Remediation of noxious pollutants using nano-titania-based photocatalytic construction materials: a review

Characterization and photocatalytic performance of cement mortars with incorporation of TiO2 and mineral admixtures

As the main components of the building envelope, construction materials have a straight relation with air contaminants from anthropogenic origins. Titanium dioxide has been recently applied in construction industry products since its photocatalytic properties can be used for pollutant degradation purposes. This study evaluated the performance of cement-based mortars with the incorporation of TiO2 nanoparticles and mineral admixtures. Six mortar compositions were defined by considering two reference mixes (with and without TiO2 incorporation), two mineral admixtures (bentonite and metakaolin) as partial cement replacement and one waste from ornamental stone processing in two levels of partial substitution of natural sand. Consistency index, density, and entrained air content of mixtures were investigated at fresh state. Compressive strength, water absorption, sorptivity, and micrographs from scanning electron microscopy were used to characterize mortars at hardened state. It was observed that incorporation of TiO2 does not considerably change mortar's properties at fresh and hardened state, despite a denser microstructure and improved interfacial transition zone. In general, the relation between the water-to-cement ratio and porosity on the performances of TiO2-added mortars was shown, which is strongly related to their photocatalytic efficiency. Metakaolin mixtures were more efficient to NO conversion, and high selectivity was observed for the bentonite mortars.

Efficient One-Pot Synthesis of TiO2/ZrO2/SiO2 Ternary Nanocomposites Using Prunus × Yedoensis Leaf Extract for Enhanced Photocatalytic Dye Degradation

A simple, efficient, and ecofriendly method was employed to synthesize TiO2/ZrO2/SiO2 ternary nanocomposites using Prunus × yedoensis leaf extract (PYLE) that shows improved photocatalytic and antibacterial properties. The characterization of the obtained nanocomposites was done by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopic (EDS) analysis. The synthesized ternary nanocomposites with nanoscale pore diameters were investigated for the elimination of Reactive Red 120 (RR120) dye. The obtained results showed about 96.2% removal of RR120 dye from aqueous solution under sunlight irradiation. Furthermore, it shows promising antibacterial activity against Staphylococcus aureus and Escherichia coli. The improved photocatalytic and antibacterial activity of TiO2/ZrO2/SiO2 may bring unique insights into the production of ternary nanocomposites and their applications in the environment and biomedical field.

Dye decomposition and air de-pollution performance of TiO2/SiO2 and N-TiO2/SiO2 photocatalysts coated on Portland cement mortar substates

In this study, the newly synthesized TiO₂ and N doped TiO₂ clusters were added to silica sol to synthesize N-TiO₂/SiO₂ composites via the sol-gel method. Afterwards, the prepared sols were applied by brushing on portland cement. Doping with nitrogen significantly increased the absorption of TiO₂ towards the visible region, thus, increasing the photocatalytic activity. SEM characterization of the treated samples showed that the clusters were distributed in form of aggregates on the samples' surface. The self-cleaning and air de-polluting performances were assessed through methylene blue degradation and the oxidation of nitrogen oxide, resulting in methylene blue (MB) removal of 85% and 78% after 60 min of irradiation for SN10TiO₂ and STiO₂, respectively. Regarding air de-pollution performance, the newly synthesized photocatalysts showed the ability of NOx reduction. However, their efficiency was somewhat lower, in which 23.81% of NO has been oxidized by the sample SN10TiO₂, while SP25 showed a total NO conversion of 38.98%. The powdered xerogels of the newly synthesized nanoparticles revealed high photocatalytic efficiency concerning NO oxidation, resulting in a higher performance compared to those obtained by the xerogel containing P25.

Photocatalytic concrete for degrading organic dyes in water

Since the advent of photocatalytic degradation technology, it has brought new vitality to the environmental governance and the response to the energy crisis. Photocatalysts harvest optical energy to drive chemical reactions, which means people can use solar energy to complete some resource-consuming activities by photocatalysts, such as environmental governance. In recent years, researchers have tried to combine photocatalyst TiO₂ with building materials to purify urban air and obtained good results. One of the important functions of photocatalysts is to degrade organic pollutants in water through light energy, but this technology has not been reported in the practical application areas. To extend this technology to practical application areas, photocatalytic concrete for degrading pollutants in waters was proposed and demonstrated for the first time in this paper. The photocatalytic concrete proposed based on the K-g-C₃N₄ shows a strong ability to degrade the organic dyes. According to the experiment results, the angle of light source plays an important role in the process of photocatalytic degradation, while waters with pH value of 6.5-8.5 hardly influenced the degradation of organic dyes. When the angle of light source is advantageous for photocatalytic concrete to absorb more visible light, more organic dyes will be degraded by photocatalytic concrete. The degradation rate of methylene blue could reach about 80% in ½ hour under desirable conditions and is satisfied compared with that of reported works. This study implicates that photocatalytic concrete can effectively degrade organic dyes in water. The influences of changes in the water environment hardly affect the degradation of organic pollutants, which means photocatalytic concrete can be widely used in green infrastructures to achieve urban sewage treatment.

Self-Cleaning Cement-Based Building Materials

The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. An increase in the power of industries and vehicles leads not only to atmospheric pollution by-products of incomplete fuel combustion but also to various microscopic particles that form aerosols, which carry an obvious danger to human health and also pollute the buildings’ facades. An environmentally friendly building material with a hybrid method “Nano-titania gradient” was developed. This method consists of forming a gradient of n-TiO2 particles concentration in the composite since the physical properties of the composite are always inextricably linked to the geometry. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide with the use of graphene oxide was proposed, which contributed to an increase in the overall photosensitivity. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning is completed after 3 h after the irradiation start. The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. Using the theory of percolation, the concentration range of the photocatalyst content was calculated. To facilitate the material, waste cellulose was introduced. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide (SS TiO2) with the use of graphene oxide was proposed. The analysis of the experimental-statistical models of the compressive strength shows that the optimum content of TiO2 was in the range from 0.8 to 1.1%, and cellulose from 0.4 to 0.8%, the optimum content of SS TiO2 was in the range from 0.7 to 1.1%, and cellulose from 0.4 to 0.8%. Analysis of the experimental and statistical model of the bending strength shows that the optimal content of TiO2 and SS TiO2 was in the range of 0.6 to 1.0%, and cellulose from 0.4 to 0.8%. When studying the structure of composites, it was found that titanium dioxide was sorbed on the surface of swollen cellulose fibers and remained there after the process of cement hydration. The effectiveness of the method of surface sensitization of titanium dioxide by combining it with graphene oxide was shown. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning was completed after 3 h after the irradiation start.