A mesoporous surface benzonitrile functionalized covalent organic framework (TpBD-CN-COF) was synthesized as a novel solid-phase microextraction (SPME) fiber coating for the extraction of six hydroxyphenyl esters (PBs), and combined with gas chromatography-flame electric-ion detector (GC-FID). PBs were sensitively determined in aqueous solution. Due to its high specific surface area, high chemical stability in both strongly acidic and alkaline media, and in polar or non-polar media, as well as its high thermal stability, the TpBD-CN-COF fiber coating showed excellent extraction performances for PBs with an enrichment factor twice as high as that of TpBD-COF. Some parameters that influenced the extraction performance, such as extraction time and temperature, pH, and stirring speed were investigated. Under optimal conditions, a wide linear range (0.06–500 μg L−1), low limits of detection (LOD, 0.003–0.042 μg L−1) were obtained for PBs determination. The relative standard deviations (RSDs, n = 6) for intra-day, inter-day, and fiber-to-fiber were less than 8.06

A multi-step growing and etching method was used to synthesize metal-organic framework materials (MIL-101) with a hollow structure of distinct shell layers. The resorcinol-formaldehyde organic aerogel (RFOA) was embedded in-situ into the triple-shelled hollow MIL-101 (TSHM) to form a novel RFOA@TSHM spherical multilayer shell composite, which was used as a fiber coating material of solid-phase microextraction for the enrichment and determination of six tetracyclines (TCs) by coupling with HPLC-UV-vis detector in aqueous solutions. Due to the embedding of the RFOA and the multilayer shell structure, the RFOA@TSHM composite is characterized by a stable structure with a larger pore size and specific surface area compared with the TSHM alone. Under optimal conditions, limits of detection of 0.13-1.16 mu g L-1 and limits of quantification of 0.43-3.83 mu g L-1 were obtained for TCs detection. Moreover, the RFOA@TSHM coating fiber was successfully applied to detect TCs in egg and milk real samples.

Detecting volatile organic compounds is essential to improving the environment and human health. This study prepared a novel composite of hollow SnO2/ZnO cubes using a self-template hydrothermal method followed by a calcination process. The morphology and structure of the composites were characterized using a series of analysis techniques, and the formation mechanism of a hollow cube-like structure was explored. Compared to the hollow SnO2 cube sensor, the hollow SnO2/ZnO cube sensor exhibited a strong response (148-100 ppm formaldehyde), fast response/recovery time (15 s/25 s), good linearity (R2 = 0.995), good repeatability, and excellent stability. The superior gas sensing property of the hollow SnO2/ZnO cubes was attributed to the combined advantages of hollow structures and heterojunctions.

In 2 O 3 octahedronswere obtained using a simple freeze-dryingprocessfollowedby a calcination treatment. The morphology and chemical composition of the samples were investigated by field emission scanning electron microscopy (SEM), transmission electron microscopy, and X-ray diffraction (XRD). The In 2 O 3 sample had an octahedron shape, a smooth surface, high crystallinity, and a particle size of approximately 4 $\mu$ m. X-ray photoelectron spectroscopy (XPS) verified the existence of chemisorbed dissociated oxygen on the surface of the In 2 O 3 octahedrons, which has a meaningful impact on the sensing performance, leading to a high response. When used as a sensing material for volatile organic compounds (VOCs) detection, In 2 O 3 octahedrons exhibited superior sensing performance for isopropanol, ethanol, methanol, and acetone. The detection limits (LODs) of isopropanol and ethanol were 0.60 and 0.57 ppm (signal-to-noise ratio, S/N = 3), respectively. In addition, the In 2 O 3 octahedron sensor exhibited a short response, rapid recovery time, and good stability under long-term testing. The influence of the relative humidity (RH) on the In 2 O 3 octahedron sensor performance was also investigated. The outstanding sensing property of In 2 O 3 octahedrons was attributed to their high crystallinity and unique morphology.

In this study, an oxygen self-doped carbon aerogel (ODCA), synthesized via ambient pressure drying and carbonization, was employed as solid-phase microextraction (SPME) coating material for phthalate esters (PAEs) detection in water samples by gas chromatography (GC) coupled with a flame ionization detector (FID). The materials were obtained by incomplete carbonization of the phenolic aerogel at a controlled temperature of 950 degrees C, which leads to a certain amount of oxygen self-doping in the carbon aerogel. The ODCA-coated fiber exhibited fascinating extraction properties for PAEs mainly due to its oxygen active sites, pi-pi interaction, high surface area, and porosity of carbon aerogel. This as-proposed fiber showed wide linearity ranges (0.5-500, 1.0-500, 1.0-1000, 2.0-500 mu g L-1, respectively), and provided low limits of detection (LOD, 0.17-0.83 mu g L-1) for PAEs analysis under the optimal conditions. The single fiber and fiber-to-fiber relative standard deviations at 100 mu g L-1 were observed in the range of 5.31%-10.37% and 9.17%-16.65%, respectively. Moreover, this method was also used for the determination of five PAEs in real water samples.

Hexavalent chromium (Cr(VI)) pollution is a global problem, and the reduction of highly toxic Cr(VI) to less toxic Cr(III) is considered to be an effective method to address Cr(VI) pollution. In this study, low-toxicity carbon quantum dots (CQDs) were used to reduce Cr(VI) in wastewater. The results show that CQDs can directly reduce Cr(VI) at pH 2 and can achieve a reduction efficiency of 94% within 120 min. It is observed that under pH higher than 2, CQDs can activate peroxymonosulfate (PMS) to produce reactive oxygen species (ROS) for the reduction of Cr(VI) and the reduction efficiency can reach 99% within 120 min even under neutral conditions. The investigation of the mechanism shows that the hydroxyl groups on the surface of CQDs can be directly oxidized by Cr(VI) because of the higher redox potential of Cr(VI) at pH 2. As the pH increases, the carbonyl groups on the surface of CQDs can activate PMS to generate ROS, O2•-, and 1O2, which result in Cr(VI) being reduced. To facilitate the practical application of CQDs, the treatment of Cr(VI) in real water samples by CQDs was simulated and the method reduced Cr(VI) from an initial concentration of 5 mg/L to only 8 μg/L in 150 min, which is below the California water quality standard of 10 μg/L. The study provides a new method for the removal of Cr(VI) from wastewater and a theoretical basis for practical application.

In this study, a hybrid composite featuring zeolitic imidazolate framework-8/carbon aerogel (ZIF-8/CA) was synthesized via in situ nucleation and growth of ZIF-8 nanoparticles inside carbon aerogels. The novel material was used as the solid-phase microextraction (SPME) coating for the five phthalic acid esters (PAEs) detection by coupling with a gas chromatography–flame ionization detector (GC-FID). Compared with bare carbon aerogel, the ZIF-8/CA presented the best performance, which is attributed to the unique advantages between the high surface area of CA and high hydrophobic properties, the thermal stability of ZIF-8, and their synergistic adsorption effects, such as molecular penetration, hydrogen bond, and π–π stacking interactions. Under the optimized conditions, the as-proposed ZIF-8/CA fiber provided a wide linearity range from 0.2 to 1000 μg L−1 and a low detection limit of 0.17–0.48 μg L−1 for PAEs analysis. The intra-day and inter-day of signal fiber and the fiber–fiber relative standard deviations were observed in the ranges of 3.50–8.16%, 5.02–10.57%, and 5.66–12.11%, respectively. The method was applied to the determination of five PAEs in plastic bottled and river water samples.

A carbon aerogel composite templated and catalyzed by ionic liquid was fabricated to obtain a meso-porous and cross-linked structure while avoiding the freeze and supercritical drying. It was then carboxylated to obtain favorable surface groups. The easily prepared material displayed excellent extraction effect of six tetracyclines (TCs) compared to the non-carboxylated carbon aerogel. A direct immersion solid-phase microextraction method to determine six TCs in aqueous samples was developed coupling with high-performance liquid chromatography (HPLC) with UV-Vis detector set at 355 nm. The experimental parameters affecting the analytical performance of this method, including sample pH, ionic strength, extraction and desorption time, extraction volume, and temperature, were optimized. Adsorption kinetics and thermodynamics models were used to clarify the extraction mechanism. Under the optimized conditions, this method has a wide linear range of 2–1000 μg L−1, low limits of detection of 0.36–0.71 μg L−1, repeatability of 1.85–10.96%, and reproducibility of 4.92–13.47% for six TCs. The method was successfully applied to detect TC residues in egg and poultry farm wastewater samples.

Free-standing cobalt oxide nanoflakes were synthetized directly on a glassy carbon electrode via an onestep electrodeposition. A stable and sensitive amperometric sensor based on the cobalt oxide nanoflakes was developed for the acetaminophen detection, with a high sensitivity of 5042 mu A center dot mM(-1)center dot cm(-2), and a detection limit of 0.015 mu M at the applied potential of 0.47 V. The high sensitivity and stability towards acetaminophen detection are mainly attributed to direct electrochemical growth and self-supported features of the cobalt oxide nanoflakes on a conducting substrate. The sensor was successfully applied for the determination of acetaminophen in serum, urine samples and commercial tablets.

A direct immersion solid-phase microextraction method for determining tetracyclines (TCs) was developed by coupling with high-performance liquid chromatography. A carbon aerogel (CA) was synthesized as a fiber coating with high extractive properties and a low density of 0.1855 g cm-3via ambient pressure drying and carbonization. The as-synthesized CA exhibited a high specific surface area and a cross-linked structure; it was characterized via scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analysis, etc. The extraction performance for six TCs was investigated, and the main experimental parameters were optimized by the Box-Behnken design. Adsorption kinetics, Langmuir and Freundlich models were used to clarify the extraction mechanism. This method showed wide linear ranges of 1-500 μg L-1, low limits of detection of 0.52-1.05 μg L-1, good repeatability of 1.37-12.47%, and satisfactory inter-fiber reproducibility of 8.51-15.81% relative standard deviation for the detection of six TCs. Moreover, this study provided an interesting insight into the detection of TCs residues in food samples.

The aim of this research is to degrade organic contaminants in aqueous solution via lead ferrite (PbFe2O4) as a catalyst to activate peroxymonosulfate (PMS). PbFe2O4 was synthesized by a citrate combustion method and analyzed by SEM, TEM and XRD. A simulated solution including thionine were used, with different conditions tested to optimize the degradation process, including comparing PbFe2O4 to other catalysts, PbO and Fe2O3, and tracking active oxygen species. The concentrations of thionine and PMS were tracked with a UV-Vis spectrophotometer in the treatment process. The data are presented as graphs and tables. A detailed analyses of this report can be found in the article “New insight into the mechanism of peroxymonosulfate activation by nanoscaled lead-based spinel for organic matters degradation: a singlet oxygen-dominated oxidation process” published in Journal of colloid and interface science.

Peptide chains that can be specifically hydrolyzed by trypsin were synthesized and fabricated with Au NPs-MCA on a QCM electrode for the sensitive quantification of trypsin in a complex matrix.

Sensitive and selective detection of nicotinamide adenine dinucleotide (NADH) is of great importance since it plays crucial roles in the living organism. In this work, a novel sandwich structural electrochemical sensor was fabricated by the electropolymerization of 3-aminophenylboronic acid (APBA) on reduced graphene oxide modified electrode for nicotinamide adenine dinucleotide (NADH) detection. Based on boronate affinity, NADH can be anchored on the sensing interface through the covalent bond between the cis-diol group of NADH and the boric acid of APBA. Moreover, due to the polyphenolic hydroxyl structure, the anchored NADH can further be bound with ferrocene boric acid (FcBA) in solution via the second boronate affinity. Thus, a dual-signal aroused from the oxidation peak currents of NADH and FcBA were employed for the detection of NADH with improved sensitivity, resulting in a wide linear range of 5.0 x 10(-8)-1.0 x 10(-5) mol/L and a low limit of detection of 2.6 x 10(-8) mol/L (S/N = 3). In addition, double boronate affinity endowed the sensor with excellent selectivity to NADH. With the good repeatability and stability, the prepared sensor was employed to determine NADH in human blood serumsamples with satisfactory results.

Crystalline iron-based nanoparticles with spinel structure have received great attention for catalyzing peroxymonosulfate (PMS). This study introduces lead ferrite (PbFe2O4) as a novel, simple, and efficient catalyst to activate PMS for the degradation of organic contaminants in aqueous solution. The results indicated that, under pH 9.0, nearly 100% of 10 mu M thionine was removed in 20 min. Operation factors, including pH, oxidant concentrations, catalyst dosage, and coexisting ions, were investigated and found to be influential for the thionine removal. PbFe2O4 showed higher catalytic activity and lower ions leaching than well-crystallized lead oxide (PbO) and ferric oxide (Fe2O3). The results from the characterization of the PbFe2O4 with X-ray diffraction (XRD) before and after reaction suggested that the structure and properties of the catalyst kept stable, and the recovered catalyst exhibited good catalytic performance during the recycling batch experiments. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra revealed that singlet-oxygen (O-1(2)) is the dominant active oxygen species rather than sulfate radical for thionine degradation in PbFe2O4/PMS system. Meanwhile, the possible pathways of O-1(2) generation were proposed: the redox reaction between Pb(IV)/Pb(II) and PMS may play an key role in PMS activation. This study provides an interesting insight in PMS activation by the high-efficient non-radical process, and the PbFe2O4 could be as efficient and recyclable heterogeneous catalyst for organic degradation. (C) 2020 Elsevier Inc. All rights reserved.

The present study develops a rapid, simple and efficient method for the determination of type IV collagenase by using a specific peptide-modified quartz crystal microbalance (QCM). A small peptide (P1), contains a specific sequence (Pro-Gly) and a terminal cysteine, was synthetized and immobilized to the surface of QCM electrode via the reaction between Au and thiol of the cysteine. The peptide bond between proline and glycine can be specific hydrolyzed cleavage by type IV collagenase, which enabled the modified electrode with a high selectivity toward type IV collagenase. The cleaving process caused a frequency change of QCM to give a signal related to the concentration of type IV collagenase. The morphologies of the modified electrodes were characterized by scanning electron microscope (SEM) and the specific hydrolyzed cleavage process was monitored by QCM. When P1 was modified with gold nanoparticles (P1-Au NPs), the signal could be amplified to further enhance the sensitivity of the designed sensor due to the high-mass of the modified Au NPs. Compared the direct unamplified assay, the values obtained for the limit of detection for type IV collagenase was 0.96 ng mL(-1), yielding about 6.5 times of magnitude improvement in sensitivity. This signal enhanced peptide based QCM biosensor for type IV collagenase also showed good selectivity and sensitivity in complex matrix.

A novel label-free strategy for the detection of bacteria was developed by using a specific antimicrobial peptide (AMP)-functionalized quartz crystal microbalance (QCM) electrode. This electrode interface was successfully applied to detect pathogenic Escherichia coli O157:H7 based on the specific affinity between the small synthetic antimicrobial peptide and the bacterial cell of pathogenic E. coli O157:H7. The concentrations of pathogenic E. coli O157:H7 were sensitively measured by the frequency response of the QCM with a detection limit of 0.4cfuμL−1. The detection can be fulfilled within 10min because it does not require germiculture process. On the other hand, if the specific antimicrobial peptides were immobilized on a gold electrode, this label-free strategy can also be performed by electrochemical impedance spectroscopy (EIS). Compared with QCM technique, the EIS measurement gives a lower sensitivity and needs a longer assay time. The combination of antimicrobial peptides with the real-time responses of QCM, as well as electronic read-out monitoring of EIS, may open a new way for the direct detection of bacteria.

An electrochemical quartz crystal microbalance (EQCM) can be used as electrochemical stripping sensor for mercury (II) detection. Due to the frequency changes of EQCM electrode were used as analytical signal instead of currents, the influence of interference current would not be considered. To improve the sensitivity and signal response range, a QCM electrode, modified with Nafion film and Au-nanoparticles (Au-NPs), was employed as a stripping detector for mercury (II) determination in 0.1 M perchloric acid. The cooperation of Au-NPs and Nafion on the gold electrode surface provided an environment for the enhanced electrodeposition of mercury (II). The prepared sensor exhibited a wide linear response to mercury (II) in the concentration range of 3-300 nM (correlation coefficient of 0.9968), with a detection limit of 0.15 nM. The Nafion film was placed between the Au-NPs and the QCM gold-based electrode, which prevented the direct deposition of mercury onto the QCM goldbased electrode surface, and resulted in the easier regeneration of composites modified electrodes. On the other hand, the roughness of electrode surface increased owing to the modification of Nafion film, which would provide much more area for the immobilization of Au-NPs.

A quartz crystal microbalance (QCM) biosensor for theophylline was developed by recognition of RNA aptamer and gold nanoparticle amplification technique. Firstly, a designed small single-stranded RNA, RNA1, was immobilized onto the QCM electrode through a thiol linker. Then, the complementary stranded RNA2, which can combine with RNA1 to form a double-stranded RNA with a recognition unit of theophylline, could be self-assembled on the QCM electrode surface through a hybrid reaction in the presence of theophylline. The recognition process could cause a frequency change of QCM to give the signal related to theophylline. When RNA2 was tethered to gold nanoparticles, the signal could be amplified to further enhance the sensitivity of the designed sensor. Under the optimal conditions, the QCM-based biosensor showed excellent sensitivity (limit of detection, 8.2 nM) and specificity with a dissociation constant of Kd = 5.26 × 10(-7) M. The sensor can be used to quantitatively detect theophylline in serum, suggesting that it can be applied in complex biological samples.