Large-Scale Production of Size-Controlled MoS 2 Nanosheets by Shear Exfoliation Eswaraiah Varrla, †,§ Claudia Backes, †,§ Keith R. Paton, †,‡ Andrew Harvey, †,§ Zahra Gholamvand, †,§ Joe McCauley, § and Jonathan N. Coleman* ,†,§ † CRANN and AMBER Research Centres and § School of Physics, Trinity College Dublin, Dublin 2, Ireland ‡ Thomas Swan & Co. Ltd., Rotary Way, Consett, County Durham DH8 7ND, United Kingdom * S Supporting Information ABSTRACT: In order to fulfill their potential for applications, it will be necessary to develop large-scale production methods for two-dimensional (2D) inorganic nanosheets. Here we demonstrate the large-scale shear-exfoliation of molybdenum disulfide nanosheets in aqueous surfactant solution using a kitchen blender. Using standard procedures, we measure how the MoS 2 concentration and production rate scale with processing parameters. However, we also use recently developed methods based on optical spectroscopy to simultaneously measure both nanosheet lateral size and thickness, allowing us to also study the dependence of nanosheet dimensions on processing parameters. We found the nanosheet concentration and production rates to depend sensitively on the mixing parameters (the MoS 2 concentration, C i ; the mixing time, t; the liquid volume, V; and the rotor speed, N). By optimizing mixing parameters, we achieved concentrations and production rates as high as 0.4 mg/mL and 1.3 mg/min, respectively. Conversely, the nanosheet size and thickness were largely invariant with these parameters. The nanosheet concentration is also extremely sensitive to the surfactant concentration. However, more interestingly the nanosheet lateral size and thickness also varied strongly with the surfactant concentration. This allows the mean nanosheet dimensions to be controlled during shear exfoliation at least in the range ∼40-220 nm for length and ∼2-12 layers for thickness. We demonstrate the importance of this by showing that the MoS 2 nanosheets prepared using different surfactant concentrations, and so displaying different nanosheets sizes, perform differently when used as hydrogen evolution catalysts. We find the nanosheets produced using high surfactant concentrations, which gives smaller flake sizes, perform significantly better, consistent with catalysis occurring at nanosheet edges. Finally, we also demonstrate that shear exfoliation using a kitchen blender is not limited to MoS 2 but can also be achieved for boron nitride and tungsten disulfide. ■ INTRODUCTION Over the past few years the study of two-dimensional nanomaterials such as graphene 1,2 and molybdenum disulfide (MoS 2 ) 3-5 has become one of the most important areas of materials science. Such materials show potential in a range of applications from electronics to electrochemistry. Perhaps the most versatile way of making two-dimensional nanosheets is by liquid phase exfoliation of layered crystals. 6-9 In this method, layered crystallites are ultrasonicated in certain stabilizing liquids such as appropriate solvents 8,10,11 or solutions of surfactants 12-14 or polymers. 15,16 This results in the production of nanosheets which are stabilized against aggregation via the interaction with the liquid. 12,15,17,18 This method has been used to successfully produce dispersions of nanosheets of a range of materials, including graphene, 8,19 BN, 6,20 and various transition metal dichalcogenides 6,10,21,22 such as MoS 2 and WSe 2 . Using sonication-assisted exfoliation, dispersions of volumes typically in the range of hundreds of milliliters can be produced. 23 The nanosheets are typically a few layers thick and of lateral sizes in the range ∼50 nm to 2 μm, depending on the material. Importantly these nanosheets tend to be free of basal plane defects. 8,23 Such dispersions can be used to process the nanosheets into functional structures such as films, networks, and composites. 20,24-26 Such structures have proven useful in a range of application areas including plasmonics, 27 photo- detectors, 24,28,29 electrodes in dye-sensitized solar cells, 30 supercapacitors 31 and batteries 26,32 or electrocatalysts 33 for hydrogen evolution. More recently it has been demonstrated that liquid exfoliation can be achieved by exposing graphite to high shear rates 34 using either rotor-stator high shear mixers 35,36 or simple kitchen blenders. 37,38 This gives graphene nanosheets of similar size and quality to those produced using sonication. The advantage of this technique is that much higher volumes can be produced compared to sonication, and so much higher production rates can be achieved. Such work has allowed liquid phase exfoliation of graphite to be scaled up toward an industrial process for graphene production. However, to date Received: December 6, 2014 Revised: January 2, 2015 Published: January 6, 2015 Article pubs.acs.org/cm © 2015 American Chemical Society 1129 DOI: 10.1021/cm5044864 Chem. Mater. 2015, 27, 1129-1139