Article pubs.acs.org/JPCC
Facile Strategy To Prepare Light-Weight PVA Membrane Based on Schiff Base Derivatives and MWCNTs for Electromagnetic Wave Absorption Jun Li, Lu Qi,* and Huihao Li Tianjin Key Laboratory of Fiber Modification and Functional Fiber,Research Institute of Biologic and spinning Materials, Tianjin Polytechnic University, Tianjin 300387, China ABSTRACT: The carbon-nanotube-doped Schiff bases (CDSBs) and their iron complexes (CDSI) were synthesized by the in situ polymerization and coordination reaction. The phase structure and morphology of the samples were investigated by X-ray diffraction analysis and field-emission scanning electron microscopy. In particular, it can be found that the diamagnetic substance CDSF turns into paramagnetic CDSI after doping Fe3+. Furthermore, the eminent electrical conductivity and microwave electromagnetic loss behavior of CDSI shed light on organic−metal ion complexes (OMICs) as a promising lightweight absorbent. The feasibility of this strategy was demonstrated by the successful fabrication of the CDSI/ MWCNTs/PVA composites membrane. The reflection loss (RL) of the electromagnetic wave arrives at the lowest value −18.6 dB at 10.32 GHz, and the effective bandwidth (RL below −10 dB) could reach 5.8 GHz (8.1 to 13.04 GHz) with the thickness of 0.54 mm and the surface density of 0.44 kg/m2. Such excellent low weight, low thickness, and broadband electromagnetic wave absorption membrane may pave the way for new applications of OMIC-derived materials. contributive for the dielectric property of Schiff base crystal.15,16 On this basis, the Schiff bases were grafted to multiwalled carbon nanotubes (MWCNTs) with the purpose of obtaining a light-weight dielectric absorber; then, Fe3+ was further doped into the composite to increase the magnetic loss property. After doping Fe3+, the charges transfer from Fe3+ to Schiff-based ligand and the phenyl rings have a π−π* intraligand transition.17 Because of the geometrical constrains and π−π stacking, the phenyl rings are twisted across the C−C single bond, the Schiff base monomers are grafted on the MWCNTs, and the Fe3+ is linked around CN, all of which contribute to forming 3D heterogeneous network structure. The most attractive advantage of this synthetic strategy is that the conductivity of the Schiff base can be altered to insulator, semiconductor, and conductor in a facile manner by controlling dopant species and conditions.14,18,19 Herein this paper is an attempt for organic−metal ion complex (OMIC) absorbents instead of ferromagnetic metal particles, the synthetic strategy has a significant potential for fabricating lightweight composite of OMIC and carbon material with 3D heterogeneous network. Poly(vinyl alcohol) (PVA) can be used as a matrix for EWA agent due to its easy fabrication in various shapes as well as excellent mechanical properties, low weight, and low cost. However, it is worth mentioning that only a few papers
1. INTRODUCTION Electromagnetic wave has been widely used in daily life, such as mobile phone, local area network, household appliances, as well as industrial production. However, the thermal effects, nonthermal effects, and cumulative effects caused by electromagnetic radiation could cause harm to human health, and this damage is becoming increasingly serious with social progress and human development.1−3 In the past decades, significant efforts have been devoted to solve these problems. The electromagnetic wave-absorbing (EWA) materials have attracted much attention due to the potential of wide frequencyabsorbing bandwidths, powerful absorption, low weight, and thin thickness. The carbon-based materials4−6 and the ironbased materials7,8 as the representative for the dielectric loss absorbers and magnetic loss absorbers have been well explored. By incorporating both kinds of absorbers together, a strong absorption of electromagnetic energy in a wide frequency range can be achieved.9,10 Hence, the multielement composites are preferred as effective absorption materials. Schiff bases11−13 as an important class of ligands play a crucial role in coordination chemistry and have been widely applied in different fields such as asymmetric catalysis, luminescent probes, and biological pharmacy. In addition, transition-metal complexes of Schiff base ligands gradually draw attention as a type of organic EWA agent.14 In this work, the Schiff base derived from condensation reaction between benzaldehyde and p-phenylenediamine contains the C−H···O (N, π) hydrogen bonds and π−π interactions, which are © XXXX American Chemical Society
Received: July 23, 2016 Revised: September 11, 2016
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DOI: 10.1021/acs.jpcc.6b07383 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 1. Synthesis route of the carbon-nanotube-doped Schiff base iron complexes.
dropwise into the flask by constant pressure funnel. After magnetic stirring for 2 h at 55 °C, pale-yellow precipitates were generated. After cooling to room temperature, the resulting precipitates were separated by filtration and washed thoroughly with anhydrous ethanol. The precipitates were further dried in a vacuum at 50 °C for 12 h. 2.3. Preparation of the Schiff Base Iron Complex (SBIC). The SFB 0.01 mol (2.88 g) was dissolved in anhydrous ethanol (50 mL), then added to a three-necked flask, equipped with a water-cooling condenser. Afterward, FeCl3 0.03 mol (4.86 g) was added dropwise to the flask by constant pressure funnel. After magnetic stirring for 4 h at 80 °C, dark-brown precipitates were generated. The mixture was condensed to 20 mL with rotary evaporator, and the precipitates were filtrated and washed thoroughly with anhydrous ethanol. The precipitates were further dried in a vacuum at 50 °C for 12 h. 2.4. Preparation of Acyl Chloride MWCNTs (MWCNTCOCl). Dried MWCNT-COOH (0.56 g) was suspended in 50 mL of SOCl2 and stirred at 60 °C for 24 h. The solid was then separated by filtration and washed with anhydrous THF. Subsequently, it was dried under vacuum at 50 °C for 12 h. 2.5. Preparation of Carbon-Nanotube-Doped Schiff Base (CDSF) Composite. The synthesis of CDSF was similar to that of SFB, except that 0.5 g MWCNT-COCl was added to the flask in the first step and the reaction time was increased to 4 h. Greyish-green powders were obtained and vacuum-dried for further test. 2.6. Synthesis of the Carbon-Nanotube-Doped Schiff Base Iron Complexes (CDSIs). The synthesis of CDSI was similar to SBIC, only that 0.3 g CNDF was used instead by SFB. Black powder was obtained and vacuum-dried for further test.
reported the actually measured value of the reflection loss (RL), which was just simulated based on the measured complex permittivity and permeability with a given absorber thickness. Because of the effect of experiment conditions and environment and artificial factors, the calculated RL value cannot accurately reflect the true value. Therefore, we synthesized the EMA membrane fabricated by incorporating MWCNTs and CDSB/CDSI into the PVA matrix with low thickness (
