Novel and Facile Method, Dynamic Self-Assemble, To Prepare SnO₂/rGO Droplet Aerogel with Complex Morphologies and Their Application in Supercapacitors

A facile and novel method to prepare SnO₂/reduced graphene oxide (rGO) droplet aerogels with complex morphologies had been developed. This method has been named dynamic self-assemble. Aerogels with both “egg-tart” and “mushroom” shapes were obtained by this method. The changes in the graphene oxide (GO) droplet morphologies during the dynamic process of a GO droplet falling into a SnCl₂ target solution were monitored using a high speed camera. The formed SnO₂/rGO aerogels were then characterized by Raman spectroscopy, thermogravimetric analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The microstructures of the SnO₂/rGO aerogels were observed with scanning electron microscopy and transmission electron microscopy. Finally, the SnO₂/rGO droplet aerogels were used as the electrode material in a symmetrical two-electrode supercapacitor and the electrochemical performance of the supercapacitor was investigated using cyclic voltammetry and galvanostatic charge/discharge methods. The SnO₂/rGO electrodes demonstrated excellent electrochemical performance and stability. At a scan rate of 5 mV/s, their highest gravimetric and volumetric specific capacitances were 310 F/g and 180 F/cm³, respectively, and their energy and power densities were as high as 30 Wh·kg^–1 and 8.3 kW·kg^–1, respectively

Fabrication of 3D Photonic Crystals from Chitosan That Are Responsive to Organic Solvents

Inspired by photonic nanostructures in nature, such as the hair-like chaetae on the body of sea mice, inverse opal photonic crystals films were fabricated with chitosan, a kind of biomacromolecule found in nature. First, monodispersed polystyrene (PS) colloidal crystal templates with different particle sizes were prepared. The inverse opal films (IOFs) were fabricated through in situ cross-linking of the PS templates. The IOFs contain periodically ordered interconnecting pores that endow the films with photonic stop bands and structural colors, which are visible to the naked eye. The IOFs exhibit rapid reversible changes in their structural colors and reflectance peaks in response to alcohols and phenols. Possible mechanisms for the shifts in the IOF’s reflectance peaks are proposed. The changes in the IOFs in response to alcohols and phenols provide a potential way to visually detect these organic solvents

Sn Powder as Reducing Agents and SnO₂ Precursors for the Synthesis of SnO₂‑Reduced Graphene Oxide Hybrid Nanoparticles

A facile approach to prepare SnO₂/rGO (reduced graphene oxide) hybrid nanoparticles by a direct redox reaction between graphene oxide (GO) and tin powder was developed. Since no acid was used, it is an environmentally friendly green method. The SnO₂/rGO hybrid nanoparticles were characterized by ultraviolet–visible spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The microstructure of the SnO₂/rGO was observed with scanning electron microscopy and transmission electron microscopy. The tin powder efficiently reduced GO to rGO, and the Sn was transformed to SnO₂ nanoparticles (∼45 nm) that were evenly distributed on the rGO sheets. The SnO₂/rGO hybrid nanoparticles were then coated on an interdigital electrode to fabricate a humidity sensor, which have an especially good linear impedance response from 11% to 85% relative humidity

Chemically Responsive Polymer Inverse-Opal Photonic Crystal Films Created by a Self-Assembly Method

The synthesis of poly-2-hydroxyethyl methacrylate inverse-opal hydrogel (IOHG_PHEMA) was realized by capillary-force-induced in situ polymerization in a polystyrene colloidal crystal template. The created IOHG_PHEMA films show brilliant blue-violet color when they are immersed in deionized water and reach swelling equilibrium. The stop band of the IOHG_PHEMA films can be tuned within the entire visible wavelength range by immersing them into different chemical solutions, such as aldehydes, ketones, amides, dimethyl sulfoxide, and alcohols. The extent of the reflective peak shift not only depends on the number of hydrogen band donors but also on the chain length and structure of the chemicals and their concentration. Since the IOHG_PHEMA films have different reflectance spectra and structural colors in response to different compounds of the same series, this provides a potential way to visually detect homologues and other compounds with similar structure and properties. This simple, yet effective, method also has the potential to be used generically to determine approximate concentration of the solution by direct visual observation of the color change

Self-Assembly Method To Fabricate Reduced Graphene Oxide Aerogels Loaded with Nickel Hydroxyl Nanoparticles and Their Excellent Properties in Absorbing and Supercapacitors

A facile method for preparing nickel hydroxyl nanoparticles loaded graphene aerogels has been established. The prepared aerogels were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. Their applications as absorbents or electrode materials for supercapacitors were investigated. They showed excellent performance on the absorption of different dyes. The absorption capacities ranged from 202 to 513 mg g^–1. They also displayed high absorption capacities toward oils and organic solvents. The aerogels demonstrated high capacitance and stability as electrode materials of supercapacitors. The specific capacitance reached 702 F g^–1 at current densities of 1 A g^–1

Theoretical Screening of Transition Metal Alloys with High Corrosion Resistance: The Case of Ta-Based Alloys as an Example

Proton exchange membrane water electrolysis (PEMWE) is one of the potential strategies to generate green hydrogen energy, and anticorrosive coatings are mandatory to protect the bipolar plates, an important component of PEMWE. However, it is still challenging to explore the high-corrosion-resistance coatings by trial and error. In this paper, the corrosion properties of Ta and its alloys as examples are studied theoretically; in particular, the influences of crystal planes and alloying elements on the corrosion resistance have been studied systematically. Four descriptors, surface energy density ξ, work function τ, electronic descriptor ψ, and d band center ς, are proposed to screen the high-corrosion-resistance coatings. It is found that the electronic descriptor ψ can well predict the atomic escape energy and thus the corrosion resistance of Ta-based binary alloys with the coefficient of determination R2 of 0.804 and 0.949, respectively. Among them, TaW and TaCr alloys exhibit the most excellent corrosion resistance with the lowest Icorr (–7 A cm–2) and the highest Ucorr (> −0.011 V vs SHE) because of the largest −IpCOHP values and thus the strongest binding strength. The screening method is also applicable to the other alloys

Factors that Affect Pickering Emulsions Stabilized by Graphene Oxide

Stable Pickering emulsions were prepared using only graphene oxide (GO) as a stabilizer, and the effects of the type of oil, the sonication time, the GO concentration, the oil/water ratio, and the pH value on the stability, type, and morphology of these emulsions were investigated. In addition, the effects of salt and the extent of GO reduction on emulsion formation and stability were studied and discussed. The average droplet size decreased with sonication time and with GO concentration, and the emulsions tended to achieve good stability at intermediate oil/water ratios and at low pH values. In all solvents, the emulsions were of the oil-in-water type, but interestingly, some water-in-oil-in-water (w/o/w) multiple emulsion droplets were also observed with low GO concentrations, low pH values, high oil/water ratios, high salt concentrations, or moderately reduced GO in the benzyl chloride–water system. A Pickering emulsion stabilized by Ag/GO was also prepared, and its catalytic performance for the reduction of 4-nitrophenol was investigated. This research paves the way for the fabrication of graphene-based functional materials with novel nanostructures and microstructures

Cost-Effective Reduced Graphene Oxide-Coated Polyurethane Sponge As a Highly Efficient and Reusable Oil-Absorbent

Reduced graphene oxide coated polyurethane (rGPU) sponges were fabricated by a facile method. The structure and properties of these rGPU sponges were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy. The rGPU sponges are hydrophobic and oleophilic and show extremely high absorption for organic liquids. For all the organic liquids tested, the absorption capacities were higher than 80 g g^–1 and 160 g g^–1 (the highest value) was achieved for chloroform. In addition, the absorption capacity of the rGPU sponge did not deteriorate after it was reused 50 times, so the rGPU sponge has excellent recyclability