Chhavi Sharma

Selective electrochemical sensing for arsenite using rGO/Fe3O4 nanocomposites.

Herein, we report rGO/Fe3O4 nanocomposites (NCs) free from noble metals, synthesized by facile one step chemical reduction method, for electrochemical detection of arsenite in water by square wave anodic stripping Voltammetry (SWASV). The synthesized NCs were characterized for its optical, morphological and structural properties. The NCs modified glassy carbon (GCE), NCs/GCE, electrodes showed a higher sensitivity (0.281μA/ppb) and lower LOD (0.12ppb) under optimized experimental conditions. The proposed NCs/GCE electrodes show no interference towards arsenite species in the presence of common cationic interferants, namely, Cu(II), Pb(II), Ni(II), Co(II), Cd(II), Cr(II), Zn(II), etc. In addition, the proposed electrode demonstrates a good stability, reproducibility and potential practical application in electrochemical detection of arsenite.

Synthesis and comparative charge transfer studies in porphyrin–fullerene dyads: mode of attachment effect

Fullerene–porphyrin dyad system has gained increasing interest because of not only their interesting optoelectronic properties but also their applications in single-material organic solar cells. In the present work, two non-metallated fullerene–porphyrin dyads are prepared, viz, H2P1-C60 (dyad I) and H2P2-C60 (dyad II), where the modes of attachment on fullerene are different, i.e. via 1,3-dipolar cyclopropanation reaction in dyad I and Prato reaction in dyad II. We compare the photophysical and thermally activated conducting properties of these two non-metallated dyads in solution as well as in film to establish the better mode of attachment for dyad preparation with exotic properties. Both the dyads are structurally characterized by FT-IR, NMR and HRMS. Photophysical studies reveal that for dyad II, the reaction rate of charge separation is much higher than for dyad I (0.62 × 109 s−1vs. 0.32 × 109 s−1) in nonpolar solvent. Moreover, dyad II shows higher quenching of porphyrin emission than dyad I (90% vs. 70%) due to faster deactivation of singlet excited state by photoinduced charge transfer between porphyrin and fullerene. The reaction rate for charge transfer (kET(CS)) for dyad II is found to be maximum with lowest activation energy value as compared to dyad I. Excited-state electronic interactions in solution as well as in film have been studied by transient absorption spectroscopy to identify charge separated states. Finally, both the dyads are tested for their thermally activated electrical conductivity where dyad II shows an increase in conductivity with increase in temperature, which is reversible. Thus, dyad II is found to be an excellent material with interesting photophysical and electronic properties that can be beneficial in various applications such as organic solar cells and sensors.

Luminescent GdVO4:Sm3+ quantum dots enhance power conversion efficiency of bulk heterojunction polymer solar cells by Förster resonance energy transfer

In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Forster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO4:Sm3+) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO4:Sm3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO4:Sm3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO4:Sm3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO4:Sm3+:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO4:Sm3+:PC71BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC71BM. This work demonstrates the potential of rare-earth based ...

Revealing charge carrier dynamics in squaraine:[6, 6]-phenyl-C 71-butyric acid methyl ester based organic solar cells

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex ...

Comparative performance of some pear cultivars on southern aspect of wet temperate zone in Western Himalaya

The studies were conducted at experimental farm of Temperate Horticultural Research Station, Kotkhai to compare the performance of 12 pear cultivars for their fruit quality and leaf nutritional status. Various cultivars under study differed significantly with respect to their fruit physico-chemical characteristics and leaf nutrient contents. Cultivar Red Bartlett had highest fruit length (82.37 mm, whereas, fruit diameter (76.65 mm) and fruit weight (193.50 g) were recorded significantly higher in cultivar Max Red Bartlett. Cultivar Starking Delicious exhibited highest total soluble solids (16.05°Brix), TSS/acid ratio (66.27) and minimum titratable acidity (0.28%). The highest fruit firmness (15.40 lbs/inch2) was recorded in cv. Beurre Hardy, whereas significantly higher total sugars content (5.95%) and reducing sugars content (5.03) were registered by Doyenne du Comice and Kala Hathi, respectively. The cultivars Aval Number, Max Red Bartlett and Flemish Beauty exhibited highest leaf nitrogen (2.31%), phosphorus (0.212%) and potassium (1.96%) contents, respectively. On the basis of fruit physicochemical characteristics, Red Bartlett, Max Red Bartlett, Starking Delicious, Doyenne du Comice and Beurre Hardy were found suitable for cultivation in zone III of Himachal Pradesh.