Multiscale design of ZnO nanostructured photocatalysts

Abstract

A systematic investigation of the photocatalytic activity (PCA) of nanostructured ZnO films showed how this is directly affected by the films' morphology at different scales, from the macroscale morphology of films (e.g. thickness and surface area), to the microscale feature arrangement (e.g. aligned vs. randomly oriented structures or interpenetrated ones), to the nanoscale structure (e.g. crystal size and orientation). The interest in immobilizing photocatalysts in water treatment stems from concerns about the potential toxicity of their slurry form, which requires expensive downstream removal. Immobilisation, though, leads to a reduction in PCA, generally attributed to a lower surface area. By reducing the films' feature size to the nanoscale, an immobilized photocatalyst with high surface area can be achieved. At this scale, however, feature structuring and morphology become important as they determine the interaction between light and the photocatalytic material. In this work, nanostructured ZnO films with different morphology, arrangement and structure were produced by electrochemical anodization of zinc and were tested using the degradation of phenol in a batch reactor as a model system. Results show that the PCA for immobilized catalysts can be optimised by controlling microscale arrangement (light absorbance capacity) and nanoscale structure (crystal size and orientation) rather than macroscale morphology (surface area). These results provide a clear direction to maximising the photocatalytic activity of immobilised photocatalysts for the removal of organic pollutants from water.

Synthesis and photoluminescence properties of hybrid 1D core–shell structured nanocomposites based on ZnO/polydopamine

“…Zinc oxide (ZnO) nanostructures are well known materials with advanced structural and optical properties. [1][2][3][4] Due to their high refractive index, wide band gap and room temperature photoluminescence, they have been used in different applications, such as optical coatings, photocatalysis, [5][6][7][8] optical sensors and biosensors. 2,9,10 The electronic and optical properties of ZnO can be tuned by forming ZnO-composite nanomaterials.…”

Photocatalytic ZnO Foams for Micropollutant Degradation

“…Higher porosity and larger pores are associated with higher penetration of light into structured photocatalyst, [16,40] in contrast to photon penetration which, for polycrystalline materials, is in the order of a tenth of a micrometer. [41] Improved light penetration translated into a higher overall quantum yield for shorter sintering times (Table 2). Furthermore, a higher porosity will also reduce mass transfer resistances for the liquid penetrating into the foam.…”

Environmentally Benign Hybrid Nanocomposite Beads for Azo Dyes Remediation via Synchronized Dual Degradation Mechanisms

“…For instance, nano-sized MgO was outstanding basic catalyst for several organic reactions (Riyadh et al 2018). Large band gap, low dielectric constant and its refractive index are the main criteria that have generated many attempts to employ MgO as a photocatalyst for dyes degradation in aqueous solution (Zheng et al 2019). However, stabilization is a signi cant issue in nanoparticles synthesis; where the particles tend to agglomerate; increase in size with subsequent occulation.…”

“…Polysaccharides have also been used for this purpose such as chitosan and its derivatives, due to their excellent synergy and bifunctional expected effects (León et al 2017). Besides, the main problems to the prospective use of MgO NPs as catalysts are their challenging separation and reusability as the exploited catalyst could not be recovered quantitatively and the pure products should be obtained after far-reaching puri cation procedures (Riyadh et al 2018;Zheng et al 2019). Consequently, incorporation of these NPs into beads may be a must to overcome these challenges.…”