Copper Active Site Research Articles

Novel unlabeled electrochemical sensing platform based on highly electroactive Cu-MOF film for nanoplastic detection in water.

Anunlabeled electrochemical sensing strategy based on electroactive copper-centered metal-organic framework (Cu-MOF) film coupled with multiwalled carbon nanotubes (MWCNTs) was proposed for the rapid assessment of nanoplastic concentration. The sensing interface was fabricated via the electro-deposition of Cu-MOF on the pre-modified MWCNTs using the cathodic reduction method. The exposed copper active sites in Cu-MOF showed excellent electrochemical activity, which was further enhanced due to rapid electron transfer induced by highly conductive MWCNTs. Through the adsorption functionality of Cu-MOF film towards polystyrene (PS) nanoplastics, the rapid recognition for nanoplastics in aqueous solution was achieved, thereby causing the inhibition of the current response. The results showed a robust dependence of the inhibition rate on the PS mass concentration. The proposed detection method was used for the quantitative determinationof PS nanoplastics with the sizes of 100nm, 500nm, and 1μm. The applicability of this electrochemical sensing platform was successfully validated in real-world water sampleanalysis.

Second-Sphere Histidine Catalytic Function in a Fungal Polysaccharide Monooxygenase.

Fungal polysaccharide monooxygenases (PMOs) oxidatively degrade cellulose and other carbohydrate polymers via a mononuclear copper active site using either O2 or H2O2 as a cosubstrate. Cellulose-active fungal PMOs in the auxiliary activity 9 (AA9) family have a conserved second-sphere hydrogen-bonding network consisting of histidine, glutamine, and tyrosine residues. The second-sphere histidine has been hypothesized to play a role in proton transfer in the O2-dependent PMO reaction. Here the role of the second-sphere histidine (H157) in an AA9 PMO, MtPMO9E, was investigated. This PMO is active on soluble cello-oligosaccharides such as cellohexaose (Glc6), thus enabling kinetic analysis with the point variants H157A and H157Q. The variants appeared to fold similarly to the wild-type (WT) enzyme and yet exhibited weaker affinity toward Glc6 than WT (WT KD = 20 ± 3 μM). The variants had comparable oxidase (O2 reduction to H2O2) activity to WT at all pH values tested. Using O2 as a cosubstrate, the variants were less active for Glc6 hydroxylation than WT, with H157A being the least active. Similarly, H157Q was competent for Glc6 hydroxylation with H2O2, but H157A was less active. Comparison of the crystal structures of H157Q and WT MtPMO9E reveals that a terminal heteroatom of Q157 overlays with Nε of H157. Altogether, the data suggest that H157 is not important for proton transfer, but support a role for H157 as a hydrogen-bond donor to diatomic-oxygen intermediates, thus facilitating catalysis with either O2 or H2O2.

Engineering a Cu-Pd Paddle-Wheel Metal-Organic Framework for Selective CO2 Electroreduction.

Optimizing the binding energy between the intermediate and the active site is a key factor for tuning catalytic product selectivity and activity in the electrochemical carbon dioxide reduction reaction. Copper active sites are known to reduce CO2 to hydrocarbons and oxygenates, but suffer from poor product selectivity due to the moderate binding energies of several of the reaction intermediates. Here, we report an ion exchange strategy to construct Cu-Pd paddle wheel dimers within Cu-based metal-organic frameworks (MOFs), [Cu3-xPdx(BTC)2] (BTC=benzentricarboxylate), without altering the overall MOF structural properties. Compared to the pristine Cu MOF ([Cu3(BTC)2], HKUST-1), the Cu-Pd MOF shifts CO2 electroreduction products from diverse chemical species to selective CO generation. In situ X-ray absorption fine structure analysis of the catalyst oxidation state and local geometry, combined with theoretical calculations, reveal that the incorporation of Pd within the Cu-Pd paddle wheel node structure of the MOF promotes adsorption of the key intermediate COOH* at the Cu site. This permits CO-selective catalytic mechanisms and thus advances our understanding of the interplay between structure and activity toward electrochemical CO2 reduction using molecular catalysts.

Studying bimetals copper-indium for enhancing PCN photocatalytic CO2 reduction activity and selectivity mechanism

In this work, a bimetallic indium-copper-doped atomically dispersed Cu-In-PCN photocatalyst was prepared by thermal polymerization, and it exhibits remarkable photocatalytic CO2 reduction activity with CO yield of 113.56 µmol g−1 and a selectivity nearly 96 %. Additionally, experimental investigations and DFT calculations reveal the mechanisms underpinning the high performance of Cu-In-PCN catalyst, that Cu 3d and In 5p orbitals contribute to the band composition of Cu-In-PCN and reduced the bandgap, the electrons from PCN transfer to copper active sites and increasing the electron density for CO2 reduction. Furthermore, the Cu-In bimetallic lowered the free energy of COOH* intermediate, which more easily conversion to CO via dehydroxylation than PCN, Cu-PCN, and In-PCN. In situ FTIR show that the COOH* is the key intermediate in the photocatalytic reduction of CO2 to CO. This work makes up for the current shortcomings of using bimetallic-doped PCN for photocatalytic CO2 with low selectivity and unclear mechanism.

Bimetallic PdCu anchored to 3D flower-like carbon material for portable and efficient detection of glyphosate

Glyphosate (Gly), as a widely used broad-spectrum herbicide, may lead to soil and water pollution due to its persistence in the environment. Herein, the co-reduction method was employed to anchor bimetallic PdCu onto the Ni and nitrogen-doped 3D Flower-like Carbon Materials (Ni@NC), creating a composite material (PdCu/Ni@NC) with high specific surface area and good catalytic performance. This composite was used to modify screen-printed electrodes (SPE) to develop a portable and efficient Gly detection platform. In the presence of Cl⁻, the copper active sites convert to CuCl, achieving signal amplification. Upon the addition of Gly, a competitive reaction between Cu and Gly converts CuCl into a Cu-Gly complex, resulting in a sharp decrease in the electrochemical signal. This signal drop is used to detect Gly. The bimetallic PdCu nanoparticles (NPs) endowed the sensing platform with better stability and electrochemical performance due to their synergistic effect, and their stability was simply verified by Density functional theory (DFT). The sensor demonstrates a linear detection range spanning from 1 × 10⁻¹ ³ to 1 × 10⁻⁵ M, with a limit of detection (LOD) of 3.72 × 10⁻¹ ⁴ M. The sensor demonstrated a recovery rate of 95.9 % to 104.5 % in actual samples such as water and soil, indicating its potential for practical application.

Formation mechanism of cation-vacancy microenvironments and the effect on hydrogen transfer reaction of 5-hydroxymethylfurfural

Two Cu/ZrO2 catalysts defect with different microenvironments and electronic structures (CZ-ag-70 and CZ-va catalysts) were synthesized by the same oxalic-acid-complexation-based method but different heat-treatment methods, and they were used to catalyze the hydrogen-transfer reaction between 5-hydroxymethylfurfural (HMF) and isopropanol. The structure–activity relationship of each catalyst was analyzed, and defect microenvironments were found to have an important influence on the product of the hydrogen-transfer reaction. The CZ-ag-70 catalyst was rich in Cuδ+- VZr+ interfacial sites (the interfacial sites between electron-deficient copper active sites (Cuδ+)) and electron-free zirconium vacancies (VZr+), and it was conducive to the formation of dehydroxylation product 2,5-dimethylfuran (DMF). Specifically, the ca-ag-70 catalyst achieved 100 % HMF conversion and 82.2 % DMF selectivity. On the other hand, the CZ-va catalyst was rich in single-electron zirconium vacancies (VZr∙), and it was conducive to the generation of reductive-etherification product 2,5-bis(propoxymethyl)furan (BPMF) (100 % HMF conversion and 55 % BPMF selectivity). Through X-ray diffraction spectrum (XRD), electron spin resonance (ESR), hydrogen temperature-programmed reduction (H2-TPR), in-situ Fourier-transform infrared spectroscopy (in-situ FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) analyses, the structure of the CZ-ag-70 catalyst and the mechanism of defect formation in the catalyst were analyzed. The precursor of the CZ-ag-70 catalyst first formed a copper-doped zirconium oxalate substrate. Then, under 500 ℃ reducing atmosphere, the substrate was converted into a copper-doped tetragonal-zirconia carrier, some of the copper species doped into the crystal lattice of the tetragonal-zirconia carrier were reduced, and the copper species migrated to the surface of the carrier, forming Cuδ+- VZr+ interfacial sites. The electrons around the zirconium vacancy of the CZ-ag-70 catalyst are in a completely delocalized state and Cu+ gains electrons which in turn produces Cuδ+- VZr+ interfacial sites.

Copper nanoparticles embedded flexible graphene aerogel for effective capture of iodine vapor

Development of highly efficient and low-cost adsorbents for radioactive iodine vapor is significant but still challenged now. In this work, we reported a novel graphene aerogel (GA-Cu-ED) decorated by zero-valence copper and nitrogen active sites, prepared via a two-step route of hydrothermal reaction and freeze-drying processes. The combination of X-ray photoelectron spectroscopy (XPS) valence imaging and high-resolution transmission electron microscope (TEM) confirms the formation of Cu0 and its uniform distribution. Besides, the good elasticity and ultra-low density of this aerogel were proved. Adsorption experiments indicate that GA-Cu-ED has a high adsorption capacity of 3.76 g/g for gaseous iodine and short adsorption equilibrium time of 90 min. Even after three cycles, this aerogel still shows an almost unchanged adsorption capacity of 3.74 g/g. Meanwhile, this aerogel can be long-term stored under air atmosphere with only slight loss in adsorption performance. In addition, the captured iodine molecules can be tightly bound in this aerogel even after being exposed in air for three days. Mechanism analysis indicates the I-benzene conjugation, I–N charge transfer, and I2–Cu0 chemisorption contribute together to the capture of gaseous iodine. Therefore, our work provides a highly efficient and reliable adsorbent for radioactive iodine vapor, which may be worthy in large-scale application in future.

2-Methylbenzimidazole-copper nanozyme with high laccase activity for colorimetric differentiation and detection of aminophenol isomers

Laccase is well-known for its eco-friendly applications in environmental remediation and biotechnology, but its high cost and low stability have limited its practical use. Therefore, there is an urgent need to develop efficient laccase mimetics. In this study, a novel laccase-mimicking nanozyme (MBI-Cu) was successfully synthesized using 2-methylbenzimidazole (MBI) coordinated with Cu2+ by mimicking the copper active site and electron transfer pathway of natural laccase. MBI-Cu nanozyme exhibited excellent catalytic activity and higher stability than laccase, and was utilized to oxidize a series of phenolic compounds. Environmental pollutant aminophenol isomers were found to display different color in solution when catalytically oxidized by MBI-Cu, which provided a simple and feasible method to identify them by the naked eye. Based on the distinct absorption spectra of the oxidized aminophenol isomers, a colorimetric method for quantitatively detecting o-AP, m-AP, and p-AP was established, with detection limits of 0.06 μM, 0.27 μM, and 0.18 μM, respectively. Furthermore, by integrating MBI-Cu-based cotton pad colorimetric strips with smartphone and utilizing color recognition software to identify and analyze the RGB values of the images, a portable colorimetric sensing platform was designed for rapid detection of aminophenol isomers without the need for any analytical instrument. This work provides an effective reference for the design of laccase nanozymes and holds significant potential for applications in the field of environmental pollutant monitoring.

Construction of multifunctional interface engineering on Cu‐SSZ‐13@Ce‐MnOx/Mesoporous-silica catalyst for boosting activity, SO2 tolerance and hydrothermal stability

Although small pore Cu-SSZ-13 catalysts have been successful as commercial catalysts for controlling NOx emissions from mobile sources, the challenges of high light-off temperature, SO2 tolerance and hydrothermal stability still need to be addressed. Here, we synthesized a multifunctional core-shell catalyst with Cu-SSZ-13 as the core phase and Ce-MnOx supported Mesoporous-silica (Meso-SiO2) as the shell phase via self-assembly and impregnation. The core-shell catalyst exhibited excellent low-temperature activity, SO2 tolerance and hydrothermal stability compared to the Cu-SSZ-13. The Ce-MnOx species dispersed in the shell are found to enhance both the acidic and oxidative properties of the core-shell catalyst. More critically, these species can rapidly activate NO and oxidize it to NO2, which allows the NH3-SCR reaction on the core-shell catalyst to be initiated in the shell phase. Meanwhile, Ce-MnOx species can react preferentially with SO2 as sacrifice components, effectively avoiding the sulfur inactivation of the copper active sites. Furthermore, the hydrophobic Meso-SiO2 shell provides an important barrier for the core phase, which reduces the loss of active species, acid sites and framework Al of the aged core-shell catalyst and mitigates the collapse of the zeolite framework. This work provides a new strategy for the design of novel and efficient NH3-SCR catalysts.

Controlling copper location on exchanged MOR-type aluminosilicate zeolites for methanol carbonylation: In situ/operando IR spectroscopic studies

Replacing homogeneous catalytic processes by heterogeneous routes based on the utilization of solid catalysts is of great interest from an environmental point of view. Owing to their genuine pore structure, zeolites such as mordenites (MOR) have emerged as game-changing materials to enable the heterogenization of catalytic processes including methanol carbonylation. Cu-exchange zeolites take the edge over pristine zeolites, leading to enhanced catalytic performance in terms of greater activity, selectivity, and stability. Herein, the overall catalytic activity and stability can be modulated upon controlling the environment and location of copper active sites in zeolites. In this study, Cu-exchanged mordenites were strategically synthesized to investigate the role of Cu location inside of MOR cavities under working conditions by means of in situ/operando infrared (IR) spectroscopic studies. The results obtained revealed that a major proportion of Cu in the MR-8 cavities notably enhances the activity and stability of the catalyst. This study provides crucial insights for fine-tuning zeolite catalysts to achieve the heterogenization of homogeneous carbonylation processes.

Replacement of Tyrosines by Unnatural Amino Acid Aminophenylalanine Leads to Metal-Mediated Aniline Free Radical Formation in a Copper Amine Oxidase.

Copper amine oxidases (CAOs) catalyze the oxidative deamination of primary amines to aldehyde, ammonia, and hydrogen peroxide as products and are widely distributed in bacteria, plants, and eukaryotes. These enzymes initiate the single turnover, post-translational conversion of an active site tyrosine to the redox cofactor 2,4,5-trihydroxyphenylalanine quinone (TPQ), subsequently employing TPQ to catalyze steady-state amine oxidation. The mechanisms of TPQ biogenesis and steady-state amine oxidation have been studied extensively, with consensus mechanisms proposed for both reactions. One unresolved issue has been whether the Cu2+ center must undergo formal reduction to Cu1+ in the course of the reaction. Herein, we investigate the properties of the active site of a yeast (Hansenula polymorpha) amine oxidase (HPAO) that has undergone site-specific insertion of a para-aminophenylalanine (pAF) into the position of either the precursor tyrosine to TPQ (Y405) or the two strictly conserved neighboring tyrosines (Y305 and Y407). While our original intention was to interrogate cofactor biogenesis using a precursor unnatural amino acid (UAA) of altered redox potential and pKa, we instead observe an unanticipated reaction assigned to an intramolecular electron transfer from pAF to the active site copper ion. We establish the generality of the observed active site chemistry using exogenously added, aniline-containing substrates under conditions that prevent side chain amine oxidation. The results support previous proposals that the activation of the TPQ precursor occurs in the absence of a formal valence change at the active site copper site. The described reaction of pAFs with the active site redox Cu2+ center of HPAO provides a prototype for either the engineering of the enzymatic oxidation of exogenous anilines or the insertion of site-specific free radical probes within proteins.

Integrated Experimental and Theoretical Investigation of Copper Active Site Properties of a Lytic Polysaccharide Monooxygenase from Serratia marcescens.

In this paper, we employed a multidisciplinary approach, combining experimental techniques and density functional theory (DFT) calculations to elucidate key features of the copper coordination environment of the bacterial lytic polysaccharide monooxygenase (LPMO) from Serratia marcescens (SmAA10). The structure of the holo-enzyme was successfully obtained by X-ray crystallography. We then determined the copper(II) binding affinity using competing ligands and observed that the affinity of the histidine brace ligands for copper is significantly higher than previously described. UV-vis, advanced electron paramagnetic resonance (EPR), and X-ray absorption spectroscopy (XAS) techniques, including high-energy resolution fluorescence detected (HERFD) XAS, were further used to gain insight into the copper environment in both the Cu(II) and Cu(I) redox states. The experimental data were successfully rationalized by DFT models, offering valuable information on the electronic structure and coordination geometry of the copper center. Finally, the Cu(II)/Cu(I) redox potential was determined using two different methods at ca. 350 mV vs NHE and rationalized by DFT calculations. This integrated approach not only advances our knowledge of the active site properties of SmAA10 but also establishes a robust framework for future studies of similar enzymatic systems.

Interactions of Phenylalanine Derivatives with Human Tyrosinase: Lessons from Experimental and Theoretical tudies.

The pigmentation of the skin, modulated by different actors in melanogenesis, is mainly due to the melanins (protective pigments). In humans, these pigments' precursors are synthetized by an enzyme known as tyrosinase (TyH). The regulation of the enzyme activity by specific modulators (inhibitors or activators) can offer a means to fight hypo- and hyper-pigmentations responsible for medical, psychological and societal handicaps. Herein, we report the investigation of phenylalanine derivatives as TyH modulators. Interacting with the binuclear copper active site of the enzyme, phenylalanine derivatives combine effects induced by combination with known resorcinol inhibitors and natural substrate/intermediate (amino acid part). Computational studies including docking, molecular dynamics and free energy calculations combined with biological activity assays on isolated TyH and in human melanoma MNT-1 cells, and X-ray crystallography analyses with the TyH analogue Tyrp1, provide conclusive evidence of the interactions of phenylalanine derivatives with human tyrosinase. In particular, our findings indicate that an analogue of L-DOPA, namely (S)-3-amino-tyrosine, stands out as an amino phenol derivative with inhibitory properties against TyH.

Atomic Design of Copper Active Sites in Pristine Metal-Organic Coordination Compounds for Electrocatalytic Carbon Dioxide Reduction.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) has emerged as a promising and sustainable approach to cut carbon emissions by converting greenhouse gas CO2 to value-added chemicals and fuels. Metal-organic coordination compounds, especially the copper (Cu)-based coordination compounds, which feature well-defined crystalline structures and designable metal active sites, have attracted much research attention in electrocatalytic CO2RR. Herein, the recent advances of electrochemical CO2RR on pristine Cu-based coordination compounds with different types of Cu active sites are reviewed. First, the general reaction pathways of electrocatalytic CO2RR on Cu-based coordination compounds are briefly introduced. Then the highly efficient conversion of CO2 on various kinds of Cu active sites (e.g., single-Cu site, dimeric-Cu site, multi-Cu site, and heterometallic site) is systematically discussed, along with the corresponding catalytic reaction mechanisms. Finally, some existing challenges and potential opportunities for this research direction are provided to guide the rational design of metal-organic coordination compounds for their practical application in electrochemical CO2RR.

Improving Copper Active Site Speciation on Cu-Ce/SSZ-13 for Ammonia Oxidation via Si/Al Ratio Modulation.

Catalytic oxidation is a promising purification technique for ammonia (NH3) emission. However, high ignition temperatures and NOx peroxide generation limit its effectiveness due to a lack of active sites. Herein, the effects of Si/Al ratio (SAR) modulation on the speciation of copper active sites and the reaction mechanism at different acidic sites were investigated by loading CuO-CeO2 onto SSZ-13 with different SARs (Cu-Ce/SAR15, 20, and 30). Among them, Cu-Ce/SAR20 exhibits the lowest induction temperature (T20 = 180 °C) and the highest nitrogen selectivity (above 95%), attributing to a higher number of Cu2+ exchange sites. In situ IR spectroscopy and isotopic (18O2) transient response experiments indicate that more active Cu2+ in Cu-Ce/SAR20 provides sufficient Lewis acidic sites for NH3 adsorption and favors the stability of Si-OH-Al structures (Brønsted acid sites). NH3 adsorbed at Lewis acidic sites tends to form peroxide byproducts (NOx), while the NH4+ adsorbed at Brønsted acidic sites generates the key intermediate NH4NO2, which decomposes to N2 at high temperatures, thus enhancing nitrogen selectivity. The whole process mainly follows the Mars-van Krevelen (M-K) mechanism, with the Langmuir-Hinshelwood (L-H) mechanism playing a supporting role. Z2Cu2+ coordinates with adjacent Al atoms within the six-membered ring (6MR) and undergoes a slight deformation at high temperatures, facilitating the migration of the lattice oxygen. SAR plays a crucial role in local environmental speciation of reactive Cu2+, where the sufficient isolated Al provided in SAR20 pulls Cu2+ into the eight-membered ring (8MR), allowing it to come into contact with NH3 more readily.

Targeted C-O bond cleavage of *CH2CHO at copper active sites for efficient electrosynthesis of ethylene from CO2 reduction

*CH2CHO, a pivotal intermediate in CO2 reduction reaction (CO2RR) on copper-based catalysts, hinges on the strength of Cu-C and C-O bonds for the selective production of ethanol and ethylene. However, the targeted cleavage of these bonds at Cu active sites presents a formidable challenge. In this study, we manipulated the selective C-O bond breaking at Cu through an electron enrichment strategy, steering the reaction towards ethylene synthesis. Both experimental and theoretical investigations reveal that Gd incorporation elevates electron density at Cu sites, thereby enhancing Cu-O interaction and concurrently weakening the C-O bond at the critical Cu-*O-CHCH2 bifurcation point. Notably, Gd-doped Cu2O (Gd-Cu2O) demonstrated a 1.43-fold increase in the ethylene/CO ratio relative to undoped Cu2O. This alteration steers the reaction mechanism towards ethylene generation. Our study highlights the pivotal role of regulating reaction intermediates in optimizing activity and selectivity of CO2RR in copper-based catalysts, providing valuable insights for future catalyst development.

Confinement Effect in Metal-Organic Framework Cu3(BTC)2 for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes.

The radical difunctionalization of alkenes plays a vital role in pharmacy, but the conventional homogeneous catalytic systems are challenging in selectivity and sustainability to afford the target molecules. Herein, the famous readily available metal-organic framework (MOF), Cu3(BTC)2, has been applied to cyano-trifluoromethylation of alkenes as a high-performance and recyclable heterogeneous catalyst, which possesses copper(II) active sites residing in funnel-like cavities. Under mild conditions, styrene derivatives and various unactivated olefins could be smoothly transformed into the corresponding cyano-trifluoromethylation products. Moreover, the transformation brought about by the active copper center in confined environments achieved regio- and shape selectivity. To understand the enhanced selectivity, the activation manner of the MOF catalyst was studied with control catalytic experiments such as FT-IR and UV-vis absorption spectroscopy of substrate-incorporated Cu3(BTC)2, which elucidated that the catalyst underwent a radical transformation with the intermediates confined in the MOF cavity, and the confinement effect endowed the method with pronounced selectivities.

Investigation on the active site location, structure and ultra-deep desulfurization performance of CuY zeolite

Y zeolites modified with Cu are promising sorbents for adsorption desulfurization due to their cost-effectiveness. Only the supercage, which is larger than thiophene molecule, is the potential location of active sites for thiophene removal. However, numerous copper species cannot serve as effective active sites due to their inability to be located in the supercages. Based on this consideration, two strategies to regulate Cu location in Y zeolite to address the aforementioned challenges were explored. One is to adjust the molecular size of copper-ammonia ligands through pH value of cuprammonia solution, and the other is to prevent the migration of copper to small cages by heat treatment. The results showed that these two strategies could effectively regulate the location of copper active sites in Y zeolite. During heat treatment, Cu could transfer into supercages from sodalite cages at 350 °C. More effective copper would be targeted to be located in the supercages in the process of adjusting pH. For the best Cu10.74Y350 sorbent, which was prepared at 350 °C under pH of 10.74, the Cu content in the supercages was the highest (25 %), and thus it has an excellent desulfurization efficiency of 82.3 %.

HOFs structured CN template enables the dual regulation of Cu–O and Cu–N active sites in porous Cu-g-CN for synergistic photo-Fenton process

Photo-Fenton catalysis with strong oxidation potential and cyclic stability represents a promising technique for addressing the escalating environmental challenges. However, the photo-Fenton activity using Fe/Cu doped graphitic carbon nitride (g-CN) catalysts is significantly hindered by the limited reaction interface and non-tunable surface-active sites. Herein, we present a novel CN polymer type hydrogen bonded organic framework (CN-HOFs) template derived Cu-g-CN (Cu/CH-g-CN) based hybriding catalyst (CN-HOFs/Cu/CH-g-CN), which process greatly optimized surface features for high-performance photo-Fenton reaction with exceptional durability in a broad pH range of 3–11. Importantly, the distinctive porous structure of CN-HOFs template offers not only high specific surface area, but also the possibility to regulate Cu active sites. The coexistence of Cu–O and Cu–N active sites is identified by XPS, which facilitates the separation and migration of photogenerated charges, expediting the redox cycle. The synergistic photo-Fenton reaction boosted by the porous CN-HOFs structure and the dual Cu active sites (Cu–O and Cu–N) was verified by degradation activity of tetracycline. Under visible light irradiation at a concentration of 20 mg/L, the degradation efficiency reaches nearly 100% within 20 min, with exceptional cycling stability. Further investigations have revealed that the Cu–O active site is conducive to the adsorption of organic pollutants, while the Cu–N active site promotes electron transfer, accelerates the cyclic conversion of Cu+ and Cu2+. The dual copper active site is beneficial for the generation of hydroxyl radicals and the stable operation of the catalyst, resulting in significant photo-Fenton activity. This work underscores the importance of regulating the nanoscale morphology and electronic structure of photofunctional catalysts, not only to increase the active sites for photo-Fenton reactions but also to facilitate charge transfer and the cycling of active metal ions, thereby improving the sustainability of heterogeneous photo-Fenton process.

Biomimetic Electrochemical Sensor Based on Single-Atom Nickel Laccase Nanoenzyme for Quercetin Detection.

Laccase, a member of the copper oxidase family, has been used as a green catalyst in the environmental and biochemical industries. However, laccase nanoenzymes are limited to materials with copper as the active site, and noncopper laccase nanoenzymes have been scarcely reported. In this study, inspired by the multiple copper active sites of natural laccase and the redox Cu2+/Cu+ electron transfer pathway, a novel nitrogen/nickel single-atom nanoenzyme (N/Ni SAE) with high laccase-like activity was prepared by inducing Ni and dopamine precipitation through a controllable water/ethanol interface reaction. Compared with that of laccase, the laccase activity simulated by N/Ni SAE exhibited excellent stability and reusability. The N/Ni SAE exhibited a higher efficiency toward the degradation of 2,4-dichlorophenol, hydroquinone, bisphenol A, and p-aminobenzene. In addition, a sensitive electrochemical biosensor was constructed by leveraging the laccase-like activity of N/Ni SAE; this sensor offered unique advantages in terms of catalytic activity, selectivity, stability, and repeatability. Its detection ranges for quercetin were 0.01-0.1 and 1.0-100 μM, and the detection limit was 3.4 nM. It was also successfully used for the quantitative detection of quercetin in fruit juices. Therefore, the single-atom biomimetic nanoenzymes prepared in this study promote the development of a new electrochemical strategy for the detection of various bioactive molecules and show great potential for practical applications.