In-Situ Deposition of Plasmonic Gold Nanotriangles and Nanoprisms onto Layered Hydroxides for Full-Range Photocatalytic Response towards the Selective Reduction of p-Nitrophenol

Javier Graus,Carlos Bueno-Alejo,Jose Hueso

doi:10.3390/catal8090354

Abstract

In this work, we present photocatalysis as a greener alternative to conventional catalysis where harsh reaction conditions, temperature and/or pressure are needed. Photodegradation of organic pollutants is a cost-effective, eco-friendly solution for the decontamination of water and air, and is a field that has been continuously growing over the last decade. Plasmonic metal nanoparticles absorb light irradiation that is transferred to the chemical reaction in a different fashion. Furthermore, plasmonic nanostructures can be combined with other materials, such as semiconductors or a basic support, to create hybrid systems capable of overcoming certain challenges that photocatalysis is facing nowadays and to expand the photocatalytic response towards the whole visible-near infrared (Vis-NIR) ranges. The main objective of this work has been to in-situ synthesize plasmonic anisotropic gold nanoparticles onto hydrotalcite (HT) and calcined hydrotalcite (CHT) supports by way of a sequential deposition-reduction (DR) process and to evaluate their efficiency as heterogeneous catalysts towards the selective oxidation of p-nitrophenol (hereafter 4-NP), a well-known model contaminant, either in the absence or the presence of full-range light irradiation sources (LEDs) spanning the whole UV-Vis-NIR range. Special attention has been paid to the optimization of the catalyst preparation parameters, including the pH and the concentration of reducing and stabilizing agents. Interestingly, the use of thermally modified hydrotalcites has enabled a strong metal-support interaction to induce the preferential formation of triangular-shaped Au nanoparticles with ca. 0.8 wt.% loading while increasing the colloidal stability and surface area of the catalyst with respect to the commercial untreated HT supports.

Highlights

Chemical and petrochemical industries produce an extensive range of harmful and highly toxic organic contaminants such as phenols or COx [1,2]
The synthesis of gold nanoparticles has been thoroughly addressed in the materials and methods section and included the use of increasing concentrations of NaOH 0.5 M to adjust the pH of the initial suspensions from 10 to 13 while keeping a fixed ratio of sodium borohydride at 2.1 mM as reducing agent
A synthesis of a hybrid photocatalyst composed of gold nanotriangles supported on different hydrotalcites has been successfully developed

Summary

Introduction

Chemical and petrochemical industries produce an extensive range of harmful and highly toxic organic contaminants such as phenols or COx [1,2]. The removal strategy has been to develop catalysts that promote or activate chemical reactions that often require the use of toxic and aggressive chemical oxidants, chromates and permanganates among them, generating toxic by-products as a result of the pollutant decomposition process [3]. Catalysts 2018, 8, 354 obtains the energy required to activate the pollutant degradation from solar [5] or artificial light [6] and take advantage of semiconductors materials and metal nanoparticles to trigger different mechanisms that promote the degradation. The number of potential possibilities with nanomaterials is endless, nanostructured hybrid catalyst, plasmonic metal nanoparticles and quantum dots stands out as three of the most promising nanostructures for many important applications [7,8]

Methods

Results

Conclusion