Photocatalytic BiOX Mortars under Visible Light Irradiation: Compatibility, NOx Efficiency and Nitrate Selectivity

Abstract

The use of new photocatalysts active under visible light in cement-based building materials represents one interesting alternative to improve the air quality in the urban areas. This work undertakes the feasibility of using BiOX (X = Cl and I) as an addition on mortars for visible-light-driven NOx removal. The interaction between BiOX photocatalysts and cement matrix, and the influence of their addition on the inherent properties of the cement-based materials was studied. The NO removal by the samples ranking as follows BiOCl-cem > BiOI-cem > TiO 2 -cem. The higher efficiency under visible light of BiOCl-cem might be ascribed to the presence of oxygen vacancies together with a strong oxidation potential. BiOI-cem suffers a phase transformation of BiOI in alkaline media to an I-deficient bismuth oxide compound with poor visible light absorbance capability. However, BiOI-cem showed considerably higher nitrate selectivity that resulted in the highest NOx global removal efficiency. These results can make its use more environmentally sustainable than TiO 2 and BiOCl cement composites.Catalysts 2020, 10, 226 2 of 21 toxicity. Nevertheless, the limited visible light absorption and high electron-hole recombination rate are considered the drawbacks of its wide application [9,10].Recently, there has been considerable research interest in layered composite materials, such as silicates [11,12], graphene [13][14][15][16], perovskites [17], graphitic carbon nitrides [18,19] and layered double hydroxides [20]. These layered materials possess several extraordinary advantages, such as high surface area, more surface-active sites, superior electron mobility, and good electron transfer, endowing them with promising potential for photocatalytic applications. Of these layered materials, bismuth oxyhalides (BiOX, X = Cl, Br, and I) belong to a new class of promising layered materials because of their unique layered-structure-mediated fascinating physicochemical properties and suitable band-structure, as well as their high chemical and optical stability, nontoxicity, low cost, and corrosion resistance [21,22]. Among all of BiOX materials, BiOI with band gap energy of 1.7 eV exhibits the highest visible light-driven photocatalytic activity attributed to its smaller band gap [21,23,24]. Many studies have investigated the removal of nitric oxide gas-phase through pure BiOX photocatalysts, but most are focused on the performance based on the decrease of NO concentration [10,[25][26][27][28]. Only a few reports focus on the final or by-products of NO removal process [9,23,29]. The mechanisms of NO removal remain unclear in the literature. Generally, NO can be oxidized by either photogenerated hole or other active species [30][31][32] to different kinds of products, such as NO 2 , HNO 2 , and HNO 3 . However, some of these products, such as NO 2 , is considerably more toxic than NO [31].Moreover, very scarce references have been found in relation to the addition of BiOX oxides into construction materials. For example, Wang et al.[33] prepare...

Photocatalytic Activity of ZnxMn3−xO4 Oxides and ZnO Prepared From Spent Alkaline Batteries

“…This factor is very important, as NO 2 is more toxic than NO, and better conversion to is preferable for mitigating the negative global effects of NO 2 on the environment and public health (Nava-Núñez et al, 2020 ). Remarkably, the ZnO sample shows acceptable nitrate selectivity under both irradiation types (although slightly lower by Vis).…”

“…The pure ZnO photocatalyst, whose preparation proceeded by using amine derivatives or ionic liquids, showed a NO conversion photo-efficiency equal to or lower than 50% (Kowsari and Bazri, 2014 ; Kowsari and Abdpour, 2017 ). On the other hand, ZnO synthetized routes in the presence of complex structuring agents have reached highest performances ~70–95%, even better than that of commercial ZnO (Morán-Lázaro et al, 2018 ; Nava-Núñez et al, 2020 ). However, the reported values of photocatalytic performance ZnO are strongly dependent on the morphology and the preferential crystalline orientation of its particles (Nava-Núñez et al, 2020 ).…”

“…On the other hand, ZnO synthetized routes in the presence of complex structuring agents have reached highest performances ~70–95%, even better than that of commercial ZnO (Morán-Lázaro et al, 2018 ; Nava-Núñez et al, 2020 ). However, the reported values of photocatalytic performance ZnO are strongly dependent on the morphology and the preferential crystalline orientation of its particles (Nava-Núñez et al, 2020 ). Furthermore, there are several variations in the procedure tests (irradiation characteristics, amount of sample, test time, NO x gas concentration, etc.…”

“…Efficiencies (η) for NO removal, NO 2 formation, and total NO x removal were determined separately. This analytical procedure is described in greater detail elsewhere (Jimenez-Relinque and Castellote, 2015 ; Jimenez-Relinque et al, 2015 ; Nava-Núñez et al, 2020 ). This test was performed under both UV and visible light irradiation.…”

“…Among the available photocatalysts, nano-sized titanium dioxide (TiO 2 ) is the most widely used because of its chemical stability, good optical transparency, high refractive index, low cost, and non-chemical toxicity. Nevertheless, its limited visible light absorption, together with its price, are considered obstacles to its wider application (Jimenez-Relinque et al, 2015 ; Nava-Núñez et al, 2020 ). Thus, the design and development of low-cost, high-performance catalysts that are preferably sustainable and active across the entire solar spectrum should be key objectives.…”