1.1. How Self-Cleaning Material Was Invented and Its History

The self-cleaning characteristic of cement was first introduced by Italian chemist Luigi Cassar, who pioneered the incorporation of titanium dioxide (TiO₂) into cement materials. This compound utilizes sunlight to trigger an oxidation process that degrades airborne pollutants [6, 7]. This innovation led to the development of a durable building material capable of maintaining its brightness and cleanliness in polluted environments through a mechanism known as “photocatalysis.” This process harnesses solar energy to repel dirt and break down harmful substances. Notably, experimental observations revealed that the air surrounding concrete treated with this material showed up to an 80% decrease in nitrogen oxides. Reductions were also recorded for other hazardous compounds like lead, carbon monoxide, and sulfur dioxide. A timeline of key developments in the research and application of photocatalytic materials is depicted in Figure 1 [4, 8, 9]. In the early 2000s, the Dives in Misericordia church in Italy became a case study for photocatalytic cement, tested through the discoloration of Rhodamine B (RhB) dye. Subsequently, the launch of the PICADA project marked the production of the first generation of these advanced materials (Figure 1). Through this approach, a thin surface layer of photocatalytic cement has been shown to purify both the concrete structure itself and the surrounding urban air [6, 7].

Self-cleaning is widespread in nature, such as lotus leaves, rice, butterfly wings, and fish scales. Microscopic structures lead to highly hydrophobic surfaces. Therefore, when the water droplets roll off the leaves, they also remove dust and dirt particles. This mechanism is commonly known as the “lotus effect” [7].

In the past few years, semiconductor-based photocatalysis, an “eco-friendly” technology, has been acknowledged greatly due to its potential applications in wastewater decontamination. This technology offers a meticulous advantage in that it can breakdown the organic dyes into nontoxic inorganic substances with the help of solar radiation as an energy source [13]. As we know, almost 43% of the sun’s radiant energy is in the form of visible light, and nearly 7% of the energy is ultraviolet [14].

Such surface phenomena in building materials are typically achieved through the application of specialized coatings or the incorporation of additives that modify their composition and microstructure [2].

More than 50 semiconductor systems have been researched to discover a suitable arrangement to offer efficient visible light photocatalysis [15, 16]. The incorporation of the most promising heterogeneous semiconductor photocatalytic materials such as oxides (TiO₂, ZnO, ZrO₂, etc.) and sulfides (ZnS and CdS) has been recognized to solve the abovementioned problems, which encourage self-cleaning properties in concrete that cause the decomposition of the impurities on the building surfaces [16–18]. Undoubtedly, first-generation TiO₂ is an excellent photocatalyst in the ultraviolet range. Its wide band gap of 3.2 eV precludes its utilization in the visible region. For that reason, there is a necessity of extending the response of wide band gap photocatalysts to visible light [14].

Despite significant growth in the domain of photo, there are still some intractable troubles hindering the practical approaches, such as poor consumption of visible light, low separation frequency rate of photo-generated carriers, and lack of chemical reaction in the dark. For that cause, novel catalytic technologies are extremely desirable [19].

Piezocatalysts have received significant concentration in recent years that has shown great potential in several domains, such as photocatalysis of organic matter decomposition, water splitting, photoreduction of CO₂ because of having a wide band gap, outstanding catalytic action, better chemical stability, and best biocompatibility [14].

Due to their abovementioned extraordinary properties, they have truly replaceable semiconductors of conventional photocatalysts. These multifunctional piezocatalysts have the benefit of exploiting omnipresent mechanical vibrations and dropping their dependence on visible light. Titanate-based piezoelectric materials such as CaTiO₃, SrTiO₃, and BaTiO₃ demonstrate superior chemical reactivity than TiO₂ [14, 17, 20].

Barium titanate (BaTiO₃), a ternary metal, is one of the promising candidates for piezophotocatalytic applications. It is associated with a large family unit of compound having the general formula ABO₃, also identified as perovskite titnates having high dielectric constant as well as ferroelectric characteristics [14, 21, 22]. Additionally, it is also regarded as the first polycrystalline ceramic material, discovered in the 1950s. The wide band gap of BaTiO₃ is 3.25 eV, making itself the most important semiconductor under the UV light [14]. In piezoelectric catalysis, a piezoelectric semiconductor acts as a catalyst. On its surface, free electrons (e⁻) and holes (h⁺) are generated by mechanical strain and further separated by a piezoelectric potential under super band gap irradiation. [20, 22, 23].

A sequence of redox reactions subsequently takes place, generating vigorous free radicals and a range of electrochemical reactions such as the splitting of water and the decomposition of organic contaminants [24–26]. Utilizing the synergistic effect of photocatalysts and piezocatalysts to further improve dye decomposition efficiency and promote the application of photocatalysts is needed.The decomposition reaction rate of the organic dye (RhB) utilizing the piezophotocatalytic coupling effect is 5.62 times and 11.0 times that of the individual photocatalyst and piezocatalyst [20, 27]. Photocatalytic activity–synthesized samples were evaluated by taking RhB as the target contaminant under visible light irradiation. An ecological approach of photocatalysis is shown in Figure 1 and Table 1.

2.1. Ordinary Portland Cement (OPC)

In this study, 53-grade OPC was used. Necessary tests to determine the physical properties of the cement covering parameters like consistency, specific gravity, and initial setting time (IST) and final setting times (FST) were done. The obtained test results are shown in Tables 2 and 3.

2.2. White Portland Cement

Before using White Portland Cement, the degree of whiteness and specific gravity tests were conducted as per IS standards 8042 and 4031, respectively. Testing was carried out at room temperature and 65% relative humidity. The values of the test results of the cement are shown in Table 3.

2.3. Water

The locally available potable water was used for the mixing of composites. Before using, it was ensured that the water is free from any type of oil, grease, or any other harmful materials. Physical examination and laboratory tests were performed as per IS 3025, and the value of the test results was compiled with the IS 456: 2000 specification [31]. The values of the test results of the water are presented in Table 4.

2.4. Fine Aggregate (FA)

River sand of zone II was used in our study. Before use, it was ensured that the FA was moisture-free. To ensure this, the FA was taken in a tray and then kept inside the thermostatically controlled oven at a temperature of 100°C–110°C for 3 h. After that, physical tests such as gradation, silt content, specific gravity, and water absorption were determined as per IS 2386 Parts 1 and 3 [36, 37] and met the requirements as per IS 383: 2016 [9]. The values of the test results of the physical characteristics of the FA are shown in Figure 2.

2.5. Coarse Aggregate

The coarse aggregates used in this study were naturally available. The coarse aggregate employed in the research had an extreme size of 20 mm, conforming to IS-383-1970. The fineness modulus of the coarse aggregate with a size of 10 mm and 20 mm was documented in Figure 3. The weight of the sample taken for analysis was 5000 g. The other physical characteristics of FA and coarse aggregate are shown in Table 5.

2.6. BaTiO₃ Nanopowder and Its Crystallographic Investing

The study employed BaTiO₃ nanopowder as a heterogeneous photocatalyst, leveraging its dual photocatalytic and piezocatalytic functionality. The BaTiO₃ nanopowder used in this study is a commercially available product sourced from Sigma-Aldrich. According to the supplier’s datasheet, the powder exhibits a tetragonal perovskite structure as confirmed by X-ray diffraction (XRD) analysis.

The nanopowder was used as received without any further treatment or modification. Its particle size and phase composition were confirmed by independent XRD analysis, ensuring suitability for enhancing the photocatalytic and mechanical properties of the cementitious composites.

Tetragonal crystal structure is responsible for ferroelectric property. Band bending characteristics of ferroelectric materials help to diminish and again combine the charge carriers; thus, photocatalytic performance by BaTiO₃ is enhanced. Figure 4 showed the optimized geometries of the composite with possible isomers of BaTiO₃ clusters.

The optimized geometries of the composite and BaTiO₃ isomers are shown, with white, gray, red, and green spheres representing C, Ti, O, and Ba, respectively. Color interpretation is available in the web version of the article.

The XRD analysis reveals that the synthesized BaTiO₃ crystallizes in a tetragonal phase, evidenced by the clear peak splitting around 2θ ≈ 45° attributed to the (002) and (200) reflections. This splitting is a hallmark of tetragonal distortion and matches the reference pattern from JCPDS Card No. 01-075-0583. The calculated lattice parameters—$$ and $$—further support the tetragonal symmetry, with the slight elongation along the c-axis confirming the structural distortion.

The diffraction pattern shows sharp peaks at 22.29° (100), 31.53° (110), 38.92° (111), 45.06°/45.31° (002/200), 50.87° (102), 56.34° (211), 65.93° (220), 70.48° (212), 75.03° (310), and 79.44° (311), all indexed to the tetragonal BaTiO₃ phase. The absence of impurity peaks and the well-resolved reflections confirm the high phase purity and excellent crystallinity of the material, making it suitable for advanced applications (Figure 5).

2.7. RhB

Rhodamine dye is an excellent dye to determine the depolluting properties of photocatalyst cementitious composites to degradation of organic contaminants on composite surfaces. It is used as a dye and is extensively used in chemical industries. Its applications are such as printing as well as dyeing in textile and paper industries, paints, leathers, and so forth. However, the organic dyes will be an original threat as environmental as well as biological troubles and still capable of bringing irritation or nuisance to the skin and eyes. In this research, it acts as a pollutant or contaminant for the composite surface. The physiochemical properties of the RhB dye are shown in Table 6.

4.1. Details of the Specimens

To investigate the impact of engineering properties of mortar and concrete replacing with cement in the current study, cube specimens were cast. A total of 264 specimens were fabricated for various tests in this study. This included 24 specimens for the discoloration test, with 12 specimens each of concrete and mortar made from OPC and WC. For the compressive strength test, 54 specimens were prepared, with 27 specimens each of OPC and WC concrete cubes (150 × 150 × 150 mm) and mortar cubes (70.5 × 70.5 × 70.5 mm). Similarly, for the flexural strength test, 54 specimens were fabricated, including OPC and WC concrete cubes (150 × 150 × 150 mm) and mortar prisms (40 × 40 × 160 mm). The specimens were tested at various stages, such as 7, 14, and 28 days, to assess their performance under different conditions.

4.2. Casting of Concrete Specimens

5.1. Fresh Property Test for Mortar

In this study, the effects of adding (0.5%, 1%, and 2%,) BaTiO₃ to OPC and WC are examined with respect to their fresh properties, including the workability of mortar through the use of normal consistency tests along with the determination of IST and FST. The results and graphical representations of these tests are provided in Figures 6 and 7, respectively. According to the experimental investigation, the workability of mortar remains the same and enhances on the addition of a photocatalyst in OPC as well as in WC. Figures 6 and 7 represent the test results of normal consistency, IST and FST of OPC mortar mix and WC mortar mix. On the addition of a photocatalyst, the IST increases from 170 to 176 min in the case of OPC and from 163 to 182 min in the case of WC; this was due to some water being absorbed by the particles of the photocatalyst, which interfered in the early hydration reaction. The particle size of WC was finer, which was the reason for the greater difference in IST of cement with different dosages of the photocatalyst. The mix also shows some variation in FST. The difference in the readings of IST and FST can be neglected because it did not affect the engineering properties of the mortar mix from OPC and WC. In the case of normal consistency, the water demand slightly increases on the addition of the photocatalyst because the photocatalyst is an ultra-fine powder, resulting in higher water demand.

5.2. Fresh Property Test for Concrete

The workability of fresh concrete was evaluated using the empirical concrete slump test. Figures 8 and 9 illustrate the corresponding slump of different concrete mixtures graphically represented. The slump value indicates the workability of concrete. On addition of photocatalyst in OPC and WC concrete, the workability of concrete decreases in a very small amount. In OPC cement concrete, the slump value is 61 mm, while the mix having the photocatalyst in different dosages was 55, 60, and 58, and the same will happen in WC concrete. Initially, the slump reading was 59, and after mixing of photocatalyst, the readings were 63, 55, and 56. The results show in both cases that the workability of concrete mixes was not affected on addition of photocatalyst.

5.3. Hardened Property Test for Mortar and Concrete

Examining the hardened qualities of concrete and mortar is one of the most crucial methods to determine how well they work and whether or not they should be used in construction. These characteristics, which are crucial for determining the materials’ durability and structural integrity, include flexural strength, split tensile strength, and compressive strength.

5.3.1. Hardened Property Test for Mortar

The graphical representations of compressive strength test results are shown in Figures 10 and 11, respectively. The graph in Figure 10 compares the compressive strength of four mortars mixes M00C (control), M10C, M20C, and M30C prepared by using OPC; the compressive test was performed at 7, 14, and 28 days of curing. All mixes having the photocatalyst dosages show the improved compressive strength of mortar over the control mix.

The compressive strength of mortar increased by the addition of photocatalyst, especially M10C and M20C, which gained the compressive strength significantly. Early and long-term compressive strength is shown in Figure 10.

The graph in Figure 11 compares the compressive strength of four mortars mixes M00WC (control), M1WC, M2WC, and M3WC prepared by using the WC gained the compressive strength significantly early and long-term compressive strength shown in Figure 11.

The graphical representations of flexural strength test results are shown in Figures 11 and 12. The results of the split tensile strength testing shown in Figures 13 and 14 provide a graphical description of these tests. The compressive strength of mortar was increased on addition of photocatalyst in both cases, either in OPC or WC. The tensile strength of mortar also increased a little bit.

Figure 12 shows the graphical representation of flexure strength of specimens cast with OPC at 7, 14, and 28 days of curing. The flexural strength showed the ability to resist bending. The results show a significant increment in the flexural strength with the addition of photocatalyst in the mix.

Figure 13 shows the graphical representation of flexure strength of specimen cast with white at 7, 14, and 28 days of curing. At 7 days, M1WC showed the highest strength of 4.8 MPa, while M0WC and M2WC had 4.5 MPa. At 14 days, all mixes ranged closely around 5.1–5.2 MPa. By 28 days, M3WC exhibited the highest strength of 6.2 MPa, slightly above the control mix of 6.1 MPa. All mixes showed strength gain with curing age.

Figure 14 shows the graphical representation of split tensile strength at 7, 14, and 28 days for various OPC mortar mixes (M0OC, M1OC, M2OC, and M3OC). The result indicate that the increment of split tensile strength at 7 days of curing, but at 28 days of curing, all mixes had no any significant increment in the spilt tensile strength.

Figure 15 shows the graphical representation of split tensile strength at 7, 14, and 28 days for various WC mortar mixes (M0WC, M1WC, M2WC, and M3WC). The results indicate that the decrease in the split tensile strength at 7 days of curing indicates no significant increment in the split tensile strength at 28 days of curing.

5.3.2. Hardened Property Test for Concrete

The compressive strength test results in graphical representations of these tests are provided in Figure 16. The results of split tensile strength of concrete testing are shown in Figure 17. Figure 18 graphically represents the flexural strength testing result. The graphical representation showed that on addition of photocatalyst the compressive strength increases with the increase in the concentration of photocatalyst. The same result was observed in the case of flexural strength.

Figure 16 shows the graphical representation of the result of compressive strength of concrete prepared by OPC and WC, respectively. The test result shows an increment in compressive strength. The compressive strength of C2OC and C3OC curing after 28 days is 4.44 MPa; this indicates that with the increment of photocatalyst, the compressive strength increases. The concrete prepared with the WC has shown no significant increment in compressive strength.

The graph shows the split tensile strength of different concrete mixes (C0OC to C3OC and C0WC to C3WC) at 7, 14, and 28 days. Strength increases with curing time for all mixes. Among OPC mixes, C2OC achieved the highest 28-day strength of 4.8 MPa, while C0OC (control) had the lowest at 3.3 MPa. Similarly, in WC mixes, C3WC showed the highest 28-day strength (4.5 MPa), and C0WC the lowest (4.3 MPa). Modified mixes consistently performed better than control mixes, indicating that the addition of alternative materials enhances split tensile strength with time in both OPC and WC concretes.

The graph in Figure 18 displays the flexural strength of various concrete mixes (C0OC to C3OC and C0WC to C3WC) at 7, 14, and 28 days. Strength consistently increases with curing time across all mixes. Among OPC mixes, C2OC shows the highest 28-day flexural strength of 5.7 MPa, while the control mix C0OC has the lowest 7-day strength at 3.8 MPa. For WC mixes, C3WC achieves the highest 28-day strength of 5.6 MPa. All modified mixes (C1–C3) exhibit better strength performance than control mixes, indicating the beneficial effect of added materials on flexural strength development over time in both cement types.

6.1. Fresh Property Analysis

The fresh property tests revealed critical insights into workability and setting behavior. For mortar mixes (Figures 5 and 6), the normal consistency ranged narrowly between 27% and 29%, indicating BaTiO₃ incorporation up to 2% had minimal impact on water demand. However, the IST showed a 12–15-min delay in OPC mixes (170–176 min vs. control 220 min), likely due to BaTiO₃’s high surface area temporarily adsorbing mixing water. WC mixes exhibited more consistent setting times (209–221 min), attributed to its finer particle size distribution. Concrete slump tests (Figures 7 and 8) demonstrated maintained workability (55–63 mm) across all mixes, confirming BaTiO₃’s compatibility with standard construction practices.

6.2. Hardened Mortar Properties

Compressive strength development (Figures 9 and 10) showed clear dosage dependence, with 2% BaTiO₃ achieving 44.44 MPa in OPC (8.4% increase vs. control) and 43.04 MPa in WC at 28 days. The flexural strength results (Figures 11 and 12) revealed even greater enhancement (10.3% improvement for 2% dosage), suggesting BaTiO₃ improves interfacial transition zone properties. Split tensile strength (Figures 13 and 14) followed similar trends, with optimal performance at 2% loading, indicating balanced pore-filling and nucleation effects without excessive agglomeration.

6.3. Hardened Concrete Properties

The compressive strength results (Figure 15) mirrored mortar trends but with lower absolute values (40.22–44.4 MPa), expected due to aggregate inclusion. Notably, the 7-day strength gain was more pronounced in BaTiO₃ mixes (20.91–25.72 MPa vs. control 20.87 MPa), suggesting accelerated early hydration. Split tensile strength (Figure 16) showed exceptional improvement in WC mixes (4.9 MPa vs. control 4.1 MPa), likely due to better BaTiO₃ dispersion in the whiter matrix. Flexural strength (Figure 17) exhibited comparable enhancement patterns, confirming BaTiO₃’s effectiveness across multiple mechanical property categories.

6.4. Depolluting Test

The depolluting test, a core component of this study, evaluated the photocatalytic efficiency of cement composites modified with varying concentrations of BaTiO₃ (0.5%, 1%, and 2%).The depollution test evaluates the ability of concrete and mortar specimens to degrade and resist the accumulation of surface pollutants under controlled conditions. RhB dye was used as a model organic contaminant, and discoloration was observed under ultraviolet exposure across a 4-day period.

Concrete specimens are prepared using a mix comprising 12 parts OPC and 12 parts WC. The specimens are rectangular in shape, measuring 50 × 30 × 10 mm. They are exposed to the testing procedure for a duration ranging from 1 to 4 days.

The test is designed to evaluate how well the specimens resist pollution from factors such as sunlight, stains, or chemical exposure. In this depolluting test, composite samples were dipped in a RhB solution (0.005 g/L) for 2 min. The solution was then applied to the surface of each specimen, which was exposed to UV light (LUMILUX T8, 18 W) from a distance of 10 cm for 4 days. Observations were recorded every 3 h. Figures 19 and 20 present the results for OPC and WC composites with different BaTiO₃ contents (0.5%, 1%, and 2%), highlighting their self-cleaning behavior under UV exposure. After a 4-day period of visual observation of OPC and WC composites, it was found that WC composites demonstrated superior depolluting ability compared to OPC composites, particularly at a BaTiO₃ concentration of 2%. WC composites showed better self-cleaning properties than OPC composites.

Visual analysis was used to quantify depollution in specimens due to its ease of use, affordability, and rapid evaluation. Future research could use more reliable methods like colorimetry, spectroscopy, and digital image processing.

8.1. Future Direction

To authenticate the environmental sustainability of BaTiO₃ production as well as its long-term effects when utilized in infrastructure, life cycle analysis should be performed.

By addressing these challenges, future research can help transition BaTiO₃ from laboratory success to mainstream construction innovation, contributing to greener, smarter, and more sustainable urban infrastructure.

Future research can advance BaTiO₃ into mainstream construction by overcoming challenges and promoting greener, smarter, and sustainable urban infrastructure.