Saikat Maitra

Metal ion removal from aqueous solution using physic seed hull

The potential of physic seed hull (PSH), Jantropha curcas L. as an adsorbent for the removal of Cd(2+) and Zn(2+) metal ions from aqueous solution has been investigated. It has been found that the amount of adsorption for both Cd(2+) and Zn(2+) increased with the increase in initial metal ions concentration, contact time, temperature, adsorbent dosage and the solution pH (in acidic range), but decreased with the increase in the particle size of the adsorbent. The adsorption process for both metal ions on PSH consists of three stages-a rapid initial adsorption followed by a period of slower uptake of metal ions and virtually no uptake at the final stage. The kinetics of metal ions adsorption on PSH followed a pseudo-second-order model. The adsorption equilibrium data were fitted in the three adsorption isotherms-Freundlich, Langmuir and Dubinin-Radushkevich isotherms. The data best fit in the Langmuir isotherm indication monolayer chemisorption of the metal ions. The adsorption capacity of PSH for both Zn(2+) and Cd(2+) was found to be comparable with other available adsorbents. About 36-47% of the adsorbed metal could be leached out of the loaded PSH using 0.1M HCl as the eluting medium.

Remediation of sulfidic wastewater by catalytic oxidation with hydrogen peroxide

Oxidation of sulfide in aqueous solution by hydrogen peroxide was investigated in the presence of hydrated ferric oxide catalyst. The ferric oxide catalyst was synthesized by sol gel technique from ferric chloride and ammonia. The synthesized catalyst was characterized by Fourier transform infrared spectroscopy, X-Ray diffraction analysis, scanning electrom microscope and energy dispersive X-ray analysis. The catalyst was quite effective in oxidizing the sulfide by hydrogen peroxide. The effects of sulfide concentration, catalyst loading, H2O2 dosing and temperature on the kinetics of sulfide oxidation were investigated. Kinetic equations and activation energies for the catalytic oxidation reaction were calculated based on the experimental results.

Some studies on the reaction between fly ash and lime

The reaction between fly ash (FA) and lime is extensively exploited for the manufacture of building bricks, blocks and aggregates. To get a better idea of this reaction, FA from different sources were mixed in different ratios with lime and compacted. The compacts were treated both by ordinary water and hydrothermal curing to promote lime bearing hydrate bond formation e.g. CaO- SiO2-H2O (C-S-H), CaO-Al2O3-H2O (C-A-H) etc. The decrease in free lime content in these compacts was measured as a function of curing time and curing process. This drop in this content was correlated to the chemical composition of the fly ashes. The mathematical relationships between free lime remaining in the compacts after its maximum decrease in concentration and lime binding modulus (a ratio between the amount of added lime and the total amount of lime binding constituents present in FA) for both types of curing were developed. Further, the rate of decrease in free CaO content under both types of curing conditions was compared from kinetic study. From this study the orders of the reactions and rate constants were found out.

Thermogravimetric analysis of different molar mass ammonium cations intercalated different cationic forms of montmorillonite

Different cationic forms of montmorillonite, mainly K-, Na-, Ca- and Mg-montmorillonites were intercalated in this study via ion exchange process with mono-, di-, and triethanolammonium cations. The developed samples were characterized by TG, XRD, and CHNS techniques. Thermogravimetric study of ammonium-montmorillonites shows three thermal transition steps, which are attributable to the volatilization of the physically adsorbed water and dehydration, followed by the decomposition of the intercalated ammonium cations and dehydroxylation of the structural water of the modified clay, respectively, while untreated and cationic forms of montmorillonite showed only two decomposition steps. The type of ammonium cation has affected both desorption temperature (Position) and the amount of the adsorbed water (intensity). XRD results show a stepwise change in the crystallographic spacings of montmorillonite with the molar mass of ammonium cation, reflecting a change in the structure of the clay. CHNS data confirm the intercalation of ammonium cations into the interlayer space of montmorillonite and corroborate the effect of the molar mass of ammonium cation on the amount adsorbed by the clay.

Some Studies on the Synthesis and Characterization of Carbon Aerogel

Porous carbon aerogels were synthesized from resorcinol-formaldehyde monomers using acetic acid, sodium carbonate and sodium hydroxide catalysts. The synthesized aerogels were characterized by XRD, TGA, SEM, BET and FTIR. The carbon aerogel developed by acetic acid catalyst produced a very high surface area (619.26 m2.g−1). All the different catalysis resulted in different surface morphology of the aerogels. The synthesized carbon aerogels contained significant amount of hydroxyl, carboxyl groups and different types of C-C linkages. These aerogels exhibited potential as adsorbents for removal of toxic materials and heavy metals.

Role of Cr2O3 on the mullittization of di-phasic Al2O3-SiO2 gel

Diphasic Al2O3-SiO2 gel was synthesized by sol-gel route from inorganic salts following aqueous phase colloidal interaction and the effect of Cr2O3 additive on the formation of mullite ceramics from this diphasic gel was investigated. The gel powder was thoroughly characterized by chemical analysis, measurement of surface area, bulk density and FTIR spectroscopy. The calcined gel was compacted with Cr2O3 additives in three different proportions (ca. 1, 2 and 3 wt%) and heat treated at different elevated temperatures (ca, 1400, 1500 and 1600 oC). The analyses of microstructure and phase composition of the sintered masses were carried out by scanning electron microscopy and XRD technique. The morphology of the mullite crystals changed significantly in the presence of the additives. It has been observed that more than 7% more mullite has been formed with the addition of maximum 3% additive only. Using the additive, the maximum reduction in apparent porosity was about 30% and maximum improvement in density in the sintered compacts was about 14%. The flexural strength and fracture toughness of the sintered compacts also improved by 16% and 6% respectively in the presence of the Cr2O3 additive under the experimental condition.

Effect of Titanium and Vanadium on Nanomullite Derived from Diphasic Precursor Gel

To process mullite ceramics, diphasic aluminosilicate gel was synthesized from inorganic salts by employing the sol-gel route. The process of mullitization was studied by FTIR, DTA and SEM analysis. The particle size of the mullite ceramics was found to be in the nanometer range. The gel was calcined at 800°C. To the calcined gel, oxides of titanium and vanadium were mixed separately. The powder masses were compacted at 100 MPa pressure and then sintered at different elevated temperatures. The mechanical and microstructural properties of the doped samples were studied, and it was found that both the oxides influenced the process of mullitization positively.

Effect of Aluminium Sol on Silica Nanoparticles Texture and Properties

This Silica sols were synthesized by alkali hydrolysis of tetraethyl orthosilicate (TEOS). These sols were modified with different percentage of aluminum sol to convert silica from hydrophilic to hydrophobic. The compositions of unmodified and modified silica nanoparticles were studied by X-ray fluorescence (XRF) and confirmed that the aluminum was anchor to the surface of silica nanoparticles. Further analysis by FESEM and Thermo gravimetric analysis (TGA) showed that the amount of modifier added to the silica sols had distinct effect on morphology and thermal stability of silica nanoparticles respectively. X-ray diffraction analysis illustrated that modified silica nanoparticles are amorphous.

Preparation and Characterization of Blended Composite Membranes

Composite membranes were prepared by incorporating inorganic silica nanoparticles into blends of polysulfone/polyimide (PSF/PI) membranes via sol-gel route. Morphological structures of the developed membranes were carried out by scanning electron microscopy (SEM). Spectroscopic analysis of the hybrid membranes were done by fourier transform infrared spectroscopy (FTIR) analysis. Differential scanning calorimetry (DSC) analysis shows that the glass transition temperature (Tg) increased from 209oC to 238oC in the hybrid membranes followed by thermogravimetric analysis (TGA) that showed significant improvement in thermal stability of the developed membranes.

Effect of Different Solvents on the Synthesis of δ-Vanadyl Phosphate and Its Performance as Cathode for Li-ion Battery

In the present work δ-vanadyl phosphate (VOPO4) was synthesized in the presence of different solvents like water, ethanol, diethyl ketone and 2-propanol. Role of these solvents on the Li-intercalation behaviour of synthesized δ-VOPO4 has been studied. The solvents affected significantly the size of the crystallites and the level of impurities in the synthesized material. δ-VOPO4 synthesized using water as solvent, possessed a significant Li-intercalation capacity ca., 124 mAh.g−1 at 3.7 V corresponding to 75% of its theoretical capacity. Among the organic solvents used, sample prepared using ethanol exhibited the highest Li intercalation capacity. Small amount of β-phase was observed in the synthesized δ-VOPO4 (with phosphate/vanadium ratio of 2) using ethanol and Li-intercalation capacity of this phase was about 137 mAh.g1, corresponding to 85% of the theoretical capacity. The capacity was found to be almost stable at 110 mAh.g−1 over 100 cycles.