Coating porous membranes with a photocatalyst: Comparison of LbL self-assembly and plasma-enhanced CVD techniques

Abstract

Two methods for coating a macroporous surface of a membrane support layer with a photocatalyst are comparatively evaluated. Layer-by-layer self-assembly of nanoTiO2 with a multilayer of poly(diallyldimethylammonium chloride) and poly(acrylic acid) as a binder produces a sub-monolayer of photocatalyst nanoparticles on the grains of the membrane support. In contrast, plasma-enhanced chemical vapor deposition gives a dense uniform coating on the membrane grains. Neither method reduces membrane permeability. The photocatalytic activity of the coated membranes was evaluated in filtration tests with methylene blue as a probe compound. To compare photocatalytic performance of the two coatings, measured values of the reactive flux (η) were normalized by reaction rate constants (k'') determined in batch tests with the same catalyst. The proposed modeling approach relates coating's reactivity (η and k'') to the reactor's geometry expressed in terms of the length of the reaction zone (l rz) and coating density (θ). Both coating techniques result in a similar coating quality as witnessed by similar values of ηk''(or, equivalently, similar values of θl rz). The proposed analysis offers insights into possible ways for improving each coating technique.