Nirmalya Moitra

Surface Functionalization of Silica by Si–H Activation of Hydrosilanes

Inspired by homogeneous borane catalysts that promote Si-H bond activation, we herein describe an innovative method for surface modification of silica using hydrosilanes as the modification precursor and tris(pentafluorophenyl)borane (B(C6F5)3) as the catalyst. Since the surface modification reaction between surface silanol and hydrosilane is dehydrogenative, progress and termination of the reaction can easily be confirmed by the naked eye. This new metal-free process can be performed at room temperature and requires less than 5 min to complete. Hydrosilanes bearing a range of functional groups, including alcohols and carboxylic acids, have been immobilized by this method. An excellent preservation of delicate functional groups, which are otherwise decomposed in other methods, makes this methodology appealing for versatile applications.

Reduction on reactive pore surfaces as a versatile approach to synthesize monolith-supported metal alloy nanoparticles and their catalytic applications

Supported metal alloy nanoparticles demonstrate high potential in designing heterogeneous catalysts for organic syntheses, pollution control and fuel cells. However, requirements of high temperature and multistep processes remain standing problems in traditional synthetic strategies. We herein present a low-temperature, single-step, liquid-phase methodology for designing monolith-supported metal alloy nanoparticles with high physicochemical stability and accessibility. Metal ions in aqueous solutions are reduced to form their corresponding metal alloy nanoparticles within hierarchically porous hydrogen silsesquioxane (HSQ, HSiO1.5) monoliths bearing well-defined macro- and mesopores and exhibiting high surface redox activity due to the presence of abundant Si–H groups. Supported bi-, tri- and tetrametallic nanoparticles have been synthesized with controlled compositions and loadings, and characterized in detail by microscopy and spectroscopy techniques. Examination of these supported metal alloy nanoparticles in catalytic reduction of 4-nitrophenol shows high catalytic activities depending on their compositions. Their recyclability and potential application in continuous flow reactors are also demonstrated.

Synthesis of robust hierarchically porous zirconium phosphate monolith for efficient ion adsorption

Hierarchically porous monolithic materials are advantageous as adsorbents, catalysts and catalyst supports due to the better accessibility of reactants to the active sites and the ease of recycle and reuse. Traditional synthetic routes, however, have limitations in designing hierarchical porosity as well as the mechanically stable monolithic shape in inorganic phosphate materials, which are useful as adsorbents and catalysts. We present a low-temperature, one-step liquid phase synthesis of hierarchically porous zirconium phosphate (ZrP) monoliths with tunable compositions (from Zr(HPO4)2 (Zr : P = 1 : 2) to NaSICON (Na super ionic conductor)-type ZrP (Zr : P = 1 : 1.5)) as well as macropore size (from 0.5 to 5 μm). The as-synthesized ZrP monolith with a high reactive surface area (600 m2 g−1) and relatively high mechanical strength (Youngs modulus 320 MPa) was applied to ion adsorption. A simple syringe device inserted tightly with the ZrP monolith as a continuous flow setup was demonstrated to remove various toxic metal ions in aqueous solutions, which shows promising results for water purification.

A new hierarchically porous Pd@HSQ monolithic catalyst for Mizoroki–Heck cross-coupling reactions

Pore architecture of catalyst supports is an important factor facilitating accessibility of reactants to catalytic sites. This holds the key to improving catalytic activities. Amongst various catalytic reactions, supported Pd nanoparticles-catalyzed C–C cross-coupling reactions have been attracting a great deal of attention in the last decade. Although various supports have been examined, applications of hierarchically porous monolithic materials have never been reported, mainly because of difficulties in multistep synthesis of catalysts. We herein report a novel on-site reduction-based methodology using hierarchically porous hydrogen silsesquioxane (HSQ) monoliths for one-step synthesis of Pd nanoparticles-embedded monoliths (Pd@HSQ). Characterization of these monoliths evidences the on-site reduction, i.e. formation of Pd nanoparticles and conversion of Si–H present in the monolith to Si–O∼. Fast, quantitative reduction of Pd2+ to Pd(0) to form supported Pd nanoparticles is achieved with preservation of the porous structure of the original monolith, which makes this material attractive as a catalyst for C–C cross-coupling reactions. The obtained Pd@HSQ catalyst has been employed in the Mizoroki–Heck cross-coupling reaction. High accessibility of reactant molecules, undetectable leaching of Pd nanoparticles and easy separation of the monolith from liquid media provide high catalytic activity, reusability and easy handling.

High‐performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles

The optimization of a porous structure to ensure good separation performances is always a significant issue in high-performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high-performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high-performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high-performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36,000 m(-1). Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans-stilbene with separation factor as 7 and theoretical plate number as 76,000 m(-1) for cis-stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long- established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.