Photocatalytic Mortars Research Articles

Effect of leaching on the hardened, microstructural and self-cleaning characteristics of titanium dioxide containing cement mortars

Abstract In this study, the effect of leaching attack on titanium dioxide (TiO2) containing photocatalytic cement mortars was investigated. Changes in the mechanical, microstructure, and photocatalytic properties of the mortars were studied with the leaching attack. The photocatalytic mortars were made with ordinary Portland cement as binder. TiO2 was added at 0%, 1.5%, 3%, 4.5%, and 6% of the binder weight. After curing for 90 days in saturated limewater, the mortars were immersed in 6 M ammonium nitrate (NH4NO3) solution for 140 days. The leaching depth, loss of compressive and flexural strengths, changes in porosity, and ultrasonic pulse velocity (UPV) were measured. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry analysis (TGA), and differential scanning calorimetry (DSC) tests were conducted to investigate the microstructural damages. The effects of leaching on the photocatalytic performance were evaluated by observing rhodamine B discoloration on the controlled and leached mortars. Experimental results showed that the addition of TiO2 increased the resistance of the mortars to the leaching attack. The loss of hardened properties and microstructural changes were reduced with the addition of TiO2. The leached mortars showed photocatalytic activity after exposure to ultraviolet light, however, self-cleaning was slightly reduced after the leaching attack.

Photocatalytic concrete for NOx abatement: Supported TiO2 efficiencies and impacts

The potential of TiO2-based photocatalysts in mitigating the effects of environmental pollutants is evident in the scientific literature but the large-scale implementation of photocatalytic concretes still appears limited, despite the current global concerns over urban NOx pollution. Improvements in cost-effectiveness are required to enhance the case for a photocatalyst-modified infrastructure and this must address catalyst efficiency, catalyst loading and performance durability. This paper compares photocatalytic efficiencies of supported TiO2 on mortar surfaces with the more conventional TiO2 dispersed in mortar. The influences of environmental conditions, such as NO concentration and flow rate, UVA light intensity and relative humidity, on photocatalytic performance are also investigated using photonic efficiency as an indicator. The supported TiO2 shows greater degradation of NOx (De-NOx), at about 9 times higher than TiO2 powder dispersed in the mortar, ca. 150 times higher utilization efficiency, than that of TiO2 in traditional photocatalytic mortar (with 5% loading).

A sustainable replacement for TiO2 in photocatalyst construction materials: Hydroxyapatite-based photocatalytic additives, made from the valorisation of food wastes of marine origin

Abstract The use of waste materials and by-products in building materials is of increasing importance to improve sustainability in construction, as is the incorporation of photocatalytic materials to both combat atmospheric pollution and protect the structures and facades. This work reports the innovative use of photocatalytic hydroxyapatite (HAp) based powders, derived from Atlantic codfish bone wastes, as an additive to natural hydraulic lime mortars. HAp is the main component of bone, and hence is non-toxic and biocompatible. This is the first time that such a calcium phosphate-based photocatalyst, or indeed any fish/marine derived wastes, have been added to building materials. A key factor is that this HAp-based photocatalyst contains only 1 wt% TiO2, the material usually used as a photocatalyst in construction materials. As we only add 1–5 wt% of our total HAp-based material to the mortar, this means our photocatalytic mortars only contain 0.01–0.05 wt% titania (100–500 ppm), two orders of magnitude less than the quantities of 2–10 wt% TiO2 which are usually needed. Our photocatalyst is made from a sustainable waste stream by simple solution and thermal processing, and thus with a much smaller impact on the environment. Specimens were made by either traditional intermixing techniques, or by a post-curing coating procedure. All showed gas-phase photocatalytic activity for abatement of NOx pollutants under solar light. With intermixing, NOx abatement of 6.3–8.3% was observed. However, for coated mortars, superior NOx conversion rates were achieved of 7.1% and 23.8%, with 1 and 5 wt% additions, respectively. These results show the potential of this naturally-derived photocatalyst for applications in the construction industry, leading to lower atmospheric pollution and the creation of more durable/lower maintenance building facades, and environmentally sustainable materials for the preservation of cultural heritage.

Photocatalytic behavior of colored mortars containing TiO2 and iron oxide based pigments

This paper analyses the effect of adding iron based pigments to produce photocatalytic colored mortars (Ph-CM) evaluating nitrogen oxide air purification-NOx, Rhodamine B self-cleaning-RhB and formation rate of hydroxyl radicals-OH. All Ph-CM tested shifted towards lower energy values with respect to the absorption-edge of the TiO2-mortar samples without pigments. However, different UV–Visible photoactivity behavior was obtained in function of the type and content of pigment. The results indicate that even though a decrease in the photocatalytic efficiency can occur, in some cases, an interfacial electron transfer between the conduction band of iron pigment and the photocatalytic mortar could also take place, resulting in an effective inhibition of electron-hole recombination, higher formation rate of OH, and thereby higher photocatalytic activity. This electron transfer ability directly depends on the band-edge position of pigment-cement heteroestructure and the iron to pigment ratio.

Airborne Pollutant inside a Highway Tunnel Coated with a Photocatalytic Mortar

Air pollution measurements were carried out at the Cavallo highway tunnel in Ancona, Italy. The tunnel is used daily by an average of 20,000 vehicles, of which 25% are gasoline fueled passenger cars, 25% diesel cars, and 50% trucks. Tunnel air concentrations of carbon dioxide, carbon monoxide, volatiles organic compounds (VOC), aromatic hydrocarbons and Nitrogen Oxides (NOx) are presented. An integrated sampling-analysis strategy has been implemented in order to get evidence on photocatalytic processes involved inside a highway tunnel freshly coated with mortar containing photocatalytic TiO2. In situ measurements, rather than laboratory material testing, has offered an efficient way for evaluating the occurrence of photocatalytic reactions, in spite of the presence of many conflicting meteorological and traffic parameters. The CO2 le vel inside the tunnel after the photocatalytic mortar treatment resulted initially 22% lower than before treatment but it reduced to a 14% within 6 months. The consistent decreases of acetates, nitrites, and sulphates, together with the sensible increase of oxalates observed on carbon adsorbing panels, point to the occurrence of oxidative reactions occurring inside the coated tunnel. Further study is required to elucidate the effect of NOx adsorption, in order to be able to make predictions of the time-dependence on the de-polluting effect, or how the mortar is influenced by the relative humidity, as well as its composition and exposure history.

TiO2 and TiO2–SiO2 coated cement: Comparison of mechanic and photocatalytic properties

An increasingly known application of nanomaterials in the construction industry is related to the photoactivity ability of semiconductors, where nano-anatase TiO2 is perhaps the most well-known photocatalytic semiconductor and one which possesses a strong oxidizing capability. To analyze the photo-efficiency of four TiO2 coatings and the effect of SiO2 interlayer on the mechanic and photocatalytic activity in Rhodamine B (RhB) and NOx photodegradation, two photocatalytic cement series have been prepared. First, cement mortar was coated with three commercial TiO2 suspensions (GG1, GC7 and CG13) and a home-made titania sol–gel (TEA), and secondly an insertion of a SiO2 layer was applied on cement surface before spraying the TiO2 layer.All studied TiO2-cements exhibited a significant RhB and NOx photodegradation, arising almost total RhB molar conversions, and upper 53% for NOx photo-oxidation respectively. Nevertheless, although SiO2 layer deposited in between mortar and TiO2-cement did not stabilize the commercial TiO2 coatings, a good adhesion was observed when silica was applied joint to the home-made titania gel (TEA), probably as a consequence of the interactions encountered between SiO2 and TiO2 gels. CG7-Si-Cem exhibited high rate at shorter irradiation times, but TEA-Cem and TEA-Si-Cem can be considered as very interesting and potential photocatalytic mortars due to useful mechanical properties, with a very good coatings adhesion that provides promising outdoor use, and good photo-efficiencies in RhB and NOx photo-oxidation.

Incorporation of titanium dioxide nanoparticles in mortars — Influence of microstructure in the hardened state properties and photocatalytic activity

The environmental pollution in urban areas is one of the causes for poor indoor air quality in buildings, particularly in suburban areas. The development of photocatalytic construction materials can contribute to clean the air and improve sustainability levels. Previous studies have focused mainly in cement and concrete materials, disregarding the potential application in historic buildings.In this work, a photocatalytic additive (titanium dioxide) was added to mortars prepared with aerial lime, cement and gypsum binders. The main goal was to study the way that microstructural changes affect the photocatalytic efficiency. The photocatalytic activity was determined using a reactor developed to assess the degradation rate with a common urban pollutant, NOx. The laboratory results show that all the compositions tested exhibited high photocatalytic efficiency. It was demonstrated that photocatalytic mortars can be applied in new and old buildings, because the nanoadditives do not compromise the mortar hardened state properties.

Evaluation of the influence of environmental conditions on the efficiency of photocatalytic coatings in the degradation of nitrogen oxides (NOx)

The incorporation of titanium dioxide (TiO 2) into cement mortars generates materials with photocatalytic properties, that is, a cement matrix able to capture and degrade atmospheric pollutants like nitrogen oxides (NOx). The chemical phenomenon of NOx degradation requires the activation of TiO 2 through ultraviolet radiation (UV-A), as well as water and oxygen molecules necessary for the generation of hydroxyl radicals (OH•), responsible for the degradation of NOx. While photocatalytic materials are in service they are subject to different environmental conditions with regard to the incidence of UV-A radiation, relative humidity of the air and movement of the pollutant masses by the wind. This study aims to evaluate the influence of these different environmental conditions on the efficiency of photocatalytic mortar in the degradation of NOx. Using a specifically-developed test apparatus, the efficiency of a photocatalytic mortar was tested under 27 different environmental conditions, obtained by varying the relative air humidity (30, 50 and 70%), UV-A radiation (10, 25 and 40 W/m 2) and pollutant mass flow rate (1, 3 and 5 l/min). All tests were carried out with an initial concentration of nitric oxide (NO) of 20 ppmv. It was observed that the higher the levels of UV-A radiation the better the performance of the mortar in the degradation of NOx. On the other hand, higher percentages of relative humidity and flow rate caused a decrease in photocatalytic activity. The experimental results verified that the environmental conditions have a considerable influence on the efficiency of photocatalytic mortar in the degradation of NOx.

Characterization of photocatalytic and superhydrophilic properties of mortars containing titanium dioxide

Environmental pollution arising from industrial implants and urban factors is constantly increasing, causing aesthetical and durability concerns to urban structures exposed to the atmosphere. This work is aimed at the study of a system which could take advantage of functionalized building materials in order to improve the quality of urban surfaces, and possibly of the environment itself: TiO 2-containing photoactive materials represent an appealing way to create self-cleaning surfaces, thus limiting maintenance costs, and to promote the degradation of polluting agents. Several mortars containing anatase TiO 2, added as suspension or as powder, were characterized: among the photocatalytic mortars, the use of a combined additive (both powder and suspension) improved the material response. The best photoefficiency was exhibited by a mortar containing TiO 2 as surface covering; nevertheless, the adhesion problems shown by the surface layer open the way for future widening of investigations focused on the optimization of layer durability.