Development of low-emission photocatalytic cement composites with co-ground TiO2–fly ash and TiO2–calcium carbonate systems

This study investigated how the surface characteristics of photocatalytic cementitious composites influenced the effectiveness of air purification from nitrogen oxides (NOx), with a particular focus on the impact of coarse aggregate exposure on the photoactive surface. Air purification efficiency tests were conducted using a custom-developed procedure that simulated NOx concentrations and UV irradiance typical of autumn and winter conditions in Warsaw, Poland. The findings revealed that the extent of exposed coarse aggregate on the photoactive surface significantly affected photocatalytic efficiency, reducing the overall NO removal rate by up to 50% compared to the reference value. The use of hydration retarders modified the surface characteristics of the photocatalytic cement matrix, enhancing its photoactive potential. The observed decline in photocatalytic efficiency in composites with exposed coarse aggregate was attributed to the coarse aggregate’s limited ability to retain nanometric photocatalyst particles, which reduced the overall TiO2 content in the composite’s near-surface layer. Nevertheless, cementitious composites incorporating a first-generation photocatalyst exhibited substantial photocatalytic activity, achieving NO removal rates of up to 340 µg/m2·h for non-exposed variants and up to 175 µg/m2·h for variants with exposed aggregate. These results demonstrated their functionality even under low-intensity UV-A irradiation (1 W/m2), making them suitable for environments with limited sunlight exposure.

Rising urban air pollution necessitates the development of innovative methods for removing harmful components, such as nitrogen oxides (NOx). Photocatalytically active layers on building facades are effective in reducing NOx; however, the production of nano-TiO₂-based photocatalysts and Portland cement is environmentally unsustainable. The use of supplementary cementitious materials, such as fly ash, might decrease the efficiency of the photocatalytic effect. This study investigated the use of R-MUD, a TiO₂ production by-product, as a partial substitute for cement in photocatalytic cement composites to enhance their sustainability. R-MUD exhibits photocatalytic properties owing to the residual TiO₂ in the rutile and anatase phases and demonstrates pozzolanic activity, enabling reduced cement usage. Tests showed that the addition of R-MUD maintained acceptable rheological properties and affected the photocatalytic activity and self-cleaning effects of cement mortars at an acceptable level. Microstructural analysis confirmed the presence of TiO₂ particles on the mortar surfaces, which actively contributed to NOx reduction. Furthermore, R-MUD increases the air content and surface voids, expanding the active surface area and potentially enhancing the photocatalytic efficiency. This approach leverages industrial waste to improve the environmental performance of cement composites while addressing air pollution challenges, thereby offering a sustainable solution for urban environments.

Photocatalytic NOx abatement and self-cleaning performance of cementitious composites with g-C3N4 nanosheets under visible light

Blending TiO2 and cement to create photocatalytic composites holds promise for low-cost, durable water treatment. However, the efficiency of such composites hinges on cross-effects of several parameters such as cement composition, type of photocatalyst, and microstructure, which are poorly understood and require extensive combinatorial tests to discern. Here, we report a new combinatorial data science approach to understand the influence of various photocatalytic cement composites based on limited datasets. Using P25 nanoparticles and submicron-sized anatase as representative TiO2 photocatalysts and methyl orange and 1,4-dioxane as target organic pollutants, we demonstrate that the cement composition is a more influential factor on photocatalytic activity than the cement microstructure and TiO2 type and particle size. Among the various cement constituents, belite and ferrite had strong inverse correlation with photocatalytic activity, while natural rutile had a positive correlation, which suggests optimization opportunities by manipulating the cement composition. These results were discerned by screening 7806 combinatorial functions that capture cross-effects of multiple compositional phases and obtaining correlation scores. We also report •OH radical generation, cement aging effects, TiO2 leaching, and strategies to regenerate photocatalytic surfaces for reuse. This work provides several nonintuitive correlations and insights on the effect of cement composition and structure on performance, thus advancing our knowledge on development of scalable photocatalytic materials for drinking water treatment in rural and resource-limited areas.

This study investigated the influence of the composition of photocatalytic dispersions made with second-generation nano-TiO2 on the air purification performance of photocatalytic cementitious composites. Nine mortar series were prepared, incorporating photocatalytic dispersions of variable content of nano-TiO2, dispersing agent (superplasticizer), and hydrophobic admixture. The total mass content of nano-TiO2 in investigated mortars was kept at the same level. For investigated composites, photocatalytic removal of NOx was evaluated under simulated laboratory conditions mimicking polish autumn/winter irradiation conditions. The results indicate that within the tested range of variability, the dispersion composition significantly influenced the granulation of the dispersed nano-TiO2 particles, which in turn affected the air purification performance of the composites. A predictive model was developed to account for environmental factors potentially influencing photocatalytic performance in urban environments. The model estimated that, depending on environmental conditions and photocatalytic dispersion composition, the composite’s photocatalytic layer could remove up to 1.067 g/m2 of NO2 per year in favorable environmental conditions. Photocatalytic cementitious composites can act as environmentally beneficial composites, contributing to carbon-negative construction practices and improving urban air quality. This highlights the dual benefits of offsetting embedded carbon emissions and enhancing air purification efficiency in sustainable urban infrastructure.

The effect of TiO2@CoAl-LDH nanosphere on early hydration of cement and its photocatalytic depollution performance under UV–visible light

This study explores the development and performance of photocatalytic cementitious composites modified with nano-TiO2 to address urban air quality and sustainability challenges. Nine mortar series were prepared, incorporating binders with varying carbon footprints and mass contents across different series. The interplay between the fundamental (abrasion resistance) and functional (air purification efficiency) properties of the composites’ surfaces and interfaces was investigated. The photocatalytic removal of airborne pollutants, specifically nitrogen oxides (NOx) and ozone (O3), was evaluated under simulated environmental conditions. The variations in binder composition influenced the composites’ overall initial carbon footprint and air purification efficiency. The assessment revealed a possible net decrease in carbon emissions over the life cycle of the composite due to the removal of ozone (greenhouse gas) and its precursor—NOx, highlighting the potential of photocatalytic cementitious composites for dual environmental benefits in an urban environment, emphasizing the critical role of surface and interface engineering in achieving carbon-negative composites.

Titania nanoparticles are intensely studied for photodegradation applications. Control of nanoscale morphology and microstructural properties of these materials is critical for photocatalytic performance. Uniform anatase-type TiO2 nanoparticles were prepared by the sol-gel process using titanium isopropoxide as precursor. Controlled annealing up to 400 °C established crystallization and particle size ranging between 20 and 30 nm. Detailed thermal examination reveals that anatase phase transformation into rutile is affected by the annealing temperature and by the initial particle size. The anatase to rutile phase transformation occurs in the nanoparticles at 550 °C. The Total Reflection X-ray Fluorescence (TXRF) study of the anatase nanoparticles shows a shift towards higher energy in the Ka Ti line of 10 eV, related to structural defects. These features were discussed in the photocatalytic behavior of several cement-based materials modified with the so-prepared anatase nanoparticles. The photocatalytic activity of the anatase-type TiO2/cement mortar system is evaluated from the degradation of Methylene Blue (MB) under UV irradiation, monitored through the absorbance at 665 nm. The results show that the photocatalytic composites exhibit up to 76.6% degradation efficiency. Mechanical testing of the nano-TiO2 modified cementitious composites evinces a moderate reinforcement of the strength properties at long ages.

This study focuses on developing new surface modification methods for photocatalytic cementitious composites. The question that was investigated was if superabsorbent polymers can act as an intermediate environment, intensifying the incorporation of TiO2 particles on the surface of the tested material. Four variants of surface modification were designed: water dispersions of TiO2 with non-saturated SAP, with SAP in a hydrogel form, and two reference series. Due to the use of SAP, the efficiency in air purification from NOx under different light conditions compared to the reference series increased significantly, exceeding a 75% increase under a UV-A light and a 600% increase under visible light.

Photocatalytic high-performance fiber-reinforced cement composites with white Portland cement, titanium dioxide, and surface treated polyethylene fibers

This research investigated the properties of photocatalytic cementitious composites, including their air-purification efficiency. A method of characterizing the removal of airborne pollutants (nitrogen oxides), simulating the actual NOx concentration and irradiation conditions in Warsaw, Poland, in the autumn/winter season was established. The study analyzed the impact of changes in the composition of cement mortars-partial substitution of the binder with mineral fillers-on the properties of the external photoactive surface of the composite. The designed experimental plan included both quantitative and qualitative variables (type and amount of fillers used). It was found that the photocatalytic performance of the composite was correlated with its pore total content and pore size distribution-the higher the content of mineral fillers, the lower the porosity and the less effective its photocatalytic properties. The selectivity of the photocatalytic NOx reactions also deteriorated as the content of the mineral fillers increased. The study confirmed the validity of increasing the binder content in cementitious composites to enhance their photocatalytic performance.

This study investigates the relationship between surface properties and microstructural characteristics of photocatalytic composites and their impact on air purification efficiency. High-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and mercury intrusion porosimetry (MIP) were employed to analyze photocatalyst distribution and pore structure quantitatively. The findings demonstrated a strong correlation between TiO2 coverage on the photoactive surface and NO removal rates and between pore structure characteristics and NO2 generation rates. Two predictive models were developed to link NOx removal rates with photocatalytic cementitious mortars’ surface and structural properties. A stepwise regression approach produced a second-degree polynomial model with an adjusted R2 of 0.98 and a Mean Absolute Percentage Error (MAPE) of 8.34%, indicating high predictive accuracy. The results underscore the critical role of uniform photocatalyst distribution and optimized pore structure in enhancing NOx removal efficiency while promoting the generation of desirable products (NO3−) and minimizing the formation of undesirable byproducts (NO2).

This work aimed to investigate the influence of selected material variables on the self-cleaning and air purification efficiency in NOx pollutants of cement-based photocatalytic composites. Tests were performed on cement mortars, with seven independent variables considered: the mass ratio between cement and quartz powder to sand, the water to cement ratio, the total mass amount of photocatalysts (two different types), the mass content of nanoparticulate silica, the percentage of quartz powder replacing part of cement, and the ratio between two sands of fine granulation. Photocatalytic cementitious materials had their self-cleaning properties tested via two methods (spectrophotometry—the degradation of rhodamine B under UVA irradiation, and the change in the contact angle—via a goniometer). Air purification properties were tested in the reaction chamber under UVA and visible light at low irradiance (0.2 W/m2 for UVA, 150 W/m2 for visible). It was found that TiO2 content and the mass ratio between cement and quartz powder to sand were the most influential variables within the selected ranges of variability, with the ratio between sands and quartz content being the least significant variable of the tested properties.

Phosphogypsum (CaSO4 ˙ 2H2O, PG), a solid by-product of phosphoric acid production, has been classified as a "Technologically Enhanced Natural Radioactive Material" (TENR), because it contains radionuclides (eg., radium 226) and some trace toxic metals in concentrations, which may pose a potential hazard to human health and the environment. The current regulated disposal method for PG is on-site stockpiling, which has created a serious environmental management problem. An appealing solution to the problem is the use of stabilized PG for aquatic enhancement activities. This solution can eliminate the airborne vector of transmission for radon 222 and therefore may provide a safe alternative to the current stockpiling practices. The determination of low cement content (<10%) stabilized PG composites has been investigated. Varying combinations of PG:cement, PG:fly ash:lime and PG:fly ash:cement were fabricated for laboratory and field experiments. Field saltwater submergence studies and response surface with process variable analysis shows that only the PG:fly ash:cement composites are able to survive in the Gulf Coast saltwater environment when cement content is less than 10%. Scanning electron microscopy (SEM) shows that ettringite formation is potentially responsible for degradation of PG stabilized composites. SEM and microprobe analysis showed that conditions necessary for stabilized PG composites to survive in the saltwater environment are: (1) the stabilized PG composites should have a strong sulfate resistant surface and (2) the local pH environments on the stabilized PG composites should be above 11. This higher local pH environment will result in the formation of calcium carbonates, which protect the PG composites and reduce the diffusion of toxic metals and radium. For PG:fly ash:cement composites, the stronger calcium carbonate coating embedded with fly ash particles covers the higher sulfate resistant composite surface and both contribute to the PG:fly ash:cement composites survival in the Gulf Coast seawater environments for more than one year. Dynamic leaching test, field experiments, SEM, and microprobe analysis showed that the calcium diffusion coefficient is a good indicator for PG:cement and PG:fly ash:cement stabilized composites long term dissolution potential but does not apply to the PG:fly ash:lime stabilized composite.

Applications of heterogeneous photocatalytic processes based on semiconductor particles in cement-based materials have received great attention in recent years to enhance the aesthetic durability of buildings and reducing global environmental pollution. Amongst all, titanium dioxide (TiO2) is the most widely used semiconductor particle in structural materials with photocatalytic activity because of its low cost, chemically stable nature, and absence of toxicity. Utilization of TiO2 in combination with cement-based materials would plunge the concentration of urban pollutants such as NOx. In fact, cementitious composites containing TiO2 have already found applications in self-cleaning buildings, antimicrobial surfaces, and air-purifying structures. This paper aims to present a comprehensive review on TiO2-based photocatalysis cement technology, its practical applications, and research gaps for further progression of cementitious materials with photocatalytic activity.