German Edition: DOI: 10.1002/ange.201502077 Photocatalysis International Edition: DOI: 10.1002/anie.201502077 Controlling the Selectivity of the Surface Plasmon Resonance Mediated Oxidation of p-Aminothiophenol on Au Nanoparticles by Charge Transfer from UV-excited TiO 2 ** Jiale Wang, Romulo A. Ando, and Pedro H. C. Camargo* Abstract: Although catalytic processes mediated by surface plasmon resonance (SPR) excitation have emerged as a new frontier in catalysis, the selectivity of these processes remains poorly understood. Here, the selectivity of the SPR-mediated oxidation of p-aminothiophenol (PATP) employing Au NPs as catalysts was controlled by the choice of catalysts (Au or TiO 2 - Au NPs) and by the modulation of the charge transfer from UV-excited TiO 2 to Au. When Au NPs were employed as catalyst, the SPR-mediated oxidation of PATP yielded p,p- dimercaptobenzene (DMAB). When TiO 2 -Au NPs were employed as catalysts under both UV illumination and SPR ex- citation, p-nitrophenol (PNTP) was formed from PATP in a single step. Interestingly, PNTP molecules were further reduced to DMAB after the UV illumination was removed. Our data show that control over charge-transfer processes may play an important role to tune activity, product formation, and selectivity in SPR-mediated catalytic processes. Nanomaterials that display both high catalytic activities and selectivities are of great importance in the field of heteroge- neous catalysis, as they make it possible to minimize the formation of side products and the need for several purifica- tion steps. [1, 2] As an example, catalytic routes for the synthesis of aromatic azocompounds from the oxidation of anilines or the reduction of nitroaromatics under mild conditions offer high yields but selectivities remain challenging. [3, 4] Nonethe- less, this is of great importance as they represent high-value compounds that are widely employed in industry. [3–5] Recently, catalytic processes mediated or enhanced by the surface plasmon resonance (SPR) excitation in plasmonic nanomaterials, such as gold (Au) and silver (Ag), have emerged as a new frontier in heterogeneous catalysis. [6–10] This approach allows for the use of light as the energy input to drive chemical transformations. The oxidation of p-amino- thiophenol (PATP) to p,p-dimercaptoazobenzene (DMAB) has been widely used as a model reaction to probe SPR- mediated catalytic activities of Au and Ag NPs. [11–15] In this process, it has been shown that the transfer of hot electrons from the SPR-excited metal NPs to adsorbed O 2 molecules from air is responsible for O 2 activation, which generates 3 O 2 species that subsequently drive the PATP oxidation. [11–16] Although several examples have been reported on the SPR- mediated or SPR-enhanced catalysis of Au and Ag NPs, studies on the selectivity of these processes remain scarce and challenging despite its great importance in catalysis. As the activation of molecular oxygen (O 2 ) represents a critical step in this and several other oxidation reactions, the control over the charge states in the metal may represent an effective approach to tune its activities and selectivities. [6, 17–20] In order to control the charge states in a metal, however, it is necessary to introduce an additional electron source into the system. In this context, charge transfer from a semiconducting material, such as TiO 2 , represents an intuitive strategy. [21, 22] Here, we show that the selectivity in SPR-mediated oxidation of PATP by Au NPs can be controlled by maneuvering its charge state via charge transfer from UV- excited TiO 2 to Au. More specifically, while the SPR- mediated oxidation of PATP in Au NPs led to the formation of DMAB, the use of TiO 2 -Au NPs as catalysts under both UV and SPR excitation led to a one-step oxidation of PATP to p- nitrophenol (PNTP). Moreover, PNTP could be further reduced to DMAB on the TiO 2 -Au NPs when the UV- excitation was turned off. Figure 1a and b shows SEM images for the Au NPs and TiO 2 colloidal spheres decorated with Au NPs (TiO 2 -Au) that were employed as catalysts in the SPR-mediated oxidation of PATP. The TiO 2 -Au colloidal spheres were obtained by a protocol recently developed in our group that consists of the use of TiO 2 colloidal spheres as physical templates for Au deposition. [23] Figure 1a shows that the TiO 2 -Au material displayed a spherical shape of relatively uniform size with a diameter of about 200 nm and comprised of 20 nm Au NPs at the surface. Moreover, the deposited Au NPs were uniformly distributed over the TiO 2 surface without signifi- cant aggregation. In order to compare the catalytic activity of the TiO 2 -Au material with their Au NPs counterpart, Au NPs were synthetized under similar experimental conditions as described in Figure 1a, but in the absence of TiO 2 . Figure 1 b shows that the size of the Au NPs was similar to those described in in TiO 2 -Au material (about 20 nm). After the synthesis, the Au and TiO 2 -Au materials were employed as catalysts towards the SPR-mediated oxidation of PATP as a model reaction. In this transformation, the transfer of electrons from Au to adsorbed O 2 molecules represents the crucial step for O 2 activation, which in turn contributes to the [*] Dr. J. Wang, Prof. Dr. R. A. Ando, Prof. Dr. P. H. C. Camargo Departamento de Química Fundamental, Instituto de Química Universidade de S¼o Paulo Avenida Lineu Prestes, 748, 05508-000 S¼o Paulo (Brazil) E-mail: camargo@iq.usp.br [**] This work was supported by the Fundażo de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP) (grant number 2013/19861-6) and the Conselho Nacional de Desenvolvimento Cientifíco e Tecnolo- gico (CNPq) (grant number 471245/2012-7). P.H.C.C. and R.A.A. thank the CNPq for research fellowships. J.W. thanks FAPESP (grant number 2013/05709-8) for a fellowship. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201502077. A ngewandte Chemi e 1 Angew. Chem. Int. Ed. 2015, 54,1–5  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü