Photocatalytic properties of layer-by-layer thin films of hexaniobate nanoscrolls

Abstract

High efficient photocatalytic surfaces were obtained through the layer-by-layer (LbL) deposition of hexaniobate nanoscrolls on conductive glasses. These films were deposited by alternative immersions of the substrate into exfoliated hexaniobated suspensions (pH = 8) and poly(allylamine hydrochloride) solutions (pH = 4). The organic species were further removed by thermal treatment leading to a fuzzy assembly of hexaniobate nanoscrolls. Pre-adsorption of [Pt(NH 3 ) 4 ] 2+ cations on the niobate layers allows the production of metallic Pt nanoclusters on the film layers. The Pt-modified films exhibited apparent quantum yields of (4.0 ± 0.5) % for H 2 evolution from water/methanol mixtures under UV-A irraditation. The H 2 evolution rates varied linearly with the number of deposited bilayers, indicating that no active sites are lost as the film is grown. The photoelectrochemical properties of the films reveal that the small size of the hole scavenger and its easy diffusion into the hexaniobate layers are key aspects for the photocatalytic activity. In the absence of alcohols as hole scavengers, irradiation of the hexaniobate LbL films in aqueous solutions leads to the production of surface-bound peroxides that limit the photocatalytic water splitting ability of these materials. The results presented here provide evidence for the effectiveness of the LbL technique to deposit thin films of layered materials retaining their interesting adsorption chemistry. This methodology can be further employed for the development of highly active photocatalytic surfaces.