Arjyabaran Sinha

Synthesis of silver–graphene nanocomposite and its catalytic application for the one-pot three-component coupling reaction and one-pot synthesis of 1,4-disubstituted 1,2,3-triazoles in water

A graphene based composite with silver nanoparticles has been synthesized via a simple chemical route and its catalytic activity has been tested for multi-component reactions and click reaction in a one-pot approach. This silver–graphene nanocomposite shows excellent catalytic activity at room temperature for three-component couplings between aldehydes, alkynes and amines (A3-coupling) and one-pot synthesis of 1,4-disubstituted 1,2,3-triazole via click reaction between in situ generated azides (derived from anilines or amines) and terminal acetylenes. This solid silver–graphene catalyst has been characterized by TEM, Raman, XRD and UV-Visible absorption spectra. The developed catalyst is air-stable, inexpensive, easy to prepare and can be facilely recovered and reused five times without significant decrease in activity and selectivity.

Enhanced catalytic performance by copper nanoparticle–graphene based composite

A graphene based composite with copper nanoparticles (Cu–G) has been synthesized and used as catalyst for N-arylation and O-arylation. The structure and composition of the nanocomposite have been characterized by TEM, AFM, Raman and XPS. The catalytic activity of the Cu–G has been tested for the N-arylation of N–H heterocycles using arylboronic acids and the O-arylation of phenols using aryl halides. The catalytic N-arylation produces N-aryl heterocyles and the catalytic O-arylation produces diaryl ethers, under mild reaction conditions with excellent yields and selectivities. The developed catalyst is air-stable, inexpensive, easy to prepare, easy to recover by simple filtration and can be reused without appreciable loss of activity.

Functional, mesoporous, superparamagnetic colloidal sorbents for efficient removal of toxic metals

γ-Fe(2)O(3) incorporated mesoporous silica particles of 50-100 nm size have been synthesized which are functionalized with chelating agents of metal ions. These particles are water dispersible but aggregate in response to the external magnetic field and have been used for high performance and selective removal of Cd, Pb, Hg and As.

Dextran-gated, multifunctional mesoporous nanoparticle for glucose-responsive and targeted drug delivery.

Design of drug delivery nanocarrier having targeted recognition followed by bioresponsive controlled release, especially via glucose-responsive release, is a challenging issue. Here, we report magnetic mesoporous silica (MMS)-based drug delivery nanocarrier that can target specific cell and release drug via glucose-responsive gate. The design involves synthesis of MMS functionalized with phenylboronic acid and folate. After drug loading inside the pores of MMS, outside of the pores are closed by dextran via binding with phenylboronic acid. Dextran-gated pores are opened for drug release in the presence of glucose that competes binding with phenylboronic acid. We found that tolbutamide and camptothecin loaded MMS can target beta cells and cancer cells, respectively, release drugs depending on bulk glucose concentration and offers glucose concentration dependent cytotoxicity. Developed functional MMS can be used for advanced drug delivery applications for diabetes and cancers with more efficient therapy.

β-Cyclodextrin Functionalized Magnetic Mesoporous Silica Colloid for Cholesterol Separation

Although cholesterol plays significant biochemical function in the human body, excess of it leads to various disorders, and thus, its control/separation is important in medical science and food industries. However, efficient and selective separation of cholesterol is challenging because cholesterol often exists in microheterogeneous or insoluble forms in remote organ and exists with other chemicals/biochemicals. Here, we have described a colloidal magnetic mesoporous silica (MMS)-based approach for efficient separation of cholesterol in different forms. MMS is functionalized with β-cyclodextrin for selective binding with cholesterol via host-guest interaction. The colloidal form of MMS offers effective interaction with cholesterol of any form, and magnetic property of MMS offers easier separation of bound cholesterol. Functionalized MMS is efficient in separating cholesterol crystals, water-insoluble cholesterol, and the microheterogeneous form of cholesterol from milk or a cellular environment. Developed material can be used to remove cholesterol from a complex bioenvironment and extended for large-scale cholesterol separation from food.

Graphene-based composite with γ-Fe2O3 nanoparticle for the high-performance removal of endocrine-disrupting compounds from water.

Graphene is a 2D sp(2)-hybridized carbon sheet and an ideal material for the adsorption-based separation of organic pollutants. However, such potential applications of graphene are largely limited, owing to their poor solubility and extensive aggregation properties through graphene-graphene interactions. Herein, we report the synthesis of graphene-based composites with γ-Fe2O3 nanoparticle for the high-performance removal of endocrine-disrupting compounds (EDC) from water. The γ-Fe2O3 nanoparticles partially inhibit these graphene-graphene interactions and offer water dispersibility of the composite without compromising much of the high surface area of graphene. In their dispersed form, the graphene component offers the efficient adsorption of EDC, whilst the magnetic iron-oxide component offers easier magnetic separation of adsorbed EDC.

Separation of Microcystin-LR by Cyclodextrin-Functionalized Magnetic Composite of Colloidal Graphene and Porous Silica

Microcystin-LR belongs to the family of microcystins produced by cyanobacteria and known to be the most toxic of this family. Existence of cyanobacteria in water bodies leads to the contamination of drinking water with microcystin-LR and thus their separation is essential for an advanced water purification system. Here we report functional nanocomposite-based selective separation of microcystin-LR from contaminated water. We have synthesized cyclodextrin-functionalized magnetic composite of colloidal graphene and porous silica where the cyclodextrin component offers host-guest interaction with microcystin-LR and the magnetic component offers easier separation of microcystin-LR from water. High surface area and large extent of chemical functional groups offer high loading (up to 18 wt %) of cyclodextrin with these nanocomposites, and the dispersible form of the nanocomposite offers easier accessibility of cyclodextrin to microcystin-LR. We have shown that microcystin-LR separation efficiency is significantly enhanced after functionalization with cyclodextrin, and among all the tested cyclodextrins, γ-cyclodextrin offers the best performance. We have also found that graphene-based nanocomposite offers better performance over porous silica-based nanocomposite due to better accessibility of cyclodextrins for interaction with microcystin-LR. The proposed graphene-based functional nanocomposite is environment friendly, reusable, and applicable for advanced water purification.

Tunable Catalytic Performance and Selectivity of a Nanoparticle–Graphene Composite through Finely Controlled Nanoparticle Loading

Graphene-based composites offer enhanced catalytic performance of metal and semiconductor nanoparticles, but their development is challenging because catalytic performance strongly depends on the structure and composition of the composite. Herein we show that the catalytic performance of a nanoparticle-graphene composite is very dependent on catalyst loading, which can be optimized for simultaneous enhancement of activity and selectivity. A glassy carbon working electrode has been modified with a gold nanoparticle-graphene (Au-G) composite with a varied number of gold nanoparticles per graphene, so that the conducting property of graphene and the electrocatalytic property of the metal were effectively coupled to give the best catalytic activity and selectivity. The modified electrode was used for simultaneous electrochemical detection of a mixture of electroactive species with high sensitivity. This result shows that the catalytic performance of a graphene-based composite is sensitive to the catalyst loading and should be optimized for the best performance.

Efficient and reusable graphene-γ-Fe2O3 magnetic nano-composite for selective oxidation and one-pot synthesis of 1,2,3-triazole using a green solvent

A graphene based composite material with γ-Fe2O3 nanoparticles has been synthesized via a simple chemical route. The structure and composition of nanocomposite material have been characterized by TEM, Raman and XRD. The catalytic activity of the composite has been investigated for the oxidation reactions of sulfides and aromatic alcohols using water as the solvent. Sulfides and aromatic alcohols have been selectively oxidized to corresponding sulfoxides and aldehydes, respectively, with excellent yields. In addition this nanocomposite also serves as an efficient catalyst for one-pot synthesis of a series of 1,4-disubstituted-1,2,3-triazoles via click chemistry. The catalyst could be easily isolated from the final product by magnetic decantation (applying an external magnetic field) and can be reused without significant loss of catalytic activity.