Stability performance analysis of Fe based MOFs for peroxydisulfates activation to effectively degrade ciprofloxacin.

Fe-based metal-organic frameworks (MOFs) show high activity toward the activation of peroxodisulfate (PDS) for the removal of organic micropollutants (OMPs) in wastewater treatment. However, there is a phenomenon of Fe ion dissolution in the Fe-based MOFs' active PDS system, and the reasons and influencing factors that cause Fe ion dissolution are poorly understood. In this study, we synthesized four types of Fe-based MOFs and confirmed their crystal structure through characterization. All types of Fe-based MOFs were found to activate PDS and form sulfate radicals (SO4 -), which effectively remove OMPs in wastewater. During the process of Fe-based MOFs activating PDS for CIP removal, activated species, oxidant reagent, and pH negatively impact the stability performance of the MOFs' structure. The coordination bond between Fe atom and O atom can be attacked by water molecules, free radicals, and H+, causing damage to the crystal structure of MOFs. Additionally, Fe (II)-MOFs exhibit the best stability performance, due to the enhanced bond energy of the coordination bond in MOFs by the F ligands. This study summarizes the influencing factors of Fe-based MOFs' damage during PDS activation processes, providing new insights for the future development of Fe-based MOFs.

Regulating the reaction pathway of nZVI to improve the decontamination performance through magnetic spatial confinement effect.

Nanoscale zero-valent iron (nZVI) shows high effectiveness in the catalyzed removal of contaminants in wastewater treatment. However, the uncontrolled interfacial electron transfer behavior and formation of surface iron oxide (FeOx) layer led to severe electron wasting and occasionally form highly toxic intermediates. Here, we constructed magnetic mesoporous SiO2 shell on surface of nZVI to stimulate a magnetic spatial confinement effect and regulate the electron transfer pattern. Therein, Fe atom facilely spread out from the nZVI core, orderly release electron to surface adsorbed H2O molecule, which is efficiently transformed into active hydrogen (H*). Meanwhile, in-situ Raman revealed that Fe atoms were involved in the formation of penetrable γ-FeOOH rather than FeOx layer, enabling the continuous inward diffusion of H2O and outward diffusion of H* . Employing the catalyzed removal of halogenated phenols as demo reaction, the presence of magnetic mesoporous SiO2 shell utilized the reaction between electrons and H2O to switch the reaction pathway from the reduction/oxidation hybrid process to hydrodehalogantion, and increased the conversion of halogenated phenols-to-phenols by 5.53 times. This study shows the forehand of improving the decontamination performance of nZVI through sophisticated designed surface coating, as well as fine regulating the environmental behavior of magnetic material via micro-magnetic field.

Fe@C activated peroxymonosulfate system for effectively degrading emerging contaminants: Analysis of the formation and activation mechanism of Fe coordinately unsaturated metal sites.

Carbon-encapsulated Fe nanocomposites (Fe@C), obtained by pyrolysis of metal-organic frameworks (MOFs), can activate peroxymonosulfate (PMS) to remove emerging contaminants (ECs). Unfortunately, the current MOFs-derived catalysts always inevitably produce more iron-oxide compounds that unfavorable for PMS activation. In this work, according to the thermogravimetric curve of Fe(II)-MOF-74, to discuss the role of pyrolysis temperature on the structural characteristics of Fe@C. The results demonstrated that Fe@C-4 could obtain abundant coordinately unsaturated metal sites and exhibited the best activation performance. Radical-quenching experiments and EPR measurements confirm that the generated sulfate radical (SO4-˙) and singlet oxygen (1O2) only degraded approximately 35% of TBBPA. Meanwhile, negatively charged complex intermediates formed by the weak interaction between Fe@C-4 and PMS was proposed as the dominant reactive species, and approximately 65% of TBBPA was degraded. This work optimizes the synthesis strategy and mechanism of Fe@C and provides a methodological reference for the design of Fe-based catalysts.

Protein Corona-Mediated Extraction for Quantitative Analysis of Nanoplastics in Environmental Waters by Pyrolysis Gas Chromatography/Mass Spectrometry.

There is a growing concern about the effects of nanoplastics on biological safety and human health because of their global ubiquity in the environment. Methodologies for quantitative analysis of nanoplastics are important for the critical evaluation of their possible risks. Herein, a sensitive yet simple and environmentally friendly extraction approach mediated by protein corona is developed and coupled to pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) for nanoplastic determination in environmental waters. The developed methodology involved the formation of protein corona by addition of bovine serum albumin (BSA) to samples and protein precipitation via salting out. Then, the resulting extract was directly introduced to Py-GC/MS for nanoplastic mass quantification. Taking 50 nm polystyrene (PS) particles as a model, the highest extraction efficiency for nanoplastics was achieved under the extraction conditions of BSA concentration of 20 mg/L, equilibration time of 5 min, pH 3.0, 10% (w/v) NaCl, incubation temperature of 80 °C, and incubation period of 15 min. The extraction was confirmed to be mediated by the protein corona by transmission electron microscopy (TEM) analysis of the extracted nanoplastics. In total, 1.92 and 2.82 µg/L PS nanoplastics were detected in river water and the influent of wastewater treatment plant (WWTP), respectively. Furthermore, the feasibility of the present methodology was demonstrated by applying to extract PS and poly(methyl methacrylate) (PMMA) nanoplastics from real waters with recoveries of 72.1-98.9% at 14.2-50.4 µg/L spiked levels. Consequently, our method has provided new insights and possibilities for the investigation of nanoplastic pollution and its risk assessment in the environment.

Quantitative Analysis of Polystyrene and Poly(methyl methacrylate) Nanoplastics in Tissues of Aquatic Animals.

Micro- and nanoplastics unavoidably enter into organisms and humans as a result of widespread exposures through drinking waters, foods, and even inhalation. However, owing to the limited availability of quantitative analytical methods, the effect of nanoplastics inside animal bodies is poorly understood. Herein, we report a sensitive and robust method to determine the chemical composition, mass concentration, and size distribution of nanoplastics in biological matrices. This breakthrough is based on a novel procedure including alkaline digestion and protein precipitation to extract nanoplastics from tissues of aquatic animals, followed by quantitative analysis with pyrolysis gas chromatography-mass spectrometry. The optimized procedure exhibited good reproducibility and high sensitivity with the respective detection limits of 0.03 µg/g for polystyrene (PS) nanoplastics and 0.09 µg/g poly(methyl methacrylate) (PMMA) nanoplastics. This method also preserved the original morphology and size of nanoplastics. Furthermore, to demonstrate the feasibility of the proposed method, 14 species of aquatic animals were collected, and PS nanoplastics in a concentration range of 0.093-0.785 µg/g were detected in three of these animals. Recovery rates of 73.0-89.1% were further obtained for PS and PMMA nanospheres when they were spiked into the tissues of Zebra snail and Corbicula fluminea at levels of 1.84-2.12 µg/g. Consequently, this method provides a powerful tool for tracking nanoplastics in animals.

ZSM-5-(C@Fe) activated peroxymonosulfate for effectively degrading ciprofloxacin: In-depth analysis of degradation mode and degradation path.

In this work, ZSM-5-(C@Fe), as a peroxymonosulfate (PMS) heterogeneous activator, was synthesized, characterized, and evaluated for activating PMS to degrade ciprofloxacin (CIP) in wastewater. Zeolite Socony Mobil-5 (ZSM-5) was utilized to enhance structural stability and provided a scaffold to graft Fe doping C nanocomposites activator. Pyrolytic metal-organic frameworks (MOFs) can use crystal structure to construct stable carbon-encapsulated Fe nanocomposites. The formation of C-O-Si, C-O-Al and C-Fe was the key to the stability of catalysts. Fe doping in ZSM-5-(C@Fe) formed non-radical degradation pathway was the key to improve the degradation efficiency. The experimental data indicated ZSM-5-(C@Fe) could completely remove 20 mg L-1 CIP within 15 min and achieve good results in the experiments of treating actual wastewater, which could reduce 40% COD of the paper mill aerobic pond effluent. The Fukui function calculation and UHPL C-H RMS/MS analysis elucidated that the 1O2-dominated electrophilic reaction and the ZSM-5-(C@Fe) complex PMS-dominated nucleophilic reaction were the main pathways for CIP degradation and the radical degradation pathway (·OH and SO4-˙) plays auxiliary role. In addition, two new degradation pathways of the N29 and C27 in quinolone ring and the N22 in piperazine ring were discovered. This finding had important implications for the removal of N from organic pollutants.

Selective removal and persulfate catalytic decomposition of diethyl phthalate from contaminated water on modified MIL100 through surface molecular imprinting.

Adsorptive removal of phthalate esters from wastewater combined with their persulfate (PS) catalytic degradation has attracted the attention of many researchers. In this study, the adsorptive and catalytic properties of an MIL100 material obtained by a green synthetic route have been optimized by a surface molecular imprinting technique. Results have shown that there are two steps in the molecular imprinting process. A polymerization is first carried out in the internal channels of the material and the imprinting layer is then formed on the surface. The relative proportions of the starting materials for the synthesis have been optimized through the design of a three-dimensional response surface. The amount of pollutant adsorbed was increased fourfold after surface imprinting, reaching 13.6 mg g-1. The homogeneity of the recognition sites has been evaluated by dynamics calculations and the Freundlich equation. The selective adsorption ability of the material for diethyl phthalate was improved, and the process involved chemical adsorption. The catalytic properties of the material after imprinting were increased about 1.5-fold, indicating that selective adsorption is important. Such molecularly imprinted polymers may potentially serve as good functional materials for the removal of phthalate esters from wastewater.

Facile construction of highly reactive and stable defective iron-based metal organic frameworks for efficient degradation of Tetrabromobisphenol A via persulfate activation.

Achieving large pore size, high catalytic performance with stable structure is critical for metal-organic frameworks (MOFs) to have more hopeful prospects in catalytic applications. Herein, we had reported a method to synthesize highly reactive yet stable defective iron-based Metal organic frameworks by using different monocarboxylic acids with varying lengths as a modulator. The physical-chemical characterization illustrating that modulators could improve the crystallinity, enlarge pore size and enhance catalytic performance and octanoic acid (OA) was screened to be the suitable choice. The catalytic performance of catalysts was detected through persulfate (PS) activation for degrading Tetrabromobisphenol A (TBBPA). The study demonstrated that the highest degradation efficiency for 0.018 mmol L-1 TBBPA was that 97.79% in the conditions of the 1.0 g L-1 Fe(BDC)(DMF,F)-OA-30 dosage and TBBPA:PS = 200:1. In addition, there was observed that no obvious change of the crystal structure, little the leachable iron concentration in the solutions and no significant loss of catalytic activities of Fe(BDC)(DMF,F)-OA-30 after 5th cycles. The iron valence state of Fe(BDC)(DMF,F)-OA-30 before and after degradation and electrochemical properties reveal that the partial substitution of organic ligands by octanoic acid, when removing OA and forming defects by heat and vacuum treatment to generate coordinatively unsaturated metal sites and accelerate the original transmission of electronic, leading to enhance the activity of persulfate activation for efficient removal TBBPA.

Ferrous metal-organic frameworks with stronger coordinatively unsaturated metal sites for persulfate activation to effectively degrade dibutyl phthalate in wastewater.

In the advanced oxidation system (AOPs) of persulfate (PS) activated by iron-based metal-organic frameworks (MOFs), aim at solving the problem on the treatment difficulty of wastewater with low concentration persistent organic pollutants (POPs), a new type of ferrous metal-organic frameworks (Fe(Ⅱ)-MOFs) with stronger coordinatively unsaturated metal sites (CUS) was successfully synthesized by different methods. The catalytic performance of Fe(Ⅱ)-MOFs was were obtained by the experiment of degrading dibutyl phthalate (DBP) through persulfate activation. It was found that the degradation efficiency of 0.018 mmol L-1 DBP was 86.73% under the conditions of 0.40 g L-1 and 2.70 mmol L-1 persulfate at a wide pH range. At the same time, the crystal structure and surface morphology of Fe(Ⅱ)-MOFs did not change significantly after reaction and it could still maintain the removal rate of 75.44% of the target pollutants in the fifth cycle. Furthermore, in the consideration of iron valence state of MOFs before and after reaction, and combined with the analysis of electrochemical properties, the possible mechanism of PS activation was proposed, namely the metastable electron layer inside ferrous ions produced the internal power to accelerate the electron transfer in CUS, leading to improve the activity of the catalyst.

Synthesis of iron-based metal-organic framework MIL-53 as an efficient catalyst to activate persulfate for the degradation of Orange G in aqueous solution.

A series of MIL-53(Fe) materials were synthesized using a solvothermal method under different temperature and time conditions and were used as catalysts to activate persulfate and degrade Orange G (OG). Influences of the above conditions on the crystal structure and catalytic behavior were investigated. Degradation of OG under different conditions was evaluated, and the possible activation mechanism was speculated. The results indicate that high synthesis temperature (larger than 170 °C) leads to poor crystallinity and low catalytic activity, while MIL-53(Fe) cannot fully develop at low temperature (100 or 120 °C). The extension of synthesis time from 5 h to 3 d can increase the crystallinity of the samples, but weakened the catalytic activity, which was caused by the reduction of BET surface area and the amount of Fe (II)-coordinative unsaturated sites. Among all the samples, MIL-53(Fe)-A possesses the best crystal structure and catalytic activity. In optimal conditions, OG can be totally decolorized after degradation for 90 min, and a removal rate of 74% for COD was attained after 120 min. The initial solution pH had great influence on OG degradation, with the greatest removal in acidic pH environment. ESR spectra showed that sulfate radical (SO4- ·), hydroxyl radical (OH·), persulfate radical (S2O8- ·), and superoxide radical (O2·) exist in this system under acidic conditions. Furthermore, with the increase of pH, the relative amount of O2· increases while that of OH· and SO4- · decreases, resulting in a reduced oxidizing capacity of the system.