Jugal Kishore Das

Synthesis of NaP zeolite at room temperature and short crystallization time by sonochemical method

NaP zeolite nano crystals were synthesized by sonochemical method at room temperature with crystallization time of 3h. For comparison, to insure the effect of sonochemical method, the hydrothermal method at conventional synthesis condition, with same initial sol composition was studied. NaP zeolites are directly formed by ultrasonic treatment without the application of autogenous pressure and also hydrothermal treatment. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, the crystallinity of the powders decreased but phase purity remain unchanged. The synthesized powders were characterized by XRD, IR, DTA TGA, FESEM, and TEM analysis. FESEM images revealed that 50 nm zeolite crystals were formed at room temperature by using sonochemical method. However, agglomerated particles having cactus/cabbage like structure was obtained by sonochemical method followed by hydrothermal treatment. In sonochemical process, formation of cavitation and the collapsing of bubbles produced huge energy which is sufficient for crystallization of zeolite compared to that supplied by hydrothermal process for conventional synthesis. With increasing irradiation energy and time, the crystallinity of the synthesized zeolite samples increased slightly.

Ag−TiO2 Nanoparticle Codoped SiO2 Films on ZrO2 Barrier-Coated Glass Substrates with Antibacterial Activity in Ambient Condition

Anatase TiO2 and Ag nanoparticles (NPs) codoped SiO2 films were prepared by the sol-gel method. Proportionate amounts of 3-(glycidoxypropyl)trimethoxysilane (GLYMO), tetraethylorthosilicate (TEOS) and 3-(methacryloxypropyl)trimethoxysilane (MEMO) derived inorganic-organic silica sol, commercially available dispersed anatase TiO2 NPs, and AgNO3 were used to prepare the sols. The films were prepared on ZrO2 (cubic) precoated soda-lime glass substrates by a single-dipping technique and heat-treated at 450 °C in air and H2/Ar atmosphere to obtain hard, relatively porous, and transparent coatings of thickness>600 nm. The ZrO2 barrier layer was previously applied on soda-lime glass to restrict the diffusion of Ag into the substrate. The Ag-TiO2 NPs incorporated SiO2 films were intense yellow in color and found to be fairly stable at ambient condition for several days under fluorescent light. These films show a considerable growth inhibition on contact with the gram negative bacteria E. coli.

Highly oriented improved SAPO 34 membrane on low cost support for hydrogen gas separation

In this paper we investigated a path towards preparation of a highly oriented improved SAPO 34 zeolite membrane on a silica modified low cost clay-Al2O3 support by selective deposition of oriented seed crystals, followed by an epitaxial secondary growth hydrothermal technique. The membrane thickness was found to be ∼26 μm. The silica layer that have an abundance of reactive hydroxyl groups while its interior is connected by the siloxane group Si–O–Si. These Si–OH groups on the silica-coated substrate could provide a hydrogen bonding interaction with surface hydroxyl groups of SAPO 34 seed crystals. This outcome is a possible result of the formation of a uniform seed monolayer with the same orientation. The stronger intensity of the single peak in XRD pattern confirms the formation of an oriented membrane layer. For comparison, a seed layer was deposited on an unmodified support surface. A discrete and randomly oriented membrane layer was obtained on that support. Highly oriented SAPO 34 membranes on the silica modified support are better for hydrogen gas separation and attained higher selectivity values for the gas mixture. A selectivity of 16.66 and 20.91 was achieved for H2–CO2 and H2–N2, respectively, at room temperature. The obtained values were improved compared to the reported literature values. Herein, we report for the first time, that this work is an improvement towards a highly crystallographic orientation of the SAPO 34 membrane layer with reduced defects and higher gas separation efficiency. The synthesized membrane enhanced the reproducibility and long term durability for hydrogen gas separation with good results.

Sonication mediated hydrothermal process – an efficient method for the rapid synthesis of DDR zeolite membranes

The formation and growth of a DDR zeolite membrane was developed on the low cost indigenous clay–alumina substrate for separation of H2 from H2–CO2 mixture by selective deposition of oriented seed crystals, followed by secondary growth method with sonication mediated hydrothermal technique. The formation of free radicals by ultrasonic irradiation in the sonochemical method enhances the rate of nucleation which ultimately reduces the DDR zeolite crystallization time. Surface seeding not only accelerates the zeolite crystallization on the support surface but also enhances the formation of an homogenous zeolite membrane layer. The DDR seeds were synthesized by a sonication mediated hydrothermal technique within a short crystallization time i.e. 2 days and used to provide nucleation for the membrane growth. Accordingly DDR zeolite membranes were synthesized on seeded substrate within 5 days. The membrane thickness was found to be ∼26 μm. The synthesized membranes along with seed crystals were characterized by XRD, FTIR, FESEM and EDAX analysis. The performance of the membrane formed was evaluated by single gas as well as mixture gas permeation measurement for H2 and CO2. The H2–CO2 separation selectivity of the membrane increased up to 3.7 at room temperature which is more than the reported values. To the best of our knowledge, there is no report on the synthesis of a DDR zeolite membrane within 7 (2 days for seed crystal and 5 days for membrane synthesis) days by a secondary growth technique.

Extremely fast Au–Ag alloy–dealloy associated reversible plasmonic modifications in SiO2 films

We report a unique alloy–dealloy phenomenon of Au–Ag nanoparticles inside SiO2 films with clear plasmonic modifications between the absorptions of Ag (∼415 nm) and Au (∼524 nm). An Au–Ag (1 : 1) alloy nanoparticles (average size: 4.5 nm)-incorporated transparent SiO2 film is prepared on a glass substrate using mercaptosuccinic acid capped Au nanoparticles and Ag+ co-doped hybrid sol. The Au–Ag (1 : 1) alloy-originated plasmon band (465 ± 1 nm) is gradually red-shifted with increasing temperature (50 to 400 °C) due to the partial oxidation of Ag, causing a systematic modification of the alloy composition. The 1 : 1 alloy, however, reverted very quickly, showing its original plasmon band in the presence of a small amount of H2 due to re-reduction of the oxidized Ag and instantaneous re-alloying. During the Ag oxidation, the Si–OH groups associated with the embedded SiO2 matrix exchange Ag+ to form Ag–O–Si linkages; they subsequently release Ag very quickly in H2 and dissolve again into the parent alloy. As a result, the films exhibit reversible and rapid optical changes while cycling in 0.1% to 1% H2 (balance Ar) and air in the temperature range from 50 to 400 °C. This unique reversible alloy–dealloy phenomenon clearly demonstrates the mechanism of plasmonic modification associated with Au–Ag nanoparticles embedded in the sol–gel SiO2 film matrix.

Effect of PVP Intermediate Layer on the Properties of SAPO 34 Membrane

SAPO 34 zeolite membranes were prepared on a tubular mullite support. Before membrane preparation, the support surfaces were coated with seed crystals. Seeds particles were prepared by hydrothermal synthesis. Before seeding, the substrates were treated with polyvinylpyrrolidone (PVP) to orient the seeds. Both the treated and untreated supports were seeded, and membranes were synthesized on those support tubes by ex situ hydrothermal method. The PVP molecule exists in the two resonance structures. Hence the acylamino bond –N

Pore modification of deca-dodecasil-rhombohedral zeolite membrane by carbon loading from in situ decomposition of 1-adamantanamine for improved gas separation

A simple method of pore modification coupled with the removal of surface defects of a deca-dodecasil-rhombohedral (DDR) zeolite membrane has been developed via carbon (C) deposition. Carbon deposition was achieved by controlled decomposition of the structure-directing agent (SDA), 1-adamantanamine (1-ADA), into the membrane pore surface. Membranes that were synthesized with and without pore modification were characterized by thermal analysis, X-ray diffraction analysis, infrared spectroscopy, transmission electron microscopy, and Raman spectroscopy. Finally, the performance of the membranes was evaluated by permeance studies. The non-wetting characteristics of C had imparted hydrophobicity to the membrane pores, leading to enhanced permeability of the gas mixture. Modified membranes were shown to offer a relatively high hydrogen permeance of 13.47 × 10−7 mol m−2 s−1 Pa−1. The selectivity of H2/CO2 was 4.9 based on single gas permeation and the separation factor increased to 8.5 for a H2–CO2 gas mixture at room temperature. In the light of these findings, the current technique is proposed to be useful for making a defect-free C-loaded membrane in a single step with high separation selectivity and permeability in tandem. This is the novelty that was achieved.