A facile and general approach for production of nanoscrolls with high-yield from two-dimensional nanosheets.

Nanoscrolls (NSs) assembled from two-dimensional nanosheets have emerged as a novel type of one-dimensional nanomaterials because of their unique topological features and properties. The scale-up preparation of the NSs is crucial for their foundational and applied research. Herein, we report a general and straightforward approach for efficiently converting two-dimensional nanosheets into the NSs with high yield. We demonstrated the converting process by illustrating the formation of the graphene nanoscrolls through characterizing their morphology and structure using a scanning electron microscope, transmission electron microscope, Raman spectra, and X-ray diffraction spectra. The graphene sheets with a few-lay number were converted immediately and entirely into the graphene nanoscrolls when they mixed with an ethanol solution of silver nitrate at room temperature. The as-prepared graphene nanoscrolls were confirmed to be formed via the layer-by-layer assembly of graphene triggered by silver cyanide formed in site. Also, we extended this approach to construct the nanoscrolls of the hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide, respectively, from their corresponding two-dimensional nanomaterials. In a broader context, this approach paves a significant new way for the large production of the NSs with cost-efficiency.

Curcumin-assisted ultrasound exfoliation of graphite to graphene in ethanol.

In this paper, we demonstrated a simple and cost-effective method to produce graphene from graphite in ethanol using ultrasound assisted with curcumin. The influence of curcumin concentration, starting graphite amount, sonication power, and sonication time on the graphene concentration was studied schematically. The π-π interaction between curcumin and graphene, being confirmed by FTIR spectrum, facilitate the exfoliation of the graphite into graphene. The concentration of the graphene in the ethanol reached up to 1.44 mg mL-1 and the exfoliated suspension was relatively stable. The content of monolayer, bilayer, and multilayer in the exfoliated graphene suspension were 21%, 37%, and 42%, respectively. The as-prepared graphene sheets were free-defect. This novel approach may not only enable to exfoliate the graphite into graphene but also to make the graphene-curcumin hybrid which might find applications in pharmaceutical industry.

Synthesis of graphene/epoxy resin composite via 1,8-diaminooctane by ultrasonication approach for corrosion protection.

In this work, the preparation of the graphene/epoxy resin composite and its corrosion protection on the copper substrate were presented. The 1,8-diaminooctane-grafted-graphene (1,8-D-g-G) was synthesized using the carboxyl functional graphite and 1,8-diaminooctane by a one-pot process under ultrasonication in supercritical CO2. The structure and morphology of the as-prepared samples characterized by FTIR, XPS, TEM, AFM, and SEM confirmed that the graphite was exfoliated into the graphene and the latter reacted with the 1,8-diaminooctane via amidation to form the 1,8-D-g-G. The graphene/epoxy resin composite was readily achieved by the reaction of the epoxy resin with the 1,8-D-g-G. The electrochemical and salt spray tests were applied to assess the corrosion protection of the composite coating on the copper substrate. The results demonstrated that the composite exhibited excellent corrosion protection. Also, the mechanism of the co-occurred exfoliating process and the amidation reaction in one-pot under ultrasonication in supercritical CO2 was explored.

Graphene-catalyzed formation of C≡N bonds via cleavage of C-C and N-O bonds in ethanol and nitrate under room temperature.

The cleavage of carbon-carbon bonds and the formation of carbon-nitrogen bonds play crucial roles in chemical synthesis. However, these reactions usually proceed at high temperature and involve multiple steps. Herein, we report an unusual and novel reaction catalyzed by graphene. The C-C bond in ethanol and the N-O bond in nitrate can be broken under room temperature, accompanied by the formation of the C≡N bond. We demonstrate these reactions and elucidate their mechanisms by verifying that the product is silver cyanide which was formed when mixing a solution of silver nitrate and ethanol with graphene dispersion in ethanol at room temperature. The pivotal reason for the reaction is the formation of the precipitated silver cyanide. In a broader context, this discovery opens a significant new path for the breakage of the C-C bond in ethanol and the synthesis of nitriles under mild conditions. Also, the graphene was first reported as a catalyst for the room-temperature reaction.

Reversible conversion between graphene nanosheets and graphene nanoscrolls at room temperature.

In this paper, the reversible conversion between pristine graphene nanosheets and pristine graphene nanoscrolls at room temperature was reported. The graphene nanosheets were rolled up into the graphene nanoscrolls by silver nitrate in ethanol solution, and the fabricated graphene nanoscrolls were unfolded back to the graphene nanosheets in ethanol solution by adding ammonium hydroxide. The dynamic conversion state of the process was confirmed by the morphology of the intermediate samples captured using an optical microscope and scanning electron microscope. Also, AFM, TEM and Raman spectroscopy displayed that the graphene transformed from its nanoscrolls remained the structure and morphology of the started graphene. The reason for the formation of the nanoscrolls was assigned to the silver cyanide particles generated on the edge of the graphene. The freshly formed silver cyanide caused the unbalanced energy of the graphene surface by changing the pi electron distribution and triggered off the graphene to roll up. The unfolding of the graphene nanoscrolls back to the graphene nanosheets was attributed to the removal of the silver cyanide by the ammonia via forming the complex. This reversible conversion might be a novel and facile approach to make graphene nanoscrolls and to store the graphene. Also, it may bring new sight to the conversion research between two-dimension and one-dimension materials.

Ultrasound coupled with supercritical carbon dioxide for exfoliation of graphene: Simulation and experiment.

Ultrasound coupled with supercritical CO2 has become an important method for exfoliation of graphene, but behind which a peeling mechanism is unclear. In this work, CFD simulation and experiment were both investigated to elucidate the mechanism and the effects of the process parameters on the exfoliation yield. The experiments and the CFD simulation were conducted under pressure ranging from 8MPa to 16MPa, the ultrasonic power ranging from 12W to 240W and the frequency of 20kHz. The numerical analysis of fluid flow patterns and pressure distributions revealed that the fluid shear stress and the periodical pressure fluctuation generated by ultrasound were primary factors in exfoliating graphene. The distribution of the fluid shear stress decided the effective exfoliation area, which, in turn, affected the yield. The effective area increased from 5.339cm3 to 8.074cm3 with increasing ultrasonic power from 12W to 240W, corresponding to the yield increasing from 5.2% to 21.5%. The pressure fluctuation would cause the expansion of the interlayers of graphite. The degree of the expansion increased with the increase of the operating pressure but decreased beyond 12MPa. Thus, the maximum yield was obtained at 12MPa. The cavitation might be generated by ultrasound in supercritical CO2. But it is too weak to exfoliate graphite into graphene. These results provide a strategy in optimizing and scaling up the ultrasound-assisted supercritical CO2 technique for producing graphene.

Green synthesis of biocompatiable chitosan-graphene oxide hybrid nanosheet by ultrasonication method.

Ultrasound-induced synthesis of chitosan-modified nano-scale graphene oxide (CS-NGO) hybrid nanosheets, which has great potential pharmaceutical applications, in supercritical CO2 without catalyst was presented for the first time. The preparation process does not require organic solvent and post-processing, and CO2 easily escapes from the product. The morphology and structure of the CS-NGO, characterized using scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, confirms that it was combined via the amide linkage, and had excellent dispersibility and stability toward acidic and physiological aqueous solution, which implies that it could be used as a drug-carrier. The sonication power played a crucial role in inducing forming amidation, and the conversion rate increased with the sonication time. The mechanism of this reaction was explained.

Controlled morphology and size of curcumin using ultrasound in supercritical CO2 antisolvent.

Controllable morphology and size of crystal materials prepared by using a supercritical antisolvent (SAS) technique is still challenge. In this study, ultrasound was introduced into the SAS process to produce the particles of curcumin, a model compound. The effects of ultrasound power on the particle morphology and size were investigated in the range of 0 and 240 W at three different pressures. The observation of jet flow indicated ultrasound could accelerate the mixing speed between the liquid solution and the CO2, and thus reduced the gaseous region and the local saturation gradient. Mixed polymorphic and uniform particles of the curcumin were produced at a low and high mixing speed, respectively, confirmed by scanning electron microscopy. The needle- or rod-like particle, irregular lumpy particle and nano spherical particle were generated with the increase of the ultrasound power, attributed to the changes of the degree of supersaturation. Therefore, the ultrasound can be potentially applied to adjust the morphology and size of the crystal materials in supercritical CO2 antisolvent.