Parimal Routh

Graphene Quantum Dots from a Facile Sono-Fenton Reaction and Its Hybrid with a Polythiophene Graft Copolymer toward Photovoltaic Application

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.

Self-sustaining, fluorescent and semi-conducting co-assembled organogel of Fmoc protected phenylalanine with aromatic amines

N-Flourenylmethoxycarbonyl (Fmoc) phenylalanine (F) produces co-assembled organogel with 2-aminoanthracene (AA) and 2-aminonaphthalene (NA) at a 1 : 1 molar ratio of the components. The deep green co-assembled F-AA gel is rigid and can be cut into different shapes. At lower concentration, 0.2% (w/v), it shows a mixture of fibre and flake morphology, while at 1.5% (w/v) concentration only flake morphology is observed but the F-NA co-assembled gel produces tape morphology. The powder diffraction data of F-AA co-assembled gel indicate π–π stacking and lamellar packing which is supported by DFT calculation. The melting point of F gel is 15 °C higher over F-AA gel but the gel strength and stiffness of the F-AA co-assembled gel is 94 and 2.5 times higher than that of F gel. The F gel shows a smooth gel breaking point at 4 Pa but the F-AA co-assembled gel shows only a slippage at 160 Pa due to its high stiffness. The UV-vis spectra suggest the formation of H-aggregates and a charge transfer complex in the F-AA gel. The emission peak of AA shows a red shift in the F-AA co-assembled gel where both fluorescence intensity and peak position decrease with an increase in temperature. The F-AA xerogel shows semiconducting behaviour with a dc conductivity value 2.3 × 10−8 S cm−1 and the I–V characteristic curves indicate a semiconducting nature with a signature of negative differential resistance.

Polythiophene-g-poly(dimethylaminoethyl methacrylate) stabilized Au nanoparticles and its morphology tuning by RNA with variation of electronic properties

The reducing ability of polythiophene-g-poly(dimethylaminoethyl methacrylate) (P) is used to produce Au nanoparticles (NPs), both in pure P and in different P–RNA (R) hybrids. The Au NPs have different morphologies, depending on the composition of P and R in the PRAu composites. The EDXS spectrum indicates the presence of RNA, P, and Au NPs in the composite. The CD spectra indicate a small distortion in the RNA conformation from A helix towards B helix and the FTIR data indicate the existence of π–π and ionic interactions between P and RNA. The Au plasmon band of the PAu composite shows a gradual red shift with increasing RNA concentration and the photoluminescence (PL) intensity of P decreases in the PAu composites. With increasing RNA concentration in the composite, there is more PL-quenching, and the quenching capacity of RNA is higher than that of DNA (D) and bovine serum albumin (BSA, B). The dc-conductivity of the PAu system is ∼6 times higher than that of P and it increases in the PRAu composites by 1–3 orders of magnitude depending on its composition. In the current–voltage (I–V) curve the PR13 hybrid exhibits rectification properties while the PAu nanocomposite exhibits an interesting feature of symmetric negative differential resistance (NDR). The PRAu31 composite (numbers indicate wt ratio of P and R) shows a small degree of NDR behavior, but the PRAu11 and PRAu13 systems do not show such a property. The rectification and NDR properties of the composites are discussed from the band diagram and the density of the state model, respectively.

Optical and electronic properties of polyaniline sulfonic acid–ribonucleic acid–gold nanobiocomposites

Finely fibrillar polyaniline sulfonic acid (PSA)/ribonucleic acid (RNA) hybrids are developed by wrapping PSA with RNA from a mixture of aqueous PSA (P) and RNA (R) solutions of different compositions. FTIR spectra suggest H-bonding and π-π interactions in the hybrids and dedoping of self doped PSA during hybrid formation. UV-vis spectra exhibit a blue shift of the π-band to polaron band transition of PSA from 870 to 581 nm due to dedoping. The PR hybrids show enhanced PL-properties when excited at 540 nm relative to PSA which also exhibits rectification behavior in current (I)-voltage (V) curves. Gold nanoparticles (Au NPs) grown on these PR hybrids by the reduction of Au(3+) by PSA show different morphologies with varying composition. FTIR spectra of the nanobiocomposites indicate that Au NPs are stabilized by the co-ordination of the nitrogen atoms of -N=Q=N- bonds of PSA (Q = quinonoid ring). The intensity of the Au plasmon band gradually decreases with time but the PL-intensities of the PAu/PRAu nanocomposites increase with time. The PL-intensity of the nanocomposites is higher than that of PSA and PR hybrids. The DC-conductivity of the PR hybrids increases by an order of magnitude on addition of Au NPs. I-V curves of the nanobiocomposites show negative differential resistance (NDR) in PSA rich systems with a stable NDR ratio of 7 in the PRAu21 and PRAu11 hybrids. Possible reasons from the accumulation of charges on the Au NPs and its stabilization through the π-clouds of RNA bases are discussed. The PRAu11 system also exhibits rectification properties with a rectification ratio of 14.

Enhanced optoelectronic properties of RNA-poly(o-methoxyaniline) hybrid containing monodispersed Au nanoparticles

In situ, gold nanoparticles are produced in poly(o-methoxy aniline) (POMA)–RNA (R) hybrids; POMA (P) acting both as reductant and stabilizer. The POMA (emeraldine base, EB) is oxidized into a mixture of POMA (emeraldine salt, ES) and POMA (pernigraniline base, PB) in the course of reaction as evident from FTIR and UV-vis spectra. The Au nanoparticles are of uniform size (diameter ∼ 14 nm) and the density of Au nanoparticles increases with increase in POMA (EB) concentration showing a maximum of 150 × 1010 particles per square centimetre in PRAu31 (the number indicates respective weight ratio). The electron diffraction pattern indicates the polycrystalline nature of the Au nanoparticles and CD spectra suggest a small conformational distortion of the A helix of RNA towards the B helix in the nanobiocomposite. The FTIR spectra indicate the presence of H-bonding, π–π and ionic interactions between POMA (ES) and RNA, and the Au nanoparticles are stabilized by complexation through nitrogen atoms of POMA (PB). The π band to polaron band transition peak of POMA shows a gradual red shift with aging time and the shift is greater in the case of POMA–RNA–Au nanobiocomposites than that of the POMA–RNA hybrid. The larger shift in the PRAu nanocomposites compared to the POMA–RNA hybrid is attributed to the more uncoiled state of POMA for stabilizing Au nanoparticles. The POMA–Au system generates new photoluminescence properties when excited at 500 nm and PL intensity increases abruptly with the addition of RNA in the hybrid. The excitation of plasmon electrons and the stabilization of excitons in the conjugated chain of POMA is attributed to the new PL property and its enhancement with addition of RNA is due to the increased conjugation length of POMA on the RNA surface. PRAu13 shows rectification property, while the other compositions do not exhibit such behavior. The rectification is explained from the band energy diagram, and its absence in PRAu11 and PRAu31 hybrids is attributed to the increased concentrations of Au and POMA causing a better conducting composite material.

Self assembly of poly(o-methoxy aniline) with RNA and RNA/DNA hybrids: Physical properties and conformational change of poly(o-methoxy aniline)

Biomolecular hybrids of a conducting polymer [poly(o-methoxy aniline) (POMA)] and RNA are prepared at the three different compositions by mixing aqueous solutions of diethyl, 2-hydroxy ethyl, ammonium salt of RNA (type IX from Torula Yeast) and POMA (ES, emeraldine salt; doping level [Cl]/[N]=0.52). A slow increase of pH up to 30 h of aging occurs in the mixture till it levels up. The TEM micrographs indicate a fibrillar network structure in all the hybrid compositions (POMA: RNA=1:3, 1:1, 3:1, by weight). In the complexes three types of supramolecular interactions, viz. (i) electrostatic, (ii) H-bonding and (iii) pi-pi interactions, are evident from the FTIR spectroscopy. The CD spectra indicate a small distortion of A-RNA conformation towards its B form during the hybrid formation. Time and temperature dependent UV-vis spectral studies indicate a slow red shift of the pi-band to polaron band transition peak (lambda(max)) for the uncoiling of the POMA (P) chain on the RNA (R) surface. The repulsive interaction between the radical cations of POMA (ES) absorbed on the RNA surface is attributed to the conformational change causing the uncoiling of POMA chain. UV-vis spectral study indicates that the uncoiling and attachment of POMA on RNA surface is much faster than that on DNA (D). In POMA-RNA-DNA (PRD) hybrid solutions slower red shift of lambda(max) indicates more disordered array of the phosphate groups than that in PR and PD systems. The conductivity values of the PR hybrids (10(-)(6) S/cm(-1)) are three orders higher than that of RNA, rendering the PR hybrids to be useful for fabricating good biosensors. In the PRD hybrids conductivity decreases by two orders than those of PR and PD hybrids suggesting a disorder arrangement of POMA chains in the PRD hybrids. The I-V characteristic curves of the PR and PRD hybrids indicate a semiconducting nature of the hybrids.

Quantum Dots Intermediated Novel Synthesis of Dual Oxides of Molybdenum from MoS2: Quantification of Supercapacitor Efficacy

The versatile technological applications of molybdenum oxides requires the efficient synthesis of various stoichiometric molybdenum oxides. Thus, herein, a controlled method to synthesize both MoO3 and MoO2 from MoS2 via quantum dot intermediates is reported. Microscopic, spectroscopic, and X-ray studies corroborate the formation of orthorhombic α-MoO3 with a microbelt structure and monoclinic MoO2 nanoparticles that self-assemble into hollow tubes. Quantitative investigations into charge-storage kinetics reveal that MoO2 exhibits an excellent pseudocapacitive response up to a mass loading of 5 mg cm-2 with an areal capacity of 327.2 mC cm-2 at 5 mV s-1 , with 41.9 % retention at 100 mV s-1 . In contrast, above a mass loading of 0.5 mg cm-2 , the charge-storage nature of MoO3 electrodes switches from that of a supercapacitor to battery type. At a sweep rate of 50 mV s-1 , 87.2 % of the total charge is contributed by a capacitive response in a 1 mg cm-2 MoO2 electrode. The charge-storage kinetics of MoO3 and MoO2 reflect on the respective asymmetric supercapacitors. A MoO2 //graphite asymmetric supercapacitor holds an outstanding energy density of 341 mW h m-2 at a power density of 4949 mW m-2 and delivers an ultrahigh power density of 28140 mW m-2 with an energy density 142 mW h m-2 and energy efficiency of 87 %.