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Photocatalytic Applications of SnO2 and Ag2O-Decorated SnO2 Coatings on Cement Paste

Danilo da Silva Vendramini
Victoria Gabriela Benatto
Alireza Mohebi Ashtiani
1 and
Felipe de Almeida La Porta
Nanotechnology and Computational Chemistry Laboratory, Federal University of Technology—Paraná, Avenida dos Pioneiros 3131, Londrina 86036-370, PR, Brazil
Post-Graduation Program in Chemistry, State University of Londrina, Londrina 86057-970, PR, Brazil
Author to whom correspondence should be addressed.
Catalysts 2023, 13(12), 1479;
Submission received: 20 September 2023 / Revised: 21 October 2023 / Accepted: 29 October 2023 / Published: 28 November 2023
(This article belongs to the Special Issue Theoretical and Experimental Investigation of Catalytic Materials)


Recently, the production of new photocatalytic materials has attracted considerable attention as a promising strategy to mitigate anthropogenic environmental degradation. In this study, cement paste composites (water/cement ratio = 0.5) were prepared using a coating based on nanoparticles of SnO2 (SnO2/cement paste) and SnO2 decorated with Ag2O (Ag2O-decorated SnO2/cement paste) for photocatalytic applications. These coatings were prepared in this study by using the hydrothermal method as the strategy. Thus, photocatalyst efficiency was evaluated through the degradation of methylene blue (MB) and methyl red (MR) as cationic and anionic dyes, respectively, and the simultaneous degradation of MB/MR (1:1 v/v) dyes. Moreover, the photocatalytic mechanism was investigated in the presence of scavengers. Notably, an increase in pH in the range of 2–6 resulted in selective degradation of the MB/MR dye mixtures. Overall, the photocatalytic performance of these materials provides a novel platform technology focused on advanced civil engineering applications, which consequently facilitates the mitigation of various environmental problems.

1. Introduction

Nowadays, one of the most significant global problems has been the contamination of the waters of rivers, lakes, seas, etc. [1,2,3,4]. This happens due to the improper disposal of partially treated or even untreated water from factories and industries that use various chemical products on a large scale. Contaminated water contains various pollutants, such as dyes, heavy metals, pharmaceutical residues, pesticides, and so on [5,6,7,8,9,10]. These pollutants affect microorganisms and aquatic life and, in addition, can also be extremely harmful to humans [1,2].
There are many widely used techniques for water treatment, such as filtration, flocculation, adsorption, biological degradation, advanced oxidation processes (AOPs), and even combinations between them [2,11,12,13,14,15]. However, some of these techniques may have limitations, including the need to use expensive equipment, slow processes, and low degradation efficiency [2,12,14,15]. Therefore, treatment techniques involving AOPs are interesting in solving such environmental issues because they generate reactive oxygen species and are known for being highly reactive and non-selective [1,15,16,17,18]. AOPs are widely studied and commonly use ozone, hydrogen peroxide, Fenton’s reagent, and irradiation in the UV region [18,19,20].
For photocatalytic activity on the surface of target materials, the chosen catalyst needs to be irradiated with light with an energy equal to or greater than its band gap, generating electron/hole pairs (e/h+) that will act as carriers to promote the desired reactions [21]. Irradiated semiconductor materials are considered promising photocatalysts due to their ability to generate an efficient separation of e/h+ pairs [22]. The photophysical properties of semiconductor materials are strongly related to their compositions, morphologies, sizes, structure, as well as imperfections in these parameters [9,23,24,25,26]. Therefore, studies evaluate ways to improve the efficiency of the photocatalytic activity of these semiconductors. For this proposal, materials with relevant valence and conduction band positions are needed to promote several photocatalytic reactions of interest, and because of this, we have other semiconductors that are even less reported, such as SnO2 [27,28,29]. Despite SnO2 being more investigated in other research fields, interest in this system as a catalyst has grown considerably over the last decade. Particularly, this is likely due to its non-toxicity, low cost, long-term stability, optical transparency, and high electron mobility [30,31].
SnO2 is a versatile n-type semiconductor material with high thermal stability and easy preparation [30,31,32,33]. Nowadays, it is already used as a catalyst in several organic syntheses, as a solid electrolyte, and as a gas sensor [22,34,35,36,37]. However, SnO2 may have certain limitations for solar applications. This happens because of its ~3.6 eV band gap and its fast recombination of the e/h+ pairs [31,38]. Recent studies have combined SnO2 with other semiconductors such as SnO2/rGO [39], BiPO4/SnO2 [40], g-C3N4/SnO2 [41,42], TiO2/SnO2 [43], and SnO2/Ag2O [44] to overcome this intrinsic limitation of the material and further improve its desired high-performance applications.
Knowing this, different processing methods have been widely developed in recent decades to obtain SnO2 and its related desired physical characteristics [29,31]. Among them, the hydrothermal method stands out, which is a simple, inexpensive, and environmentally friendly strategy for obtaining a wide variety of materials [45,46,47]. Other than that, synthesizing a catalyst through the hydrothermal method has some advantages, such as high particle purity, good dispersion, and uniform particle sizes [48]; these reactions usually occur in a closed system using water [49] at high temperature and high pressure [50,51].
At the same time, it has been observed that the development of Portland cement-based materials, such as concrete and mortar, has a strong relationship with the progress in civil engineering. These Portland cement composites are widely used because they have a low cost and are adaptable to different use situations [52,53,54,55,56,57]. The research involving cementitious materials is advancing toward the production of lighter, stronger, and more durable structures [58,59]. To corroborate the improvement in the performance of cementitious materials, nanoparticles of various oxides are being tested, such as SnO2 [60,61,62], TiO2 [63,64], and Al2O3 [58]. In addition, the coating of these materials with nanoparticles can promote a high photocatalytic activity, which is also largely responsible for the self-cleaning characteristic observed in these new materials developed for advanced applications in civil engineering [63,65,66,67]. This self-cleaning characteristic that accompanies the photocatalytic property brings an increase in the lifetime of cementitious material, due to its ability to reduce the presence of pollutants on its surface in the presence of light [63,65,67,68].
In this work, nanostructured SnO2 and Ag2O-decorated SnO2 as coatings of the cement paste composite were prepared by using the hydrothermal method as a strategy. As is well-known, silver oxide (Ag2O) materials are stable and have broad-spectrum microbial properties. Therefore, our choice is based on the objective of including this functionality in the prepared SnO2-based coatings. Then, the photocatalytic activity of the SnO2/cement paste composite was investigated through the degradation of methylene blue (MB) and methyl red (MR) dyes under ultraviolet light irradiation. The simple chemical structure of these dyes and well-understood degradation pathways makes them convenient model compounds for developing and optimizing new catalysts. In addition, the pH conditions on the Fenton-like process were investigated for the nanostructured SnO2 and Ag2O-decorated SnO2 as a coating of the cement paste composite. Our results showed that the increasing pH (using a variation between 2 and 6) could lead to selective degradation in MB/MR dye mixtures. This work offers a new perspective for the use of photocatalytic materials in civil construction. As far as we know, this is the first study in the literature that uses SnO2 and SnO2 decorated with Ag2O as a coating on cementitious materials (cement paste) as a strategy to mitigate environmental problems, especially those related to the treatment of effluents with complex characteristics. Finally, the need to develop new advanced cementitious materials encourages study in this area.

2. Results and Discussion

The appearance of the synthesized materials is shown in Figure 1a–f, with Figure 1a showing a reference cement paste block for comparison. A visible change in the appearance of the cement paste blocks was observed at each step of the process. As shown in Figure 1b, the nucleating layer was deposited with a slightly whitish color. Moreover, the block darkened in color because of the extended period in the muffle furnace during the preparation process. As shown in Figure 1c, the surface layer became more visible with the growth of the SnO2 film. The white layer of the film caused more contrast than the dark color of the substrate; thus, the defects in the film caused by the porosity of the cement paste surface were more evident. Another noteworthy characteristic is the defects at the interface between the film and block. These defects were mainly observed at the edges of the surface where the film was absent. These defects occurred during the deposition of the nucleating layer because the surface of the block is not uniformly flat, which complicates the deposition process. As shown in Figure 1d–f, samples decorated with Ag2O exhibited identical defects because they underwent the same preparation process before being decorated. When the material was decorated, a reddish color appeared, which became slightly stronger with increasing concentration during the decoration process. This is owing to the dark brown color of Ag2O [69].
The wettability of a solid surface can be evaluated based on its contact angle. Generally, a high contact angle value indicates a relatively low surface wettability [70]. The contact angle results for the analyzed samples are listed in Table 1. Consequently, the high contact angle observed for the cement paste sample was probably owing to its surface roughness. The surface roughness decreased with the addition of the nucleating layer and film; consequently, the contact angle decreased.
Notably, the sample with the smallest contact angle possessed the film layer. Therefore, the objective of the study was achieved because the samples that had the smallest contact angle were those that underwent hydrothermal growth. Furthermore, the obtained contact angle of approximately 11° for the SnO2 film is similar to that reported in the literature; however, the reported value was for a different substrate [71].
The XRD patterns of the as-prepared samples are shown in Figure 2a,b. In Figure 2a, a new peak was observed at approximately 27° when the nucleating layer and SnO2 film were added to the samples, confirming the presence of SnO2. The crystalline structure obtained for the SnO2 phase was identified as tetragonal cassiterite (space group P42/mnm) according to the inorganic crystal structure database (ICDD) card no. 00-211-250, whereas the cement paste exhibited the main hydrated cement products: C-S-H (ICDD card no. 00-029-0373), calcium hydroxide (ICDD card no. 00-050-0008), and hydrated calcium sulfoaluminates (ICDD card no. 00-720-646), as well as the presence of calcite (ICDD card no. 00-471-743). Figure 2b shows a new peak in the region between 40° and 50° for the decorated samples, which confirms the formation of Ag2O (ICDD card no. 00-420-874). In addition to the presence of diffraction peaks, the crystalline fraction of the material increased from 44% in the sample with the SnO2 film to 66% in the Ag2O decorated samples. After the hydrothermal process, a powder was obtained and characterized by XRD. As shown in Figure 2c, XRD confirmed the presence of the SnO2 phase in the powder samples, and the unindexed peaks are attributed to cement paste substrate residues. Furthermore, as listed in Table 2, the crystallite size of the SnO2 and Ag2O phases in all the prepared samples was calculated using the Scherrer equation [72].
Figure 3a shows the SEM images of the cement paste in the presence of C-S-H. As shown in Figure 3b, the deposition of the nucleating layer indicated the presence of SnO2. The block surface was analyzed, indicating that these points were present at a certain distance from each other. After the process of nucleation layer deposition and hydrothermal growth, the appearance of SnO2 nanoparticles covering the sample surface was observed, as shown in Figure 3c. For the decorated samples, the presence of the decorator material (Ag2O) on the surface was investigated because only some evidence of its presence was observed by the reddish color of the blocks and a minor XRD peak. Therefore, as shown in Figure 3d–f, the presence of Ag2O was confirmed for the decorated samples. For all the decorated samples (Ag1, Ag2, and Ag3), the Ag2O exhibited a cubic morphology and agglomerated in regions with a relatively higher concentration of the material.
In general, cementitious materials are formed by particles in different size scales. For this reason, e.g., when analyzing the roughness of such systems based on traditional methods, there are generally significant deviations in these estimations, representing a great challenge for researchers. Therefore, aiming to improve the accuracy in describing the roughness of such samples, this study developed a code (see Supplementary Material) to analyze and extract this information directly from SEM data. In sequence, Figure 3a–f are analyzed again, and some parts of them (the demarcated regions in yellow) are selected for the next steps of the process. In GNU Octave [73], the region is read and a matrix is created as the first return, and, then, a morphological surface plot is reconstructed by the 3D surface function, as shown in Figure 4, which, in its turn, has solid faces and border colors. Then, the fractal dimension is calculated. Also, by means of the program’s regression function, the curve fitting curve is plotted, which enables a direct estimation of the roughness of this sample. To do this, as the images obtained through the scanning electron microscope are not RGB, they do not need previous treatment, but it is important that the demarcated regions be almost 1:1 of 2s size (for some s) because, otherwise, the image needs to be filled with zeros for the image to be 1:1. Then, the traditional box-counting method (BCM) is employed to determine the fractional properties of our demarcated 2D images. Regarding the yellow sample zone, as the used BCM is based on counting the number of the non-zero submatrices of its corresponding binary image (equivalent to those boxes covering the fractal), its change may imply some different results but not as significant. In other words, all analyses used the same selected area, meaning the values obtained are statistically reproducible.
According to the BCM, to analyze a complex pattern, a sequence of boxes of various smaller and smaller sizes is extracted from the original pattern, in which the size of boxes is always a power of two. Thus, one counts how many boxes overlap the image of interest. It is worth saying that since the size of the boxes varies, the number of boxes overlapping the image also varies. Therefore, by decreasing the size of the boxes more and more, one can observe how this relationship varies and so the fractional dimension is calculated. In fact, the box-counting dimension is estimated by the least squares method through a linear function (see [74] for some discussion). In regard to the quantity of the displayed submatrices, for a yellow sample zone of order n × n pixels, the developed BCM is of a complexity of 0( n 2 [ log 2 n ) , according to lines 76 to 87 of the code available in the Supplementary Material.
In addition, the bandgap energy provides critical information for a deeper understanding of novel advanced civil engineering materials. Figure 4a shows the experimental direct bandgap values estimated based on the Tauc plots for the diffuse reflectance measurement of Ag2O-decorated SnO2 coatings of the cement paste composites. The peak associated with Ag2O becomes more evident with an increase in the composition of this phase. As expected, a reduction in the bandgap of the Ag2O phase was observed in Figure 4, which is associated with the growth of this material on the SnO2 phase. However, the bandgap of the SnO2 phase decreased by increasing the Ag2O phase, which is mainly associated with a large structural polarization, i.e., due to lattice mismatch that leads to the formation of complex defects in the Ag2O/SnO2 interface.
Figure 5 shows the photocatalytic degradation of the MB solution by the SnO2/cement paste composite in the presence of different scavengers, and the degradation results without the addition of a scavenger (denoted here as WS). Reactive oxygen species are known to promote photodegradation reactions [31,47,75]. They can react with micropollutants, bacteria, or other target species (depending on the specific application) that come into contact with the photocatalyst surface. Based on the observed results, all scavengers play an important role in the photocatalytic mechanism. The photocatalytic reduction of MB in the presence of scavengers was significant in all cases, resulting in MB degradation of approximately 31%, 46%, 42%, and 37% for Ag, AO, ISO, and p-BQ, respectively, compared with the reference value (WS sample). Table 3 lists the kinetic constants obtained from the photocatalytic performance of these samples. Particularly, the cement paste substrate exhibited a kinetic constant (k) of approximately 0.0059 during the photocatalysis process, which is higher than that obtained for dye degradation by films based on titanium [76] and glass [71]. These results are likely owing to the large surface area and porosity of the cement paste sample. Notably, it has a kinetic constant similar to that of SnO2 films coated on polyetherimide [77] confirming that cement paste can be used as an alternative substrate. Moreover, after the photocatalytic process, the cementitious materials exhibited a different surface color, indicating that these samples have a large absorption capacity (see Figure 5h). Also, in Figure 5i, the samples displayed their self-cleaning properties after being exposed again to UV light. The samples visibly had decreased the strong blue color, characteristic of MB, on their surface, after a period of 120 min of exposure to UV light.
The MB for photo-Fenton was evaluated similarly to the previous test; however, for the photo-Fenton process was added H2O2. The reference photocatalysis (WI) showed a degradation rate of 64%; in contrast, the reference sample (Ref) for photo-Fenton degraded 82% of the MB due to the combination of photocatalysis and Fenton reactions.
Furthermore, in Figure 6, it is also possible to notice the increase in degradation with the presence of Ag2O. The best result obtained was a degradation of 93% in the Ag3 sample, in which we had an 11% improvement in efficiency compared to the Ref sample. This result is corroborated in Table 3, in which we can observe the comparison between the kinetic constants. A similar improvement is seen in the literature for the degradation of methyl orange using 1 mMol and 3 mMol of AgNO3 as a precursor of the decorator material [29]. However, this result was obtained using SnO2 in powder form. For comparative purposes, Table 4 presents the kinetic constants and the respective degradation values at the end of the experiment for the samples submitted to photo-Fenton, which used only MB as a dye. Figure 6 illustrates the photo-Fenton degradation results of MB solutions by Ag2O-decorated SnO2/cement paste composites.
The MR is an anionic dye that also works very well as a pH indicator. For example, this compound is red for pH values below 4.4 and becomes yellow for pH values above 6.2; this characteristic also causes changes in its UV–Vis absorption spectrum [78,79,80]. Therefore, pH control is a variable that needs to be controlled during the process. Figure 7 shows the result of MR degradation at pH 6, the same pH used for solutions with MB. Hence, the maximum absorbance of MR for pH 6 occurred at a wavelength of about 426 nm, as shown in Figure 7c [79,81]. Regarding the degradation of the MR dye, its behavior differs from that observed in MB. The first aspect to be analyzed is the reference sample, where the degradation is 19% lower than that observed for the cationic dye.
Thus, the second aspect to be analyzed refers to the decorated material with Ag2O; the respective absorption spectra are shown in Figure 7. With the increase in Ag2O in the composition of the SnO2 coating, we can clearly observe a displacement of the absorption region to a wavelength close to 400 nm; i.e., this movement indicates the possible presence of Ag2O nanoparticles in the collected aliquots [82]. In addition to the possible presence of Ag2O nanoparticles, the decorated samples presented results lower than the reference, reaching a reduction of 51% when compared to the SnO2 coating for the lowest degradation result obtained. A possible explanation for this behavior can relate to the electronic charges of the surface of these materials, which, in turn, can lead to the repulsion of dye molecules due to similar surface charges [81,83,84,85]. The values of the kinetic constant for MR are lower than those obtained for MB; this is due to the low degradation of the dye during the photocatalysis process. Table 5 presents these kinetic constant and degradation values obtained for the samples. This decrease in MR degradation with Ag2O-decorated SnO2 raised the possibility of the coating being selective in relation to pollutants. Due to the possibility of having a selectivity, it was necessary to verify the capacity of the material to degrade different dyes simultaneously. Then, for this purpose, the two dyes were mixed and subjected to the photo-Fenton process, similar to the analysis of the individual dyes.
Figure 8 displays the photocatalytic selective degradation of the MB/MR dye mixtures by the Ag2O-decorated SnO2 coating of the cement paste composite. Since the dyes have different absorption regions in the spectrum, as shown in Figure 8, the different graphs refer to the different wavelengths analyzed for each dye. Despite noting the difference in degradation efficiency, the behavior of MB in the mixture is similar to when analyzed individually. Table 6 presents the kinetic constant values, and it can be observed that the kinetic constant of Ag3 is lower. However, for the mixture, the behavior of MR follows the MB trend with a reduction in the degradation efficiency in Ag1 and an increase in Ag3, when compared to the reference. Therefore, the combination of anionic and cationic dyes presents a favorable characteristic regarding the degradation of MR, once the literature shows that solutions of individual dyes may give better results than when there is more than one dye in the same solution [85,86,87].
Another characteristic of photocatalysis is that it is sensitive to pH variations. In general, the pH of the aqueous medium can influence photocatalysis through absorption between the dyes and the catalyst surface, because the change in pH can affect the charges of the catalyst surface [88]. Therefore, until this moment, all samples that underwent the photocatalysis process were close to neutral with pH ~6. However, to verify the impact of pH in relation to the material produced, it was decided to choose the Ag3 sample that presented the best degradation results so far. Figure 9 shows the comparison of the pH effect on the photo-Fenton process for the Ag3 sample. At different pH levels, the surface of the photocatalyst may become positively or negatively charged. Hence, from this perspective, the surface charge of as-prepared materials can influence the adsorption of reactants and micropollutants onto the catalyst surface. Furthermore, it is well-known that the different pH conditions can also lead to variations in the energy levels of the VB and CB. This, in turn, affects the generation and separation of electron-hole pairs when the photocatalyst is irradiated with UV light.
In an acidic environment, the charge surface of the catalyst becomes positive; because of this, there is a better interaction with the anionic dye, improving the photocatalytic activity [64]. These results are presented in Table 7, where we see that the highest degradation results were obtained in acidic environments. It is also noted that MR is the most affected dye with pH change, thus showing that the coating prefers MB degradation under neutral pH conditions. The MR still showed a change in absorption when the pH of the solution became acidic. Figure 8h shows that the absorption region previously identified at a wavelength of 425 nm for pH 6, moves slightly to 533 nm in solutions with pH 2 and 4, respectively [78,79,80,81].
The acidic pH, in addition to totally degrading the dyes, also degraded it before the 180 min point of the experiment. Thus, the new coating for cementitious materials proposed in this work proved to be efficient for the degradation of pollutants, with this being demonstrated by the complete degradation of both MB and MR dyes. Additionally, the band edge alignment of SnO2 and Ag2O exhibits a specific configuration of type-I straddling gap photocatalysts. Figure 9g displays the charge transfer mechanism occurring in the Ag2O/SnO2 under UV-light irradiation, making them well-suited for photocatalytic applications. Therefore, optimizing the photocatalyst and reaction conditions is crucial for effective and selective photodegradation reactions.

3. Materials and Methods

3.1. Materials

Portland Cement, CP-II-Z (Votorantim Co., Sao Paulo, Brazil), produced in accordance with ABNT NBR 16697:2018 was used. Tin chloride (SnCl2, Sigma-Aldrich, St. Louis, MO, USA) and silver nitrate (AgNO3, Synth, Sao Paulo, Brazil) were used as precursors, and sodium hydroxide (NaOH, Neon, Suzano, SP, Brazil) as mineralizing agent.

3.2. Cemen Paste Mixture

For the samples’ production, we used a water/cement ratio of 0.5 in a silicone mold (25 mm × 25 mm × 4 mm) greased with demolding agent. For the mixing process: (1) cement was added; (2) then water; (3) then, the materials were mixed by hand until completely homogenized. All samples were demolded after 24 h and cured in water until needed for testing.

3.3. SnO2 Coatings of Cement Paste Prepared by Hydrothermal Approaches

It is well-known that there is more growth of nanostructures on a nucleation layer than when grown directly on various substrates [89]. Hence, in this study, the nucleation layer was produced as follows: (1) adding 10 mg of SnCl2 for every 1 mL of acetone; (2) mixing for 16 min with a magnetic stirrer; (3) applying layers of 100 µL (0.1 mL) on the cement samples surface, totaling 5 layers at the end, and always waiting for the previous layer to dry before applying a new one; (4) holding at 350 °C for 30 min inside the muffle furnace, using a heating rate of 10 °C/min.
In parallel, after this procedure described above, the 0.003 mol of SnCl2 was mixed at room temperature with 20 mL of deionized water until the solution turned to a homogeneous yellow color; then, 30 mL of 1 M NaOH solution was added under vigorous agitation. After 10 min, the resulting mixture reaction was added to the cement paste samples with the nucleation layer inside a Teflon-coated stainless-steel autoclave to be heated at 180 °C for 8 h. At the end of the process, the samples were collected at room temperature, then washed with deionized water and dried at the same temperature.

3.4. Ag2O-Decored SnO2/Cement Paste Composites

After hydrothermal growth of nanostructured SnO2 film, a solution containing AgNO3 and deionized water was prepared. The solution was added to the samples inside another autoclave to be heated at 180 °C for 30 min. This procedure was performed using 50 mL of deionized water as a standard and changing the concentrations of AgNO3 (Ag1: 0.01 mmol, Ag2: 0.02 mmol, and Ag3: 0.04 mmol). A schematic diagram of this fabrication process based on one or two-step hydrothermal approach is illustrated in Figure 1.

3.5. Photocatalytic Activity Evaluation

The coated cement paste samples were placed vertically in contact with 100 mL of MB solution (10 mg/L) under magnetic stirring inside a wooden box containing 3 UVC lamps (15 W, G15T8/OF, 254 nm, OSRAM, München, Germany) [64]. The solution was stirred continuously for 60 min in the dark to establish an adsorption–desorption equilibrium, then lights were turned on. These results in the dark were then used to calculate the adsorption of these samples. After lights were turned on for 180 min (3 h), 1 mL aliquots were collected at 20 min intervals. It is well known that photocatalytic reactions are mainly driven by intrinsic reactive oxygen species, such as holes (h), electrons (e), superoxide (O2), and hydroxyl (OH) radicals [64,65,66]. Here, for a better understanding, the generation mechanisms of reactive oxygen species involved in photocatalytic degradation was investigated by used of different radical scavengers, such as isopropanol (ISO as OH scavenger), AgNO3 (Ag as e scavenger), ammonium oxalate (AO as h scavenger), and p-benzoquinone (p-BQ as a O2 scavenger), in similar intervals of time to the photocatalytic process carried out without the scavenger [64,65,66].

3.6. Photo-Fenton Activity Evaluation

The nanostructured SnO2 and Ag2O-decorated SnO2 as a coating of cement paste composite prepared were evaluated for photo-Fenton activity through the decomposition of individual and mixed MB and MR dyes. Again, the cement paste samples were placed in 100 mL of solution; however, the solution now has a 9:1 ratio of peroxide (H2O2), with 90 mL made up of dye solution (10 mg/L) and the remaining 10 mL is H2O2 in a 100 mL solution, using the same time and photocatalytic reactor described above. For the mixture scenario the MB and MR dyes were mixed in a 1:1 ratio, so within 100 mL of solution, we have 45 mL of MB, 45 mL of MR, and 10 mL of H2O2. Furthermore, the highest degradation result for the dye mixture was evaluated under different pH conditions (2, 4, and 6). The collected aliquots were analyzed by the UV–Vis spectrometer in the absorbance mode using a Biochrom spectrometer, model Libra S60. All measures were performed at room temperature with quartz cuvettes.

3.7. Material Characterizations

To characterize the properties of materials from a structural and morphological point of view we used a diffractometer (XRD), D2 Phaser (Bruker, Karlsruhe, Germany) with an X-ray source with a copper anode tube (Cu-Kα), 30 kV, and 10 mA, with a step of 0.02°/s and 60 s for the angular step. The crystalline fraction was obtained by a simple ratio between the crystalline regions (sum of areas corresponding to the peaks in the diffractogram) divided by all-spectrum area (area total of diffractogram). Then, scanning electron microscopy (SEM), Tescan Vega 4 (Brno, Czech Republic), was used to obtain images to verify the presence of the SnO2 coating, as well as its modification with Ag2O, based on the analysis of their respective morphologies; also, the contact angle measurement was performed using the goniometric method, characterized by the direct measurement of the contact angle. Then, the bandgap of these coatings was determined by means of the diffuse reflectance measurements using UV-3600i Plus UV–Vis–NIR spectrophotometer (Shimadzu Corporation, Kyoto, Japan).

4. Conclusions

In summary, we have investigated the processes of hydrothermal synthesis, characterization, and evaluation of the photocatalytic properties of SnO2 and Ag2O-decorated SnO2 as a coating of cement paste composites. The high porosity of the cement paste composites favors the adsorption process of MB and MR dyes on the surface of the photocatalyst, contributing to maximizing its catalytic performance. The degradation of MR showed a lower efficiency when compared to MB for all analyzed samples. The mechanism was studied using different radical scavengers, confirming the formation of reactive oxygen species. For tests carried out in the presence of these scavengers, we observed a reduction in the efficiency of this process between 31% and 46%. The highlight goes to the electron scavenger that had a higher effect on the dye degradation mechanism. On the other hand, we have demonstrated that the Ag2O-decorated SnO2 coating of the cement paste composite exhibits photocatalytic selective degradation of the MB/MR dye mixtures. Using pH values 2 and 4, the degradation of the dyes took place completely; a result that had not been obtained by any of the previous compositions. Furthermore, complete degradation for both dyes took place before 180 min for the two acidic pH values. With pH 6, the degradation of MB stands out compared to MR with a difference of 34% between them. Highlighting the preference of MB degradation, and indicating a selectivity in the process. Hence, this involves considering the material properties, the target pollutants, and the reaction kinetics. On the other hand, it is important to highlight that the application of SnO2 as a catalyst is not as popular as other semiconductors. These findings are elucidated by a structural and morphological analysis of such materials, and may provide new clues to an in-depth understanding of their catalytic nanoscale behavior.

Supplementary Materials

The following supporting information can be downloaded at:, The code used in SEM analysis (see Figure 3) can be downloaded.

Author Contributions

D.d.S.V., V.G.B. and A.M.A. Conceptualization, methodology, software, validation, formal analysis, investigation, data curation, and writing—original draft preparation. F.d.A.L.P. Conceptualization, resources, formal analysis, investigation, data curation, writing—review and editing, supervision, project administration, and funding acquisition. All authors have read and agreed to the published version of the manuscript.


This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data Availability Statement

Data are contained within the article.


The authors gratefully acknowledge the support from the Brazilian agencies CNPq and CAPES. We are also grateful to the LabMulti-LD equipment infrastructure at UTFPR.

Conflicts of Interest

The authors declare no conflict of interest.


  1. De Araújo, K.S.; Antonelli, R.; Gaydeczka, B.; Granato, A.C.; Malpass, G.R.P. Advanced oxidation processes: A review regarding the fundamentals and applications in wastewater treatment and industrial wastewater. Ambiente Agua-Interdiscip. J. Appl. Sci. 2016, 11, 387–401. [Google Scholar] [CrossRef]
  2. Holkar, C.R.; Jadhav, A.J.; Pinjari, D.V.; Mahamuni, N.M.; Pandit, A.B. A critical review on textile wastewater treatments: Possible approaches. J. Environ. Manag. 2016, 182, 351–366. [Google Scholar] [CrossRef]
  3. Bashir, I.; Lone, F.A.; Bhat, R.A.; Qadri, H. Concerns and Threats of Contamination on Aquatic Ecosystems. In Bioremediation and Biotechnology; Hakeem, K., Bhat, R., Qadri, H., Eds.; Springer: Cham, Switzerland, 2020; pp. 1–26. [Google Scholar] [CrossRef]
  4. Senthil Rathi, B.; Senthil Kumar, P.; Dai-Viet Vo, N. Critical review on hazardous pollutants in water environment: Occurrence, monitoring, fate, removal technologies and risk assessment. Sci. Total Environ. 2021, 797, 149134. [Google Scholar] [CrossRef] [PubMed]
  5. Briffa, J.; Sinagra, E.; Blundell, R. Heavy metal pollution in the environment and their toxicological effects on humans. Heliyon. 2020, 6, e04691. [Google Scholar] [CrossRef]
  6. Elgarahy, A.M.; Elwakeel, K.Z.; Mohammad, S.H.; Elshoubaky, G.A. A critical review of biosorption of dyes, heavy metals and metalloids from wastewater as an efficient and green process. Clean. Eng. Technol. 2021, 4, 100209. [Google Scholar] [CrossRef]
  7. Velempini, T.; Prabakaran, E.; Pillay, K. Recent developments in the use of metal oxides for photocatalytic degradation of pharmaceutical pollutants in water—A review. Mater. Today Chem. 2021, 19, 100380. [Google Scholar] [CrossRef]
  8. Benatto, V.G.; de Jesus, J.P.A.; de Castro, A.A.; Assis, L.; Ramalho, T.; La Porta, F. Prospects of ZnS and ZnO as smart semiconductor materials in light-activated antimicrobial coatings for mitigation of severe acute respiratory syndrome coronavirus-2 infection. Mater. Today Commun. 2023, 34, 105192. [Google Scholar] [CrossRef]
  9. Benatto, V.G.; Fabris, G.d.S.L.; Sambrano, J.R.; Taft, C.A.; Porta, F.d.A.L. Influence of structural disorder on the photocatalytic properties of ZnS nanocrystals prepared by the one-pot solvothermal approach. Eclética Química 2022, 47, 17–31. [Google Scholar] [CrossRef]
  10. Vaya, D.; Surolia, P.K. Semiconductor based photocatalytic degradation of pesticides: An overview. Environ. Technol. Innov. 2020, 20, 101128. [Google Scholar] [CrossRef]
  11. Suzuki, V.Y.; Amorin, L.H.C.; Fabris, G.S.L.; Dey, S.; Sambrano, J.R.; Cohen, H.; Oron, D.; La Porta, F.A. Enhanced Photocatalytic and Photoluminescence Properties Resulting from Type-I Band Alignment in the Zn2GeO4/g-C3N4 Nanocomposites. Catalysts 2022, 12, 692. [Google Scholar] [CrossRef]
  12. Aragaw, T.A.; Bogale, F.M. Biomass-Based Adsorbents for Removal of Dyes from Wastewater: A Review. Front. Environ. Sci. 2021, 9, 764958. [Google Scholar] [CrossRef]
  13. Bojanowska-Czajka, A. Application of Radiation Technology in Removing Endocrine Micropollutants from Waters and Wastewaters—A Review. Appl. Sci. 2021, 11, 12032. [Google Scholar] [CrossRef]
  14. Wang, X.; Chen, Z.; Wang, Y.; Sun, W. A review on degradation of perfluorinated compounds based on ultraviolet advanced oxidation. Environ. Pollut. 2021, 291, 118014. [Google Scholar] [CrossRef] [PubMed]
  15. Zhang, Y.; Shaad, K.; Vollmer, D.; Ma, C. Treatment of Textile Wastewater Using Advanced Oxidation Processes—A Critical Review. Water 2021, 13, 3515. [Google Scholar] [CrossRef]
  16. Ma, D.; Yi, H.; Lai, C.; Liu, X.; Huo, X.; An, Z.; Li, L.; Fu, Y.; Li, B.; Zhang, M.; et al. Critical review of advanced oxidation processes in organic wastewater treatment. Chemosphere 2021, 275, 130104. [Google Scholar] [CrossRef] [PubMed]
  17. Nogueira, R.F.P.; Trovó, A.G.; Silva, M.R.A.d.; Villa, R.D.; Oliveira, M.C.d. Fundamentos e aplicações ambientais dos processos fenton e foto-fenton. Quím. Nova 2007, 30, 400–408. [Google Scholar] [CrossRef]
  18. Ramos, P.H.; La Porta, F.A.; Resende, E.C.; Giacoppo, J.O.S.; Guerreiro, M.C.; Ramalho, T.C. Fe-DPA as Catalyst for Oxidation of Organic Contaminants: Evidence of Homogeneous Fenton Process. Z. Für Anorg. Allg. Chem. 2015, 641, 780–785. [Google Scholar] [CrossRef]
  19. Suzuki, V.Y.; Amorin, L.H.C.; Lima, N.M.; Machado, E.G.; Carvalho, P.E.; Castro, S.B.R.; Alves, C.C.S.; Carli, A.P.; Li, M.S.; Longof, E.; et al. Characterization of the structural, optical, photocatalytic and in vitro and in vivo anti-inflammatory properties of Mn2+ doped Zn2GeO4 nanorods. J. Mater. Chem. C 2019, 7, 8216–8225. [Google Scholar] [CrossRef]
  20. De Souza, B.M. Avaliação de Processos Oxidativos Avançados Acoplados com Carvão Ativado Granulado com Biofilme para Reúso de Efluentes de Refinaria de Petróleo. Master’s Thesis, Federal University of Rio de Janeiro (COPPE-UFRJ), Rio de Janeiro, Brazil, 2010. Available online: (accessed on 28 April 2022).
  21. Wang, Y.; Torres, J.A.; Shviro, M.; Carmo, M.; He, T.; Ribeiro, C. Photocatalytic materials applications for sustainable agriculture. Prog. Mater. Sci. 2022, 130, 100965. [Google Scholar] [CrossRef]
  22. Fathima Beevi, A.; Sreekala, G.; Beena, B. Synthesis, characterization and photocatalytic activity of SnO2, ZnO nanoparticles against congo red: A comparative study. Mater. Today Proc. 2021, 45, 4045–4051. [Google Scholar] [CrossRef]
  23. La Porta, F.A.; Taft, C.A. Functional Properties of Advanced Engineering Materials and Biomolecules; Springer International Publishing: Berlin/Heidelberg, Germany, 2021. [Google Scholar] [CrossRef]
  24. La Porta, F.A.; Taft, C.A. Emerging Research in Science and Engineering Based on Advanced Experimental and Computational Strategies; Springer International Publishing: Berlin/Heidelberg, Germany, 2020. [Google Scholar] [CrossRef]
  25. Longo, E.; La Porta, F.A. Recent Advances in Complex Functional Materials: From Design to Application; Springer International Publishing: Berlin/Heidelberg, Germany, 2017. [Google Scholar] [CrossRef]
  26. de Jesus, J.P.A.; Santos, A.C.L.; Pinto, F.M.; Taft, C.A.; La Porta, F.A. Review: Theoretical and experimental investigation of the intrinsic properties of Zn2GeO4 nanocrystals. J. Mater. Sci. 2021, 56, 4552–4568. [Google Scholar] [CrossRef]
  27. La Porta, F.A.; Andrés, J.; Vismara, M.V.G.; Graeff, C.F.O.; Sambrano, J.R.; Li, M.S.; Varela, J.A.; Longo, E. Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals. J. Mater. Chem. C 2014, 47, 10164–10174. [Google Scholar] [CrossRef]
  28. Silva Junior, E.; La Porta, F.A.; Liu, M.S.; Andrés, J.; Varela, J.A.; Longo, E. A relationship between structural and electronic order–disorder effects and optical properties in crystalline TiO2 nanomaterials. Dalton Trans. 2015, 44, 3159–3175. [Google Scholar] [CrossRef] [PubMed]
  29. Wang, H.; Li, W. Photochemical Preparation of Ag/SnO2 Composites and their Photocatalytic Properties. In Proceedings of the International Conference on Chemical, Material and Food Engineering, Kunming, China, 25–26 July 2015. [Google Scholar] [CrossRef]
  30. Ayeleru, O.O.; Dlova, S.; Ntuli, F.; Kupolati, W.K.; Olubambi, P.A. Synthesis and characterization of SnO2 nanofiller from recycled expanded polystyrene. Procedia Manuf. 2019, 30, 635–641. [Google Scholar] [CrossRef]
  31. Puga, F.; Navío, J.A.; Hidalgo, M.C. Enhanced UV and visible light photocatalytic properties of synthesized AgBr/SnO2 composites. Sep. Purif. Technol. 2021, 257, 117948. [Google Scholar] [CrossRef]
  32. do Nascimento, J.L.A.; Chantelle, L.; dos Santos, I.M.G.; de Oliveira, A.L.M.; Alves, M.C.F. The Influence of Synthesis Methods and Experimental Conditions on the Photocatalytic Properties of SnO2: A Review. Catalysts 2022, 12, 428. [Google Scholar] [CrossRef]
  33. Sun, C.; Yang, J.; Xu, M.; Cui, Y.; Ren, W.; Zhang, J.; Zhao, H.; Liang, B. Recent intensification strategies of SnO2-based photocatalysts: A review. J. Chem. Eng. 2022, 427, 131564. [Google Scholar] [CrossRef]
  34. Akhir, M.A.M.; Rezan, S.; Mohamed, K.; Arafat, M.; Haseeb, A.; Lee, H. Synthesis of SnO2 Nanoparticles via Hydrothermal Method and Their Gas Sensing Applications for Ethylene Detection. Mater. Today Proc. 2019, 17, 810–819. [Google Scholar] [CrossRef]
  35. Feng, Y.; Wu, K.; Ke, J.; Guo, Z.; Deng, X.; Bai, C.; Sun, Y.; Wang, Q.; Yang, B.; Dong, H.; et al. Synthesis of ternary SnO2–MoO3–C composite with nanosheet structure as high-capacity, high-rate and long-lifetime anode for lithium-ion batteries. Ceram. Int. 2021, 47, 9303–9309. [Google Scholar] [CrossRef]
  36. Gervillié, C.; Boisard, A.; Labbé, J.; Guérin, K.; Berthon-Fabry, S. Relationship between tin environment of SnO2 nanoparticles and their electrochemical behaviour in a lithium ion battery. Mater. Chem. Phys. 2021, 257, 123461. [Google Scholar] [CrossRef]
  37. Zhang, L.; Tong, R.; Ge, W.; Guo, R.; Shirsath, S.E.; Zhu, J. Facile one-step hydrothermal synthesis of SnO2 microspheres with oxygen vacancies for superior ethanol sensor. J. Alloys Compd. 2020, 814, 152266. [Google Scholar] [CrossRef]
  38. Prakash, K.; Senthil Kumar, P.; Pandiaraj, S.; Saravanakumar, K.; Karuthapandian, S. Controllable synthesis of SnO2 photocatalyst with superior photocatalytic activity for the degradation of methylene blue dye solution. J. Exp. Nanosci. 2016, 11, 1138–1155. [Google Scholar] [CrossRef]
  39. Tuan, P.V.; Hieu, L.T.; Tan, V.T.; Phuong, T.T.; Qu, H.T.T.; Khiem, T.N. The dependence of morphology, structure, and photocatalytic activity of SnO2/rGO nanocomposites on hydrothermal temperature. Mater. Res. Express 2019, 6, 106204. [Google Scholar] [CrossRef]
  40. Zhao, H.; Wu, R.J.; Yu, Z.; Han, X.-n.; Zhao, W.-X.; Ma, F. Synthesis of BiPO4/SnO2 heterojunction for the photocatalytic degradation of RhB under visible light emitting diode irradiation. J. Chin. Chem. Soc. 2021, 68, 1663–1672. [Google Scholar] [CrossRef]
  41. Pham, V.V.; Mai, D.Q.; Bui, D.P.; Van Man, T.; Zhu, B.; Zhang, L.; Sangkaworn, J.; Tantirungrotechai, J.; Reutrakul, V.; Cao, T.M. Emerging 2D/0D g-C3N4/SnO2 S-scheme photocatalyst: New generation architectural structure of heterojunctions toward visible-light-driven NO degradation. Environ. Pollut. 2021, 286, 117510. [Google Scholar] [CrossRef] [PubMed]
  42. Peng, F.; Ni, Y.; Zhou, Q.; Kou, J.; Lu, C.; Xu, Z. New g-C3N4 based photocatalytic cement with enhanced visible-light photocatalytic activity by constructing muscovite sheet/SnO2 structures. Constr. Build. Mater. 2018, 179, 315–325. [Google Scholar] [CrossRef]
  43. Rajput, R.B.; Jamble, N.S.; Kale, B.R. A review on TiO2/SnO2 heterostructures as a photocatalyst for the degradation of dyes and organic pollutants. J. Environ. Manag. 2022, 307, 114533. [Google Scholar] [CrossRef]
  44. Kumar, M.R.; Murugadoss, G.; Venkatesh, N.; Sakthivel, P. Synthesis of Ag2O-SnO2 and SnO2-Ag2O Nanocomposites and Investigation on Photocatalytic Performance under Direct Sun Light. ChemistrySelect 2020, 5, 6946–6953. [Google Scholar] [CrossRef]
  45. Darr, J.A.; Zhang, J.; Makwana, N.M.; Weng, X. Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions. Chem. Rev. 2017, 117, 11125–11238. [Google Scholar] [CrossRef]
  46. Shi, W.; Song, S.; Zhang, H. Hydrothermal synthetic strategies of inorganic semiconducting nanostructures. Chem. Soc. Rev. 2013, 42, 5714. [Google Scholar] [CrossRef]
  47. Viet, P.V.; Thi, C.M.; Hieu, L.V. The High Photocatalytic Activity of SnO2 Nanoparticles Synthesized by Hydrothermal Method. J. Nanomater. 2016, 2016, 4231046. [Google Scholar] [CrossRef]
  48. Qi, Y.; Xiu-Juan, G.; Ru, F.; Li, M.-J.; Zhang, J.-F.; Zhang, Q.-D.; Han, Y.-Z. MoO3-SnO2 catalyst prepared by hydrothermal synthesis method for dimethyl ether catalytic oxidation. J. Fuel Chem. Technol. 2019, 47, 934–941. [Google Scholar]
  49. Sudrajat, H.; Hartuti, S.; Babel, S.; Nguyen, T.K.; Tong, H.D. SnO2/ZnO heterostructured nanorods: Structural properties and mechanistic insights into the enhanced photocatalytic activity. J. Phys. Chem. Solids 2021, 149, 109762. [Google Scholar] [CrossRef]
  50. Nagaraju, Y.S.; Ganesha, H.; Veeresha, S.; Vandana, M.; Ashokkumar, S.P.; Vijeth, H.; Devendrappa, H. Single crystalline hierarchical SnO2 microsphere and fluoride-mediated hollow structures for photocatalytic activity. Mater. Today Proc. 2021, 45, 3833–3836. [Google Scholar] [CrossRef]
  51. Wei, Q.; Sun, J.; Song, P.; Yang, Z.; Wang, Q. Synthesis of reduced graphene oxide/SnO2 nanosheets/Au nanoparticles ternary composites with enhanced formaldehyde sensing performance. Phys. E Low-Dimens. Syst. Nanostruct. 2020, 118, 113953. [Google Scholar] [CrossRef]
  52. Dobrovolski, M.E.G.; Munhoz, G.S.; Pereira, E.; Medeiros-Junior, R.A. Effect of crystalline admixture and polypropylene microfiber on the internal sulfate attack in Portland cement composites due to pyrite oxidation. Constr. Build Mater. 2021, 308, 125018. [Google Scholar] [CrossRef]
  53. Wang, L.; Ma, H.; Li, Z.; Ma, G.; Guan, J. Cementitious composites blending with high belite sulfoaluminate and medium-heat Portland cements for largescale 3D printing. Addit. Manuf. 2021, 46, 102189. [Google Scholar] [CrossRef]
  54. Luo, D.; Wei, J. Hydration kinetics and phase evolution of Portland cement composites containing sodium-montmorillonite functionalized with a Non-Ionic surfactant. Constr. Build Mater. 2022, 333, 127386. [Google Scholar] [CrossRef]
  55. Claverie, J.; Wang, Q.; Kamali-Bernard, S.; Bernard, F. Assessment of the reactivity and hydration of Portland cement clinker phases from atomistic simulation: A critical review. Cem. Concr. Res. 2022, 154, 106711. [Google Scholar] [CrossRef]
  56. Natalli, J.F.; Thomaz, E.C.S.; Mendes, J.C.; Peixoto, R.A.F. A review on the evolution of Portland cement and chemical admixtures in Brazil. Rev. Ibracon Estrut. Mater. 2021, 14, 14603. [Google Scholar] [CrossRef]
  57. Zhou, J.; Chen, L.; Liu, Z.; He, F.; Zheng, K. Effect of transitional aluminas on Portland cement hydration, phase assemblage and the correlation to ASR preventing effectiveness. Cem. Concr. Res. 2022, 151, 106622. [Google Scholar] [CrossRef]
  58. Norhasri, M.S.M.; Hamidah, M.S.; Fadzil, A.M. Applications of using nano material in concrete: A review. Constr. Build. Mater. 2017, 133, 91–97. [Google Scholar] [CrossRef]
  59. Chen, X.-F.; Kou, S.-C.; Sun Poon, C. Rheological behaviour, mechanical performance, and NOx removal of photocatalytic mortar with combined clay brick sands-based and recycled glass-based nano-TiO2 composite photocatalysts. Constr. Build. Mater. 2020, 240, 117698. [Google Scholar] [CrossRef]
  60. Wang, D.; Hou, P.; Stephan, D.; Huang, S.; Zhang, L.; Yang, P.; Cheng, X. SiO2/TiO2 composite powders deposited on cement-based materials: Rhodamine B removal and the bonding mechanism. Constr. Build. Mater. 2020, 241, 118124. [Google Scholar] [CrossRef]
  61. Flores, Y.C.; Cordeiro, G.C.; Toledo Filho, R.D.; Tavares, L.M. Performance of Portland cement pastes containing nano-silica and different types of silica. Constr. Build. Mater. 2017, 146, 524–530. [Google Scholar] [CrossRef]
  62. Nogueira, G.S.F.; Schwantes-Cezario, N.; Souza, I.C.; Cavaleiro, C.D.; Porto, M.F.; Toralles, B.M. Incorporação de nanossílica em compósitos cimentícios. Matér. Rio Jan. 2018, 23, e12182. [Google Scholar] [CrossRef]
  63. Nath, R.K.; Zain, M.F.M.; Alam, R.; Kadhum, A.A.H.; Kaish, A.B.M.A. Hybrid photocatalyst for corrosion reducing and sustainable concrete construction. Int. J. Sustain. Constr. Eng. Technol. 2012, 3, 38–44. [Google Scholar]
  64. Fernandes, C.N.; Ferreira, R.L.S.; Bernardo, R.D.S.; Avelino, F.; Bertini, A.A. Using TiO2 nanoparticles as a SO2 catalyst in cement mortars. Constr. Build. Mater. 2020, 257, 119542. [Google Scholar] [CrossRef]
  65. Barbudo, A.; Lozano-Lunar, A.; López-Uceda, A.; Galvín, A.P.; Ayuso, J. Photocatalytic Recycled Mortars: Circular Economy as a Solution for Decontamination. Appl. Sci. 2020, 10, 7305. [Google Scholar] [CrossRef]
  66. Tobón, J.I.; Cohen, J.D.; Dorkis, L.I. Photocatalytic activity under visible light irradiation of cement based materials containing TiO2-xNy nanoparticles. Rev. Fac. Ing. Univ. Antioq. 2020, 94, 87–96. [Google Scholar] [CrossRef]
  67. Sakthivel, R.; Kitcha, T.A.; Dhanabal, M.; Aravindan, V.; Aravindh, S. Experimental Study of Photocatalytic Concrete using Titanium Dioxide. Int. J. Innov. Res. Sci. Technol. 2018, 4, 117–123. [Google Scholar]
  68. Luna, M.; Delgado, J.J.; Romero, I.; Montini, T.; Almoraima Gil, M.L.; Martínez-López, J.; Fornasiero, P.; Mosquera, M.J. Photocatalytic TiO2 nanosheets-SiO2 coatings on concrete and limestone: An enhancement of de-polluting and self-cleaning properties by nanoparticle design. Constr. Build. Mater. 2022, 338, 127349. [Google Scholar] [CrossRef]
  69. Torabi, S.; Mansoorkhani, M.J.K.; Majedi, A.; Motevalli, S. Review: Synthesis, Medical and Photocatalyst Applications of Nano-Ag2O. J. Coord. Chem. 2020, 73, 1861–1880. [Google Scholar] [CrossRef]
  70. Zancan, P.H. Influência dos Parâmetros de Deposição na Molhabilidade de Filmes de a-C:H. Master’s Thesis, The University of the State of Santa Catarina (UDESC), Joinville, Brazil, 2017. Available online: (accessed on 28 April 2022).
  71. Talinungsang; Paul, N.; Purkayastha, D.D.; Krishna, M.G. TiO2/SnO2 and SnO2/TiO2 heterostructures as photocatalysts for degradation of stearic acid and methylene blue under UV irradiation. Superlattices Microstruct. 2019, 129, 105–114. [Google Scholar] [CrossRef]
  72. Katz, L. X-ray diffraction in crystals, imperfect crystals, and amorphous bodies (Guinier, A.). J. Chem. Educ. 1964, 41, 292. [Google Scholar] [CrossRef]
  73. GNU Octave (Version 8.1.0): A High-Level Interactive Language for Numerical Computations. Available online: (accessed on 10 August 2023).
  74. Wu, J.; Jin, X.; Mi, S.; Tang, S. An effective method to compute the box-counting dimension based on the mathematical definition and intervals. Results Eng. 2020, 6, 100–106. [Google Scholar] [CrossRef]
  75. Suzuki, V.Y.; Amorin, L.H.C.; de Paula, N.H.; Albuquerque, A.R.; Li, M.S.; Sambrano, J.R.; Longo, E.; La Porta, F.A. New insights into the nature of the bandgap of CuGeO3 nanofibers: Synthesis, electronic structure, and optical and photocatalytic properties. Mater. Today Commun. 2021, 26, 101701. [Google Scholar] [CrossRef]
  76. Testoni, G.O.; Amoresi, R.A.C.; Lustosa, G.M.M.M.; Costa, J.P.C.; Nogueira, M.V.; Ruiz, M.; Zaghete, M.A.; Perazolli, L. Increased photocatalytic activity induced by TiO2/Pt/SnO2 heterostructured films. Solid State Sci. 2018, 76, 65–73. [Google Scholar] [CrossRef]
  77. Ben Ameur, S.; Bel Hadjltaief, H.; Barhoumi, A.; Duponchel, B.; Leroy, G.; Amlouk, M.; Guermazi, H. Physical investigations and photocatalytic activities on ZnO and SnO2 thin films deposited on flexible polymer substrate. Vacuum 2018, 155, 546–552. [Google Scholar] [CrossRef]
  78. Badr, Y.; Abd El-Wahed, M.G.; Mahmoud, M.A. Photocatalytic degradation of methyl red dye by silica nanoparticles. J. Hazard. Mater. 2008, 154, 245–253. [Google Scholar] [CrossRef]
  79. Comparelli, R.; Cozzoli, P.D.; Curri, M.L.; Agostiano, A.; Mascolo, G.; Lovecchio, G. Photocatalytic degradation of methyl-red by immobilised nanoparticles of TiO2 and ZnO. Water Sci. Technol. 2004, 49, 183–188. [Google Scholar] [CrossRef] [PubMed]
  80. Jadhav, R.; Debnath, N.C. Computation of X-ray powder diffractograms of cement components and its application to phase analysis and hydration performance of OPC cement. Bull. Mater. Sci. 2011, 34, 1137–1150. [Google Scholar] [CrossRef]
  81. Ahmed, K.B.A.; Senthilnathan, R.; Megarajan, S.; Anbazhagan, V. Sunlight mediated synthesis of silver nanoparticles using redox phytoprotein and their application in catalysis and colorimetric mercury sensing. J. Photochem. Photobiol. B 2015, 151, 39–45. [Google Scholar] [CrossRef] [PubMed]
  82. Paramelle, D.; Sadovoy, A.; Gorelik, S.; Free, P.; Hobley, J.; Fernig, D.G. A rapid method to estimate the concentration of citrate capped silver nanoparticles from UV-visible light spectra. Analyst 2014, 139, 4855–4861. [Google Scholar] [CrossRef] [PubMed]
  83. Huang, K.; Lv, Y.; Zhang, W.; Yang, B.; Chi, F.; Ran, S.; Liu, X. One-step Synthesis of Ag3PO4/Ag Photocatalyst with Visible-light Photocatalytic Activity. Mater. Res. 2015, 18, 939–945. [Google Scholar] [CrossRef]
  84. Venkatesh, D.; Pavalamalar, S.; Anbalagan, K. Selective Photodegradation on Dual Dye System by Recoverable Nano SnO2 Photocatalyst. J. Inorg. Organomet. Polym. Mater. 2019, 29, 939–953. [Google Scholar] [CrossRef]
  85. Yang, Q.; Chen, F.; Li, X.; Wang, D.; Zhong, Y.; Zeng, G. Self-assembly Z-scheme heterostructured photocatalyst of Ag2O@Ag-modified bismuth vanadate for efficient photocatalytic degradation of single and dual organic pollutants under visible light irradiation. RSC Adv. 2016, 6, 60291–60307. [Google Scholar] [CrossRef]
  86. Lebedev, A.; Anariba, F.; Li, X.; Seng Hwee Leng, D.; Wu, P. Ag/Ag2O/BiNbO4 structure for simultaneous photocatalytic degradation of mixed cationic and anionic dyes. Sol. Energy 2019, 178, 257–267. [Google Scholar] [CrossRef]
  87. Reshma, T.S.; Pan, S.; Das, A. Uncapped SnO2 quantum dots for selective adsorption, separation and photocatalytic degradation of a mixture of dyes. New J. Chem. 2023, 47, 16136–16147. [Google Scholar] [CrossRef]
  88. Groeneveld, I.; Kanelli, M.; Ariese, F.; van Bommel, M.R. Parameters that affect the photodegradation of dyes and pigments in solution and on substrate—An overview. Dyes Pigm. 2023, 210, 110999. [Google Scholar] [CrossRef]
  89. Gorup, L.F.; Amorin, L.H.; Camargo, E.R.; Sequinel, T.; Cincotto, F.H.; Ramesar, G.B.N.; La Porta, F.A. Methods for design and fabrication of nanosensors: The case of ZnO-based nanosensor. In Micro and Nano Technologies, Nanosensors for Smart Cities; Han, B., Tomer, V.K., Nguyen, T.A., Farmani, A., Singh, P.K., Eds.; Elsevier: Amsterdam, The Netherlands, 2020; pp. 9–30. [Google Scholar] [CrossRef]
Figure 1. Samples with dimensions of 25 mm × 25 mm × 4 mm of cement paste: (a) Reference; (b) with nucleating layer; (c) with SnO2 film; (d) film decorated with 0.01 mMol of AgNO3 (Ag1); (e) film decorated with 0.02 mMol of AgNO3 (Ag2); and (f) film decorated with 0.04 mmol of AgNO3 (Ag3). Illustration of the (g) SnO2 and (h) Ag2O unit cells and (i) schematic diagram for the fabrication process of SnO2 and Ag2O-decorated SnO2 coatings of the cement paste composites.
Figure 1. Samples with dimensions of 25 mm × 25 mm × 4 mm of cement paste: (a) Reference; (b) with nucleating layer; (c) with SnO2 film; (d) film decorated with 0.01 mMol of AgNO3 (Ag1); (e) film decorated with 0.02 mMol of AgNO3 (Ag2); and (f) film decorated with 0.04 mmol of AgNO3 (Ag3). Illustration of the (g) SnO2 and (h) Ag2O unit cells and (i) schematic diagram for the fabrication process of SnO2 and Ag2O-decorated SnO2 coatings of the cement paste composites.
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Figure 2. Result of XRD analysis for the preparation steps: (a) SnO2 and (b) Ag2O-decorated SnO2 coatings of the cement paste composites and (c) SnO2 powder formed in the hydrothermal processing. The peaks identified in Figure (b) are, respectively, (2) Ag2O; (3) CaOH2; (4) C-S-H; (5) Ettringite; (6) Calcite.
Figure 2. Result of XRD analysis for the preparation steps: (a) SnO2 and (b) Ag2O-decorated SnO2 coatings of the cement paste composites and (c) SnO2 powder formed in the hydrothermal processing. The peaks identified in Figure (b) are, respectively, (2) Ag2O; (3) CaOH2; (4) C-S-H; (5) Ettringite; (6) Calcite.
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Figure 3. SEM images of (a) Cement paste; (b) Nucleation layer; (c) SnO2 Film; (d) Ag1; (e) Ag2; (f) Ag3. Red arrows as inset in SEM indicate the corresponding phase of the analyzed samples.
Figure 3. SEM images of (a) Cement paste; (b) Nucleation layer; (c) SnO2 Film; (d) Ag1; (e) Ag2; (f) Ag3. Red arrows as inset in SEM indicate the corresponding phase of the analyzed samples.
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Figure 4. (ad) Tauc plot for the UV–Vis diffuse reflectance spectra of the Ag2O-decorated SnO2 coatings of the cement paste composites.
Figure 4. (ad) Tauc plot for the UV–Vis diffuse reflectance spectra of the Ag2O-decorated SnO2 coatings of the cement paste composites.
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Figure 5. (a) Degradation of the MB dye during the photocatalysis process; (b) Kinetic constant; Absorbance spectra for (c) WS, (d) Ag, (e) ISO, (f) AO, and (g) p-BQ; (h) Sliced WS sample after MB photocatalysis process; (i) Samples after self-cleaning process.
Figure 5. (a) Degradation of the MB dye during the photocatalysis process; (b) Kinetic constant; Absorbance spectra for (c) WS, (d) Ag, (e) ISO, (f) AO, and (g) p-BQ; (h) Sliced WS sample after MB photocatalysis process; (i) Samples after self-cleaning process.
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Figure 6. (a) Degradation of MB dye during the photo-Fenton process; (b) Kinetic constant; Absorbance spectra for (c) Ref, (d) Ag1, (e) Ag2 and (f) Ag3.
Figure 6. (a) Degradation of MB dye during the photo-Fenton process; (b) Kinetic constant; Absorbance spectra for (c) Ref, (d) Ag1, (e) Ag2 and (f) Ag3.
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Figure 7. (a) Degradation of the MR dye during the photo-Fenton process; (b) Kinetic constant; Absorbance spectra for (c) Ref, (d) Ag1, (e) Ag2, and (f) Ag3.
Figure 7. (a) Degradation of the MR dye during the photo-Fenton process; (b) Kinetic constant; Absorbance spectra for (c) Ref, (d) Ag1, (e) Ag2, and (f) Ag3.
Catalysts 13 01479 g007
Figure 8. Degradation of (a) MB and (b) MR dyes during the photo-Fenton process; Kinetic constant for (c) MB and (d) MR solutions; Absorbance spectra for degraded MB/MR dye mixtures of composites: (e) Ref, (f) Ag1, (g) Ag2, and (h) Ag3.
Figure 8. Degradation of (a) MB and (b) MR dyes during the photo-Fenton process; Kinetic constant for (c) MB and (d) MR solutions; Absorbance spectra for degraded MB/MR dye mixtures of composites: (e) Ref, (f) Ag1, (g) Ag2, and (h) Ag3.
Catalysts 13 01479 g008
Figure 9. Ag3 sample submitted to photo-Fenton process with pH ranging from 2 to 6: (a) MB degradation; (b) MR degradation, analyzed at wavelength 426 nm for pH 6 and at wavelength 533 nm for pH 2 and 4; (c) Kinetic constant for MB; (d) Kinetic constant for the MR; (e) Absorbance spectrum for pH 2; (f) Absorbance spectrum for pH 4. (g) Schematic diagram of charge carrier transfer process for the Ag2O-decorated SnO2 coating of cement paste composites during UV light illumination.
Figure 9. Ag3 sample submitted to photo-Fenton process with pH ranging from 2 to 6: (a) MB degradation; (b) MR degradation, analyzed at wavelength 426 nm for pH 6 and at wavelength 533 nm for pH 2 and 4; (c) Kinetic constant for MB; (d) Kinetic constant for the MR; (e) Absorbance spectrum for pH 2; (f) Absorbance spectrum for pH 4. (g) Schematic diagram of charge carrier transfer process for the Ag2O-decorated SnO2 coating of cement paste composites during UV light illumination.
Catalysts 13 01479 g009
Table 1. Results of contact angle measurement for each sample.
Table 1. Results of contact angle measurement for each sample.
Sample Contact Angle (θ)
Cement paste126°
Nucleation layer30°
Table 2. Crystallite size for SnO2 and Ag2O at different samples.
Table 2. Crystallite size for SnO2 and Ag2O at different samples.
Samples Crystallite Size (tc)
SnO2—Powder6 nm
SnO2—Film33 nm
SnO2—Ag126 nm
SnO2—Ag232 nm
SnO2—Ag329 nm
Ag2O—Ag137 nm
Ag2O—Ag235 nm
Ag2O—Ag333 nm
Table 3. Photocatalysis parameters with and without scavengers for MB degradation.
Table 3. Photocatalysis parameters with and without scavengers for MB degradation.
Scavenger Kinetic Constant (k) (min−1)Degradation
Adsorption (%)R2
AO 0.003546220.9925
Table 4. Kinetic constant and degradation values at 180 min for photo-Fenton processes for MB.
Table 4. Kinetic constant and degradation values at 180 min for photo-Fenton processes for MB.
Sample k (min−1)Degradation
Adsorption (%)R2
Ag1 (0.01 mMol)0.007976280.9954
Ag2 (0.02 mMol)0.014291340.9873
Ag3 (0.04 mMol)0.015493220.9929
Table 5. Kinetic constant and degradation values at 180 min for photo-Fenton processes for MR.
Table 5. Kinetic constant and degradation values at 180 min for photo-Fenton processes for MR.
Sample k (min−1)Degradation
Adsorption (%)R2
Ag1 (0.01 mMol)0.001929280.9463
Ag2 (0.02 mMol)0.001427180.8895
Ag3 (0.04 mMol)0.000712220.9020
Table 6. Kinetic constant and degradation values at 180 min for photo-Fenton processes for the MB/MR dye mixtures.
Table 6. Kinetic constant and degradation values at 180 min for photo-Fenton processes for the MB/MR dye mixtures.
Samplesk (min−1)Degradation
Adsorption (%)R2
Photo-Fenton—Wavelength 665 nm (MB)
Ag1 (0.01 mMol)0.005863190.9730
Ag2 (0.02 mMol)0.007573140.9993
Ag3 (0.04 mMol)0.008479300.9712
Photo-Fenton—Wavelength 425 nm (MR)
Ag1 (0.01 mMol)0.001219310.9220
Ag2 (0.02 mMol)0.002131220.9735
Ag3 (0.04 mMol)0.003245230.9282
Table 7. Kinetic constant and degradation values at 180 min for the Ag3 sample for the mixture of MB and MR under different pH conditions.
Table 7. Kinetic constant and degradation values at 180 min for the Ag3 sample for the mixture of MB and MR under different pH conditions.
pH k (min−1)Degradation
Adsorption (%)R2
Wavelength 665 nm (MB)
Wavelength 425 nm (pH 6) and 533 nm (pH 2 and 4) (MR)
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MDPI and ACS Style

Vendramini, D.d.S.; Benatto, V.G.; Ashtiani, A.M.; La Porta, F.d.A. Photocatalytic Applications of SnO2 and Ag2O-Decorated SnO2 Coatings on Cement Paste. Catalysts 2023, 13, 1479.

AMA Style

Vendramini DdS, Benatto VG, Ashtiani AM, La Porta FdA. Photocatalytic Applications of SnO2 and Ag2O-Decorated SnO2 Coatings on Cement Paste. Catalysts. 2023; 13(12):1479.

Chicago/Turabian Style

Vendramini, Danilo da Silva, Victoria Gabriela Benatto, Alireza Mohebi Ashtiani, and Felipe de Almeida La Porta. 2023. "Photocatalytic Applications of SnO2 and Ag2O-Decorated SnO2 Coatings on Cement Paste" Catalysts 13, no. 12: 1479.

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