MnO2 Nanorods Research Articles

Anticancer activity of manganese dioxide/reduced graphene oxide nanocomposites against A549 human lung adenocarcinoma cell line

A modified version of Hummers’ process was used to synthesize graphene oxide (GO), whereas solar radiation was used to create reduced graphene oxide (rGO) and MnO2/rGO (1%, 3%, 5%) nanostructures were synthesized using a facile hydrothermal method. The X-ray diffraction (XRD) pattern revealed the tetragonal structure of α-MnO2 and determined the crystallite size of MnO2/rGO as 14.36 nm. A scanning electron microscope (SEM) analysis confirms the growth of MnO2 nanorods on the rGO surface. MnO2/rGO (1%, 3%, 5%) contains elements such as carbon, oxygen and manganese, as verified by energy-dispersive X-ray analysis (EDAX). When the rGO percentage was increased, the surface area of MnO2/rGO was decreased to 16.340 m2/g, which enhances the interaction between A549 cells, according to Brunauer–Emmett–Teller (BET) analysis. The allotropes of carbon and the functional groups were examined using Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). A (dimethyl thiazolyl tetrazolium bromide) MTT assay was used to assess the cytotoxicity of GO, rGO and MnO2/rGO (1%, 3%, 5%) nanostructures against the human lung adenocarcinoma cell line (A549) and human lung epithelial cell line (L132). The half maximum inhibitory concentration (IC50) value for MnO2/5% rGO towards A549 cells was determined to be 120 μg/mL, which shows appreciable results when compared to GO (180 μg/mL), rGO (160 μg/mL), MnO2/1% rGO (180 μg/mL) and MnO2/3% rGO (160 μg/mL). The morphological changes in A549 cells were investigated using an AO/EtBr dual stain, the intracellular reactive oxygen species produced were evaluated using a DCFH-DA stain and the fragmented nuclei were examined using a Hoechst stain. According to the findings, the synthesized MnO2/rGO nanocomposites can be efficiently used for cytotoxicity against A549 cells and possess significant potential for the human lung cancer cell line.

Amine-aldehyde resin derived porous N-doped hollow carbon nanorods for high-energy capacitive energy storage

Electrochemical double layer capacitors (EDLCs) are known for their high power density but hampered by low energy density. Herein, N-doped hollow carbon nanorods (NHCRs) have been constructed by a hard templating method using MnO2 nanorods as the hard templates and m-phenylenediamine-formaldehyde resin as the carbon precursor. The NHCRs after activation (NHCRs-A) manifest abundant micropores/mesopores and an ultrahigh surface area (2166 m2 g−1). When employed in ionic liquid (IL) electrolyte-based EDLCs, the NHCRs-A delivers a high specific capacitance (220 F g−1 at 1 A g−1), an impressive energy density (110 Wh kg−1), and decent cyclability (97% retention over 15 000 cycles). The impressive energy density is derived from the abundant ion-available micropores, while the decent power density is originated from the hollow ion-diffusion channels as well as excellent wettability in ILs. In situ infrared spectroscopy together with in situ Raman unveil that both counter-ion adsorption and ion exchange are involved in the charge storage of NHCRs-A. This study provides insight into the construction of porous carbon materials for EDLCs.

Synergetic effect on enhanced electrochemical properties of MnO2 nanorods on g-C3N4/rGO nanosheet ternary composites for pouch-type flexible asymmetric supercapattery device

In this work, one-dimensional MnO2 nanorods are distributed evenly over two-dimensional g-C3N4/rGO nanosheets using a simple hydrothermal approach. The structure, functional group, morphologies, elemental analyses and surface area of prepared samples have been investigated. Moreover, the electrochemical performance of MnO2/g-C3N4/rGO in 1 M Na2SO4 aqueous electrolyte solution was tested using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and capacitance retention. The MnO2/g-C3N4/rGO material has superior electrochemical performance than pure and binary electrode materials due to the high surface area of ternary composite (469.26 m2/g) compared to pure (38.083 m2/g). The ternary MnO2/g-C3N4/rGO electrode obtained the high specific capacitance of 716.6 Fg−1 at 1 Ag−1 and kept 97 % capacitance retention after 10,000 cycles at a current density of 10 Ag−1. Since the synergistic effects of MnO2 and g-C3N4/rGO improve electrochemical performance, the ternary composite is an excellent option for high-performance supercapacitors. Moreover, the pouch-type supercapattery device was assembled using MnO2/g-C3N4/rGO and activated carbon electrodes. The supercapattery device exhibits a maximum specific capacitance of 108.5 Fg−1 with 91.5 % capacitance retention after 10,000 cycles at a high current density of 10 Ag−1. The device achieved a high energy density of 48.6 Wh kg−1 at a power density of 899.9 W kg−1 in the operating potential value of 0–1.8 V. The fabricated supercapattery device was tested for real practical application by charging 30 s and attained a self-discharging time of 5 min.

Nano MNO2 production from fine-grained and low-grade manganese ore using a mixture of citric acid and molasses as reductant

ABSTRACT This study was carried out to investigate the production of manganese nanomaterials by enriching fine-grained and low-grade manganese ores. Ore was taken from Balıkesir region in Turkey. Experimental studies were discussed in two different stages. In the first stage, the ore was enriched by a leaching method and optimum enrichment conditions were determined. For this, different mixtures of acids and reducing agents were used. The optimum Mn dissolution was 120 minutes. 97.05% Mn dissolution efficiency was obtained from the ore containing 29% MnO under a 120 minute leaching time, 600 rpm stirring speed, 2 M HCl and HNO3 (3:1) concentration, 0.5 M citric acid + 10% molasses reducers and at 90 °C. In the second stage, the Mn solution dissolved under optimum conditions was photo-reduced by exposure to sunlight and then MnCO3 was produced using Na2CO3. The produced MnCO3 was roasted and 200 nm MnO2 nanorods were obtained.

The role of AgNPs in selective oxidation of benzyl alcohol in vapor phase using morphologically tailored MnO2 nanorods in the presence of air

Vapor phase benzyl alcohol (BnOH) oxidation reaction is investigated over a pre–synthesised morphologically designed shape controlled spherical silver nanoparticles (AgNPs) decorated on manganese oxide nanorods (α–MnO2NRs) in the presence of air. The combination of silver nanoparticles and the α–MnO2NRs interface enabled the increased oxygen vacancies (Ov) and exhibited the strong metal–support interactions (SMSI) in surface oxygen activation. The effect of Ag loadings is significant and the optimal 1 wt% Ag loaded catalyst (1Ag/MnO2NRs) showed excellent performance in benzyl alcohol oxidation due to high adsorption capacity, enhanced oxygen vacancies and red–ox properties. The DFT calculations confirmed that the high BnOH surface adsorption was exhibited over Ag modified MnO2NRs than the bare α–MnO2NRs. The optimized 1Ag/α–MnO2NRs catalytic system achieved 2.6 fold higher activity compared to bare α–MnO2NRs. These results provided novel insights on the rational design of shape dependent metal/metal oxide based heterogeneous catalysts.

Graphene Oxide Addition Induces the Improvement of ORR Catalysis Properties of Low-Cost Mn-Based Catalyst Used for Al-Air Battery

To further improve the oxygen reduction reaction (ORR) activity of low-cost Mn based catalyst, graphene oxide (GO) was added in the preparation of one dimensional (1D) α-MnO2 nanorod using KMnO4-MnSO4 system via hydrothermal method. Experimental results showed that the GO addition (20 wt%) could induce the formation of MnO(OH) nanorod. The Mn based@GO catalyst had more surface defects and oxygen vacancies compared with pure α-MnO2. The onset potential, half-wave potential (E1/2) and limiting current density were significantly enhanced from 0.86 V/0.66 V/3.56 mA cm-2 to 0.91 V/0.77 V/5.41 mA cm-2, indicating that GO addition could greatly improve the catalytic activity of Mn based catalyst. Furthermore, the discharge voltage, power density, mass energy density of Al-air battery using Mn based@GO catalyst were greatly improved comparing with the usage of pure MnO2 catalyst, and it was also found that the application effect of Mn based @GO catalyst in the Al-air battery was almost comparable to the commercial 20% Pt/C catalyst. Our research revealed for the first time the commercial potential of the novel and low-cost MnO2/MnO(OH)@GO nanocomposite in the Al-air battery.

Binary metal oxide (MnO2/SnO2) nanostructures supported triazine framework-derived nitrogen-doped carbon composite for symmetric supercapacitor

A high-performance supercapacitor was fabricated using binary metal oxide (manganese oxide and tin oxide) decorated triazine framework-derived nitrogen-doped carbon (MnO2@SnO2/T-NC) composites. Morphological analysis showed that the SnO2/T-NC composite surface was densely decorated with MnO2 nanorods (<20 nm). The MnO2@SnO2/T-NC (5:1) composite delivered a capacitance of 676 F g−1 at 1 A g−1current density. The symmetric system displayed a capacitance of 91.1 F g−1 at 1 A g−1 with good cycling stability. After 7000 cycles, the device withheld 92.3 % of its total capacitance at 3 A g−1. The electrode's high performance may be ascribed to the redox reaction of metal oxides and fast electrolyte transport through porous carbon. After charging the symmetric supercapacitor device for 23 s at 4.4 V, green (2.0 V) and blue (3.3 V) light-emitting diodes were powered for 21 and 10 min, respectively.

Room-temperature coating of Mn3O4–2D material (graphene and MoS2) nanocomposites for improving oxygen evolution reaction kinetics

Two-dimensional nanomaterials such as graphene nanosheets and molybdenum disulfide nanoflakes were easily hybridized with spinel Mn3O4 in a single deposition process at low temperature by a facile kinetic spray approach under low vacuum conditions using a nano-particle deposition system. The heterostructured Mn3O4–2D hybrid nanocomposites (NCs) were utilized to enhance the reaction kinetics of oxygen evolution. Hybrid NCs of Mn3O4 with MoS2 and graphene showed nanoflakes and nanosheet morphologies, respectively. The synergy improvement in nanocomposites of Mn3O4-graphene nanosheets and Mn3O4−MoS2 nanoflakes was examined by x-ray photoemission spectroscopy and analysis of Raman spectra that results in a decrease in OER overpotential to 289 mV at 10 mA⋅cm−2 for Mn3O4-graphene nanosheets and 295 mV for Mn3O4−MoS2 nanoflakes. The estimated Tafel slope strongly decreased from 88 mV⋅dec−1of pure Mn3O4 nanorods to around 44 mV⋅dec−1 for hybrid NCs. This behavior indicates improved charge transfer kinetics due to the decrease in charge transfer resistance. Furthermore, all fabricated nanostructure electrocatalysts exhibited very good stability for prolonged galvanostatic polarization up to 50 h.

Ionic-Liquid-Assisted Synthesis of Mixed-Phase Manganese Oxide Nanorods for a High-Performance Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (ZIBs) provide a safer and cost-effective energy storage solution by utilizing nonflammable water-based electrolytes. Although many research efforts are focused on optimizing zinc anode materials, developing suitable cathode materials is still challenging. In this study, one-dimensional, mixed-phase MnO2 nanorods are synthesized using ionic liquid (IL). Here, the IL acts as a structure-directing agent that modifies MnO2 morphology and introduces mixed phases, as confirmed by morphological, structural, and X-ray photoelectron spectroscopy (XPS) studies. The MnO2 nanorods developed by this method are utilized as a cathode material for ZIB application in the coin-cell configuration. As expected, Zn//MnO2 nanorods show a significant increase in their capacity to 347 Wh kg-1 at 100 mA g-1, which is better than bare MnO2 nanowires (207.1 Wh kg-1) synthesized by the chemical precipitation method. The battery is highly rechargeable and maintains good retention of 86% of the initial capacity and 99% Coulombic efficiency after 800 cycles at 1000 mA g-1. The ex situ XPS, X-ray diffraction, and in-depth electrochemical analysis confirm that MnO6 octahedra experience insertion/extraction of Zn2+ with high reversibility. This study suggests the potential use of MnO2 nanorods to develop high-performance and durable battery electrode materials suitable for large-scale applications.

Augmented electrochemical properties of manganese oxide nanorods on low energy nitrogen ion irradiation

For the development of versatile and high-performance storage devices, nanorods-based supercapacitors hold great promise due to their high energy density per unit volume and their resilience in the face of high mechanical stress. In this study, we demonstrated how to increase charge storage capacity by using an ion beam to join manganese oxide nanorods on a massive scale, thereby creating surface defects. Hydrothermally synthesized Mn3O4 nanorods were spin-coated on a silicon wafer and subjected to low energy (5 keV) N+ ion-beam at varying ion fluences before undergoing extensive electrochemical characterizations to verify their charge storage performance. At a mass normalized current of 10 A/g, the areal capacitance for pristine and irradiated Mn3O4 nanorods is 45 mF/cm2 and 132 mF/cm2. Hence, irradiated Mn3O4 nanorods were found to have better charge storage performance than their untreated counterparts. Insights into the improved charge-storage performance of irradiated nanorods are made clear by the detailed experimental findings. The irradiated sample further retains 90% of its initial capacitance for more than 5000 cycles of measurements. The enhanced areal capacitance performance after irradiation is due to the oxygen vacancy supported by TRI3DYN simulations. The high charge storage performance of the irradiated samples can be attributed to several factors, including the induced oxygen vacancy and improved surface area. This research adds to the growing body of evidence that ion beam irradiation can be used to fine-tune the supercapacitor electrode's surface area, conductivity, and storage capacity.

Fabrication of electrochemical sensor based on MnO2 nanorods for tetracycline detection

ABSTRACT A highly efficient, green and simple method has been reported, for the detection of tetracycline at μM level. An improved redox co-precipitation method was used to make highly MnO2 nanorods from MnCl2.4 H2O and KMnO4. High-resolution transmission electron microscopy (HRTEM) analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett Teller (BET) surface area analysis were used to describe the structure and morphology of the material. The MnO2 material was amorphous and mesoporous, with a surface area of 89.908 m2/g and an average pore size of 6.023 nm. The oxidising property of the produced nano MnO2, as well as its porosity and surface area, have rendered the MnO2 material a potent sensor for tetracycline hydrochloride (TC) detection in an aqueous medium at room temperature. The effect of pH, MnO2 dosage of TC was more favourable at pH 5. The sensor has good electrochemical performance, with a linear response for TC concentration varying from 1 μM to 1 mM and a Limit of Detection (LOD) of 0.513 µM. Furthermore, the prepared sensor exhibited excellent repeatability, portability, reproducibility, specificity, sensitivity and was cost-effective, all of which were the characteristics of a good electrochemical sensor material. The synthesised sensor was employed to determine TC in real-world samples (water and food) to demonstrate its capabilities.

Ag nanoparticle-loaded to MnO2 with rich oxygen vacancies and Mn3+ for the synergistically enhanced oxygen reduction reaction

MnO2 is considered to be one of the most promising electrocatalysts for oxygen reduction reactions (ORR) in alkaline media and can be applied to various electrochemical energy conversion and storage devices. However, it is limited by the relatively slow kinetics of the cathodic electrochemical reactions. In addition, it is difficult to control the presence state of Ag during the modification of MnO2. To this end, an efficient ORR electrocatalyst of Ag nanoparticles supported by MnO2 nanorods was successfully synthesized by using NH3·H2O as a complexing agent to inhibit the Ag+ intercalating into the tunnels of MnO2. The half-wave potential (E1/2) and limiting current density (Jlim) of the obtained Ag/MnO2 electrocatalysts are 0.81 V and −5.6 mA cm−2, respectively, showing comparable ORR catalytic activity to commercial Pt/C catalysts. The excellent catalytic performances can be attributed to the presence of abundant oxygen vacancies and Mn3+ species on the MnO2 surface, as well as the synergistic effect between MnO2 substrates and Ag nanoparticles. Among them, oxygen vacancies enhances the adsorption of O2, Mn3+ facilitates the displacement of O22−/OH−, MnO2 inhibits the accumulation of peroxide species to improving the oxygen environment on the Ag surface and Ag accelerates the electron transfer in the whole process. This work provides a useful guide for the design of efficient Mn-based ORR electrocatalysts.

Surface Modification of β-MnO2 Nanorods as Nanolubricant

Introduction: Nanolubricants are substances that use nanoparticles as lubricant additives. The proposal for wear reduction has piqued interest in nanolubricants. Particle agglomeration is the main drawback of using nanomaterials as lubricating oil additives, and creating novel nanolubricants is one of the most difficult challenges. Objective: Evaluation of the nano β-MnO2 nanorods as nanoadditives for enhancing lubricating oil characteristics. Methods: After producing β-MnO2 nanorods by a modified hydrothermal process, oleic acid was used to modify their surfaces. Next, the physical and tribological characteristics of lubricating oil before and after the addition of nanoadditives were assessed. Results: The physical parameters of lubricating oil, including flash point, pour point, thermal stability, antiwear ability, and viscosity, were all improved by varying concentrations of surface-modified MnO2 nanorods by rates 8.19%, 50%, 63.04%, 10.9%, 8.96% at 40ºC and 4.18% at 100ºC, respectively. The findings demonstrate that the shear strain is reduced and an anti-wear boundary coating is created as a result of the deposition of nanoparticles produced by tribochemical reaction products during the friction process. Conclusion: The development of a protective film using nanoadditives improves lubricant requirements, ushering in a revolution in the lubricant industry.

The morphology and phase conversion of MnO2 in g-CN@MnO2 composite with supercapacitor applications

This paper presents a method or preparing a composite with morphology and phase conversion appropriate for use in a supercapacitor. Manganese dioxide (MnO2) nanoflakes composed of MnO2 nanorods (α and γ phases) with protonated g-C3N4 (g-CN), were prepared via a hydrothermal method. As synthesized composite showed district morphology and phase conversion of MnO2. The composite was thoroughly evaluated by field emission electron microscopy (FESEM), transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Based on characterizations, morphology and phase conversion phenomenon of MnO2 in g-CN/MnO2 composite is suggested and discussed. The electrochemical performance of the composite was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) and compared to the performance of bare g-CN and MnO2 nanoflakes in alkaline electrolyte solution. The composite showed more specific capacitance (148.66 F/g) at 0.5 A/g than the pristine form of its components. An asymmetric supercapacitor (g-CN@MnO2//PCNFs), assembled through a g-CN@MnO2 composite and with porous carbon nanofibers (PCNFs), achieved an energy density of 1.6 Wh/Kg and a power density of 84 W/kg. This study suggests a new avenue for the development of MnO2 based composites use as energy storage materials.

Improved bioelectrochemical performance of MnO2 nanorods modified cathode in microbial fuel cell.

The property of cathode in the microbial fuel cell (MFC) was one of the key factors limiting its output performance. MnO2 nanorods were prepared by a simple hydrothermal method as cathode catalysts for MFCs. There were a number of typical characteristic crystal planes of MnO2 nanorods like (110), (310), (121), and (501). Additionally, there were great many hydroxyl groups on the surface of nanorod-like MnO2, which provided a rich set of active adsorption sites. The maximum power density (Pmax) of MnO2-MFC was 180 mW/m2, which was 1.51 times that of hydrothermally synthesized MnO2 (119.07 mW/m2), 4.28 times that of naturally synthesized MnO2 (42.05 mW/m2), and 5.61 times that of the bare cathode (32.11 mW/m2). The maximum voltage was 234mV and the maximum stabilization time was 4days. The characteristics of MnO2, including rod-like structure, high specific surface area, and high conductivity, were conducive to providing more active sites for oxygen reduction reaction (ORR). Therefore, the air cathode modified by MnO2 nanorods was a kind of fuel cell electrode with great application potential.

Cellulose grafted poly acrylic acid doped manganese oxide nanorods as novel platform for catalytic, antibacterial activity and molecular docking analysis

Various concentrations of cellulose nanocrystal grafted poly acrylic acid (CNC-g-PAA) doped MnO2 nanorods (NRs) were synthesized through a hydrothermal process. This work aimed to analyze the influence of CNC-g-PAA (3, 6, and 9 mL) on MnO2 for catalysis and antibacterial behavior. Various characterization approaches were utilized to investigate the optical, structural, morphological features, and chemical composition of synthesized materials. FTIR results were used to assess the vibrational and rotational modes of the presence of functional groups (OH, CO and Mn-O) in synthesized samples. Electronic spectra revealed a bathochromic shift upon doping that led to decrease in band gap energy. The catalytic activity of CNC-g-PAA doped MnO2 increased gradually with a higher doping ratio owing to a reduction in electron-hole (e−-h+) pair recombination. As a result, 9 mL CNC-g-PAA doped MnO2 is suggested as a valuable and superior catalyst for cleaning the environment and wastewater. In addition, 9 mL CNC-g-PAA doped MnO2 revealed a significant inhibition area for Escherichia coli in comparison to Staphylococcus aureus at high and low doses correspondingly. Further, molecular docking studies of these NRs were performed to get insight into the mystery behind these bactericidal activities.

MOF-derived core–shell MnO@Cu/C as high-efficiency catalyst for reduction of nitroarenes

The design of catalysts for competitive pricing and high-performance reduction reactions has attracted increasing attention. The low resistance to aggregation and sintering as well as the uneven size distribution during reaction and preparation of such catalysts, considerably limit their practical applications. This paper presents the preparation of highly stable copper nanoparticles (Cu-NPs) by coating MnO2 nanorods with Cu metal–organic frameworks (MOF) via simple layer-by-layer assembly. The high-temperature reduction of MnO2/Cu-MOF generates MnO/Cu-C as catalyst. The obtained Cu-NPs in a Cu/C@MnO catalyst, with partially uncovered free active surfaces, are encapsulated by a carbon-matrix. This unique structure, with homogeneously distributed Cu-NPs in the carbon matrix, significantly retards the sintering and oxidation of the Cu-NPs in solution. Excellent activity (100 % conversion in 90 s) and recyclability after six cycles [>98 % (conversion) in 120 s] in water are achieved for the reduction of 4-nitrophenol by sodium borohydride (NaBH4) under mild conditions. This high performance is attributed to the high adsorption ability of the carbon matrix and the high catalytic activity of Cu-NPs on the MnO surface. This study provides novel MOF-derived catalysts for use in various valuable applications.

Selective Voltammetric Sensor for the Simultaneous Quantification of Tartrazine and Brilliant Blue FCF.

Tartrazine and brilliant blue FCF are synthetic dyes used in the food, cosmetic and pharmaceutical industries. The individual and/or simultaneous control of their concentrations is required due to dose-dependent negative health effects. Therefore, the paper presents experimental results related to the development of a sensing platform for the electrochemical detection of tartrazine and brilliant blue FCF based on a glassy carbon electrode (GCE) modified with MnO2 nanorods, using anodic differential pulse voltammetry. Homogeneous and stable suspensions of MnO2 nanorods have been obtained involving cetylpyridinium bromide solution as a cationic surfactant. The MnO2 nanorods-modified electrode showed a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in the electron transfer resistance. The developed sensor allowed the simultaneous quantification of dyes for two linear domains: in the ranges of 0.10-2.5 and 2.5-15 μM for tartrazine and 0.25-2.5 and 2.5-15 μM for brilliant blue FCF with detection limits of 43 and 41 nM, respectively. High selectivity of the sensor response in the presence of typical interference agents (inorganic ions, saccharides, ascorbic and sorbic acids), other food dyes (riboflavin, indigo carmine, and sunset yellow), and vanillin has been achieved. The sensor has been tested by analyzing soft and isotonic sports drinks and the determined concentrations were close to those obtained involving the chromatography technique.

A dual channel fluorescence tongue for catechin recognition based on the MnO2 nanorods-Amplex Red-o-phenylenediamine reaction system.

Here, we report a dual-channel fluorescence sensor array for catechin discrimination based on the MnO2 nanorods (NRs)-Amplex Red (AR)-o-phenylenediamine (OPD) catalytic reaction system. MnO2 catalyzes both OPD and AR oxidation, and the fluorescence intensity values generated at 550 nm and 590 nm provide "fingerprints" for the sensor array. Different catechins have varying degrees of inhibitory effects on the MnO2 NRs-AR-OPD catalytic reaction system, thus obtaining unique fluorescence response fingerprints. Through linear discriminant analysis (LDA), the sensor array can not only successfully distinguish 5 catechins with concentrations as low as 500 nM and different concentrations of catechins, but also realize the identification of catechin mixtures. Notably, this method only requires the preparation of a single nanomaterial that catalyzes two substrates simultaneously and can generate two different fluorescence signal outputs, greatly facilitating the design of the sensor array.

The use of ex-situ nitrogen-doped olive oil-derived carbon nano-onions for application in chemi-resistive gas sensors to detect acetone at room temperature

This study reports on the synthesis of carbon nano-onions (CNOs; ca. d &lt; 55 nm) and nitrogen-doped CNOs (N-CNOs) using a facile pyrolysis method and ex-situ doping of the CNOs. Elemental analysis of the N-CNOs revealed that their nitrogen content depended on the ammonia flow rate. Analysis of the N-CNOs revealed that they all exhibited structural defects. After the successful synthesis of CNOs and N-CNOs, polyvinylpyrrolidone (PVP):CNOs/N-CNOs:MnO2-nanorods (MONRs) composites were prepared and used as active sensing materials. In every case, the PVP polymer was used to stabilize the MONRs for acetone detection at 25 °C. The chemi-resistive gas sensors that showed the highest acetone sensitivity (pS = 2.0 x 10-4 ppm-1) was fabricated using a pristine CNOs (pCNOs) based composite. However, the N-CNOs based sensor (a15S) presented the lowest acetone limit of detection (LoD) at 1.2 ppm. The study implicated the effect of the nitrogen and oxygen content of the CNOs surfaces on the acetone detection. Thus, a higher sensitivity with lower LoD was observed at room temperature using the pCNOs based sensor, when compared to earlier literature reports.