Atomic Layer Deposition Brings Applications of Two-Dimensional Silica to the Fore

The explosion of interest in two-dimensional (2D) materials has spurred advances in catalysis in the confined space between a 2D van der Waals layer and a catalytic surface, as well as ultimate permeation through single atomic layers. An intriguing material in this regard is a 2D silica polymorph discovered about 10 years ago. The structure intrinsically includes small molecule-sized pores; thus, defects are not required to permeate the layer and access the catalytic surface. Surface science studies have shown the potential for 2D silica to act as a size-selective membrane and to alter catalytic rates, mechanisms and selectivity. The advent of an atomic layer deposition (ALD) process for 2D silica that does not require ultra-high vacuum or single crystal substrates promises advances in exploring and applying perm-selective 2D silica layers to challenging problems in catalysis. Recent work using ALD-grown 2D silica as single layer membranes revealed that permeation through the layer proceeds through an adsorption-diffusion-permeation mechanism rather than ballistic transport leading to counterintuitive permeation trends. Nonetheless, comparison of straight and branched alcohols revealed preferential permeation of the straight-chain alcohols, demonstrating shape-selectivity. Results for initial catalytic studies under 2D silica confinement are analyzed and the prospects for the future discussed.