Abstract
Geopolymer (GP) spheres made from coal fly ash (FA) and rice hull ash (RHA) waste products are utilized as both support matrix and dopant applied to titania (TiO2) photocatalyst for organic dye degradation in wastewater. Processing of FA and RHA via suspension-solidification method resulted in GP spheres with nanoporous morphology. The nanocrevices enabled low-energy sol-gel TiO2 coating technique because they served as anchoring sites on the geopolymer surface that favored rigidity and larger surface area. The GP-TiO2 system has been characterized by infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Diffuse reflectance spectroscopy revealed a narrowing of the GP-TiO2 system optical band gap due to the interaction of metal dopants contained in RHA and FA with TiO2, thus making the GP-TiO2 system a visible-light-active photocatalyst, as confirmed by methylene blue dye degradation measured through UV-Vis spectroscopy.
Highlights
Titania (TiO2 ) is a nontoxic, inexpensive and stable ultraviolet photocatalyst used in wastewater treatment facilities that produces reactive hydroxyl (·OH) and superoxide (O2 − ·) radical species when it comes in contact with water and oxygen that converts organic dyes into nontoxic anionic by-products [1]
In our previous study [20], we reported the optimum amounts of energy for its production
In our previous study [20], we reported the optimum conditions conditions for maximum extraction of silicate species in rice hull ash
Summary
Titania (TiO2 ) is a nontoxic, inexpensive and stable ultraviolet photocatalyst used in wastewater treatment facilities that produces reactive hydroxyl (·OH) and superoxide (O2 − ·) radical species when it comes in contact with water and oxygen that converts organic dyes into nontoxic anionic by-products [1]. Anatase TiO2 has better photoactivity than rutile despite its wider band gap due to its crystallographic orientation that allows better exciton transport and faster charge carrier migration on its surface, which leads to the formation of more radical species that facilitates the oxidative degradation process [3,4]. Solar light, which is the conventional photocatalytic activator of titania, produces low conversion efficiency due to the fact that the absorption range of anatase (λ = 385 nm) constitutes only 3–5% of the solar spectrum. These issues can be addressed by (1) particle size reduction and (2) doping [5].
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