Goutam De

Pd/Cu bimetallic nanoparticles embedded in macroporous ion-exchange resins: an excellent heterogeneous catalyst for the Sonogashira reaction

Cationic and macroporous amberlite resins with formate (HCOO−) as the counter anion (ARF) have been used to prepare a new class of heterogeneous Pd/Cu bimetallic composite nanoparticles (NPs) (Pd/Cu–ARF). The physicochemical characteristics of Pd/Cu–ARF were examined with the help of FTIR spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and atomic absorption spectroscopy (AAS). XRD and TEM showed the existence of composite NPs made of metallic Pd, PdO and CuO. The TEM analysis revealed fairly uniform distributions of composite NPs of average size ∼4.9 nm. The as-synthesized nanocomposite material (Pd/Cu–ARF) exhibited high catalytic activity in the Sonogashira cross-coupling reaction between aryl iodide and terminal alkynes. Heterogeneity of the catalytic activity was evidenced from different tests (hot-filtration and catalyst-poisoning experiments) and the recycling ability of the catalyst was examined for five consecutive runs without any significant loss of activity.

Spontaneous generation and shape conversion of silver nanoparticles in alumina sol, and shaped silver nanoparticle incorporated alumina films

Stable and well-dispersed Ag nanoparticles were generated by spontaneous reduction of AgNO3 in the partially acetylacetonato complexed aluminium tri-sec-butoxide solution without using any additional reducing agent. The addition of higher concentration of AgNO3 caused agglomeration of Ag nanoparticles resulting in precipitation. Use of polyvinylpyrrolidone as capping agent not only prevents the agglomeration but also causes a controlled growth of Ag nanoparticles in different shapes in alumina sol. The addition of varying concentrations of polyvinylpyrrolidone caused transformation of yellow alumina sol to green and blue coloured sol. These changes were due to the conversion of spherical (yellow) to a mixture of hexagonal and triangular (green), and finally truncated/filleted triangular (blue) Ag nanoparticles. These yellow, green and blue coloured alumina sols were used to prepare different shaped Ag nanoparticle doped optically transparent amorphous alumina films on glass substrates. The shape conversions of the Ag nanoparticles were studied systematically by UV/visible spectrometry, transmission electron microscopy and grazing incidence X-ray diffraction, and a mechanism of growth of the Ag nanoparticles in alumina sol was established.

Electrospun anatase TiO2 nanofibers with ordered mesoporosity

Anatase TiO2 nanofibers (200–300 nm in diameter) with 3-dimensionally (3D) ordered pore structure and high surface area were synthesized by electrospinning technique. The unique combination of partially acetylacetone chelated Ti-alkoxide, viscosity-controlling cum high positive charge balancing agent PVP and structure director F127 yielded nanofibers with ordered mesoporosity similar to the Pmm structure. Dynamic heating of the fibers in the temperature range 350–540 °C and simultaneous XRD studies revealed that the amorphous to anatase transformation initiated at about 400 °C with the retention of 3D mesoporosity up to the final heat-treatment stage. TEM studies also confirmed this. During amorphous to anatase conversion, the surface area decreased from 165 (350 °C) to 90 m2 g−1 (540 °C). The crystalline mesoporous nanofibers showed enhanced photocatalytic activity with reusability.

Transformation of Pd → PdH0.7 nanoparticles inside mesoporous Zr-modified SiO2 films in ambient conditions

Pd nanoparticles were generated in situ in a mesoporous Zr-modified SiO2 film and transformed into PdHx (x ≈ >0–0.7) nanoparticles by dipping in aqueous NaBH4 solution in ambient conditions, and the adsorbed hydrogen can be released to regenerate the original Pd nanoparticles at 120 °C.

Au nanoparticles doped ZrTiO4 films and hydrogen gas induced Au-plasmon shifting

Au nanoparticle (NP) doped ZrTiO4 films were prepared on glass substrates using the sol–gel process and characterized. An increase of annealing temperature of the doped film from 400 to 800 °C caused growth of the Au NPs from about 7 nm to 17 nm in size, respectively. The matrix ZrTiO4 remained amorphous up to 600 °C and transformed into highly crystalline (orthorhombic) form at 800 °C. The 400 °C annealed Au doped amorphous film showed remarkable blue-shifting (10–11 nm) of the Au surface plasmon resonance (Au-SPR) band in H2 gas (1 and 0.1% in Ar) at 200 °C with appreciable enhancement of optical density (OD). The shifting as well as enhancement of OD of Au-SPR can be reversibly switched between H2 gas (1–0.1%) and air, and found to be repeatable for several cycles. On the contrary, the Au NP doped crystalline ZrTiO4 film showed less shifting (4–5 nm) of Au-SPR with insignificant difference in OD value after exposure in H2 gas at 200–350 °C. The reversible dynamic responses of the transmittance data of Au-SPR in cases of 400 °C annealed films towards H2 gas and air showed quick response and recovery times at the operating temperature 200 °C. Large Au-SPR shifting in H2 with significant OD enhancement can be related to the increase of electron transfer on Au NPs facilitating through the embedding amorphous ZrTiO4 medium.

Improved photoluminescence properties of sol-gel derived Er3+ doped silica films

Silica films (amorphous and crystalline) doped with erbium were fabricated on silica glass substrate and characterized. The inorganic-organic hybrid sol-gel method was used to prepare the films and the Na codoping induced the crystallization of silica film. Photoluminescence (PL) measurements revealed that the Er3+ ions can be excited from the ground state through an energy transfer process mediated by active defective sites in SiO2 film matrix. The annealing temperature and atmospheres have large effects on the local environment of Er3+ and the 1.54 μm PL intensity can be improved significantly by suitable heating treatments. We could correlate Er3+ sensitization effect due to the presence of carbon related species in the films. The PL intensity at nonresonant (476.5 nm) condition can be made as intense as the resonant (488 nm) one, for particular annealing conditions. Noticeable changes in PL emission intensities have not been observed whether the matrix silica film is amorphous or crystalline in nature...

In Situ Mg/MgO-Embedded Mesoporous Carbon Derived from Magnesium 1,4-Benzenedicarboxylate Metal Organic Framework as Sustainable Li–S Battery Cathode Support

Development of advanced carbon cathode support with the ability to accommodate high sulfur (S) content as well as effective confinement of the sulfur species during charge–discharge is of great importance for sustenance of Li–S battery. A facile poly(vinylpyrrolidone)-assisted solvothermal method is reported here to prepare Mg–1,4-benzenedicarboxylate metal organic framework (MOF) from which mesoporous carbon is derived by thermal treatment, where the hexagonal sheetlike morphology of the parent MOF is retained. Existence of abundant pores of size 4 and 9 nm extended in three dimensions with zigzag mazelike channels helps trapping of S in the carbon matrix through capillary effect, resulting in high S loading. When tested as a cathode for lithium–sulfur battery, a reversible specific capacity of 1184 mAh g–1 could be achieved at 0.02 C. As evidenced by X-ray photoelectron spectroscopy, in situ generated Mg in the carbon structure enhances the conductivity, whereas MgO provides support to S immobilization through chemical interactions between Mg and sulfur species for surface polarity compensation, restricting the dissolution of polysulfide into the electrolyte, the main cause for the “shuttle phenomenon” and consequent capacity fading. The developed cathode shows good electrochemical stability with reversible capacities of 602 and 328 mAh g–1 at 0.5 and 1.0 C, respectively, with retentions of 64 and 67% after 200 cycles. The simple MOF-derived strategy adopted here would help design new carbon materials for Li–S cathode support.