend; the former shows a sigmoidal decrease in fluorescence intensity during gelation, but the latter shows a sigmoidal increase. The gelation rate constants calculated from Avrami treatment on the time-dependent fluorescence data manifest that PVPS effectively enhances the gelation rate showing a maximum for F-PVPS5 gel. The hybrid gel exhibit 5 orders increase of dc conductivity than that of F-gel showing semiconducting nature in the current-voltage plot. The Nyquist plot in impedance spectra of F-PVPS5 xerogel exhibit a depressed semicircle with a spike at lower frequency region, and the equivalent circuit represents a complex combination of resistance-capacitance circuits attributed to the hybrid morphology of the gel fibers.

10.
Chem Commun (Camb) ; 51(53): 10680-3, 2015 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-26051426

RESUMO

A multiresponsive organogel of (E)-N'-(anthracene-10-ylmethylene)-3,4,5-tris(dodecyloxy)benzohydrazide (I) showed a decrease of fluorescence intensity, decrease in mechanical strength and a change in gel morphology on irradiation with a wavelength of 365 nm. This is attributed to the E-Z isomerization across the C=N bond of I as evidenced from (1)H NMR spectroscopy.

11.
J Phys Chem B ; 119(18): 5933-44, 2015 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-25885454

RESUMO

Polyethylene glycol (PEG) is incorporated to improve the mechanical properties of N-fluorenylmethoxycarbonyl-l-tryptophan (FT) hydrogel producing the hybrid (FTP) gels designated as FTP1, FTP2.5, etc. having PEG concentrations of 0.05 and 0.125% (w/v), respectively. Both the FT and FTP1 gels exhibit fibrillar network morphology; the fibers of the FTP1 gel are thinner than those of the FT gel. FTP gels exhibit a magnificent improvement in mechanical properties, and the storage and complex moduli increase with a maximum of ∼2800% for the FTP2.5 gel. Creep recovery experiment exhibits a maximum strain recovery of 90% for the FTP1 gel. The thixotropic property is observed for both FT and FTP gels and the rate of recovery increases with increase of PEG concentration; the latter acts as a molecular adhesive to the gel fibers bringing back the network structure easily. Gelation of FT causes a 5-fold increase of fluorescence intensity due to molecular aggregation, and with increase of FT concentration the ratio of fluorescence intensities at 470 and 395 nm increases. Exploiting the thixotropic property of FT and FTP hybrid gels, doxorubicin (DOX) is successfully encapsulated, and tunable release of DOX using appropriate amount of PEG in the gel matrix under physiological conditions is observed.

12.
J Phys Chem B ; 118(48): 13969-80, 2014 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-25383628

RESUMO

A metastable coassembled hydrogel of N-Fluorenylmethoxycarbonyl (Fmoc) phenylalanine (FP) with aniline (FP-ANI), upon polymerization, produces a stable green-colored coassembled FP-polyaniline (FP-PANI) hydrogel. The coassembly is produced by supramolecular interactions between FP and ANI/PANI. WAXS spectra suggest that structures of FP powder, FP-ANI, and FP-PANI xerogels are different from each other. The FP-ANI gel exhibits a mixture of doughnut and fiber morphology, but the FP-PANI gel exhibits a nanotubular morphology. UV-vis spectroscopy suggests that the doped state of PANI and the fluorescence property of FP completely vanish in the FP-PANI gel. The storage and loss modulii (G' and G″) of the FP-PANI gel are higher than those of the FP-ANI gel. The FP-ANI gel breaks at a lower oscillator stress (57 Pa) than the FP-PANI gel (93 Pa), which exhibits a good strain recovery demonstrating excellent viscoelastic properties. The FP-PANI gel also exhibits a dc conductivity (1.2 × 10(-2) S·cm(-1)) that is seven orders higher than that of the FP-ANI gel because of the doped nature of PANI. The current-voltage (I-V) characteristic curve of FP-PANI xerogel resembles the behavior of a semiconductor-metal junction, and upon white light irradiation, it exhibits a reversible on-off cycle with a constant photocurrent value of 0.1 mA. The Nyquist plot obtained from impedance measurements of the FP-PANI xerogel is different from that obtained for the FP-ANI xerogel, and it exhibits almost a semicircle, indicating the existence of both resistive and capacitive features connected in parallel mode.


Assuntos
Compostos de Anilina/química , Hidrogel de Polietilenoglicol-Dimetacrilato/química , Fenilalanina/análogos & derivados , Espectroscopia Dielétrica , Condutividade Elétrica , Fluorenos/química , Microscopia Eletrônica de Transmissão , Reologia , Viscosidade , Difração de Raios X
13.
Langmuir ; 30(25): 7547-55, 2014 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-24912087

RESUMO

5,5'-(1,3,5,7-Tetraoxopyrrolo[3,4-f]isoindole-2,6-diyl)diisophthalic acid (PMDIG) is used to produce a supramolecular hydrogel via acid-base treatment. The field emission scanning electron micrograph and atomic force microscopy micrographs exhibit a fibrillar network structure from intermolecular supramolecular interaction, supported from Fourier transform infrared (FTIR) and UV-vis spectra. The fluorescence intensity of the PMDIG gel is 16 times higher than that of the sodium salt of PMDIG with a 42 nm red shift of the emission peak. Upon addition of an anilinium chloride solution to the PMDIG gel, it transforms into the sol, and when a solid ammonium persulfate is spread over it, a stable hydrogel is produced. The co-assembled PMDIG-polyaniline (PANI) gel exhibits a fibrillar network morphology, and the co-assembly is formed by the supramolecular interaction between the polyaniline (donor) and the PMDIG (acceptor) molecules, which is evident from FTIR spectra and wide angle X-ray scattering results. The UV-vis spectrum of the PMDIG-PANI hydrogel exhibits the characteristic peaks of polaron band transitions of the doped PANI. The PMDIG-PANI co-assembled hydrogel has a 51-fold higher storage modulus, a 52-fold higher elasticity, a 1.4-fold increase in stiffness, and a 5-fold increase of fragility compared to the values of the PMDIG hydrogel. The PMDIG-PANI xerogel exhibits a 4 order of magnitude increase in dc conductivity compared to that of PMDIG, and the I-V characteristic curve exhibits a rectification property under white light illumination showing photocurrent rectification, a new phenomenon reported here for the supramolecular gel systems. A dye-sensitized solar cell fabricated with an ITO/PMDIG-PANI/graphite device shows a power conversion efficiency (η) of 0.1%. A discussion of the mechanism of gel formation and the sol state of the PMDIG-aniline system is included considering the contact angle values of the xerogels.

14.
Langmuir ; 30(26): 7833-41, 2014 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-24926619

RESUMO

Herein, we report a new strategy to remove toxic Cr(VI) ion from aqueous solution using metal-organic hybrid gel as sorbent. The gel could be easily synthesized from the commercially available organic ligand 2-mercaptobenzimidazole (2-MBIm) and copper(II) chloride in alcoholic medium. The synthesis involves one-electron reduction of Cu(II) to Cu(I) by 2-MBIm, and then gel formation is triggered through Cu(I)-ligand coordination and extensive hydrogen-bonding interactions involving the "-NH" protons (of 2-MBIm ligand), solvent molecules, and chloride ions. The gel shows entangled network morphology. Different microanalytical techniques (FTIR, powder XRD, FESEM, TEM, rheology etc.) have been employed for complete characterizations of the gel sample. Both Cu(I) (in situ formed) and Cl(-) ions trigger the gel formation as demonstrated from systematic chemical analyses. The gel also exhibits its stimuli-responsive behavior toward different interfering chemical parameters (pH, selective metal ions and anions, selective complexing agents, etc.). Finally the gel shows its redox-responsive nature owing to the distinguished presence of Cu(I) metal centers throughout its structural backbone. And this indeed helps in the effective removal of Cr(VI) ions from aqueous solution. Reduction of Cr(VI) to Cr(III) ions and its subsequent sorption take place in the gel matrix. The reductive removal of Cr(VI) has been quantitatively interpreted through a set of different kinetic measurements/models, and the removal capacity of the gel matrix has been observed to be ∼331 mg g(-1) at pH ∼ 2.7, which is admirably higher than the commonly used adsorbents. However, the capacity decreases with the increase in pH of the solution. The overall removal mechanism has been clearly demonstrated. Again, the gel could also be recycled. Thus, the low-cost and large-scale fabrication of the redox-active metallogel makes it an efficient matrix for the toxic ion removal and hence indicates the high promise of this new generation hybrid material for environmental pollution abatement.


Assuntos
Cromo/química , Cobre/química , Adsorção , Oxirredução , Espectroscopia de Infravermelho com Transformada de Fourier , Poluentes Químicos da Água/química
15.
Soft Matter ; 10(28): 5114-20, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-24910287

RESUMO

An equimolar mixture of riboflavin-5'-phosphate sodium salt (RP) and adenine (AD) dissolved in a phosphate buffer (pH 4.0, 1.0% w/v) produces a red coloured transparent thixotropic hydrogel at 30 °C. The gelation of the RPAD system occurs in the pH range of 2­5. FTIR spectra and WAXS patterns indicate self-assembly via H-bonding between the >C=O group of RP and the amino/imino group of AD followed by supramolecular organization through a π-stacking process producing a fibrillar network structure. FESEM images clearly indicate that the nanofibres are produced from the intertwining of helical fibrils. The dynamic frequency sweep experiment of the supramolecular gel at a constant strain of 1% exhibits a wide linear viscoelastic region and a considerably higher G' value (460 Pa) than that of G'' (21 Pa) confirming the gel nature of the RPAD system. The hydrogel shows high stiffness (G'/G'' = 3.3), a high yield stress (σ*) (79.5 Pa) and a moderate critical strain (γ = 17.5%). Time sweep experiments at both low (0.1%) and high strain (100%) indicate the thixotropic property of the gel. The RPAD hydrogel shows non-Newtonian viscosity in the shear rate region (0.1­158 s(−1)) and after that there is a sudden fall of viscosity. The gel melting point obtained by the falling ball method is 6° higher than that obtained by the DSC method probably due to the presence of the thixotropic property of the gel. The UV-vis spectra indicate a red shift of the π­π* transition band of RP in the RPAD xerogel. On excitation of the RPAD hydrogel at 373 nm it shows twelve times enhancement of emission intensity with a 7 nm red shift of the emission peak. This has been attributed to the enhancement of lifetime from 2.2 ns in RP to 3.4 ns in the RPAD hydrogel. With increase of temperature, the fluorescence intensity of the RPAD hydrogel at first increases till 40 °C, then decreases up to 55 °C and it again increases after 60 °C.


Assuntos
Mononucleotídeo de Flavina/química , Fluorescência , Hidrogéis/química , Adenina/química , Elasticidade , Transição de Fase , Temperatura , Viscosidade
16.
ACS Appl Mater Interfaces ; 6(9): 6308-16, 2014 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-24749894

RESUMO

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

17.
ACS Appl Mater Interfaces ; 6(5): 3615-22, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24495072

RESUMO

Co-assembled folic acid (F) gel with aniline (ANI) (ANI:F = 1:2, w/w) is produced at 2% (w/v) concentration in water/DMSO (1:1, v/v) mixture. The gel is rigid and on polymerization of the gel pieces in aqueous ammonium persulfate solution co-assembled folic acid - polyaniline (F-PANI) gel is formed. Both the co-assembled F-ANI and F-PANI gels have fibrillar network morphology, the fiber diameter and its degree of branching increase significantly from those of F gel. WAXS pattern indicates co-assembled structure with the F fiber at the core and ANI/PANI at its outer surface and the co-assembly is occurring in both F-ANI and F-PANI systems through noncovalent interaction of H-bonding and π stacking processes between the components. FTIR and UV-vis spectra characterize the doped PANI formation and the MALDI mass spectrometry indicates the degree of polymerization of polyaniline in the range 24-653. The rheological experiments support the signature of gel formation in the co-assembled state and the storage (G') and loss (G″) modulii increase in the order F gel< F-ANI gel < F-PANI gel, showing the highest increase in G' ≈ 1100% for the F-PANI gel. The stress at break, elasticity, and stiffness also increase in the same order. The dc-conductivity of F-ANI and F-PANI xerogels is 2 and 7 orders higher than that of F xerogel. Besides, the current (I)-voltage (V) curves indicate that the F-xerogel is insulator, but F-ANI xerogel is semiconductor showing both electronic memory and rectification; on the other hand, the F-PANI xerogel exhibits a negative differential resistance (NDR) property with a NDR ratio of 3.0.


Assuntos
Compostos de Anilina/química , Ácido Fólico/química , Géis/química , Elasticidade , Géis/síntese química , Teste de Materiais , Tamanho da Partícula , Propriedades de Superfície
18.
ACS Appl Mater Interfaces ; 5(23): 12672-80, 2013 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-24245528

RESUMO

A new and facile approach for synthesizing graphene quantum dots (GQDs) using sono-Fenton reaction in an aqueous dispersion of graphene oxide (GO) is reported. The transmission electron microscopy (TEM) micrographs of GQDs indicate its average diameter as ∼5.6 ± 1.4 nm having a lattice parameter of 0.24 nm. GQDs are used to fabricate composites (PG) with a water-soluble polymer, polythiophene-g-poly[(diethylene glycol methyl ether methacrylate)-co-poly(N,N-dimethylaminoethyl methacrylate)] [PT-g-P(MeO2MA-co-DMAEMA), P]. TEM micrographs indicate that both P and PG possess distinct core-shell morphology and the average particle size of P (0.16 ± 0.08 µm) increases in PG (0.95 ± 0.45 µm). Fourier transform infrared and X-ray photoelectron spectrometry spectra suggest an interaction between -OH and -COOH groups of GQDs and -NMe2 groups of P. A decrease of the intensity ratio of Raman D and G bands (ID/IG) is noticed during GQD and PG formation. In contrast to GO, GQDs do not exhibit any absorption peak for its smaller-sized sp(2) domain, and in PG, the π-π* absorption of polythiophene (430 nm) of P disappears. The photoluminescence (PL) peak of GQD shifts from 450 to 580 nm upon a change in excitation from 270 to 540 nm. PL emission of PG at 537 nm is quenched, and it shifts toward lower wavelength (∼430 nm) with increasing aging time for energy transfer from P to GQDs followed by up-converted emission of GQDs. Both P and PG exhibit semiconducting behavior, and PG produces an almost reproducible photocurrent. Dye-sensitized solar cells (DSSCs) fabricated with an indium-titanium oxide/PG/graphite device using the N719 dye exhibit a short-circuit current (Jsc) of 4.36 mA/cm(2), an open-circuit voltage (Voc) of 0.78 V, a fill factor of 0.52, and a power conversion efficiency (PCE, η) of 1.76%. Extending the use of GQDs to fabricate DSSCs with polypyrrole, both Voc and Jsc increase with increasing GQD concentration, showing a maximum PCE of 2.09%. The PG composite exhibits better cell viability than the components.

19.
ACS Appl Mater Interfaces ; 5(12): 5478-85, 2013 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-23725201

RESUMO

A coassembled light-harvesting hydrogel of melamine (M), 6,7-dimethoxy-2,4[1H, 3H]-quinazolinedione (Q) with riboflavin (R), is used to produce a white-light-emitting hydrogel (W-gel) by mixing with the dye rhodamine B (RhB) in a requisite proportion. Addition of R to the Q solution causes both static and dynamic quenching to the emission of Q as evident from the Stern-Volmer plot and the emission of R shows a gradual increase in intensity. On addition of RhB to an aqueous solution of R, fluorescence resonance energy transfer (FRET) occurs, showing an emission peak at 581 nm. In a solution of constant molar ratio of Q and R, addition of RhB causes a quenching of emission of R with no effect on the emission of Q, indicating that the energy transfer takes place only between R and RhB. In the MQR coassembled hydrogel containing RhB, the gel melting temperature is lower than those of MQ and MQR gel, but the storage modulus remains almost unaffected. The oscillatory stress experiment indicates a gradual decrease of critical stress values for breaking of MQ, MQR, and W-gels attributed to the coassembly. In contrast to the solution of Q and R, energy transfer occurs on addition of RhB to the MQ gel. By varying the RhB and R concentration in the 1:1 MQ gel white light emission is observed for the W-gel composition having molar ratio of M:Q:R:RhB = 100:100:0.5:0.02 with the Commission Internationale de L'eclairage (CIE) coordinates of 0.31 and 0.36 for the excitation at 360 nm. However, in the sol state, the CIE coordinates of the hybrid differ significantly from those of the white light.


Assuntos
Hidrogel de Polietilenoglicol-Dimetacrilato/química , Triazinas/química , Fluorescência , Quinazolinonas/química , Reologia , Riboflavina/química , Espectrometria de Fluorescência
20.
Chem Commun (Camb) ; 48(88): 10850-2, 2012 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-23022775

RESUMO

A light harvesting hydrogel, working in a wide range of temperature and pH, of a two component supramolecular complex of melamine and 6,7-dimethoxy-2,4[1H,3H]-quinazolinedione (donor) with riboflavin (acceptor) shows a gradual quenching and red shift of the acceptor emission peak with increase in its concentration through a co-assembly process.


Assuntos
Bismuto/química , Hidrogéis/química , Riboflavina/química , Transferência Ressonante de Energia de Fluorescência , Concentração de Íons de Hidrogênio , Luz , Quinazolinonas/química , Temperatura , Triazinas/química
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