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At present, new electrode materials still need to be developed to enhance the energy density, cyclability, initial coulombic efficiency and rate capability of lithium-ion batteries (LIBs). Here, we report a simple, rapid, cost-effective and novel technology to prepare MnO2 through the decomposition of KMnO4 under different pH values without surfactants or high temperatures. Moreover, the formation mechanisms of curly MnO2 nanosheets, flower-like MnO2 and onion-like MnO2 are analyzed in depth. The great variation in the electrochemical performance of MnO2 prepared under different pH values clearly indicates the importance of the nanostructure. Furthermore, curly MnO2 nanoflakes fabricated at pH 2 (pH2-MnO2) show good initial coulombic efficiency (ca. 80%) and long cyclability (ca. 1038 mAh g−1 over 150 cycles), which is attributed to their relatively large surface area and stable structure.

Graphene nanosheets prepared by liquid-phase exfoliation tend to aggregate easily and irreversibly in most solvents due to van der Waals forces and high surface energy. This article presents a facile, low-cost and novel approach for the preservation and separation of graphene dispersions by adjusting the temperature and solvent. Using IPA-water mixtures can realize green production of graphene nanosheets, and different physicochemical parameters are achievable by changing the proportion of components. Two valid methods for improving stability were discussed in depth: low-temperature storage as a liquid and as a solid. When graphene dispersions are stored in a liquid phase, agglomeration of nanosheets in mixed solvents can be effectively retarded by strong viscous resistance induced by low temperatures. Frozen powder prepared by liquid nitrogen maintains the nanosheets in a dispersed state and is suitable for long-term preservation in the solid phase in ordinary freezers. Furthermore, rapid separation of graphene nanosheets is a challenging problem that retards industrial production. Flocculation induced by slow freezing can accelerate solid–liquid separation, offering a novel approach to obtain easily dispersed powders. Various patterns could be printed on paper and poly(ethylene terephthalate) by a simple and low-cost screen printing technique using the graphene powder, providing a new platform for scalable, low-cost printing of electronics. Consequently, this scalable and simple strategy can be satisfactorily applied to the preservation and separation of graphene and is expected to extend to other nanomaterials, including MoS2 and h-BN.

Nonmetal materials of waste printed circuit boards (PCBs) contain 50–70 wt% fiberglasses, which are usually abandoned as waste-byproducts during the recycling of waste PCBs. In this paper, we demonstrated a novel reuse of the fiberglasses recovered from waste PCBs for noise reduction application. The sound absorption performance of the recovered fiberglasses (RFG) was investigated by considering the effect of material thickness and bulk density. Also, the influence of covering layers on the absorption ability was studied. Results show that the high porous structure of the RFG leads to an excellent sound absorption ability in a broad-band frequency range. Average sound absorption coefficient of over 0.8 can be achieved in 100–6,400 Hz for 30 mm RFG sample. It is found that when the sample thickness increases the low-frequency absorption of RFG is significantly improved. All the results indicate that the reuse of RFG for noise reduction represents a promising way to realize high value-added utilization of waste PCBs.

In this study, we have demonstrated a strategy by which graphene was used to reduce the bubble defects and enhance the mechanical properties in graphene/cellulose acetate (Gr/CA) composite films. Mono- and multilayer graphene flakes were successfully prepared in the water–acetone mixtures by a jet cavitation method. Moreover, outstanding enhancement of mechanical properties of Gr/CA composite films were obtained at relatively low concentration of graphene flakes. Young’s modulus of these composite films increased linearly with the graphene flakes loading, due to the significantly high surface area of graphene and strong interactions between graphene flake and CA. Furthermore, three-dimensional channel formed by graphene flakes could increase the degassing speed and reduce the negative effects of bubbles. The Gr/CA composite has excellent mechanical properties and, more importantly, it is a natural and environmentally friendly polymer composite.

The aim of this study is to investigate the feasibility of using glass fibers, a recycled material from waste printed circuit boards (WPCB), as sound absorption and thermal insulation material. Glass fibers were obtained through a fluidized-bed recycling process. Acoustic properties of the recovered glass fibers (RGF) were measured and compared with some commercial sound absorbing materials, such as expanded perlite (EP), expanded vermiculite (EV), and commercial glass fiber. Results show that RGF have good sound absorption ability over the whole tested frequency range (100-6400 Hz). The average sound absorption coefficient of RGF is 0.86, which is prior to those of EP (0.81) and EV (0.73). Noise reduction coefficient analysis indicates that the absorption ability of RGF can meet the requirement of II rating for sound absorbing material according to national standard. The thermal insulation results show that RGF has a fair low thermal conductivity (0.046 W/m K), which is comparable to those of some insulation materials (i.e., EV, EP, and rock wool). Besides, an empirical dependence of thermal conductivity on material temperature was determined for RGF. All the results showed that the reuse of RGF for sound and thermal insulation material provided a promising way for recycling WPCB and obtaining high beneficial products.

Atomic oxygen (AO) is a dominant component of the low earth orbit and can erode most spacecraft material. We demonstrated the application of graphene to enhance AO erosion resistance of spacecraft polymers. Graphene-reinforced epoxy resin nanocomposites were prepared by solidification of epoxy resin in solution with dispersed graphene flakes and their AO erosion resistance was investigated in a plasma-type ground-based AO effects simulation facility. The nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Results based on erosion kinetics revealed that a 46 % decrease in mass loss and a 47 % decrease in erosion yield were achieved by addition of only 0.5 wt% of graphene. Further analysis of the surface morphology and composition showed that the graphene nanoflakes could serve as barriers to protect underneath from AO erosion. Thus, this approach provides a novel route for improving durability and reliability of spacecraft material, especially polymers.

Sonication-assisted liquid-phase exfoliation of graphite makes facile, scalable, and low-cost graphene production possible, but there is little information about how sonication-related factors such as vessel diameter (D) and liquid height (H) affect this process and how to scale-up this technique. In this article, the dependence of the sonication-assisted few-layer graphene (FLG) production on D and H was investigated based on experiments and numerical simulation which was performed by finite element method to determine cavitation-related parameters. It was found that by essentially changing the cavitation phenomenon, D and H could critically affect the FLG concentration, FLG yield, injected power, and production efficiency. Combined experimental and simulational analyses reveal that though D and H can change both cavitation volume and cavitation volume fraction, it is the cavitation volume fraction that directly relates to the FLG concentration and production efficiency with a monotonically increasing trend, while the FLG yield and injected power are almost proportional to the cavitation volume, which in turn follows a linear increasing trend with the sample volume. The practical importance for industrial FLG production may lie in the following: (1) D and H should be carefully designed to obtain high cavitation volume fraction to gain high production efficiency and FLG concentration or output-input ratio and (2) large D, H, or sample volume is necessary for achieving large cavitation volume to enhance the FLG yield. Moreover, enhancement in pressure amplitude or cavitation intensity could also favor FLG production. These results have verified the importance of D and H which are often ignored when studying graphene production, and will provide important information on designing large-sized vessels for mass-producing graphene by sonication.

In this study, a jet cavitation device aimed at producing two-dimensional nanosheets was designed. The effects of cavitation generator type and jet pressure on the cavitation inception and intensity were examined by monitoring the changes of sound pressure level (ΔSPL). As such, the optimized cavitation generator with the best cavitation capability under the same ambient condition was determined. Further, BN and MoS2, two kinds of layered materials, were exfoliated into individual flakes in aqueous solutions by this jet cavitation device. By investigating the morphology of these exfoliated flakes via scanning electron microscopy and transmission electron microscope, it was found that these pristine materials were mostly exfoliated into two-dimensional nanosheets, among which even monolayers were generally presented. This exfoliation process happened mainly due to the cavitation-induced intensive tensile stress acting on the layered materials. As graphene has been produced by this device successfully, it is anticipated that this jet cavitation device is suitable for producing other various two-dimensional nanosheets.

A novel technology for powder dispersion and surface modification was studied by experiment in this paper. In the process, powders are dispersed by the nozzle and the atomized modifying agent is sprayed into the dispersed particles and coated on the surface at the same time. Silica, mica and talc powders were dispersed and modified by this technology, the performance of powder dispersion is evaluated by the scanning electron microscope (SEM), and the performance of surface modification is evaluated in advance by the viscosity of powder-paraffin suspension. In experiment, the modified silica was filled in the polypropylene (PP), the impact fractographs, notched impact and tensile properties of the PP composites were studied, the results indicate that the developed technology is effective for powders dispersion and surface modification.

The growth behavior and surface topography of the deposited films formed from silane coupling agents on silicon dioxide substrate (0001) via vapor phase deposition was investigated using atomic force microscopy (AFM). The surface topography of the films adsorbed on the silicon dioxide substrates is dissimilar with different silane coupling agents and different deposition conditions: (1) the films adsorbed on the silicon dioxide substrate become smoother with the increasing temperature of the silicon dioxide substrate; (2) the surface roughness of the films increases with the increasing concentration of the silane coupling agent solutions; (3) with the increasing temperature of the carrier gas, the surface roughness of the films decreases firstly and then increases; (4) with the increasing time of deposition, the surface roughness of the films increases firstly, then decreases and subsequently increases again. In experiments, the films adsorbed on the silicon dioxide substrate was rinsed ultrasonically with toluene, the results indicate that the silane coupling agent adsorbed on the substrate by physisorption and chemisorption: the chemisorbed coupling agents present island morphology and the physisorbed coupling agents are deposited on the substrate between the islands to decrease the surface roughness of the film.

A versatile and scalable mixed-solvent strategy, by which two mediocre solvents could be combined into good solvents for exfoliating graphite, is demonstrated for facile and green preparation of graphene by liquid-phase exfoliation of graphite. Mild sonication of crystal graphite powder in a mixture of water and alcohol could yield graphene nanosheets, which formed a highly stable suspension in the mixed solvents. The graphene yield was estimated as *10 wt%. The optimum mass fraction of ethanol in water-ethanol mixtures and isopropanol in water- isopropanol mixtures was experimentally determined as *40 and *55 % respectively, which could be roughly predicted by the theory of Hansen solubility parameters. Statistics based on atomic force micro- scopic analysis show that up to*86 % of the prepared nanosheets were less than 10-layer thick with a monolayer fraction of *8 %. High resolution trans- mission electron microscopy, infrared spectroscopy, X-ray diffraction, and Raman spectrum analysis of the vacuum-filtered films suggest the graphene sheets to be largely free of defects and oxides. The proposed mixed-solvent strategy here extends the scope for liquid-phase processing graphene and gives research- ers great freedom in designing ideal solvent systems for specific applications.