Cobalt oxide nanoparticles anchored to multiwalled carbon nanotubes: Synthesis and application for enhanced electrocatalytic reaction and highly sensitive nonenzymatic detection of hydrogen peroxide

Experimental and theoretical aspects of the growth of vertically aligned CNTs by CCVD on AZO substrate

An efficient and reproducible growth of vertically aligned carbon nanotubes by CCVD requires accurate and specific setting of the synthesis parameters and the properties of catalyst thin layers. In this work, the growth of vertically aligned carbon nanotubes onto AZO (= aluminum doped zinc oxide) glass substrate covered by Al2O3 and Fe-Co catalyst layer system is presented. Investigation of the effect of catalyst composition and synthesis temperature on CVD growth revealed the optimum condition of the synthesis. The analysis of as-prepared samples by SEM, TEM and Raman spectroscopy was carried out to prove the structure and quality of carbon deposit. Theoretical considerations have supported speculative ideas about the role of the support layer, the transformation of the catalyst layer in the presence of hydrogen gas and the growth mechanism of carbon nanotubes. The mechanism of CNT growth is modelled and the order of magnitude of experimentally observed vertical linear growth rate of CNT (several nm/s) is reproduced.

Electrochemical-Based Sensing Platforms for Detection of Glucose and H2O2 by Porous Metal-Organic Frameworks: A Review of Status and Prospects

Establishing enzyme-free sensing assays with great selectivity and sensitivity for glucose and H₂O₂ detection has been highly required in biological science. In particular, the exploitation of nanomaterials by using noble metals of high conductivity and surface area has been widely investigated to act as selective catalytic agents for molecular recognition in sensing platforms. Several approaches for a straightforward, speedy, selective, and sensitive recognition of glucose and H₂O₂ were requested. This paper reviews the current progress in electrochemical detection using metal-organic frameworks (MOFs) for H₂O₂ and glucose recognition. We have reviewed the latest electrochemical sensing assays for in-place detection with priorities including straightforward procedure and manipulation, high sensitivity, varied linear range, and economic prospects. The mentioned sensing assays apply electrochemical systems through a rapid detection time that enables real-time recognition. In profitable fields, the obstacles that have been associated with sample preparation and tool expense can be solved by applying these sensing means. Some parameters, including the impedance, intensity, and potential difference measurement methods have permitted low limit of detections (LODs) and noticeable durations in agricultural, water, and foodstuff samples with high levels of glucose and H₂O₂.

A Review on Non-Enzymatic Electrochemical Biosensors of Glucose Using Carbon Nanofiber Nanocomposites

Diabetes mellitus has become a worldwide epidemic, and it is expected to become the seventh leading cause of death by 2030. In response to the increasing number of diabetes patients worldwide, glucose biosensors with high sensitivity and selectivity have been developed for rapid detection. The selectivity, high sensitivity, simplicity, and quick response of electrochemical biosensors have made them a popular choice in recent years. This review summarizes the recent developments in electrodes for non-enzymatic glucose detection using carbon nanofiber (CNF)-based nanocomposites. The electrochemical performance and limitations of enzymatic and non-enzymatic glucose biosensors are reviewed. Then, the recent developments in non-enzymatic glucose biosensors using CNF composites are discussed. The final section of the review provides a summary of the challenges and perspectives, for progress in non-enzymatic glucose biosensors.

Co3O4 Nanoparticles Uniformly Dispersed in Rational Porous Carbon Nano-Boxes for Significantly Enhanced Electrocatalytic Detection of H2O2 Released from Living Cells

A facile and ingenious method to chemical etching-coordinating a metal-organic framework (MOF) followed by an annealing treatment was proposed to prepare Co₃O₄ nanoparticles uniformly dispersed in rational porous carbon nano-boxes (Co₃O₄@CNBs), which was further used to detect H₂O₂ released from living cells. The Co₃O₄@CNBs H₂O₂ sensor delivers much higher sensitivity than non-etching/coordinating Co₃O₄, offering a limit of detection of 2.32 nM. The wide working range covers 10 nM-359 μM H₂O₂, while possessing good selectivity and excellent reproducibility. Moreover, this biosensor was used to successfully real-time detect H₂O₂ released from living cells, including both healthy and tumor cells. The excellent performance holds great promise for Co₃O₄@CNBs’s applications in electrochemical biomimetic sensing, particularly real-time monitor H₂O₂ released from living cells.

Electrochemical sensor for the non-enzymatic reduction of hydrogen peroxide and oxidation of gallic acid using a polyamidoblack-10B (PAB)-modified electrode

A novel electrochemical sensor for the oxidation of gallic acid and reduction of hydrogen peroxide using a paraffin impregnated graphite electrode modified with polyamidoblack 10B is developed.

Methods to evaluate the scavenging activity of antioxidants toward reactive oxygen and nitrogen species (IUPAC Technical Report)

This project was aimed to identify the quenching chemistry of biologically important reactive oxygen and nitrogen species (ROS/RNS, including radicals), to show antioxidant action against reactive species through H‐atom and electron transfer reactions, and to evaluate the ROS/RNS scavenging activity of antioxidants with existing analytical methods while emphasizing the underlying chemical principles and advantages/disadvantages of these methods. In this report, we focused on the applications and impact of existing assays on potentiating future research and innovations to evolve better methods enabling a more comprehensive study of different aspects of antioxidants and to provide a vocabulary of terms related to antioxidants and scavengers for ROS/RNS. The main methods comprise the scavenging activity measurement of the hydroxyl radical (•OH), dioxide(•1–) (O2 •–: commonly known as the superoxide radical), dihydrogen dioxide (H2O2: commonly known as hydrogen peroxide), hydroxidochlorine (HOCl: commonly known as hypochlorous acid), dioxidooxidonitrate(1–) (ONOO−: commonly known as the peroxynitrite anion), and the peroxyl radical (ROO•). In spite of the diversity of methods, there is currently a great need to evaluate the scavenging activity of antioxidant compounds in vivo and in vitro. In addition, there are unsatisfactory methods frequently used, such as non-selective UV measurement of H2O2 scavenging, producing negative errors due to incomplete reaction of peroxide with flavonoids in the absence of transition metal ion catalysts. We also discussed the basic mechanisms of spectroscopic and electrochemical nanosensors for measuring ROS/RNS scavenging activity of antioxidants, together with leading trends and challenges and a wide range of applications. This project aids in the identification of reactive species and quantification of scavenging extents of antioxidants through various assays, makes the results comparable and more understandable, and brings a more rational basis to the evaluation of these assays and provides a critical evaluation of existing ROS/RNS scavenging assays to analytical, food chemical, and biomedical/clinical communities by emphasizing the need for developing more refined, rapid, simple, and low‐cost assays and thus opening the market for a wide range of analytical instruments, including reagent kits and sensors.

A Novel Nonenzymatic Hydrogen Peroxide Sensor Based on Magnetic Core-Shell Fe3O4@C/Au Nanoparticle Nanocomposite

Fe₃O₄@C/Au nanoparticle (AuNP) nanocomposites were prepared through electrostatic adsorption of AuNPs onto PDDA-functionalized core/shell Fe₃O₄@C magnetic nanospheres, which had been synthesized by a facile solvothermal method. The morphology and composition of the nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), etc. Moreover, highly electrocatalytic activity to the reduction of hydrogen peroxide (H₂O₂) was also exhibited on the Fe₃O₄@C/AuNP-modified indium tin oxide (ITO) electrode. The effect of solution pH and the modification amount of Fe₃O₄@C/AuNPs on the performance of electrocatalytic H₂O₂ reduction was investigated. Under the optimal conditions, the catalytic current showed a linear relationship with the increase of H₂O₂ concentration in the range of 0.007–15 mM and a detection limit of 5 μM. The H₂O₂ sensor showed high selectivity for H₂O₂ detection, which could effectively resist the interference of ascorbic acid (AA), uric acid (UA), and citric acid (CA). Finally, the H₂O₂ sensor was used in the real fetal bovine serum to detect H₂O₂ and obtained satisfactory results with the recovery values ranging from 95.14 to 103.6%.

Cobalt Phosphide (Co2P) with Notable Electrocatalytic Activity Designed for Sensitive and Selective Enzymeless Bioanalysis of Hydrogen Peroxide

In this work, cobalt phosphide nanoparticles (Co₂P NPs) were prepared by simple and mild hydrothermal method without the use of harmful phosphorous source. The morphological structure and surface component of Co₂P were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy measurements. Considering the excellent electrocatalytic reduction activity and good electrical conductivity of transition-metal phosphide, we fabricated Co₂P NPs on indium tin oxide (ITO) substrate (Co₂P/ITO) for H₂O₂ detection. The Co₂P/ITO transducer displayed a rapid amperometric response less than 5 s, a broader response range from 0.001 to 10.0 mM and a low detection limit of 0.65 μM. In addition, the non-enzymatic Co₂P/ITO sensor showed outstanding selectivity, reproducibility, repeatability and stability, all of which qualified the Co₂P/ITO electrode for quite a reliable and promising biosensor for H₂O₂ sensing.

Hard template synthesis of 2D porous Co3O4 nanosheets with graphene oxide for H2O2 sensing

In this work, we used graphene oxide (GO) as a template that was removed by calcination to finally successfully prepare Co₃O₄ with 2D porous nanostructure. The results show that 2D porous structure Co₃O₄ nanosheets were only prepared at pH = 2. After electrochemical tests, the as-prepared Co₃O₄ nanosheets showed electrochemical properties that are highly suitable for H₂O₂ detection, such as high current response, short response time (less than 3 s), wide linear range (0.388-44.156 mM), low limit of detection (2.33 μM) and high sensitivity (0.0891 mA mM^-1 cm^-2). These excellent properties are mainly due to GO, as a 2D template, which connects Co₃O₄ nanoparticles to each other on a 2D plane, preventing the agglomeration of Co₃O₄ nanoparticles. The abundant pores between Co₃O₄ nanoparticles can greatly increase the reaction between the nanoparticles and H₂O₂ molecules.

Electrocatalytic Properties of 3D Hierarchical Graphitic Carbon-Cobalt Nanoparticles for Urea Oxidation

A 3D hierarchical graphitic carbon nanostructure encapsulating cobalt(0)/cobalt oxide nanoparticles (CoGC) has been prepared by solid-state pyrolysis of a mixture of anthracene and cobalt 2,2'-bipyridine terephthalate complex at 850 °C. Based on the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, the prepared material has high surface area (186.8 m² g^-1) with an average pore width of 205.5 Å. XPS reveals the functionalization of carbon with different oxygen-containing groups, such as carboxylic acid groups. The presence of metallic cobalt nanoparticles with cubic and hexagonal crystalline structures encapsulated in graphitized carbon is confirmed using XRD and TEM. Raman spectroscopy indicates a graphitization degree of I _D/I _G = 1.02. CoGC was cast onto a glassy carbon electrode and used for urea electrooxidation in an alkaline solution. The electrochemical investigation shows that the newly prepared CoGC has a promising electrocatalytic activity toward urea. The specific activity is 128 mA cm^-1 mg^-1 for the electrooxidation of 0.3 M urea in 1 M KOH at a relatively low onset potential (0.31 V vs Ag/AgCl). It can be mainly attributed to the morphological structure of carbon and the high reactivity of cobalt nanoparticles. The calculated charge-transfer resistance, R _ct, of the modified electrode in the presence of urea (10.95 Ω) is significantly lower than that in the absence of urea (113.5 Ω), which indicates electrocatalytic activity. The value of charge-transfer rate constant, k _s, for the anodic reaction is 0.0058 s^-1. Electrocatalytic durability in 1000 s chronoamperometry of the modified electrode suggests high structure stability. The modified electrode retained about 60% of its activity after 100 cycles as indicated by linear sweep voltammetry.

One-Step Electrodeposition of Silver Nanostructures on 2D/3D Metal-Organic Framework ZIF-67: Comparison and Application in Electrochemical Detection of Hydrogen Peroxide

Metal-organic frameworks (MOFs) have been widely used as supporting materials to load or encapsulate metal nanoparticles for electrochemical sensing. Herein, the influences of morphology on the electrocatalytic activity of Co-containing zeolite imidazolate framework-67 (ZIF-67) as supporting materials were studied. Three types of morphologies of MOF ZIF-67 were facilely synthesized by changing the solvent because of the influence of the polar solvent on the nucleation and preferential crystal growth. Two-dimensional (2D) ZIF-67 with microplate morphology and 2D ultrathin ZIF-67 nanosheets were obtained from pure H₂O (H-ZIF-67) and a mixed solution of dimethylformamide and H₂O (D-ZIF-67), respectively. Three-dimensional ZIF-67 with rhombic dodecahedron morphology was obtained from pure methanol (M-ZIF-67). Then, one-step electrodeposition of silver nanostructures on ZIF-67-modified glassy carbon electrode (Ag/ZIF-67/GCE) was performed for the reduction of hydrogen peroxide (H₂O₂). Cyclic voltammetry can be used to investigate the electrocatalytic activity of Ag/ZIF-67/GCE, and Ag/H-ZIF-67/GCE displayed the best electrocatalytic property than Ag/D-ZIF-67/GCE and Ag/M-ZIF-67/GCE. The electrochemical H₂O₂ sensor showed two wide linear ranges of 5 μM to 7 mM and 7 to 67 mM with the sensitivities of 421.4 and 337.7 μA mM^-1 cm^-2 and a low detection limit of 1.1 μM. In addition, the sensor exhibited good selectivity, high reproducibility, and stability. Furthermore, it has been utilized for real-time detection of H₂O₂ from HepG2 human liver cancer cells. This work provides a novel strategy for enhancing the detection performance of electrochemical sensors by changing the crystalline morphologies of supporting materials.

Hetero-structured MnO-Mn3O4@rGO composites: Synthesis and nonenzymatic detection of H2O2

The construction of metal-oxide heterojunction architecture has greatly widened applications in the fields of optoelectronics, energy conversions and electrochemical sensors. In this study, olive-like hetero-structured MnO-Mn₃O₄ microparticles wrapped by reduced graphene oxide (MnO-Mn₃O₄@rGO) were synthesized through a facile solvothermal-calcination treatment. The morphology and structure of MnO-Mn₃O₄@rGO were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. The as-synthesized MnO-Mn₃O₄@rGO exhibited prominent catalyzing effect on the electroreduction of H₂O₂, due to the combination of good electrical conductivity of rGO and the synergistic effect of MnO and Mn₃O₄. The MnO-Mn₃O₄@rGO modified glassy carbon electrode provided a wide linear response from 0.004 to 17 mM, a low detection limit of 0.1 μM, and high sensitivity of 274.15 μA mM^-1 cm^-2. The proposed sensor displayed noticeable selectivity and long-term stability. In addition, the biosensor has been successfully applied for detecting H₂O₂ in tomato sauce with good recovery, revealing its promising potential applications for practical electrochemical sensors.

Nanoporous platinum-copper flowers for non-enzymatic sensitive detection of hydrogen peroxide and glucose at near-neutral pH values

Multimodal nanoporous PtCu flowers (np-PtCu) were prepared via a two-step dealloying strategy under mild conditions. The np-PtCu alloy possesses an interconnected flower-like network skeleton with multiscale pore distribution. This material was placed on a glassy carbon electrode where it shows outstanding detection performance towards hydrogen peroxide and glucose in near-neutral pH solutions. It can be attributed to the specific structure in terms of interconnected nanoscaled ligaments, rich pore openings and a synergistic alloying effect. Figures of merit for detection H₂O₂ assay include (a) a working voltage of 0.7 V (vs. the reversible hydrogen electrode); (b) a wide linear response range (from 0.01 to 1.7 mM), and (c) a low detection limit (0.1 μM). The respective data for the glucose assay are (a) 0.4 V, (b) 0.01-2.0 mM, and (c) 0.1 μM. The method is not interfered in the presence of common concentrations of dopamine, acetaminophen and ascorbic acid. Graphical abstract Multimodal nanoporous (np) PtCu alloy was prepared via a two-step dealloying strategy under mild conditions. Np-PtCu exhibits superior electrocatalytic activity. The assay is highly sensitive, selective, and it allows for a long-term detection of H₂O₂ and glucose.

Electrospun CuO-ZnO nanohybrid: Tuning the nanostructure for improved amperometric detection of hydrogen peroxide as a non-enzymatic sensor

Hydrogen peroxide (H₂O₂) is a by-product of some biochemical processes which is catalyzed by enzymes such as glucose oxidase (GOx), cholesterol oxidase (ChoOx), etc and its overproduction in living cells can trigger cancer growth and various diseases. Therefore, H₂O₂ sensing is of great importance in the determination of diseases as well as industries and environmental health plans. We produced ZnO-CuO nanofibers by electrospinning method for non-enzymatic electrochemical H₂O₂ sensing. The sensing properties of the carbon paste electrode (CPE) modified with ZnO (0.3 wt%)/CuO (0.7 wt%) nanofibers (named as ZnO3-CuO7) for detection of H₂O₂ were explored in phosphate-buffered saline (PBS) at pH ∼ 7.4 solution. The ZnO3-CuO7 nanofiber exhibited the lowest charge transfer resistance and the highest electrocatalytic performance among other modified electrodes for detection of H₂O₂ and considered as an optimized sample. The effect of scan rate and H₂O₂ concentration in the reduction process were also investigated by cyclic voltammetry (CV) and the mechanism for the electrochemical reaction of H₂O₂ at the surface of the optimized electrode was studied. The diffusion coefficient of H₂O₂ and the catalytic rate constant were evaluated by chronoamperometry as 1.65 × 10^-5 cm² s^-1 and 6 × 10³ cm³ mol^-1 s^-1, respectively. Furthermore, amperometric detection of H₂O₂ with a low detection limit of 2.4 µM and a wide linear range of 3 to 530 µM were obtained. Meanwhile, the optimized electrode displayed no recognizable response towards some biomolecules such as ascorbic acid, uric acid, dopamine and glucose. The obtained results confirmed that the modified electrode shows high sensitivity and selectivity as a H₂O₂ biosensor with improved reproducibility and stability.

Bifunctional and highly sensitive electrochemical non-enzymatic glucose and hydrogen peroxide biosensor based on NiCo2O4 nanoflowers decorated 3D nitrogen doped holey graphene hydrogel

In this work, a simple strategy for fabricating a 3D nitrogen doped holey graphene hydrogel decorated with NiCo₂O₄ nanoflowers (NHGH/NiCo₂O₄) via a one-pot hydrothermal method with subsequent calcination is reported for the first time. The novel NHGH/NiCo₂O₄ nanocomposites featured high electrical conductivity, large and accessible surface areas, abundant active sites, and excellent electrocatalytic performance. Considering the excellent catalytic activity of NiCo₂O₄, a sensitive and bifunctional electrochemical non-enzymatic biosensor was established for the determination of glucose and hydrogen peroxide (H₂O₂). The obtained biosensor exhibited wide linear ranges (glucose: 0.005-10.95 mM; H₂O₂: 1-510 μM) and a low detection limits (glucose: 0.39 μM; H₂O₂: 0.136 μM) in alkaline solution (S/N = 3). Excellent electrocatalytic activity of this sensor was ascribed to the synergistic effects of the hybrid structure between the NiCo₂O₄ nanoflowers and NHGH. Furthermore, the sensitive biosensor also exhibited high selectivity and could be applied to determine glucose in real blood samples. Taken together, the results reveal that the proposed hybrid nanocomposite could be a promising electrochemical biosensor.

Ultrafast one-pot anodic preparation of Co3O4/nanoporous gold composite electrode as an efficient nonenzymatic amperometric sensor for glucose and hydrogen peroxide

For fabrication of composite electrode, one-pot strategy is highly attractive for convenience and efficiency. Here, a self-supporting Co₃O₄/nanoporous gold (NPG) composite electrode was one-pot prepared via one-step in situ anodization of a smooth gold electrode in a CoCl₂ solution within 100 s. It worked as a bifunctional electrocatalyst for glucose oxidation and H₂O₂ reduction in NaOH solution. Under optimized conditions, the electrocatalytic oxidation of glucose exhibits a wide linear range from 2 μM to 2.11 mM with a limit of detection as low as 0.085 μM (S/N = 3) and an ultrahigh sensitivity of 4470.4 μA mM^-1 cm^-2. Detection of glucose in human serum samples are also realized with results comparable to those from local hospital. The electrocatalytic reduction of H₂O₂ shows a linear response range from 20 μM to 19.1 mM and a high sensitivity of 1338.7 μA mM^-1 cm^-2. The present results demonstrate that the facilely prepared Co₃O₄/NPG is a promising nonenzymatic sensor for rapid amperometric detection of glucose and H₂O₂ with ultrasensitivity, high selectivity, satisfactory reproducibility, good stability and long duration.

Recent uses of carbon nanotubes & gold nanoparticles in electrochemistry with application in biosensing: A review

The innovation of nanoparticles assumes a critical part of encouraging and giving open doors and conceivable outcomes to the headway of new era devices utilized as a part of biosensing. The focused on the quick and legitimate detecting of specific biomolecules using functionalized gold nanoparticles (Au NPs), and carbon nanotubes (CNTs) has turned into a noteworthy research enthusiasm for the most recent decade. Sensors created with gold nanoparticles or carbon nanotubes or in some cases by utilizing both are relied upon to change the very establishments of detecting and distinguishing various analytes. In this review, we will examine the current utilization of functionalized AuNPs and CNTs with other synthetic mixes for the creation of biosensor prompting to the location of particular analytes with low discovery cutoff and quick reaction.

Microstructured prealloyed Titanium-Nickel powder as a novel nonenzymatic hydrogen peroxide sensor

At present, commercial pure Titanium (Ti) and microstructured pre-alloyed Titanium-Nickel (TiNi) powders are employed as a sensitive electrochemical hydrogen peroxide (H₂O₂) sensor. Surface characterization of these materials are performed by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical characterization is achieved via cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) on Ti and TiNi modified glassy carbon electrode (GCE). The electrochemical behavior of H₂O₂ at the pure Ti/GCE and microstructure pre-alloyed TiNi/GCE are studied by CV in 0.1 M phosphate buffer solution (PBS) containing as the supporting electrolyte. In addition, CA is employed for the determination of H₂O₂ at the applied potential of 0 V vs. Ag/AgCl. The sensor has a linear response range of 0.5-17.5 mM with a sensitivity of 280 µA mM^-1 cm^-2. Moreover, the limit of detection (LOD) and limit of quantification (LOQ) are 0.5 µM and 1.7 µM, respectively. The electrochemical sensor exhibits fast and selective responses to H₂O₂ concentration. The applicability of the sensor is checked using a hair coloring as a real sample with satisfactory results.

Curing the Toxicity of Multi-Walled Carbon Nanotubes through Native Small-molecule Drugs

With the development and application of nanotechnology, large amounts of nanoparticles will be potentially released to the environment and possibly cause many severe health problems. Although the toxicity of nanoparticles has been investigated, prevention and treatment of damages caused by nanoparticles have been rarely studied. Therefore, isotope tracing and improved CT imaging techniques were used to investigate the biodistribution influence between oMWCNTs(oxidized multi-walled carbon nanotubes) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/or simvastatin (TD) in vivo. What’s more, biochemical indices in plasma and tissue histology were measured to further study therapeutic effects on the damages of oMWCNTs in mice. Isotope tracing and improved CT imaging results showed that low dosages of DOPC and TD didn’t affect the distribution of oMWCNTs in mice; conversely, the distribution and metabolism of DOPC and TD were influenced by oMWCNTs. Moreover, DOPC and/or TD improved the biocompatibility of oMWCNTs in erythrocyte suspension in vitro. Biochemical index and histopathological results indicated that DOPC and TD didn’t prevent injuries caused by oMWCNTs effectively. But TD showed a good therapeutic effect for damages. This study is the first to investigate prevention and treatment effects of drugs on damages caused by oMWCNTs and provides new insights and breakthroughs for management of nanoparticles on health hazards.

Graphene Oxide Directed One-Step Synthesis of Flowerlike Graphene@HKUST-1 for Enzyme-Free Detection of Hydrogen Peroxide in Biological Samples

A novel metal-organic framework (MOF)-based electroactive nanocomposite containing graphene fragments and HKUST-1 was synthesized via a facile one-step solvothermal method using graphene oxide (GO), benzene-1,3,5-tricarboxylic acid (BTC), and copper nitrate (Cu(NO₃)₂) as the raw materials. The morphology and structure characterization revealed that the GO could induce the transformation of HKUST-1 from octahedral structure to the hierarchical flower shape as an effective structure-directing agent. Also, it is interesting to find out that the GO was torn into small fragments to participate in the formation of HKUST-1 and then transformed into the reduction form during the solvothermal reaction process, which dramatically increased the surface area, electronic conductivity, and redox-activity of the material. Electrochemical assays showed that the synergy of graphene and HKUST-1 in the nanocomposite leaded to high electrocatalysis, fast response, and excellent selectivity toward the reduction of hydrogen peroxide (H₂O₂). Based on these remarkable advantages, satisfactory results were obtained when the nanocomposite was used as a sensing material for electrochemical determination of H₂O₂ in the complex biological samples such as human serum and living Raw 264.7 cell fluids.

Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C1C2Im][OTf] Monitored by In Situ IR Spectroscopy

The synthesis of ionic-liquid-modified nanomaterials has attracted much attention recently. In this study we explore the potential to prepare such systems in an ultraclean fashion by physical vapor codeposition (PVCD). We codeposit metallic cobalt and the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C1C2Im][OTf] simultaneously onto a Pd(111) surface at 100 K. This process is performed under ultrahigh-vacuum (UHV) conditions in the presence of CO, or in the presence of O2 and CO. We use time-resolved (TR) and temperature-programmed (TP) infrared reflection absorption spectroscopy (IRAS) to investigate the formation and stability of the IL-modified Co deposits in situ during the PVD-based synthesis. CO is used as a probe molecule to monitor the growth. After initial growth of flat Co films on Pd(111), multilayers of Co nanoparticles (NPs) are formed. Characteristic shifts and intensity changes are observed in the vibrational bands of both CO and the IL, which originate from the electric field at the IL/Co interface (Stark effect) and from specific adsorption of the [OTf](-) anion. These observations indicate that the Co aggregates are stabilized by mixed adsorbate shells consisting of CO and [OTf](-). The CO coverage on the Co particle decreases with increasing temperature, but some CO is preserved up to the desorption temperature of the IL (370 K). Further, the IL shell suppresses the oxidation of the Co NPs if oxygen is introduced in the PVCD process. Only chemisorbed oxygen is formed at oxygen partial pressures that swiftly lead to formation of Co3O4 in the absence of the IL (5 × 10(-6) mbar O2). This chemisorbed oxygen is found to destabilize the CO ligand shell. The oxidation of Co is not suppressed if IL and Co are deposited sequentially under otherwise identical conditions. In this case we observe the formation of fully oxidized cobalt oxide particles.

In situ Immobilization of Copper Nanoparticles on Polydopamine Coated Graphene Oxide for H2O2 Determination

Nanostructured electrochemical sensors often suffer from irreversible aggregation and poor adhesion to the supporting materials, resulting in reduced sensitivity and selectivity over time. We describe a versatile method for fabrication of a H₂O₂ sensor by immobilizing copper nanoparticles (Cu NPs; 20 nm) on graphene oxide (GO) sheets via in-situ reduction of copper(II) on a polydopamine (PDA) coating on a glassy carbon electrode. The PDA film with its amino groups and catechol groups acts as both a reductant and an adhesive that warrants tight bonding between the Cu NPs and the support. The modified electrode, best operated at a working voltage of −0.4 V (vs. Ag/AgCl), has a linear response to H₂O₂ in the 5 μM to 12 mM concentration range, a sensitivity of 141.54 μA∙mM‾¹∙cm‾², a response time of 4 s, and a 1.4 μM detection limit (at an S/N ratio of 3). The sensor is highly reproducible and selective (with minimal interference to ascorbic acid and uric acid). The method was applied to the determination of H₂O₂ in sterilant by the standard addition method and gave recoveries between 97% and 99%.