Aptamer-aided plasmonic nano-urchins for reporter-free surface-enhanced Raman spectroscopy analysis of cortisol.

Cortisol is a vital glucocorticoid hormone reflecting stress levels and related disease processes. In this study, we report an aptamer-functionalized plasmonic nano-urchin (α-FeOOH@Au-aptamer)-aided cortisol-capturing and surface-enhanced Raman spectroscopy (SERS) analysis approach. The designed α-FeOOH@Au-aptamer exhibits a well-patterned plasma structure, which combines the good SERS enhancement ability of reduced nanogaps between the Au plasma and the hot spot-favored structure of anisotropic tips from α-FeOOH urchins, with the high affinity of the aptamer towards cortisol molecules. The α-FeOOH@Au-aptamer achieved reporter-free SERS quantification for cortisol with good sensitivity (limit of detection <0.28 µmol L-1), robust salt (1.0 mol per L NaCl) and protein (5.0 mg per mL bovine serum protein) tolerance, favorable reproducibility, as well as good reusability. We further demonstrated the good cortisol-capturing ability and SERS efficacy of the α-FeOOH@Au-aptamer profiling in the serum and urine samples. Our approach provides an alternative tool for cortisol analysis and a reference strategy for report-free SERS detection of small molecules.

Selective detection of ascorbic acid by tuning the composition and fluorescence of the cesium lead halide perovskite nanocrystals.

Lead halide perovskite nanocrystals (PNCs) have attracted intense attention due to their excellent optoelectronic properties. In this work, a series of water-stable CsPb(Br/I)3PNCs fluorescent probes were prepared using an anion exchange method. It was found that the PNCs probes could be used to detect ascorbic acid (AA) in water, and interestingly, the FL spectra of the PNCs probes can be adjusted by controlling the concentration of KI in anion exchange to improve the detection selectivity of AA. The high sensitivity and selectivity make CsPb(Br/I)3PNCs an ideal material for AA sensing. The concentration of AA can be linearly measured in the range from 0.01 to 50µM, with a detection limit of 4.2 nM. The reason for the enhanced FL of CsPb(Br/I)3PNCs was studied, and it is considered that AA causes the aggregation of CsPb(Br/I)3PNCs. This strategy of improving the selectivity of the probe to the substrate by adjusting the spectrum will significantly expand the application of PNCs in the field of analysis and detection.

A luminescent organic cocrystal for detecting 2,4-dinitroaniline.

2,4-dinitroaniline (2,4DNBA), a significant hazardous chemical, is extensively used in industry and agriculture. The chemical accumulates in the environment for a long time, causing irreversible damage to the ecosystem. Currently, it is quite challenging to identify it by common analysis and detection techniques. Herein, a luminescent organic cocrystal (TCNB-8HQ) was prepared using 1,2,4,5-tetracyanobenzene (TCNB) as the electron acceptor and 8-hydroxyquinoline (8HQ) as the electron donor. The prepared TCNB-8HQ was used as a fluorescent probe with a fast and specific response to 2,4DNBA. This detection method possessed a linear range of 0.5-200 µmol/L with a detection limit as low as 0.085 µmol/L to detect 2,4DNBA in real samples with satisfactory spiking recovery. As revealed by fluorescence spectrum and UV-vis absorption spectrum, the detection mechanism involved competitive absorption between cocrystal material and 2,4DNBA. Moreover, the feasibility of the system was explored by preparing portable indicator strips for 2,4DNBA from organic cocrystal (TCNB-8HQ). This study not only provided an environmentally friendly gram-level preparation strategy to synthesize the fluorescent material but also investigated their application in chemical detection.

A pH-regulated fluorescence covalent organic framework for quantitative water content detection in methanol.

In this paper, we designed and synthesized a two-dimensional fluorescent covalent organic framework (TAPB-DMTP-COF) for the precise determination of H2O content in methanol. The COF was synthesized using two typical monomers by grinding method, which significantly reduced the synthesis time. By adjusting the pH value of the COF suspension to 4.0, the portion of the COF material structure is disrupted, thereby mitigating π-π stacking and resolving the aggregation-caused quenching (ACQ) effect. Consequently, the non-fluorescent TAPB-DMTP-COF exhibited blue-purple fluorescence emission in methanol. At the same time, it is observed that in the presence of H2O, there is a red shift in the maximum fluorescence emission peak of TAPB-DMTP-COF, which correlates with the H2O content within a specific range. Notably, this redshift demonstrates a linear relationship with H2O content from 4% to 80% in methanol. Our work presents novel insights for efficient analysis and detection of H2O content in methanol and could be used for H2O detection in other organic solvents.

Chiral Assembly of Perovskite Nanocrystals: Sensitive Discrimination of Amino Acid Enantiomers.

Chirality is a widespread phenomenon in nature and in living organisms and plays an important role in living systems. The sensitive discrimination of chiral molecular enantiomers remains a challenge in the fields of chemistry and biology. Establishing a simple, fast, and efficient strategy to discriminate the spatial configuration of chiral molecular enantiomers is of great significance. Chiral perovskite nanocrystals (PNCs) have attracted much attention because of their excellent optical activity. However, it is a challenge to prepare perovskites with both chiral and fluorescence properties for chiral sensing. In this work, we synthesized two chiral fluorescent perovskite nanocrystal assembly (PNA) enantiomers by using l- or d-phenylalanine (Phe) as chiral ligands. PNA exhibited good fluorescence recognition for l- and d-proline (Pro). Homochiral interaction led to fluorescence enhancement, while heterochiral interaction led to fluorescence quenching, and there is a good linear relationship between the fluorescence changing rate and l- or d-Pro concentration. Mechanism studies show that homochiral interaction-induced fluorescence enhancement is attributed to the disassembly of chiral PNA, while no disassembly of chiral PNA was found in heterochiral interaction-induced fluorescence quenching, which is attributed to the substitution of Phe on the surface of chiral PNA by heterochiral Pro. This work suggests that chiral perovskite can be used for chiral fluorescence sensing; it will inspire the development of chiral nanomaterials and chiral optical sensors.

An all-inorganic lead-free metal halide double perovskite for the highly selective detection of norfloxacin in aqueous solution.

Lead-based perovskites are highly susceptible to environmental influences, and their application in analytical chemistry, especially in aqueous solution, has been reported rarely. All-inorganic lead-free metal halide perovskites have been considered as a substitute for lead-based perovskites. Herein, a Cs2RbTbCl6 perovskite microcrystal (PMCs), which emits strong yellow-green fluorescence with a maximum emission wavelength at 547 nm, was for the first time  synthesized and characterized. The Cs2RbTbCl6 PMCs could be well dispersed in N,N-dimethylacetamide (DMF), and its fluorescence could be significantly enhanced by the addition of norfloxacin (NOR) in the aqueous solution. We found that the Cs2RbTbCl6 PMCs can be used as fluorescent probes (excitation, 365 nm; emission, 547 nm) to selectively detect NOR in a concentration range from 10.0 to 200.0 µM with the limit of detection (LOD) being 0.04 µM. The Cs2RbTbCl6 PMCs could also be adsorbed on filter paper to fabricate as a fluorescent test paper for visual detection of NOR under 365-nm ultraviolet (UV) lamp irradiation. The proposed method has the potential to establish a new analytical method to visualize the detection of NOR in aqueous environments and also promotes the application of all-inorganic lead-free perovskites for analytical detection in aqueous environments.

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis.

BACKGROUND: Driven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. RESULTS: In this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SIGNIFICANCE: This analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Synthesis of a water-stable CsPbBr3 perovskite for selective detection of mercury ion in water.

By using the method of low-temperature crystallization, CsPbBr3 perovskite nanocrystals (PNCs) coated with trifluoroacetyl lysine (Tfa-Lys) and oleamine (Olam) were synthesized in aqueous solution. The structure of the CsPbBr3 PNCs was characterized by many methods, such as ultraviolet (UV)-visible absorption spectrophotometer, fluorescence spectrophotometer, transmission electron microscopy (TEM), and X-ray diffraction (XRD) pattern. The fluorescence emission of the CsPbBr3 PNCs is stable in water for about 1 day at room temperature. It was also found that the fluorescence of the PNCs could be obviously and selectively quenched after the addition of mercury ion (Hg2+ ), allowing a visual detection of Hg2+ by the naked eye under UV light illumination. The fluorescence quenching rate (I0 /I) has a good linear relationship with the addition of Hg2+ in the concentration range 0.075 to 1.5 mg/L, with a correlation coefficient (R2 ) of 0.997, and limit of detection of 0.046 mg/L. The fluorescence quenching mechanism of the PNCs was determined by the fluorescence lifetime and X-ray photoelectron spectroscopy (XPS) of the PNCs. Overall, the synthesis method for CsPbBr3 PNCs is simple and rapid, and the as-prepared PNCs are stable in water that could be conveniently used for selective detection of Hg2+ in the water environment.

CuI-p-DPA coordination polymer isomers for "turn-on" fluorescence detection of thiophanate-methyl.

Three copper iodide coordination polymer (CuI-p-DPA) isomers were prepared from the fluorescent organic ligand p-DPA and cuprous iodide (CuI) under different solvothermal conditions, which exhibited quenched fluorescence behaviors after forming coordination polymers (CPs). These CuI-p-DPA isomers showed discrepant fluorescence responses to thiophanate-methyl (TM). Among these CuI-p-DPA isomers, α-CuI-p-DPA exhibited the maximum fluorescence enhancement after its incubation with TM in aqueous solution. The fluorescence enhancement mechanism was that TM competed with the ligand p-DPA to coordinate with CuI clusters, and then α-CuI-p-DPA released p-DPA into the solution and induced fluorescence enhancement. The present detection method possesses the advantages of good selectivity, high sensitivity, short response time, and strong anti-interference ability with a linear range of 0.5-100 µM and a detection limit of 0.01 µM. This study not only reveals that the spatial structures of CPs play an important role in the fluorescence response ability, but also provide a new fluorescence signal-on analysis method to rapidly and sensitively determine the pesticide residue for TM.

Transformable nano-antibiotics for mechanotherapy and immune activation against drug-resistant Gram-negative bacteria.

The dearth of antibiotic candidates against Gram-negative bacteria and the rise of antibiotic resistance create a global health concern. The challenge lies in the unique Gram-negative bacterial outer membrane that provides the impermeable barrier for antibiotics and sequesters antigen presentation. We designed a transformable nano-antibiotics (TNA) that can transform from nontoxic nanoparticles to bactericidal nanofibrils with reasonable rigidity (Young's modulus, 21.6 ± 5.9 MPa) after targeting ß-barrel assembly machine A (BamA) and lipid polysaccharides (LPSs) of Gram-negative bacteria. After morphological transformation, the TNA can penetrate and damage the bacterial envelope, disrupt electron transport and multiple conserved biosynthetic and metabolic pathways, burst bacterial antigen release from the outer membrane, and subsequently activate the innate and adaptive immunity. TNA kills Gram-negative bacteria in vitro and in vivo with undetectable resistance through multiple bactericidal modes of action. TNA treatment-induced vaccination results in rapid and long-lasting immune responses, protecting against lethal reinfections.

Lanthanide Metal-Organic Framework Isomers with Novel Water-Boosting Lanthanide Luminescence Behaviors.

Lanthanide metal-organic frameworks (Ln-MOFs) with exceptional optical performance and structural diversity offer a unique platform for the development of luminescent materials. However, Ln-MOFs often suffer from luminescence quenching by high-vibrating oscillators, especially in aqueous solution. Thus, multiple strategies have been adopted to improve the luminescence of Ln3+. Anomalous research about water-induced lanthanide luminescence enhancement of Ln-MOFs is in the primary stage. Here, two Eu-based metal-organic framework (Eu-MOF) isomers named QXBA-Eu-1 and QXBA-Eu-2 were constructed by using the same ligand under different solvent thermal conditions, which exhibited distinctive water- and methanol-boosting emission behaviors. As for QXBA-Eu-1, water and methanol molecules replaced the free N,N-dimethylacetamide (DMA) molecules in the framework, repressed the rotation or libration suppression of the QXBA linker, and formed hydrogen bonds with the coordinated water molecules, which suppressed the O-H high-energy vibrations, reduced nonradiative transitions, stabilized the T1 state, and facilitated the intersystem crossing (ISC) process. For QXBA-Eu-2, water molecules tended to replace the coordinated DMA ligands, which altered the S1 and T1 energy levels of the ligand and facilitated the ligand-to-metal energy transfer (LMET) process and strengthened the luminescence of Eu3+. Importantly, free solvent molecules and the hydroxylation of Eu3+ centers also restrained the rotation or libration of the QXBA linker, by which the nonradiative transition was further inhibited and the lanthanide luminescence enhanced. Thus, this work not only opened an unprecedented path to enhance lanthanide luminescence in aqueous solution but also expanded its application scope.

Hydrogenation of levulinic acid to γ-valerolactone over single-atom Pt confined in Sn-modified MIL-101(Fe).

We synthesize a Sn-modified MIL-101(Fe), which can confine Pt to the single-atom scale. This novel Pt@MIL(FeSn) catalyst efficiently hydrogenates levulinic acid to γ-valerolactone (TOF: 1386 h-1, yield: >99%) at only 100 °C and 1 MPa of H2via α-angelica lactone as an intermediate. This could be the first report on switching the reaction path from 4-hydroxypentanoic acid to α-angelica lactone under very mild conditions. Incorporating Sn into MIL-101(Fe) enables the creation of abundant micro-pores less than 1 nm and Lewis acidic sites that stabilize Pt0 atoms. The ensemble of active Pt atoms and a Lewis acid can synergistically enhance adsorption of the CO bond and facilitate dehydrative cyclization of levulinic acid.

Time-dependent photo-activated aminoborane room-temperature phosphorescence materials with unprecedented properties: simple, versatile, multicolor-tuneable, water resistance, optical information writing/erasing, and multilevel data encryption.

Triarylboranes-based pure organic room-temperature phosphorescence (RTP) materials are rarely investigated because of their large steric hindrance and the electron defect of the boron atom. As a result, creating functional triarylborane RTP materials is difficult. Herein, we report the first photo-activated RTP materials with lifetimes/quantum yields ≤0.18 s/6.83% based on donor (D)-π-acceptor (A) from methylene carbazole-functionalized aminoborane (BN)-doped polymethyl methacrylate (BN-o-Met-Cz@PMMA) under 365 nm UV irradiation (30 s). Incredibly, BN-o-Met-Cz@PMMA films exhibited unprecedented photo-activated RTP dual-response properties (e.g., air + 365 nm: τ P = 0.18 s, Φ P = 6.83%; N2 + 365 nm: τ P = 0.42 s, Φ P = 17.34%). Intriguingly, the BN (D-π-A) system demonstrated good versatility for photo-activated RTP whether the electron-donating group or electron-withdrawing group was placed in the ortho (meta)-position of the B atom. As a result, a series of photo-activated single-molecule organic RTP materials with multi-color emission, high quantum yields, and ultra-long lifetimes can be prepared rapidly. BN-X@PMMA films showed broad application prospects for information encryption, data erasure, anti-counterfeiting, and water resistance. Our method provides new strategies for the design, synthesis, and application of RTP materials, thereby enriching the types of organic RTP materials and facilitating further developments in this area.

Novel Lanthanide-Based Metal-Organic Framework Isomer as a Double Ratiometric Fluorescent Probe for Vanillymandelic Acid.

The concentration of vanillymandelic acid (VMA) in urine is closely related with pheochromocytoma diagnosis. Thus, it is essential to develop more accurate and convenient fluorescence sensing strategies toward VMA. Until now, the design of double ratiometric detection methods for VMA was still in the unexplored stage. In this work, novel Ln3+-based metal-organic frameworks (QBA-Eu and QBA-Gd0.875Eu0.125) possessing dual emission peaks was fabricated successfully, which served as isomers of YNU-1 and exhibited more excellent water stability in fluorescence and structure than the ones of YNU-1. The formation of the complex between QBA ligands and VMA molecules via hydrogen bonds within QBA-Eu frameworks produced a new emission band centered at 450 nm and resulted in the decline of monomer emission intensity for QBA at 390 nm. Owing to the reduced energy gap [ΔE (S1 - T1)], the antenna effect was hampered and luminescence of Eu3+ ions also decreased. The developed double ratiometric (I615nm/I475nm, I390nm/I475nm) fluorescence sensors based on QBA-Eu and QBA-Gd0.875Eu0.125 possessed the advantages of fast response (4 min), low detection limits (0.58 and 0.51; 0.22 and 0.31 µM), and wide linear ranges (2-100 and 2-80 µM), which met the requirements of pheochromocytoma diagnosis. We also applied them to determine VMA in an artificial urine sample and diluted human urine sample and obtained satisfactory results. They will become prospective fluorescence sensing platforms for VMA.

Multicolor Adjustable B-N Molecular Switches: Simple, Efficient, Portable, and Visual Identification of Butanol Isomers.

As intelligent probes, dynamic and controllable molecular switches are useful tools for probing and intervening in life processes. However, the types and properties of molecular switches are still relatively single and often can only make two actions: "off" and "on". Therefore, the development of novel molecular switches with multiple colors and multiple instructions is very challenging. Herein, we propose a novel strategy based on the instability of the Lewis acid-base pair (boron (B) and nitrogen (N)), such as introducing the Schiff base (C═N) group into the aminoborane skeleton and preparing the novel molecular switches BN-HDZ and BN-HDZ-N. These two molecules were found to have good multicolor fluorescence switching capability for methanol. Surprisingly, the compound BN-HDZ-N shows unprecedented visual identification for the butanol isomers and could be made into a portable strip for simple and rapid visual identification of the four isomers of butanol, promising an alternative to conventional Lucas reagents. This provides a novel strategy for the design and fabrication of novel multicolor-tunable molecular switches with visual identification of isomers.

A Cu(II) MOF with laccase-like activity for colorimetric detection of 2,4-dichlorophenol and p-nitrophenol.

Metal-organic framework (MOF) materials with aqueous stability have a good potential application in the field of mimetic enzymes. However, most of them have poor robustness in aqueous solution due to competitive coordination effects between water molecules and central metal ions. Herein, a copper-based MOF (Cu-SM MOF) was prepared using copper ions and 5-(sulfomethyl) isophthalic acid (5-SMIPA) by a hydrothermal process. Considering the similarity of coordination and morphology with HKUST-1, the aqueous stability and laccase-like activity of the Cu-SM MOF were investigated using HKUST-1 as the reference. The Cu-SM MOF shows superior aqueous stability to HKUST-1 after immersion in buffer solutions, especially under alkaline conditions. Moreover, the Cu-SM MOF possesses higher catalytic activity than HKUST-1 at a high salt concentration, high temperature, etc., because the Cu-SM MOF exhibits lower Km and higher Vmax values than those of laccase and reported mimetic enzymes. The mimetic enzyme behavior of the Cu-SM MOF is demonstrated in the oxidation of phenols, as well as in the detection of 2,4-dichlorophenol (2,4-DP) and p-nitrophenol with linear ranges of 1-100 µM and 2-250 µM, and limits of detection of 0.53 µM and 1.62 µM, respectively. Owing to the excellent aqueous stability and laccase-like activity of the Cu-SM MOF, it has great application prospects in many fields, such as the determination of phenols and the treatment of industrial wastewater.

Metal-Organic Framework with Near-Infrared Luminescence for "Switch-on" Determination of Kaempferol and Quercetin by the Antenna Effect.

The establishment of a reliable and sensitive method for the detection of flavonoids, such as kaempferol (Kae) and quercetin (Que), is important and challenging in food chemistry and pharmacology because numerous structural analogues may interfere with the detection. Until now, designing an efficient switch-on fluorescence sensing strategy for Kae and Que was still in the unachievable stage. In this work, a switch-on near-infrared (NIR) luminescence sensing assay for Kae and Que was fabricated based on a metal-organic framework (MOF) called IQBA-Yb for the first time. The fluorescence enhancing mechanism was that analytes served as additional "antenna" of Yb3+, leading to the efficient switch-on NIR emission under excitation at 467 nm. Meanwhile, the combination results of experiment and theoretical calculation revealed that there existed hydrogen bonds between Kae, Que, and the MOF skeleton, further promoting the energy transfer between the analyte and Yb3+ and facilitating fluorescence enhancement response. The developed probe possessed excellent sensing capability for Kae and Que, accompanied by a wide linear range (0.04-70, 0.06-90 µM), low detection limit (0.01, 0.06 µM), and short response time (20 min, 6 min), which was used to determine the Kae and Que contents in Green Lake and eatable Que samples with satisfactory results.

Simple Stimulus-Responsive Organic Long Persistent Luminescence Systems Based on Methoxy-Functionalized Triphenylphosphine.

Triarylphosphine-based pure organic long persistent luminescence materials are rarely investigated because of their poor stability and low photoluminescence quantum yield. Herein, we demonstrate that the introduction of a methoxy group (TPP-o-3OMe) at the ortho position of triphenylphosphine (TPP) can essentially promote the n → π* transition and promote intersystem crossing to generate more triplet excitons. Simultaneously, generating abundant intramolecular and intermolecular hydrogen bonds to stable excited triplet excitons is beneficial, thereby causing high-efficiency phosphorescence emission (τp = 394.1 ms; Φp = 9.28%). Interestingly, it shows a good acid response to protonic acids and can often be cycled many times under the heating or ammonia fumigation conditions. This research provides a new idea for enriching the types of pure organic room-temperature phosphorescent materials, widening their applications in the fields of anticounterfeiting and smart response, and promotes the further development of this field.

A lead-free Cs2ZnCl4 perovskite nanocrystals fluorescent probe for highly selective detection of norfloxacin.

The abuse of antibiotics would seriously affect human health and has become of worldwide critical concern, thus it is urgent to develop an environmentally friendly and nontoxic fluorescent probe for antibiotics sensing. In this work, a lead-free Cs2ZnCl4 perovskite nanocrystals (PNCs) probe was fabricated for sensing norfloxacin (NOR) employing a modified ligand-assisted reprecipitation method. The prepared Cs2ZnCl4 PNCs probe had strong blue emission around 440 nm, and the characteristics of PNCs were systematically characterized by X-ray photoelectric spectroscopy (XPS), Fourier transforms infrared spectroscopy (FTIR), transmission electron microscope (TEM) and powder X-ray diffraction (XRD). The results revealed that the fluorescence intensity of the Cs2ZnCl4 PNCs was significantly enhanced after the introduction of norfloxacin. The Cs2ZnCl4 PNCs can be used as a fluorescent probe to selectively and sensitively detect norfloxacin in the concentration range from 0.2 to 50.0 µM, with a correlation coefficient (R2) of 0.9954 and the limit of detection (LOD, 3σ) of 0.1499 µM. The preparation and application of a lead-free perovskite fluorescent probe for norfloxacin would promote the application of perovskite fluorescent probes in biochemical assays.

Single-Atom Catalysts Supported on the Graphene/Graphdiyne Heterostructure for Effective CO2 Electroreduction.

Electrochemical reduction of CO2 to high-energy chemicals is a promising strategy for achieving carbon-neutral energy circulation. However, designing high-performance electrocatalysts for the CO2 reduction reaction (CO2RR) remains a great challenge. In this work, by means of density functional theory calculations, we systematically investigate the transition metal (TM) anchored on the nitrogen-doped graphene/graphdiyne heterostructure (TM-N4@GRA/GDY) as a single-atom catalyst for CO2 electroreduction applications. The computational results show that Co-N4@GRA/GDY exhibits remarkable activity with a low limiting potential of -0.567 V for the reduction of CO2 to CH4. When the charged Co-N4@GRA/GDY system is immersed in a continuum solvent, the reaction barrier decreases to 0.366 eV, which is ascribed to stronger electron transfer between GDY and transition metal atoms in the GRA/GDY heterostructure. In addition, the GRA/GDY heterostructure system significantly weakens the linear scaling relationship between the adsorption free energy of key CO2 reduction intermediates, which leads to a catalytic activity that is higher than that of the single-GRA system and thus greatly accelerates the CO2RR. The electronic structure analysis reveals that the appropriate d-π interaction will affect the d orbital electron distribution, which is directly relevant to the selectivity and activity of catalysis. We hope these computational results not only provide a potential electrocatalyst candidate but also open up an avenue for improving the catalytic performance for efficient electrochemical CO2RR.