Subhasis Das

Preferential growth of Au on CdSe quantum dots using Langmuir–Blodgett technique

Oleyl amine capped CdSe quantum dots (QD) were synthesised by hot injection technique. These QDs formed a self-assembled monolayer on an aqueous subphase of a Langmuir–Blodgett (LB) trough. Here, in this report we introduced a simple but very efficient route to form a metal (Au)–QD hybrid nanostructure via the LB technique. In this method, the metal counterpart of the hybrid nanostructure could be deposited exclusively on one side of the QDs. The formation of stable monolayer of QDs was evidenced from a surface pressure–area (Π–A) isotherm. The development of gold tip was confirmed and monitored by detailed TEM study on the monolayer deposited on TEM grids from the LB trough. Other characterizations like UV-Vis spectroscopy, FTIR, XPS and EDX also suggested the same. Oleyl amine was shown to act both as a reducing agent as well as a capping agent in this strategy.

Role of Caesium in Higher Alcohol Synthesis over Modified Copper-Cobalt Nanocomposites under Mild Conditions

Cu–Co nanocomposites with and without Cs promoter on a modified lanthanum–alumina support were prepared by the combination of two unique synthesis methods. The synthesized materials were exclusively characterized by means of XRD, BET surface area determination, H2 temperature‐programmed reduction, CO2 temperature‐programmed desorption, N2O frontal chromatography, X‐ray photoelectron spectroscopy, high‐resolution TEM, and elemental mapping techniques, and its catalytic properties were thoroughly investigated for the selective synthesis of higher alcohols in the CO hydrogenation reaction by using a H2/CO ratio of 1, a temperature range of 180–300 °C and a pressure variation of 15–60 bar. Cs incorporation and a Cu/Co ratio of three was found to be a very efficient combination to obtain alcohol selectivities up to 55 %. This was explained by the fact that Cs increases the surface area of Cu particles by migrating Cu towards the surface layer and strengthens the surface interaction of Cu and Co. The further increase in higher alcohols selectivity then results from the limited formation of methane and carbon dioxide.

Seeding of Au on CdSe/CdS nanoplates using Langmuir–Blodgett technique

Oleyl amine capped CdSe/CdS nanoplates were synthesized by hot injection technique which formed a stable monolayer over both a water subphase and an aqueous HAuCl4 subphase using a Langmuir–Blodgett trough. Au islands were generated at the edge as well as on one specific surface of the flat nanoplates by exploiting the reducing capacity of oleyl amine to form Au nanoseeds from AuCl4− ions. The initial Au nanoseeds changed to a shell surrounding these nanoplates on prolonged exposure to the subphase containing the Au precursor. Monolayer of the hybrid structures was deposited onto suitable substrates for characterization by a number of different techniques and to study the photocatalytic activity. The same substrate with the monolayers could be re-used in several cycles of photocatalysis.

Deposition of Au nanoparticles inside porous CeO2 nanocubes using Langmuir–Blodgett technique

Porous 3D CeO2 nanocubes were synthesized using hot injection technique. These nanocubes were able to form a stable monolayer over water and HAuCl4 subphase in Langmuir–Blodgett (LB) trough due to the presence of surface capped oleic acid and oleylamine. CeO2–Au nanocomposites were synthesized exploiting the ability of oleylamine to reduce AuCl4− ions to Au0, via LB method. CeO2 nanocubes gave rise to excellent long-range assembly at air/water interface and gold nanoparticles were formed inside these porous nanocubes without disturbing this arrangement. The formation of a stable monolayer was evidenced from the surface pressure–area (Π–A) isotherm. The development of Au nanoparticles was confirmed with great effort from a comprehensive study using UV-Vis spectroscopy, XRD, XPS, FTIR, TEM, STEM, EDX, tomography and chemical mapping.

A facile synthesis strategy to couple porous nanocubes of CeO2 with Ag nanoparticles: an excellent catalyst with enhanced reactivity for the ‘click reaction’ and carboxylation of terminal alkynes

Oleic acid and oleylamine capped 3-D porous CeO2 nanocubes were synthesized by the hot injection method. The surface of the nanocube was modified with 2,4-dimethylphenol (DMP). The reducing and capping abilities of DMP to form Ag nanoparticles were explored to form noble metal nanoparticles over the porous CeO2 nanocubes support at room temperature. The surface modification and formation of Ag nanoparticles over the CeO2 support were thoroughly characterized with FTIR, UV-Vis spectroscopy, XRD, XPS, TEM, HRTEM, STEM, EDX and chemical mapping. This CeO2–Ag nanocomposite was found to have enhanced catalytic activities in the ‘click reaction’ as compared to unsupported Ag nanoparticles and porous CeO2 nanocubes; it was also found to have optimized catalytic activity in the carboxylation of terminal alkynes when Cs2CO3 was used as the base in DMF solvent at 80 °C. The reaction can give the desired product in yields as high as 98% under several experimental conditions via the green pathway. Recycling data showed that the catalyst could be reused five times without considerable loss of its activity and without any deterioration of physical conditions as observed by various characterization methods like TEM, EDX, XRD and XPS.

Phase Behavior of GM1-Containing DMPC–Cholesterol Monolayer: Experimental and Theoretical Study

Organization and distribution of lipids in cellular membranes play an important role in a diverse range of biological processes, such as membrane trafficking and signaling. Here, we present the combined experimental and simulated results to elucidate the phase behavioral features of ganglioside monosialo 1 (GM1)-containing mixed monolayer of the lipids 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and cholesterol (CHOL). Two monolayers having compositions DMPC-CHOL and GM1-DMPC-CHOL are investigated at air-water and air-solid interfaces using Langmuir-Blodgett experiments and scanning electron microscopy (SEM), respectively, to ascertain the phase behavior change of the monolayers. Surface pressure isotherms and SEM imaging of domain formation indicate that addition of GM1 to the monolayer at low surface pressure causes a fluidization of the system but once the system attains the surface pressure corresponding to its liquid-condensed phase, the monolayer becomes more ordered than the system devoid of GM1 and interacts among each other more cooperatively. Besides, the condensing effect of cholesterol on the DMPC monolayer was also verified by our experiments. Apart from these, the effects induced by GM1 on the phase behavior of the binary mixture of DMPC-CHOL were studied with and without applying liquid-expanded (LE)-liquid-condensed (LC) equilibrium surface pressure using molecular dynamics (MD) simulation. Our molecular dynamics (MD) simulation results give an atomistic-level explanation of our experimental findings and furnish a similar conclusion.

Keggin-lysine hybrid nanostructures in the shape modulation of gold

We show here that L-lysine effectively complexes with phosphomolybdic acid (PMA) and the solution mixture when added to a 10 �3 M aqueous solution of HAuCl4 after UV-irradiation for 3 h leads to the slow reduction and consequent formation of gold nanotriangles with a high degree of anisotropy. The same reaction carried out in a 12.5 kDa cutoff dialysis bag where the irradiated PMAlysine solution was kept inside and stirred in a beaker containing aqueous HAuCl4, did not lead to the formation of gold nanotriangles. This implies that L-lysine plays the role of a shape-modulating agent and hence this study proves an improvement in the understanding of the role of such organic–inorganic hybrid structures in the synthesis and growth of anisotropic nanoparticles. S Online supplementary data available from stacks.iop.org/MRX/1/015007/ mmedia