Rajesh Madhu

Eco-friendly synthesis of activated carbon from dead mango leaves for the ultrahigh sensitive detection of toxic heavy metal ions and energy storage applications

A novel spherical carbon nanoparticle decorated activated carbon (SNAC) material with a high surface area of about 1555 m2 g−1 is prepared from the dead mango leaves by an eco-friendly method for the detection of toxic heavy metal ions and energy storage applications. The limits of detection (LODs) for the determination of Cd(II), Pb(II), Cu(II), and Hg(II) ions at the SNAC-modified GCE are 24.4 × 10−9 M, 5.7 × 10−9 M, 23.2 × 10−9 M and 24.6 × 10−9 M, respectively. On the other hand, the obtained maximum specific capacitance for the single electrode from galvanostatic charge discharge is 478 F g−1 at 1 A g−1. The symmetric supercapacitor cell provides a higher specific capacitance (SC) of 55 F g−1 at 1 A g−1, and energy density of 10.75 W h kg−1 at a power density of 300 W kg−1.

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.

Solvent-free mechanochemical synthesis of graphene oxide and Fe3O4–reduced graphene oxide nanocomposites for sensitive detection of nitrite

We report a versatile and eco-friendly approach to prepare large-scale defect-free high quality graphene nanosheets from graphite by simple mechanochemical ball milling in the presence of KMnO4 and aspartic acid. Two foremost concerns such as surface chemistry and physical properties must be considered for potential application of the functionalized ball milled graphene. The surface chemistry was studied for the functionalized graphene anchored with 10, 20 and 30 wt% of Fe3O4 nanoparticles prepared by a simple hydrothermal process. The obtained samples were systematically studied by a variety of analytical and spectroscopic techniques to understand the structural, morphological, functional, compositional, electrical and magnetic properties. An electrochemical sensor was developed based on the prepared nanocomposite loaded on a glassy carbon electrode (GCE). The sensor based on the modified GCE exhibits good electrocatalytic activity, high sensitivity and stability for the detection of nitrite. The current response was linear over two different ranges between 0.5 and 58 μM with a wide range of 0.5 μM–9.5 mM, and low detection limit and sensitivity of 0.03 μM and 202.5 μA mM−1 cm−2 respectively. In addition, validation of the applicability of the prepared biosensor was carried out by detecting nitrite in tap, river and rain water samples.

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.

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.

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 m2 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.

Highly stable and active palladium nanoparticles supported on porous carbon for practical catalytic applications

Carbon porous materials (CPMs) containing highly dispersed palladium nanoparticles (PdNPs) with an average size of ca. 5 nm were synthesized by microwave (MW) irradiation procedure, during which the Pd2+ ions were effectively reduced to the Pd0 form and highly dispersed on the carbon support. The Pd/CPM samples were characterized by a variety of analytical and spectroscopy techniques, viz. N2 adsorption/desorption isotherm measurements, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning and field emission transmission electron microscopy (SEM/FETEM), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. The Pd/CPM composites were employed as heterogeneous catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in aqueous media. The reaction was monitored by UV-Visible spectroscopy, yielding a pseudo-first-order rate constant (k) of 6.87 × 10−2 s−1. Moreover, the catalysts were exploited for C–C coupling reactions using the microwave (MW) method. In addition, a novel electrochemical sensor for the detection of 4-NP was developed based on a Pd/CPM-modified glassy carbon electrode (GCE) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The 4-NP sensor was found to exhibit excellent sensitivity, lower detection limit, reliability, and durability surpassing the reported modified electrodes, rendering practical industrial applications.

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.

Electrochemical detection of 4-nitrophenol based on biomass derived activated carbons

A novel method for detecting an environmental pollutant, 4-nitrophenol (4-NP), by exploiting biomass-derived activated carbon (AC) is reported. The electrochemical performances of the 4-NP sensor were assessed by cyclic and linear sweep voltammetries. The presence of oxygen surface functional groups and heteroatoms (72.6% C, 6.1% H, 6.5% N, and 7.5% S) in the biomass-derived AC with high surface area (1555 m2 g−1) are found to be responsible for the excellent catalytic activities and reversible redox behaviors observed during the detection of 4-NP. The effects of pH of the electrolyte buffer solution, accumulated potential and duration as well as the analyte concentration on the electrocatalytic performance of the sensor were investigated. Consequently, a linear correlation between the cathodic reduction peak current with 4-NP concentration up to 500 μM with a detection limit and sensitivity of 0.16 μM and 5.810 μA μM−1 cm−2, respectively, were observed over the AC-modified GCE in 0.05 M acetate buffer solution (pH 5.0), surpassing the existing modified electrodes in the literature. The facile 4-NP sensor thus implemented is also advantageous for its simplicity, stability, reliability, durability, and low cost, rendering practical applications for real sample systems.

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.