No abstract

Functionalized graphene oxide quantum dots (GOQDs)-poly(vinyl alcohol) (PVA) hybrid hydrogels were prepared using a simple, facile and cost-effective strategy. GOQDs bearing different surface functional groups were introduced as the cross-linking agent into the PVA matrix thereby resulting in gelation. The four different types of hybrid hydrogels were prepared using graphene oxide, reduced graphene oxide, ester functionalized graphene oxide and amine functionalized GOQDs as cross-linking agents. It was observed that the hybrid hydrogel prepared with amine functionalized GOQDs was the most stable. The potential applicability of using this solid sensing platform has been subsequently explored in an easy, simple, effective and sensitive method for optical detection of M(2+) (Fe(2+), Co(2+) and Cu(2+)) in aqueous media involving colorimetric detection. Amine functionalized GOQDs-PVA hybrid hydrogel when put into the corresponding solution of Fe(2+), Co(2+) and Cu(2+) renders brown, orange and blue coloration respectively of the solution detecting the presence of Fe(2+), Co(2+) and Cu(2+) ions in the solution. The minimum detection limit observed was 1 × 10(-7) M using UV-visible spectroscopy. Further, the applicability of the sensing material was also tested for a mixture of co-existing ions in solution to demonstrate the practical applicability of the system. Insight into the probable mechanistic pathway involved in the detection process is also being discussed.

We demonstrate carbon dot based sensor of catecholamine, namely, dopamine and ascorbic acid. Carbon dots (CDs) were prepared from a green source: commercially available Assam tea. The carbon dots prepared from tea had particle sizes of ∼0.8 nm and are fluorescent. Fluorescence of the carbon dots was found to be quenched in the presence of dopamine and ascorbic acid with greater sensitivity for dopamine. The minimum detectable limits were determined to be 33 μM and 98 μM for dopamine and ascorbic acid, respectively. The quenching constants determined from Stern-Volmer plot were determined to be 5 × 10−4 and 1 × 10−4 for dopamine and ascorbic acid, respectively. A probable mechanism of quenching has been discussed in the paper.

The present study reports a facile and green method for reduction of graphene oxide using carbon dots (CDs) derived from “Assam CTC (crush tear curl) Tea”. The efficient reduction of graphene oxide by tea-CDs was monitored using UV–visible spectroscopy. The reduced graphene oxide (rGO) prepared by this method adsorbs some amount of tea-CDs on its surface and forms a very good dispersion in aqueous medium without the use of any other capping or stabilizing agents. Subsequently, the tea-CDs reduced graphene oxide (TCD-rGO) was used for fabrication of a cotton-based conducting fabric with anticipated applicability in different electronic gadgets where high flexibility of the conducting material is required. Coating of cotton with TCD-rGO improved the thermostability of the fabric. The initial degradation temperature for the TCD-rGO coated fabric was found to increase by 30 °C compared to that of the bare cotton fabric. The electrical property of the coated fabric was evaluated. TCD-rGO coated fabric possessed a sheet resistance of 229 ± 20 Ω/sq and electrical conductivity 623 ± 54 S/m, which was comparable to that of the other graphitic conducting textile materials reported so far. The ohmic behavior and the electrical stability of the material was also studied. This particular approach eliminates the use of any toxic chemicals and other high cost synthetic products for fabrication of conducting textiles. Finally, to test the practical viability of the material developed, a stripe from the fabricated conducting fabric was used in a circuit to light up a series of light-emitting diode bulbs.

We demonstrate a simple, facile, and reversible on/off fluorescence switching by functionalization of carbon dots (CDs) via esterification. The CDs synthesized from citric acid show pH-dependent photoluminescence (PL), with higher PL intensity observed at pH 7 than at pH 1. The hydroxyl and carboxyl group-bearing CDs were also esterified with different alcohols, and their PL properties were studied. It is interesting to note that in all the cases, low PL intensity of CDs at pH 1 can be transformed into a high PL system by esterification of CDs. However, at neutral pH 7, the PL intensity was found to be lower after esterification of CDs. Moreover, at pH 1, the subsequent hydrolysis of esterified CDs again results in low PL intensity, thereby demonstrating the reversibility of the process.