Carbon dots-cadmium sulfide quantum dots nanocomposite for 'on-off' fluorescence sensing of chromium(vi) ions.

This work involves fluorescent probe which is composed of carbon dots (CD) and cadmium sulfide quantum dots (CdS QD) for the sensitive and selective fluorescence detection of chromium(vi) ions. The blue fluorescent carbon dots were synthesized by hydrothermal method from natural precursor apricot. The carbon dots-cadmium sulfide quantum dots (CD-CdS QD) nanocomposite was synthesized and all as-synthesized products were characterized using different characterization techniques. It showed white fluorescence under UV light which was quenched selectively in the presence of chromium(vi) ions due to the inner filter effect (IFE). The linear decrease in the white fluorescence was observed in the concentration range 2-120 µM of chromium(vi) ions with the limit of detection 2.07 µM. This is novel probe for the sensitive, selective and rapid detection of chromium(vi) ions.

Highly sensitive, room temperature operated gold nanowire-based humidity sensor: adoptable for breath sensing.

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing. Both humidity and breath sensors are widely needed. Despite a lot of research on humidity and breath sensors, there is a need for simple, inexpensive, reliable, sensitive and selective sensors, which will operate at room temperature. Here we have synthesized gold nanowires by a simple, wet chemical route. The nanowires synthesized by us are 4-7 nm in diameter and a few micrometers long. The nanowires are amine functionalized. The sensor was prepared by drop casting gold nanowires on an alumina substrate to form a AuNW layer with different thicknesses (10, 20, 30 µm). The AuNW sensor is highly selective towards humidity and shows minimum cross sensitivity towards other gases and organic vapors. At an optimum thickness of 20 µm, the humidity sensing performance of the AuNW sensor over 11% to 92% RH was found to be superior to that of 10 and 30 µm thick layers. The response time of the sensor is found to be 0.2 s and the recovery time is 0.3 s. The response of the AuNW sensor was 3.3 MΩ/% RH. Further, the AuNW sensor was tested for sensing human breathing patterns.

A nanostructured SnO2/Ni/CNT composite as an anode for Li ion batteries.

A SnO2/Ni/CNT nanocomposite was synthesized using a simple one-step hydrothermal method followed by calcination. A structural study via XRD shows that the tetragonal rutile structure of SnO2 is maintained. Further, X-ray photoelectron spectroscopy (XPS) and Raman studies confirm the existence of SnO2 along with CNTs and Ni nanoparticles. The electrochemical performance was investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge measurements. The nanocomposite has been used as an anode material for lithium-ion batteries. The SnO2/Ni/CNT nanocomposite exhibited an initial discharge capacity of 5312 mA h g-1 and a corresponding charge capacity of 2267 mA h g-1 during the first cycle at 50 mA g-1. Pristine SnO2 showed a discharge/charge capacity of 1445/636 mA h g-1 during the first cycle at 50 mA g-1. This clearly shows the effects of the optimum concentrations of CNTs and Ni. Further, the nanocomposite (SnNiCn) shows a discharge capacity as high as 919 mA h g-1 after 210 cycles at a current density of 400 mA g-1 in a Li-ion battery set-up. Thus, the obtained capacity from the nanocomposite is much higher compared to pristine SnO2. The higher capacity in the nanoheterostructure is due to the well-dispersed nanosized Ni-decorated stabilized SnO2 along with the CNTs, avoiding pulverization as a result of the volumetric change of the nanoparticles being minimized. The material accommodates huge volume expansion and avoids the agglomeration of nanoparticles during the lithiation and delithiation processes. The Ni nanoparticles can successfully inhibit Sn coarsening during cycling, resulting in the enhancement of stability during reversible conversion reactions. They ultimately enhance the capacity, giving stability to the nanocomposite and improving performance. Additionally, the material exhibits a lower Warburg coefficient and higher Li ion diffusion coefficient, which in turn accelerate the interfacial charge transfer process; this is also responsible for the enhanced stable electrochemical performance. A detailed mechanism is expressed and elaborated on to provide a better understanding of the enhanced electrochemical performance.

Selective antifungal and antibacterial activities of Ag-Cu and Cu-Ag core-shell nanostructures synthesized in-situ PVA.

A simple chemical reduction method was employed to synthesize Cu-Ag and Ag-Cu core-shell nanostructures inside polyvinyl alcohol (PVA) matrix at room temperature. The core-shell nanostructures have been synthesized by varying the two different concentrations (i.e. 0.1 and 0.01 M) of the respective metal ions in equimolar ratios using successive reduction with hydrazine hydrate (HH) as a reducing agent. The core-shell nanostructures have been further characterized by different characterization techniques. The UV-visible spectroscopy exhibit the respective shift in the band positions suggesting the formation of core-shell nanostructures, which was further confirmed by field emission transmission electron microscopy-high-angle-annular dark field elemental mapping. The effect of metal ion concentration of the core-shell nanostructure on various Gram positive and Gram negative bacteria like Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa and one fungal species Aspergillus fumigatus was observed by performing MIC and MBC/MFC study. Cu-Ag core-shell nanostructures were found to be effective antibacterial agent against all tested Gram-positive and Gram-negative bacteria, whereas Ag-Cu core-shell nanostructures were more efficient against a particular fungal species known as A. fumigatus. The highest value of MIC (75 µg ml-1) for Ag-Cu 0.1M core shell nanostructures (D1) was noted against S. aureus and E. coli whereas the lowest value (20 µg ml-1) was observed with P. aeruginosa. While in case of Cu-Ag 0.1M core shell nanostructures (E1) the highest value of MIC (100 µg ml-1) was noted against S. aureus and P. aeruginosa whereas the lowest value (15 µg ml-1) was observed with A. fumigatus. Also, field effect scanning electron microscope (FESEM) images of untreated and core-shell nanoparticles treated micro-organisms showed that 0.1 M Ag-Cu and 0.1 M Cu-Ag core-shell nanostructure can successfully break the cell wall of the fungi A. fumigatus and bacteria P. aeruginosa, respectively. Thus the present study concludes that, Cu-Ag & Ag-Cu core-shell nanostructures damage the cell structure of micro-organisms and inhibits their growth. Hence, the present Cu-Ag & Ag-Cu core-shell nanostructure acts as good antimicrobial agent against the bacteria and fungi, respectively.

Unique N doped Sn3O4 nanosheets as an efficient and stable photocatalyst for hydrogen generation under sunlight.

Unique N doped Sn3O4 nanosheets have been demonstrated successfully using a facile hydrothermal method. Investigations of the triclinic phase and the impurities were performed using powder X-ray diffraction analysis (XRD) and Raman spectroscopy. The morphological analysis demonstrated a rectangular intra- and inter-connected nanosheet-like structure. The length of the nanosheets was observed to be in the range of 200-300 nm and the thickness of the nanosheets was less than 10 nm. The optical study reveals an extended absorption edge into the visible region, owing to the incorporation of nitrogen into the lattice of Sn3O4, which was further confirmed using X-ray photoelectron spectroscopy (XPS). Considering the band structure in the visible region, the photocatalytic activities of pristine and N doped Sn3O4 nanosheets for hydrogen evolution from water under natural sunlight were investigated. 4% N-Sn3O4 showed a higher photocatalytic activity (654.33 µmol-1 h-1 0.1 g-1) for hydrogen production that was eight times that of pristine Sn3O4. The enhanced photocatalytic activity is attributed to the inhibition of charge carrier separation owing to the N doping, morphology and crystallinity of the N-Sn3O4 nanostructures. A stable efficiency was observed for three cycles, which clearly shows the stability of N-Sn3O4.

Synthesis and characterization of Abhraka (mica) bhasma by two different methods.

BACKGROUND: Bhasmas are traditional Ayurvedic medicines prepared from minerals and metals by tedious process which removes toxic properties of metals and minerals and enhances medicinal properties. We have synthesized abhraka bhasma by two traditional methods and were analyzed during each stage of preparation. OBJECTIVE: The present study deals with the synthesis and characterization of abhraka bhasma by two different methods, method-1 is commonly used for treating anemia and tropical sprue and method-2 for treating chronic cough. Hence attempts have been made to see the physico-chemical differences between these methods by using different analytical techniques. MATERIAL AND METHODS: Different steps in preparation of abhraka bhasma includes shodhana (purification), dhanyabhraka, marana (incineration) and amritikarana. The prepared bhasma were analyzed by classical ayurvedic tests and modern analytical techniques like XRD, FTIR, Raman spectroscopy, SEM, TEM, EDX, BET, DLS and TGA/DTA. RESULTS: The morphological characterization revealed that as-prepared abhraka bhasma products were nano crystalline in nature. Elemental analysis confirms presence of various elements along with carbon suggesting bhasma as herbo-mineral compound. The XRD studies revealed the presence of KMg3(Si3Al)O10(OH)2 in bhasmas. CONCLUSION: Characterization study revealed presence of various bonds of different functional groups and formation of nano particles. Abhraka bhasma prepared by method-2 has more proportion of nano particles than that prepared by method-1 and hence will be more effective in its use.

ZnO decorated Sn3O4 nanosheet nano-heterostructure: a stable photocatalyst for water splitting and dye degradation under natural sunlight.

Herein, a facile hydrothermally-assisted sonochemical approach for the synthesis of a ZnO decorated Sn3O4 nano-heterostructure is reported. The phase purity of the nano-heterostructure was confirmed by X-ray diffraction and Raman spectroscopy. The morphological analysis demonstrated a nanosheet-like structure of Sn3O4 with a thickness of 20 nm, decorated with ZnO. The optical band gap was found to be 2.60 eV for the ZnO@Sn3O4 nano-heterostructure. Photoluminescence studies revealed the suppression of electron-hole recombination in the ZnO@Sn3O4 nano-heterostructure. The potential efficiency of ZnO@Sn3O4 was further evaluated towards photocatalytic hydrogen production via H2O splitting and degradation of methylene blue (MB) dye. Interestingly, it showed significantly superior photocatalytic activity compared to ZnO and Sn3O4. The complete degradation of MB dye solution was achieved within 40 min. The nano-heterostructure also exhibited enhanced photocatalytic activity towards hydrogen evolution (98.2 µmol h-1/0.1 g) via water splitting under natural sunlight. The superior photocatalytic activity of ZnO@Sn3O4 was attributed to vacancy defects created due to its nano-heterostructure.

Ruthenium-decorated vanadium pentoxide for room temperature ammonia sensing.

Layer structured vanadium pentoxide (V2O5) microparticles were synthesized hydrothermally and successfully decorated by a facile wet chemical route, with ∼10-20 nm sized ruthenium nanoparticles. Both V2O5 and ruthenium nanoparticle decorated V2O5 (1%Ru@V2O5) were investigated for their suitability as resistive gas sensors. It was found that the 1%Ru@V2O5 sample showed very high selectivity and sensitivity towards ammonia vapors. The sensitivity measurements were carried out at 30 °C (room temperature), 50 °C and 100 °C. The best results were obtained at room temperature for 1%Ru@V2O5. Remarkably as short a response time as 0.52 s @ 130 ppm and as low as 9.39 s @ 10 ppm recovery time at room temperature along with high selectivity towards many gases and vapors have been noted in the 10 to 130 ppm ammonia concentration range. Short response and recovery time, high reproducibility, selectivity and room temperature operation are the main attributes of the 1%Ru@V2O5 sensor. Higher sensitivity of 1%Ru@V2O5 compared to V2O5 has been explained and is due to dissociation of atmospheric water molecules on 1%Ru@V2O5 as compared to bare V2O5 which makes hydrogen atoms available on Brønsted sites for ammonia adsorption and sensing. The presence of ruthenium with a thin layer of oxide is clear from X-ray photoelectron spectroscopy and that of water molecules from Fourier transform infrared spectroscopy.

Nanocomposite of polypyrrol and silica rods-gold nanoparticles core-shell as an ammonia sensor.

Ammonia is widely needed in the chemical industry as well as in fertilizers for agriculture. However, in small as well as large quantities, it is not only hazardous for human health but also for our ecosystem. Therefore, ammonia sensing at low concentration with high sensitivity, selectivity and low response time as well as recovery time is important. Here, various nanosensors are fabricated using gold nanoparticles (∼15 nm), silica-gold nanoparticles coreshell particles and coreshell particles embedded in polypyrrol. Comparisons with bare polypyrrol and coreshell particles are also made. In fact, two types of coreshell particles with rod (∼300 nm × 2 µm) shape and spheres (200 nm) of silica were used to anchor gold nanoparticles on them. A comparison showed that silica-gold core-shell particle with silica rods had the highest sensitivity (∼166% @ 130 ppm) amongst all. The sensor is simple to operate (only resistance change is measured), requires no heater as the sensing occurs at room temperature, and showed no response, except for ammonia, to other gases or humidity. It also has a low response time (4 s) and recovery time (10 s) at the lowest (10 ppm) ammonia concentration measured here. Thus, a simple, economical ammonia sensor has been demonstrated here.

Thickness-dependent humidity sensing by poly(vinyl alcohol) stabilized Au-Ag and Ag-Au core-shell bimetallic nanomorph resistors.

We herein report a simple chemical route to prepare Au-Ag and Ag-Au core-shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)-Au(s) core-shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)-Ag(s) core-shell structures show formation of merely nanocubes. Although UV-visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)-Au(s) and Au(c)-Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy-high-angle annular dark field elemental mapping in the case of Au(c)-Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2-93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.

Single-Stroke Synthesis of Tin Sulphide/Oxide Nanocomposites Within Engineering Thermoplastic and Their Humidity Response.

SnS nanostructured materials have attracted enormous interest due to their important properties and potential application in low cost solar energy conversion systems and optical devices. From the perspective of SnS based device fabrication, we offer single-stroke in-situ technique for the generation of Sn based sulphide and oxide nanostructures inside the polymer network via polymer-inorganic solid state reaction route. In this method, polyphenylene sulphide (PPS)-an engineering thermoplastic-acts as chalcogen source as well as stabilizing matrix for the resultant nano products. Typical solid state reaction was accomplished by simply heating the physical admixtures of the tin salts (viz. tin acetate/tin chloride) with PPS at the crystalline melting temperature (285 °C) of PPS in inert atmosphere. The synthesized products were characterized by using various physicochemical characterization techniques. The prima facie observations suggest the concurrent formation of nanocrystalline SnS with extraneous oxide phase. The TEM analysis revealed formation of nanosized particles of assorted morphological features with polydispersity confined to 5 to 50 nm. However, agglomerated particles of nano to submicron size were also observed. The humidity sensing characterization of these nanocomposites was also performed. The resistivity response with the level of humidity (20 to 85% RH) was compared for these nanocomposites. The linear response was obtained for both the products. Nevertheless, the nanocomposite product obtained from acetate precursor showed higher sensitivity towards the humidity than that of one prepared from chloride precursor.

Nanostructured WO3/graphene composites for sensing NO x at room temperature.

WO3 has emerged as an outstanding nanomaterial composite for gas sensing applications. In this paper, we report the synthesis of WO3 using two different capping agents, namely, oxalic acid and citric acid, along with cetyltrimethyl ammonium bromide (CTAB). The effect of capping agent on the morphology of WO3 material was investigated and presented. The WO3 materials were characterized using X-ray diffraction analysis (XRD), field emission transmission electron microscopy (FETEM), field emission scanning electron microscopy (FESEM), particle size distribution (PSD) analysis, and UV-visible spectroscopic analysis. WO3 synthesized using oxalic acid exhibited orthorhombic phase with crystallite size of 10 nm, while WO3 obtained using citric acid shows monoclinic phase with crystallite size of 20 nm. WO3 obtained using both capping agents were used to study their gas sensing characteristics, particularly for NO x gas. The cross sensitivity towards interfering gases and organic vapors such as acetone, ethanol, methanol and triethylamine (TEA) was monitored and explained. Furthermore, the composites of WO3 were prepared with graphene by physical mixing to improve the sensitivity, response and recovery time. The composites were tested for gas sensing at room temperature as well as at 50 °C and 100 °C. The results indicated that the citric acid-assisted WO3 material exhibits better response towards NO x sensing when compared with oxalic acid-assisted WO3. Moreover, the sensitivity of the WO3/graphene nanocomposite was better than that of the pristine WO3 material towards NO x gas. The WO3 composite prepared using citric acid as capping agent and graphene exhibits sensing response and recovery time of 29 and 24 s, respectively.

Humidity sensing performance of in-situ fabricated Cu/Cu2O/Cu2S-polymer nanocomposite via polyphenylene sulphide cyclisation route.

We herein report the feasibility of novel polymer-inorganic solid state reaction route for simultaneous in situ generation of Cu2S and Cu nanostructures in polymer network. Polyphenylene Sulphide (PPS) which is engineering thermoplastic acts as chalcogen source as well as stabilizing matrix for the resultant nano products. Typical solid state reaction was accomplished by simply heating the physical admixtures of the two reactants i.e., copper acetate and PPS by varying molar ratios mainly 1:1, 1:5, 1:10, 1:15, 1:20 at the crystalline melting temperature (285 degrees C) of PPS. The synthesized products were characterized using various physicochemical characterization techniques like X-ray Diffractometry, Field emission Scanning Electron Microscopy, Transmission Electron Microscopy, UV-Visible spectroscopy and X-ray photoelectron spectroscopy. The prima facie observations suggest occurrence of nanocrystalline Cu2S in case of product obtained with equimolar ratio, whereas remaining samples show mixture of Cu and Cu2O. The TEM analysis reveals nanoscale polydispersity (5-60 nm) and prevalence of mainly spherical morphological features in all the cases with occasional indications of plate like and cubical morphological features depending upon the molar ratio of the reactants. The humidity sensing characterization of these nanocomposites was also performed. The resistivity response with the level of humidity (20 to 70% RH) was compared for these nanocomposites. The linear response is obtained for all the samples. The sensitivity of 1:1 molar ratio sample was found to be maximum among all the samples.

One-pot synthesis of semiconducting PbS nanorods within polyphenylene sulphide matrix.

Herein we report an extremely simple one-pot synthesis of lead sulphide nanorods inside the engineering thermoplastic (i.e. polyphenylene sulphide) which plays a dual role of stabilizing matrix as well as a chalcogen source. The effect of molar ratios of the reactants on the morphology of the samples was studied. The prima facie observations suggest the effective formation of 1-D PbS nanorods along with cubic lead as an impurity phase. The average aspect ratio is found to be approximately 4 to 42 depending upon the reactant molar ratio.