Sudhir Mulik

The effect of compactness on the carbothermal conversion of interpenetrating metal oxide/resorcinol-formaldehyde nanoparticle networks to porous metals and carbides

This study establishes that the necessary and sufficient condition for efficient reaction between nanoparticles includes both high surface-to-volume ratios and high compactness. For this, a wide range of interpenetrating networks of resorcinol-formaldehyde (RF) and metal oxide (MOx, M: Fe, Co, Ni, Sn, Cu, Cr, Ti, Hf, Y, Dy) nanoparticles were synthesized via a simple one-pot process using the acidity of gelling solutions of hydrated metal ions to catalyze gelation of RF. The compactness of the nanoparticles in the dry composites is controlled by the drying method: supercritical fluid (SCF) CO2 drying affords aerogels with open skeletal frameworks, while drying under ambient pressure yields much more compact xerogels. A second independent method to impart compactness is by crosslinking the framework nanoparticles with a conformal polyurea (PUA) coating followed by drying with SCF CO2: although those materials (X-aerogels) have an open aerogel-like structure, upon heating in the 200 °C range, the conformal PUA coating melts and causes local structural collapse of the underlying framework creating macropores defined by xerogel-like walls. Depending on the chemical identity of the metal ion, pyrolysis at higher temperatures sets off carbothermal processes yielding pure metal monolithic nanostructures (up to 800 °C; cases of M; Fe, Co, Ni, Sn, Cu) or carbides (up to 1400 °C; cases of M: Cr, Ti, Hf). Irrespective of the specific chemical processes responsible for those transformations, the rate determining factor is the innate compactness of the xerogels, or the induced skeletal compactness in X-aerogels: both kind of materials react at as much as 400 °C lower temperatures than their corresponding native aerogels. By comparison, bulk (micron size) mixtures of the corresponding oxides and carbon black remained practically unreacted in the entire temperature range used for the nanoparticle networks. In addition to the significance of the RF-MOx interpenetrating networks in the design of new materials (mesoporous and macroporous monolithic metals and carbides), the effect of compactness on the activation of the carbothermal processes has important implications for process-design engineering.

Resorcinol–Formaldehyde Aerogels

Resorcinol–formaldehyde (RF) aerogels comprise an important class of organic aerogels, and they are studied intensely for their potential uses in thermal insulation, catalysis, and as precursors of electrically conducting carbon aerogels with applications in filtration, energy storage, and the green energy initiative. This broad overview focuses on how the chemical, microscopic, as well as macroscopic characteristics of RF and thereby carbon aerogels can be tailored to desired application-specific structure–property relationships by varying processing conditions such as the monomer concentration, the pH, and the catalyst-to-monomer ratio.

Immobilization of Pd Catalysts on Mesoporous Silica for Amine-and Copper-Free Sonogashira Coupling Reactions

Abstract Immobilization of catalysts on solid supports is a promising approach to combine the advantages of heterogeneous and homogeneous catalysts. Pd(PPh3)2Cl2, known as an extremely active homogeneous catalyst for the Sonogashira coupling reaction, has been immobilized on high-surface-area MCF (mesocellular foams)–type mesoporous silica powder modified with 3-aminopropyltriethoxysilane and subsequently with diphenylphosphine. The functionalized MCF-type silica and supported catalysts have been characterized by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), elemental analysis, nitrogen sorption porosimetry, and scanning electron microscopy (SEM). Such supported Pd catalysts have proven to be useful recyclable reagents for copper- and amine-free Sonogashira coupling reactions of haloaromatic compounds with terminal alkynes.

Robust PEDOT films by covalent bonding to substrates using in tandem sol–gel, surface initiated free-radical and redox polymerization

Poly(3,4-ethylenedioxythiophene), PEDOT, films are used as antistatic coatings on electrically insulating substrates such as plastic and glass. A novel method for the synthesis of conducting PEDOT films on insulators relies on sol–gel chemistry to attach a di-Si(OEt)3 functionalized free radical initiator (AIBN) on oxidized surfaces, followed by: (a) attachment of 3,4-(vinylenedioxy)thiophene (VDOT: an analogue to EDOT susceptible to radical addition through its vinylenedioxy group); and, (b) oxidative (with FeCl3) co-polymerization of surface-confined VDOT with 3,4-ethylenedioxythiophene (EDOT). In conjunction with classical photolithography, the method yields thin (∼150 nm) yet dense, pinhole-free (confirmed electrochemically), hard (>6H), extremely adhesive (5B), patterned, highly conducting (52 mho cm−1) films. The process is applied mainly on glass but it works equally well on oxidized metal surfaces (aluminum, steel, Pt). Control studies related to “grafting from” with surface-confined AIBN were conducted by growing inexpensive poly(styrene) and poly(methylmethacrylate) films.