Clay-Supported Metal Oxide Nanoparticles in Catalytic Advanced Oxidation Processes: A Review

Abstract

Advanced oxidation processes (AOPs) utilizing heterogeneous catalysts have attracted great attention in the last decade. The use of solid catalysts, including metal and metal oxide nanoparticle support materials, exhibited better performance compared with the use of homogeneous catalysts, which is mainly related to their stability in hostile environments and recyclability and reusability. Various solid supports have been reported to enhance the performance of metal and metal oxide catalysts for AOPs; undoubtedly, the utilization of clay as a support is the priority under consideration and has received intensive interest. This review provides up-to-date progress on the synthesis, features, and future perspectives of clay-supported metal and metal oxide for AOPs. The methods and characteristics of metal and metal oxide incorporated into the clay structure are strongly influenced by various factors in the synthesis, including the kind of clay mineral. In addition, the benefits of nanomaterials from a green chemistry perspective are key aspects for their further considerations in various applications. Special emphasis is given to the basic schemes for clay modifications and role of clay supports for the enhanced mechanism of AOPs. The scaling-up issue is suggested for being studied to further applications at industrial scale.

Keywords: advanced oxidation process; clay; metal nanoparticles; nanoparticles; photocatalysis.

Figure 1

Various AOP methods.

Figure 2

Diagram of the reduction–oxidation by Fe²⁺/Fe³⁺.

Figure 3

The popularity of metal oxides in AOPs observed based on publications during 2019–2020.

Figure 4

ZnO (a) nanoflowers, (b) nanorods, (c) nanoflakes, and (d) nanospheres. Reproduced from ref. [54,58,59,60] with permission from the publishers (Springer Nature, 2015; PLOS ONE, 2020; Science Publication, 2009; IOP Publishing, 2020).

Figure 5

The possible formation of porous structures and new surfaces as adsorption sites by metal/metal oxide impregnation.

Figure 6

Schematic representation of clay pillarization.

Figure 7

XRD patterns and SEM images of Fe-pillared bentonite with varied Fe content (5 and 10 mmol/10 g). Adapted from Ref. [123] with permission from BCREC Group.

Figure 8

TEM images of SnO₂/montmorillonite at Sn/montmorillonite ratios of (a) 2.5 and (b) 10.0 mmol/10 g. Adapted from Ref. [80] with permission from the Elsevier B.V., 2021.

Figure 9

The effect of the metal:clay ratio on the Δd₀₀₁ of pillared clays.

Figure 10

Schematic representation of metal nanoparticle impregnation onto PILC.

Figure 11

Schematic representation of porous clay heterostructure synthesis.

Figure 12

Schematic representation of the dispersion of metal nanoparticles in clay structure.

Figure 13

Potential diagram of some semiconductors.