Yanan Huang,Jibing Shen,Shuai Lin,Wenhai Song,Xuebin Zhu,Yuping Sun
High-quality few-layer M 4 C 3 T x (M = V, Nb, Ta) MXenes are very important for applications and are necessary for clarifying their physicochemical properties. However, the difficulty in etching for themselves and the existence of MC/MC 1−δ and M-Al alloy impurities in their M 4 AlC 3 precursors seriously hinder the achievement of defect-free few-layer M 4 C 3 T x (M = V, Nb, Ta) MXenes nanosheets. Herein, three different defect-free few-layer M 4 C 3 T x (M = V, Nb, Ta) nanosheets are obtained by using a universal synthesis strategy of calcination, selective etching, intercalation, and exfoliation. Comprehensive characterizations confirm their defect-free few-layer structure feature, large interlayer spacing (1.702–1.955 nm), types of functional groups (–OH, –F, –O), and abundant valance states (M 5+ , M 4+ , M 3+ , M 2+ , M 0 ). M 4 C 3 T x (M = V, Nb, Ta) free-standing films obtained by vacuum filtration of few-layer M 4 C 3 T x inks show good hydrophilia, high thermostability, and conductivity. A roadmap on synthesis of defect-free few-layer M 4 C 3 T x (M = V, Nb, Ta) nanosheets are proposed and three key points are summarized. This work provides detailed guidelines for the synthesis of other defect-free few-layer MXenes nanosheets, but also will stimulate extensive functional explorations for M 4 C 3 T x (M = V, Nb, Ta) MXenes nanosheets in the future.
Jingjing Chen,Xiaoli Wu,Chongchong Chen,Yihao Chen,Wenpeng Li,Jingtao Wang
Two-dimensional lamellar membranes featuring well-defined nanochannels hold great promise for efficient organics separation. However, the extensively existed non-selective microdefects within laminate architecture would impair separation efficiency and structure stability of membranes. Herein, defect-free metal-organic framework (MOF) lamellar membrane is facilely constructed by triple-needle electrostatic atomization technology. Specifically, one needle atomizes small-sized Cu-TCPP MOF nanosheets (TCPP = meso-tetra(4-carboxyphenyl)porphyrin) to build lamellar skeleton, and the other two needles meantime atomize Cu 2+ and TCPP to secondary-assemble crystals among nanosheets. In this manner, these non-selective microdefects are subtly sutured by the regenerated crystals with identical chemical components, resulting in a defect-free MOF lamellar membrane with enhanced structural stability. Importantly, this novel secondary-assembly method highly enhances the separation efficiency and meanwhile keeps high organics permeation for MOF membrane, with rejection of 93.8% for Rose Bengal (1.2 nm) and acetone permeance of 86.9 L m −2 h −1 bar −1 . In addition, the multipoint connection between nanosheets and crystals ensures excellent surface shearing and compaction resistance for MOF membrane, permitting high and steady operation performance for over 100 h. This secondary-assembly methodology by one-step process to construct defect-free and steady lamellar membrane provides a new avenue for the development of efficient separation membranes .
Graphene, a two-dimensional nanomaterial, has shown tremendous promising applications in a broad range of fields. Mass production of defect-free graphene is a prerequisite for its applications. In this work, by using a needle valve, we propose a simple hydrodynamic-assisted exfoliation method to produce high-quality few-layer graphene flakes. The prepared graphene flakes, with an average layer of 5 (~ 71% less than five layers) and a Raman D/G intensity ratio as low as 0.1, are free of defects and oxidation. The average thickness and length of the few-layer graphene flakes are 2.3 nm (~ 90% < 4 nm) and 1.9 μm (~ 50% in the range of 1–7 μm), respectively. In a lab-scale trial, the concentration of graphene can reach 0.40 g/ml under mild operating conditions (working pressure 20 MPa, 16 cycles), and the corresponding production rate is 0.40 g/h. The hydrodynamic-assisted exfoliation by needle valve potentially offers a simple and efficient method for large-scale production of high-quality graphene.
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