ABSTRACT
The removal and detection of soluble hydrazine is of importance due to its harm to soil and subterranean water, but challenging. Herein, we preferentially disposed a porous and redox active covalent-organic framework (DAAQ-TFP COF, denoted as DQ-COF) to simultaneously removal and detect hydrazine. Electroactive sites (anthraquinone units) can be intelligently incorporated into the channel walls/pores of COF. DQ-COF has high crystallinity and good thermal stability, and DQ-COF dropped onto nickel matrix (DQ-COF/Ni composite) still retains high surface area, characterized by PXRD, FT-IR, nitrogen adsorption and TGA. Subsequently, a detailed study of DQ-COF towards hydrazine uptake and detection potentials is explored. DQ-COF as adsorbent unfolds strong removal ability towards hydrazine, the maximum removal capacity of which is up to 1108â¯mgâ¯g-1, following Friedrich and pseudo-second-order kinetic models. Meanwhile, the DQ-COF supported on nickel renders attractive electrochemical properties, which is efficiently responsive to hydrazine at a part per billion (ppb) level, coupled with a wide linear range (0.5 Ë 1223⯵M), low detection limit (0.07⯵M) and high anti-interference ability. There is no other COFs with such a favorable capability in synchronous removal and selective detection towards hydrazine, probably applying in superintending water quality and disposing wastewater.
ABSTRACT
The first example of metallic bismuth encapsulated into a mesoporous metal-organic framework of the type MIL-101(Cr) matrix is presented. Bi(III)-impregnated MIL-101(Cr) (Bi(III)/MIL-101(Cr)) was dropped onto a conductive carbon cloth electrode (CCE). Then, bismuth was generated by electrochemical reduction of the Bi(III)/MIL-101(Cr) supported on CCE (Bi/MIL-101(Cr)/CCE). The resulting Bi/MIL-101(Cr)/CCE display impressive performance in terms of peak currents for the ions Cd(II) and Pb(II) when compared to the single-component counterparts. Differential pulse anodic stripping voltammetry (DPASV) enabled sensing of the two ions over linear working range of 0.1 to 30 µg L-1 and 30 to 90 µg L-1. The parameters are refined before the detection of two metal ions, including the amount of bismuth in MIL-101(Cr), optimum pH (5.0), deposition potential (-1.2 V) and deposition time (600 s). The respective detection limits are 60 and 70 ng L-1 (at S/N = 3). This is strikingly lower than the guideline values of domestic water given by the WHO which are 3 µg L-1 for Cd(II) and 10 µg L-1 for Pb(II). The Bi/MIL-101(Cr) onto CCE is fairly specific for Cd(II) (at around -0.76 V) and Pb(II) (at around -0.54 V), well reproducible and has excellent recovery in real water analysis. Graphical abstract Schematic illustration of the preparation of a Bi(III)/MIL-101(Cr) metal-organic framework, its deposition on a carbon cloth electrode (CCE), and its application for detection of Cd(II) and Pb(II) by differential pulse adsorptive stripping voltammetry (DPASV).
ABSTRACT
A novel ZIF-Ni composite film has been successfully prepared by a facile method involving the in situ deposition of ZIF-8 on a nickel porous film which is fabricated by selectively etching copper from a dense Ni/Cu alloy film. The nanostructures of the resulting ZIF-Ni composite films are carefully examined by a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray (EDX), and nitrogen adsorption-desorption. Cyclic voltammetric and amperometric studies show the enhanced electrocatalytic properties of the ZIF-Ni composite film electrodes toward hydrazine oxidation relative to the synergistic effect of ZIF-8 and porous Ni films. The application potential of the composite films as amperometric detectors is explored for the determination of hydrazine. A high sensitivity of 805.5 µA mM-1 for hydrazine detection with a low detection limit of 0.021 µM (S/N = 3) and a wide linear range from 2.5 µM to 28 mM are revealed for this new type of composite film as the detecting electrode. Moreover, the composite films exhibit excellent selectivity and remarkable stability for the oxidation of hydrazine. This can offer new opportunities for the fast and selective detection of hydrazine and provide a promising platform for sensor designs for hydrazine detection.
ABSTRACT
A facile electrochemical plating strategy has been employed to prepare the electroactive metal-organic framework film (NENU-3) onto a copper electrode in the acid electrolyte containing 1,3,5-benzenetricarboxylic acid (H3BTC) and phosphotungstic acid (PTA). The as-made NENU-3 films have been characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analyses (TGA). These analyses indicate that NENU-3 films have high phase purity and high stability. Further, different electrochemical techniques are utilized for measuring the electrochemical behaviors of the NENU-3 film electrodes. Accordingly, the kinetic parameters of a NENU-3 film electrode towards the electrocatalytic reduction of bromate are obtained, including the electron transfer coefficient (α), the catalytic rate constant (ks), and the diffusion coefficient (D). The film electrodes present excellent electrocatalytic ability for the bromate reduction, and can be used successfully for the amperometric detection of bromate. Under the optimized conditions, the proposed sensor exhibits a wide linear range (0.05-72.74 mM) and a lower detection limit (12 µM) measured by chronoamperometry (CA). Moreover, the films possess high electrochemical stability and strong anti-interference capability in the bromate detection process. It has been demonstrated that the electrochemical plating method reported here offers a reliable and efficient way to fabricate MOF films on conductive substrates for bromate detection.
