Veerappan V. Balasubramanian

Highly Ordered Mesoporous Carbon Nitride Nanoparticles with High Nitrogen Content: A Metal‐Free Basic Catalyst

Nitrogen-rich carbon nitride is obtained as ultrasmall, discrete, mesoporous nanoparticles (see picture) by reaction of ethylenediamine with CCl in the nanochannels of a mesoporous silica template. Its high nitrogen content, large surface area, and large pore volume make it a highly active catalyst for transesterification of β-keto esters of aryl, aliphatic, and cyclic primary alcohols.

Highly Crystalline and Conductive Nitrogen‐Doped Mesoporous Carbon with Graphitic Walls and Its Electrochemical Performance

We present a rational and simple methodology to fabricate highly conductive nitrogen-doped ordered mesoporous carbon with a graphitic wall structure by the simple adjustment of the carbonization temperature of mesoporous carbon nitride without the addition of any external nitrogen sources. By simply controlling the heat-treatment temperature, the structural order and intrinsic properties such as surface area, conductivity, and pore volume, and the nitrogen content of ordered graphitic mesoporous carbon can be controlled. Among the materials studied, the sample heat-treated at 1000  °C shows the highest conductivity, which is 32 times higher than that for the samples treated at 800  °C and retains the well-ordered mesoporous structure of the parent mesoporous carbon nitride and a reasonable amount of nitrogen in the graphitic framework. Since these materials exhibit high conductivity with the nitrogen atoms in the graphitic framework, we further demonstrate their use as a support for nanoparticle fabrication without the addition of any external stabilizing or size-controlling agent, as well as the anode electrode catalysts. Highly dispersed platinum nanoparticles with a size similar to that of the pore diameter of the support can be fabricated since the nitrogen atoms and the well-ordered porous structure in the mesoporous graphitic carbon framework act as a stabilizing and size-controlling agent, respectively. Furthermore the Pt-loaded, nitrogen-doped mesoporous graphitic carbon sample with a high conductivity shows much higher anodic electrocatalytic activity than the other materials used in the study.

Heteropoly Acid Encapsulated SBA-15/TiO2 Nanocomposites and Their Unusual Performance in Acid-Catalysed Organic Transformations

The preparation of SBA-15/TiO(2) nanocomposites with different loadings of Keggin-type 12-tungstophosphoric acid (TPA) nanocrystals in their mesochannels through a simple and effective vacuum impregnation method is reported for the first time. The catalysts have been characterised by various sophisticated techniques, including XRD, HRSEM, and TEM. It has been found that the acidity and the textural parameters of the nanocomposites can be controlled by simply changing the loadings of TPA and TiO(2) or the calcination temperature. TPA and TiO(2) loadings of 15 and 22.4 wt %, respectively, and a calcination temperature of 1123 K have proved to be optimal for obtaining mesoporous nanocomposite materials with the highest acidity. Moreover, the activities of these catalysts in promoting hydroamination as well as Mannich and Claisen rearrangement reactions have been extensively investigated. The results show that the amount of TPA has a great influence on the activity of the nanocomposites in all of the reactions studied. The effects of other reaction parameters, such as temperature and reaction time, on the conversion and product selectivity have also been studied in detail. A kinetic analysis of the formation of the products under various reaction conditions is presented. It has been found that the activity of the nanocomposite composed of 15 wt % TPA deposited on 22.4 wt of TiO(2) on SBA-15 in promoting the studied reaction is remarkably higher than the catalytic activities shown by pure TPA, TiO(2)-loaded SBA-15, or TPA-loaded SBA-15. The results obtained have indicated that the acidity and the structural control of the nanocomposite materials are highly critical for obtaining excellent catalytic activity, and the presented highly acidic nanocomposites are considered to show great potential for use as catalysts in promoting many acid-catalysed organic transformations.

Influence of functional organic groups on the structure of CTAB templated organosilica thin films

Highly ordered mesoporous organosilica thin films containing functional organic terminal groups covalently bonded to the silica matrix were synthesized by co-condensation of tetraethylorthosilicate (TEOS) and organotriethoxysilane RSi(OEt)3 (R = Cl(CH2)3, CN(CH2)3) in the presence of cetyltrimethylammonium bromide (CTAB) as structure directing agent under acidic conditions. The influence of the nature and concentration of these organic groups on the structure of the thin films is evidenced by Grazing Incidence Small Angle Scattering (GISAXS) and X-ray reflectivity. We show that the introduction of chloropropyl groups strongly affects the structure of these films while cyanopropyl groups weakly perturb it. In the case of the chloropropyl groups, the presence of trans and gauche conformers in the films is clearly evidenced by using micro-Raman spectrometry. Their effects on the phase behaviour versus the concentration are discussed.

A facile synthesis of alkylated nitrogen heterocycles catalysed by 3D mesoporous aluminosilicates with cage type pores in aqueous medium

Friedel–Crafts alkylation of nitrogen heterocycles such as indoles and pyrroles with epoxides has been efficiently carried out using cage-type mesoporous aluminosilicates as recyclable catalysts in water under environmentally benign and mild conditions.

Highly Ordered Nanoporous Carbon Films with Tunable Pore Diameters and their Excellent Sensing Properties

Ordered porous carbon films with tunable pore diameters, immobilized with glucose oxidase (GOD) have been fabricated and employed for the construction of a biosensor for glucose molecules. The as-prepared porous films have large specific surface areas and highly ordered porous structure with uniform pore sizes, which are critical for the immobilization of large amounts of GOD and support the promotion of heterogeneous electron transfer. The developed biosensors give enough room for the encapsulation of a high amount of GOD molecules and show excellent biosensing performance with a linear response to glucose concentration ranging from 0.5 to 9 mM and a detection limit of 1.5 μM. It is also demonstrated that the sensitivity of the biosensor can be easily tuned by modulating the pore size of carbon film as it dictates the amount of immobilization of GOD in the porous channels. The fabricated carbon-film-based biosensor has a good stability and a high reproducibility, which opens the gateway for the commercialization of this excellent technology.

Preparation of Highly Active Triflic Acid Functionalized SBA-15 Catalysts for the Synthesis of Coumarin under Solvent-Free Conditions

Highly acidic SBA‐15 with different pore diameters has been prepared by functionalizing the mesoporous walls with different amounts of triflic acid (TFA). The structure of the SBA‐15 before and after the functionalization with TFA was investigated by powder X‐ray diffraction and nitrogen adsorption isotherms. The interaction of TFA with the surface silanol groups of SBA‐15 and the acidity of the materials have been investigated by FTIR spectroscopy and temperature‐programmed desorption of ammonia, respectively. The characterization results reveal that the mesoporous structure of the SBA‐15 is retained even after the loading of TFA in the mesochannels and that the TFA molecules are bonded with the surface silanol groups of the SBA‐15 supports. The acidity of the materials increases with increasing amount of TFA from 5 to 20 wt %. These functionalized, highly acidic materials are found to be highly active in the synthesis of coumarin and the catalytic efficiency was found to correlate with the total acidity or the amount of TFA in the porous channels of the SBA‐15 catalysts. It has also been found that the activity of the TFA‐functionalized SBA‐15 in the synthesis of coumarin is much higher than that of different zeolites, pure mesoporous silica SBA‐15, and other mesoporous catalysts used in this study.

Mesoporous BN and BCN nanocages with high surface area and spherical morphology

Novel mesoporous BN and BCN materials with cage type porous structure and spherical morphology have been synthesized using carbon nanocages with 3D porous structure as a template via an elemental substitution method at a low synthesis temperature. The obtained materials exhibit a large specific pore volume with uniform pore size distribution and the specific surface area ranging from 945 to 1023 m(2) g(-1).

Titania Nanoparticles Stabilized HPA in SBA‐15 for the Intermolecular Hydroamination of Activated Olefins

A liquid phase hydroamination (HA) of α,β‐ethylenic compounds with amines was investigated with TiO2 nanoparticles stabilized 12‐tungstophosphoric acid (TPA) in SBA‐15. The catalysts were prepared by wet impregnation of TPA/TiO2 nanoparticles into the SBA‐15 and calcined at different temperatures. The characterization results reveal that the textural properties and the acidity of the prepared catalysts can be finely controlled with the simple adjustment of the calcination temperature and the structure of the support, decorated with the TiO2 and TPA nanoparticles, was intact even after the modification. The prepared catalysts were investigated for HA of ethyl acrylate with different aromatic and aliphatic amines over a wide range of reaction conditions to optimize the yield and the selectivity of product. It was found that this process is 100 % atom efficient and the catalytic performance depended significantly on the loading of TPA over the catalyst and the calcination temperature. Under optimized reaction conditions, the best catalyst, 15 wt %TPA/22.4 wt %TiO2/SBA‐15 calcined at 1123 K, offered the highest conversion of p‐ethylaniline (70 %) with 100 % chemo‐selectivity to the anti‐Markovnikov product, i.e., the mono‐addition product. The reaction was heterogeneously catalyzed and no contribution from leached TPA into the reaction was observed.

One and three dimensional mesoporous carbon nitride molecular sieves with tunable pore diameters

One- and three-dimensional mesoporous carbon nitride materials have been synthesized using SBA-15 and SBA-16 mesoporous silica hard templates, respectively. The obtained materials have been unambiguously characterized by sophisticated techniques such as XRD, HRTEM, EELS, XPS, FT-IR and nitrogen adsorption. The pore diameter of the above materials can easily be tuned by changing the pore diameter of mesoporous silica template with keeping the weight ratio of carbon and nitrogen source constant.