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Abstract This article presents a one-step ultrasonication technique for generating biomass carbon dots (BCDs) from neem bark (Azadirachta indica) powder. The BCDs were characterized using modern techniques such as UV–Vis, FTIR, Raman, XRD, HRTEM, FESEM, EDAX, and Zeta potential analyses. Unlike traditional nanocomposite bed systems, this study utilized BCDs as a liquid-phase adsorbent for the regenerative adsorption of the environmentally harmful dye, methylene blue (MB), through an in-situ precipitation reaction. This involved the formation of BCDs-MB adduct via an electrostatic mechanism. The adsorption capacity and percentage of removal were remarkable at 605 mg g–1 and 64.7% respectively, exceeding various solid-based adsorption methods in the literature. The Langmuir isotherm and pseudo-second-order kinetics model provided an excellent fit for this system. The calculated thermodynamic parameter, Gibbs free energy change (ΔG) was negative, indicating a spontaneous, exothermic, and physisorption-based mechanism. The regenerative capacity of our system was further demonstrated by successfully extracting and recovering the MB dye (64%) using ethyl alcohol as the solvent. This method provides an efficient means of recovering valuable cationic organic dye compounds from contaminated environments.

Abstract Nanobiotechnology is a unique class of multiphase and recently become a branch of contemporary science and a paradigm shift in material research. One of the two main problems facing the field of nanomaterial synthesis is the discovery of new natural resources for the biological production of metal nanoparticles and the absence of knowledge about the chemical composition of bio-source required for synthesis and the chemical process or mechanism behind the production of metal nanoparticles presents the second difficulty. We reported template-free green synthesized copper oxide nanoparticles using Tribulus terrestris seed natural extract without any isolation process. XRD, TEM, SEM, UV–Vis, DLS, zeta potential, and BET evaluated the synthesized metal nanoparticle. The TEM analysis confirmed that the CuO NPs are well dispersed and almost round in shape with an average size of 58 nm. EDAX confirms that copper is the prominent metal present in the nanomaterial. The greener fabricated copper oxide nanoparticle was employed to degrade methyl orange dye, almost 84% of methyl orange was degraded within 120 min. The outcomes demonstrated the nanomaterial’s effective breakdown of contaminants, highlighting their potential for environmental rehabilitation. The electrochemical investigation of the CuO NPs was utilized for supercapacitor application. An appreciable value of specific capacitance is 369 F/g specific capacitances with 96.4% capacitance retention after 6000 cycles. Overall, the results of the current study show that the biologically produced copper oxide nanoparticles have intriguing uses as photocatalysts for treating water contaminants and are suitable for energy storage devices.

A straightforward, environmentally friendly, and rapid in-situ electrochemical functionalization of Rutin (Rut) and Caffeic acid (Caf) on a multiwalled carbon nanotube-modified glassy carbon electrode, denoted as GCE/MWCNT@Herb-Redox (Herb-Redox =redox active species from the plant extract), has been demonstrated. This method utilizes an eco-friendly, plant-based water extract from Indian Borage (Coleus amboinicus), referred to as IBE, as a precursor sample. The as-prepared molecular bio-electrode showed a well-defined and stable surface-confined redox response at standard electrode potentials, Eo’ = 0.160 and 0.200 V vs Ag/AgCl in pH 7 phosphate buffer solution. By performing physicochemical and molecular characterisations using TEM, SEM, UV–Vis, FTIR, high-performance thin-layer chromatographic techniques, it has been confirmed that Rut and Caf from the Herbal-plant were selectively immobilized on the MWCNT-modified electrode. Using scanning electrochemical microscopy (SECM), the electroactive sites of the molecular-electrode were mapped. The electrocatalytic function of the GCE/MWCNT@Herb-Redox was demonstrated by performing a dopamine (DA) oxidation reaction as a model system in pH 7 PBS using CV and amp-it techniques. The results showed 100—10,000 times increase in the DA- oxidation current response over the values quoted with many of the literature reports highlighting the efficient functionality of the new molecular electrocatalytic system. As a proof of concept, batch injection analysis based elegant dopamine sensing using screen-printed electrode/MWCNT@Herb-Redox as an electrochemical detector has been demonstrated and there is no biochemical interference was observed. Since the electrochemical approach follows a green chemistry route for the modification, this bioelectrode showed a new platform for eco-friendly electrocatalytic applications.

Owing to the high-surface area and macromolecular architecture, metal-organic frame (MOF) material has been referred to as an advanced system for supercapacitor applications. Indeed, poor electrical property and structural instability under electrified conditions are the major limitations. In this work, we wish to introduce a new strategy for marked enhancement in the electrical and redox property of the MOF by simple chemical mixing followed by ultrasonication of pristine MOF with low-cost carbon black (CB) material. As a model system, Ni-MOF, prepared using 2,2’-bipyridine and benzene-1,4-dicarboxylic acid (provides a rich source for π-π interaction with graphic carbon), functionalized CB, designated as CB@Ni-MOF, has been developed for improved energy storage application. Electrochemical studies of CB@Ni-MOF modified screen-printed carbon electrode showed about ten times enhanced peak current and surface excess value (24.8 nmol.cm−2) over the respective pristine Ni-MOF modified electrode (1.9 nmol.cm−2) in 1 M NaOH solution. Physicochemical and electrochemical characterization using TEM, X-ray, Raman, FTIR, BET Surface area and electrochemical impedance measurements collectively revealed that there are multiple hydrogen-bonding interactions between the oxygen functional groups of Ni-MOF and CB, and strong π-π interaction between the aromatic units of Ni-MOF and sp2 carbon-graphitic sites of CB. These interactions help de-agglomeration and active-site inter-connection and a marked reduction in the multi-shell hollow structure of the CB (55nm→30nm). Capacitance measurement by galvanostatic charge and discharge (GCD) method yield value, 2700 F g−1 at a biased-current, 2 A g−1. It is about seven times higher than the values obtained with the respective pristine Ni-MOF (415 F g−1) and markedly higher than several literature-based MOF values. A GCD cyclic stability of the CB@Ni-MOF showed about 2% and 10% decrement at 2000 and 5000 cycles, respectively.

Pencil graphite electrode (PGE) is an alternative, commercially available, ready-to-use, screen-printed electrode for a wide range of electroanalytical applications. Due to the complex-matrix composition and unpredictable electro-inactive nature of PGE in its native form, a surface pre-treatment/activation procedure is highly preferred for using it as an electroactive working electrode for electroanalytical applications. In this article, we review various surface pre-treatment and modification procedures adopted in the literature with respect to the sensitive and selective detection of dopamine as a model system. Specific generation of the carbon–oxygen functional group, along with partial surface exfoliation of PGE, has been referred to as a key step for the activation. Based on the Scopus® index, the literature collection was searched with the keywords “pencil and dopamine”. The obtained data were segregated into three main headings as: (i) electrochemically pre-treated PGE; (ii) polymer-modified PGEs; and (iii) metal and metal nanocomposite-modified PGE. This critical review covers various surface activation procedures adopted for the activation for PGE suitable for dopamine electroanalytical application.

A simple, one-step and facile method has been introduced to prepare fluorescent and electrochemically active carbon nanoparticles with single-size distribution and good long-term stability by electrochemical exfoliation of polyacrylonitrile-based carbon fibers in an alkaline solution-phase condition. The preparation condition was systematically optimized by studying the effect of temperature and electrolytes. It has been found that an electrochemical exfoliation reaction carried out at an applied potential of 2 V vs. Ag/AgCl in a phosphate-ion-containing alkaline solution at a temperature of 40 °C is an ideal condition for the preparation of 14 ± 4 nm-sized carbon nanoparticles. Unlike the literature protocols, there are no filtration and membrane dialysis-based off-line sample pretreatments adopted in this work. The as-prepared carbon nanoparticles were characterized by fluorescence, Raman spectrum, transmission electron microscope, and X-ray photoelectron spectroscopic characterization methods. It was found that the carbon–oxygen functional group rich in graphene–oxide quantum dots (GOQDs) such as carbon nanoparticles were formed in this work. A preliminary study relating to simultaneous electrochemical oxidation and the sensing of uric acid and ascorbic acid with well-resolved peaks was demonstrated as a model system to extend the new carbon material for electroanalytical applications. Furthermore, in situ synthesis of 2 nm-sized gold nanoparticles stabilized by GOQDs was presented. The carbon nanoparticles prepared by the direct method in this work have shown good stability over 6 months when stored at room temperature. The electrochemical exfoliation reaction has been found to be highly reproducible and suitable for bulk synthesis of luminescence-effective carbon nanoparticles to facilitate fundamental studies and practical applications.