Study on the Behavior of Self-Cleaning Impregnated Photocatalyst (Tio 2 ) with Cement Mortar

Cement-based materials are increasingly and widely employed in infrastructure development; however, they pollute our environment by generating carbon dioxide, which is detrimental to our civilization. In self-cleaning concrete, photocatalysts accelerate the decomposition of organic particles; thus, photocatalytic degradation of gaseous pollutants could reduce pollution. The incorporation of photocatalytic components enhanced the mechanical self-cleaning properties of cement mortar. In this study, 4–6 percent by weight of rutile TiO2 was added to mortar, and the results were compared to those of a control sample. On the proposed mortar cubes, both fresh mortar and hardening mortar experiments were conducted. Because the initial and final setting times of TiO2 differ from those of conventional cement mortar, the surplus TiO2water-cement ratio had to be modified. The adaptability of the sol-gel method enables the use of various process parameters to influence the properties of the produced TiO2 nanoparticles. The compressive strength was calculated for 7, 14, 21, and 28 days, and an ultrasonic velocity test was performed after 28 days. On mortar samples, acid and sulfate attack experiments were performed. The M-3 mortar mixture containing 5% rutile exhibited the highest level of strength compared to the other mixtures. The M-3 exhibits a strength that is 10.96% greater than that of the control mix. The impact of acid and sulfate attack on the strength of mix M-2 is relatively modest in comparison to other mixtures. Using RhB (rhodamine color) discoloration under UV light, such as sunlight, the photocatalytic mortar is concentrated; a typical test for self-cleaning cementitious materials reveals the presence of more photocatalytic material, which yields the best results.


Introduction
Air pollution is a big environmental problem all over the world.Vehicle emissions of several air pollutants pose risks to human health and the environment every day.Te rising cost of construction is mostly attributable to the rising cost of living generally and the rising demand for naturally occurring raw materials.Reusing and recycling landfll trash must be prioritized as a viable construction material option [1].Cultural heritage (CH) preservation and protection is a key issue that concerns governments all over the world.A major concern is the degradation of its materials, such as natural stones and mortar.Numerous cultural artifacts may be lost due to biological colonization, as well as the urban area and the quality of air in particular.To prevent biodeterioration and soot formation on CH artifacts, which alters both their aesthetic and physical-chemical aspects, chemical treatments such as water repellent and cleaning agents are frequently utilized as conservation treatments for historic monuments [2].Water repellents, for example, do not provide long-term protection and must be used frequently [3].Furthermore, cleaning techniques and the aging of shielding coverings may cause those materials to change even more.Tus, those maintenance methods should be minimized, taking into account their potential invasiveness and environmental impact, to prevent or lessen aesthetic and physical-chemical deterioration.As a result, novel technologies are aimed at preventing deterioration, with a particular focus on novel nanomaterials [4][5][6][7][8].
Due to photocatalysis, nanocrystalline TiO 2 has been utilized in self-cleaning construction materials (primarily concrete, stone, and mortars) [4][5][6][7][8].Numerous evaluations of TiO 2 's self-cleaning action, focusing on its photocatalytic activity, have been published [9][10][11].Te mortar is a workable mixture of cement, grit, and water that is used to fll irregular gaps and spaces and bind masonry units together.To create a fawless surface and protect the structure, cement mortar is frequently used to plaster wall structures [12].Cement plaster, on the other hand, is weak, accumulates a great deal of water and air pollutants, and degrades the structure, leading to surface cracks and dampness.Cement plaster is mixed with nanoparticles and pozzolanic elements to combat these defects [13].Te purpose of this experiment is to synthesize nanoparticles in cement mortar and investigate their efects.Due to the photocatalytic properties of TiO 2 , this study also contributes to the reduction of carbonic acid gas emissions into the atmosphere.A new object has begun to appear on new infrastructure that simultaneously cleans itself and flters the air around it.Self-cleaning materials could contribute to a clearer city by reducing air pollution levels.Cement, or calcium-silicate-hydrate (C-S-H) products, is utilized to produce photo-catalytic nanoparticles with an ultrasmooth surface, such as titanium oxide [14].Because of its ultrasmooth surface and photocatalytic properties, the rain will wash away the impurities.Tis innovative mortar could be used as a self-cleaning coating for urban structures [15].Titanium oxide in its rutile phase possesses the greatest photoactivity as an environmental depollutant.A photocatalytic reaction is illustrated in Figure 1.
Because of its many advantages, such as strong oxidizing power, antibacterial qualities, self-cleaning and depolluting capabilities, nontoxicity, chemical stability, and a high index of refraction, TiO 2 as a photocatalyst appears to be a very promising material.When the hydrophilic or hydrophobic TiO 2 cement surfaces are subjected to irradiation, the catalyst is photostimulated, and the photocatalytic activity commences [13].Photocatalysts, when exposed to UV light, degrade organic substances including dirt (soot, oil, flth, and particulates), living organisms (mold, bacteria, algae, and allergens), airborne contaminants (VOC, cigarette smoke, NOx, and SO 2 ), and odor-causing components.Smog is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) in polluted urban air break down in the presence of sunlight, and photocatalytic air cleaning can reduce these levels, making cities safer places to live.In the presence of moisture in the air, titanium dioxide nanoparticles absorb UV radiation and function as a catalyst to form reactive hydroxyl (OH) radicals.Most contaminants can be oxidized and destroyed by these radicals [14,15].Te creation of an acid arises from the photocatalytic oxidation of NO (HNO 3 ).Most cement formulations are alkaline, which causes the acid to be neutralized and, as a result, the substrate to slowly erode.Carbonate is a desired addition to other product compositions to increase porosity and neutralize the acid.Te efcacy of photocatalytic air cleaning technology based on titanic oxide nanoparticles was investigated in this project.Debris (soot, oil, flth, and particles), microorganisms (mold, algae, bacteria, and allergens), airborne pollutants, and odor-causing substances can all be broken down by photocatalysts when exposed to UV light.It would appear that most inorganic pollutants, such as rust stains, do not require a catalyst for their formation [17].Catalyzing the decomposition of the materials results in the formation of oxygen, carbonic acid, gas, water, sulfate, nitrate, and other inorganic molecules.Self-cleaning materials based on photo-catalytic reactions are employed in a wide variety of consumer products.Photocatalysis has emerged as a promising approach to address contemporary environmental and climatic issues by facilitating the conversion or removal of perilous greenhouse gases from the atmosphere [18].
Te physical and mechanical properties of nanocrystalline TiO 2 were investigated by Antonio and Dionisio in mortar specimens made with lime and cement.TiO 2 concentrations are 1, 2, and 5% [19].Te numerous applications of TiO 2 for cleaning the air, self-cleaning, and studying the microstructure of cement mortar were detailed by Marcin et al. 2022.Te impact of increasing the TiO 2 concentration from 1 to 5% was discussed.Te discussion included thin polycrystalline flms as well as powder forms of TiO 2 [20].Previous studies indicate that TiO 2 is extensively used as a mortar coating.Moreover, no evaluations were conducted until the TiO 2 concentration reached 6%.Tis article examines the addition of 4-6% rutile TiO 2 (a type of titanium dioxide) to cement mortar and compares the results to those obtained with a control specimen.
Te impact of TiO 2 nanoparticles on the self-cleaning and mechanical characteristics of cement was explored by [21].Te hydrothermal method was utilized to synthesize anatase 2 Advances in Materials Science and Engineering TiO 2 nanoparticles, which exhibited an average particle size of 60 ± 20 nm.Te evaluation of the self-cleaning efcacy of TiO 2 cement composite was performed through the decolorization assay of rhodamine B, in contrast to unaltered cement specimens.Te fndings of the study suggest that an increase in the quantity of TiO 2 nanoparticles in the modifed cement led to an enhancement in the self-cleaning characteristic of the samples [22].Table 1 presents a comparison between the present study and previous research.

Study of Titanium Dioxide (TiO 2 ).
After being catalyzed, the materials decompose into oxygen, carbonic acid gas, water, sulfate, nitrate, and other inorganic molecules.To create selfcleaning materials, several commercial goods use photocatalytic processes.Titanium dioxide (TiO 2 ) can be found in nanocrystals or nanodots with a large surface area.Flamenco, rutile, titania, and di-oxo-titanium are all names for the pigment.It is widely known that nanoparticles of pigment can inhibit bacterial growth and the formation of new cells [13].
Rutile is essentially a white pigment [24].Te particle size of TiO 2 is commonly in the 200-300 nm range.Photocatalytic activity is seen in TiO 2 nanoparticles.Ultraviolet radiation is absorbed by TiO 2 nanoparticles.It is a nontoxic, nonreactive substance.
Antifogging coatings and self-cleaning windows are just two examples of the many ways in which titanium dioxide (TiO 2 ) is put to use in the building industry [14,24].TiO 2 is also employed as a stain remover and as an ingredient in paints, plastics, Portland cement, windows, and tiles, among other things, due to its UV absorption and photocatalytic sterilizing capabilities.Te crystalline form of TiO 2 is seen in Figure 2. TiO 2 is frequently utilized to degrade organic compounds in wastewater and gas pollutants due to its photocatalytic activity.

Synthesis of TiO 2 by Sol-Gel
Technique.TiO 2 nanoparticles were made using a sol-gel technique.To make the titanium tetra-isopropoxide (TTIP) combination, 1 mole of TTIP was dissolved in 10 milliliters of ethanol and 35 milliliters of deionized water.Te liquid was then agitated at pH 2.5 for 10 minutes.After 50 minutes of magnetic stirring at pH 1 with 1 mole hydrochloric acid (HCl), the liquid was titrated to pH 1. Te fnal solution was a translucent, homogenous, and slightly yellowish liquid.For the gel preparation, the prepared sol was left out at room temperature for 2 hours.Te resulting gel was baked for 6 hours at 110 degrees Celsius, dried, and ground into a powder (with a yellowish hue) for use in subsequent characterization and testing of the material's photocatalytic activity.Titanium dioxide's photocatalytic activity and optical characteristics are improved after calcination, owing to the augmented crystallinity of the nanoparticles [26].Tree batches of the TiO 2 powder were calcined at diferent temperatures: 300 degrees Celsius, 500 degrees Celsius, and 800 degrees Celsius.A programmable tube furnace was used for the calcination process, with a heating rate of 100 °C/hour.After heating to 300 degrees Celsius, 500 degrees Celsius, and 800 degrees Celsius and holding for one hour to evaporate all traces of water and solvent, the mixture was allowed to cool of on its own.

Properties of Rutile Form of TiO 2 .
Rutile's structural formula is Ti 2 O 4 .Rutile is a white 6 pigment categorization powder with a density of 4.5 g/ml and an average crystal size of 20.6-30 nm that is odorless.Te rutile phase's melting and boiling points are 1843 °C and 2972 °C, respectively [24].It has a low elasticity modulus and a small coefcient of expansion.It can be found in metamorphic rocks, such as eclogite, as well as igneous rocks, plutonic igneous rocks generated at greater depths, as well as kimberlites and other deep-source volcanic rocks, and the ash of plants and animals [27].Rutile powder has a beautiful white color and is used in paints, plastics, and other applications, where a bright white tone is required.Titanium is a valuable monetary mineral that is mined [28].Te physical characteristics of TiO 2 rutile powder are depicted in Table 2.A sample of TiO 2 rutile powder is displayed in Figure 3.

Microstructural
Characterization.SEM analysis of nano-TiO 2 sample at 1 µm magnifcation is depicted in Figure 4. Cube-like shape and spherical morphology may be seen in the SEM images of nano-TiO 2 samples.In the SEM analysis, clusters of particles can be seen.Te TiO 2 particle Advances in Materials Science and Engineering size is limited to a maximum of 2 μm.Prepared TiO 2 samples' phase composition was identifed by XRD examination.Figure 5 shows an XRD pattern indicative of the formation of an amorphous crystal at 50 °C, with a highest peak at 2θ of 20-23 and a weak wide peak at 2θ of 58-65.Te phase purity of the produced TiO 2 can be inferred from the lack of any other peak.
2.5.Self-Cleaning Reaction Process.Te evaluation of selfcleaning properties in cement mortar is commonly conducted through the examination of the material's capacity to eliminate or decompose organic pollutants under light exposure.
Te predominant technique employed to assess the degree of self-cleaning efcacy is the evaluation of photocatalytic activity.Te photocatalytic reaction of rutile mortar [29] absorbs atmospheric pollutants such as SO 2 , NO 2 , and other toxic gases.Since rutile titania nanoparticles have been shown to photocatalyze the oxidation of pollutants such as nitrogen oxides (NOx) [30] and volatile organic compounds [31], their use in outdoor air purifcation was explored in this study.Utilizing nanoparticles of titania for photocatalytic pollution reduction is technically feasible.According to proponents, the application of TiO 2 to exterior walls [32], windows [33], roofs [17], road surfaces [28], and other surfaces will signifcantly enhance air quality.Tis initiative aims to demonstrate the signifcance of photocatalytic TiO 2 nanoparticles' positive efects on air quality [33,34].Figure 6 shows the photocatalytic oxidation procedure.
Te word photocatalysis could be a compound word made up of two parts: photo and catalysis.Catalysis is a process in which a material helps to control the rate at which a molecule changes its reactants without being altered or burned inside the end product [37,38].Tis chemical is

Properties of Mortar.
Ordinary surface mortar is typically employed to secure structures while also enhancing their exteriors.Te self-cleaning capability of modifed rutile mortar prevents contamination [41].Modifed rutile mortar is energy-efcient for the building's age.Polluted urban air can have nitrogen oxides and volatile organic compounds removed [32].

Setting and Hardening of Mortar.
Tere are isolated solid grains in an extremely linked structure when the mortar mixture is in the liquid phase.Hydration begins at the grain's surface.Te hydration process is slowed by the thickening of the outer layer.Te development of hydrates around each grain transforms the liquid into a solid state [39].Te fuid state's mobility reduces when the water content drops as a result of the reaction.As a result, highstrength concrete with a low water-cement ratio is more susceptible to drying.
2.9.Shrinkage.Early drying sensitivity and rapid autogenous shrinkage are characteristics of high-strength mortar.Tis result is due to the large amount of paste applied.High autogenous shrinkage causes early-age cracking.Tis happens in mortars with a low water-cement ratio, as well as mortars that use silica fume.

Components of Mortar.
Te four basic components of cement mortar are as follows: (1) Grade 43 Portland cement (2) M-Sand (3) Nano TiO 2 of assorted proportions (4) Water Te mortar within the masonry protects it from water damage and weathering, so it lasts longer.Te key properties of fne mortar should have greater workability, water retention, bond strength, and durability.

Tests on Cement with TiO 2 .
Cement is a crucial component of mortar, and one of the most important factors to consider when selecting cement is its capacity to improve the microstructure of the mortar.Identifying high-quality cement of the right grade is essential for reaching HSC [42].Cement is chosen based on several factors, including the agedependent compressive strength, fneness, heat of hydration, alkali content, tricalcium aluminate (C3A) content, tricalcium silicate (C3S) content, dicalcium silicate (C2S) content, and compatibility with admixtures.Regular hydraulic cement (OPC) is now widely used on construction sites.Diferences in compound composition and fneness [43,44] give diferent cement brands distinctive features in terms of how their  Advances in Materials Science and Engineering strength develops and how they behave rheologically.Cement from a single source was chosen as a consequence.Regular hydraulic cement with the brand name RAMCO which complies with IS 1489(PT 1): 1991 was used in this study.
Te Vicat needle penetration values are shown in Table 3. Tus, when the water quantity is 96 ml and the water consistency is 32 percent, the plunger settlement is 7 mm.Te initial and ultimate setting time values are shown in Table 4.

Experimentation.
Trials are conducted to determine the strength of both traditional rutile mortar and modifed rutile mortar.Te durability of mortar can be measured with a compressive strength test.TiO 2 's response to cement mortar can be evaluated using two diferent tests: the stain removal test and the self-cleaning reaction test [38].

Compression Tests for Cubes.
Standard and modifed cement mortar cubes were tested for compressive strength at 7, 14, 21, and 28 days after application.A 70 mm-sized cube mold was utilized as the specimen for the mortar compression tests [41].After drying the surface, every cube underwent testing.

Stain Removal Test.
Te specimens were made by impregnating the surfaces of hardened cement mortar by applying 50 mg, 100 mg, or 150 mg of TiO 2 [24,35,45].A control specimen was prepared without any TiO 2 impregnation.A specimen is allowed to dry in direct sunlight for thirty minutes.Te surfaces are then sprayed with rhodamine B (RhB) solution [40] and exposed to sunlight for some time.Figures 5 and 6 depict the specimen's appearance immediately after the application of rhodamine dye and several hours later.

Self-Cleaning Reaction Test.
Te rutile mortar uses a photocatalytic technique to remove hazardous chemicals from the air, such as sulfur dioxide (SO 2 ) and nitrogen oxide (NO 2 ).Smog is formed on hot, bright days from a combination of nitrogen oxides and volatile organic compounds that can be removed using photocatalytic air cleaning to reduce harmful and irritating ozone levels [43].When exposed to atmospheric moisture, nanoparticles of titanium dioxide absorb UV light and catalyze the production of reactive hydroxyl (OH) radicals.Most hazardous chemicals are oxidized and eliminated by these radicals [34,46].Tiny particles of titanic oxide catalyze the oxidation of adsorbed molecules when exposed to ultraviolet light with wavelengths shorter than 390 nanometers (above band gap actinic light).Particle size can vary from about 5 nm to about 50 nm.Figures 8(a) and 8(b) depict the specimen before and after the photocatalytic treatment.
Te titanium dioxide particles form electron-hole pairs as a result of UV light absorption.When the electron is recombined with the exit, it travels to the particle surface, where it can react with hydroxyl (OH) ions from adsorbed surface water to form highly reactive hydroxyl radicals [40].Tese radicals are formed when the hydroxyl (OH) group loses an electron.Air pollution molecules can be adsorbed onto TiO 2 particles, where they react with hydroxyl radicals that have also been adsorbed.If everything was perfect, byproducts of reactions would remain at the surface until they were fully oxidized.Te goal of this study is to characterize the photocatalytic rates and reaction pathways for a range of VOC pollutants that contribute to smog formation.Even NOx and SOx, which are produced in industrial settings, can be catalyzed by TiO 2 nanoparticles.

6
Advances in Materials Science and Engineering

Ultrasonic Velocity Test.
Based on the relationship between wave velocity and mechanical characteristics, ultrasonic wave technologies have been widely researched for monitoring the setting and hardening processes of cementitious mortar and concrete materials [47].Te P-wave velocity distribution is shown in Figure 9 for the four diferent mortar types that were analyzed.P-wave velocities were found to be greater in the control mix mortars (those without the photocatalyst ingredient) [48]; this was to be expected given that cement-based mortars were used.It was discovered that increasing the amount of TiO 2 improved the velocity [19].Mortars with 4 and 5% TiO 2 have higher velocities, whereas those with 6% TiO 2 have lower velocities.
It was discovered that the surface of hardened cement mortar containing 5% TiO 2 was extremely dense and had fewer pores as shown in Figure 10.Te reason for this was obvious: the particles were stuck together.When compared to 0 percent, 4 percent, and 6 percent cement mortar specimens, the P-wave velocity of the 5 percent TiO 2 content specimen is high.Figure 11 depicts the EDS spectra of the 5% TiO 2 specimen.Te concentrations of titanium, silicon (SiO 2 ), and aluminum were 33.42, 46.02, and 14.00%, respectively.

Durability of TiO 2 -Modifed Cement Mortar.
For up to 28 days, mortar cube samples were submerged in 5% sodium chloride and 5% magnesium sulfate solutions.After being submerged in the solution for 28 days, the samples were removed from the chemical solution and the mortar cubes' residual compressive strength was determined.Strength loss was calculated for specimens from each mix.Mortar cube specimens submerged for chemical resistance testing are depicted in Figure 12.
After being submerged in acid and sulfate for 28 days, the percentage of strength lost owing to attack is shown in Figure 12.CM lost 8.46% and 8.01% of its strength when exposed to acid and sulfate, respectively.Te strength loss caused by acid and sulfate attack is rather moderate in mix M-2 compared to other mixes.Advances in Materials Science and Engineering multiharm pores (>200 nm).Tis occurs as the hydration of the cement binder accelerates, resulting in a denser pore structure and increased microstructure compaction [20].As a result of densifying the microstructure of the cement composite and decreasing the proportion of porosity in the total volume of cement binder [16,[49][50][51][52], materials with reduced water absorption and increased resistance to chloride, CO 2 , and sulphates have been developed.

Conclusions
Te present research idea demonstrates that the maximum photocatalytic efciency was achieved with the impregnation of titanium dioxide under natural sunlight on cement mortarhardened surfaces; the photocatalyst and natural sunlight were combined to provide a solution to environmental urban pollution.Te compressive strength of the 5 percent powdered rutile phase impregnated with cement mortar (M-2) is greater than that of other mixtures, and the photocatalyst reaction efciency is enhanced when rutile is present in high concentrations in the cement mortar.Compared to other mixtures, mix ID M-2 undergoes comparatively little potency loss due to acid and sulfate attacks.Consequently, the experimental fndings of the current study demonstrate a simple and practical method for applying a photocatalyst with high photocatalytic efciency, as well as its prospective application in the prevention of building facade pollution.From the SEM image of a 5% TiO 2 specimen, it was determined that the surface of hardened cement mortar containing 5% TiO 2 was extremely dense and comprised fewer fractures.With the aid of sunlight, atmospheric oxygen, and water present as humidity and precipitation, TiO 2 photocatalysis in cement provides an efective method for simultaneously achieving self-cleaning of building facades, a delay in the natural aging of surfaces, and a reduction in air pollution.Utilizing nanoparticles of titanium dioxide for photocatalytic air pollution reduction is technically feasible.Due to the vast air volumes that must be managed, it will be difcult to achieve this objective in a cost-efective manner.
Photo-Catalyst Titanium Dioxide

Figure 7 :
Figure 7: Resultant compressive strength of cement mortar for various mix designs for various curing days.

Table 1 :
Comparison with previous studies over the present study.

Table 3 :
Consistency result of rutile impregnated cement mortar.