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

Abstract

Two methods for coating a microporous surface of a membrane support layer with a photocatalyst are comparatively evaluated. Layer-by-layer self-assembly of nanoTiO 2 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 (, m/s) were normalized by reaction rate constants (′′, m/s) determined in batch tests with the same catalyst. The proposed modeling approach relates coating's reactivity (and ′′) to the reactor's geometry expressed in terms of the length of the reaction zone () and coating density (). Both coating techniques result in a similar coating quality as witnessed by similar values of / ′′ (or, equivalently, similar values of). The proposed analysis offers insights into possible ways for improving each coating technique.

Proof of Concept for Light Conducting Membrane Substrate for UV-Activated Photocatalysis as an Alternative to Chemical Cleaning

“…A novel configuration in which the feed solution was fed from the uncoated side of the membrane was studied, mainly to independently control the separation and photocatalytic functions of the membrane [6]. Separating the separation and photocatalysis functionalities increases process robustness because failure of one does not necessarily result in the failure of the other [8]. Another advantage cited for this configuration is retention of particulates capable of shielding UV light on the feed side of the membrane, thus making photocatalysis more efficient because the permeated side has more optical transparency than the feed side.…”

Chemical Vapor Deposition of Photocatalyst Nanoparticles on PVDF Membranes for Advanced Oxidation Processes

“…Even if kinetic rate constants are strongly dependent on membrane composition, investigated pollutants and the UV lamp power used [ 48 ], it is important to note that the obtained values of kinetic rate constants are the same order of magnitude as those found in other literature works where the photoactive nanomaterial was either directly synthesized or immobilized on polymer substrates [ 49 , 50 , 51 ]. These rate values make the CVD of photocatalyst nanoparticles on porous polymer membranes a suitable technique for applications in the field of advanced oxidation processes.…”

Ceramic Membranes Photocatalytically Functionalized on the Permeate Side and Their Application to Water Treatment

“…The overall efficiency of these photocatalytic contactors can be discussed considering the elemental photocatalytic microreactors corresponding to the individual pores opened at the permeate surface, the surface of which is coated with photocatalyst and is irradiated by UV light [29]. The residence time of the solute in these elemental microreactors is a complex function of the permeate flow, of the solute self-diffusion in the liquid phase, and of the pore size and geometry.…”

“…Until now, very few papers dealt with photocatalytic functionalization of a membrane on the permeate side. They were mainly published by us [26,27,28,29], but also by Romanos et al [30,31,32,33,34], Guo et al [35], and Horovitz et al [36,37].…”

“…Another pathway was considered for covering the substrate grains with an anatase coating. It was done by PECVD, using titanium tetra-isopropoxide as a TiO 2 precursor, with a thermal post-treatment for anatase crystallization [29,40,41]. Grains of alumina disks with an 800 nm pore-sized top layer, covered with such a PECVD coating, are shown in Figure 2c.…”