Ultrasonic-assisted Exfoliation Research Articles

Inspired by nacre: α-ZrP three-dimensional network structures for interlaminar toughening of laminates

This work enhancing the mechanical properties of composite laminates by using a three-dimensional network structure that mimics the nacre-like structure. The optimal interlaminar structure was developed by utilizing α-ZrP with ultrasonic-assisted exfoliation for 6 min. The mode-I critical energy release rate (GIC) and mode-II critical energy release rate (GIIC) of the toughened composite are 104.44 % and 74.20 % higher than those of the unmodified sample. Observation of the region around the crack by SEM and OM reveals that the three-dimensional network structure across the fiber fabric undergoes energy dissipation behaviors, such as fracture, slip and pull-out when cracks penetrate thin walls. In addition, the effect of the thin-walled structure of the α-ZrP aerogel on interlaminar crack propagation is discussed, taking into account the inhomogeneous and multi-surface of the composite interfaces, and the toughening mechanism is investigated.

Ti2NTx quasi-MXene modified polyamide thin film composite reverse osmosis membrane with effective desalination and antifouling performance

In this study, considering the serious problem of lack of fresh water worldwide and the effectiveness of reverse osmosis (RO) membranes in water purification, we prepared improved RO membranes with two-dimensional quasi-MXene nanosheets. In this study, the MAX phase with the chemical formula of Ti2AlN was prepared through the reactive sintering route. Prosperous preparation of the MAX phase with the hexagonal crystalline structure was approved by an X-ray diffraction pattern. Compacted sheets morphology was recognized for the prepared MAX phase from transmittance electron microscopy and scanning electron microscopy micrographs. Then, Ti2NTx quasi-MXene nanosheets were prepared by selective ultrasonic-assisted exfoliation of the MAX phase. Polyamide (PA) thin-layer composite RO membranes with different weight percentages of Ti2NTx quasi-MXene were fabricated by the interfacial polymerization (IP) method. The addition of ultrasonic-assisted prepared quasi-MXene creates numerous and coherent nanochannels on the surface of the membrane. The optimum membrane with 0.01 wt% of quasi-MXene showed the highest pure water flux of 31.9 L m−2. h−1 with an improved salt rejection of 98.2%. Therefore, these nanosheets showed that they can partially solve the trade-off between water permeability and salt rejection, which is a serious challenge in RO membranes. Also, the membranes containing quasi-MXene showed good resistance against fouling by humic acid. This research can be a scalable development in making high-performance membranes.

Ultrathin MgB2 nanosheet-modified polypropylene separator for high-efficiency lithium-sulfur batteries

The separator is an important component in lithium-sulfur (Li-S) batteries. However, the conventional polypropylene (PP) separators have the problem of easy shuttling of lithium polysulfide (LiPSs). Herein, ultrathin magnesium boride (MgB2) nanosheets were prepared by ultrasonic-assisted exfoliation technology, and were suction-filtered onto a separator to serve as a separator modification layer. The introduction of a microporous structure into MgB2 nanosheets after ultrasonic peeling increases the specific surface area and pore volume, with more adsorption sites, which can fully utilize the surface adsorption/catalytic performance of MgB2 for LiPSs and accommodate the volume expansion of lithium sulfide (Li2S). Therefore, MgB2@PP as a separator significantly improves the sulfur utilization and cycle stability in Li-S batteries. When the MgB2@PP separator is used, the reversible specific capacity of the assembled Li-S battery at 0.1 C (current rate) is 1184 mAh/g, and the specific capacity at 2 C is 732 mAh/g. After 500 cycles at 2 C, it remains at 497 mAh/g.

Ultrasonic-Assisted Exfoliation Bulk-Phase of MoS2 with Chitosan/Acetic Acid Solution

Ultrasonic-Assisted Exfoliation Bulk-Phase of MoS2 with Chitosan/Acetic Acid Solution

Cobalt(III) corrole-tethered semiconducting graphdiyne film for efficient electrocatalysis of oxygen reduction reaction

Inspired from nature, transition metal porphyrins and corroles have been designed and synthesized for electrocatalytic oxygen reduction reaction (ORR). However, the efficiency is limited by their low conductivity and thus carbonization is usually required. Herein, we report a new strategy by covalently linking cobalt(III) corrole and cobalt(II) porphyrin onto a semiconducting fluoro-graphdiyne (F-GDY) film through nucleophilic substitution reaction. The crystalline F-GDY film was prepared by Glaser-Hay coupling at the water/dichloromethane interface, followed by ultrasonic-assisted exfoliation in liquid. The Co(III) corrole-tethered F-GDY material exhibited excellent four-electron ORR activity, with a half-wave potential of 0.875 V (vs reversible hydrogen electrode). It also displayed high discharge performance and capacity in a zinc-air battery device, superior to the commercial Pt/C. Our study provides a pyrolysis-free approach toward biomimetic catalysts for efficient small molecule activation.

Large-scale fabrication of graphene/polyamide-6 composite as a high thermal conductivity engineering composite for thermal radiators

In this study, graphene was mass-produced from graphite through ultrasonic-assisted exfoliation in N-methyl-2-pyrrooxone (NMP) and then mixed with polyamides Nylon (PA6) to obtain a high thermal conductivity engineering polymer (GP6). The thermal conductivity of GP6 is 30 W m−1 K−1 and the density is 1.8 g cm−1. GP6 could be used in heat dissipation systems of LED lamps and cameras with injection molding at 260 °C, thus cutting the cost by 30% and reducing the carbon emission.

Ultrasonic-Assisted Exfoliation of Pristine Graphite into few Layers of Graphene Sheets Using NH<sub>3</sub> as Intercalation Agent

Few-layer graphene sheets were synthesis using LPE with ultrasonic-assisted. The pristine graphite is directly exfoliated in deionized water with small addition of NH3 solution. In this study, we will investigate the relationship between concentration of NH3 solution corresponds to the graphene yield. The concentration of the NH3 solution varies from 18% to 26%. NH3 solution plays an important role as a medium to peel of graphite in the exfoliation process to form few-layer graphene sheets. The structural properties of the few-layer graphene sheets were examined using XRD, Raman Analysis, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) followed by UV-Vis Spectroscopy for its optical properties. The finest of few-layer graphene sheets was produced at 26% of NH3 concentration. This optimization results in a few layers of graphene sheets that may be used in the fields of nanoelectronics and optoelectronics.

Oxygen vacancy mediated step-scheme heterojunction of WO2.9/g-C3N4 for efficient electrochemical sensing of 4-nitrophenol

Excitonic effects induced via Coulomb interactions and an appropriate interfacial contact of electrode modified materials play crucial roles in transfer/separation of interfacial charge carriers during the electrochemical sensing process. Herein, an oxygen vacancy (Vo) mediated step-scheme (S-scheme) heterojunction of WO2.9/g-C3N4 was fabricated by electrostatic self-assembly of high-purity commercial WO2.9 nanoparticles and ultrathin g-C3N4 nanosheets, where g-C3N4 nanosheets were prepared via polymerization followed ultrasonic-assisted exfoliation. The fabricated Vo-S-scheme WO2.9/g-C3N4 heterojunction-based sensor exhibited superior electrochemical performance for detecting environmental hormone 4-nitrophenol (4-NP). Due to the introduction of Vo, an increased free-charge-carriers, a built-in electric field and a high adsorption energy are generated at the heterojunction interface, which all can significantly improve the sensitivity of this proposed sensor. It also showed good reproducibility, high accuracy, good recovery, and strong feasibility for 4-NP detection in real samples. This work not only conduces significantly to understanding the defective structures and S-scheme heterojunctions, but also provides new insights into designing and constructing novel efficient electrochemical sensors.

Ultrasonic-assisted top-down preparation of NbSe2 micro/nanoparticles and hybrid material as solid lubricant for sliding electrical contact

2H-NbSe2 single crystal flake (ca. 2 × 2 × 0.5 mm in size) by chemical vapor transport is employed as the precursor for a top-down preparation of NbSe2 micro/nanoparticles by two kinds of processes, i.e. (1) mechanical exfoliation; (2) ultrasonic-assisted exfoliation in ethanol without ageing and with ageing for 210 days. NbSe2 micro/nanoparticles are applied on top of a Cu disk by a drop-casting process and the tribological property in sliding against a Cu pin under sliding electrical contact is investigated at room temperature. Mechanical exfoliation produces NbSe2 microplatets with typical sizes of 1 μm to 30 μ m with a thickness less than 2 μm. Ultrasonic-assisted exfoliation without aging facilitates the formation of NbSe2 micro/nanoplatets with sizes of 0.1 μm to 25 μm and nano-whiskers with 100 nm in diameter and 1 ~ 3 μm in length, but Nb2O5 and Se are also found on the basis of XPS results. Prolonged aging of the suspensions modifies the morphology by converting platets and whiskers into corrugated floccules (hybrid material), which are composed of Nb2O5, Se, NbSe2, and graphene. Notably, NbSe2 micro/nanoparticles by ultrasonic-assisted exfoliation without ageing exhibit an excellent lubricating property with low friction coefficient (0.3), mild wear, and longer wear lifetime (120 min) than that of mechanical exfoliated NbSe2 microplatets (10 min). The wear lifetime for the aged NbSe2 micro/nanoparticles can be as long as 504 min and are 4.2 times of the sample without aging, which can be a good solid lubricant for sliding electrical contact

Coupling of MoSe2 and graphitic carbon nitride (g-C3N4) by facile hydrothermal route for enhanced visible-light photocatalytic properties

Environmental issues have become an inevitable problem all over the world. By employing green renewable and abundant solar energy, semiconductor based photocatalysis is considered as an efficient process for the remediation of environmental pollution. g-C3N4 a stable π-conjugated system is a low cost and metal free photocatalysts that have the potential to remove various pollutants under visible light irradiation. In the present work, bulk g-C3N4 was synthesized by thermal polymerization of nitrogen rich precursor, melamine. To improve the photocatalytic performance, exfoliated g-C3N4 have been prepared by two different methods: a two steps liquid-phase ultrasonic-assisted exfoliation method and thermal exfoliation method. Protonation of bulk g-C3N4 followed by sonication was employed to obtain exfoliated g-C3N4. Second method is simple thermal treatment of bulk g-C3N4 to form exfoliated graphitic nitride. The exfoliated graphitic nitride was then coupled with MoSe2 and a comparative study has been done with pristine MoSe2. The prepared composite, MoSe2/g-C3N4, demonstrates a visible light degradation of 98% for Rhodamine-B (RhB) in 50 min.

Ultrasonic-Assisted Exfoliation of Graphitic Carbon Nitride and its Electrocatalytic Performance in Process of Ethanol Reforming

Graphitic carbon nitride was synthesized via thermolysis of urea and then ultrasonic exfoliated from colloidal solution to obtain phase pure ultrafine powder of g-C3N4. It was shown that ultrasonic-assisted exfoliation of the initial graphitic carbon nitride powder leads to an increase in its phase purity (PXRD), a change in the morphology (SEM), a decrease in the band gap from 2.93 eV to 2.85 eV (DRS) and an increase in the specific surface from 58.6 m2/g to 136.7 m2/g (BET). In addition, it was found that the exfoliated g-C3N4 is an effective catalyst for the process of electrocatalytic reforming – the hydrogen evolution from the water-alcohol solution. Based on volamperometry, it was found that the hydrogen overpotential of graphitic carbon nitride is equal to 249 mV (at 10 mA/cm2), and the Taffel slope is 112 mV/dec. The results of cyclic voltammetry of the electrode based on exfoliated g-C3N4 indicate its high stability, which allows us to consider the exfoliated graphitic carbon nitride as a promising basis of materials for electrocatalytic reforming of alcohols.

Rationally designed MoS2/protonated g-C3N4 nanosheet composites as photocatalysts with an excellent synergistic effect toward photocatalytic degradation of organic pollutants

The positively charged ultrathin g-C3N4 nanosheets are prepared by ultrasonic-assisted exfoliation of the protonated g-C3N4. Compared with the protonated g-C3N4 and exfoliated g-C3N4, the positively charged ultrathin g-C3N4 has abundant functional groups as well as desired dispersibility in deionized water, thus it could serve as a basic building block for designing related heterojunction composites. To take a full advantage of these features, the positively charged ultrathin g-C3N4/MoS2 composites are fabricated through a simple electrostatic adsorption and self-assembly process followed by a hydrothermal method. By loading an appropriate amount of MoS2 on the ultrathin g-C3N4 nanosheets, the as-fabricated composites exhibit considerable improvement on the photocatalytic activities toward the degradation of typical organic pollutants (i.e., methyl orange and phenol) under visible light irradiation. The composite containing 2 wt% MoS2 shows the highest efficiency of about 96.5% for the methyl orange degradation, which is about 3.5 times and 8 times compared to those of the positively charged ultrathin g-C3N4 and bulk g-C3N4, respectively. The superb photocatalytic performance benefits from the unique advantages, including richly available reaction sites, aligned energy levels between g-C3N4 and the MoS2, and efficient electron transfer. This work opens new possibilities for the rational design and construction of the g-C3N4 based composites as highly efficient and stable visible-light driven photocatalysts for the degradation of organic pollutants.

High-yield production of mesoporous nanoscrolls from kaolinite by ultrasonic assisted exfoliation

This study presents a novel idea to prepare large amounts of kaolinite nanoscrolls using ultrasonic assisted liquid exfoliation method. Ultrasonication was used to facilitate the intercalation of cetyltrimethylammonium chloride (CTAC) and also, to promote the exfoliation process greatly. The formation of the kaolinite nanoscrolls was confirmed by X-ray diffraction (XRD), SEM, and TEM. New mesopores formed among the nanoscrolls were in the range of 12–30 nm. The specific surface area (SBET) of liquid exfoliated kaolinite nanoscrolls was found to be 5 times larger than that of the original kaolinite. However, SBET increased 10 times when ultrasonication was used. The maximum SBET of the prepared kaolinite nanoscrolls with sonication was found to be 100 m2/g. The total pore volume increased from 0.049 cm3/g of original kaolinite to 0.22 cm3/g for liquid exfoliated product and 0.48 cm3/g for ultrasonic assisted liquid exfoliated product.