Polymer Precursors Effect in the Macromolecular Metal-Polymer on the Rh/RhO 2 /Rh 2 O 3 Phase Using Solvent-Less Synthes

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Polymer Precursors Effect in the Macromolecular Metal‑Polymer on the Rh/RhO2/Rh2O3 Phase Using Solvent‑Less Synthesis and Its Photocatalytic Activity C. Diaz1 · M. L. Valenzuela2   · O. Cifuentes‑Vaca3 · M. Segovia1 Received: 1 April 2020 / Accepted: 18 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract A mixture of a nanostructured Rh/RhO2 phase was easily obtained by thermally treating the macromolecular Chitosan·(RhCl3)x precursor, while the Rh/Rh2O3 phase was obtained by pyrolyzing PSP-4-PVP·(RhCl3)x, precursors. The nature of the polymeric precursor acting as a solid-state template does not significantly influence the “foam-like” morphology of the Rh/ RhO2 and Rh/Rh2O3 nanoparticles. The size of the obtained products is within the range of 16 nm, as confirmed by HRTEM. A possible formation of the Rh/RhO2 and Rh/Rh2O3 nanoparticles is proposed. The bandgap values estimated from Tauc plots are 3.7 eV, and 3.0 eV for Rh/RhO2 and R ­ h2O3, respectively. Their photocatalytic activity was measured, for the first time, using a methylene blue pollutant, achieving a photodegradation of 78% for Rh/RhO2 and 70% for Rh/Rh2O3 in 300 min.

1 Introduction From the precious metals of the periodic table, the Ir, Rh Pd, and Pt are the most catalytically active [1], and their activity is hugely enhanced at the nano-level [2, 3]. Among these, rhodium plays an essential role in several catalytic applications [4, 5]. However, the catalytic mechanism of rhodium materials is still elusive. Recent investigations suggest that the active centers could be in rhodium oxide rather than rhodium [5, 6], and the most common rhodium oxides are ­Rh2O3 and ­RhO2. Although they have a wide range of Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s1090​4-020-01634​-2) contains supplementary material, which is available to authorized users. * C. Diaz [email protected] * M. L. Valenzuela [email protected] 1



Departamento de Química, Facultad de Química, Universidad de Chile, La Palmeras 3425, Nuñoa, Casilla 653, Santiago de Chile, Chile

2



Instituto de Ciencias Químicas Aplicadas, Facultad de Ingeniería, Universidad Autónoma de Chile, Llano Subercaseaux 2801, San Miguel, Santiago de Chile, Chile

3

Facultad de Ciencias Exactas, Universidad Andrés Bello, Concepción, Autopista Concepción‑Talcahuano 7100, Talcahuano, Chile



applications in catalysis, scarce preparation methods of nanostructured ­Rh2O3 and ­RhO2 have been reported, and their morphological and size control remains poorly known [4, 5, 7–9]. All the described R ­ h2O3 preparation methods are solution-based and solid-state methods that have not been reported yet. For instance, Rh(NO3)3 [7, 8], usually produces Rh oxides leading to R ­ hO2 and R ­ hO2 mixtures. Different mixtures can be obtained based on the thermal treatment temperature [8]. A mixture of α-and β-Rh2O3 can be obtained by heating to 797 °C, while a further increase up to 1000 °C is required to obtain pure β-Rh2O3 [8]. B