Synthesis of Potassium‐Modified Graphene and Its Application in Nitrite‐Selective Sensing

Chemical modification with foreign atoms is a leading strategy to intrinsically modify the properties of host materials. Among them, potassium (K) modification plays a critical role in adjusting the electronic properties of carbon materials. Graphene, a true 2D carbon material, has shown fascinating applications in electrochemical sensing and biosensing. In this work, a facile and mild strategy to K‐modifying in graphene at room‐temperature is reported for the first time. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry are used to characterize this K‐modified graphene. The K‐modified graphene is capable of acting as an electron transfer medium and more efficiently promotes charge transfer than unmodified graphene. A highly sensitive and stable amperometric sensor based on its excellent electrocatalytic activity toward the oxidation of NO₂^? is proposed. The sensor shows a linear range from 0.5 μM to 7.8 mM with a detection limit of 0.2 μM at a signal‐to‐noise ratio of 3. The modified electrode has excellent analytical performance and can be successfully applied in the determination of NO₂^? released from liver cancer and leukemia cells and shows good application potential in biological systems.     

One‐Step Electrochemical Synthesis of Graphene/Polyaniline Composite Film and Its Applications

This work describes a new one‐step large‐scale electrochemical synthesis of graphene/polyaniline (PANI) composite films using graphite oxide (GO) and aniline as the starting materials. The size of the film could be controlled by the area of indium tin oxide (ITO). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible absorption spectrum (UV–vis) results demonstrated that the graphene/PANI composite film was successfully synthesized. The obtained graphene/PANI composite film showed large specific area, high conductivity, good biocompatibility, and fast redox properties and had perfect layered and encapsulated structures. Electrochemical experiments indicated that the composite film had high performances and could be widely used in applied electrochemical fields. As a model, horseradish peroxidase (HRP) was entrapped onto the film‐modi?ed glassy carbon electrode (GCE) and used to construct a biosensor. The immobilized HRP showed a pair of well‐de?ned redox peaks and high catalytic activity for the reduction of H₂O₂. Furthermore, the graphene/PANI composite film could be directly used as the supercapacitor electrode. The supercapacitor showed a high specific capacitance of 640 F g^?1 with a retention life of 90% after 1000 charge/discharge cycles.     

Amplifying Charge‐Transfer Characteristics of Graphene for Triiodide Reduction in Dye‐Sensitized Solar Cells

The fabrication and functionalization of large‐area graphene and its electrocatalytic properties for iodine reduction in a dye‐sensitized solar cell are reported. The graphene film, grown by thermal chemical vapor deposition, contains three to five layers of monolayer graphene, as confirmed by Raman spectroscopy and high‐resolution transmission electron microscopy. Further, the graphene film is treated with CF₄ reactive‐ion plasma and fluorine ions are successfully doped into graphene as confirmed by X‐ray photoelectron spectroscopy and UV‐photoemission spectroscopy. The fluorinated graphene shows no structural deformations compared to the pristine graphene except an increase in surface roughness. Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction increases with increasing plasma treatment time, which is attributed to an increase in catalytic sites. Further, the fluorinated graphene is characterized in use as a counter‐electrode in a full dye‐sensitized solar cell and shows ca. 2.56% photon to electron conversion efficiency with ca. 11 mA cm^?2 current density. The shift in work function in F^? doped graphene is attributed to the shift in graphene redox potential which results in graphene's electrocatalytic‐activity enhancement.     

Layered Titanate Nanosheets Intercalated with Myoglobin for Direct Electrochemistry

The application of nanolayered inorganic materials as supports for immobilizing biomolecules has attracted attention because the host structures not only have “flexible pores” to adapt to the size of the biomolecule guests but they also protect the immobilized biomolecules from disturbances created by environmental variations. In this paper, layered titanate sheets (TNSs) were used as support matrixes for immobilizing myoglobin (Mb) to fabricate protein electrodes suitable for studying the direct electron transfer between the redox centers of proteins and the electrode and establish an example of a mediator‐free (third‐generation) biosensor. The uniform, porous morphology and ordered structure of the protein electrode were characterized by scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray diffraction. The native structure of the intercalated Mb was maintained in the TNSs, and its behavior was characterized by UV‐vis and Fourier‐transform IR spectroscopy. Immobilized Mb in TNS films showed a fast direct electron transfer for the Mb–Fe^III/Fe^II redox couple. Based on the direct electron transfer of the immobilized Mb, the protein electrode exhibited excellent catalytic performance for H₂O₂. Furthermore, in order to improve the stability of immobilized Mb in the TNS films, the thermal stability of the protein electrode and its electrochemical catalytic reduction of H₂O₂ in a low pH environment were discussed.     

High‐Performing Monometallic Cobalt Layered Double Hydroxide Supercapacitor with Defined Local Structure

Through a topochemical oxidative reaction (TOR) under air, a β‐Co(OH)₂ brucite type structure is converted into a monometallic Co^IICo^III–CO₃ layered double hydroxide (LDH). The structural and morphological characterizations are performed using powder X‐ray diffraction, Fourier‐transformed IR spectroscopy, and scanning and transmission electron microscopy. The local structure is scrutinized using an extended X‐ray absorption fine structure, X‐ray absorption near‐edge structure, and pair distribution function analysis. The chemical composition of pristine material and its derivatives (electrochemically treated) are identified by thermogravimetry analysis for the bulk and X‐ray photoelectron spectroscopy for the surface. The electrochemical behavior is investigated on deposited thin films in aqueous electrolyte (KOH) by cyclic voltammetry and electrochemical impedance spectroscopy, and their capacitive properties are further investigated by Galvanostatic cycling with potential limitation. The charge capacity is found to be as high as 1490 F g^?1 for Co^IICo^III–CO₃ LDH at a current density of 0.5 A g^?1. The performances of these materials are described using Ragone plots, which finally allow us to propose them as promising supercapacitor materials. A surface‐to‐bulk comparison using the above characterization techniques gives insight into the cyclability and reversibility limits of this material.     

Efficient Dye‐Sensitized Solar Cells with Potential‐Tunable Organic Sulfide Mediators and Graphene‐Modified Carbon Counter Electrodes

A new class of organic sulfide mediators with programmable redox properties is designed via density functional theory calculations and synthesized for efficient dye‐sensitized solar cells (DSCs). Photophysical and electrochemical properties of these mediators derived from systematical functionalization of the framework with electron donating and withdrawing groups (MeO, Me, H, Cl, CF₃, and NO₂) are investigated. With this new class of organic mediators, the redox potential can be fine‐tuned over a 170 mV range, overlapping the conventional I^?/I₃^?couple. Due to the suitable interplay of physical properties and electrochemical characteristics of the mediator involving electron‐donating MeO group, the DSCs based on this mediator behave excellently in various kinetic processes such as dye regeneration, electron recombination, and mass transport. Thus, the MeO derivative of the mediator is identified as having the best performance of this series of redox shuttles. As inferred from electrochemical impedance spectroscopy and cyclic voltammetry measurements, the addition of graphene into the normal carbon counter electrode material dramatically improves the apparent catalytic activity of the counter electrode towards the MeO derivative of mediator, resulting in N719 based DSCs showing a promising conversion efficiency of 6.53% under 100 mW·cm^?2 simulated sunlight illumination.     

Atomic and Molecular Layer Deposition of Hybrid Mo–Thiolate Thin Films with Enhanced Catalytic Activity

A synthetic route toward hybrid MoS₂‐based materials that combines the 2D bonding of MoS₂ with 3D networking of aliphatic carbon chains is devised, leading to a film with enhanced electrocatalytic activity. The hybrid inorganic–organic thin films are synthesized by combining atomic layer deposition (ALD) with molecular layer deposition (MLD) using the precursors molybdenum hexacarbonyl and 1,2‐ethanedithiol and characterized by in situ Fourier transform infrared spectroscopy, and the resultant material properties are probed by X‐ray photoelectron spectroscopy, Raman spectroscopy, and grazing incidence X‐ray diffraction. The process exhibits a growth rate of 1.3 Å per cycle, with an ALD/MLD temperature window of 155–175 °C. The hybrid films are moderately stable for about a week in ambient conditions, smooth (σ_RMS ≈ 5 Å for films 60 Å thick) and uniform, with densities ranging from 2.2–2.5 g cm^?3. The material is both optically transparent and catalytically active for the hydrogen evolution reaction (HER), with an overpotential (294 mV at ?10 mA cm^?2) superior to that of planar MoS₂. The enhancement in catalytic activity is attributed to the incorporation of organic chains into MoS₂, which induces a morphological change during electrochemical testing that increases surface area and yields high activity HER catalysts without the need for deliberate nanostructuring.     

Block‐Copolymer‐Templated Synthesis of Electroactive RuO2‐Based Mesoporous Thin Films

RuO₂‐based mesoporous thin films of optical quality are synthesized from ruthenium‐peroxo‐based sols using micelle templates made of amphiphilic polystyrene‐polyethylene oxide block copolymers. The mesoporous structure and physical properties of the RuO₂ films (mesoporous volume: 30%; pore diameter: ～30 nm) can be controlled by the careful tuning of both the precursor solution and thermal treatment (150–350 °C). The optimal temperature that allows control of both mesoporosity and nanocristallinity is strongly dependent on the substrate (silicon or fluorine‐doped tin oxide). The structure of the resulting mesoporous films are investigated using X‐ray diffraction, X‐ray photoelectron spectroscopy, and atomic force microscopy. Mesoporous layers are additionally characterized by transmission and scanning electron microscopy and ellipsometry while their electrochemical properties are analyzed via cyclic voltammetry. Thick mesoporous films of ruthenium oxide hydrates, RuO₂ · xH₂O, obtained using a thermal treatment at 280 °C, exhibit capacitances as high as 1000 ± 100 F g^?1 at a scan rate of 10 mV s^?1, indicating their potential application as electrode materials.     

Nitrogen‐Doped Single‐Walled Carbon Nanotubes Grown on Substrates: Evidence for Framework Doping and Their Enhanced Properties

Nitrogen‐doped single‐walled carbon nanotubes (SWCNTs) are synthesized directly on silicon and quartz substrates through a normal chemical vapor deposition (CVD) method. Thermogravimetry mass spectrometry measurements and Raman spectroscopy give firm evidence for framework nitrogen doping. X‐ray‐photoelectron‐spectroscopy analysis further obtains the bonding style of the nitrogen atoms in the carbon framework. The nitrogen doping significantly changes the properties of the SWCNTs. All of the tubes behave like metallic tubes in field‐effect transistors. The doped nitrogen atoms introduce a stronger affinity for the SWCNTs to metal nanoparticles. Compared with pristine SWCNTs, the nitrogen‐doped tubes show enhanced sensitivity and selectivity for electrochemical detection of some electrophilic species including O₂, H₂O₂, and Fe³⁺. They also present improved electrocatalytic activity for oxygen reduction. These unique properties of the nitrogen‐doped SWCNTs endow them with important potential applications in various fields.     

Helical 3D‐Printed Metal Electrodes as Custom‐Shaped 3D Platform for Electrochemical Devices

3D‐printing represents an emerging technology that can revolutionize the way object and functional devices are fabricated. Here the use of metal 3D printing is demonstrated to fabricate bespoke electrochemical stainless steel electrodes that can be used as platform for different electrochemical applications ranging from electrochemical capacitors, oxygen evolution catalyst, and pH sensor by means of an effective and controlled deposition of IrO₂ films. The electrodes have been characterized by scanning electrode microscopy and energy dispersive X‐ray spectroscopy before the electrochemical testing. Excellent pseudocapacitive as well as catalytic properties have been achieved with these 3D printed steel‐IrO₂ electrodes in alkaline solutions. These electrodes also demonstrate Nernstian behavior as pH sensor. This work represents a breakthrough in on‐site prototyping and fabrication of highly tailored electrochemical devices with complex 3D shapes which facilitate specific functions and properties.     

A Controllable Self‐Assembly Method for Large‐Scale Synthesis of Graphene Sponges and Free‐Standing Graphene Films

A simple method to prepare large‐scale graphene sponges and free‐standing graphene films using a speed vacuum concentrator is presented. During the centrifugal evaporation process, the graphene oxide (GO) sheets in the aqueous suspension are assembled to generate network‐linked GO sponges or a series of multilayer GO films, depending on the temperature of a centrifugal vacuum chamber. While sponge‐like bulk GO materials (GO sponges) are produced at 40 °C, uniform free‐standing GO films of size up to 9 cm² are generated at 80 °C. The thickness of GO films can be controlled from 200 nm to 1 µm based on the concentration of the GO colloidal suspension and evaporation temperature. The synthesized GO films exhibit excellent transparency, typical fluorescent emission signal, and high flexibility with a smooth surface and condensed density. Reduced GO sponges and films with less than 5 wt% oxygen are produced through a thermal annealing process at 800 °C with H₂/Ar flow. The structural flexibility of the reduced GO sponges, which have a highly porous, interconnected, 3D network, as well as excellent electrochemical properties of the reduced GO film with respect to electrode kinetics for the [Fe(CN)₆]^3?/4? redox system, are demonstrated.     

X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO3 Interfaces

Tunable electronic properties of transition metal oxides and their interfaces offer remarkable functionalities for future devices. The interest in these materials has been boosted with the discovery of a 2D electron gas (2DEG) at SrTiO₃ (STO)‐based interfaces. For the majority of these systems, oxygen vacancies play a crucial role in the emergence of interface conductivity, ferromagnetism, and high electron mobility. Despite its great importance, controlling the density and spatial distribution of oxygen vacancies in a dynamic way remains extremely challenging. Here, lithography‐like writing of a metallic state at the interface between SrTiO₃ and amorphous Si using X‐ray irradiation is reported. Using a combination of transport techniques and in operando photoemission spectroscopy, it is revealed in real time that the X‐ray radiation induces transfer of oxygen across the interface leading to the on‐demand formation of oxygen vacancies and a 2DEG in STO. The formed 2DEG stays stable in ambient conditions as the interface oxygen vacancies are stabilized by the capping of Si. The study provides a fundamental understanding of X‐ray‐induced redox reactions at the SrTiO₃‐based interfaces and in addition shows the potential of X‐ray radiation for patterning stabile conductive pathways for future oxide‐based electronic devices.     

Two Birds with One Stone: Metal–Organic Framework Derived Micro‐/Nanostructured Ni2P/Ni Hybrids Embedded in Porous Carbon for Electrocatalysis and Energy Storage

The construction of bifunctional electrode materials for hydrogen evolution reaction (HER) and lithium‐ion batteries (LIBs) has been a hot topic of research. Herein, metal–organic frameworks (MOFs) derived micro‐/nanostructured Ni₂P/Ni hybrids with a porous carbon coating (denoted as Ni₂P/Ni@C) are prepared using a feasible pyrolysis–phosphidation strategy. On the one hand, the optimal Ni₂P/Ni@C catalyst exhibits superior HER performance with a low overpotential of 149 mV versus a reversible hydrogen electrode (RHE) at 10 mA cm^?2 and excellent durability. The density functional theory computations verify that the strong synergistic effect between Ni₂P and Ni could optimize the electronic structure, thus rendering the enhanced electrocatalytic performance. On the other hand, the Ni₂P/Ni@C electrode displays a reversible capacity of 597 mAh g^?1 after 1000 cycles at 1000 mA g^?1 and improved rate capability as an anode for LIBs, owing to the well‐organized micro‐/nanostructure and conductive Ni core. In addition, the electrochemical reaction mechanism of the Ni₂P/Ni@C electrode upon lithiation/delithiation is investigated in detail via ex situ X‐ray powder diffraction and X‐ray photoelectron spectroscopy methods. It is expected that the facile and controllable approach can be extended to fabricate other MOF‐based metal phosphides/metal hybrids for electrochemical energy storage and conversion systems.     

Self‐Assembled Graphene–Enzyme Hierarchical Nanostructures for Electrochemical Biosensing

The self‐assembly of sodium dodecyl benzene sulphonate (SDBS) functionalized graphene sheets (GSs) and horseradish peroxidase (HRP) by electrostatic attraction into novel hierarchical nanostructures in aqueous solution is reported. Data from scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray diffraction demonstrate that the HRP–GSs bionanocomposites feature ordered hierarchical nanostructures with well‐dispersed HRP intercalated between the GSs. UV‐vis and infrared spectra indicate the native structure of HRP is maintained after the assembly, implying good biocompatibility of SDBS‐functionalized GSs. Furthermore, the HRP–GSs composites are utilized for the fabrication of enzyme electrodes (HRP–GSs electrodes). Electrochemical measurements reveal that the resulting HRP–GSs electrodes display high electrocatalytic activity to H₂O₂ with high sensitivity, wide linear range, low detection limit, and fast amperometric response. These desirable electrochemical performances are attributed to excellent biocompatibility and superb electron transport efficiency of GSs as well as high HRP loading and synergistic catalytic effect of the HRP–GSs bionanocomposites toward H₂O₂. As graphene can be readily non‐covalently functionalized by “designer” aromatic molecules with different electrostatic properties, the proposed self‐assembly strategy affords a facile and effective platform for the assembly of various biomolecules into hierarchically ordered bionanocomposites in biosensing and biocatalytic applications.     

Synthesis of Phase‐Pure Ferromagnetic Fe3P Films from Single‐Source Molecular Precursors

A new method for the preparation of phase‐pure ferromagnetic Fe₃P films on quartz substrates is reported. This approach utilizes the thermal decomposition of the single‐source precursors H₂Fe₃(CO)₉PR (R = ^tBu or Ph) at 400 °C. The films are deposited using a simple, home‐built metal‐organic chemical vapor deposition (MOCVD) apparatus and are characterized using a variety of analytical methods. The films exhibit excellent phase purity, as evidenced by X‐ray diffraction, X‐ray photoelectron spectroscopy, and field‐dependent magnetization measurements, the results of which agree well with measurements obtained from bulk Fe₃P. Using scanning electron microscopy and atomic force microscopy techniques, the films are found to have thicknesses between 350 and 500 nm with a granular surface texture. As‐deposited Fe₃P films are amorphous, and little or no magnetic hysteresis is observed in plots of magnetization versus applied field. Annealing the Fe₃P films at 550 °C results in improved crystallinity as well as the observation of magnetic hysteresis.     

Graphene‐Based Nanoporous Materials Assembled by Mediation of Polyoxometalate Nanoparticles

A kind of graphene‐based nanoporous material is prepared through assembling graphene sheets mediated through polyoxometalate nanoparticles. Owing to the strong interaction between graphene and polyoxometalate, 2D graphene sheets with honeycomb‐latticed carbon atoms could assemble into a porous structure, in which 3D polyoxometalate nanoparticles serve as the crosslinkers. Nitrogen and hydrogen sorption analysis reveal that the as‐prepared graphene‐based hybrid material possesses a specific surface area of 680 m² g^?1 and a hydrogen uptake volume of 0.8?1.3 wt%. Infrared spectrometry is used to probe the electron density changes of polyoxometalate particle in the redox‐cycle and to verify the interaction between graphene and polyoxometalate. The as‐prepared graphene‐based materials are further characterized by Raman spectroscopy, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy.     

Greener Electrochemical Synthesis of High Quality Graphene Nanosheets Directly from Pencil and its SPR Sensing Application

A green, simple, and cost effective electrochemical method to synthesize pure graphene oxide (GO) and graphene nanosheets (GNs) using pencil in ionic liquid medium is reported. The morphology and microstructure of prepared GNs and GO are examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X‐ray diffraction (XRD), and Raman spectroscopy; the experiments confirm the formation of high quality graphene. The synthesized GO is used for the real‐time and label‐free surface plasmon resonance (SPR) sensing of the biological warfare agent Salmonella typhi.     

From 3D ZIF Nanocrystals to Co–Nx/C Nanorod Array Electrocatalysts for ORR,OER, and Zn–Air Batteries

Designing a highly active electrocatalyst with optimal stability at low cost is must and non‐negotiable if large‐scale implementations of fuel cells are to be fully realized. Zeolitic‐imidazolate frameworks (ZIFs) offer rich platforms to design multifunctional materials due to their flexibility and ultrahigh surface area. Herein, an advanced Co–N_x/C nanorod array derived from 3D ZIF nanocrystals with superior electrocatalytic activity and stability toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) compared to commercial Pt/C and IrO₂, respectively, is synthesized. Remarkably, as a bifunctional catalyst (E_{j = 10} (OER) ? E_1/2 (ORR) ≈ 0.65 V), it further displays high performance of Zn–air batteries with high cycling stability even at a high current density. Such supercatalytic properties are largely attributed to the synergistic effect of the chemical composition, high surface area, and abundant active sites of the nanorods. The activity origin is clarified through post oxygen reduction X‐ray photoelectron spectroscopy analysis and density functional theory studies. Undoubtedly, this approach opens a new avenue to strategically design highly active and performance‐oriented electrocatalytic materials for wider electrochemical energy applications.     

Single‐Crystalline Gallium Nitride Microspindles: Synthesis,Characterization, and Thermal Stability

This paper describes a facile procedure for synthesizing high‐quality gallium nitride microspindles on a large scale using a solid‐state reaction of GaI₃, NaNH₂, and NH₄Cl in a sealed system at 500 °C for 6 h. The structures, compositions, and morphologies of the as‐synthesized products are derived from X‐ray powder diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field‐emission scanning electron microscopy (FE‐SEM). The selected‐area electron diffraction (SAED) patterns and high‐resolution transmission electron microscopy (HRTEM) images show that the as‐synthesized GaN spindles are composed of many single‐crystalline platelets. The GaN microspindles show different optical properties depending on their shape (e.g., nanowires or nanoparticles) in photoluminescence (PL) emission spectroscopy and Raman spectroscopy. The possible growth mechanism of GaN microspindles is controlled by linear kinetics with a driving force proportional to the difference between a local supersaturation and an equilibrium chemical potential. Furthermore, the thermal stability of the GaN microspindles is investigated under various annealing conditions and discussed on the basis of additional TEM and XRD analyses.     

Investigation of the Structure of MCM‐41 Samples with a High Copper Content

A series of MCM‐41s with a high copper content were synthesized at room temperature from sodium metasilicate (Na₂SiO₃) as the silicon source, tetraamminecopper(II ) nitrate [Cu(NH₃)₄(NO₃)₂] as the copper source and cetyltrimethylammonium bromide (CTABr) as the template. The resulting material was characterized by using the following characterization techniques: X‐ray diffraction (XRD), N₂‐adsorption isotherms, high‐resolution transmission electron microscopy (HRTEM), inductively coupled plasma (ICP), temperature‐programmed reduction (H₂‐TPR), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), UV‐vis spectroscopy, electron‐spin resonance (ESR) and ²⁹Si magic‐angle sample spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The characterization techniques demonstrated the following: i) the copper atoms are incorporated into the framework of MCM‐41 and ii) the copper species in the samples are in a distorted octahedral coordination environment, with between four and six oxygen atoms in the first coordination sphere. The maximum copper content determined by ICP was 26 wt.‐% in the ordered mesoporous sample with a surface area of 525 m² g^–1 and an average pore diameter of 3.1 nm. The synthesized materials exhibited a high activity for nitrogen monoxide (NO) reduction by carbon monoxide (CO).