Confined self-assembly of S, O co-doped GCN short nanotubes/EG composite towards HMIs electrochemical detection and removal

Highly selective detection and removal of mercury ions in the aquatic environment based on magnetic ZIF-71 multifunctional composites with sufficient chlorine functional groups

The development of both detection and removal technologies for heavy metal ions is of great importance. Most of the existing adsorbents that contain oxygen, nitrogen or sulfur functional groups can remove heavy metals, but achieving both selective detection and removal of a single metal ion is difficult because they bind to a wide range of heavy metal ions. Herein, we selected zeolite imidazolium hydrochloride framework-71 (ZIF-71) with sufficient chlorine functional groups to fabricate magnetic ZIF-71 multifunctional composites (M-ZIF-71). M-ZIF-71 had a large specific surface area, excellent water stability, and good magnetic properties, which made M-ZIF-71 conducive to the separation and recovery of adsorbents and the assembly of electrodes. M-ZIF-71 exhibited high selectivity, wide linear range (1-500 μg/L), and low detection limit (0.32 μg/L) for electrochemical detection of mercury ions (Hg2+). Meanwhile, M-ZIF-71 demonstrated rapid Hg2+ adsorption with a high capacity of 571.2 mg/g and excellent recyclability. The high selectivity for Hg2+ was attributed to the powerful affinity of highly electronegative chlorine and Hg2+. Moreover, XPS spectra demonstrated the interaction between chlorine and Hg2+. This work provides a new inspiration for applications in the targeted monitoring and removal of heavy metal pollution.

Three-dimensional conductive network constructed by in-situ preparation of sea urchin-like NiFe2O4 in expanded graphite for efficient microwave absorption

Expanded graphite (EG) is a modified conductive lamellar carbon that has been widely studied in the field of electromagnetic wave absorption due to its low density, good electrical conductivity, and unique structure. However, its application is limited because the interlayer gap cannot match microwave wavelength, and its single composition has less microwave loss. In this study, sea urchin-like NiFe2O4/EG composites are prepared in situ between expanded graphite layers by microwave treatment. The sea urchin-like NiFe2O4 grows between the expanded graphite to form a three-dimensional conductive network structure, which enhances conductive loss of composites and further increases the interlayer distance of EG. The extended interlayer distance promotes multiple reflections and scattering of electromagnetic waves in composites and improves dielectric properties. In addition, EG with a large specific surface area provides many active sites, further promoting interface and dipole polarization. Benefiting from synergistic effect of NiFe2O4 and EG, magnetic loss and dielectric loss of NiFe2O4/EG composites have been improved and impedance matching is further enhanced. The results indicate that the minimal reflection loss of NiFe2O4/EG-4 reaches -53.47 dB at 2.69 mm, and the effective absorption bandwidth reaches 2.97 GHz. In addition, based on the computer simulation technology results, NiFe2O4/EG can attenuate microwave energy under experimental conditions. This work provides a strategy for synthesizing carbon matrix composites with adjustable dielectric parameters and electromagnetic wave properties.

Photo-assisted "co-movement catalysis": CoFe2O4/CNS heterojunction based portable electrochemical sensor for simultaneous detection of Pb2+ and Cd2+ in natural water

Heavy metal ions (HMIs) seriously threaten human health even under trace conditions. Therefore, accurate, efficient and simultaneous detection of multiple HMIs is of great significance. Here, a strategy of "co-movement catalysis" based on photo-assisted electrochemical catalysis is proposed by constructing a flexible electrochemical sensor with CoFe2O4/CNS heterojunction-modified nickel foam as the working electrode for simultaneous detection of HMIs. Regarding photo-assisted catalysis, CoFe2O4/CNS nanocomposites formed a p-n type heterojunction, effectively separating photo-generated electron-hole pairs and reducing photo-generated carriers' recombination rate, leading to the catalytic reaction of photogenerated electrons and holes with HMIs and atoms to improve the efficiency of preconcentration and stripping, further amplifying the electrochemical signal. Regarding electrochemical catalysis, the CoFe2O4 spinel contains variable valence transition metal ions Fe2+/Fe3+ and Co2+/Co3+, which can reduce and oxidize HMIs circularly, further enhancing the sensor's sensitivity. The portable sensor based on "co-movement catalysis" exhibited sensitive detection performance. The linear range is 0.100-10.0 μM for Pb2+ and 1.00-10.0 μM for Cd2+, with the detection limit of 0.0310 μM for Pb2+ and 0.219 μM for Cd2+, respectively. The recovery rate of the sensor to natural water samples is between 96% and 105%, which proves its development potential in environmental monitoring.