c) on photocatalytic efficiency in the presence of NO and NO2. It was found that
cof the material altered the pore structure of cementitious materials [
In recent years, there is an increasing interest in applying photocatalysts in cementitious materials to eliminate urban air pollutants [ 1 5 ]. However, cementitious materials have many disadvantages, such as complex constituent, low specific surface area, surface carbonation and poor light transmittance, etc. Previous studies [ 6 8 ] showed that the photocatalytic activity of photocatalysts, especially the long-term photocatalytic performance, decreased obviously after being applied in cementitious materials, whether TiOwas coated on the surface or mixed with the substrates. This phenomenon was attributed to the surface carbonation of gas–solid interface, the peeling of photocatalyst layer and the influence of ion species (Ca, Na, OH, etc.) [ 9 ]. Many studies have attempted to improve the photocatalytic activity of photocatalysts in cementitious materials. Janus et al. [ 10 ] prepared cement pastes containing nitrogen and carbon co-modified TiO(TiO-N,C) to enhance photocatalytic activity of photocatalysts in cementitious materials. Vaish et al. [ 11 ] presented visible light active photocatalytic filler based on BaTiOand reduced graphene oxide immobilized in Portland cement could be readily reinforced the photocatalytic performance for xanthene dye degradation. Moreover, Lee et al. [ 12 ] evaluated the influence of water-to-cement ratio () on photocatalytic efficiency in the presence of NO and NO. It was found thatof the material altered the pore structure of cementitious materials [ 13 ], the amount of effective surface area available for photocatalytic oxidation and the binding of oxidation products [ 14 15 ]. Generally, there are two ways to improve the photocatalytic activity of photocatalytic cementitious materials effectively: increasing the absorption of air pollutant and reducing the coverage of photocatalysts by cementitious materials or hydration products [ 16 ]. Therefore, some methods such as introducing the high porosity expanded shale into concrete [ 17 ], controlling the pore structure of cement pastes [ 18 ] and regulating the microstructure of mortar cement [ 19 ] have been developed to enhance the photocatalytic activity of photocatalytic cementitious materials.2 because of physicochemical stability and porous structure. It has been applied in exposed aggregate concrete to build concrete pavement and sidewalk for sound absorption and noise reduction in replace of traditional aggregate. In addition, the exposed aggregate concrete exhibited better surface strength and abrasion performance compared with ordinary concrete [2 as the intermediate.
Aggregates are important components of cement concrete materials, which have potential to act as the substrate of photocatalysts due to the stable composition and structure. Among many aggregates, ceramsite is a promising aggregate to load photocatalysts such as TiObecause of physicochemical stability and porous structure. It has been applied in exposed aggregate concrete to build concrete pavement and sidewalk for sound absorption and noise reduction in replace of traditional aggregate. In addition, the exposed aggregate concrete exhibited better surface strength and abrasion performance compared with ordinary concrete [ 20 21 ]. However, the functional ceramsites with large particle size brought some difficulties in construction when being loaded on the surface of cement concrete. Therefore, ceramsites were crushed into ceramsite sands (CS), which could facilely being used in photocatalytic cement material (PCM) to increase the reaction areas of photocatalysis and improve the stability of TiOas the intermediate.
In this paper, photocatalytic ceramsite sand (PCS) was prepared by negative pressure method and then loaded on the surface of cement pastes at the initial set. The photocatalytic activity was improved significantly by using CS as intermediate of TiO2 and cementitious materials. Comparing with cementitious materials, PCS could not only prevent the aggregation of TiO2 particles but also provide more active sites, high specific surface areas and more gas diffusion. The preparation of PCS increased the reacting areas and utilization rate of TiO2 in cement concrete constructions compared with coating on the surface or mixing with substrates. Therefore benzene was chosen as target contaminant in experiments which was rarely selected in other studies because of its difficulty in degradation. As we all know, benzene is an organic solvent which is very stable compared with other organic or air contaminants. It is rather hard to degrade especially for photocatalysts applied in cementitious materials. In this study, 2 μL benzene was degraded completely in 300 min by PCM in a closed cylindrical stainless steel gas-phase reactor (5.56 L), which proved extraordinary photocatalytic property of PCM. The photocatalytic activity of specimens in simulation conditions were studied in detail.
In addition, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and gas chromatography (GC) were conducted to comprehensively characterize the photocatalytic materials and mechanisms governing the catalytic process.
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