Search

Solvent-less synthesis of nanostructures is highly significant due to its economical, eco-friendly and industrially viable nature. Here we report a solid state synthetic approach for the fabrication of Fe3O4@M (where M = Au, Ag and Au-Ag alloy) core-shell nanostructures in nearly quantitative yields that involves a simple physical grinding of a metal precursor over Fe3O4 core, followed by calcination. The process involves smooth coating of low melting hybrid organic-inorganic precursor over the Fe3O4 core, which in turn facilitates a continuous shell layer post thermolysis. The obtained core-shell nanostructures are characterized using, XRD, XPS, ED-XRF, FE-SEM and HR-TEM for their phase, chemical state, elemental composition, surface morphology, and shell thickness, respectively. Homogeneous and continuous coating of the metal shell layer over a large area of the sample is ascertained by SAXS and STEM analyses. The synthesized catalysts have been studied for their applicability towards a model catalytic hydrogen generation from NH3BH3 and NaBH4 as hydrogen sources. The catalytic efficacy of the Fe3O4@Ag and Ag rich alloy shell materials are found to be superior to the corresponding Au counterparts. The saturation magnetization studies reveal the potential of the core-shell nanostructured catalysts to be magnetically recoverable and recyclable.

Owing to the eco-friendly nature of biomolecules, there lies a huge interest in exploring them as capping agents for nanoparticles to achieve stability and biocompatibility. Lipase extracted from the probiotic Lactobacillus plantarum is utilized for the first time to study its efficacy in capping gold nanoparticles (GNPs) in the room temperature synthesis using HAuCl4. The synthesized lipase-capped GNPs are characterized using UV–visible spectroscopy, FT-IR, HR-TEM, DLS and zeta potential measurements. Importantly, selected area electron diffraction (SAED) studies with HR-TEM have revealed the effect of lipase capping in tuning the polycrystallinity of the GNPs. The lipase-capped GNPs are explored for their catalytic efficiency towards an environmentally and industrially important conversion of 4-nitrophenol to 4-aminophenol. Exploiting the amine functional groups in the protein, the recoverability and reusability of the GNPs have been demonstrated through immobilization over amine-functionalized Fe3O4 nanoparticles.

UV-nanoimprint lithography (UV-NIL) is a promising technique for direct fabrication of functional oxide nanostructures. Since it is mostly carried out in aerobic conditions, the free radical polymerization during imprinting is retarded due to the radical scavenging ability of oxygen. Therefore, it is highly desirable to have an oxygen-insensitive photo-curable resin that not only alleviates the requirement of inert conditions but also enables patterning without making substantial changes in the process. Here we demonstrate the formulation of metal-containing resins that employ oxygen-insensitive thiol–ene photo-click chemistry. Allyl acetoacetate (AAAc) has been used as a bifunctional monomer that, on one hand, chelates with the metal ion, and on the other hand, offers a reactive alkene group for polymerization. Pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), a four-arm thiol derivative, is used as a crosslinker as well as an active component in the thiol–ene photo-click chemistry. The FT-IR analyses on the metal-free and metal-containing resin formulations revealed that the optimum ratio of alkene to thiol is 1 : 0.5 for an efficient photo-click chemistry. The thiol–ene photo-click chemistry has been successfully demonstrated for direct imprinting of oxides by employing TiO2 and Ta2O5 as candidate systems. The imprinted films of metal-containing resins were subjected to calcination to obtain the corresponding patterned metal oxides. This technique can potentially be expanded to other oxide systems as well.

A polymerizable sol–gel approach has been employed to synthesize bulk and nano-crystalline WO 3 . A W-containing sol–gel resin is formed and subjected to thermally induced free radical polymerization followed by calcination at 450, 650 and 850 °C. TGA analysis was performed to reveal the calcination temperature required for WO 3 formation. The synthesized oxides have been characterized with XRD, SEM, XPS, TEM and diffuse reflectance spectroscopy to probe the crystallinity, surface morphology and electronic structures. BET surface area measurements were carried out for the synthesized materials to follow the effect of calcination temperature on surface area. The calcination temperature was found to be crucial in tuning the crystallinity and non-stoichiometry of the materials. The synthesized catalysts were explored for the efficiency of Cr(VI) photoreduction in aqueous medium under visible light and the results are correlated with the structural and electronic properties of the materials.

Researchers debate on if it is only the crystalline properties of TiO 2 or also the surface morphology and even optical properties of different types of TiO 2 are the instrumental parameters on photocatalysis. It is a subject of exploration whether the phase pure anatase TiO 2 or the heterojunctions and band alignment in the two polymorphs of TiO 2 (anatase and rutile) plays the determining role in efficacy of a photocatalytic reaction. Three different synthetic routes such as polymerizable sol–gel, solution combustion and customized microwave assisted hydrothermal method have been employed to synthesize TiO 2 . The materials are characterized systematically using XRD, FE-SEM, HR-TEM, diffuse reflectance, photoluminescence, BET surface area and Raman spectroscopy. It is found that TiO 2 synthesized by polymerizable sol–gel approach yields a mixed phase of anatase and rutile, while the other two approaches yield phase pure anatase. The band gap obtained from diffuse reflectance measurements are compared with the direct and indirect band gaps derived from Kubelka–Munk plots. Among the three synthetic routes, TiO 2 synthesized by customized microwave assisted hydrothermal method exhibits the highest surface area, pore volume and diameter, and lowest recombination, which in turn play a crucial role in high rate of photocatalytic degradation of methylene blue. On the other hand, the phase pure anatase made out of solution combustion route with moderate surface area, pore volume and diameter outperformed the rest two catalysts in photocatalytic hydrogen production. The different reaction specific photocatalytic efficacies of these two materials are discussed with respect to the combinatorial role of nano-crystallinity, surface properties, and optical properties.

Palladium is one of the widely used precious metals toward catalysis, energy, and environmental applications. Efficient recovery and reusability of palladium from the spent catalysts is not only highly desirable for sustainable industrial processing but also for preventing environmental contamination. Here, we present a facile citrate-mediated amine functionalization of alumina nanopowder (AO) in aqueous medium. The surface functionalization is probed using infrared (IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, surface area, and zeta potential measurements. The amine-functionalized sorbent is thoroughly studied for its vital palladium-sorption parameters such as amount of adsorbent, pH, adsorption capacity, thermodynamics, and kinetics. The palladium adsorption over amine-functionalized AO is further characterized with X-ray diffraction and XPS. IR analysis of palladium adsorbed over polyethyleneimine is performed to elucidate the mechanistic insight on the role of nitrogen in capturing palladium. The amine-functionalized sorbent after adsorbing palladium is studied for the catalytic reduction of 4-nitrophenol and Cr(VI) and hydrogen generation from ammonia borane, which demonstrated its excellent catalytic activity and reusability toward energy and environmental applications. The environmentally benign materials and all-aqueous reactions employed in this work demonstrate the potential of the strategy for efficient and economical industrial transformations and waste-stream management.

Core-shell type Fe 3 O 4 @Fe 2 O 3 was dispersed over nano Al 2 O 3 support using aqueous medium co-precipitation method. The Fe 3 O 4 core offers magnetic recoverability, while the shell Fe 2 O 3 , due to its optimal band gap, provides photocatalytic activity in the visible light region. The concentration of Fe 3 O 4 @Fe 2 O 3 was varied and the synthesized materials were characterized using XRD, TEM, XPS, Raman spectroscopy, diffuse reflectance spectroscopy and BET surface area measurement. The synthesized materials were studied for Cr(VI) visible light photoreduction. Oxalic acid was used as a hole scavenger and Cr(VI) was efficiently reduced under visible light in aerobic condition. Even with 5% Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 the rate of photoreduction was orders of magnitude higher than that of bulk Fe 3 O 4 @Fe 2 O 3 . The obtained rates with the synthesized catalysts were compared with the literature and were found to be superior to the reported catalysts. The 40% Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 catalyst showed magnetic recoverability and the catalytic efficiency was stable up to 4 cycles.

The presence or absence and nature of the free patchy ends in DNA sequences has a decisive effect on the performance of colorimetric sensors based on the use of gold nanoparticles (Au NPs). The authors have designed two unmodified gene probes (probe 1: a 19-mer; probe 2: an 18-mer). They are complementary to either half of a 37-mer target derived from the conserved region of Hepatitis C Virus (HCV) RNA. Each probe has further been modified with 10-mer poly(A) and thiol-functionalized 10-mer poly(A) at the 5' positions. Nine combinations of probe and HCV RNA were then designed to investigate the effect of free patchy ends on the stability of citrate-modified Au NPs against salt-induced aggregation which lead to color change from red to blue. The aggregation of Au NPs can be monitored by ratiometric spectroscopy at wavelengths of 520 and 700 nm. The differentiation between HCV RNA and control has also been studied by varying the concentration of probe and analyte. The particle size and zeta potentials were determined before and after aggregation. It is demonstrated that the change in surface charge density of the Au NPs governs the critical coagulation concentration of NaCl. The method presented here can be used to quantify HCV RNA in the 370 nM to 3 μM concentration range, and the detection limit is 500 nM. The results obtained with Au NPs that are chemically non-conjugated with the oligonucleotides have been found to be valuable in rationally devising the design rules for rapid and efficient colorimetric sensing of oligonucleotides. Graphical abstract Schematic representation of the nine combinatorial pairs of oligonucleotides that vary in the length of patchy ends and their position to unearth their effect in rapid gold nanoparticle-based colorimetric gene sensing without time-consuming and expensive thiol-conjugation step.

Solvent-less synthesis of nanostructures is highly significant due to its economical, eco-friendly and industrially viable nature. Here we report a solid state synthetic approach for the fabrication of Fe3O4@M (where M = Au, Ag and Au-Ag alloy) core-shell nanostructures in nearly quantitative yields that involves a simple physical grinding of a metal precursor over Fe3O4 core, followed by calcination. The process involves smooth coating of low melting hybrid organic-inorganic precursor over the Fe3O4 core, which in turn facilitates a continuous shell layer post thermolysis. The obtained core-shell nanostructures are characterized using, XRD, XPS, ED-XRF, FE-SEM and HR-TEM for their phase, chemical state, elemental composition, surface morphology, and shell thickness, respectively. Homogeneous and continuous coating of the metal shell layer over a large area of the sample is ascertained by SAXS and STEM analyses. The synthesized catalysts have been studied for their applicability towards a model catalytic hydrogen generation from NH3BH3 and NaBH4 as hydrogen sources. The catalytic efficacy of the Fe3O4@Ag and Ag rich alloy shell materials are found to be superior to the corresponding Au counterparts. The saturation magnetization studies reveal the potential of the core-shell nanostructured catalysts to be magnetically recoverable and recyclable.

TiO2 synthesized by polymerizable sol–gel approach is used to demonstrate the photoreduction of Cr(VI) in aqueous medium. Fe3O4 is chosen as the magnetically recoverable support, onto which, 10, 20, 30 and 50% of TiO2 have been dispersed following the polymerizable sol–gel approach. The synthesized materials are characterized using XRD, SEM, XPS, Raman spectroscopy, diffuse reflectance spectroscopy and BET surface area measurement. Different hole-scavengers (oxalic acid, ammonium oxalate and ethanol) and an electron scavenger (potassium periodate) have been studied to compare the efficiency of Cr(VI) photoreduction in nitrogen as well as air atmosphere. With 5 mM oxalic acid as the hole-scavenger, the TiO2/Fe3O4 materials have demonstrated superior activity to the nonsupported bulk TiO2 toward Cr(VI) photoreduction in aerobic atmosphere. Particularly, 30% TiO2/Fe3O4 has shown the highest Cr(VI) photoreduction rate among the lot. The 30% TiO2/Fe3O4 catalyst has also demonstrated good recoverability as well...

A bifunctional nanocomposite photocatalyst that possesses high photocatalytic activity as well as enhanced adsorption capability was developed. The adsorption component, graphene oxide was synthesized following an improved oxidation method from graphite flakes; while the photoactive component, TiO2 was synthesized by the polymerizable sol–gel route. The as-synthesized graphene oxide was partially photo-reduced, and got anchored as reduced graphene oxide onto TiO2. The materials have been thoroughly characterized with XRD, FT-IR, Raman spectroscopy, TGA, SEM and diffuse reflectance spectroscopy techniques. This reduced-graphene oxide/TiO2 was dispersed over the Zeolite-4A and this nanocomposite hybrid system exhibited remarkable adsorption capability as well as high photocatalytic degradation efficiency for methylene blue. Keywords: Reduced graphene oxide, TiO2, Zeolite, Adsorption, Photocatalytic degradation

Enzyme-embedded polymer degradation was reported to be an attractive alternative approach to the conventional surface pouring method for efficient degradation of polymers using fungal-derived enzyme Candida antarctica lipase B. Despite the enormous potential, this approach is still in its infancy. In the present study, a probiotic lipase obtained from Lactobacillus plantarum has been employed for the first time to study the enzyme-embedded polymer degradation approach using poly(ε-caprolactone) (PCL) as the semicrystalline polymer candidate. PCL films embedded with 2 to 8 wt % lipase are studied under static conditions for their enzymatic degradation up to 8 days of incubation. Thermogravimetric analyses (TGA) have shown a clear trend in decreasing thermal stability of the polymer with increasing lipase content and number of incubation days. Differential thermal analyses have revealed that the percentage crystallinity of the leftover PCL films increases with progress in enzymatic degradation because of the efficient action of lipase over the amorphous regions of the films. Thus, the higher lipase loading in the PCL matrix and more number of incubation days have resulted in higher percentage crystallinity in the leftover PCL films, which has further been corroborated by X-ray diffraction analyses. In a similar line, higher percentage mass loss of the PCL films has been observed with increased enzyme loading and number of incubation days. Field emission scanning electron microscopy (FE-SEM) has been employed to follow the surface and cross-sectional morphologies of the polymer films, which has revealed micron-scale pores on the surface as well as a bulk polymer matrix with progress in enzymatic polymer degradation. Additionally, FE-SEM studies have revealed the efficient enzyme-catalyzed hydrolysis of the polymer matrix in a three-dimensional fashion, which is unique to this approach. In addition to the first-time utility of a probiotic lipase for the embedded polymer degradation approach, the present work provides insight into the PCL degradation under static and ambient temperature conditions with no replenishment of enzymes.

The microbial resistance to different drugs due to excessive usage of antibiotics in various domains has become a serious environmental threat in recent years. This gave the impetus to researchers to find alternatives that do not lead to multi-drug resistant microbes. In this backdrop, silver nanoparticles (Ag NPs) have become a popular choice due to their potential broad spectrum of antimicrobial attributes. Recent literature caution that about 400 metric tons of Ag NPs are synthesized annually all over the world that could cause environmental hazards when used at higher concentrations than the toxicity limit. However, most of the literature reports use higher concentrations of Ag NPs and exposure to such concentrations may lead to environmental and health hazards. In this study, a series of Ag NPs have been synthesized using a lipase derived from a probiotic source Lactobacillus plantarum as the stabilizing agent. The Ag NPs synthesized through different combinations of lipase and AgNO3 are characterized using various techniques such as UV-visible spectroscopy, FT-IR, ED-XRF, DLS and HR-TEM. The lipase capped Ag NPs have been studied for their antimicrobial activity against representative microbes such as Pseudomonas putida, Staphylococcus aureus and Aspergillus niger. Our initial results reveal that the lipase capped Ag NPs possess high potential towards broad spectrum antimicrobial applications at concentrations much lower than the toxicity limit of the standard model, zebra fish.

A polymerizable sol–gel method has been employed to synthesize tailored TiO 2 supported zeolite-4A. The synthetic procedure was optimized by using FTIR, TGA and DSC to prepare various TiO 2 loading ranging from 10 to 30 wt% on the support. The as-synthesized materials were characterized thoroughly with powder XRD, SEM, UV–Vis spectroscopy and BET surface area measurements. The characterization reveals that the polymerizable sol–gel approach yields highly dispersed nano-crystalline TiO 2 on the zeolite-4A support. The tailored materials exhibited high rate of photocatalytic degradation of methylene blue at alkaline pH. The used catalysts were subjected to recyclability investigations, which demonstrated highly stable surface of these materials.

Photocatalytic valorization of harmful pollutants like nitroarenes to important intermediates like aminoarenes has been carried out with the help of TiO2 supported zeolite-4A catalyst, synthesized by polymerizable sol–gel route. A series of solvents such as water, primary and secondary alcohols have been studied for their role on photocatalytic reduction. The reduction of nitrobenzene has been found to be faster compared to that of 4-nitrophenol. The rate of reduction of nitrobenzene is independent of the type of alcohol, whereas the reduction rate of 4-nitrophenol is faster with primary alcohol compared to secondary alcohol. Reduction of 4-nitrophenol has been found to exhibit alcohol concentration dependency and the rate of reduction is dependent on initial concentration of substrate.