RESUMO
Dopamine-derived cavities/Fe3O4 nanoparticles-encapsulated carbonaceous composites with self-generating three-dimensional (3D) network structure were successfully fabricated by a facile synthetic method, in which sodium alginate provided carbon matrix pores and excellent microwave absorption performance was established. The hollow cavities derived from the core-shell-like CaCO3@polydopamine were creatively introduced into the 3D absorber to significantly improve the absorption performance. The sample calcined at 700 °C exhibited the most outstanding microwave absorption performance, with minimal reflection loss up to -50.80 dB at 17.52 GHz with a rare thickness of only 1.5 mm when filler loading was 35% in paraffin matrix. The effective absorption bandwidth of reflection loss < -10 dB reached 3.52 GHz from 14.48 GHz to 18 GHz, corresponding to the same thickness of 1.5 mm. In contrast, the sample without hollow dopamine-derived cavities showed poor performance due to poor impedance matching, and this highlights the role of hollow cavities brought into the 3D structure, which led to a difference in interfacial polarization, multiple reflections and scattering. The novel dopamine-derived cavities/Fe3O4 nanoparticles-encapsulated carbonaceous composites with 3D network structure can be regarded as a promising candidate for application as a microwave absorber with strong absorption.
RESUMO
Carbonaceous composites with tailored porous architectures and magnetic Fe3O4 components derived from walnut shells were fabricated by a solvothermal method and used as effective microwave absorbers. The porous composites were obtained by two carbonization processes at different temperatures and an etching process using potassium hydroxide. The introduction of a developed porous architecture inside the resulting materials distinctly improved the microwave absorption performance. Moreover, investigations revealed that the Fe3O4 nanoparticles were chemically bonded and uniformly decorated on the porous framework without aggregation. Owing to the combined advantages of the lightweight conductive biochar-like porous framework with a favorable dielectric loss and Fe3O4 nanoparticles with magnetic loss features, these newly fabricated porous carbonaceous composites exhibited excellent microwave absorption performance. A reflection loss (RL) of -51.6 dB was achieved at a frequency of 13.6 GHz. Besides, the effective absorption (below -10 dB) bandwidth reached 5.8 GHz (from 11.9 to 17.7 GHz) at an absorber thickness of only 2 mm. These results indicated that this type of porous Fe3O4-biochar composite derived from biomass substances and prepared via an easy-to-handle process can be considered as attractive candidates for the design and manufacture of high-efficiency microwave-absorbing materials.
RESUMO
Using sensors to quantify clinically relevant biological species has emerged as a fascinating research field due to their potential to revolutionize clinical diagnosis and therapeutic monitoring. Taking advantage of the wide utility in clinical analysis and low cost of potentiometric ion sensors, we demonstrate a method to use such ion sensors to quantify bioanalytes without chemical labels. This is achieved by combination of chronopotentiometry with a mussel-inspired surface imprinting technique. The biomimetic sensing method is based on a blocking mechanism by which the recognition reaction between the surface imprinted polymer and a bioanalyte can block the current-induced ion transfer of an indicator ion, thus causing a potential change. The present method offers high sensitivity and excellent selectivity for detection of biological analytes. As models, trypsin and yeast cells can be measured at levels down to 0.03â U mL-1 and 50â CFU mL-1 , respectively.
