Haribandhu Chaudhuri

SBA-15 functionalised with high loading of amino or carboxylate groups as selective adsorbent for enhanced removal of toxic dyes from aqueous solution

Amino or carboxylic acid group-containing SBA-15 materials were prepared after activation of surface silanol groups using concentrated HCl. As a result, grafting of amino or carboxylic acid groups on SBA-15 occurred more effectively, due to the presence of active surface silanol groups (3.09 mmol g−1 of SBA-15-NH2, 2.16 mmol g−1 of SBA-15-COOH). These materials can selectively remove toxic dyes (SBA-15-NH2 removes congo red, CR and SBA-15-COOH removes malachite green, MG) from aqueous solution. Various instrumental techniques like DTA, elemental analysis, FTIR, nitrogen adsorption–desorption isotherms, HRXRD, FESEM and HRTEM were employed to examine the pre- and post-adsorption surface morphology. The adsorption behaviour of the nano adsorbents toward toxic dyes was evaluated by examining the effect of pH, solution temperature, time, adsorbent dose, dye concentration, and agitation speed. The obtained kinetic and thermodynamic data fitted best with a pseudo-second-order model and the Langmuir model, respectively. Both the SBA-15-NH2 and SBA-15-COOH adsorbents have large and enhanced adsorption capacities (SBA-15-NH2/CR, qm: 230.95 mg g−1; SBA-15-COOH/MG, qm: 390.63 mg g−1) for these toxic dyes. These adsorbents require less maintenance, resulting in low operating cost. Additionally, these materials have efficient regeneration capabilities.

Surface Modified Nano Fly Ash as an Activator in the Reduction of Ketones

Surface modified nano fly ash has been used as an activator, in the reduction of a few cyclic and acyclic ketones with NaBH4 as reducing agent. Exclusive formation of trans-4--butyl cyclohexanol was observed in such case. Reduction of 3-methylcyclohexanone yielded only cis-3-methylcyclohexanol (equatorial -OH). In case of reduction of other substituted cyclohexanones, propensity to form more of equatorial alcohol was observed. The chemical yields of various alcohols were high (∼95-99%). The rates of reductions of the ketones were also appreciably high. It appears that the silanol groups present in the surface modified fly ash cause nucleophilic activation of the carbonyl groups leading to faster reaction rate. Exclusive formation of the epimer with equatorially disposed -OH group is most likely due to the same reason. Finally, the advantage of the activator lies in its low cost.