TiO₂-Based Photocatalytic Geopolymers for Nitric Oxide Degradation.

Alberto Strini,Davide Corsaro,Luca Schiavi,Laura Ricciotti,Giuseppina Roviello,Francesco Messina,Claudio Ferone,Raffaele Cioffi

doi:10.3390/ma9070513

Abstract

This study presents an experimental overview for the development of photocatalytic materials based on geopolymer binders as catalyst support matrices. Particularly, geopolymer matrices obtained from different solid precursors (fly ash and metakaolin), composite systems (siloxane-hybrid, foamed hybrid), and curing temperatures (room temperature and 60 °C) were investigated for the same photocatalyst content (i.e., 3% TiO2 by weight of paste). The geopolymer matrices were previously designed for different applications, ranging from insulating (foam) to structural materials. The photocatalytic activity was evaluated as NO degradation in air, and the results were compared with an ordinary Portland cement reference. The studied matrices demonstrated highly variable photocatalytic performance depending on both matrix constituents and the curing temperature, with promising activity revealed by the geopolymers based on fly ash and metakaolin. Furthermore, microstructural features and titania dispersion in the matrices were assessed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analyses. Particularly, EDS analyses of sample sections indicated segregation effects of titania in the surface layer, with consequent enhancement or depletion of the catalyst concentration in the active sample region, suggesting non-negligible transport phenomena during the curing process. The described results demonstrated that geopolymer binders can be interesting catalyst support matrices for the development of photocatalytic materials and indicated a large potential for the exploitation of their peculiar features.

Highlights

The photocatalytic oxidation (PCO) technology gained great attention in recent years thanks to the possible applications in both energy production and pollution control
An initial comparative assessment of the activated materials (AAMs) binders potentials as photocatalyst support matrices was carried out using four different types of AAM: metakaolin geopolymer; fly ash geopolymer; hybrid siloxane–metakaolin geopolymer; and foamed hybrid siloxane–metakaolin geopolymer
The photocatalytic activity of the samples was evaluated in terms of NO abatement

Summary

Introduction

The photocatalytic oxidation (PCO) technology gained great attention in recent years thanks to the possible applications in both energy production (e.g., hydrogen generation by water splitting [1] or photovoltaic generation with Graetzel cells [2]) and pollution control (as advanced oxidation process for polluted air [3] and water [4] treatment). Starting from the basis of geopolymers, hybrid organic-geopolymer/inorganic binders have been proposed in the literature These innovative functional materials are obtained by the in situ co-reticulation of metakaolin, a mixture of dialkylsiloxane oligomers with different degrees of polymerization and an alkaline solution. These hybrid materials, despite the small amount of contained siloxanes, are characterized by highly interpenetrated structures, whose properties are not the sum of the single contributions from each phase, but derive from the synergistic interaction between the phases that arises from interfacial forces at the nanometric scales [22,23,24]. These materials revealed widely tunable performance depending on composition and preparation, with significant potential in the fields of structural [25], fire-resistant, and insulating [26,27] applications

Methods

Results

Conclusion