Tailoring the Coordination Environment of Fe/Zn-BDC to Boost Peroxidase-like Activity for Highly Selective Detection of PFOS.

Perfluorooctanesulfonic acid potassium salt (PFOS) residues in ecosystems over long periods are of increasing concern and require a selective and stable optical probe for monitoring. Herein, two functional groups (-F and -NH2) with opposite electronic modulation ability were introduced into Fe/Zn-BDC (denoted as Fe/Zn-BDC-F4 and Fe/Zn-BDC-NH2, respectively) to tailor the coordination environment of the Fe metal center, further regulating the nanozyme activity efficiently. Notably, the peroxidase-like activity is related to the coordination environment of the nanozymes and obeys the following order Fe/Zn-BDC-F4 > Fe/Zn-BDC > Fe/Zn-BDC-NH2. Based on the excellent peroxidase-like activity of Fe/Zn-BDC-F4 and the characteristics of being rich in F atoms, a rapid, selective, and visible colorimetric method was developed for detecting PFOS with a detection limit of 100 nM. The detection mechanism was attributed to various interaction forces between Fe/Zn-BDC-F4 and PFOS, including electrostatic interactions, Fe-S interactions, Fe-F bonds, and halogen bonds. This work not only offers new insights into the atomic-scale rational design of highly active nanozymes but also presents a novel approach to detecting PFOS in environmental samples.

Multifunctional Polymer Vesicles for Synergistic Antibiotic-Antioxidant Treatment of Bacterial Keratitis.

As an acute ophthalmic infection, bacterial keratitis (BK) can lead to severe visual morbidity, such as corneal perforation, intraocular infection, and permanent corneal opacity, if rapid and effective treatments are not available. In addition to eradicating pathogenic bacteria, protecting corneal tissue from oxidative damage and promoting wound healing by relieving inflammation are equally critical for the efficient treatment of BK. Besides, it is very necessary to improve the bioavailability of drugs by enhancing the ocular surface adhesion and corneal permeability. In this investigation, therefore, a synergistic antibiotic-antioxidant treatment of BK was achieved based on multifunctional block copolymer vesicles, within which ciprofloxacin (CIP) was simultaneously encapsulated during the self-assembly. Due to the phenylboronic acid residues in the corona layer, these vesicles exhibited enhanced muco-adhesion, deep corneal epithelial penetration, and bacteria-targeting, which facilitated the drug delivery to corneal bacterial infection sites. Additionally, the abundant thioether moieties in the hydrophobic membrane enabled the vesicles to both have ROS-scavenging capacity and accelerated CIP release at the inflammatory corneal tissue. In vivo experiments on a mice model demonstrated that the multifunctional polymer vesicles achieved efficient treatment of BK, owing to the enhanced corneal adhesion and penetration, bacteria targeting, ROS-triggered CIP release, and the combined antioxidant-antibiotic therapy. This synergistic strategy holds great potential in the treatment of BK and other diseases associated with bacterial infections.

Surfactant encapsulating N-doped carbon dots with enhanced optical properties as a selective sensor for Cr(VI) detection.

Detecting hexavalent chromium (Cr(VI)) is important for human health and environmental protection due to its high toxicity, carcinogenicity and persistence, but developing a sensor to selectively detect Cr(VI) remains challenging. Here, we proposed a selective fluorescent sensor for Cr(VI) detection using cetyltrimethylammonium chloride (CTAC) modified N-doped carbon dots (N-CDs-CTAC) synthesized via a post-modification strategy. Specifically, the introduced CTAC molecules could self-assemble into micelles for encapsulating fluorescent N-CDs, causing the aggregation of N-CD particles and then displaying enhanced fluorescence emission owing to the aggregation-induced emission effect. Moreover, the positively charged CTAC can interact with negatively charged Cr(VI) in the form of an anion (Cr2O72-), boosting the ability of the selective recognition of Cr(VI). Thus, a N-CDs-CTAC fluorescent probe was designed to selectively monitor Cr(VI) with an ultralow detection limit down to 40 nM, and was further used for Cr(VI) detection in real environmental samples. The fluorescence quenching mechanism of N-CDs-CTAC by Cr(VI) was attributed to dynamic quenching. The proposed assay opens an avenue for the selective detection of Cr(VI) in the environmental monitoring field.

Fluorescence turn-off sensing strategy based on Al-based MOF for selective detection of tricresyl phosphate.

Tricresyl phosphate (TCP), a notable emerging pollutant with a high bioconcentration factor and biotoxicity, is a typical representative of aryl-organophosphorus flame retardants. The electrochemical and chromatographic technologies used in conventional TCP detection have a variety of drawbacks. Hence, it is crucial to suggest an easy, accurate, and selective method for detecting TCP. In this study, we presented a brand-new method based on NH2-MIL-53(Al) nanoprobe for the direct luminescence assay of TCP. NH2-MIL-53(Al) possessed an excellent crystal structure and superior optical qualities. Notably, the introduction of TCP caused a considerable dampening of the photoluminescence signal of the nanoprobe. The fluorescence response based on static quenching was verified by fluorescence lifetime decay curves. The thermodynamic analysis further concluded that TCP and nanoprobe spontaneously produced non-fluorescent complexes due to hydrophobic interaction. The quenching efficiency (F0-F)/F0 of the nanoprobe and the TCP concentration displayed good linearity in the scope of 0.3-3.0 µM (R2 = 0.996), and the LOD was 0.058 µM under the ideal detection conditions. More significantly, the technique was effectively used to identify TCP in lake and tap water (RSD ≤5.79%), which provided a fresh perspective on how to recognize OPFRs in environmental water.

Mussel-Inspired Microgel Encapsulated NLRP3 Inhibitor as a Synergistic Strategy Against Dry Eye.

The inflammatory response mediated by oxidative stress is the main pathogenesis of dry eye, but clinical observations have shown that scavenging oxygen-free radicals alone has limited therapeutic effect. Moreover, the unique anatomy and physiology of the ocular surface result in low bioavailability of drugs, and higher concentration is required to achieve the desired efficacy, which, however, may bring systemic side effects. These problems pose a challenge, but the revelation of the ROS-NLRP3-IL-1ß signaling axis opens up new possibilities. In this investigation, an NLRP3 inhibitor was successfully encapsulated in polydopamine-based microgels and used for dry eye treatment. It was demonstrated that the well-designed microgels exhibited good biocompatibility, prolonged drug retention time on the ocular surface, and effective inhibition of corneal epithelial damage and cell apoptosis. In addition, due to the synergistic effect, the NLRP3 inhibitor-loaded microgels could exert enhanced oxygen radical scavenging and inflammation-inhibiting effects at a lower dose than monotherapy. These findings suggest that polydopamine-based microgels have advantages as ocular surface drug delivery platforms and have promising applications in oxidative damage-related inflammatory diseases in synergy with anti-inflammatory drugs.

Chemiluminescence based on UV-assisted persulfate activation for sensitive detection of triphenyl phosphate.

Triphenyl phosphate (TPHP), a typical kind of organophosphorus flame retardants (OPFRs) with aryl groups, has been recognized as an emerging contaminant that causes environmental and health hazards. It is a pervasive threat that can be frequently detected in the environment and living organisms. Hence, establishing an efficient analytical method for TPHP is an urgent issue. In this work, a heteropolyacid (HPA)-luminol chemiluminescence strategy coupled with UV-assisted persulfate (PS) activation was proposed for the sensitive and selective detection of TPHP. The UV-assisted PS oxidation pretreatment could decompose the water-insoluble TPHP into smaller orthophosphates, which were further converted into HPA with the subsequently introduced vanadium­molybdenum acid. The formed HPA served as a catalyst to oxidize luminol, and strong chemiluminescence at 425 nm was generated immediately. Furthermore, the degradation process of TPHP and chemiluminescence mechanism were also investigated. The results demonstrated that some reactive oxygen radicals such as SO4-, OH, 1O2, and O2-, were involved in the degradation and chemiluminescence reaction. Notably, this proposed chemiluminescence analytical strategy realized a highly sensitive detection for TPHP, and granted the limit of detection down to 0.38 ppt. This study provides an attractive perspective for the detection of emerging OPFRs.

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.

Constructing Cylindrical Nanostructures Via Directional Morphology Evolution Induced by Seeded Polymerization.

Herein, spindle-shaped block copolymer (BCP) nanoparticles are used in seeded polymerization of methyl methacrylate as a novel approach to generating cylindrical nanostructures. The chain-extension of BCP seeds by an amorphous coil-type polymer within the seed core composed of semifluorinated liquid-crystalline blocks triggers the deforming, stretching, and directional growth of the seeds along the long axis, eventually leads to nanorods.

Constructing helical nanowires via polymerization-induced self-assembly.

While reliable strategies for constructing block copolymer (BCP) nanowires have been developed, helical nanowires are rarely reported in polymerization-induced self-assembly (PISA). Herein, in this work, a new strategy for constructing helical nanowires was developed via PISA mediated by a fluorinated stabilizer block. Ultralong nanowires with helical structure can be readily produced in a wide range of block compositions. In addition, the generality of this strategy was well testified by expanding monomer types. The achiral BCP nano-objects underwent a morphology transition from spheres to helical nanowires during aging. We believe this work will provide a general strategy for producing helical nanowires through PISA of achiral BCPs.

Directional effect on the fusion of ellipsoidal morphologies into nanorods and nanotubes.

Particle fusion is well-recognized as an important spontaneous process to produce higher-order nanostructures during morphology transition in polymerization-induced self-assembly (PISA). However, to our knowledge, the directional contact, adhesion, and fusion of adjacent nanoparticles have been rarely elucidated in PISA. Herein, a directional fusion of ellipsoidal morphologies was demonstrated during PISA of semi-fluorinated liquid-crystalline (SFLC) block copolymers. The ellipsoidal nanostructures, including micelles and vesicles, preferred to undergo a directional fusion in a head-to-head model, leading to the formation of nanorods and nanotubes, respectively. We believe the directional fusion will offer insightful guidance in PISA to the preparation of complicated functional nanostructures.

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 magnetic N-doped porous carbon with super-high ciprofloxacin adsorption capacity and wide pH adaptability.

We report a high performance magnetic N-doped nanoporous carbon (MNPC) adsorbent synthesized by a simple single-step pyrolysis protocol. Grinding the mixture of ZnO nanoparticles, cobalt hydroxide and 2-methylimidazole produced Zn/Co-ZIFs that were converted into MNPC following subsequent pyrolysis in N2 atmosphere. The optimized MNPC-700-0.4 adsorbent, obtained at 700 °C with Co/(Zn + Co) molar ratio of 0.4, is featured with super-high ciprofloxacin (CIP) adsorption capacity of 1563.7 mg g-1 at 25 °C, fast adsorption dynamics (1.5 h of adsorption equilibrium time), wide pH adaptability (almost unchanged CIP adsorption capacity in pH 4-10), and good magnetic property. The magnetic property and CIP adsorption performance can be easily regulated by modulating the molar ratio of Co/(Zn + Co) and the pyrolysis temperature. The optimal MNPC-700-0.4 was chosen to explore adsorption kinetics and isotherm. The effects of pH, ionic strength and humic acid on CIP adsorption were investigated. CIP adsorption obeyed pseudo-second-order kinetics and well fitted the Langmuir adsorption model. The favorable textural properties (high surface area and pore volume), riched nitrogen structure and large amounts of defects endow the MNPC-700-0.4 lots of sites for CIP adsorption. The CIP adsorption onto MNPC-700-0.4 was mainly controlled by the electrostatic interaction, hydrophobic interaction, π-π stacking and hydrogen bond.

Promoting Active Sites in MOF-Derived Homobimetallic Hollow Nanocages as a High-Performance Multifunctional Nanozyme Catalyst for Biosensing and Organic Pollutant Degradation.

Nanozymes are one of the ideal alternatives to natural enzymes for various applications. The rational design of nanozymes with improved catalytic activity stimulates increasing attention to address the low activity of current nanozymes. Here, we reported a general strategy to fabricate the Co-based homobimetallic hollow nanocages (HNCs) (C-CoM-HNC, M = Ni, Mn, Cu, and Zn) by ion-assistant solvothermal reaction and subsequent low-temperature calcination from metal-organic frameworks. The C-CoM-HNCs are featured with HNCs composed of interlaced nanosheets with homogeneous bimetallic oxide dispersion. The hierarchical structure and secondary metallic doping endow the C-CoM-HNC highly active sites. In particular, the Cu-doped C-CoCu-HNCs nanostructures exhibit superior performances over the other C-CoM-HNC as both the oxidase mimicking and peroxymonosulfate (PMS) activator. A sensitive bioassay for acetylcholinesterase (AChE) was established based on the excellent oxidase-like activity of C-CoCu-HNC, offering a linear detection range from 0.0001 to 1 mU/mL with an ultralow detection limit of 0.1 mU/L. As the PMS activator, the C-CoCu-HNC was applied for targeted organic pollutant (rhodamine B, RhB) degradation. A highly efficient RhB degradation was realized, along with good adaptability in a wide pH range and good reusability during the eight-cycle run. The results suggest that C-CoCu-HNC holds a practical potential for clinical diagnostics and pollution removal. Further density functional theory calculation reveals that Cu doping leads to a tighter connection and more negative adsorption energy for O2/PMS, as well as an upshifted d-band center in the C-CoCu-HNCs nanostructures. These changes facilitated the adsorption of O2/PMS on the C-CoCu-HNC surface for dissociation. This work not only offers a promising multifunctional nanozyme catalyst for clinical diagnostics and pollution removal but also gives some clues for the further development of novel nanozymes with high catalytic activities.

Introducing bifunctional metal-organic frameworks to the construction of a novel ratiometric fluorescence sensor for screening acid phosphatase activity.

Restricted to single sensing mechanisms, most luminescent metal-organic framework (LMOF)-based sensors were constructed for detection of limited targets. Here, a new biosensor is described for screening acid phosphatase (ACP) activity via bifunctional NH2-MIL-101 MOFs acting as both fluorescent indicator and biomimetic catalyst. NH2-MIL-101 possesses an inherent fluorescence emission at 456 nm (F456). As a peroxidase-like nanozyme, it catalyzes oxidation of o-phenylenediamine (OPD) by H2O2 to generate fluorescent 2,3-diaminophenazine with the maximum emission at 556 nm (F556). Upon introducing NH2-MIL-101 into a mixture of OPD and H2O2, F456 is quenched, while F556 increases. The ACP sensing is based on pyrophosphate ion (PPi) mediated fluorescence tuning of the NH2-MIL-101/OPD/H2O2 system. PPi inhibits the NH2-MIL-101 catalytic ability by specific binding to its Fe center, while ACP addition recovers the activity by hydrolyzing PPi. Upon addition of PPi and ACP into the NH2-MIL-101/OPD/H2O2 system, a ratiometric luminescence signal (F556/F456) is obtained, and a ratiometric fluorescent sensor can be developed for the sensitive detection of PPi and for screening ACP activity. Plots of F556/F456 vs. ACP concentration were linear over 0.01-30 U/L, with a detection limit of 0.005 U/L. The proposed sensor was successfully used for ACP detection in serum samples. This ratiometric fluorescence assay will open new applications for LMOF-based biosensors.

Co3O4/CuO hollow nanocage hybrids with high oxidase-like activity for biosensing of dopamine.

Here, we report the synthesis, characterization, and oxidase-like activity of Co3O4/CuO hollow nanocage (HNC) nanocomposites. The Co3O4/CuO HNCs were successfully prepared by hydrothermal treatment of ZIF-67 in copper nitrate solution, followed by carbonization in air. The obtained nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Co3O4/CuO HNCs possess enhanced oxidase-like activity compared with pure Co3O4 and CuO, and they can catalytically oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the absence of H2O2 to produce an intense blue product. Reactive oxygen species (ROS) measurements indicate that 1O2 and O2- radicals are the major ROS in catalytic oxidation of TMB by dissolved oxygen in the TMB-Co3O4/CuO HNC system. We then developed a simple, sensitive, visual, and colorimetric biosensing method for dopamine (DA) based on its inhibiting effect on TMB oxidation. The proposed method allows for DA detection with a limit of detection of 0.027 µM and a dynamic range of 0.05-8 µM. This new colorimetric method was successfully used to detect DA in biological samples. The present work demonstrates a simple strategy to fabricate an efficient oxidase mimic with potential applications in bioanalysis and clinical diagnosis.

One-step synthesis of 1,6-hexanediamine modified magnetic chitosan microspheres for fast and efficient removal of toxic hexavalent chromium.

Here, we reported a novel one-step hydrothermal route for the facile synthesis of 1,6-hexanediamine functionalized magnetic chitosan microspheres (AF-MCTS), which were characterized by TEM, FT-IR and XPS to look into its morphology, surface functional groups, and adsorption mechanism of Cr(VI) from the aqueous solution. Cr(VI) adsorption on AF-MCTS as a function of contact time, Cr(VI) concentration, pH, and ionic strength was investigated. The adsorption process follows the Langmuir isotherm model and pseudo-second-order kinetic model. The AF-MCTS exhibited high performance for Cr(VI) removal with very fast adsorption rate (reaching equilibrium within 5 min) and high adsorption capacity (208.33 mg/g), which was 1.1 to 12 times that of other chitosan-based adsorbents. Cr(VI) adsorption onto AF-MCTS was an endothermic and spontaneous process. The recovery and reuse of AF-MCTS was demonstrated 11 times without obvious decrease in adsorption capacity. Mechanism study suggested that -OH rather than -NH2 groups in AF-MCTS were the electron donors for reducing Cr(VI) to Cr3+. Consumption or addition of H+ could trigger the reversible supramolecular coordination between Cr3+ and chitosan. Given the easy preparation, low cost, and remarkable performance, AF-MCTS composite is expected to show promising potential for the practical application in removing toxic Cr(VI) from aqueous media.

High oxidase-mimic activity of Fe nanoparticles embedded in an N-rich porous carbon and their application for sensing of dopamine.

The N-doped porous carbon (NC) has been regarded as one of the promising support materials for nanoparticles (NPs) catalyst due to its inherent virtues such as porosity, large surface areas, and heteroatom incorporation. In this work, Fe/NC-800 hybrid was facilely prepared by uniform dispersion of in situ formed FeNPs onto NC-800 from carbonization of ZIF-8 at 800 °C for the first time. The optimized Fe/NC-800 catalyst was characterized by TEM, XPS and XRD. Compared with sole FeNPs and NC-800, the Fe/NC-800 catalyst exhibited an enhanced oxidase-like activity that could oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the heavy blue without extra oxidants such as H2O2. The possible reason for the enhanced oxidase-like activity of the Fe/NC-800 was discussed on the basis of the experiments of radical scavengers, indicating the importance of superoxide (O2•-) and singlet (1O2) in colorimetric reaction between TMB and Fe/NC-800 hybrid. Furthermore, the oxidase-like activity of Fe/NC-800 was significantly inhibited by dopamine (DA), leading to blue color fading. On this basis, a sensitive and selective colorimetric sensor was fabricated for the quantitative analysis of DA with a linear range of 0.01-40 µM and a low detection limit of 10 nM. The proposed colorimetric method was successfully applied to determine DA in human serum and injection samples, suggesting a promising application in biological analysis.

Ultrasound-Assisted Removal of Tetracycline by a Fe/N-C Hybrids/H2O2 Fenton-like System.

In this work, the degradation of tetracycline (TC) in water by the integrated ultrasound (US)-Fenton process was investigated. For this, a new composite Fe/N-C-x (x is the molar ratio of iron salt Fe(NO3)3·9H2O) catalyst was synthesized through simple carbonization of the mixture of glucose and iron salt Fe(NO3)3·9H2O in the presence of ammonium chloride as the nitrogen source. The resultant catalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometer, and N2 adsorption-desorption, showing a typical graphite porous structure and good magnetic properties. The results indicated that the optimized Fe/N-C-2 catalyst prepared with a mole ratio of glucose/Fe(NO3)3·9H2O/NH4Cl of 5:2:16.8 exhibited the highest TC removal in the Fe/N-C-2/H2O2/US system at a wide pH range from 3.0 to 11.0. At an initial pH of 7.0, TC removal in the Fe/N-C-2/H2O2/TC/US system was 1.83, 18.69, and 28.75 times of that in Fe/N-C-2/TC/H2O2, H2O2/TC/US, and TC/H2O2 systems, showing a positive synergistic action between US and Fe/N-C-2. The effects of catalyst dosage, H2O2 concentration, ultrasonic power, humic acid, and coexisting anions on TC removal were investigated. The preliminary analysis suggested that the Fe-N species and the graphite N dispersed in the carbon matrix are responsible for the efficient catalytic activity. By a simple magnetic separation, the Fe/N-C-2 catalyst was easily recovered and used for the next degradation experiment. Above 88% catalytic ability of Fe/N-C-2 was retained even after six successive runs, suggesting its good reusability. The simple preparation strategy, good magnetic property, and good catalytic ability of the Fe/N-C-2 materials make them promising alternative Fenton-like catalysts for the antibiotics abatement in water.