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Diatoms become silica scaffolds for growing molybdenum disulfide

Hybrid silica-MoS2 material could be used in optoelectronics, catalysis, and sensing

by Prachi Patel
August 12, 2016

Scanning electron micrographs of diatoms speckled with molybdenum disulfide.
Credit: Chem. Mater.
Scanning electron micrographs show a hybrid material in which nanosheets of molybdenum disulfide decorate the silica surface of a fossilized diatom.

Sheets of molybdenum disulfide just a few atoms thick show promise as semiconductors and light-emitting materials for electronic and optical devices. But there is no easy, cheap process to make the nanometers-thin sheets. Now, researchers report a one-step method that grows MoS2 nanosheets using the silica shells of marine diatoms as a scaffold (Chem. Mater. 2016, DOI: 10.1021/acs.chemmater.6b01738).

Credit: Chem. Mater.
A close-up of a molybdenum disulfide flake shows that it is made of several nanosheets, the edges of which are visible as bright lines.
Micrograph of a molybdenum disulfide flake.
Credit: Chem. Mater.
A close-up of a molybdenum disulfide flake shows that it is made of several nanosheets, the edges of which are visible as bright lines.

The technique yields a hybrid material consisting of silica particles tens of micrometers wide speckled with MoS2 flakes. The material’s blend of photonic and semiconducting properties and high surface area could make it useful for catalysis, sensing, energy storage, and optoelectronics, the researchers say.

MoS2 nanosheets are typically made using mechanical exfoliation or chemical vapor deposition. Exfoliation, which involves peeling off ultrathin layers from bulk crystals, is slow and gives limited amounts of material, while chemical vapor deposition requires expensive materials and tools.

Paul O’Brien, Sarah J. Haigh, and David J. Lewis at the University of Manchester used porous diatom shells as a scaffold to grow MoS2 nanosheets. The silica in the shells is a passive insulator material, making it an ideal scaffold for other functional materials. What’s more, the periodic arrangement of the pores helps the particles trap light and gives them a high surface area. Scientists have tried to recruit diatoms for nanotechnology, photonics, and drug delivery applications, and have coated them with materials like titanium and tin dioxide. “Nature has already preformed the shell as a nanoscaffold for us to use,” O’Brien says. “It’s cheap as chips and dug out of the ground by the ton.”

To make the hybrid material, the team mixed a powder of fossilized diatom shells, known as diatomaceous earth, into a tetrahydrofuran solution containing an organometallic precursor to MoS2, which coats the particles. After filtering out the solvent, the researchers dried the powder and heated it at 450 °C, converting the precursor into crystalline MoS2 flakes that dot the silica surface. The flakes have an average diameter of about 132 nm and range in thickness from one to six atomic layers.

There are thousands of diatom species. Combining diatoms of particular architectures with other two-dimensional metal sulfides could give materials with precisely tailored properties, the researchers say. For now, they are using the method to make materials for supercapacitor electrodes.



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