Role of Interface of Metal-Organic Frameworks and Their Composites in Persulfate-Based Advanced Oxidation Process for Water Purification.

The persulfate activation-based advanced oxidation process (PS-AOP) is an important technology in wastewater purification. Using metal-organic frameworks (MOFs) as heterogeneous catalysts in the PS-AOP showed good application potential. Considering the intrinsic advantages and disadvantages of MOF materials, combining MOFs with other functional materials has also shown excellent PS activation performance and even achieves certain functional expansion. This Review introduces the classification of MOFs and MOF-based composites and the latest progress of their application in PS-AOP systems. The relevant activation/degradation mechanisms are summarized and discussed. Moreover, the importance of catalyst-related interfacial interaction for developing and optimizing advanced oxidation systems is emphasized. Then, the interference behavior of environmental parameters on the interfacial reaction is analyzed. Specifically, the initial solution pH and coexisting inorganic anions may hinder the interfacial reaction process via the consumption of reactive oxygen species, affecting the activation/degradation process. This Review aims to explore and summarize the interfacial mechanism of MOF-based catalysts in the activation of PS. Hopefully, it will inspire researchers to develop new AOP strategies with more application prospects.

Tuning nanozyme property of Co@NC via V doping to construct colorimetric sensor array for quantifying and discriminating antioxidant phenolic compounds.

Through V2O5 etching of ZIF-67 and subsequent pyrolysis in an argon flow, the V doped Co@NC (V/Co@NC) with mixed-valence Co(II)/Co(III) and V(III)/V(IV) was successfully obtained. V doping plays an important role in regulating the enzyme-like activity of Co@NC. Specifically, the Co@NC has both oxidase-like activity and peroxidase-mimic activity, while the V/Co@NC possesses the specific oxidase-like activity. Benefiting from the elevated Co2+ level due to electrons transfer from the reduced V(III) to Co3+ and recyclable redox reactions between the Co(III)/Co(II) and V(IV)/V(III) couples, the V/Co@NC displays 4-fold increase in the oxidase-like activity, smaller Km (0.18 mM) and larger Vmax (4.01 × 10-8 M s-1) toward TMB relative to Co@NC. The origin of V/Co@NC as oxidase mimic is likely attributed to the generation of 1O2 and •OH. Different phenolic compounds (PC), like gallic acid, kaempferol, caffeic acid, quercetin, and catechin, have distinct antioxidant capacity, showing a differential inhibiting effect on the V/Co@NC-TMB system. The different PC antioxidants in the V/Co@NC-TMB system lead to unique decrease in the absorbance at 652 nm (A652), resulting in a unique absorbance signal response mode. By choosing different combinations of A652 signals at various time points, multichannel information can be extracted from a single nanozyme for pattern recognition. Based on this, a colorimetric array sensing platform for the identification of PC is established successfully. Furthermore, the constructed sensor array can be used for quantifying and discriminating multiple PC antioxidants.

Atomically dispersed Fe/Bi dual active sites single-atom nanozymes for cascade catalysis and peroxymonosulfate activation to degrade dyes.

Constructing single-atom nanozymes (SAzymes) with densely exposed and dispersed double metal-Nx catalytic sites for pollution remediation remains rare and challenging. Herein, we report a novel Fe-Bi bimetallic MOF-derived carbon supported Fe-N4 and Bi-N4 dual-site FeBi-NC SAzyme for cascade catalysis and peroxymonosulfate activation to degrade dye pollutants, which is synthesized from the Fe-doped Bi-MOF as a precursor. The formation of both Fe-N4 and Bi-N4 sites is demonstrated by XANES and EXAFS. The FeBi-NC SAzyme has high single atoms loadings of Fe (2.61 wt%) and Bi (8.01 wt%), and displays 5.9- and 9.8-fold oxidase mimicking activity enhancement relative to the Fe-NC and Bi-NC SAzymes, respectively. When integrated acetylcholinesterase (AChE) and FeBi-NC SAzyme, a cascade enzyme-nanozyme system is developed for selective and sensitive screening of AChE activity with a low detection limit of 1 × 10-4 mU mL-1. Both Fe-N4 and Bi-N4 in FeBi-NC display a strong binding energy and electron donating capability to promote peroxymonosulfate activation to generate highly active intermediates for rhodamine B degradation. 100% rhodamine B removal occurs within 5 min via FeBi-NC mediated activation of peroxymonosulfate. The DFT calculations reveal that high activity of FeBi-NC is due to the isolated Fe-N4 and Bi-N4 sites and their synergy.

Two-dimensional iron MOF nanosheet as a highly efficient nanozyme for glucose biosensing.

Two-dimensional (2D) nanomaterials are attractive in catalysis due to their rich accessible active sites. Iron-based metal organic frameworks (MOFs) are promising nanozymes because of their iron center and pore structure. However, it is challenging to obtain iron-based 2D MOF nanozymes due to the coordinated form of iron. Herein, we report a cation substitution strategy to transform an easily obtained Cu(HBTC)(H2O)3 (represented as Cu(HBTC)-1, the product of only two carboxylate groups in 1,3,5-benzenetricarboxylic acid (H3BTC) ligands linked by Cu ions) nanosheet into a 2D Fe-BTC nanosheet, which was characterized by SEM (scanning electron microscopy), AFM (atomic force microscopy), XPS (X-ray photoelectron spectroscopy), FT-IR (Fourier transform infrared spectroscopy), and XRD (X-ray diffraction). The 2D Fe-BTC nanosheet can catalyze TMB (3,3',5,5'-tetramethylbenzidine) oxidation by H2O2, showing its intrinsic peroxidase mimetic characteristic. The catalytic performance of 2D Fe-BTC was superior to those of its template Cu(HBTC)-1 nanosheet and 3D MIL-100(Fe). Their catalytic activities follow the order of 2D Fe-BTC > MIL-100(Fe) > 2D Cu(HBTC)-1. The peroxidase-like activity of 2D Fe-BTC is 77 times that of its template Cu(HBTC)-1, and 2.2 times that of MIL-100(Fe), a well known 3D crystalline form of iron trimesates. The Km values of 2D Fe-BTC for TMB and H2O2 were 0.2610 mM and 0.0334 mM, which were 1.6 and 1.9-fold lower than those of 3D MIL-100(Fe), respectively. The TMB oxidation rate and H2O2 reduction rate at unit mass concentration of the catalyst (Kw) for 2D Fe-BTC were 2.7-72.3 and 1.5-37.9 times those for the previously reported 3D MOF nanozymes, respectively. In terms of the excellent peroxidase mimetic characteristic of 2D Fe-BTC, a sensitive and selective colorimetric biosensing platform for hydrogen peroxide and glucose was developed. The linear ranges are 0.04-30 µM and 0.04-20 µM for H2O2 and glucose, with a low detection limit of 36 nM and 39 nM, respectively. The assay was satisfactorily applied to glucose determination in biological matrices.

A tunable bifunctional hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxide nanozyme for sensing H2O2 and screening acetylcholinesterase activity and its inhibitor.

A self-templated strategy was adopted to design hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxides via the Mo or W doping of ZIF-67, and subsequent pyrolysis under an atmosphere of air at a low temperature of 450 °C. The hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxides displayed tunable oxidase-like and peroxidase-like activities able to efficiently catalyze the oxidation of TMB to generate a deep blue color in the absence or presence of H2O2. Relative to that of the un-doped Co3O4, the oxidase mimic activity of the Mo-doped Co3O4 increased to 1.3 to 2.1-fold, while its peroxidase mimic activity increased to 7.1 to 19.9-fold, depending on different Mo doping amounts. The oxidase mimic activity of the W-doped Co3O4 increased to 2.1 to 2.3-fold, while its peroxidase mimic activity increased to 4.8 to 5.9-fold, depending on the different W doping amounts. The Mo- and W-doped Co3O4 nanohybrid exhibited both higher O2 and H2O2 activating capability, and their H2O2 activating capacity was superior to the O2 activating capability. Furthermore, the Mo- and W-doped Co3O4 nanohybrids exhibited similar O2 activating abilities, while the Mo-doped one displayed a higher H2O2 activating capability than the W-doped one. The discrepant peroxidase-like nature of Mo- and W-doped Co3O4 nanohybrids is likely attributed to their different catalytic mechanisms. The peroxidase-like activity of Mo-doped Co3O4 is highly related to the ˙OH free radical, while that of W-doped Co3O4 is likely ascribed to the electron transfer between TMB and H2O2. The Km values of Co3O4/MoO3 for TMB and H2O2 were 0.0352 mM and 0.134 mM, which were 3.2- and 1.9-fold lower than that of pure Co3O4, respectively. A Co3O4/MoO3-based colorimetric platform was developed for the determination of H2O2 in the 0.1-200 µM range, with a limit of detection of 0.08 µM (3σ). Based on the thiocholine (TCh) inhibition of the excellent peroxidase-like activity of Co3O4/MoO3 and the TCh generation via acetylcholinesterase (AChE) catalyzed hydrolysis of acetylthiocholine chloride (ATCh), the colorimetric platform was extended to screen AChE activity and its inhibitor.

Engineering FeCo alloy@N-doped carbon layers by directly pyrolyzing Prussian blue analogue: new peroxidase mimetic for chemiluminescence glucose biosensing.

Herein, we report the synthesis of FeCo alloy@N-doped carbon layers (FeCo@NC), a new peroxidase mimetic, by directly pyrolyzing the FeIII-Co Prussian blue analogue (FeIII-Co PBA). The FeCo@NC composite showed excellent peroxidase-like activity due to its highly active FeCo alloy, M-N species (Co-N and Fe-N) and N-doped carbon layers with hierarchical pore nanostructures, which were formed via simple heat treatment of FeIII-Co PBA without additional C and N sources. In particular, the obtained FeCo@NC hybrid presented high CL activity with more than 85-fold enhancement in the CL emission of the H2O2-luminol system, and long-term stability compared with FeCo alloy nanoparticles. The CL response showed a linear range of 0.01-40 µM H2O2 with a limit of detection of 2.5 nM. When coupled with glucose oxidase, we developed a new CL sensing method for the detection of glucose in the linear range of 10 nM to 10 µM with a detection limit of 8.5 nM. This FeCo@NC-based glucose biosensor displayed rapidity, high precision and good reproducibility when utilized to analyze real biological samples. Expectedly, FeCo@NC, as a new peroxidase mimetic, exhibits great potential for monitoring glucose levels in clinical diagnosis.

ß-Cyclodextrin functionalization of metal-organic framework MOF-235 with excellent chemiluminescence activity for sensitive glucose biosensing.

Herein, we developed a new CL method for the detection of glucose, exhibiting high sensitivity, low limit of detection, good stability and reliability for analysis of real biological samples. The MOF-235/ß-cyclodextrin (ß-CD) hybrids were facilely prepared by a simple method, and characterized by XRD, TGA, FT-IR and SEM. The as-prepared hybrids exhibited highly catalytic activity for the hydrogen peroxide-luminol system, and gave more than 30-fold enhancement in CL response as compared with that of hydrogen peroxide-luminol system, thus could be used for sensitive detection of H2O2 and glucose. The excellent catalytic performance of the MOF-235/ß-CD hybrids is ascribed to the large surface area of MOF-235 as well as the synergistic effect between ß-CD and MOF-235. The proposed sensing strategy coupled with CL detection method showed low detection limits of 5 nM and 10 nM for H2O2 and glucose, respectively. Successful application of the MOF-235/ß-CD hybrid in CL assay of glucose in real human serum samples is demonstrated as an efficient catalyst for sensitive chemiluminescence-based analyses. The success of this work favors to facilitate the future development in CL catalysts via MOF functionalization.