Abstract
The photocatalytic activity of a series of anatase TiO2 materials with different amounts of exposed (001) facets (i.e., 12% (TiO2-1), 38% (TiO2-3), and 63% (TiO2-3)) was tested in a batch slurry reactor towards liquid-phase bisphenol A (BPA, c0(BPA) = 10 mg/L, ccat. = 125 mg/L) degradation. Photo-electrochemical and photo-luminescence measurements revealed that with the increasing amount of exposed anatase (001) facets, the catalysts generate more electron-hole pairs and OH∙ radicals that participate in the photocatalytic mineralization of pollutants dissolved in water. In the initial stages of BPA degradation, a correlation between % exposure of (001) facets and catalytic activity was developed, which was in good agreement with the findings of the photo-electrochemical and photo-luminescence measurements. TiO2-1 and TiO2-3 solids achieved 100% BPA removal after 80 min in comparison to the TiO2-2 sample. Adsorption of BPA degradation products onto the TiO2-2 catalyst surface was found to have a detrimental effect on the photocatalytic performance in the last stage of the reaction course. Consequently, the global extent of BPA mineralization decreased with the increasing exposure of anatase (001) facets. The major contribution to the enhanced reactivity of TiO2 anatase (001) surface is the Brønsted acidity resulting from dissociative chemisorption of water on a surface as indicated by FTIR, TPD, and MAS NMR analyses.
Highlights
Heterogeneous photocatalytic oxidation of organic pollutants present in an aqueous medium is one of the most promising advanced oxidation processes (AOPs) for waste water treatment
The % exposures of (001) planes were calculated based on the A and C dimensions of TiO2 nanocrystals (Figure 3) as described in [37]
It should be noted that the HRTEM micrographs of TiO2 nanocrystals with an appropriate orientation relative to the electronic beam (Figure 2) demonstrate a clear trend of a gradual refining of the nanocrystals’
Summary
Heterogeneous photocatalytic oxidation of organic pollutants present in an aqueous medium is one of the most promising advanced oxidation processes (AOPs) for waste water treatment. Due to its properties (high photocatalytic activity, chemical stability, low cost, nontoxicity, long-term stability against photo-corrosion, biological inertness, etc.) semiconductor titanium dioxide (TiO2 ) presents one of the most suitable material to be used in AOPs as a photo-catalyst [1,2]. A major drawback of TiO2 is its band gap energy of 3.0 to 3.2 eV, meaning that it can be excited only by ultraviolet (UVA) light (λ < 387 nm). One of the strategies to overcome this drawback is nitrogen doping of TiO2 [3]. This results in the Catalysts 2019, 9, 447; doi:10.3390/catal9050447 www.mdpi.com/journal/catalysts
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