Wang Xiaoxia,Yu Jianhua,Dong Hongzhou,Yu Mingxun,Zhang Baoqin,Wang Wen,Dong Lifeng
In this work, metal oxide (MnO 2 , SnO 2 and Co 3 O 4 )–graphene composite materials were successfully prepared via different synthesis methods. Uniform metal oxide nanoparticles were well dispersed on graphene sheets, and transmission electron microscopy characterizations showed that the average sizes of MnO 2 , SnO 2 , and Co 3 O 4 particles were about 60, 5, and 10 nm, respectively. Reflection losses of graphene composites and pure graphene were systematically evaluated between 2 and 18 GHz, which revealed that all composites exhibited enhanced microwave absorption properties compared to pure graphene. The minimum reflection losses of MnO 2 -graphene, SnO 2 –graphene, and Co 3 O 4 –graphene composites with a thickness of 2.0 mm were −20.9, −15.28, and −7.3 dB at the frequency of 14.8, 15.94, and 9.6 GHz, respectively, whereas −4.5 dB for pure graphene. The enhanced absorption ability probably originated from the combined advantage of metal oxide particles and graphene, which proved beneficial to improve the impedance matching of permittivity and permeability. Besides, the intrinsic characteristics of MnO 2 , SnO 2 , and Co 3 O 4 nanoparticles, the interface between nanostructured metal oxides and graphene sheets, and the multi-dielectric relaxation processes are all influence factors to improve the properties of microwave absorption.
Lei Shi,Xudong Zhou,Yujie Guo,Yunyu Li,Chenxu Yan,Qifeng Han,Lingfan Zhang,Wenqing Zhang
The Mn-based catalysts, with low cost and high activity, are believed to be the effective composites for eliminating in-door formaldehyde (HCHO), while the powdered form nanosized catalysts are hardly to apply for practical application. Herein, hetero-structure of nanosheets manganese oxide (MnO 2 ) encapsulating N-doping graphene sphere ( GS ) were deposited in network-like sponge for constructing 3D catalyst. The prepared MnO 2 -GS-Sponge composite catalyst exhibited excellent performance for removing HCHO at room temperature compared with GS and commercial MnO 2 . The MnO 2 -GS with larger specific surface area (209.1 m 2 ·g −1 ) was dispersed evenly in 3D network of sponge, which facilitated exposing more activate sites and achieving fast transport kinetics accelerating catalytic reaction for converting 97.1 % of 100 ppm of HCHO continuously to CO 2 for 120 h. Moreover, rely on the chemisorption of amino groups on N-doping GS surface, HCHO could be enriched even at low concentrations and efficient elimination (from 1000 ppb to12 ppb, at 35 ℃ in 48 h). The average oxidation state and infrared spectra analysis suggested that abundant oxygen vacancies on MnO 2 -GS-Sponge could be identified as surface-active sites of converting HCHO into the intermediates of dioxymethylene and formate. This work might inspire the designing 3D composite material for potential application in other fields of environmental engineering or energy industrial.
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