Two-Dimensional Cr5Te8@Graphite Heterostructure for Efficient Electromagnetic Microwave Absorption.

Two-dimensional (2D) transition metal chalcogenides (TMCs) hold great promise as novel microwave absorption materials owing to their interlayer interactions and unique magnetoelectric properties. However, overcoming the impedance mismatch at the low loading is still a challenge for TMCs due to the restricted loss pathways caused by their high-density characteristic. Here, an interface engineering based on the heterostructure of 2D Cr5Te8 and graphite is in situ constructed via a one-step chemical vapor deposit to modulate impedance matching and introduce multiple attenuation mechanisms. Intriguingly, the Cr5Te8@EG (ECT) heterostructure exhibits a minimum reflection loss of up to - 57.6 dB at 15.4 GHz with a thin thickness of only 1.4 mm under a low filling rate of 10%. The density functional theory calculations confirm that the splendid performance of ECT heterostructure primarily derives from charge redistribution at the abundant intimate interfaces, thereby reinforcing interfacial polarization loss. Furthermore, the ECT coating displays a remarkable radar cross section reduction of 31.9 dB m2, demonstrating a great radar microwave scattering ability. This work sheds light on the interfacial coupled stimulus response mechanism of TMC-based heterogeneous structures and provides a feasible strategy to manipulate high-quality TMCs for excellent microwave absorbers.

Synthesis and Microwave Absorption Properties of Sulfur-Free Expanded Graphite/Fe3O4 Composites.

In this study, sulfur-free expanded graphite (EG) was obtained by using flake graphite as the raw material, and EG/Fe3O4 composites with excellent microwave absorption properties were prepared by a facile one-pot co-precipitation method. The structure and properties of as-prepared EG/Fe3O4 were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectrometry (XPS), thermogravimetric (TG), and vibrating sample magnetometry (VSM) characterizations. The Fe3O4 intercalated between the layers of expanded graphite forms a sandwich-like structure which is superparamagnetic and porous. When applied as a microwave absorber, the reflection loss (RL) of EG/Fe3O4 reaches -40.39 dB with a thickness of 3.0 mm (10 wt% loading), and the effective absorption bandwidth (EAB < -10 dB) with RL exceeding -10 dB is 4.76-17.66 GHz with the absorber thickness of 1.5-4.0 mm. Considering its non-toxicity, easy operation, low cost, suitability for large-scale industrial production, and excellent microwave absorbing performance, EG/Fe3O4 is expected to be a promising candidate for industrialized electromagnetic absorbing materials.

Efficient Gold Recovery from E-Waste via a Chelate-Containing Porous Aromatic Framework.

Extracting gold from wastes of electronic equipment (e-waste) is a sustainable strategy for the recovery of the precious metal, reducing environmental pollution, and addressing the growing demands for gold resources. In this work, we synthesized a thiourea-modified porous aromatic framework (PAF-1-thiourea) with exceptional gold-extraction ability. The optimum adsorption capacity for PAF-1-thiourea to gold reaches up to 2629.87 mg g-1. The adsorption process can be well fitted according to the pseudo-second-order kinetic model and Langmuir model, featuring strong affinity caused by strong soft-soft interactions between Au(III) and the S and N donor atoms of the modified PAF and the electrostatic interactions between protonated amino groups and AuCl4-. PAF-1-thiourea was especially capable of extracting gold rapidly and efficiently (capturing 98.73% of gold within 5 min) from a central processing unit (CPU) in extremely acidic conditions. It is found that PAF-1-thiourea captures gold ions and simultaneously converts it to a Au(0) solid, obtaining gold with purity up to 23.5 karat. PAF-1-thiourea with its high acid resistance and anti-interference against cheap metals in the recovery process presents a practical means to extract gold from e-waste.

Evaporation of mixed citric acid/(NH4)2SO4/H2O particles: Volatility of organic aerosol by using optical tweezers.

The condensation and evaporation processes of semi-volatile organic compounds (SVOCs) in atmospheric aerosols can induce significant evolutions of their chemical and physical properties. Hence, for interpreting and predicting composition changes of atmospheric aerosols, it is indispensable to provide insight into the partitioning behaviors of SVOCs between condensed and gas phases. In this research, optical tweezers coupled with cavity-enhanced Raman spectroscopy were employed to observe the volatility of internally mixed citric acid (CA)/(NH4)2SO4 (AS) particles, and the effect of AS on the gas/particle partitioning behaviors of atmospheric organic acids was investigated. The radii and refractive indexes of the levitated droplets were determined in real time from the wavelength positions of simulated Raman spectra and the effective vapor pressures of CA at different relative humidities (RHs) were obtained according to Maxwell equation. For the CA/AS particle with organic to inorganic mole ratio (OIR) of 1:1, the effective vapor pressure of CA decreased with the decreasing of RH. When the RH decreased from 67% to 8.2%, the effective vapor pressure of CA decreased from (1.35±0.508)×10-4Pa to (3.0±1.0)×10-6Pa. Meanwhile, the CA/AS particles with OIR of 3:1, 1:3 were also studied, and the results show the same phenomenon compared to the particles with OIR of 1:1. When under constant RHs, the effective vapor pressures of CA decreased with the increasing of AS contents, suggesting that the presence of AS suppressed the partitioning of CA to aqueous particles. In addition, the mass transfer processes of water in CA and CA/AS/H2O systems were further studied. The characteristic time ratio between the droplet radius and RH was used to describe the water mass transfer difference dependent on RH. Compared to the characteristic time ratio of pure CA, the characteristic time ratio of CA/AS particles apparently increased. For CA/AS particles under the same RH steps, the characteristic time ratio increased with the AS content increase. According to the differential isotherm, the diffusion coefficients of citric acid and citric acid/ammonium sulfate at low RHs (RH ≈7%-1%, RH≈1%-7%) were calculated respectively. Generally, the key aspect of the current work was to deeply explore the relationship between the evaporation rates of SVOCs and water transport process.

Investigation of gel formation and volatilization of acetate acid in magnesium acetate droplets by the optical tweezers.

Hygroscopicity and volatility of single magnesium acetate (MgAc2) aerosol particles at various relative humidities (RHs) are studied by a single-beam optical tweezers, and refractive indices (RIs) and morphology are characterized by cavity enhanced Raman spectroscopy. Gel formation and volatilization of acetate acid (HAc) in MgAc2 droplets are observed. Due to the formation of amorphous gel structure, water transposition in droplets at RH < 50% is significantly impeded on a time scale of 140,000 s. Different phase transition at RH < 10% is proposed to explain the distinct water loss after the gel formation. To compare volatilization of HAc in different systems, MgAc2 and sodium acetate (NaAc) droplets are maintained at several different stable RHs during up to 86,000 s. At RH ≈ 74%, magnesium hydroxide (Mg(OH)2) inclusions are formed in MgAc2 droplets due to the volatilization of HAc, and whispering gallery modes (WGMs) of MgAc2 droplets in the Raman spectrum quench after 50,000 s. In sharp contrast, after 86,000 s at RH ≈ 70%, NaAc droplets are in well-mixed liquid states, containing soluble sodium hydroxide (NaOH). At this state, the RI of NaAc droplet is increased, and the quenching of WGMs is not observable.