Amrita Chakravarty

Cu2O Nanoparticles Anchored on Amine-Functionalized Graphite Nanosheet: A Potential Reusable Catalyst

Synthesis of Cu2O-amine-functionalized graphite nanosheet (AFGNS) composite has been accomplished at room temperature. In the first step, AFGNS is synthesized by wet chemical functionalization where the -NH2 groups formed on nanosheet surface help to anchor the Cu(2+) ions homogeneously through coordinate bonds. Reduction of Cu(2+) (3.4 × 10(-2) mmol) in the presence of NaBH4 (1.8 mmol) can be restricted to Cu(1+) on AFGNS surface at room temperature. This leads to the formation of uniform Cu2O nanoparticles (NP) on AFGNS. The role played by the -NH2 groups in anchoring Cu(2+) ions and followed by stabilizing the Cu2O NP on AFGNS was understood by controlled reactions in the absence of -NH2 groups and without any graphitic support, respectively. The prepared Cu2O-AFGNS composite shows excellent catalytic activity toward degradation of an azo dye, methyl orange, which is an environmental pollutant. The dye degradation proceeds with high rate constant value, and the composite shows high stability and excellent reuse capability.

Synthesis of amine functionalized graphite nanosheets and their water-soluble derivative for drug loading and controlled release†

A facile route to synthesize amine (–NH2) functionalized graphite nanosheets (AFGNS) by 2-step controlled chemical modification of microcrystalline graphite is described. The method begins with nitration by mixed acid (HNO3 : H2SO4 in 1 : 1 v/v ratio), followed by reduction with Na2S to form AFGNS. The AFGNS was reacted with carboxylic acid-terminated polyethylene glycol (PEG) chains (MeO–mPEG–COOH, MW = 5000 Da) in the presence of a carbodiimide coupling agent to obtain a water-soluble PEGylated AFGNS (P-AFGNS) composite. Anticancer drug doxorubicin (DOX) was loaded on this composite with a loading capacity of 0.296 mg mg−1 for an initial concentration of 0.232 mg mL−1 DOX and 0.136 mg mL−1 of P-AFGNS and the release of DOX from this water-soluble DOX loaded P-AFGNS composite at two different temperatures was found to be strongly pH dependent.

Carbon nanodot–ORMOSIL fluorescent paint and films

Controlled carbonisation of P123 block-co-polymer in ethanol yielded micelle-protected carbon nanodots (CNDs) at room temperature. A purified and concentrated CND solution (quantum yield 10%) was incorporated into the organically-modified SiO2 (ORMOSIL) sol for the fabrication of transparent fluorescent coatings of thickness ∼3 μm on glass. These films are scratch resistant with a surface hardness value of 8H. The sol can also be useful as a fluorescent ink/paint. The films retained the pristine photophysical properties of CNDs.

MnO2 nanowires anchored on amine functionalized graphite nanosheets: highly active and reusable catalyst for organic oxidation reactions

A facile method of synthesizing MnO2 nanowires on amine functionalized graphite nanosheet (AFGNS) has been accomplished. A probable mechanism has been proposed where the –NH2 groups on the AFGNS surface create a weakly basic environment assisting the reduction of KMnO4 to MnO2 nanoparticles followed by their anchoring and oriented growth to form MnO2 nanowires. The as prepared MnO2@AFGNS composite has been efficiently used as a selective heterogeneous catalyst for oxidation of primary and secondary benzyl alcohols to corresponding carbonyl compounds under aerobic condition in high yields in the absence of any other oxidizing or activating agent. While MnO2 is considered as the most efficient and selective catalyst for the oxidation of benzyl and allyl alcohols, its large excess use (200 mol% with respect to the substrate) has been circumvented in this work by using heterogeneous AFGNS supported MnO2 (only 7 mol% with respect to the substrate). The synergistic effect between the 1-D MnO2 nanowires and AFGNS facilitates very fast e− transfer enabling such huge enhancement of the catalytic activity of the MnO2@AFGNS composite. The composite also shows sufficient reuse capability and stability after 3 cycles of catalysis thus making it a potentially cheap and active catalyst in the field of organic catalysis.

Enrichment of Metallic Single-Walled Carbon Nanotubes with Simultaneous Purification by Nitric Acid Treatment

Controlled treatment of pristine single-walled carbon nanotubes (SWCNT) with HNO3 (11 M) for 20 hours at 50°C with subsequent repeated cycles of washing, centrifugation and ultrasonication in aqueous media have shown enrichment of the product with pure and debundled nanotubes of metallic variety. On the other hand, no such enrichment was observed when the tubes were treated with a mixture of concentrated nitric acid and sulfuric acid. The electrical varieties of the tubes were ascertained from the analysis of Raman and UV-Vis spectra and dc-resistivities. The purity of the product was gauged from transmission electron microscope images, energy dispersive spectra, thermogravimetric analysis and Raman spectra. A mechanism involving preferential attack of NO3− on the semiconducting tubes under the condition of the adopted protocol has been proposed from the comparison of the results after the treatment of the same pristine SWCNT with mixed acid (conc. HNO3 and H2SO4).

Carboxylic acid terminated, solution exfoliated graphite by organic acylation and its application in drug delivery

AbstractGraphite nanosheets are considered as a promising material for a range of applications from flexible electronics to functional nanodevices such as biosensors, intelligent coatings and drug delivery. Chemical functionalization of graphite nanosheets with organic/inorganic materials offers an alternative approach to control the electronic properties of graphene, which is a zero band gap semiconductor in pristine form. In this paper, we report the aromatic electrophilic substitution of solution exfoliated graphite nanosheets (SEGn). The highly conjugated π-electronic system of graphite nanosheets enable it to have an amphiphilic characteristic in aromatic substitution reactions. The substitution was achieved through Friedel–Crafts (FC) acylation reaction under mild conditions using succinic anhydride as acylating agent and anhydrous aluminum chloride as Lewis acid. Such reaction renders towards the carboxylic acid terminated graphite nanosheets (SEGn–FC) that usually requires harsh reaction conditions. The product thus obtained was characterized using various spectroscopic and microscopic techniques. Highly stable water-dispersed sodium salt of carboxylic acid terminated graphite nanosheets (SEGn–FC-Na) was also prepared. A comparative sheet-resistance measurements of SEGn, SEGn–FC and SEGn–FC-Na were also done. Finally, the anticancer drug doxorubicin (DOX) was loaded on water dispersible SEGn–FC-Na with a loading capacity of 0.266 mg mg−1 of SEGn–FC-Na and the release of DOX from this water-soluble DOX-loaded SEGn–FC-Na at two different temperatures was found to be strongly pH dependent. Graphical AbstractSelective carboxylic acid terminated solution exfoliated graphite nanosheets were achieved through Friedel–Crafts acylation reaction and dispersed in water by making Na-salt of the same. Anticancer drug doxorubicin was successfully loaded onto this highly water dispersible Na-salt and the drug release was found to be pH dependant. The low cost and efficient drug release make it a potential carrier for targeted drug delivery.