A Facile Synthesis of Novel Amorphous TiO2 Nanorods Decorated rGO Hybrid Composites with Wide Band Microwave Absorption

Innovative microwave in situ approach for crystallizing TiO2 nanoparticles with enhanced activity in photocatalytic and photovoltaic applications

This investigation introduces an innovative approach to microwave-assisted crystallization of titania nanoparticles, leveraging an in situ process to expedite anatase crystallization during microwave treatment. Notably, this technique enables the attainment of crystalline material at temperatures below 100 °C. The physicochemical properties, including crystallinity, morphology, and textural properties, of the synthesized TiO2 nanomaterials show a clear dependence on the microwave crystallization temperature. The presented microwave crystallization methodology is environmentally sustainable, owing to heightened energy efficiency and remarkably brief processing durations. The synthesized TiO2 nanoparticles exhibit significant effectiveness in removing formic acid, confirming their practical utility. The highest efficiency of formic acid photodegradation was demonstrated by the T_200 material, reaching almost 100% efficiency after 30 min of irradiation. Furthermore, these materials find impactful application in dye-sensitized solar cells, illustrating a secondary avenue for the utilization of the synthesized nanomaterials. Photovoltaic characterization of assembled DSSC devices reveals that the T_100 material, synthesized at a higher temperature, exhibits the highest photoconversion efficiency attributed to its outstanding photocurrent density. This study underscores the critical importance of environmental sustainability in the realm of materials science, highlighting that through judicious management of the synthesis method, it becomes feasible to advance towards the creation of multifunctional materials.

Microstructure regulation and microwave absorption properties of ZnO/RGO composites

Electromagnetic waves can cause different degrees of damage to the human body. People are developing unique nanomaterials with excellent reflection loss (RL), thin thickness, wide frequency band and light weight to improve the absorption efficiency of electromagnetic waves. Using a hydrothermal method, ZnO nanocrystals are combined with graphene oxide (GO). After heat treatment, evenly dispersed ZnO nanocrystals are attached to the GO surface or inserted into the lamellae, and the amount of Zn(CH3COO)2·2H2O and GO is selected to obtain ZnO/RGO nanocomposites with different mass ratios (1 : 1, 1 : 2, 1 : 3). The ZnO/RGO nanocomposites were mixed with paraffin wax with different mass ratios (15, 20, 25, 30 wt%) to explore their electromagnetic parameters and wave absorption properties. It is found that at 25 wt%, ZnO : GO = 3 : 1 and thickness of 3 mm, the sample exhibits excellent wave absorption performance (-36.6 dB) and wide effective absorption bandwidth (6.6 GHz). The microwave absorption performance is enhanced because ZnO nanocrystals inhibit RGO agglomeration and improve impedance matching between the heterostructure interface and RGO.

Boosting Conductive Loss and Magnetic Coupling Based on "Size Modulation Engineering" toward Lower-Frequency Microwave Absorption

The rational design of absorber size is a promising strategy for obtaining excellent electromagnetic wave (EMW) absorption performance. However, achieving controllable tuning of the material size through simple methods is challenging and the associated EMW attenuation mechanisms are still unclear. In this study, the sizes of metal-organic frameworks (MOFs) are successfully tailored by changing the growth time and the molar ratio of iron (Fe)/organic ligands. The lateral and vertical lengths of MOFs vary in the range of 200 nm to 2 µm and 100 nm to 1 µm, respectively. Both experiments and simulations confirm that the decrease of MOF size favors the formation of more conductive networks, which is beneficial for improving the conductivity loss. Meanwhile, the micromagnetic simulation reveals that the magnetic coupling can be effectively enhanced by the decrease of MOF size, which is conducive to the improvement of magnetic loss, especially in low-frequency range. The reflection loss of Fe-based MOFs with optimized size reaches -46.4 dB at 6.2 GHz with an effective absorption bandwidth of 3.1 GHz. This work illustrates the important role of size effect in EMW dissipation and provides an effective strategy for enhancing the low-frequency EMW absorption performance.

Ultralight MOF-Derived Ni3S2@N, S-Codoped Graphene Aerogels for High-Performance Microwave Absorption

To develop high-performance microwave absorption materials with the features of lightweight, thin thickness, broad bandwidth, and strong absorption, an ultralight Ni₃S₂@N, S-codoped graphene aerogel with a density of 13.5 mg/cm³ has been fabricated by the use of metal-organic frameworks (MOFs) to directly initiate the gelation of graphene oxide strategy. In such a strategy, dual-functional 1D Ni-MOF nanorods not only act as the gelation agent but also afford the doping elements (N and S) originated from the organic species and the precursor for metal sulfide. Due to the synergistic effects of good impedance matching and multiple losses, the optimal reflection loss (RL) of as-prepared Ni₃S₂@N, S-codoped graphene aerogel reaches −46.9 dB at 17.1 GHz with only 2.0 mm and ultralow filling content (1.75 wt%). The maximum effective absorption bandwidth (EAB) reaches 6.3 GHz (11.7–18.0 GHz) at 2.38 mm, covering the whole Ku band. Moreover, the value of EAB with the RL less than −30 dB can be tuned to 12.2 GHz (5.8–18 GHz) at the absorber thickness ranging from 1.9 to 5.0 mm. This work provides insight for rational design and fabrication of multicomponent-containing graphene aerogels, showing the potential application in lightweight and high-performance microwave absorption.

Surface modification of helical carbon nanocoil (CNC) with N-doped and Co-anchored carbon layer for efficient microwave absorption

Surface modification and composition control for nanomaterials are effective strategies for designing high-performance microwave absorbing materials (MWAMs). Herein, we have successfully fabricated Co-anchored and N-doped carbon layers on the surfaces of helical carbon nanocoils (CNCs) by wet chemical and pyrolysis methods, denoted as Co@N-Carbon/CNCs. It is found that pure CNCs show a very good microwave absorption performance under a filling ratio of only 6%, which is attributed to the uniformly dispersed conductive network and the cross polarization induced by the unique chiral and spiral morphology. The coating of N-doped carbon layers on CNCs further enriches polarization losses and the uniform anchoring of Co nanoparticles in these layers generates magnetic losses, which enhance the absorption ability and improve the low frequency performance. As compared with the pure CNCs-filling samples, the optimized Co@N-Carbon/CNCs-2.4 enhances the absorption capacity in the lower frequency range under the same thickness, and realizes the decreased thickness from 3.2 to 2.8 mm in the same X band, as well as the decreased thickness from 2.2 to 1.9 mm in the Ku band. Resultantly, a specific effective absorption wave value of 22 GHz g^-1 mm^-1 has been achieved, which enlightens the synthesis of ultrathin and light high-performance MWAMs.

Structural Engineering of Hierarchical Aerogels Comprised of Multi-dimensional Gradient Carbon Nanoarchitectures for Highly Efficient Microwave Absorption

Recently, multilevel structural carbon aerogels are deemed as attractive candidates for microwave absorbing materials. Nevertheless, excessive stack and agglomeration for low-dimension carbon nanomaterials inducing impedance mismatch are significant challenges. Herein, the delicate "3D helix-2D sheet-1D fiber-0D dot" hierarchical aerogels have been successfully synthesized, for the first time, by sequential processes of hydrothermal self-assembly and in-situ chemical vapor deposition method. Particularly, the graphene sheets are uniformly intercalated by 3D helical carbon nanocoils, which give a feasible solution to the mentioned problem and endows the as-obtained aerogel with abundant porous structures and better dielectric properties. Moreover, by adjusting the content of 0D core-shell structured particles and the parameters for growth of the 1D carbon nanofibers, tunable electromagnetic properties and excellent impedance matching are achieved, which plays a vital role in the microwave absorption performance. As expected, the optimized aerogels harvest excellent performance, including broad effective bandwidth and strong reflection loss at low filling ratio and thin thickness. This work gives valuable guidance and inspiration for the design of hierarchical materials comprised of dimensional gradient structures, which holds great application potential for electromagnetic wave attenuation.