Square-Facet Nanobar MOF-Derived Co3O4@Co/N-doped CNT Core-Shell-based Nanocomposites as Cathode Materials for High-Performance Supercapacitor Studies.

The binary as well as ternary nanocomposites of the square-facet nanobar Co-MOF-derived Co3O4@Co/N-CNTs (N-CNTs: nitrogen-doped carbon nanotubes) with Ag NPs and rGO have been synthesized via an easy wet chemical route, and their supercapacitor behavior was then studied. At a controlled pH of the precursor solution, square-facet nanobars of Co-MOF were first synthesized by the solvothermal method and then pyrolyzed under a controlled nitrogen atmosphere to get a core-shell system of Co3O4@Co/N-CNTs. In the second step, different compositions of Co3O4@Co/N-CNT core-shell structures were formed by an ex-situ method with Ag NPs and rGO moieties. Among several bare, binary, and ternary compositions tested in 6 M aqueous KOH electrolyte, a ternary nanocomposite having a 7.0:1.5:1.5 stoichiometric ratio of Co3O4@Co/N-CNT, Ag NPs, and rGO, respectively, reported the highest specific capacitance (3393.8 F g-1 at 5 mV s-1). The optimized nanocomposite showed the energy density, power density, and Coulombic efficiency of 74.1 W h.kg-1, 443.7 W.kg-1, and 101.3%, respectively, with excellent electrochemical stability. After testing an asymmetrical supercapacitor with a Co3O4@Co/N-CNT/Ag NPs/rGO/nickel foam cathode and an activated carbon/nickel foam anode, it showed 4.9 W h.kg-1 of energy density and 5000.0 W.kg-1 of power density.

Structural refinement and electrochemical properties of one dimensional (ZnO NRs)1-x(CNs)x functional hybrids for serotonin sensing studies.

Herein, the efficient serotonin (5-HT) sensing studies have been conducted using the (ZnO NRs)1-x(CNs)x nanocomposites (NCs) having appropriate structural and electrochemical properties. Initially, the different compositions of ZnO nanorods (NRs), with varying content of carbon nanostructures (CNs=MWCNTs and RGO), are prepared using simple in-situ wet chemical method and thereafter these NCs have been characterized for physico-chemical properties in correlation to the 5-HT sensing activity. XRD Rietveld refinement studies reveal the hexagonal Wurtzite ZnO NRs oriented in (101) direction with space group 'P63mc' and both orientation as well as phase of ZnO NRs are also retained in the NCs due to the small content of CNs. The interconnectivity between the ZnO NRs with CNs through different functional moieties is also studied using FTIR analysis; while phases of the constituents are confirmed through Raman analysis. FESEM images of the bare/NCs show hexagonal shaped rods with higher aspect ratio (4.87) to that of others. BET analysis and EIS measurements reveal the higher surface area (97.895 m2/g), lower charge transfer resistance (16.2 kΩ) for the ZCNT 0.1 NCs to that of other NCs or bare material. Thereafter, the prepared NCs are deposited on the screen printed carbon electrode (SPCE) using chitosan as cross-linked agent for 5-HT sensing studies; conducted through cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements. Among the various composites, ZCNT0.1 NCs based electrodes exhibit higher sensing activity towards 5-HT in accordance to its higher surface area, lower particle size and lower charge transfer resistance. SWV measurements provide a wide linear response range (7.5-300 µM); lower limit of detection (0.66 µM), excellent limit of quantification (2.19 µM) and good reproducibility to ZCNT 0.1 NCs as compared to others for 5-HT sensing studies.

Interfacially Interactive Ternary Silver-Supported Polyaniline/Multiwalled Carbon Nanotube Nanocomposites for Catalytic and Antibacterial Activity.

Herein, a protocol strategy has been designed for the preparation of ternary silver nanoparticles-supported polyaniline multiwalled carbon nanotube (Ag NPs-PANI/MWCNT) nanocomposites with a chemical interaction for catalytic and antibacterial activity. The morphological study confirmed that Ag NPs were immobilized on the surface of PANI, and afterward, Ag NPs-PANI were mixed with the MWCNTs. The X-ray diffraction technique revealed the face-centered cubic structure of Ag NPs, and the X-ray photoelectron spectroscopy study revealed the chemical constituent and signature of π-π* and C-N interactions in the nanocomposites. The ternary Ag NPs-PANI/MWCNTs nanocomposites have the apparent rate of reaction (K app) as 5.4 × 10-3 s-1, higher than binary nanocomposites for catalytic reduction of 4-nitrophenol to 4-aminophenol at room temperature. Antibacterial activity of Ag NPs-PANI/MWCNT nanocomposites is higher against pathogenic bacteria. Thereafter, because of multifold applications of ternary nanocomposites, they have a broad scope in the field of environmental and healthcare sectors.

Catalytic Reclamation of Silver Present in Photographic Waste Using Magnetically Separable TiO2@CuFe2O4 Nanocomposites and Thereof Its Use in Antibacterial Activity.

In the present investigation, the silver present in photographic waste is reclaimed catalytically using magnetically separable TiO2@CuFe2O4 nanocomposites (NCs), and further, the recovered silver nanoparticles [Ag(0) NPs] are tested against the representative bacteria for the antibacterial activity. Initially, a series of the different composites between TiO2 nanoparticles and CuFe2O4 nanoparticles are synthesized by a sol-gel "ex situ" method to enhance the catalytic activity of bare nanomaterials toward the visible region of the electromagnetic spectrum. X-ray diffraction reveals the presence of characteristic patterns for the tetragonal structure in the bare materials or TiO2@CuFe2O4 NCs; however, the dominance in the phase as well as intensity of the respective XRD reflections in the NCs is observed according to the content of TiO2 or CuFe2O4 in the NCs. Field-emission electron microscopic images show the uniform spherical particles for the representative TiO2@CuFe2O4 NCs, which is also confirmed through the HRTEM images. The magnetically separable behavior of the representative TiO2@CuFe2O4 NCs is confirmed through the VSM measurements, which also shows the superparamagnetic properties due to the S-shaped nature of the hysteresis loop. Thereafter, a photoconversion reaction of Ag(I) ions to Ag(0) NPs as a model reaction is carried out using the different TiO2@CuFe2O4 NCs under visible light irradiation, and hence, the higher catalytic recovery of Ag(0) NPs is observed for a composite containing 10 wt % TiO2 and 90 wt % CuFe2O4 than that of other NCs or the bare one alone. The optimized protocol of the model reaction is adopted for reclaiming Ag(0) NPs from photographic waste. The progress of the catalytic reclamation reaction is monitored using UV-visible, and then sizes of the recovered Ag(0) NPs are confirmed through the HRTEM images. Thereafter, the recovered Ag(0) NPs are tested for complete photoinactivation of Escherichia coli bacteria within 120 min.

Synthesis of Ni2+ ion doped ZnO-MWCNTs nanocomposites using an in situ sol-gel method: an ultra sensitive non-enzymatic uric acid sensing electrode material.

Nickel (Ni2+) ion doped zinc oxide-multi-wall carbon nanotubes (NZC) with different composition ratios of MWCNTs (from 0.01 to 0.1 wt%) are synthesized through an in situ sol-gel method. The synthesized NZC nanocomposites (NCs) are used as electrode materials with glassy carbon electrodes (GCEs) for electrochemical detection of uric acid (UA). The cyclic voltammogram of the representative NZC 0.1 modified GCE (NZC 0.1/GCE) revealed the highest electrochemical sensing activity towards the oxidation of UA at 0.37 V in 0.2 M phosphate buffer solution (PBS) having pH 7.4 ± 0.02. The limit of detection (LOD) and limit of quantification (LOQ) for the NZC 0.1/GCE are determined to be 5.72 nM and 19.00 nM (S/N = 3) respectively, which is the lowest compared to the literature values reported for enzymatic and non-enzymatic detection techniques. The synergistic effect of NZC 0.1 NCs is proposed as one of the factors for the enhanced electrochemical oxidation of UA complemented by the phase, lattice parameters, functional groups, morphology, elemental compositions, types of bonding and specific surface area with pore size ascertained using various techniques. The synthesized NZC 0.1 NCs are further proposed as selective electrode materials for the electrochemical detection of UA as authenticated further by performing interference tests with other metabolites such as ascorbic acid (AA), dopamine (DA) and d-glucose. The optimized electrochemical studies are further adopted for sensing of UA from human excretion samples using NZC 0.1 NCs.

Ag Nanoparticles Connected to the Surface of TiO2 Electrostatically for Antibacterial Photoinactivation Studies.

Supported silver nanoparticles (Ag NPs) were prepared by chemical reduction method with a sol-gel method. The structure, morphology, and interconnectivity of Ag/TiO2 nanocomposites (NCs) were analyzed using different instrumental techniques. Transmission electron microscopy reveals the Ag NPs have uniformly distributed and anchored on the surface of TiO2 . The reduction in electron-hole recombination was measured by Photoluminescence measurements lead, to an increased photocatalytic inactivation of bacteria. Increase in the amount of Ag NPs on TiO2 resulted in a slight decrease in optical band gap energy of TiO2 . The effect of Ag NPs content on the photocatalytic properties of TiO2 for inhibition of bacteria in visible light irradiation was studied. Furthermore, the antibacterial activity of Ag/TiO2 NCs in the presence of UVA light was studied against gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacterial strain by plate count method. Lower values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the catalysts were observed and used to determine the tolerance factor which is shown bactericidal nature of the NCs. Subsequently, time-killing assay of Ag/TiO2 NCs was shown dynamics of antimicrobial activity. These multifold antibacterial studies exhibited potent antibacterial nature of the NCs and employed in the wider range of biomedical fields.

Structural and Optical Properties of Nanocrystalline TiO2 with Multiwalled Carbon Nanotubes and Its Photovoltaic Studies Using Ru(II) Sensitizers.

In this study, the in situ sol-gel method has been deployed to prepare the titanium dioxide/multiwalled carbon nanotubes (TiO2/MWCNTs) nanocomposite (NCs) powders with varying content of MWCNTs (0.01-1.0 wt %), to construct the dye-sensitized solar cells (DSSCs). First, binder-free NCs were deposited on a transparent-conducting F:SnO2 (FTO) glass substrate by a doctor-blade technique and then anchored with Ru(II)-based dyes to either N719 or ruthenium phthalocyanine (RuPc). The structural and optical properties and interconnectivity of the materials within the composite are investigated thoroughly by various spectral techniques (XRD, XPS, Raman, FT-IR, and UV-vis), electron microscopy (HRTEM), and BET analysis. The experimental results suggest that the ratio of MWCNTs and TiO2 in NCs, morphology, and their interconnectivity influenced their structural, optical, and photovoltaic properties significantly. Finally, the photovoltaic performances of the assembled DSSCs with different content of MWCNTs to TiO2 films anchored with two different dyes were tested under one sun irradiation (100 mW/cm2). The measured current-voltage (IV) curve and incident photon-to-current conversion efficiency (IPCE) spectra of TiO2/0.1 wt % MWCNTs (T@0.1 C) for N719 dye show three times more power conversion efficiency (η = 6.21%) which is opposed to an efficiency (η = 2.07%) of T@0.1 C for RuPc dye under the same operating conditions.

Photoinactivation of bacteria by using Fe-doped TiO2-MWCNTs nanocomposites.

In this study, nanocomposites of Fe-doped TiO2 with multi-walled carbon nanotubes (0.1- 0.5 wt. %) were prepared by using sol-gel method. The structural and morphological analysis were carried out with using X-ray diffraction pattern and transmission electron microscopy, which confirm the presence of pure anatase phase and particle sizes in the range 15-20 nm. X-ray photoelectron spectroscopy was used to determine the surface compositions of the nanocomposites. UV-vis diffuse reflectance spectra confirm redshift in the optical absorption edge of nanocomposites with increasing amount of multi-walled carbon nanotubes. Nanocomposites show photoinactivation against gram-positive Bacillus subtilis as well as gram-negative Pseudomonas aeruginosa. Fe-TiO2-multi-walled carbon nanotubes (0.5 wt. %) nanocomposites show higher photoinactivation capability as compared with other nanocomposites. The photoluminescence study reveals that the Fe-TiO2-multi-walled carbon nanotubes nanocomposites are capable to generate higher rate of reactive oxygen species species than that of other nanocomposites. Our experimental results demonstrated that the Fe-TiO2-multi-walled carbon nanotubes nanocomposites act as efficient antibacterial agents against a wide range of microorganisms to prevent and control the persistence and spreading of bacterial infections.