Photocatalytic Nanostructured Self-Assembled Poly(allylamine hydrochloride)/Poly(acrylic acid) Polyelectrolyte Films Containing Titanium Dioxide-Gold Nanoparticles for Hydrogen Generation Nicolle Dal’Acqua, † Francine Ramos Scheffer, ‡ Rosiana Boniatti, † Barbara Virgínia Mendonc ̧ a da Silva, § Janaina Viana de Melo, § Janaina da Silva Crespo, † Marcelo Giovanela, † Marcelo Barbalho Pereira, ‡ Daniel Eduardo Weibel, ‡ and Giovanna Machado* ,§ † Universidade de Caxias do Sul (UCS), Caxias do Sul, RS, Brazil ‡ Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil § Centro de Tecnologias Estrate ́ gicas do Nordeste (CETENE), Recife, PE, Brazil * S Supporting Information ABSTRACT: In this study, we developed a facile layer-by-layer (LbL) method of incorporating gold (Au) and titanium dioxide (TiO 2 ) nanoparticles (NPs) into self- assembled photocatalytic films (SAPFs). The resulting SAPFs were then systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV-vis spectrophotometry, profilometry, and atomic force microscopy (AFM). The results revealed that the SAPFs incorporated TiO 2 and Au NPs with sizes of 21.2 ± 0.30 and 12.5 ± 0.05 nm, respectively. Moreover, the SAPFs with 40, 60, 80, and 100 layers exhibited thicknesses of 410, 472, 917, and 945 nm, respectively. The hydrogen produced by the SAPFs increased with increasing UV irradiation time in a linear relationship. Hydrogen was also produced within the bulk of the polymer/TiO 2 - Au NP assemblies because water hydrates the network, allowing for facile hydrogen production in the bulk under irradiation. The present approach represents a significant advance over traditional nanostructured catalysts, for which the highest possible surface area is desired to maximize photocatalytic activity. ■ INTRODUCTION In heterogeneous photocatalysis, a general concern is synthesiz- ing photocatalysts with the maximum surface area to increase their ability to degrade pollutants or generate hydrogen upon exposure to light. The maximum number of active sites can be gradually increased by decreasing the photocatalyst size (nanoparticles, nanotubes, nanowires). 1-4 Both simple and highly sophisticated methodologies are used to pursue this objective. One example of this effort is the use of titanium dioxide (TiO 2 ) semiconductors in a wide range of applications because of its availability, stability, low cost, and favorable band-gap energy (E g ). Suspended TiO 2 powder, especially in its commercial form (P-25), has been widely investigated and results in efficient photocatalysts because of the large surface area available for reaction. On the other hand, suspended TiO 2 powder has several disadvantages, including the fact that it cannot be efficiently recovered and reused for continuous systems, which increases treatment costs and makes the process economically unfeasible. 5 A great deal of research has been conducted in this field, particularly in the area of new materials as components for the development of photovoltaic devices. 6-17 TiO 2 -gold (Au) nanoparticles (NPs) have frequently been used, although the detailed mechanism of efficient electron injection upon plasmon band excitation on the surface of TiO 2 -Au NPs remains unclear. However, a recent study reported an improved photo- electrochemical effect of the TiO 2 -Au composite the charging of metal nanoparticles followed by Fermi level equilibration between Au and TiO 2 nanostructures. Chandrasekharan and Kamat 5 evaluated the dependence of the zero-current potential on the solution pH. The band energies of metal oxide semiconductors such as TiO 2 exhibit a strong pH dependence. This results from the surface protonation/deprotonation equilibrium, confirming that adsorbed Au NPs improve the accumulation of electrons within the TiO 2 particulate film by facilitating hole transfer at the electrolyte interface with minimal charge-recombination losses. The adsorbed Au NPs facilitate charge stabilization within the nanostructured TiO 2 films and play an important role in increasing the photovoltage, improving the interfacial charge-transfer kinetics. Received: May 5, 2013 Revised: October 8, 2013 Published: October 8, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 23235 dx.doi.org/10.1021/jp404429r | J. Phys. Chem. C 2013, 117, 23235-23243