Flexible manipulations of morphology and composition have been considered as an art to achieve excellent microwave absorption performance for absorbers derived from metal-organic frameworks (MOFs). In this work, a strategy combining ligand-exchange induced hollow engineering and high-temperature one-step sulfuration has been proposed to fabricate the Co 9 S 8 /Co@N, S dual-doped carbon-based absorbers with tailored solid, yolk-shelled and entirely hollow polyhedral morphologies. The progressive hollow engineering not only enables composition control in the sulfuration process, but also endows the proposed absorbers with superior microwave absorption capacity due to the enhanced conductivity loss and Maxwell-Wagner polarization as well as optimized impedance matching. The yolk-shelled Co 9 S 8 /Co@N, S dual-doped carbon-based composite achieves a broad effective absorption bandwidth of 5.13 GHz at 1.88 mm with 20 wt% loading and realizes a minimum microwave loss of − 51.78 dB @ 11.63 GHz with 2.37 mm. This work reveals that the joint strategy of ligand-exchange induced hollow engineering and gas-solid reactive thermal process is an effective path to construct high-efficient lightweight multi-interfacial microwave absorbers for addressing the electromagnetic pollutions.
Zhonghui Guo,Yuan Jiao,Fangfang Du,Yifang Gao,Wenjing Lu,Shaomin Shuang,Chuan Dong,Yu Wang
A novel ratiometric emission N, S dual-doped carbon dots (N, S-CDs) were facilely developed for pH visual sensing via one-step hydrothermal method . The proposed N, S-CDs displayed intrinsic pH-sensitive behavior and exhibited ratiometric fluorescence emission (F 563 nm /F 645 nm ) characteristic with the variation of pH values. Interestingly, a significant red shift of emission wavelength can be observed at 645 nm along with the emission at 563 nm decreased accordingly when the pH changed from 3.0 to 1.0. Simultaneously, the fluorescence of N, S-CDs aqueous solution was visually varied from yellow to red. The ratiometric pH linear response was in the region of 3.6 to 2.4 and the pK a was 2.90. Moreover, the N, S-CDs hold unique optical properties , good reversibility, superior biocompatibility and low cytotoxicity, which was further employed to monitor the intracellular pH fluctuations through the visible fluorescence changes between yellow and red. All these findings demonstrated that N, S-CDs can be utilized as the visual biosensor platform for tracking pH variations in extremely acidic environments such as gastric juice, which provided novel insights for clinical medical disease diagnosis (e.g., stomach disease detection) and other biomedical fields.
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