Manganese dioxide based ternary nanocomposite for catalytic reduction and nonenzymatic sensing of hydrogen peroxide

Highly efficient Ag doped δ-MnO2 decorated graphene: Comparison and application in electrochemical detection of H2O2

Cytotoxic H₂O₂ is an inevitable part of our life, even during this contemporary pandemic COVID-19. Personal protective equipment of the front line fighter against coronavirus could be sterilized easily by H₂O₂ for reuse. In this study, Ag doped δ-MnO₂ nanorods supported graphene nanocomposite (denoted as Ag@δ-MnO₂/G) was synthesized as a nonenzymatic electrochemical sensor for the sensitive detection of H₂O₂. The ternary nanocomposite has overcome the poor electrical conductivity of δ-MnO₂ and also the severe aggregation of Ag NPs. Furthermore, δ-MnO₂/G provided a rougher surface and large numbers of functional groups for doping more numbers of Ag atoms, which effectively modulate the electronic properties of the nanocomposite. As a result, electroactive surface area and electrical conductivity of Ag@δ-MnO₂/G increased remarkably as well as excellent catalytic activity observed towards H₂O₂ reduction. The modified glassy carbon electrode exhibited fast amperometric response time (<2 s) in H₂O₂ determination. The limit of detection was calculated as 68 nM in the broad linear range (0.005-90.64 mM) with high sensitivity of 104.43 µA mM^-1 cm^-2. No significant interference, long-term stability, excellent reproducibility, satisfactory repeatability, practical applicability towards food samples and wastewater proved the efficiency of the proposed sensor.

An electrochemical platform for the selective detection of azathioprine utilizing a screen-printed carbon electrode modified with manganese oxide/reduced graphene oxide

Scheme representing the electro-reduction of AZT at Mn₂O₃–rGO/SPCE.

Synthesis of High Surface Area α-KyMnO2 Nanoneedles Using Extract of Broccoli as Bioactive Reducing Agent and Application in Lithium Battery

With the aim to reduce the entire cost of lithium-ion batteries and to diminish the environmental impact, the extract of broccoli is used as a strong benign reducing agent for potassium permanganate to synthesize α-KyMnO2 cathode material with pure nanostructured phase. Material purity is confirmed by X-ray powder diffraction and thermogravimetric analyses. Images of transmission electron microscopy show samples with a spider-net shape consisting of very fine interconnected nanoneedles. The nanostructure is characterized by crystallite of 4.4 nm in diameter and large surface area of 160.7 m2 g-1. The material delivers an initial capacity of 211 mAh g-1 with high Coulombic efficiency of 99% and 82% capacity retention after 100 cycles. Thus, α-KyMnO2 synthesized via a green process exhibits very promising electrochemical performance in terms of initial capacity, cycling stability and rate capability.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

A novel non-enzymatic H2O2 sensor using ZnMn2O4 microspheres modified glassy carbon electrode

With a facile solvothermal technique, ZnMn₂O₄ microspheres were synthesized in this work, which were used as enzyme mimics for the electrocatalytic reduction of H₂O₂. The morphology, crystal phase and structure of the ZnMn₂O₄ microspheres underwent characterization under X-ray diffraction spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy. The synthesized ZnMn₂O₄ microspheres showed an average diameter of 2 μm with great crystallinity, and exhibited excellent catalytical activity towards H₂O₂ electroreduction in alkaline media. The glassy carbon electrode modified by ZnMn₂O₄ microspheres showed a linear amperometric response for H₂O₂ in a wide concentration range of 0.02 ˜ 15 mM with detection limit of 0.13 μM under the optimized conditions. Besides, the sensor proposed here was successfully used to determine H₂O₂ in milk, suggesting that ZnMn₂O₄ microspheres can be used for non-enzymatic electrochemical sensor applications.

A novel hydrogen peroxide sensor based on electrodeposited copper/cuprous oxide nanocomposites

Copper/cuprous oxide nanocomposites were electrodeposited on a fluorine doped tin oxide (FTO) glass substrate for sensitive determination of hydrogen peroxide.

Construction of a Biosensor Based on a Combination of Cytochrome c, Graphene, and Gold Nanoparticles

A biosensor based on a combination of cytochrome c (Cyt c), electrochemical reduced graphene oxides (ERGO), and gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) was fabricated. The proposed biosensor electrode was denoted as GCE/ERGO-Nafion/AuNPs/Cyt c/Nafion, where ERGO-Nafion was deposited by dropping graphene oxides-Nafion mixed droplet first and following electrochemical reduction, AuNPs were directly deposited on the surface of the ERGO-Nafion modified electrode by electrochemical reduction, and other components were deposited by the dropping-dry method. The effect of the deposition amount of AuNPs on direct electrochemistry of Cyt c in the proposed electrode was investigated. The hydrogen peroxide was taken to evaluate the performance of the proposed biosensor. The results showed that the biosensor has great analytical performance, including a high sensitivity, a wide linear range, a low detection limit, and good stability, reproducibility, and reliability.

Exploring the potential of electroless and electroplated noble metal-semiconductor hybrids within bio- and environmental sensing

Over the last two decades, the rapid development and widespread application of nanomaterials has significantly influenced research in various fields, including analytical chemistry and biosensing technologies. In particular, the simple functionalization and tuning of noble metal nanoparticle (NP) surface chemistry resulted in the development of a series of novel biosensing platforms with quick read-out and enhanced capabilities towards specific analyte detection. Moreover, noble metal NPs possess a number of unique properties, viz. high surface-to-volume ratio and excellent spectral, optical, thermal, electrical and catalytic characteristics. This manuscript provides an elaborate review on galvanic noble metal NPs deposited onto semiconductor surfaces, from the preparation stage towards their application in biosensors and gas sensing. Two types of deposition approaches, viz. galvanic displacement/electroless and conventional electroplating, are introduced and compared. Furthermore, the analytical merit of hybrid nanomaterials towards the improvement of sensing abilities is highlighted. Finally, some limitations and challenges related to progress in the development and application of analytical devices based on electroless and electroplated noble metal NPs-semiconductor hybrids (NMNPsHs) in biochemical and environmental sensing are discussed.

Sustainable Generation of Ni(OH)2 Nanoparticles for the Green Synthesis of 5-Substituted 1H-Tetrazoles: A Competent Turn on Fluorescence Sensing of H2O2

A mutually correlated green protocol has been devised that originates from a sustainable production of β-Ni(OH)₂ nanoparticles which is used for an efficient catalytic synthesis of versatile substituted tetrazoles, under mild reaction conditions in water via a simple, one-pot, eco-friendly method. The synthesis is followed by derivatization into a highly fluorescence active compound 9-(4-(5-(quinolin-2-yl)-1H-tetrazol-1-yl)phenyl)-9H-carbazole that can be used at tracer concentrations (0.1 μM) to detect as well as quantify hydrogen peroxide down to 2 μM concentration. The nanocatalyst was synthesized by a simple, proficient, and cost-effective methodology and characterized thoroughly by UV-vis absorption and Fourier transform infrared spectra, N₂ adsorption/desorption, high resolution transmission electron microscopy, powder X-ray diffraction pattern, field emission scanning electron microscopy, and thermogravimetric analysis. Broad substrate scope, easy handling, higher efficiency, low cost, and reusability of the catalyst are some of the important features of this heterogeneous catalytic system. The strong analytical performance of the resultant derivative in low-level quantification of potentially hazardous hydrogen peroxide is the key success of the overall green synthesis procedure reported here.

A novel H2O2 biosensor based on three-dimensional micro/nano-biointerfaces

A novel H₂O₂ biosensor was first reported to directly grow living cells on three-dimensional micro/nano-biointerfaces to promote electrochemical performance.

A critical study of the generality of the two step two electron pathway for water splitting by application of a C3N4/MnO2 photocatalyst

A novel C3N4-CDot composite photocatalyst was very recently shown to be highly efficient and very stable in water splitting by solar radiation without using any sacrificial reagent (J. Liu, et al., Science, 2015, 347(6225), 970). This photocatalyst utilizes a two-electron/two-step process in which the production of H2O2 and H2 is photocatalyzed by using C3N4 in the first step and H2O2 is decomposed by using CDots in the second step. The present work is a study on the generality of this approach by application of a C3N4/MnO2 catalyst. This new catalyst indeed splits water by a two step process in a stable way, without any sacrificial agent. It was however found that though the absorbance of the new catalyst in the visible range of 500-600 nm is much larger than that of the C3N4-CDot catalyst, its water splitting efficiency is much lower. These findings add insight into and assist in the further optimization of this new class of photocatalysts to meet the requirements of commercial water splitting systems.

One-step synthesis of Au nanoparticle–graphene composites using tyrosine: electrocatalytic and catalytic properties

The in situ synthesis of a reduced graphene oxide/Au nanoparticle composite for nonenzymatic H₂O₂ detection and nitrophenol reduction.

A novel δ-MnO2 with carbon nanotubes nanocomposite as an enzyme-free sensor for hydrogen peroxide electrosensing

We have reported the synthesis and application of carbon nanotubes supported δ-MnO₂ (δ-MnO₂/CNTs) nanocomposite as enzyme-free sensor for the detection of H₂O₂, where δ-MnO₂ serves as the catalytic center and CNTs as the highly conductive base.

Cobalt ferrite nanoparticles decorated on exfoliated graphene oxide, application for amperometric determination of NADH and H2O2

Here, cobalt ferrite nanohybrid decorated on exfoliated graphene oxide (CoFe2O4/EGO) was synthesized. The nanohybrid was characterized by different methods such as X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray diffraction microanalysis, transmission electron microscopy, FT-IR, Raman spectroscopy and electrochemical methods. The CoFe2O4/EGO nanohybrid was used to modify glassy carbon electrode (GCE). The voltammetric investigations showed that CoFe2O4/EGO nanohybrid has synergetic effect towards the electro-reduction of H2O2 and electro-oxidation of nicotinamide adenine dinucleotide (NADH). Rotating disk chronoamperometry was used for their quantitative analysis. The calibration curves were observed in the range of 0.50 to 100.0 μmol L(-1) NADH and 0.9 to 900.0 μmol L(-1) H2O2 with detections limit of 0.38 and 0.54 μmol L(-1), respectively. The repeatability, reproducibility and selectivity of the electrochemical sensor for analysis of the analytes were studied. The new electrochemical sensor was successfully applied for the determination of NADH and H2O2 in real samples with satisfactory results.

Hierarchical nanostructured noble metal/metal oxide/graphene-coated carbon fiber: in situ electrochemical synthesis and use as microelectrode for real-time molecular detection of cancer cells

We report the design and fabrication of a new type of nanohybrid microelectrode based on a hierarchical nanostructured Au/MnO2/graphene-modified carbon fiber (CF) via in situ electrochemical synthesis, which leads to better structural integration of different building blocks into the CF microelectrode. Our finding demonstrates that wrapping CF with graphene nanosheets has dramatically increased the surface area and electrical conductivity of the CF microelectrode. The subsequent template-free electrodeposition of MnO2 on graphene-wrapped CF gives rise to a porous nanonest architecture built up from twisted and intersectant MnO2 nanowires, which serves as an ideal substrate for the direct growth of Au nanoparticles. Owing to the structural merit and synergy effect between different components, the hierarchical nanostructured noble metal/metal oxide/graphene-coated CF demonstrates dramatically enhanced electrocatalytic activity. When used for nonenzymatic H2O2 sensing, the resultant modified microelectrode exhibits acceptable sensitivity, reproducibility, stability, and selectivity, which enable it to be used for real-time tracking H2O2 secretion in human cervical cancer cells. Graphical abstract A schematic illustration of preparation of hierarchical Au/MnO2/ERGO/CF nanohybrid electrode for real-time molecular detection of cancer cells.

Effects of hydrogen peroxide on an upward flow biological filter bed (BFB) containing manganese dioxide fillers

An upward flow BFB with a high decomposition efficiency of H₂O₂ is constructed. This BFB removes the detrimental effect of H₂O₂ and turns it into DO to boost aerobic metabolism. A concentration of 120 mg L⁻¹ H₂O₂ in feed wastewater increases COD removal efficiency by 39%.