Porous carbon-NiO nanocomposites for amperometric detection of hydrazine and hydrogen peroxide.

A hydrothermal route is reported for the preparation of a composite consisting of sheet-like glucose-derived carbon and nickel oxide nanoparticles. The nanocomposites were prepared at different annealing temperatures and exploited as electrode materials for amperometric (i-t) determination of hydrazine (N2H4) and hydrogen peroxide (H2O2) at trace levels. The performances of the sensors were assessed by cyclic voltammetry and amperometry detection using a rotating disk electrode (RDE) technique. The modified electrode annealed at ca. 300 °C was found to exhibit the best electrocatalytic performance in terms of sensitive and selective detection of N2H4 and H2O2 even in the presence of interfering species. The electrode is inexpensive, robust, easy to prepare in large batches, highly stable, and has a low overpotential. H2O2 can be sensed, best at a working voltage of typically 0.13 V vs Ag/AgCl; rotationg speed 1200 rpm) over a wide concentration range (0.01 to 3.9 µM) with a detection limit of 1.5 nM. N2H4 can be sensed, best at a working voltage of typically 0.0 V within the concentration range from 0.5 µM to 12 mM with an excellent detection limit of 1.5 µM. Thus, this cost-effective and robust modified electrode, which may be readily prepared in large batch quantity, represents a practical platform for industrial sensing. Graphical abstract Schematic of the hydrothermal method for synthesis of carbon and nickel oxide nanoparticle composites (GCD/NiO-150, GCD/NiO-300, and GCD/NiO-450). The composite was used for the electro-oxidation of hydrazine (N2H4) and hydrogen peroxide (H2O2) by cyclic voltammetry and amperometry (i-t).

Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li-O2 batteries.

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium-oxygen (Li-O2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels.

Functional porous carbon-ZnO nanocomposites for high-performance biosensors and energy storage applications.

A one-pot synthesis method for the fabrication of biomass-derived activated carbon-zinc oxide (ZAC) nanocomposites using sugarcane bagasse as a carbon precursor and ZnCl2 as an activating agent is reported. For the first time, we used ZnCl2 as not only an activating agent and also for the synthesis of ZnO nanoparticles on the AC surface. ZAC materials with varying ZnO loading were prepared and characterized by a variety of analytical and spectroscopic techniques such as FE-SEM, FE-TEM, XRD, EA, XPS, and Raman spectroscopy. ZAC-modified glassy carbon electrodes (GCEs) were found to exhibit remarkable electrochemical properties for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) as well as hazardous pollutants such as hydrogen peroxide (H2O2) and hydrazine (N2H4) with desirable sensitivity, selectivity, and detection limits. Moreover, ZAC-modified stainless steel electrodes also showed superior performances for supercapacitor applications. The ZAC nanocomposites, which may be mass produced by the reported facile direct route from sugarcane bagasse, are not only eco-friendly but also cost-effective, and thus, are suitable as a practical platform for bio-sensing and energy storage applications.

Functional porous carbon/nickel oxide nanocomposites as binder-free electrodes for supercapacitors.

High-surface-area, guava-leaf-derived, heteroatom-containing activated carbon (GHAC) materials were synthesized by means of a facile chemical activation method with KOH as activating agent and exploited as catalyst supports to disperse nickel oxide (NiO) nanocrystals (average size (2.0±0.1) nm) through a hydrothermal process. The textural and structural properties of these GHAC/NiO nanocomposites were characterized by various physicochemical techniques, namely, field-emission SEM, high-resolution TEM, elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy. The as-synthesized GHAC/NiO nanocomposites were employed as binder-free electrodes, which exhibited high specific capacitance (up to 461 F g(-1) at a current density of 2.3 A g(-1)) and remarkable cycling stability, which may be attributed to the unique properties of GHAC and excellent electrochemical activity of the highly dispersed NiO nanocrystals.

Decoration of silver nanoparticles on nitrogen-doped nanoporous carbon derived from zeolitic imidazole framework-8 (ZIF-8) via in situ auto-reduction.

We discovered an in situ auto-reduction method to embed silver nanoparticles onto a nanoporous carbon (NC) derived from the zeolitic imidazole framework-8 (ZIF-8), without any requirement of the reducing agents. The detailed analysis demonstrated the formation of Ag NPs by the replacement of the metallic Zn residue in the NC with Ag ions. The synthesized Ag@NC exhibited a superior catalytic activity toward the reduction reaction of 4-nitrophenol into 4-aminophenol.

Highly Efficient Photoelectrochemical Hydrogen Generation Reaction Using Tungsten Phosphosulfide Nanosheets.

The initiation of hydrogen energy production from sunlight through photoelectrochemical (PEC) system is an important strategy for resolving contemporary issues in energy requirement. Although precious Pt and other noble metals offer a desirable catalytic activity for this method, earth-abundant nonprecious metal catalysts must be developed for wide-scale application. In this regard, P-type silicon (P-Si) micropyramids (Si MPs) are a favorable photocathode because of their effective light-conversion properties and appropriate band gap position. In this study, we developed amorphous tungsten phosphosulfide nanosheets (WS2- xP x NSs) on Si MPs through a simple thermal annealing process for solar-driven hydrogen evolution reaction. The P substitution in the nanostructure effectively produced many defective sites at the edges. The product exhibited an efficient photocurrent density of 19.11 mA cm-2 at 0 V and a low onset potential of 0.21 VRHE compared with tungsten disulfide (WS2; 13.43 mA cm-2). The fabricated catalyst also showed desirable stability for up to 8 h for the WS0.60P1.40@Si MPs photocathode. The extraordinary activity could be due to numerous active sites provided by heteroatoms (sulfur and phosphorus) in the edges, resulting in dwindling reaction kinetics barrier and enhanced PEC activity.

Palladium Nanoparticle Incorporated Porous Activated Carbon: Electrochemical Detection of Toxic Metal Ions.

A facile method has been developed for fabricating selective and sensitive electrochemical sensors for the detection of toxic metal ions, which invokes incorporation of palladium nanoparticles (Pd NPs) on porous activated carbons (PACs). The PACs, which were derived from waste biomass feedstock (fruit peels), possess desirable textural properties and porosities favorable for dispersion of Pd NPs (ca. 3-4 nm) on the graphitic PAC substrate. The Pd/PAC composite materials so fabricated were characterized by a variety of different techniques, such as X-ray diffraction, field-emission transmission electron microscopy, gas physisorption/chemisorption, thermogravimetric analysis, and Raman, Fourier-transform infrared, and X-ray photon spectroscopies. The Pd/PAC-modified glassy carbon electrodes (GCEs) were exploited as electrochemical sensors for the detection of toxic heavy metal ions, viz., Cd(2+), Pb(2+), Cu(2+), and Hg(2+), which showed superior performances for both individual as well as simultaneous detections. For simultaneous detection of Cd(2+), Pb(2+), Cu(2+), and Hg(2+), a linear response in the ion concentration range of 0.5-5.5, 0.5-8.9, 0.5-5.0, and 0.24-7.5 µM, with sensitivity of 66.7, 53.8, 41.1, and 50.3 µA µM(-1) cm(-2), and detection limit of 41, 50, 66, and 54 nM, respectively, was observed. Moreover, the Pd/PAC-modified GCEs also show perspective applications in detection of metal ions in real samples, as illustrated in this study for a milk sample.

Ruthenium nanoparticles decorated curl-like porous carbons for high performance supercapacitors.

The synthesis of highly dispersed and stable ruthenium nanoparticles (RuNPs; ca. 2-3 nm) on porous activated carbons derived from Moringa Oleifera fruit shells (MOC) is reported and were exploited for supercapacitor applications. The Ru/MOC composites so fabricated using the biowaste carbon source and ruthenium acetylacetonate as the co-feeding metal precursors were activated at elevated temperatures (600-900 (o)C) in the presence of ZnCl2 as the pore generating and chemical activating agent. The as-prepared MOC carbonized at 900 (o)C was found to possess a high specific surface area (2522 m(2) g(-1)) and co-existing micro- and mesoporosities. Upon incorporating RuNPs, the Ru/MOC nanocomposites loaded with modest amount of metallic Ru (1.0-1.5 wt%) exhibit remarkable electrochemical and capacitive properties, achiving a maximum capacitance of 291 F g(-1) at a current density of 1 A g(-1) in 1.0 M H2SO4 electrolyte. These highly stable and durable Ru/MOC electrodes, which can be facily fabricated by the eco-friendly and cost-effective route, should have great potentials for practical applications in energy storage, biosensing, and catalysis.

Nickel Nanoparticle-Decorated Porous Carbons for Highly Active Catalytic Reduction of Organic Dyes and Sensitive Detection of Hg(II) Ions.

High surface area carbon porous materials (CPMs) synthesized by the direct template method via self-assembly of polymerized phloroglucinol-formaldehyde resol around a triblock copolymer template were used as supports for nickel nanoparticles (Ni NPs). The Ni/CPM materials fabricated through a microwave-assisted heating procedure have been characterized by various analytical and spectroscopic techniques, such as X-ray diffraction, field emission transmission electron microscopy, vibrating sample magnetometry, gas physisorption/chemisorption, thermogravimetric analysis, and Raman, Fourier-transform infrared, and X-ray photon spectroscopies. Results obtained from ultraviolet-visible (UV-vis) spectroscopy demonstrated that the supported Ni/CPM catalysts exhibit superior activity for catalytic reduction of organic dyes, such as methylene blue (MB) and rhodamine B (RhB). Further electrochemical measurements by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) also revealed that the Ni/CPM-modified electrodes showed excellent sensitivity (59.6 µA µM(-1) cm(-2)) and a relatively low detection limit (2.1 nM) toward the detection of Hg(II) ion. The system has also been successfully applied for the detection of mercuric ion in real sea fish samples. The Ni/CPM nanocomposite represents a robust, user-friendly, and highly effective system with prospective practical applications for catalytic reduction of organic dyes as well as trace level detection of heavy metals.

Honeycomb-like Porous Carbon-Cobalt Oxide Nanocomposite for High-Performance Enzymeless Glucose Sensor and Supercapacitor Applications.

Herein, we report the preparation of Pongam seed shells-derived activated carbon and cobalt oxide (∼2-10 nm) nanocomposite (PSAC/Co3O4) by using a general and facile synthesis strategy. The as-synthesized PSAC/Co3O4 samples were characterized by a variety of physicochemical techniques. The PSAC/Co3O4-modified electrode is employed in two different applications such as high performance nonenzymatic glucose sensor and supercapacitor. Remarkably, the fabricated glucose sensor is exhibited an ultrahigh sensitivity of 34.2 mA mM(-1) cm(-2) with a very low detection limit (21 nM) and long-term durability. The PSAC/Co3O4 modified stainless steel electrode possesses an appreciable specific capacitance and remarkable long-term cycling stability. The obtained results suggest the as-synthesized PSAC/Co3O4 is more suitable for the nonenzymatic glucose sensor and supercapacitor applications outperforming the related carbon based modified electrodes, rendering practical industrial applications.

Biomass-derived functional porous carbons as novel electrode material for the practical detection of biomolecules in human serum and snail hemolymph.

The biomass-derived activated carbons (ACs) have been prepared with high surface areas up to 793 m(2) g(-1) is by ZnCl2 activation at three different temperatures, viz. AC700, AC800, and AC900. The AC samples were characterized by a variety of analytical and spectroscopy techniques. The as-synthesized ACs were adopted for the simultaneous electrochemical detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). For comparison, reduced graphene oxide (RGO) was employed for the proposed sensor. The high surface area, modulated pore size and the presence of oxygen surface functional groups like heteroatoms (83.427% C, 1.085% N, 0.383% S, and 0.861% H) in the biomass-derived AC is found to be responsible for the excellent catalytic activities of biomolecules. Fascinatingly, the facile sensor further used to detect biomolecules levels in the snail hemolymph and human blood serum. Notably, the obtained analytical parameters for the biomolecules detection over the AC modified GCE, outperforming several carbon-based modified electrodes in literatures.

Immobilization of myoglobin on Au nanoparticle-decorated carbon nanotube/polytyramine composite as a mediator-free H2O2 and nitrite biosensor.

A novel composite film was designed for use as a highly selective mediator-free amperometric biosensor, and a method was created for accomplishing direct electrochemistry of myoglobin on a multi-walled carbon nanotube and tyramine-modified composite decorated with Au nanoparticles on a glassy carbon electrode. The ultraviolet-visible and electrochemical impedance spectroscopy results showed that myoglobin retained its native conformation in the interaction with Au-PTy-f-MWCNT. The surface coverage of Mb-heme-Fe((II)/(III)) immobilized on Au-PTy-f-MWCNT and the heterogeneous electron-transfer rate constant were 2.12 × 10(-9) mol cm(-2) and 4.86 s(-1), respectively, indicating a higher loading capacity of the nanocomposite for direct electron transfer of Mb onto the electrode surface. The proposed Mb/Au-PTy-f-MWCNT biofilm exhibited excellent electrocatalytic behavior toward the reduction of H2O2 and the oxidation of nitrite with linear ranges of 2 to 5000 µM and 1 to 8000 µM and lower detection limits of 0.01 µM and 0.002 µM, respectively. An apparent Michaelis-Menten constant of 0.12 mM indicated that the Mb immobilized on the Au-PTy-f-MWCNT film retained its native activity. This biosensor can be successfully applied to detect H2O2 and nitrite in disinfectant cream, eye drops, pickle juice, and milk samples.

Facile synthesis of MnO2/carbon nanotubes decorated with a nanocomposite of Pt nanoparticles as a new platform for the electrochemical detection of catechin in red wine and green tea samples.

Herein, we report a simple and facile synthesis strategy of MnO2/carbon nanotubes decorated with a nanocomposite of Pt nanoparticles using a simple electrodeposition method. The Pt/MnO2/f-MWCNT modified electrode were characterized by several analytical and spectroscopy techniques and were adopted as a composite for a novel catechin sensor. The as-prepared Pt/MnO2/f-MWCNT modified glassy carbon electrode (GCE) exhibited a smaller peak potential separation (ΔEp), and electron transfer kinetics during the oxidation reaction of catechin. This can be attributed to the larger effective surface area, greater porosity, and more reactive sites on the Pt/MnO2/f-MWCNT-modified GCE. Notably, we achieved a very low detection limit (under optimized conditions) of catechin ca. 0.02 µM (S/N = 3); the linear range is 2-950 µM with excellent sensitivity. The real time application of catechin in red wine, black tea, and green tea samples with excellent performance. The proposed sensor was successfully developed and the advantages of low cost, ease of preparation, long-term stability, and good reproducibility were demonstrated which are superior to recently reported modified electrodes, thereby enabling practical industrial applications.

Enzymatic electrochemical glucose biosensors by mesoporous 1D hydroxyapatite-on-2D reduced graphene oxide.

A novel hydrothermal process was used for the preparation of hydroxyapatite (HAp) nanorods on two-dimensional reduced graphene oxides (RGO). The hydrothermal reaction temperature improves the crystallinity of HAp and partially reduces graphene oxide (GO) to RGO. The crystalline structure, chemical composition and morphology of the prepared nanocomposites were characterized by using various analytical techniques. Nanorods of HAp with a diameter and length of ∼32 and 60-85 nm were grown on basal planes and edges of the layered RGO sheets. The estimated specific surface area and pore-size distribution are 120 m2 g-1 and 5.6 nm, respectively. We also report the direct electrochemistry of glucose oxidase (GOx) on 1D HAp-on-2D RGO nanocomposite-modified glassy carbon electrode (GCE) for glucose sensing. The electrocatalytic and electroanalytical applications of the proposed RGO/HAp/GOx-modified GCE were studied by cyclic voltammetry (CV) and amperometry. The increased electron rate constant of 3.50 s-1 was obtained for the modified GCE. The reported biosensor exhibits a superior detection limit and higher sensitivity ca. 0.03 mM and 16.9 µA mM-1 cm-2, respectively, with a wide linear range of 0.1-11.5 mM. The tremendous analytical parameters of the reported sensor surpass those of related modified electrodes and are promising for practical industrial applications.

Heteroatom-enriched and renewable banana-stem-derived porous carbon for the electrochemical determination of nitrite in various water samples.

For the first time, high-surface-area (approximately 1465 m(2) g(-1)), highly porous and heteroatom-enriched activated carbon (HAC) was prepared from banana stems (Musa paradisiaca, Family: Musaceae) at different carbonization temperatures of 700, 800 and 900 °C (HAC) using a simple and eco-friendly method. The amounts of carbon, hydrogen, nitrogen and sulfur in the HAC are 61.12, 2.567, 0.4315, and 0.349%, respectively. Using X-ray diffraction (XRD), CHNS elemental analysis, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, the prepared activated carbon appears amorphous and disordered in nature. Here, we used HAC for an electrochemical application of nitrite (NO2(-)) sensor to control the environmental pollution. In addition, HAC exhibits noteworthy performance for the highly sensitive determination of nitrite. The limit of detection (LODs) of the nitrite sensor at HAC-modified GCE is 0.07 µM. In addition, the proposed method was applied to determine nitrite in various water samples with acceptable results.