Bakul C. Dave

Synthesis of sol-gel encapsulated heme proteins with chemical sensing properties

Heme proteins such as cytochrome-c (cyt-c), hemoglobin (Hb), and myoglobin (Mb) have been successfully encapsulated in sol-gel derived silica matrices, retaining their spectroscopic properties and chemical function. The thermal stability of cyt-c was significantly improved by immobilization in a porous silica network. Results from optical absorption, resonance Raman, and thermal denaturation studies suggest that biomolecules such as cyt-c design self-specific pores in the silica network according to the size and shape requirements of the biomolecule. Hb and Mb, immobilized using the sol-gel process, bound ligands similar to the proteins in aqueous buffer, and silica-encapsulated manganese myoglobin (MnMb) was a viable detector for nitric oxide (NO).

Synthesis and characterization of polypyrrole/vanadium pentoxide nanocomposite aerogels

Vanadium pentoxide/polypyrrole aerogel (ARG) composites have been synthesized by sol–gel routes, and investigated as cathode materials in Li batteries. The primary method utilized simultaneous polymerisation of pyrrole and vanadium alkoxide precursors. Hydrolysis of VO(OC3H7)3 using pyrrole–water–acetone mixtures yielded monolithic green–black gels with polypyrrole/V ratios ranging from 0.15 to 1.0. Supercritical drying yielded high surface (150–257 m2 g–1) aerogels with densities between 0.1 and 0.2 g cm–3 , that were of sufficient mechanical integrity to allow them to be cut without fracturing. TEM studies of the ARGs show that they are comprised of fibers similar to that of V2O5 ARGs, but with a significantly shorter chain length. The interaction between the polypyrrole (PPy) and V2O5 aerogel in the nanocomposites was probed using IR spectroscopy. Our results suggest that the inorganic and organic components strongly interact during the initial stages, thus perhaps impeding the vanadium condensation process. Hence, the PPy/V2O5 nanocomposites exhibited lower electrical conductivity with increased polypyrrole content. The addition of (NH4)2S2O8 as an oxidizing agent improved the conductivity of the nanocomposites. The deleterious effect of the conductive polymer on the bulk conductivity does not necessarily affect the electrochemical properties of these materials. Nanocomposite materials that were subjected to post-oxidative treatment show enhanced Li insertion capacity compared to the pristine ARG. The physical properties of these ‘nanocomposite aerogels’ are different from ‘microcomposites’ prepared by an alternate route, in which the oxide gel is formed in the presence of a dispersion of preformed micrometer-sized polypyrrole particles.

Fungal bioremediation of chromates: Conformational changes of biomass during sequestration, binding, and reduction of hexavalent chromium ions

This paper highlights the mechanistic aspects of white rot fungus Coriolus versicolor as a complexing/reducing agent for chromium bioremediation. The chemical reduction of Cr(VI) to Cr(III) via the formation of Cr(VI) thio ester as an intermediate, is pH dependent and controls the overall chromium adsorption kinetics. The strong adsorption affinity of the biomass towards Cr(VI) anions was evaluated by the Freundlich and the Langmuir adsorption isotherms. The FTIR spectroscopic analysis suggested the involvement of amino, carboxylate, and thiol groups from fungal cell wall in chromium binding and reduction. The mechanism of the adsorption was preferential sequestration along with binding of the metal to the ligating groups present in the biomass followed by reduction to trivalent state. The results indicate step-wise progression of overall reaction dictated and modulated by structural and conformation effects in the biomass that lead to saturation, acceleration, and ultimate saturation kinetics effects.

Efficient sequestration and reduction of hexavalent chromium with organosilica sol–gels

Sol–gel materials prepared from organically-modified silanes are used for sequestration and reduction of Cr(VI). These sol–gels act as matrices for sequestration and reduction of Cr(VI) as well as binding of Cr(III) ions in the porous structure. Acid treated sol–gels obtained from bis[3-(trimethoxysilyl)propyl]ethylenediamine (EnTMOS) and 3-mercaptopropyltrimethoxysilane (SHTMOS) sequester and reduce Cr(VI) from an external solution. The removal of Cr(VI) from solution was monitored spectrophotometrically and the sol–gels were characterized with FTIR and TEM. The amino and thiol groups in the hybrid sol–gels play a critical role and the gels containing both these functional groups are considerably more effective at removal of Cr(VI) than those containing just one of these functional groups. Finally, the pH of the medium is also found to be an important parameter in kinetics and efficiency of removal of Cr(VI).

Sol–Gel Encapsulation of Molecules to Generate Functional Optical Materials: A Molecular Programming Approach

The extraordinary opportunities offered by integrating solution chemistry of molecular entities with the solid-state nature of the gel provide the basis for designing a number of novel molecular materials. Herein, we present a strategy based on encapsulation of suitable response active species to impart useful optical properties to sol–gel glasses. The basic concept of this molecular programming approach is based on deliberate incorporation of response-active species in the silica gel framework to elicit specific optical responses. Design of molecular materials for device applications depends on selection of molecules which exhibit well-defined electronic or optical response, and assembly of these molecular components into a geometric structure that retains the rigidity, addressability, and stability necessary for practical applications. The approach is based on using molecules as active species and sol–gel glass as structural matrix in which the molecules are selectively integrated. A designer approach that employs specific molecules for generating optical signals is described. As such the properties of these silica-based glasses can be tuned by varying the composition of encapsulated species. These modified glasses exhibit substantially altered optical properties as compared to pristine silica sol–gels. The optical response of these materials provide initial examples toward designing novel materials whose optical and/or photonic responses can be modulated by structural integration of specific dopant entities.

Wet plasma reactor for remidiation of SO2

In pollution control applications, the presence of water in the electrical discharge enhances oxidation of pollutants. The results of an electrical discharge in gas when it flows through a heterogeneous mixture of water and dielectric pellets are reported. The discharge in the wet plasma reactor is more uniform compared to dry dielectric-barrier reactors. The electrical characteristics of such a discharge are discussed. Also the results of removal of SO2 with the wet reactor are reported. The wet reactor was found to be 5–10 times more energy efficient in removing SO2 compared to conventional dry plasma reactors.

Novel Materials for the Direct Removal of Water and Ions from the Body for Patients with Dialysis Needs

This paper describes a novel material for the direct removal of water and ions from the body of patients with End Stage Renal Disease (ESRD). The work is part of a larger project that is envisioned to be a new type of dialysis process that could replace or enhance existing dialysis methods. The main idea is to implant a unit either and/or outside the body of the patients with renal failure so that they do not have to go through the painstaking and exhausting hemodialysis or peritoneal dialysis processes existing today. The proposed work in its final embodiment will eliminate such processes and allow the patients to lead a more normal life than is possible with current state-of-the-art processes and equipment. This paper provides preliminary results to show that a sol gel based material has been formulated that can absorb 30% water, 30% sodium ions and almost 50% potassium ions in a laboratory setting from a mixture that simulates the amounts produced by the human body with ESRD.

Magnetic Behavior of Iron-Oxoclusters Prepared in an Organosilica Sol–Gel Matrix

The crystal structure and magnetization of nanoscale enTMOS–Fe2O3 sol–gel composites with weight iron concentration x, varying from 0.003 to 0.065, have been studied by the transmission electron microscopy technique and a superconducting quantum interference device magnetometer. The clusters are crystallized in a hexagonal crystal structure. All the samples demonstrate a superparamagnetic behavior with antiferomagnetic cluster–cluster coupling at low temperature. The effective paramagnetic moment, μeff, has been found to vary in the range from 5.9 (S=5/2) to 2.5 μB per iron ion. The concentration dependence of the μeff shows a minimum for x∼0.01. At a low iron concentration x<0.01, μeff is practically independent of x and equals about 6 μB per Fe ion. The concentration interval 0.01<x<0.07 is characterized by a monotonical increase of μeff from 2.5 to about 3 μB per Fe ion. Thus, an abrupt variation of μeff (about two times) is observed at x≈0.01. It has been shown that such behavior can be caused by comp...

A Generic Synthesis Route for Matrix Assisted Self-Assembly of Metal-Oxo Clusters in Organosilica Sol-Gels

The use of an organically modified silica sol-gel matrix containing ligating groups that assist in the formation of metal-oxo clusters is described. The metal-ligand interactions can be tuned by change in external environment such that: a) under overload metal ion concentrations, the sol-gel matrix sequesters the metal ions to promote the growth of 4-7 nm size metal-oxo clusters within the porous structure of the matrix, b) a change in pH releases the metal ions from the bound metal-oxo clusters, thereby making the sol-gel matrix behave as ferritin analogues. These characteristics of the matrix assisted self-assembly of metal-oxo clusters are shown using UVVis, TEM, AES, and EDX data.

Molecular Design of Organically-Modified ‘Smart’ Sol-Gel Materials

The design, synthesis and stimuli-responsive behavior of organically-modified silicates (ORMOSILS) is reported. The ORMOSILS behave as ‘smart’ materials by undergoing structural changes at the molecular level to respond to changes in environmental variables. Typical responses in the form of swelling/shrinkage with respect to changes in temperature, pH, and salt concentrations are presented. Finally, the nature of predominant mechanism responsible for the sol-gels behavior towards combined stimuli of high temperature and low pH is discussed.