Improvement of Noble Metal Based Photocatalysts by Spray Pyrolysis Processes: A review of progress in photocatalytic materials for water treatment applications

Oxidation technologies and advanced oxidation processes (AOPs) have been regarded as a competitive method for the remediation of persistent pollutants in water. Among AOPs, the use of photocatalysis has particularly attracted interest in recent decades. However, attempts to improve the efficiency of photocatalysts in terms of both enhanced activity and applicability under visible light have proved challenging. In this context, there is a need for processes able to achieve the synthesis of innovative nanostructured materials meeting these criteria with reproducibility and scalability in mind. The aim of this review is to focus on two themes of interest, namely noble metal based catalysts and spray pyrolysis (SP) processes. Several alternative SP methods have been reported and these will be described. The emphasis is placed on the recent use of SP for the synthesis of noble metal/semiconductor nanomaterials and their enhanced photocatalytic activity. Recent innovations in the design of SP processes and their potential to further improve noble metal-based photocatalysts are also examined. Finally, the possibility of using SP processes as a flexible tool to achieve immobilisation of photocatalysts onto substrates and in reactor for real water treatment application is considered.