Recognized as a critical environmental hazard in modern industry, electromagnetic radiation poses substantial risks to human health and the ecosystem, necessitating lightweight and broadband microwave absorption materials as essential components of electromagnetic safety strategies. This work demonstrates a hollow engineering strategy for magnetic graphene composites, wherein centrifugal spray drying combined with subsequent high-temperature pyrolysis yields graphene hollow microspheres with magnetic nanoparticles uniformly anchored onto their inner and outer walls. The influence of pyrolysis temperature on the microwave absorption properties of the resulting composites is systematically investigated. Experimental results reveal that the pyrolysis temperature critically governs the phase crystallinity, graphitization degree and magnetic characteristics, thereby determining both their dielectric loss and magnetic loss capacities as well as the impedance matching behavior. An optimal pyrolysis temperature (800 ℃) yields superior broadband microwave absorption, achieving a minimum reflection loss (RLmin) of -45.3 dB and an effective absorption bandwidth (EAB, RL<-10 dB) exceeding 5.8 GHz at a thin thickness of 1.82 mm. The exceptional performance is attributed to the synergistic interplay of multiple attenuation mechanisms, including dielectric loss from the defective rGO and hollow cavity-induced multiple reflections, magnetic loss from the embedded nanoparticles, and enhanced impedance matching enabled by the hollow architecture. These findings advance the understanding of pyrolysis-temperature effects on microwave absorption and establish a promising platform for hollow-structure engineering.

Aqueous zinc-ion batteries suffer from severe water-induced side reactions and irregular Zn dendrite growth, leading to low Coulombic efficiency and rapid capacity decay. Herein, a sub-micro dual-functional zinc octylphosphonate (OPA) interphase is constructed on Zn anode through a facile immersion method, achieving a distinctive three-level hierarchical modulation mechanism on the Zn anode. The hydrophobic alkyl network accelerates Zn2+ desolvation and isolates the Zn surface from aqueous corrosion. Meanwhile, the zincophilic phosphonate groups possess preferential Zn2+ adsorption ability, acting as active sites to homogenize ion flux and guide uniform Zn deposition. Benefiting from the synergistic interfacial regulation, the OPA-modified Zn anode exhibits stable cycling over 1600 h at 5 mA cm−2, and the assembled OPA@Zn//NVO full cell achieves excellent long-term cycling stability. This work provides a facile molecular interfacial engineering strategy for high-performance aqueous zinc-ion battery anodes.

Photocatalytic reduction of carbon dioxide (CO2) has been expected to be an effective way to reduce carbon emissions. Designing photocatalytic materials with long-term effectiveness is the key of photocatalytic technology. In this work, CoO nanoparticles loaded on the surface of reduced graphene oxide (rGO) membranes on silicon substrate were in-situ fabricated by one-step method. The resulting materials can convert CO2 into carbon monoxide (CO) up to 70 h at a steady rate of similar to 185 +/- 30 mu mol g(-1) h(-1) with a selectivity of nearly 100%. This material system contained rich oxygen vacancies and generated new oxygen vacancies during the photocatalytic process. Oxygen vacancies mediate the interactions with excitons: (i) promoting the dissociation of free excitons; (ii) leading to form bound excitons under the coupling effect with phonons, inhibiting the recombination of photogenerated electrons and holes as well as enhancing the long-term effectiveness of photocatalytic CO2 reduction. We hope this work can provide valuable insights for the design and optimization of photocatalytic materials.

Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.

The interactions between metal ions and graphene oxide (GO) nanosheets were investigated by in situ two-dimensional grazing incidence X-ray diffraction (GIXRD). We found that metal cations (Mn2+, Co2+, Cu2+, Fe3+) and GO can self-assemble into a hydroxide/GO superlattice by drop-casting a metal chloride and GO solution due to the electrostatic interactions between the positively charged hydroxide and the negatively charged GO nanosheets and the interlayer spacing of the superlattice can be controlled by the cation species. Moreover, based on this superlattice template, graphene-based metal oxide nanosheets can be facilely obtained by subsequent annealing. The growth mechanism and structural evolution of the GO/cation systems can be described in four stages: (1) hydrated cation intercalation of the GO interlayer in an aqueous solution; (2) metal hydroxide growth between the GO layers during annealing, with the formation of a superlattice structure at approximately 250 degrees C; (3) metal oxide nucleation between the reduced GO (rGO) interlayers with increasing temperature; and (4) complete graphene layer decomposition at a temperature of 600 degrees C, along with metal oxide nanosheet formation. This work gives a new perspective for understanding the interactions between and growth behaviour of metal cations and GO. (C) 2021 Elsevier Ltd. All rights reserved.

The metal-free synthesis of graphene on single-crystal silicon substrates, the most common commercial semiconductor, is of paramount significance for many technological applications. In this work, we report the growth of graphene directly on an upside-down placed, single-crystal silicon substrate using metal-free, ambient-pressure chemical vapor deposition. By controlling the growth temperature, in-plane propagation, edge-propagation, and core-propagation, the process of graphene growth on silicon can be identified. This process produces atomically flat monolayer or bilayer graphene domains, concave bilayer graphene domains, and bulging few-layer graphene domains. This work would be a significant step toward the synthesis of large-area and layer-controlled, high-quality graphene on single-crystal silicon substrates.

Metallic gate electrodes are often employed to control the conductivity of graphene based field effect devices. The lack of transparency of such electrodes in many optical applications is a key limiting factor. We demonstrate a working concept of a double layer graphene field effect device that utilizes a thin film of sputtered aluminum nitride as dielectric gate material. For this system, we show that the graphene resistance can be modified by a voltage between the two graphene layers. We study how a second gate voltage applied to the silicon back gate modifies the measured microwave transport data at around 8.7 GHz. As confirmed by numerical simulations based on the Boltzmann equation, this system resembles a parallel circuit of two graphene layers with different intrinsic doping levels. The obtained experimental results indicate that the graphene-aluminum nitride-graphene device concept presents a promising technology platform for terahertz-to-optical devices as well as radio-frequency acoustic devices where piezoelectricity in aluminum nitride can also be exploited.

A study of the growth of graphene on the silicon-face (0001) and the carbon-face (000(-)1) of SiC is presented. The morphology and layer thickness is investigated using atomic force microscopy and scanning Kelvin probe microscopy and demonstrates the more wrinkled and less uniform thickness of the graphene growth on the C-face compared to the Si-face which shows uniform monolayer growth with some bilayer areas. Raman spectroscopy confirms the predominantly monolayer nature of the Si-face graphene and the inhomogeneous nature of the C-face graphene growth. Raman studies on the C-face show overlapping peaks as observed for spectra of Bernal-stacked graphene but we argue that the graphene is turbostratic with nanoscale differences in substrate effects leading to shifting of the Raman modes. Further samples show uniform scanning Kelvin probe maps of the carbon face along with very low bilayer coverage on the Si-face. Epitaxially grown graphene on the Si-face of SiC is reported to have a high carrier concentration and low mobility, however, van Der Pauw measurements demonstrate the low sheet resistance and relatively low carrier concentration of the graphene on the Si-face, in agreement with microwave measurements (Hao et al 2013 Appl. Phys. Lett. 103 123103) and scanning Kelvin probe maps which demonstrate the uniformity of the graphene.

Porous Li4Ti5O12 coated with few-layer graphene was prepared via the low-temperature pyrolysis of C28H16Br2 at 400 °C. The coating layer was very thin and uniform. The coated sample shows superior Li storage performance compared with the as-prepared sample. Capacities of 131 and 104 mA h g−1 can be reached at current rates of 5 and 10 C, respectively. Moreover, cyclic performance is significantly improved after coating. The capacity decreases from 144.6 to 124.4 mA h g−1 after 2400 cycles at a current rate of 2 C in a half cellversusLi/Li+, with high capacity retention of 86%.