Metal Sites Research Articles

Mesoporous carbon nanospheres doped with rich non-metallic and metallic catalytic active sites: A high-performance electrochemical platform for sensing of chloramphenicol in food samples

The development of a low-cost, accurate sensing strategy for trace levels of chloramphenicol (CAP) residues in food is crucial but remains challenging. In this study, a high-performance electrochemical platform was developed to detect CAP in animal-derived foods using Ni2P embedded N, P-co-doped mesoporous carbon nanospheres (Ni2P@N,P-MCS). The Ni2P@N,P-MCS material, with a unique mesoporous structure and large specific surface area, exhibited excellent adsorption properties. The N, P-co-doped heteroatoms enhanced the electric conductivity and active centers of MCS, facilitating fast mass transport and electron transfer. The introduction of Ni2P increased the active sites and enhanced the electrocatalytic activity. Leveraging these advantages, the electrochemical sensor based on Ni2P@N,P-MCS demonstrated outstanding detection performance with a wide linear range from 0.04 to 250 μM and a low limit of detection of 12 nM. The sensor also showed good reproducibility, stability, and anti-interference properties. Furthermore, the sensor was successfully tested in milk and pork samples, showing satisfactory recovery rates and indicating its feasibility for real sample analysis.

Bifunctional catalytic activity of anion-doped LaSrCoO4 for oxygen reduction and evolution reactions.

Here, we synthesized Co-based, anion-incorporated‍ ‌R‌u‌d‌d‌l‌e‌s-d‌e‌n‌-‌Popper perovskite electrocatalysts (LaSrCoO4-x X y ) and compared their catalytic performances in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The ORR mechanism with the newly synthesized F-doped LaSrCoO4 catalyst was dominated by a four-electron process, and the number of electrons involved in the reaction increased compared with that for LaSrCoO4. The OER activity of the hydride-doped LaSrCoO4 catalyst was the highest among the LaSrCoO4 system catalysts. Density functional theory calculations revealed that there is a correlation between the Co 3d unoccupied orbital band centre and the OER activity. The addition of anions and substitution of metal sites improved the ORR and OER activities of the catalysts. Our findings confirmed that the addition of heteroatom anions can improve the activity of perovskite-type electrocatalysts, promoting their application in various fields.

Valence electronic engineering of hollow-nanocube-structured CoFeNi-layered double hydroxides for highly efficient oxygen evolution

The sluggish kinetics of oxygen evolution reaction (OER) and the high-cost of catalysts currently limit the large-scale industrialization of hydrogen production through water electrolysis, so developing efficient and inexpensive catalysts is a top priority. Herein, we employed a facile solvent method to synthesize a well-defined hollow nanocube-structured CoFeNi layered double hydroxide (LDH) with an optimized valence electronic structure of metal sites as an efficient electrocatalyst for accelerating the kinetics of OER. The optimal catalyst with the regulated valence electronic structure exhibited a strong synergistic catalytic effect and an excellent activity and stability. It achieved a lower overpotential of 294 mV at 100 mA cm−2, and high durability exceeding 100 h at 1 A cm−2, surpassing the performance of commercial Ir-/Ru-based catalysts. The optimized the coordination environment and valence electronic structure of metal sites can definitely serve as active centers for triggering OER, thereby improving the intrinsic electrocatalytic performance.

Efficient polycarbonate plastic upcycling into jet fuel cycloalkanes over a bifunctional MoCo/NiC hetero-catalyst

While there are significant economic benefits associated with plastic recycling, the practical options for treating plastic waste remain relatively limited. This study introduces a novel bimetallic MOF-derived catalyst designed specifically for upcycling polycarbonate plastic into cycloalkanes within jet fuel range. By incorporating dual metals (MoCo) onto the MOF framework, the catalyst creates single metal sites and constructs heterojunctions. Characterizations revealed that the bifunctional catalyst can chemically adsorb phenolic compounds on a highly synergistic heterogeneous surface and lower the energy barrier of hydrodeoxygenation. Integrating the catalyst into a tandem reactor facilitates the conversion of PC plastics into jet-fuels. Achieving an average cycloalkane yield of 84.5% underscores the catalyst’s potential for deep hydrodeoxygenation of actual plastic waste. Furthermore, using waste CDs as feedstock, the cycloalkanes yield remains consistent even after three regeneration cycles, demonstrating the catalyst’s stability. In the low-carbon future, this high hydrodeoxygenation performance catalyst can be applied in chemical upcycling for pursuing a circular plastic economy.

PdMoPtCoNi High Entropy Nanoalloy with d Electron Self-Complementation-Induced Multisite Synergistic Effect for Efficient Nanozyme Catalysis.

Engineering multimetallic nanocatalysts with the entropy-mediated strategy to reduce reaction activation energy is regarded as an innovative and effective approach to facilitate efficient heterogeneous catalysis. Accordingly, conformational entropy-driven high-entropy alloys (HEAs) are emerging as a promising candidate to settle the catalytic efficiency limitations of nanozymes, attributed to their versatile active site compositions and synergistic effects. As proof of the high-entropy nanozymes (HEzymes) concept, elaborate PdMoPtCoNi HEA nanowires (NWs) with abundant active sites and tuned electronic structures, exhibiting peroxidase-mimicking activity comparable to that of natural horseradish peroxidase are reported. Density functional theory calculations demonstrate that the enhanced electron abundance of HEA NWs near the Fermi level (EF) is facilitated via the self-complementation effect among the diverse transition metal sites, thereby boosting the electron transfer efficiency at the catalytic interface through the cocktail effect. Subsequently, the HEzymes are integrated with a portable electronic device that utilizes Internet of Things-driven signal conversion and wireless transmission functions for point-of-care diagnosis to validate their applicability in digital biosensing of urinary biomarkers. The proposed HEzymes underscore significant potential in enhancing nanozymes catalysis through tunable electronic structures and synergistic effects, paving the way for reformative advancements in nano-bio analysis.

Tuning the Reactivity of Copper(II)-Nitrite Core Towards Nitric Oxide Generation.

Insights into the molecular mechanism and factors affecting nitrite-to-NO transformation at transition metal sites are essential for developing sustainable technologies relevant to NO-based therapeutics, waste water treatment, and agriculture. A set of copper(II)-nitrite complexes1-4have been isolated employing tridentate pincer-type ligands (quL,pyL,ClArOL-,PhOL-) featuring systematically varied donors. Although the X-ray crystal structures of the copper(II)-nitrite cores in1-4are comparable, electrochemical studies on complexes1-4reveal that redox properties of these complexes differ due to the changes in thes-donor abilities of thephenolate / N-heterocycle based donor sites. Reactivity of these nitrite complexes with oxygen-atom-transfer (OAT) reagent (e.g. triphenyl phosphine Ph3P) and H+/e-donor reagent (e.g. substituted phenols ArOH) show the reduction of nitrite to NO gas. Detailed kinetic investigations including kinetic isotope effect (KIE), Eyring analyses for determining the activation parameters unfold that reduction of nitrite at copper(II) by Ph3P or ArOH are influenced by the CuII/CuIredox potential. Finally, this study allows mechanism driven development of catalytic nitrite reduction by ArOH in the presence of 10 mol% copper complex (1).

Synergistic catalytic degradation of Methotrexate using Ce-based high-entropy metal oxides: Insights from DFT calculations and CWPO performance

Methotrexate (MTX), a widely used anticancer drug, is a refractory organic pollutant posing serious threats to ecosystems and human health. This study focuses on the development of a novel catalyst composed of Ce-based high-entropy metal oxides (NHEMO) supported on nepheline for the catalytic wet peroxide oxidation (CWPO) process, targeting MTX degradation in simulated wastewater. The NHEMO catalyst exhibited a unique high-entropy structure that enhances catalytic performance by facilitating diverse electronic interactions, which was confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showing a well-defined crystal structure and uniform dispersion of metal oxides. Additionally, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) revealed a stable metal composition and high oxidation states of active metal sites. At a reaction temperature of 160 °C, with a residence time of 150 s and an oxidation coefficient of 5, the catalyst achieved a MTX removal rate of 93.49 % and a chemical oxygen demand (COD) removal of 99.95 %. Density Functional Theory (DFT) calculations further demonstrated that H2O2 decomposes into both adsorbed (surface-bound) and free (solution-phase) hydroxyl radicals (·OH). These radicals synergistically degrade MTX through both radical and non-radical pathways, ensuring comprehensive pollutant breakdown. The catalyst also showed excellent stability and a very low metal dissolution rate during the reaction, maintaining high catalytic activity after repeated recycling. This catalyst offers high cost-effectiveness, activity, and stability, providing a promising solution for treating refractory organic pollutants in pharmaceutical wastewater.

C-H amination chemistry mediated by trinuclear Cu(I) sites supported by a ligand scaffold featuring an arene platform and tetramethylguanidinyl residues.

Tripodal ligands that can encapsulate single or multiple metal sites in C3-symmetric geometric configurations constitute valuable targets for novel catalysts. Of particular interest in ligand development are efforts toward incorporating apical elements that exhibit little if any electron donicity, to enhance the electrophilic nature of a trans positioned active oxidant (e.g., metal-oxo, -nitrene). The tripodal ligand TMG3trphen-Arene has been synthesized, featuring an arene platform 1,3,5-substituted with phenylene arms possessing tetramethylguanidinyl (TMG) residues. Compound [(TMG3trphen-Arene)Cu3(μ-Cl)3] has been subsequently synthesized by extracting a Cu3(μ-Cl)3 cluster from anhydrous CuCl and shown to encapsulate a crown-shaped Cu3(μ-Cl)3 fragment, supported by Cu-NTMG bonds and modest Cu3⋯arene long-range contacts. Energy decomposition analysis (EDA) indicates that electrostatic contributions to the total interaction energy far exceed those due to orbital interactions. The latter involve orbital pairings largely associated with the NTMG stabilization of the Cu3(μ-Cl)3 cluster. The independent gradient model based on the Hirshfeld partition (IGMH) corroborates that contacts between the arene platform and the Cu3 triangle are noncovalent in nature. Catalyst [(TMG3trphen-Arene)Cu3(μ-Cl)3] enables amination of sec-benzylic and tert-C-H bonds of a panel of substrates by pre-synthesized PhINTces in solvent matrices that incorporate small amounts of HFIP. The involvement of an electrophilic aminating agent is evidenced by the better yields obtained for electron-rich benzylic sites and is further supported by Hammett analysis that reveals the development of a small positive charge during C-H bond activation. A rather modest KIE effect (2.1) is obtained from intramolecular H(D) competition in the amination of ethylbenzene, at the borderline of reported values for concerted and stepwise C-H amination systems. DFT analysis of the putative copper-nitrene oxidant indicates that the nitrene N atom is bridging between two copper sites in closely spaced triplet (ground state) and broken-symmetry singlet electronic configurations.

One-pot synthesis of Ir subnanosized clusters supported on MWW nanosheets as effective catalysts for C-C bond hydrogenolysis

The rational design synthesis of metal catalysts with high dispersion and ordered structure is a challenging subject in materials chemistry and heterogeneous catalysis. In this study, we report one-pot synthesis of Ir subnanosized particles supported on MWW nanosheets and their application in hydrogenolysis of decalin. Here, it has been found that C-C bond cleavage occurs via a synergistic carbocation and carbene mechanism on Ir-containing catalysts, and via carbocation in the case of solid acids. The combination of optimal acidic and metallic site characteristics in the subnanosized Ir supported on MWW nanosheets Pill_Ir-ZN_150 sample contributes to the high activity of the final catalysts. We expect that these Ir catalytic systems will open up more opportunities for hydrogenolysis of naphthenics to high-value products.

Direct quantitative assessment of single-atom metal sites supported on powder catalysts

Rational design of effective catalyst demands a profound understanding of active-site structures. Single-atom supported powder catalysts, depicting unique features like enhanced metal dispersion, hold promise in different applications. Here, we present an approach to directly quantify the detailed structural nature of metal sites in single-atom, high surface area, powder catalysts. By combining advanced high-resolution scanning-transmission electron microscopy, deep learning and density functional theory calculations, we determine, with statistical significance, the exact location and coordination environment of Pd single-atoms supported on MgO nanoplates. Our findings reveal a preferential interaction of Pd single-atoms with cationic vacancies (V-centers), followed by occupation of anionic defects on the {001} MgO surface. The former interaction results in stabilization of PdO species within V-centers, while partially embedded Pd states are found in F-defects. This methodology opens a route to the ultimate structural analysis of metal-support interaction effects, key in the design of advanced nanocatalysts for sustainable and energy-efficient processes.

Manipulating Electron Delocalization of Metal Sites via a High-Entropy Strategy for Accelerating Oxygen Electrode Reactions in Lithium-Oxygen Batteries.

High-entropy perovskite oxides, in which the B-type metal site of perovskite oxides (ABO3) is occupied by over five kinds of transition metal ions, show promising applications in energy storage and conversion fields. Herein, high-entropy perovskite oxides (LaSr(5TM)O3) composed of Cr, Mn, Fe, Co, and Ni at the B-type metal site are prepared as oxygen electrocatalysts for Li-O2 batteries. The presence of compressive strain in LaSr(5TM)O3 effectively regulates the 3d orbit occupancy of the active Co site (Co2+ → Co3+) and lifts the energy level of the Co d-band center, thus leading to enhanced adsorption toward the LiO2 intermediate on Co sites. Furthermore, the high electron-drawing capability of Cr sites ensures sufficient electron exchange and further strengthens the adsorption of LiO2. As expected, the Li-O2 battery with a LaSr(5TM)O3 electrode delivers a low overpotential (0.79 V) and superior cyclability (226 cycles). This study provides a meaningful strain strategy to improve the electrocatalytic activity of multicomponent oxides via fabricating high-entropy materials.

Quantum refinement in real and reciprocal space using the Phenix and ORCA software.

X-ray and neutron crystallography, as well as cryogenic electron microscopy (cryo-EM), are the most common methods to obtain atomic structures of biological macromolecules. A feature they all have in common is that, at typical resolutions, the experimental data need to be supplemented by empirical restraints, ensuring that the final structure is chemically reasonable. The restraints are accurate for amino acids and nucleic acids, but often less accurate for substrates, inhibitors, small-molecule ligands and metal sites, for which experimental data are scarce or empirical potentials are harder to formulate. This can be solved using quantum mechanical calculations for a small but interesting part of the structure. Such an approach, called quantum refinement, has been shown to improve structures locally, allow the determination of the protonation and oxidation states of ligands and metals, and discriminate between different interpretations of the structure. Here, we present a new implementation of quantum refinement interfacing the widely used structure-refinement software Phenix and the freely available quantum mechanical software ORCA. Through application to manganese superoxide dismutase and V- and Fe-nitrogenase, we show that the approach works effectively for X-ray and neutron crystal structures, that old results can be reproduced and structural discrimination can be performed. We discuss how the weight factor between the experimental data and the empirical restraints should be selected and how quantum mechanical quality measures such as strain energies should be calculated. We also present an application of quantum refinement to cryo-EM data for particulate methane monooxygenase and show that this may be the method of choice for metal sites in such structures because no accurate empirical restraints are currently available for metals.

Silica gel supported Cu nanoparticles for selective reductive etherification of furfural into isopropyl furfuryl ether

Furfural (FF) is one of the important platform molecules of biomass, which can be obtained by hydrolysis from lignocellulose and can produce many high value-added chemicals. In this study, a new 4.5 wt% Cu-supported silica gel (SG) catalyst with dual functions of metal and acid site was prepared by acid-base adsorption impregnation method. Isopropyl furfuryl ether (IPFE) with 80.4 % yield was obtained by one-pot reductive etherification of FF in 2-propanol at 150 °C under 2 MPa H2. The characterization of the catalyst proved that the Cu synthesized by this method was well dispersed, and the average size of Cu NPs was 3.34 nm. The reduction of FF to IPFE in a one-pot reaction system is deduced as follows: the existence of a hydrogenation-etherification pathway (main path) and an acetalization-hydrogenolysis pathway. The study in this paper provides a reference for the development of non-noble metal hydroetherification catalysts.

Eneolithic and Bronze Age of the Forest Zone of Eastern Europe: disharmony of archaeological periodization

The results of the study of the discrepancies problem between regional cultural and chronological schemes in the context of the modified "system of three centuries" are presented. The study is based on the materials of the Garino and Chirki cultures, which sites are located in the extreme northeast of Europe, and on the results of radiocarbon dating of the Eneolithic and Bronze Age complexes of the Eastern European Plain forest zone. The disharmony of the archaeological periodization is expressed in the presence of both populations of the culture attributed to the Late Bronze Age and the Eneolithic culture in the studied region. As a result, it was determined that the sites with Chirkovsko-Seiminskiy or Fatianoid pottery types including the complexes of the Atamannur culture, are synchronous with the Garino culture within the Eneolithic or the 2nd half of the 3rd millennium B.C. However, the main arguments in favor of the Eneolithic of the Chirki culture are the use of pure copper artefacts together with intensive flint knapping with a developed bifacial industry. Therefore, it is predicted that existing ideas about the periodization of early metal sites in north-eastern Europe will be corrected. The comparison of radiocarbon dates showed that complexes with porous and asbestos pottery with sparse decoration (Orovnavolok XVI and Pelya types) are generally older than the pottery of the Garino (Choinovty) culture. This complicates the problem of the origin of the latter, since it is likely that its ceramic traditions originated to the west of the extreme north-east of Europe.

Tip-like copper sites on high curvature supports for non-covalent to covalent interaction tuning in CO2 photoreduction

Single-atom engineering offers a promising method to transform CO2 into high-value chemicals. The local coordination structure design of the metal-support is crucial for overcoming slow reaction kinetics. In this study, Cu single atoms are immobilized on curved Bi12O17Br2 surface to create a tip-like metal site structure named Cutip-Bi12O17Br2. Due to the high curvature Bi12O17Br2 surface with tensile strain, the tip Cu creates significant electronegativity differences between adjacent Bi atomic sites, creating the vigorous polarization centers. The strong charge redistribution character of tip asymmetric Cu-Bi site favor the polarization of CO bond in nonpolar CO2 and adjust the noncovalent to covalent interaction of reaction intermediates. Benefiting from these features, the optimized Cutip-Bi12O17Br2 enhance the CO production rate by a factor of 34 relative to bulk-Bi12O17Br2, reaching a rate of 96.99 μmol g−1 h−1. This work provides a comprehensive understanding of the structural regulation of single-atom on high curvature surface for CO2 photoreduction.

Defects trigger redox reactivities between metal and lattice oxygen in high-entropy layered double hydroxide for boosting oxygen evolution in alkaline

The oxygen evolution reaction (OER) at the anode undergoes a sluggish multi-step process, thereby impeding overall water splitting. As the classical adsorbate evolution mechanism (AEM) involves multiple oxygen-containing intermediates, such as *OH, *O and *OOH, breaking the linear relationship of the adsorption energies between *OH and *OOH is the key to efficient oxygen evolution. Herein, we report a high-entropy FeCoNiAlZn layered double hydroxide decorated with defects (E-FeCoNiAlZn LDH) for boosting oxygen evolution in alkaline. The product exhibits high OER activity with a low overpotential of 220 at 10 mA cm−2 and outstanding stability with negligible decline after 100 h operation. The defects in E-FeCoNiAlZn LDH not only enhance the adsorption of *OH by metal sites but also foster the release of oxygen from lattice, which triggers the coupled oxygen evolution mechanism (COM). This mechanism has only *OH and *OO intermediates, perfectly avoiding the obstacles of linear relationship between *OH and *OOH. Theoretical calculations demonstrate that the introduction of defects enhances the adsorption of *OH due to the presence of unsaturated bonds. Additionally, it is evidence that the O 2p band is elevated, leading to a weakening of the metal-O bond and a reduction of the energy barrier for OO coupling.

Enhancing photocatalytic performance of rose-shaped Co/Ni bimetallic organic framework for reducing CO2 to CO under visible light

Co-MOF-74, composed of Co salt as the metal source and 2,5-dihydroxyterephthalic acid as the organic ligand, is widely used as a catalyst for the photocatalytic reduction of CO2 due to its open metal sites, high porosity, large specific surface area, and high CO2 adsorption capacity. However, its effectiveness in CO2 conversion is limited by weak electron transfer capabilities and a high rate of electron/hole pair recombination. To address these limitations, a bimetallic strategy was employed to significantly improve the catalytic performance of Co-MOF-74 for photocatalytic CO2 reduction. Stable bimetallic Co/Ni-MOF-74-x (x = 1, 2, 3) with controllable morphology and metal ratios were synthesized by adjusting the molar ratios of Co2+ and Ni2+ and combining them with 2,5-dihydroxyterephthalic acid. The introduction of Ni2+ led to a significant increase in the specific surface area, from 204.999 m2/g (Co/Ni-MOF-74) to 790.873 m2/g (Co/Ni-MOF-74-1). In addition, the band gap of bimetallic Co/Ni-MOF-74-1 was narrowed to 1.4 eV, which enhanced charge transfer. As a result, photocatalytic experiments demonstrated that the CO2 conversion efficiency of bimetallic Co/Ni-MOF-74-1 was significantly improved, reaching 4.539 mmol/g/h, compared to that of the monometallic Co-MOF-74. Finally, a synergistic photocatalytic mechanism involving ligand activation was proposed to explain the reaction process of the bimetallic Co/Ni-MOF-74 catalyst. Meanwhile, this study highlights that the bimetallic strategy is an effective approach to optimizing the performance of MOF catalysts for the photocatalytic reduction of CO2.

Hydrogen activation by rhodium under the cover of a copper oxide thin film

The activation of reactants by catalytically active metal sites at metal-oxide interfaces is important for understanding the effect of metal-support interactions on nanoparticle catalysts and for tuning activity and selectivity. Using a combined experimental and theoretical approach, we studied the activation of H2 and the effect of CO poisoning on isolated Rh atoms completely or partially covered by a copper oxide (Cu2O) thin film. Temperature-programmed desorption (TPD) experiments conducted in ultra-high vacuum (UHV) show that neither a partially nor a fully oxidized Cu2O layer grown on a Rh/Cu(111) single-atom alloy can activate hydrogen in UHV. However, in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) experiments performed at elevated H2 pressures reveal that Rh significantly accelerates the reduction of these Cu2O thin films by hydrogen. Remarkably, the fastest reduction rate is observed for the fully oxidized sample with all Rh sites covered by Cu2O. Both TPD and AP-XPS data demonstrate that these covered Rh sites are inaccessible to CO, indicating that Rh under Cu2O is active for H2 dissociation but cannot be poisoned by CO. In contrast, an incomplete oxide film leaves some of the Rh sites exposed and accessible to CO, and hence prone to CO poisoning. Density functional theory calculations demonstrate that unlike many reactions in which hydrogen activation is rate limiting, the rate-determining step in the dissociation of H2 on thin-film Cu2O with Rh underneath is the adsorption of H2 on the buried Rh site, and once adsorbed, the dissociation of H2 is barrierless. These calculations also explain why H2 can only be activated at higher pressures. Together, these results highlight how different the reactivity of atomically dispersed Rh in Cu can be depending on its accessibility through the oxide layer, providing a way to engineer Rh sites that are active for hydrogen activation but resilient to CO poisoning.

Unlocking Efficient Alkaline Hydrogen Evolution Through Ru-Sn Dual Metal Sites and a Novel Hydroxyl Spillover Effect.

Alkaline hydrogen evolution reaction (HER) has great potential in practical hydrogen production but is still limited by the lack of active and stable electrocatalysts. Herein, the efficient water dissociation process, fast transfer of adsorbed hydroxyl and optimized hydrogen adsorption are first achieved on a cooperative electrocatalyst, named as Ru-Sn/SnO2 NS, in which the Ru-Sn dual metal sites and SnO2 heterojunction are constructed based on porous Ru nanosheet. The density functional theory (DFT) calculations and in situ infrared spectra suggest that Ru-Sn dual sites can optimize the water dissociation process and hydrogen adsorption, while the existence of SnO2 can induce the unique hydroxyl spillover effect, accelerating the hydroxyl transfer process and avoiding the poison of active sites. As results, Ru-Sn/SnO2 NS display remarkable alkaline HER performance with an extremely low overpotential (12mV at 10mA cm-2) and robust stability (650h), much superior to those of Ru NS (27mV at 10mA cm-2 with 90h stability) and Ru-Sn NS (16mV at 10mA cm-2 with 120h stability). The work sheds new light on designing of efficient alkaline HER electrocatalyst.

Multiwalled Carbon Nanotube-Templated Nickel Porphyrin Covalent Organic Framework for Pencil-Drawn Noninvasive Respiration Sensors.

Paper-integrated configuration with miniaturized functionality represents one of the future main green electronics. In this study, a paper-based respiration sensor was prepared using a multiwalled carbon nanotube-templated nickel porphyrin covalent organic framework (MWCNTs@COFNiP-Ph) as an electrical identification component and pencil-drawn graphite electric circuits as interdigitated electrodes (IDEs). The MWCNTs@COFNiP-Ph not only inherited the high gas sensing performance of porphyrin and the aperture induction effect of COFs but also overcame the shielding effect between phases through the MWCNT template. Furthermore, it possessed highly exposed M-N4 metallic active sites and unique periodic porosity, thereby effectively addressing the key technical issue of room-temperature sensing for the respiration sensor. Meanwhile, the introduction of a pencil-drawing approach on common printing papers facilitates the inexpensive and simple manufacturing of the as-fabricated graphite IDE. Based on the above advantages, the MWCNTs@COFNiP-Ph respiration sensor had the characteristics of wide detection range (1-500 ppm), low detection limit (30 ppb), acceptable flexibility for toluene, and rapid response/recovery time (32 s/116 s). These advancements facilitated the integration of the respiration sensor into surgical masks and clothes with maximum functionality at a minimized size and weight. Moreover, the primary internal mechanism of COFNiP-Ph for this efficient toluene detection was investigated through in situ FTIR spectra, thereby directly elucidating that the chemisorption interaction of oxygen modulated the depletion layers, resulting in alterations in sensor resistance upon exposure to the target gas. The encouraging results revealed the feasibility of employing a paper-sensing system as a wearable platform in green electronics.