A Perspective on the Flame Spray Synthesis of Photocatalyst Nanoparticles.

Wey Teoh

doi:10.3390/ma6083194

Abstract

The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, that is, high surface area and surface energetics. For these reasons, FSP finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by FSP requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since FSP appears to be an elegant tool in synthesising oxide nanoparticles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by FSP in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted, especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by FSP.

Highlights

Flame Spray Synthesis of NanoparticlesFlame aerosol synthesis is an established manufacturing technique for producing commodity nanoparticles at the industrial scale
The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries
We investigated the polymorphic effect of FSP TiO2 nanocrystals on the photocatalytic degradation of different organic compounds

Summary

Flame Spray Synthesis of Nanoparticles

Flame aerosol synthesis is an established manufacturing technique for producing commodity nanoparticles at the industrial scale. Whilst the extremely short residence time of flame particles formation (typically in the range of milliseconds, that is, from the liquid precursor spray right up to agglomerated particles leaving the flame), was advantageous in fabricating nanoscale particles, the time spent by the aerosol particles at high temperature flame zone was too short for sufficient defects healing to take place [42,43] This is in contrast to the syntheses by solid-state sintering, where materials are typically subjected to prolonged high temperature exposure (>1273 K, >6 h) to yield oxide crystals with minimum defects as necessary for applications in superconductors and solar water splitting [44]. Perspective, we revisit some case studies in the development of photocatalysts by FSP, highlighting the progress as well as the scientific and technical challenges in bridging the FSP and photocatalysis

Simple Metal Oxide Photocatalysts—Starting from the Basics

In situ Flame-doping of Photocatalysts—A Small Addition Makes Big Changes

Flame-Made Mixed Metal Oxide Photocatalysts—Trying out Complexities

Flame Deposition of Noble Metals on Oxide Photocatalysts

Findings

Concluding Remarks