In situ fabrication of Fe3C nanoparticles and porous-carbon composites as high-performance electromagnetic wave absorber.

This study successfully utilized a straightforward approach, choosing liquid-liquid phase separation to build a porous structure and synthesize composite absorbers based on polyimide-based porous carbon/Fe3C (PIC/Fe3C-1, PIC/Fe3C-2) nanoparticles and porous carbon/FeCo alloy nanoparticles (PIC/FeCo). The specially designed network structure pore structures contributed multiple reflection, conduction loss and strong interfacial polarization. After characterization, PIC/Fe3C-2 obtained minimum RL of -35.37 dB at 17.04 GHz with 1.55 mm thickness and effective absorption bandwidth of 4.95 GHz with 1.66 mm thickness. Furthermore, PIC/FeCo, with a thickness of 1.63 mm, exhibits the most robust electromagnetic wave loss ability at 15.6 GHz, with a minimum RL of -56.32 dB and an effective absorption bandwidth of 4.88 GHz. Thus, the design strategy presented in this study could serve as a model for synthesizing other high-performance absorbers, effectively mitigating electromagnetic wave-induced pollution.

Polyimide-based porous carbon and cobalt nanoparticle composites as high-performance electromagnetic wave absorbers.

This study successfully utilized a straightforward approach, choosing liquid-liquid phase separation to build a porous structure and synthesize composite absorbers based on polyimide-based porous carbon and cobalt nanoparticles (designated as PPC/Co-700 and PPC/Co-800). A fine porous structure was achieved as a result of the excellent heat resistance of polyimide resulting in an excellent electromagnetic wave absorption ability of PPC/Co composites. The results obtained clearly indicated that PPC/Co-700 and PPC/Co-800 exhibit a porous structure with coral-like pores, enhancing both impedance matching properties and microwave attenuation abilities. This improvement in impedance matching conditions and dissipation capability is attributed to the synergistic effect of dielectric loss induced by carbon and magnetic loss induced by Co nanoparticles. PPC/Co-700 showed the strongest absorption performance with a minimum reflection loss of -59.85 dB (30 wt% loading, thickness of 3.42 mm) and an effective absorption bandwidth (EABW, RL ≤ -10 dB) of 6.24 GHz (30 wt% loading, thickness of 2.78 mm). Therefore, this work provides a facile strategy for the development of a promising absorbing material with outstanding electromagnetic wave absorption performance.

Polyimide aerogel-derived amorphous porous carbon/crystalline carbon composites for high-performance microwave absorption.

High-performance polyimide-based porous carbon/crystalline composite absorbers (PIC/rGO and PIC/CNT) were prepared by vacuum freeze-drying and high-temperature pyrolysis. The excellent heat resistance of polyimides (PIs) ensured the integrity of their pore structure during high-temperature pyrolysis. The complete porous structure improves the interfacial polarization and impedance-matching conditions. Furthermore, adding appropriate rGO or CNT can improve the dielectric losses and obtain good impedance-matching conditions. The stable porous structure and strong dielectric loss enable fast attenuation of electromagnetic waves (EMWs) inside PIC/rGO and PIC/CNT. The minimum reflection loss (RLmin) for PIC/rGO is -57.22 dB at 4.36 mm thickness. The effective absorption bandwidth (EABW, RL below -10 dB) for PIC/rGO is 3.12 GHz at 2.0 mm thickness. The RLmin for PIC/CNT is -51.20 dB at 2.02 mm thickness. The EABW for PIC/CNT is 4.08 GHz at 2.4 mm thickness. The PIC/rGO and PIC/CNT absorbers designed in this work have simple preparations and excellent EMW absorption performances. Therefore, they can be used as candidate materials in EMW absorbing materials.

Polyimide-derived porous carbon/Co particle-based composites for high-performance microwave absorption.

A simple method that combines liquid-liquid phase separation and high-temperature pyrolysis has been developed for the synthesis of polyimide-derived porous carbon/Co particle-based composite absorbers (PIC/Co-800 and PIC/Co-1000). The excellent heat resistance of polyimide allows the composite precursor to maintain its porous structure during pyrolysis. According to the results, PIC/Co-800 and PIC/Co-1000 have a coral-like porous structure, which can enhance the impedance matching property and microwave attenuation ability of the synthesized materials. The impedance matching condition and dissipation ability of PIC/Co-800 and PIC/Co-1000 have been enhanced due to the synergistic effect between the carbon-induced dielectric loss and Co nanoparticle-induced magnetic loss. PIC/Co-1000 shows the highest absorption performance with a minimum reflection loss (RL) of -40.22 dB at a thickness of 5.3 mm and an effective absorption bandwidth (EABW, RL ≤ -10 dB) of 4.10 GHz at a thickness of 1.4 mm. With thicknesses in the range of 1.4 mm to 5.3 mm, the minimum RL value of each thickness is lower than -15 dB. Therefore, this work provides a new strategy for the synthesis of promising absorbing materials with outstanding EMW absorption performance.

In situ growth of CoNi bimetallic alloys inside polyetheretherketone-derived hierarchical porous carbon as a broadband and efficient electromagnetic wave absorber.

Both morphological structure and chemical composition are the important factors that determine the electromagnetic wave (EMW) absorption properties of EMW absorbers. Herein, hierarchical porous carbon (HPPC) was synthesized by using polyetheretherketone (PEEK) as the starting material via the salt template method combined with KOH activation. Then, taking advantage of the hierarchical porous characteristics of the carbon, a novel EMW absorber (HPPC/CoNi) was synthesized by in situ growth of CoNi bimetallic alloys inside the above porous carbon. The as-synthesized HPPC/CoNi exhibits excellent EMW absorption performance with a minimum reflection loss (RLmin) value of -65.56 dB at 2.00 mm and a maximum effective absorption bandwidth (EAB) of 5.92 GHz at 1.80 mm. The superior EMW absorption property is ascribable to the multiple reflection/scattering induced by the hierarchical porous structure of HPPC, dielectric loss, magnetic loss, and good impedance matching. The results show that HPPC/CoNi is a potential EMW absorber with characteristics of ultra-light weight, ultrathin thickness, broad bandwidth, and strong absorption.

A low-cost and effective bagasse-based magnetic porous biochar as an adsorbent for solid phase extraction of triazine herbicides in brown sugar.

A rapid and sensitive approach for enriching and extracting triazines from brown sugar samples was developed by combining magnetic dispersive solid-phase extraction and HPLC/UV. In this work, a magnetic porous biochar (MPB) derived from low-cost bagasse was prepared and successfully employed as an adsorbent. A particular emphasis was placed on optimizing the extraction conditions, including the amount of MPB, extraction time, pH, type and volume of eluent, and salt concentration. Under optimized MSPE conditions, the method showed satisfactory linearity over concentration ranges of 2-200 µg L-1 for four triazines, with correlation coefficient values no less than 0.9981. Low limits of detection (0.27-0.33 µg L-1), good recoveries (81.7-100.7%), and satisfactory repeatability (RSDs ≤ 8.1%) were also demonstrated with respect to the analytical performance. The results demonstrated that the developed method was simple, rapid, sensitive, and efficient, indicating that it could extract and enrich trace triazines from real samples.

[Methylation of CHD5 Gene Promoter Regulates p19Arf/p53/p21Cip1 Pathway to Facilitate Pathogenesis of Acute Myeloid Leukemia].

OBJECTIVE: To investigate the methylation status of CHD5 gene promoter in bone marrow from acute myeloid leukemia (AML) patients, and the underlying mechanism for initiating the pathogenesis of AML via p19Arf/p53/p21Cip1 pathway. METHODS: Methylation status of the CHD5 gene promoter was detected by using methylation-specific polymerase chain reaction (MSPCR) in bone marrow from AML patients, and the iron-deficiency anemia (IDA) samples were served as control. The expression of CHD5, p19Arf, p53 and p21Cip1 was determined by real-time quantitative reverse transcriptase PCR and Western blot. RESULTS: The methylation of CHD5 gene in bone marrow from AML patients increased significantly (39.06%) as compared with control group (6.67%). The methylation of CHD5 gene significantly correlated with chromosome karyotype differentiation (P＜0.01), but did not correlate with the patient's sex, age and clinical classification (P＞0.05). The mRNA expression of CHD5 gene in AML decreased, compared with control group, the mRNA and protein expression of p19Arf, p53 and p21Cip1 in AML with CHD5 methylation promoter decreased. CONCLUSION: The hypermeltylation of CHD5 gene promoter in AML patients can lead to decrease of CHD5, p19Arf, p53 and p21Cip1 expression levels which may reduce the inhibitory effect on proliferation of leukemia cells through the regulation of p19Arf, p53 and p21Cip1 pathway, thus promotes the occurence of AML.

A wormhole-like porous carbon/magnetic particles composite as an efficient broadband electromagnetic wave absorber.

A method combining liquid-liquid phase separation and the pyrolysis process has been developed to fabricate the wormhole-like porous carbon/magnetic nanoparticles composite with a pore size of about 80 nm (WPC/MNPs-80). In this work, the porous structure was designed to enhance interaction between the electromagnetic (EM) wave and the absorber, while the magnetic nanoparticles were used to bring about magnetic loss ability. The structure, morphology, porosity and magnetic properties of WPC/MNPs-80 were investigated in detail. To evaluate its EM wave attenuation performance, the EM parameters of the absorber and wax composite were measured at 2-18 GHz. WPC/MNPs-80 has an excellent EM wave absorbency with a wide absorption band at a relatively low loading and thin absorber thickness. At the absorber thickness of 1.5 and 2.0 mm, minimum RL values of -29.2 and -47.9 dB were achieved with the RL below -10 dB in 12.8-18 and 9.2-13.3 GHz, respectively. The Co and Fe nanoparticles derived from the chemical reduction of Co0.2Fe2.8O4 can enhance the graphitization process of carbon and thus improve dielectric loss ability. Polarizations in the nanocomposite absorber also play an important role in EM wave absorption. Thus, EM waves can be effectively attenuated by dielectric loss and magnetic loss through multiple reflections and absorption in the porous structure. WPC/MNPs-80 could be an excellent absorber for EM wave attenuation; and the design strategy could be extended as a general method to synthesize other high-performance absorbers.

New promising hybrid materials for electromagnetic interference shielding with improved stability and mechanical properties.

A novel transparent Co0.2Fe2.8O4@SiO2-polyetheretherketone hybrid material is prepared for electromagnetic interference shielding via in situ sol-gel process. 20% amino-functionalized polyetheretherketone (AFPEEK), containing trifluoromethyl units with excellent solubility is designed and synthesized to improve the stability and mechanical properties of Co0.2Fe2.8O4@SiO2 nanoparticles. The hydrophilic nanoparticles and hydrophobic polymer matrix are covalently connected after the effective interface modification with 3-isocyanatopropyltriethoxysilane. SEM and TEM images demonstrate that the strong interaction between inorganic-organic phases results in great improvement of dispersion and compatibility at even 40 wt% nanoparticles contents. The functional integration of organic polymer and inorganic nanoparticles leads to excellent comprehensive performances such as high transparency, thermal stability and mechanical properties of the hybrid material, as well as the high adhesion with substrate, which benefits its application as coating materials. This high performance material exhibits good superparamagnetic behaviour and microwave electromagnetic properties (RLmax ∼ -13 dB), which can be utilized as a promising electromagnetic interference shielding material.