Uniform Au@Pt core-shell nanodendrites supported on molybdenum disulfide nanosheets for the methanol oxidation reaction

Coupling methanol oxidation with CO2 reduction: A feasible pathway to achieve carbon neutralization

The energy consumption of up to 90 % of the total power input in the anodic oxygen evolution reaction (OER) slows down the implementation of electrochemical CO2 reduction reaction (CO2RR) to generate valuable chemicals. Herein, we present an alternative strategy that utilizes methanol oxidation reaction (MOR) to replace OER. The iron single atom anchored on nitrogen-doped carbon support (Fe-N-C) use as the cathode catalyst (CO2RR), low-loading platinum supported on the composites of tungsten phosphide and multiwalled carbon nanotube (Pt-WP/MWCNT) use as the anode catalyst (MOR). Our results show that the Fe-N-C exhibits a Faradaic selectivity as high as 94.93 % towards CO2RR to CO, and Pt-WP/MWCNT exhibits a peak mass activity of 544.24 mA mg-1Pt, which is 5.58 times greater than that of PtC (97.50 mA mg-1Pt). The well-established MOR||CO2RR reduces the electricity consumption up to 52.4 % compared to conventional OER||CO2RR. Moreover, a CO2 emission analysis shows that this strategy not only saves energy but also achieves carbon neutrality without changing the existing power grid structure. Our findings have crucial implications for advancing CO2 utilization and lay the foundation for developing more efficient and sustainable technologies to address the rising atmospheric CO2 levels.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Tetrahedral DNA Nanostructure-Engineered Paper-Based Electrochemical Aptasensor for Fumonisin B1 Detection Coupled with Au@Pt Nanocrystals as an Amplification Label

Fumonisin B1 (FB1), as one of the highest toxicity mycotoxins, poses a serious threat to animal and human health, even at low concentrations. It is significant and challenging to develop a sensitive and reliable analytical device. Herein, a paper-based electrochemical aptasensor was designed utilizing tetrahedral DNA nanostructures (TDNs) to controllably anchor an aptamer (Apt), improving the recognition efficiency of Apt to its target. First, gold nanoparticles (AuNPs)@MXenes were used as a sensing substrate with good conductivity and modified on the electrode for immobilization of complementary DNA-TDNs (cDNA-TDNs). In the absence of FB1, numerous Apt-Au@Pt nanocrystals (NCs) was hybridized with cDNA and assembled on the sensing interface, which accelerated the oxidation of TMB with H2O2 and produced a highly amplified differential pulse voltammetry (DPV) signal. When the target FB1 specifically bound to its Apt, the electrochemical signal was decreased by releasing the Apt-Au@Pt NCs from double-stranded DNA (dsDNA). On account of the strand displacement reaction by FB1 triggering, the aptasensor had a wider dynamic linear range (from 50 fg/mL to 100 ng/mL) with a lower limit of detection (21 fg/mL) under the optimized conditions. More impressively, the designed FB1 aptasensor exhibited satisfactory performance in corn and wheat samples. Therefore, the TDN-engineered sensing platform opens an effective approach for sensitive and accurate analysis of FB1, holding strong potential in food safety and public health.

A label-free colorimetric 3D paper-based device for ochratoxin A detection using G-quadruplex/hemin DNAzyme with a smartphone readout

The colorimetric sensor usually depends on enzyme-mediated signal amplification to achieve trace analysis of ochratoxin A (OTA) residues in food samples. However, the enzyme labeling and manual addition of reagents steps increased assay time and operation complexity, restricting their application in point-of-care testing (POCT). Herein, we report a label-free colorimetric device integrating a 3D paper-based analytical device and a smartphone as handheld readout for rapid and sensitive detection of OTA. Using vertical-flow design, the paper-based analytical device enables the specific recognition of target and self-assembly of G-quadruplex (G4)/hemin DNAzyme to be performed, then employs DNAzyme for transducing the OTA binding event signal into a colorimetric signal. The design of independent functional units, including biorecognition unit, self-assembly unit and colorimetric units, which can address crowding and disorder of biosensing interfaces and improve the recognition efficiency of aptamer (apta). In addition, we eliminated signal losses and nonuniform coloring by introducing carboxymethyl chitosan (CMCS) to obtain perfectly focused signals on colorimetric unit. On the basis of parameter optimization, the device exhibited a detection range of 0.1-500 ng/mL and a detection limit of 41.9 pg/mL for OTA. Importantly, good results were obtained in spiked real samples, indicating applicability and reliability of developed device.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Modification of multi-walled carbon nanotubes with platinum-osmium to develop stable catalysts for direct methanol fuel cells

In the study, a new bimetallic catalyst was synthesized for methanol oxidation using multi-walled carbon nanotube (MWCNT)-supported platinum-osmium (PtOs) nanoparticles (PtOs@MWCNT NPs). The morphological structures of the prepared NPs were examined using different techniques, such as scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical characterization of the synthesized PtOs@MWCNT catalysts, such as chronoamperometry (CA), cyclic voltammetry (CV), scan rate (SR) analysis, cyclic catalytic test, and electrochemical surface area (ECSA) evaluation, were performed in an alkaline medium. From the results obtained, the size of the NPs was found to be 3.12 nm according to the Debye-Schrrer equation, and the MWCNTs were clearly observed by SEM imaging. After the characterization of the prepared nanomaterials, the PtOs@MWCNT catalysts were employed in the methanol oxidation reaction, and a high oxidation current value of 220.86 mA cm^-2 was observed. Besides, according to the CA results, the catalyst exhibited high stability for 4000 s, and it was seen that Os metal improved the catalytic activity of the main catalyst. These results show that the PtOs@MWCNT catalyst is highly stable and reusable, and provides high electrocatalytic activity in the methanol oxidation reaction. Moreover, the obtained catalyst gave ideal results in terms of CO tolerance and activity. These data show that the obtained catalyst will provide significant improvement and superior efficiency in fuel-cell applications.

MnCo2O4/NiCo2O4/rGO as a Catalyst Based on Binary Transition Metal Oxide for the Methanol Oxidation Reaction

The demands for alternative energy have led researchers to find effective electrocatalysts in fuel cells and increase the efficiency of existing materials. This study presents new nanocatalysts based on two binary transition metal oxides (BTMOs) and their hybrid with reduced graphene oxide for methanol oxidation. Characterization of the introduced three-component composite, including cobalt manganese oxide (MnCo₂O₄), nickel cobalt oxide (NiCo₂O₄), and reduced graphene oxide (rGO) in the form of MnCo₂O₄/NiCo₂O₄/rGO (MNR), was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) analyses. The alcohol oxidation capability of MnCo₂O₄/NiCo₂O₄ (MN) and MNR was evaluated in the methanol oxidation reaction (MOR) process. The crucial role of rGO in improving the electrocatalytic properties of catalysts stems from its large active surface area and high electrical conductivity. The alcohol oxidation tests of MN and MNR showed an adequate ability to oxidize methanol. The better performance of MNR was due to the synergistic effect of MnCo₂O₄/NiCo₂O₄ and rGO. MN and MNR nanocatalysts, with a maximum current density of 14.58 and 24.76 mA/cm² and overvoltage of 0.6 and 0.58 V, as well as cyclic stability of 98.3% and 99.7% (at optimal methanol concentration/scan rate of 20 mV/S), respectively, can be promising and inexpensive options in the field of efficient nanocatalysts for use in methanol fuel cell anodes.

Recent Developments and Future Perspective on Electrochemical Glucose Sensors Based on 2D Materials

Diabetes is a health disorder that necessitates constant blood glucose monitoring. The industry is always interested in creating novel glucose sensor devices because of the great demand for low-cost, quick, and precise means of monitoring blood glucose levels. Electrochemical glucose sensors, among others, have been developed and are now frequently used in clinical research. Nonetheless, despite the substantial obstacles, these electrochemical glucose sensors face numerous challenges. Because of their excellent stability, vast surface area, and low cost, various types of 2D materials have been employed to produce enzymatic and nonenzymatic glucose sensing applications. This review article looks at both enzymatic and nonenzymatic glucose sensors made from 2D materials. On the other hand, we concentrated on discussing the complexities of many significant papers addressing the construction of sensors and the usage of prepared sensors so that readers might grasp the concepts underlying such devices and related detection strategies. We also discuss several tuning approaches for improving electrochemical glucose sensor performance, as well as current breakthroughs and future plans in wearable and flexible electrochemical glucose sensors based on 2D materials as well as photoelectrochemical sensors.

Two-Dimensional Material-Based Electrochemical Sensors/Biosensors for Food Safety and Biomolecular Detection

Two-dimensional materials (2DMs) exhibited great potential for applications in materials science, energy storage, environmental science, biomedicine, sensors/biosensors, and others due to their unique physical, chemical, and biological properties. In this review, we present recent advances in the fabrication of 2DM-based electrochemical sensors and biosensors for applications in food safety and biomolecular detection that are related to human health. For this aim, firstly, we introduced the bottom-up and top-down synthesis methods of various 2DMs, such as graphene, transition metal oxides, transition metal dichalcogenides, MXenes, and several other graphene-like materials, and then we demonstrated the structure and surface chemistry of these 2DMs, which play a crucial role in the functionalization of 2DMs and subsequent composition with other nanoscale building blocks such as nanoparticles, biomolecules, and polymers. Then, the 2DM-based electrochemical sensors/biosensors for the detection of nitrite, heavy metal ions, antibiotics, and pesticides in foods and drinks are introduced. Meanwhile, the 2DM-based sensors for the determination and monitoring of key small molecules that are related to diseases and human health are presented and commented on. We believe that this review will be helpful for promoting 2DMs to construct novel electronic sensors and nanodevices for food safety and health monitoring.

Construction of a Molybdenum Disulfide-Based Colorimetric Sensor for Label-Free Infectious Disease Analysis Coupled with a Catalyzed Hairpin Assembly Reaction

The simple and accurate determination of pathogenic infectious diseases is very beneficial to public health prevention and control. For this purpose, we designed a colorimetric sensor for label-free avian influenza A (H7N9) virus gene sequence detection based on gold@platinum core-shell bimetallic-nanoparticle-decorated molybdenum disulfide (MoS₂-Au@Pt) nanocomposites. MoS₂-Au@Pt nanocomposites were used as nanoenzymes to catalyze 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide (H₂O₂) because of their intrinsic peroxidase-mimicking activity. Coupled with different affinities of MoS₂-Au@Pt nanocomposites toward single-stranded (ss) and double-stranded (ds) DNA and the target-triggered catalyzed hairpin assembly (CHA) reaction, the proposed sensor can qualitatively and quantitatively determine H7N9 by the naked eye. Experimental results showed that this sensor can detect H7N9 in buffer and real samples because of its high sensitivity, selectivity, and repeatability.

Electrochemically active site-rich nanocomposites of two-dimensional materials as anode catalysts for direct oxidation fuel cells: new age beyond graphene

Direct oxidation fuel cell (DOFC) has been opted as a green alternative to fossil fuels and intermittent energy resources as it is economically viable, possesses good conversion efficiency, as well as exhibits high power density and superfast charging. The anode catalyst is a vital component of DOFC, which improves the oxidation of fuels; however, the development of an efficient anode catalyst is still a challenge. In this regard, 2D materials have attracted attention as DOFC anode catalysts due to their fascinating electrochemical properties such as excellent mechanical properties, large surface area, superior electron transfer, presence of active sites, and tunable electronic states. This timely review encapsulates in detail different types of fuel cells, their mechanisms, and contemporary challenges; focuses on the anode catalyst/support based on new generation 2D materials, namely, 2D transition metal carbide/nitride or carbonitride (MXene), graphitic carbon nitride, transition metal dichalcogenides, and transition metal oxides; as well as their properties and role in DOFC along with the mechanisms involved.

Platinum-Based Electrocatalysts for Direct Alcohol Fuel Cells: Enhanced Performances toward Alcohol Oxidation Reactions

In the past few decades, Pt-based electrocatalysts have attracted great interests due to their high catalytic performances toward the direct alcohol fuel cell (DAFC). However, the high cost, poor stability, and the scarcity of Pt have markedly hindered their large-scale utilization in commerce. Therefore, enhancing the activity and durability of Pt-based electrocatalysts, reducing the Pt amount and thus the cost of DAFC have become the keys for their practical applications. In this minireview, we summarized some basic concepts to evaluate the catalytic performances in electrocatalytic alcohol oxidation reaction (AOR) including electrochemical active surface area, activity and stability, the effective approaches for boosting the catalytic AOR performance involving size decrease, structure and morphology modulation, composition effect, catalyst supports, and assistance under other external energies. Furthermore, we also presented the remaining challenges of the Pt-based electrocatalysts to achieve the fabrication of a real DAFC.

Simultaneous electrochemical aptasensing of patulin and ochratoxin A in apple juice based on gold nanoparticles decorated black phosphorus nanomaterial

Simultaneous detection of patulin (PAT) and ochratoxin A (OTA) in food products is in great demand, which can prevent toxins from being exposed to human and animal bodies. However, simultaneous detection of multiple targets still faces a challenge. Herein, we developed a novel electrochemical aptasensor for the simultaneous detection of PAT and OTA in apple juice based on gold nanoparticles decorated black phosphorus (AuNPs-BP) nanomaterial. AuNPs-BP function?/work? as a sensing platform for loading much different electrochemical signal molecules functionalized aptamers. In this context, methylene blue functionalized PAT aptamers (Mb-PAT-aptamers) and ferrocene functionalized OTA aptamers (Fc-OTA-aptamers) have been introduced here to fabricate the aptasensor. Fc close to electrode surface showed a strong signal, whereas Mb was far away from electrode surface so exhibited a weak signal in the absence of OTA and PAT. Two kinds of electrochemical signal changes have been recorded dependent on target of OTA and PAT concentrations. So, simultaneous detection of OTA and PAT is achieved. Under the optimum conditions, using this developed biosensor, PAT and OTA can be quantified at a linearity range of 0.01 × 10^-7 μg·mL^-1 ~ 0.10 μg·mL^-1. In addition, it also has good selectivity, stability and repeatability. For the practical application, it shows promising performance for the simultaneous detection of PAT and OTA in apple juice.

Electrochemical/visual dual-readout aptasensor for Ochratoxin A detection integrated into a miniaturized paper-based analytical device

Development of portable, sensitive and reliable devices for Ochratoxin A (OTA) detection is highly demanded, especially for resource-limited regions. Herein, a novel paper-based analytical device (PAD) is designed through wax printing and screen-printed technologies, which integrates sample flowing, electrode modification, cleaning and electrochemical (EC)/colorimetric signal output. To greatly enhance the detection sensitivity, we synthesized a chitosan functionalized MoS₂-Au@Pt (Ch-MoS₂-Au@Pt) via electrostatic self-assembly, and used it to immobilize the label aptamer (apta₂) for signal regulation and amplification. Concretely, with the addition of analytes, the Ch-MoS₂-Au@Pt-apta₂ could be combined on the sensing interface by specific biorecognition and catalyzed reduction of H₂O₂, resulting in a remarkable EC response. Meanwhile, the released hydroxyl radicals (·OH) flowed to the visualization zone and promoted the oxidation of 3,3',5,5'-tetramethylbenzidine for colorimetric detection. Consequently, the dual-mode PAD achieved acceptable prediction and accurate analysis in the range of 0.1-200 ng mL^-1 and 1 × 10^-4-200 ng mL^-1 by matching the visual and EC signal intensity, respectively. Compared with traditional single-mode sensor for OTA, the proposed dual-mode aptasensor featuring independent signal conversion and readout, not only avoided the false-positive signal associated with detection condition and operation, but also enlarged the detection ranges and improved the sensitivity. Furthermore, the consistency of EC/colorimetric assay was validated in real OTA samples. Overall, this work provided a portable, cost-effective, sensitive and visualized aptasensor platform, which could be extended to various other mycotoxins in the field of food safety.

Geometric and electronic properties of AulPtm (l + m ≤ 10) clusters: a first-principles study

The structural evolutions and electronic properties of AulPtm (l + m ≤ 10) clusters are investigated by using the first-principles methods. We use the inverse design of materials using the multi-objective differential evolution (IM2ODE) package to globally search the equilibrium structures and investigate the evolving trend from a two-dimensional structure to a three-dimensional structure on horizontal extension and vertical extension for AulPtm (l + m ≤ 10) clusters. The three-dimensional stable geometry of Au8Pt and Au8Pt2 is discovered for the first time in our work. We also notice that the equilibrium structures of AulPtm (l + m = 10 and l ≤ 8) tend to form a tetrahedral geometry and can be obtained by replacing the Au atom in the most stable structure of Aul+1Ptm-1 with the Pt atom, where Pt atoms assemble together and occupy the center of clusters and Au atoms prefer to lie on the vertex or edge position. The average binding energy (Eb) is mostly decided by Pt-Pt bond numbers, namely the numbers of Pt atoms, followed by Au-Pt bond numbers. The second-order energy difference (Δ2Ev and Δ2Eh) and the nearest-neighbor energy difference (Δ4Enn) show that Au6Pt, Au4Pt2, Au3Pt3, Au2Pt4 and AuPt7 clusters exhibit high relative physical stability, so we suggest that these clusters could be defined as the magic number clusters for AulPtm (l + m ≤ 10) clusters. The HOMO-LUMO energy gap (Eg), adiabatic ionization potential (AIP) and the adiabatic electron affinity (AEA) are also investigated to elaborate the relative electronic stability of all the clusters.

Au2Pt-PEG-Ce6 nanoformulation with dual nanozyme activities for synergistic chemodynamic therapy / phototherapy

Although synergistic therapy for tumors has displayed significant promise for effective treatment of cancer, developing a simple and effective strategy to build a multi-functional nanoplatform is still a huge challenge. By virtue of the characteristics of tumor microenvironment, such as hypoxia, slight acidity and H₂O₂ overexpression, Au₂Pt-PEG-Ce6 nanoformulation is constructed for collaborative chemodynamic/phototherapy of tumors. Specifically, the Au₂Pt nanozymes with multiple functions are synthesized in one step at room temperature. The photosensitizer chlorin e6 (Ce6) is covalently linked to Au₂Pt nanozymes for photodynamic therapy (PDT). Interestingly, the Au₂Pt nanozymes possess catalase- and peroxidase-like activities simultaneously, which not only can generate O₂ for relaxation of tumor hypoxia and enhancement of PDT efficiency but also can produce ∙OH for chemodynamic therapy (CDT). In addition, the high photothermal conversion efficiency (η = 31.5%) of Au₂Pt-PEG-Ce6 nanoformulation provides the possibility for photoacoustic (PA) and photothermal (PT) imaging guided photothermal therapy (PTT). Moreover, the presence of high-Z elements (Au and Pt) in Au₂Pt-PEG-Ce6 nanoformulation endows it with the ability to act as an X-ray computed tomography (CT) imaging contrast agent. All in all, the Au₂Pt-PEG-Ce6 exhibits great potential in multimodal imaging-guided synergistic PTT/PDT/CDT with remarkably tumor specificity and enhanced therapy.

Revealing Sintering Kinetics of MoS2-Supported Metal Nanocatalysts in Atmospheric Gas Environments via Operando Transmission Electron Microscopy

The decoration of two-dimensional (2D) substrates with nanoparticles (NPs) serve as heterostructures for various catalysis applications. Deep understanding of catalyst degradation mechanisms during service conditions is crucial to improve the catalyst durability. Herein, we studied the sintering behavior of Pt and bimetallic Au-core Pt-shell (Au@Pt core-shell) NPs on MoS₂ supports at high temperatures under vacuum, nitrogen (N₂), hydrogen (H₂), and air environments by in situ gas-cell transmission electron microscopy (TEM). The key observations are summarized as effect of environment: while particle migration and coalescence (PMC) was the main mechanism that led to Pt and Au@Pt NPs degradation under vacuum, N₂, and H₂ environments, the degradation of MoS₂ substrate was prominent under exposure to air at high temperatures. Pt NPs were less stable in H₂ environment when compared with the Pt NPs under vacuum or N₂, due to Pt-H interactions that weakened the adhesion of Pt on MoS₂. Effect of NP composition: under H₂, the stability of Au@Pt NPs was higher in comparison to Pt NPs. This is because H₂ promotes the alloying of Pt-Au, thus reducing the number of Pt at the surface (reducing H₂ interactions) and increasing Pt atoms in contact with MoS₂. Effect of NP size: The alloying effect promoted by H₂ was more pronounced in small size Au@Pt NPs resulting in their higher sintering resistance in comparison to large size Au@Pt NPs and similar size Pt NPs. The present work provides key insights into the parameters affecting the catalyst degradation mechanisms on 2D supports.

Construction of Embedded Heterostructured SrZrO3/Flower-like MoS2 with Enhanced Dye Photodegradation under Solar-Simulated Light Illumination

SrZrO3/flower-like MoS2 composites with an embedded heterostructure were synthesized via a simple two-step hydrothermal method and their performance was evaluated by photodegradation of methylene blue (MB) under solar-simulated light irradiation. The sandwiched flower-like MoS2 with a high Mo(VI) ratio was adopted as the matrix, and SrZrO3 was grown between the MoS2 layers, forming an intense contact interface, which promotes the efficient separation and transport of photoinduced carriers. The enhanced photocatalytic degradation of 99.7% after 80 min of irradiation is exhibited over the MS5 sample (5 wt % SrZrO3 loading amount on the MoS2 matrix). Moreover, the ratio of Mo(VI) and the superoxide radical plays a crucial role in the photodegradation of MB, and the higher the ratio the better the performance. This work provided a strategy to design a new kind of photocatalyst for photocatalysis and indicated that MoS2 is preferably adopted as a matrix rather than as a loading component.

Competitive Bio-Barcode Immunoassay for Highly Sensitive Detection of Parathion Based on Bimetallic Nanozyme Catalysis

A competitive sensitive bio-barcode immunoassay based on bimetallic nanozyme (Au@Pt: gold@platinum) catalysis has been designed for the detection of the pesticide parathion. Gold nanoparticles (AuNPs) were modified with single-stranded thiol oligonucleotides (ssDNAs) and monoclonal antibodies (mAbs) to form AuNP probes; magnetic nanoparticles (MNPs) were coated with ovalbumin (OVA)-parathion haptens as MNP probes, and bimetallic nanozyme (Au@Pt) nanoparticles functionalized with the complementary thiolated ssDNA were used as Au@Pt probes. The Au@Pt probes reacted with the AuNP probes through complementary base pairing. Further, parathion competed with MNP probes to bind the mAbs on the AuNP probes. Finally, the complex system was separated by a magnetic field. The released Au@Pt probes catalyzed a chromogenic system consisting of teramethylbenzidine (TMB). The bimetallic nanozyme-based bio-barcode immunoassay was performed on rice, pear, apple, and cabbage samples to verify the feasibility of the method. The immunoassay exhibited a linear response from 0.01 to 40 μg·kg^-1, and the limit of detection (LOD) was 2.13 × 10^-3 μg·kg^-1. The recoveries and relative standard deviations (RSDs) ranged from 73.12 to 116.29% and 5.59 to 10.87%, respectively. The method was found to correlate well with data obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In conclusion, this method exhibits potential as a sensitive alternative method for the detection of a variety of pesticides, ensuring the safety of fruits and vegetables in agriculture.

Chemical Sensors Based on Two-Dimensional (2D) Materials for Selective Detection of Ions and Molecules in Liquid

Up until now, two-dimensional (2D) materials have been researched vigorously for application to sensing ions and molecules in liquid due to their unique structural, chemical, and electronic properties. Features of 2D materials such as high surface area-to-volume ratios and various reaction sites are ideal characteristics for fabricating state-of-the-art high-performed chemical sensors. This review particularly focuses on the detection of pH, metal ions, and biomolecules in liquid media. The final goal of the ion/molecule sensors is a development of the electronic tongue or taste sensors that can be used in medical, food, biotechnology, and health applications. Herein, we introduce recent advances in the field of ion/molecule sensors in liquid media based on 2D materials, especially concentrating in graphene and MoS₂, and will emphasize the opportunities and challenges of these unique sensing materials and devices.

Challenges and recent advancements of functionalization of two-dimensional nanostructured molybdenum trioxide and dichalcogenides

Atomically thin two-dimensional (2D) semiconductors are the thinnest functional semiconducting materials available today. Among them, both molybdenum trioxide and chalcogenides (MT&Ds) represent key components within the family of different 2D semiconductors for various electronic, optoelectronic and electrochemical applications due to their unique electronic, optical, mechanical and electrochemical properties. However, despite great progress in research dedicated to the development and fabrication of 2D MT&Ds observed within the last decade, there are significant challenges that affected their charge transport behavior and fabrication on a large scale as well as there is high dependence of the carrier mobility on the thickness. In this article, we review the recent progress in the carrier mobility engineering of 2D MT&Ds and elaborate devised strategies dedicated to the optimization of MT&D properties. Specifically, the latest physical and chemical methods towards the surface functionalization and optimization of the major factors influencing the extrinsic transport at the electrode-2D semiconductor interface are discussed.

Scalable Epitaxial Growth of WSe2 Thin Films on SiO2/Si via a Self-Assembled PtSe2 Buffer Layer

The growth of large-area epitaxial transition metal dichalgogenides (TMDCs) are of central importance for scalable integrated device applications. Different methods have been developed to achieve large-sized high quality films. However, reliable approaches for centimeter-sized or even wafer-level epitaxial growth of TMDCs are still lacking. Here we demonstrate a new method to grow inch-sized epitaxial WSe₂ films on SiO₂/Si substrates at a much lower temperature with high repeatability and scalability. High quality crystalline films are achieved through direct selenization of a tungsten film with platinum as the underlayer. The self-assembled PtSe₂ buffer layer, formed during selenization, assists epitaxial growth of WSe₂. Using fabricated WSe₂ films, excellent performance memory devices are demonstrated. As a member of the TMDC family, our findings based on WSe₂ may also be applied to other TMDC materials for large-scale production of high quality TMDC films for various applications.

Ultrafine Pt Nanoparticles Stabilized by MoS2/N-Doped Reduced Graphene Oxide as a Durable Electrocatalyst for Alcohol Oxidation and Oxygen Reduction Reactions

Direct alcohol fuel cells play a pivotal role in the synthesis of catalysts because of their low cost, high catalytic activity, and long durability in half-cell reactions, which include anode (alcohol oxidation) and cathode (oxygen reduction) reactions. However, platinum catalysts suffer from CO tolerance, which affects their stability. The present study focuses on ultrafine Pt nanoparticles stabilized by flowerlike MoS₂/N-doped reduced graphene oxide (Pt@MoS₂/NrGO) architecture, developed via a facile and cost-competitive approach that was performed through the hydrothermal method followed by the wet-reflux strategy. Fourier transform infrared spectra, X-ray diffraction patterns, Raman spectra, X-ray photoelectron spectra, field-emission scanning electron microscopy, and transmission electron microscopy verified the conversion to Pt@MoS₂/NrGO. Pt@MoS₂/NrGO was applied as a potential electrocatalyst toward the anode reaction (liquid fuel oxidation) and the cathode reaction (oxygen reduction). In the anode reaction, Pt@MoS₂/NrGO showed superior activity toward electro-oxidation of methanol, ethylene glycol, and glycerol with mass activities of 448.0, 158.0, and 147.0 mA/mg_Pt, respectively, approximately 4.14, 2.82, and 3.34 times that of a commercial Pt-C (20%) catalyst. The durability of the Pt@MoS₂/NrGO catalyst was tested via 500 potential cycles, demonstrating less than 20% of catalytic activity loss for alcohol fuels. In the cathode reaction, oxygen reduction reaction results showed excellent catalytic activity with higher half-wave potential at 0.895 V versus a reversible hydrogen electrode for Pt@MoS₂/NrGO. The durability of the Pt@MoS₂/NrGO catalyst was tested via 30 000 potential cycles and showed only 15 mV reduction in the half-wave potential, whereas the Pt@NrGO and Pt-C catalysts experienced a much greater shift (Pt@NrGO, ∼23 mV; Pt-C, ∼20 mV).

Synthetic Techniques and Functionalization Approaches of 2D Transition Metal Dichalcogenides

As typical graphene analogues, two-dimensional (2D) transition-metal dichalcogenides (TMDs), including MoS2, WS2, etc., have attracted increasing research interest due to their semiconducting characteristics, sizable bandgap, large surface area, and outstanding performance in various applications such as electronics/optoelectronics, sensing, catalysis, and energy storage. For the widespread exploration of TMD nanosheets in fundamental studies and promising applications, a rapid pace of progress has recently been achieved in developing methodologies for reliable and scale-up production of atomically thin TMD nanosheets. In this chapter, we will present a comprehensive overview of different synthetic techniques of 2D TMDs and evaluate their relative merits and demerits. Particularly, the design principle, fabrication mechanism, typical process and special conditions will be emphasized to understand or follow the effective methods for obtaining required TMD nanosheets in single and few layers. Based on these synthetic techniques, further functionalization of TMD nanosheets with ligands and other nanocomponents are also discussed for gaining some specific properties. Based on our knowledge, we finally propose some possible challenges and potential opportunities in the exploitation of TMD nanosheets for novel applications.

Methanol oxidation on the Pt(321) surface: a theoretical approach on the role of surface morphology and surface coverage effects

We investigated methanol oxidation, decomposition and carbonylation reactions on a high indexed Pt(321) surface.

Tuning Ion Complexing To Rapidly Prepare Hollow Ag-Pt Nanowires with High Activity toward the Methanol Oxidization Reaction

Hollow Pt-based nanowires (NWs) have important applications in catalysis. Their preparation often involves a two-step process in which M (M=Ag, Pd, Co, Ni) NWs are prepared and subsequently subjected to galvanic reaction in solution containing a Pt precursor. It is challenging to achieve a simple one-step preparation, because the redox potential of Pt^IV /Pt or Pt^II /Pt to Pt is high, and therefore, Pt atoms always form first. This work demonstrates that an appropriate pH can decrease the redox potential of Pt^IV /Pt and allows the one-step preparation of high-quality hollow Pt-Ag NWs rapidly (10 min). Moreover, it is easy to realize large-scale preparation with this method. The NW composition can be adjusted readily to optimize their performance in the electrocatalytic methanol oxidization reaction (MOR). Compared with commercial Pt/C, NWs with appropriate Ag/Pt ratios exhibit high stability, activity, and CO tolerance ability.

Molecular chemistry approaches for tuning the properties of two-dimensional transition metal dichalcogenides

Two-dimensional (2D) semiconductors, such as ultrathin layers of transition metal dichalcogenides (TMDs), offer a unique combination of electronic, optical and mechanical properties, and hold potential to enable a host of new device applications spanning from flexible/wearable (opto)electronics to energy-harvesting and sensing technologies. A critical requirement for developing practical and reliable electronic devices based on semiconducting TMDs consists in achieving a full control over their charge-carrier polarity and doping. Inconveniently, such a challenging task cannot be accomplished by means of well-established doping techniques (e.g. ion implantation and diffusion), which unavoidably damage the 2D crystals resulting in degraded device performances. Nowadays, a number of alternatives are being investigated, including various (supra)molecular chemistry approaches relying on the combination of 2D semiconductors with electroactive donor/acceptor molecules. As yet, a large variety of molecular systems have been utilized for functionalizing 2D TMDs via both covalent and non-covalent interactions. Such research endeavours enabled not only the tuning of the charge-carrier doping but also the engineering of the optical, electronic, magnetic, thermal and sensing properties of semiconducting TMDs for specific device applications. Here, we will review the most enlightening recent advancements in experimental (supra)molecular chemistry methods for tailoring the properties of atomically-thin TMDs - in the form of substrate-supported or solution-dispersed nanosheets - and we will discuss the opportunities and the challenges towards the realization of novel hybrid materials and devices based on 2D semiconductors and molecular systems.

Size-Tunable Natural Mineral-Molybdenite for Lithium-Ion Batteries Toward: Enhanced Storage Capacity and Quicken Ions Transferring

Restricted by the dissatisfied capacity of traditional materials, lithium-ion batteries (LIBs) still suffer from the low energy-density. The pursuing of natural electrode resources with high lithium-storage capability has triggered a plenty of activities. Through the hydro-refining process of raw molybdenite ore, containing crushing-grinding, flotation, exfoliation, and gradient centrifugation, 2D molybdenum disulfide (MoS2) with high purity is massively obtained. The effective tailoring process further induce various sizes (5, 2, 1 and 90 nm) of sheets, accompanying with the increasing of active sites and defects. Utilized as LIB anodes, size-tuning could serve crucial roles on the electrochemical properties. Among them, MoS2-1 μm delivers an initial charge capacity of 904 mAh g-1, reaching up to 1,337 mAh g-1 over 125 loops at 0.1 A g-1. Even at 5.0 A g-1, a considerable capacity of 682 mAh g-1 is remained. Detailedly analyzing kinetic origins reveals that size-controlling would bring about lowered charge transfer resistance and quicken ions diffusion. The work is anticipated to shed light on the effect of different MoS2 sheet sizes on Li-capacity ability and provides a promising strategy for the commercial-scale production of natural mineral as high-capacity anodes.

In situ study of nucleation and growth dynamics of Au nanoparticles on MoS2 nanoflakes

Two-dimensional (2D) substrates decorated with metal nanoparticles offer new opportunities to achieve high-performance catalytic behavior. However, little is known on how the substrates control the nucleation and growth processes of the nanoparticles. This paper presents the visualization of dynamic nucleation and growth processes of gold nanoparticles on ultrathin MoS2 nanoflakes by in situ liquid-cell transmission electron microscopy (TEM). The galvanic displacement resulting in Au nuclei formation on MoS2 was observed in real time inside the liquid cell. We found that the growth mechanism of Au particles on pristine MoS2 is in between diffusion-limited and reaction-limited, possibly due to the presence of electrochemical Ostwald ripening. A larger size distribution and more orientation variation is observed for the Au particles along the MoS2 edge than on the interior. Differing from pristine MoS2, sulfur vacancies on MoS2 induce Au particle diffusion and coalescence during the growth process. Density functional theory (DFT) calculations show that the size difference is because the exposed molybdenum atoms at the edge with dangling bonds can strongly interact with Au atoms, whereas sulfur atoms on the MoS2 interior have no dangling bonds and weakly interact with gold atoms. In addition, S vacancies on MoS2 generate strong nucleation centers that can promote diffusion and coalescence of Au nanoparticles. The present work provides key insights into the role of 2D materials in controlling the size and orientation of noble metal nanoparticles vital to the design of next generation catalysts.

Bimetallic Pt-Pd nanostructures supported on MoS2 as an ultra-high performance electrocatalyst for methanol oxidation and nonenzymatic determination of hydrogen peroxide

The authors report on a composite based electrocatalyst for methanol oxidation and H₂O₂ sensing. The composite consists of Pt nanoparticles (NPs), Pd nanoflakes, and MoS₂. It was synthesized by chemical reduction followed by template-free electro-deposition of Pt NPs. FESEM images of the Pd nanoflakes on the MoS₂ reveal nanorod-like morphology of the Pd NPs on the MoS₂ support, whilst FESEM images of the Pt-Pd/MoS₂ composite show Pt NPs in high density and with the average size of ~15 nm, all homogeneously electrodeposited on the Pd-MoS₂ composite. A glassy carbon electrode (GCE) was modified with the composite to obtain an electrode for methanol oxidation and H₂O₂ detection. The modified GCE exhibits excellent durability with good catalytic efficiency (the ratio of forward and backward peak current density, I_f/I_b, is 3.23) for methanol oxidation in acidic medium. It was also used to sense H₂O₂ at an applied potential of -0.35 V vs. Ag|AgCl which can be detected with a 3.4 μM lower limit of detection. The sensitivity is 7.64 μA μM^-1 cm^-2 and the dynamic range extends from 10 to 80 μM. This enhanced performance can be explained in terms of the presence of higher percentage of metallic 1T phase rather than a semiconducting 2H phase in MoS₂. In addition, this is a result of the high surface area of MoS₂ with interwoven nanosheets, the uniform distribution of the Pt NPs without any agglomeration on MoS₂ support, and the synergistic effect of Pt NPs, Pd nanoflakes and MoS₂ nanosheets. In our perception, this binder-free nano-composite has promising applications in next generation energy conversion and in chemical sensing. Graphical abstract A composite consisting of palladium nanoflakes and molybdenum disulfide was decorated with platinum nanoparticles and then placed on a glassy carbon electrode which is shown to be a viable electrocatalyst for both methanol oxidation and detection of hydrogen peroxide.

BSA-caged metal clusters to exfoliate MoS2 nanosheets towards their hybridized functionalization

Herein, we develop a facile exfoliation and in situ functionalization strategy to produce hybridized Au/MoS2 nanostructures comprised of size-controlled gold nanoparticles (Au NPs) and ultrathin MoS2 nanosheets by using bovine serum albumin (BSA)-caged Au25 clusters as both exfoliating and functionalizing agents. As revealed, BSA molecules are strongly adsorbed on MoS2via their hydrophobic interaction, and this drives the expansion of the BSA molecules that initially protect Au25 cores at pH 4, leading to the effective exfoliation of MoS2 nanosheets together with the epitaxial growth of Au25 cores into 5 nm-sized Au NPs on MoS2 nanosheets due to their reduced surface protection. Upon the addition of H2O2, the resulting Au NPs can further grow to achieve a controlled size from 5 to 30 nm with an increase of the reaction time. It is demonstrated that the hybridized Au/MoS2 nanosheets exhibit a better performance in the photocatalytic degradation of substrates compared to the individual components or their mixture. Moreover, the hybridized Ag/MoS2, Au/WO3 and Au/graphene nanosheets are further produced by the usage of BSA-caged Ag and Au clusters, respectively. Overall, this work reports the first utilization of protein-caged metal clusters for the exfoliation and hybridized functionalization of 2D materials, and this brings more opportunities to exploit unusual properties of hybridized 2D materials for novel applications.

Bimetallic Platinum-Rhodium Alloy Nanodendrites as Highly Active Electrocatalyst for the Ethanol Oxidation Reaction

Rationally designing and manipulating composition and morphology of precious metal-based bimetallic nanostructures can markedly enhance their electrocatalytic performance, including selectivity, activity, and durability. We herein report the synthesis of bimetallic PtRh alloy nanodendrites (ANDs) with tunable composition by a facile complex-reduction synthetic method under hydrothermal conditions. The structural/morphologic features, formation mechanism, and electrocatalytic performance of PtRh ANDs are investigated thoroughly by various physical characterization and electrochemical methods. The preformed Rh crystal nuclei effectively catalyze the reduction of Pt²⁺ precursor, resulting in PtRh alloy generation due to the catalytic growth and atoms interdiffusion process. The Pt atoms deposition distinctly interferes in Rh atoms deposition on Rh crystal nuclei, resulting in dendritic morphology of PtRh ANDs. For the ethanol oxidation reaction (EOR), PtRh ANDs display the chemical composition and solution pH co-dependent electrocatalytic activity. Because of the alloy effect and particular morphologic feature, Pt₁Rh₁ ANDs with optimized composition exhibit better reactivity and stability for the EOR than commercial Pt nanocrystals electrocatalyst.

Voltammetric chiral discrimination of tryptophan using a multilayer nanocomposite with implemented amino-modified β-cyclodextrin as recognition element

An electrochemical chiral multilayer nanocomposite was prepared by modifying a glassy carbon electrode (GCE) via opposite-charge adsorption of amino-modified β-cyclodextrin (NH₂-β-CD), gold-platinum core-shell microspheres (Au@Pts), polyethyleneimine (PEI), and multi-walled carbon nanotubes (MWCNTs). The modified GCE was applied to the enantioselective voltammetric determination of tryprophan (Trp). The Au@Pts enable an effective immobilization of the chiral selector (NH₂-β-CD) and enhance the electrochemical performance. Scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, FTIR and electrochemical methods were used to characterize the nanocomposite. Trp enantiomers were then determined by differential pulse voltammetry (DPV) (with a peak potential of +0.7 V vs. Ag/AgCl). The recognition efficiency was expressed by an increase in peak height by about 32% for DPV determinations of L-Trp compared to D-Trp in case of a 5 mM Trp solution of pH 7.0. Response was linear in the 10 μM to 5.0 mM concentration range, and the limits of detection were 4.3 μM and 5.6 μM with electrochemical sensitivity of 43.5 μA·μM^-1·cm^-2 and 34.6 μA·μM^-1·cm^-2 for L-Trp and D-Trp, respectively (at S/N = 3). Graphical Abstract Schematic of an electrochemical chiral multilayer nanocomposite composed of multi-walled carbon nanotubes (MWCNTs), polyethyleneimine (PEI), gold-platinum core-shell microspheres (Au@Pt) and amino-modified β-cyclodextrin (NH₂-β-CD). It was prepared by modifying a glassy carbon electrode (GCE) for enantioselective voltammetric determination of tryptophan (Trp) enantiomers.

MoS2–Au@Pt nanohybrids as a sensing platform for electrochemical nonenzymatic glucose detection

A MoS₂–Au@Pt nanohybrid was used as a sensing platform for electrochemical nonenzymatic glucose detection with high sensitivity, selectivity and stability.

Noble metal nanostructure-decorated molybdenum disulfide nanocomposites: synthesis and applications

Noble metal nanostructure-decorated MoS₂ nanocomposites have been used in sensors, catalysts, antibacterial materials and batteries due to their excellent properties.

One-pot synthesis of CuPt nanodendrites with enhanced activity towards methanol oxidation reaction

CuPt nanodendrites have special electrocatalytic performance due to their unique morphologies and structures. In this work, we report a facile and one-pot synthesis of highly branched and dispersed CuPt nanodendrites with a size of about 22 nm and Pt/Cu ratio of 2 : 1. X-ray photoelectron spectra indicate a Pt-rich surface of the prepared CuPt nanodendrites. The combination of a highly branched structure with a Pt-rich shell would be very beneficial for catalytic properties, which was confirmed by electrochemical tests towards MOR. A systematic study on morphology evolution of the products and understanding of their growth mechanism was carried out using the effects of reaction time and reducing agents.

CuPt nanodendrites have special electrocatalytic performance due to their unique morphology and structures.

Au@Pt nanoparticles as catalase mimics to attenuate tumor hypoxia and enhance immune cell-mediated cytotoxicity

Hypoxic tumor microenvironment (TME) is closely linked to tumor progression, heterogeneity and immune suppression. Therefore, the development of effective methods to overcome hypoxia and substantially enhance the immunotherapy efficacy remains a desirable goal. Herein, we engineered a biocompatible Au core/Pt shell nanoparticles (Au@Pt NPs) to reoxygenate the TME by reacting with endogenous H₂O₂. Treatment with Au@Pt NPs appeared to improve oxygen in intracellular environments and decrease hypoxia-inducible factor-1α expression. Furthermore, the integration of high catalytic efficiency of Au@Pt NPs with cytokine-induced killer (CIK) cell immunotherapy, could lead to significantly improve the effect of CIK cell-mediated cytotoxicity. These results suggest great potential of Au@Pt NPs for regulation of the hypoxic TME and enhance immune cell mediated anti-tumor immunity.