Controllable assembly of hollow interpenetrated zeolite imidazole framework nanocomposite for dopamine charge collection.

The synergistic armor-etching (SAE) approach was proposed using natural organic weak acid (tannic acid, i.e., TA) for the controllable assembly of hollow and interpenetrated HZIF-8@MWCNTs hybrid nanomaterial (ZIF-8, zeolitic imidazolate framework-8; MWCNTs, multi-walled carbon nanotubes), which exhibited highly ordered crystal structure and unique morphological characteristics. The SAE strategy not only can rapidly etch solid ZIF- material into a hollow structure (~ 10 min), but also form the TA shell (~ 33 nm) on its surface. Then, the HZIF-8@MWCNTs electrochemical sensor was constructed for selective and sensitive detection of the target molecule (dopamine, DA). A sequence of studies indicated that the fabricated TA coating was capable of promoting the spread of DA into the reactive centers of hollow MOF and MWCNTs, which exhibited outstanding electroanalytical characteristics through the synergistic effect. The DPV oxidation peak of DA was strongest at 50 mV vs. Ag/AgCl reference electrode. Under the optimal conditions, there are two linear dynamic ranges of current response of 0.01 ~ 10 and 10 ~ 550 µmol L- 1 with a detection limit of 0.003 µmol·L- 1 (S/N = 3). Simultaneously, the HZIF-8@MWCNTs electrochemical sensor could detect low levels of DA in real products. The recoveries of the actual sample tests were between 98.2% and 102%, and the relative standard deviation (R.S.D.) of all studies was less than 3.0%. The statistical analyses (F-test and t-test) were employed to demonstrate the accuracy of method developed. This work will enlighten researchers operating in the domain of MOFs composites, accelerating the advancement of electrochemical sensing on the basis of hollow MOFs materials.

Triple-signaling amplification strategy based electrochemical sensor design: boosting synergistic catalysis in metal-metalloporphyrin-covalent organic frameworks for sensitive bisphenol A detection.

A covalent organic framework (COF) is a promising type of porous material with customizable surface characteristics. Confining multiple catalytic units within a mesoporous COF can generate abundant active sites and improve the catalytic performance. In this work, a COF with both metalloporphyrin and a metal nanoparticle complex denoted as hemin/TAPB-DMTP-COF/AuNPs (TAPB: 1,3,5-tris(4-amino-phenyl)benzene, DMTP: 2,5-dimethoxyterephaldehyde, AuNPs: Au nanoparticles) has been successfully fabricated through a hierarchical encapsulation method. The as-synthesized composite was then employed to construct an electrochemical sensing platform for the efficient detection of bisphenol A (BPA). Under the optimal conditions, the hemin/TAPB-DMTP-COF/AuNP sensor presented a linear range of 0.01-3 µmol L-1 and a low detection limit of 3.5 nmol L-1. The satisfactory signal amplification is based on a triple-signaling amplification strategy due to the abundant Fe3+ sites of Fe-porphyrin, high conductivity of AuNPs and a large specific surface area of the TAPB-DMTP-COF. The proposed method was used to measure the content of BPA in different water samples with a satisfactory recovery from 95.5 to 104.0%, suggesting the great potential of the sensor in practical applications.

Ultrasensitive Electrochemical Detection of Butylated Hydroxy Anisole via Metalloporphyrin Covalent Organic Frameworks Possessing Variable Catalytic Active Sites.

Three novel two-dimensional metalloporphyrin COFs (MPor-COF-366, M = Fe, Mn, Cu) were fabricated by changing the metal atoms in the center of the porphyrin framework. The physicochemical characteristics of MPor-COF-366 (M = Fe, Mn, Cu) composites were fully analyzed by diverse electron microscopy and spectroscopy. Under optimal conditions, experiments on determining butylated hydroxy anisole (BHA) at FePor-COF-366/GCE were conducted using differential pulse voltammetry (DPV). It is noted that the FePor-COF-366/GCE sensor showed excellent electrocatalytic performance in the electrochemical detection of BHA, compared with MnPor-COF-366/GCE and CuPor-COF-366/GCE. A linear relationship was obtained for 0.04-1000 µM concentration of BHA, with a low detection limit of 0.015 µM. Additionally, the designed sensor was successfully employed to detect BHA in practical samples, expanding the development of COF-based composites in electrochemical applications.

In-situ anchoring bimetallic nanoparticles on covalent organic framework as an ultrasensitive electrochemical sensor for levodopa detection.

Covalent organic frameworks (COFs) have been studied in many fields. However, their electrochemical properties were seldom reported. In this work, a novel high electrocatalytic material was synthesized by incorporating bimetallic nanoparticles (AgCoNPs) in a two-dimensional (2D) porous TAPB-DMTP-COF, (AgCo/TAPB-DMTP-COF, TAPB, 1,3,5-tris(4-aminophenyl)benzene; DMTP, 2,5-dimethoxyterephaldehyde). Subsequently, the resulting composite was further used to construct a novel electrochemical sensor for the ultrasensitive determination of levodopa. The analytical performance has been improved significantly due to the synergistic effect of both TAPB-DMTP-COF and AgCoNPs by increasing effective electroactive surface area and electron transfer efficiency. The linear detection range of the levodopa sensor was 0.010-100 µmol L-1. The limits of detection and quantitation were found to be 0.002 and 0.006 µmol L-1, respectively. Moreover, the sensor exhibits an excellent stability and maintains its catalytic activity after 100 scanning rounds. The applicability of the electrochemical sensor was successfully applied for the determination of levodopa content in human urine and blood serum samples. Our study not only supplies a useful tool to accurately detect levodopa in actual samples and, meanwhile, but paves a feasible way to unlock high performance 2D COF based electrode materials.

A bi-metallic MOF catalyst via sensitive detection & adsorption of Fe3+ ions for size-selective reaction prompting.

A cadmium(ii)-based MOF, Cd-MDIP, was successfully prepared by hydrothermal reaction between the tetra-carboxylic ligand 5,5'-methylenebisophthalic acid (H4MDIP) and cadmium perchlorate. The X-ray crystal structure analysis showed that there are two uncoordinated carboxyl groups in each ligand and a 1D elliptical channel along the [001] direction. Because of the existence of uncoordinated carboxyl groups within open frameworks, Cd-MDIP exhibited a high sensitivity (Stern-Volmer constant KSV = 4.13 × 104 L mol-1) and a low detection limit (80 nM) for Fe3+ ions in pure water, which is much lower than the national standard for Fe3+ in daily drinking water (5.4 µM) set by the Ministry of Environmental Protection of P. R. China. Most importantly, Cd-MDIP also featured the ultrahigh adsorption of Fe3+ in aqueous solution that cannot be destroyed even by EDTA/base. Importantly, the MOF material (Cd-MDIP⊃Fe3+) after adsorbing Fe3+ could act as the first example of an excellent bi-metallic Lewis-acid catalyst for the cyanosilylation reaction of aromatic aldehydes in a size-selective fashion, and its efficiency was almost 10-times higher than that of the original Cd-MDIP.