Biplab Banerjee

CO2 fixation at atmospheric pressure: porous ZnSnO3 nanocrystals as a highly efficient catalyst for the synthesis of cyclic carbonates

An efficient methodology for the synthesis of cyclic carbonates from epoxides and CO2 has been developed using self-assembled, ultra small, porous zinc stannate nanocrystals as a catalyst under atmospheric pressure. The catalyst is synthesized by using sodium salicylate as a soft template and the material is thoroughly characterized by powder XRD, HR TEM, N2-sorption and UV-visible spectroscopic tools. Moreover, the catalyst smoothly catalyzes a wide range of reactants to produce a series of cyclic carbonates in excellent yields, under atmospheric pressure of CO2 and in the presence of PEG-600 as a green solvent. The catalyst can be easily recovered from the reaction medium and be reused without significant loss in its catalytic activity and selectivity, suggesting the future potential of this nanocatalyst in the clean-up of the environment.

Silver nanoparticles embedded over porous metal organic frameworks for carbon dioxide fixation via carboxylation of terminal alkynes at ambient pressure.

Ag nanoparticles (NPs) has been supported over a porous Co(II)-salicylate metal-organic framework to yield a new nanocatalyst AgNPs/Co-MOF and it has been thoroughly characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), energy dispersive X-ray spectrometry (EDX), high-resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflection spectroscopy (DRS) and N2 adsorption/desorption analysis. The AgNPs/Co-MOF material showed high catalytic activity in the carboxylation of terminal alkynes via CO2 fixation reaction to yield alkynyl carboxylic acids under very mild conditions. Due to the presence of highly reactive AgNPs bound at the porous MOF framework the reaction proceeded smoothly at 1atm CO2 pressure. Moreover, the catalyst is very convenient to handle and it can be reused for several reaction cycles without appreciable loss of catalytic activity in this CO2 fixation reaction, which suggested a promising future of AgNPs/Co-MOF nanocatalyst.

Cu(II) anchored nitrogen-rich covalent imine network (CuII-CIN-1): an efficient and recyclable heterogeneous catalyst for the synthesis of organoselenides from aryl boronic acids in a green solvent

A new heterogeneous copper catalyst has been synthesized by immobilizing Cu(II) onto the surface of a nitrogen rich porous covalent imine network material CIN-1 and it was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), EDAX, X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TGA), and EPR spectroscopic analyses. The material has been successfully used to catalyze the cross-coupling reaction between aryl boronic acids and diphenyldiselenide to synthesize unsymmetrical organoselenides. Due to its high surface area and highly accessible catalytic sites, it shows good to excellent catalytic activity for the C–Se bond forming reaction, which was evident from the high TOF of the catalyst in this reaction. The catalyst was recycled for six repetitive runs without any appreciable loss of catalytic activity suggesting its potential usefulness in C–Se bond forming reaction.

Faceted Titania Nanocrystals Doped with Indium Oxide Nanoclusters As a Superior Candidate for Sacrificial Hydrogen Evolution without Any Noble-Metal Cocatalyst under Solar Irradiation

Development of unique nanoheterostructures consisting of indium oxide nanoclusters like species doped on the TiO2 nanocrystals surfaces with {101} and {001} exposed facets, resulted in unprecedented sacrificial hydrogen production (5.3 mmol h(-1) g(-1)) from water using methanol as a sacrificial agent, under visible light LED source and AM 1.5G solar simulator (10.3 mmol h(-1) g(-1)), which is the highest H2 production rate ever reported for titania based photocatalysts, without using any noble metal cocatalyst. X-ray photoelectron spectroscopy (XPS) analysis of the nanostructures reveals the presence of Ti-O-In and In-O-In like species on the surface of nanostructures. Electron energy-loss spectroscopy (EELS) elemental mapping and EDX spectroscopy techniques combined with transmission electron microscope evidenced the existence of nanoheterostructures. XPS, EELS, EDX, and HAADF-STEM tools collectively suggest the presence of indium oxide nanoclusters like species on the surface of TiO2 nanostructures. These indium oxide nanocluster doped TiO2 (In2O3/T{001}) single crystals with {101} and {001} exposed facets exhibited 1.3 times higher visible light photocatalytic H2 production than indium oxide nanocluster doped TiO2 nanocrystals with only {101}facets (In2O3/T{101}) exposed. The remarkable photocatalytic activity of the obtained nanoheterostructures is attributed to the combined synergetic effect of indium oxide nanoclusters interacting with the titania surface, enhanced visible light response, high crystallinity, and unique structural features.

Towards rational design of core–shell catalytic nanoreactor with high performance catalytic hydrogenation of levulinic acid

We have described herein the synthesis and characterization of a uniquely designed mesoporous silica shell@Pd nanoparticle tethered amine functionalized silica core catalyst and its catalytic properties in the hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone, using formic acid as a sustainable H2 source. Monodispersed silica core particles (∼300 nm in diameter) were prepared and further functionalized by amine groups and then the in situ loading of Pd nanoparticles was carried out. Pd0-NPs are sandwiched between the nonporous silica core and the mesoporous silica shell, leading to the exceptional stability of the catalyst. The nanostructured material was thoroughly characterised by means of powder XRD patterns, N2 sorption, FE-SEM, UHR-TEM, TG-DTA, and XPS analysis. Our core–shell nanostructure catalyst encapsulated with Pd nanoparticles exhibited a significant increase in catalytic activity and excellent selectivity towards γ-valerolactone (99%) compared with control catalysts for levulinic acid hydrogenation, including Pd@C and Pd@SiO2 (without a mesoporous SiO2 shell). Our results suggest that the core–shell silica based nanocatalyst offers tremendous recyclability (up to the 10th catalytic run with consistent conversion and selectivity of γ-valerolactone), stability (no leaching of Pd and structure collapsing) and no sign of deactivation.

Tailored Synthesis of Porous TiO2 Nanocubes and Nanoparallelepipeds with Exposed {111} Facets and Mesoscopic Void Space: A Superior Candidate for Efficient Dye-Sensitized Solar Cells

Anatase TiO2 nanocubes and nanoparallelepipeds, with highly reactive {111} facets exposed, were developed for the first time through a modified one pot hydrothermal method, through the hydrolysis of tetrabutyltitanate in the presence of oleylamine as the morphology-controlling capping-agent and using ammonia/hydrofluoric acid for stabilizing the {111} faceted surfaces. These nanocubes/nanoparallelepipeds were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and high angle annular dark-field scanning TEM (HAADF-STEM). Accordingly, a possible growth mechanism for the nanostructures is elucidated. The morphology, surface area and the pore size distribution of the TiO2 nanostructures can be tuned simply by altering the HF and ammonia dosage in the precursor solution. More importantly, optimization of the reaction system leads to the assembly of highly crystalline, high surface area, {111} faceted anatase TiO2 nanocubes/nanoparallelepipeds to form uniform mesoscopic void space. We report the development of a novel double layered photoanode for dye sensitized solar cells (DSSCs) made of highly crystalline, self-assembled faceted TiO2 nanocrystals as upper layer and commercial titania nanoparticles paste as under layer. The bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as upper layer shows a much higher power conversion efficiency (9.60%), than DSSCs fabricated with commercial (P25) titania powder (4.67%) or with anatase TiO2 nanostructures having exposed {101} facets (7.59%) as the upper layer. The improved performance in bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as the upper layer is attributed to high dye adsorption and fast electron transport dynamics owing to the unique structural features of the {111} facets in TiO2. Electrochemical impedance spectroscopy (EIS) measurements conducted on the cells supported these conclusions, which showed that the bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as the upper layer possessed lower charge transfer resistance, higher electron recombination resistance, longer electron lifetime and higher collector efficiency characteristics, compared to DSSCs fabricated with commercial (P25) titania powder or with anatase TiO2 nanostructures having exposed {101} facets as the upper layer.

Cubic Ag2O nanoparticle incorporated mesoporous silica with large bottle-neck like mesopores for the aerobic oxidative synthesis of disulfide

Highly stable, environmentally benign cubic Ag2O nanoparticles dispersed on mesoporous silica with large bottle-neck like mesopores were synthesized and characterized by BET surface area analysis, HR TEM, EDX, FTIR and powder XRD studies. The Ag2O nanoparticles were homogeneously distributed having an average size of 20–40 nm. The activity of the catalyst was probed through an efficient aerobic chemoselective oxidation of thiols to disulfides in water under atmospheric oxygen as the cheapest oxidant. Alkyl, aryl and imine containing symmetrical disulfides can be easily obtained in high yields under mild reaction conditions with no over oxidized product. The efficiency of the catalyst was further demonstrated as the highly sensitive imine bond was well sustained under these mild reaction conditions. Moreover, unlike the other literature precedents, in this present work, single crystal structures of both simple symmetrical disulphide as well as imine containing disulphides are reported for the first time. The catalyst is very much water compatible and can be recycled and reused for at least five cycles. The standard leaching experiment proved that the reaction was heterogeneous with this recyclable catalyst.

Mesoporous Titania‐Iron(III) Oxide with Nanoscale Porosity and High Catalytic Activity for the Synthesis of β‐Amino Alcohols and Benzimidazole Derivatives

A mesoporous TiO2‐Fe2O3 mixed oxide material (MTF‐1E) with nanoscale porosity and a high BET surface area was synthesized using sodium dodecyl sulfate (SDS) as a structure‐directing agent. The material was characterized by powder XRD, high‐resolution TEM, N2 sorption, and NH3 temperature‐programmed desorption studies. The catalyst shows an excellent regioselectivity for the ring‐opening of epoxides with amines under solvent‐free conditions at room temperature for the synthesis of a series of β‐amino alcohols. It also showed a very high catalytic efficiency for the synthesis of benzimidazole derivatives in water. The catalyst can be recovered easily from the reaction medium and reused six times without a significant decrease in its catalytic activity and selectivity.

A novel silver nanoparticle embedded mesoporous polyaniline (mPANI/Ag) nanocomposite as a recyclable catalyst in the acylation of amines and alcohols under solvent free conditions

A mesoporous polyaniline/silver (mPANI/Ag) nanocomposite has been prepared using mesoporous organic polymer polyaniline with silver nitrate via radical polymerization of aniline monomer in the presence of hydrochloric acid. The mPANI/Ag nanocomposite has been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectra (EDX), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible absorption spectra (UV-vis). The XRD patterns indicated that the crystalline phase of Ag is cubic. TEM images show that the Ag nanoparticles are well dispersed in the mesoporous polyaniline matrix. The mPANI/Ag acts as an efficient heterogeneous nanocatalyst in the acylation of substituted amines and alcohols using acetic acid. The catalyst is air-stable, inexpensive, easy to prepare and can be reused several times without a significant decrease in activity and selectivity.

Activated Alumina Balls under Neat Conditions: A Green Catalyst for the Synthesis of Spiro‐Heterocyclic Scaffolds by Ring‐Opening versus Annulation of the Isatin Moiety

We report a green, efficient and straightforward approach for the regioselective synthesis of new spiro‐heterocyclic scaffolds using environmentally benevolent activated alumina balls (3–5 mm diameter) as a catalyst under neat reaction conditions. The methodology is advantageous because of its short reaction time, moderate to excellent yields, easy work‐up, practical simplicity and high regioselectivity without any troublesome/hazardous disposal of the catalyst or toxic byproducts. The pore size of the catalyst plays a key role in the formation of the spiro derivatives. Specifically, we observed that the reaction yield was hardly affected by the surface area or pore volume, but surprisingly, the yield correlated directly with the pore size of the catalyst.