Organic Intercalant-Free Liquid Exfoliation Route to Layered Metal-Oxide Nanosheets via the Control of Electrostatic Interlayer Interaction

Abstract

A scalable organic intercalant-free liquid exfoliation route to 2D nanosheets (NSs) of layered transition-metal oxides (TMOs) is developed by employing hydronium-intercalated derivatives as precursors. The replacement of interlayer alkali metal ions with larger hydronium ions via acid treatment makes possible the efficient liquid exfoliation of TMOs without any assistance of organic intercalant cations. Not only a weakening of interlayer electrostatic interaction upon hydronium intercalation but also an efficient solvation of deintercalated hydronium ions via hydrogen bonding with polar solvents is mainly responsible for the high efficacy of hydronium-intercalated TMOs as precursors for liquid exfoliation. The nature of the solvent employed also has a profound effect on the exfoliation yield of these TMO NSs; viscosity, surface tension, density, and Hansen solubility parameter as well as the capability to solvate the exfoliated NSs and hydronium ions are crucial factors for determining the exfoliation efficiency of the hydronium-intercalated precursor. All the obtained Ti 1−x O 2 , MnO 2 , and RuO 2 NSs show highly anisotropic 2D morphologies and distinct negative surface charges with a zeta potential of −30 to −50 mV. Such distinct surface charges of these NSs render them versatile hybridization matrices for the synthesis of novel nanohybrids with enhanced functionalities. The hybridization with the liquid-exfoliated TMO NSs is quite effective in improving the photocatalytic activity of CdS and the electrode functionalities of graphene and graphene-layered double hydroxide nanohybrids. The present study underscores the usefulness of the present liquid exfoliation method in synthesizing organic-free TMO NSs and their nanohybrids as well as in widening the application field of exfoliated TMO NSs.

Lattice Engineering to Simultaneously Control the Defect/Stacking Structures of Layered Double Hydroxide Nanosheets to Optimize Their Energy Functionalities

“…Moreover, as determined from N 2 adsorption−desorption isotherm measurements, a lowering of the stacking number increases the surface areas and pore volumes of the restacked LDH NSs (Table 1), which was attributed to the formation of loosely stacked assemblies of thinner LDH layers with larger surface areas and larger pore-sizes (Figure 2b). 24,25 The poresize calculation carried out using the Barrett−Joyner−Halenda (BJH) equation clearly demonstrates the presence of mesopores with average sizes of ∼2−4 nm in the restacked LDH NSs (Figure 2c). 26 Restacking with larger intercalants leads to a significant increase in the average pore-size, indicating the formation of a loosely stacked structure of LDH NSs.…”

Two‐Dimensional Transition Metal Oxides and Chalcogenides for Advanced Photocatalysis: Progress, Challenges, and Opportunities

“…[ 60 ] In comparison, the exfoliation of TMOs, which are mostly of nonlayered structures, is basically hampered. The few examples of TMOs possessing layered structures include RuO 2 , [ 51 ] Na 2 Ti 3 O 7 , [ 61 ] V 2 O 5 , [56b,62] Bi 2 Sr 2 CaCu 2 O x , [ 63 ] WO 3 , [ 64 ] LiCoO 2 , [ 65 ] LiCo 0.95 Mg 0.05 O 2 , [ 65 ] MoO 3 , [ 66 ] K 0.45 MnO 2 , [ 67 ] KCa 2 Nb 3 O 10 , [ 68 ] K 2 Ln 2 Ti 3 O 10 , [ 69 ] KLnNb 2 O 7 , [ 69 ] RbLnTa 2 O 7 , [ 69 ] HNbMoO 6 , [ 70 ] MnO 2 [ 53,71 ] , etc. Compared with TMOs, more TMCs are of layered structures, e.g., MoS 2 , [ 72 ] ZnIn 2 S 4 , [ 73 ] TaS 2 , [ 74 ] TiS 2 , [ 75 ] WS 2 , [ 76 ] In 2 S 3 , [ 77 ] SnS, [ 78 ] SnS 2 , [ 79 ] SnSe, [ 80 ] SnSe 2 , [ 81 ] K 2 x Mn x Sn 3− x S 6 , [ 82 ] H 2 x Mn x Sn 3− x S 6 , [ 83 ] K 2 x Sn 4− x S 8− x , [ 84 ] etc.…”

“…The cation exchange‐assisted solution‐phase exfoliation has been explored for KMnO 2 or Na–MnO 2 with interlayer Na + or K + , [ 87 ] H 1.07 Ti 1.73 O 4 ·H 2 O with interlayer H + , [ 88 ] KCa 2 Nb 3 O 10 with interlayer K + , [ 68 ] K 0.4 MoS 2 or K 2 MoS 4 with interlayer K + , [ 89 ] and Li x /Na x /K 0.6 VS 2 with interlayer Li + /Na + /K + . [ 90 ] In the case of Na–MnO 2 , [71b] ion exchange of Na + by H + is conducted by immersing the bulk Na–MnO 2 in 0.1 mol L −1 HCl at room temperature to give the bulk H–MnO 2 precursor. The MnO 2 NSs can then be peeled off from the bulk H–MnO 2 under vigorous stirring in a solution of tetrabutylammonium hydroxide (TBAOH).…”

An electrochemically reversible lattice with redox active A-sites of double perovskite oxide nanosheets to reinforce oxygen electrocatalysis

“…In this case the conuence of solvent surface tension (g) and hydrogen bonding ability determines the extent of NS exfoliation. 37,38 To achieve better exfoliation, g should have parity with the low surface energy of the NSs. The thinner NSs in ethanol are due to its lower g (22.1 mN m À1 ) while water with higher g (72.8 mN m À1 ) results in thicker NSs.…”