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Article

Implementing All-Weather Photocatalysis of Exhaust Fumes Based on the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ Ternary Composite Coating

by
Bochao Zhou
1,
Hailong Li
1,
Ao Cui
1,
Di Wang
2,
Fucheng Guo
3 and
Chao Wang
1,*
1
Department of Road & Railway Engineering, Beijing University of Technology, Beijing 100124, China
2
Department of Civil Engineering, University of Ottawa, Ottawa, ON K1N 6N5, Canada
3
School of Civil Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(6), 1743; https://doi.org/10.3390/buildings14061743
Submission received: 11 April 2024 / Revised: 2 June 2024 / Accepted: 6 June 2024 / Published: 10 June 2024
(This article belongs to the Special Issue Carbon-Neutral Infrastructure)
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Abstract

:
This study examines the use of SrAl2O4: Eu2+, Dy3+ long-afterglow materials doped into g-C3N4/TiO2 coatings for photodegradation. The prepared sample was tested for the purification of automotive exhaust fumes, with the optimal mass ratio of g-C3N4/TiO2 and SrAl2O4: Eu2+, Dy3+ determined to be 1:1. Characterization tests, including XRD, FT-IR, XPS, and TG-DSC, were conducted to evaluate the microstructure and properties of the samples. Under poor lighting conditions, g-C3N4/TiO2 reduced CH and NOx by 59 ppm and 13 ppm within 4 h, respectively, while g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ decreased CH and NOx by 98ppm and 34ppm, respectively, resulting in a significant improvement in degradation efficiency. The addition of long-afterglow materials significantly improves the efficiency of photocatalysts in purifying exhaust fumes in low-light environments, providing potential value for all-weather exhaust treatment in the future.

1. Introduction

With the development of modern industry and transportation, vehicle exhaust pollution is becoming an increasingly serious concern. Exhaust fumes contain a large amount of harmful substances, such as nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (CH) [1], which threaten human health and exacerbate air pollution. Therefore, the treatment of vehicle exhaust fumes is an urgent matter.
Numerous studies have shown that photocatalytic technology has significant potential in the field of exhaust degradation and purification [2,3,4]. It offers an attractive opportunity to address environmental remediation effectively and sustainably [5,6]. As automotive exhaust fumes first come into contact with the road, the application of photocatalytic materials to purify harmful gases on the road surface can improve the air quality in cities. As one of the typical semiconductor materials, titanium dioxide (TiO2) is widely used in the field of photocatalysis due to its low cost, positive effect on environmental protection, stable chemical properties, and excellent photocatalytic performance compared to other materials [7,8,9]. However, its wide band gap of 3.28 eV can only absorb ultraviolet light, and its photogenerated electrons and holes are prone to recombination, reducing its photocatalytic efficiency and limiting its widespread use [10]. In order to improve the photocatalytic efficiency of TiO2, there are studies on TiO2 integrated with metal materials, non-metallic materials, and various semiconductors. Researchers in recent years have attempted to narrow the band gap and improve the photocatalytic efficiency of titanium dioxide by adding metals (Pt, Zn, Ag, Cu, Au) [11,12,13,14,15]. Nevertheless, the metal-doped TiO2 exhibits instability and is prone to corrosion issues. This will lead to a gradual decline in the photocatalytic activity of the materials [16]. Zhang et al. introduced a new material made of N-doped TiO2 into the road field, and when simulating exhaust fumes with CO and NO, it was found that its degradation efficiency was significantly improved [17]. Heffner et al. demonstrated that doping TiO2 with C resulted in a significant improvement in optical performance, achieving a band gap reduction of 0.3 eV [18]. However, the non-metallic doping process involves high-temperature heat treatment or long-term hydrothermal treatment, which will consume a large amount of energy [19]. The composite of MoS2 and TiO2 successfully constructed a heterojunction, which can increase the separation rate of photogenerated carriers and significantly enhance photocatalytic activity [20]. In addition, the heterojunction will also provide a large surface area, promote the adsorption of reactants on the catalyst surface and accelerate photocatalysis [21]. The previous research has put forward innovative ideas to enhance the efficiency of TiO2.
Graphite carbon nitride (g-C3N4) is widely used in the field of photocatalysis due to its advantages such as low cost, non-toxicity, good photochemical stability, and environmental friendliness [22]. However, its low specific surface area and easy recombination of photogenerated carriers hinder its practical application. Constructing a heterojunction to produce electron hole pairs with a high separation efficiency and wide light response range is an effective way to improve the photocatalytic ability of materials [23,24]. Therefore, the composite of g-C3N4 and TiO2 offers a potential way to develop a new effective photocatalysis. Tan et al. developed a green route to prepare TiO2 and g-C3N4 composite materials with two types of heterojunctions. The material has a large interface surface contact, which can accelerate electron migration and efficiently degrade indoor formaldehyde [25]. After successful recombination of TiO2 and g-C3N4, the heterostructure between the two can effectively promote the separation of electrons and holes, significantly improving the photocatalytic reduction efficiency of carbon dioxide (CO2) [26].
As infrastructure is booming, monofunctional building materials can no longer meet the needs of development. Instead, it is desirable for one material to have multiple functions, so the field of composites has grown rapidly [27]. Photocatalysts are unlikely to undergo photocatalytic reactions in low-light environments. In order to ensure that TiO2/g-C3N4 continues to undergo photocatalytic degradation reactions in the absence of light, it is necessary to find an all-weather photocatalytic material to solve the above problem [28]. Aluminum salt long-afterglow material (SrAl2O4: Eu2+, Dy3+) is a good type of photoluminescence material with a good light storage performance. Its application and research are also the most extensive [29]. It is non-toxic, inexpensive, and has good chemical stability [30]. When there is light, it can store energy; when there is no light, electrons can be released, resulting in luminescence [31,32]. There are studies demonstrating that long-afterglow materials can be regarded as an additional light source that can tsupport TiO2 for photocatalysis in a dark environment [33]. This integration aims to achieve a synergistic effect, thereby enhancing the catalytic activity of the photocatalyst and facilitating the degradation of automotive exhaust fumes.
This study aimed to develop a ternary composite photocatalyst of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ for the degradation of road vehicle exhaust emissions. The ternary composite photocatalyst degradation coating was prepared, and comprehensive testing was conducted to assess its fundamental properties. A self-made reaction chamber was irradiated with different intensities of visible light, and the purification rate of automobile exhaust fumes was tested. On this basis, the successful formation of the composite was verified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis differential scanning calorimetry (TG-DSC), and the mechanism of performance improvement was explained. This study proposes a composite material that can degrade automotive exhaust fumes in both low-light and no-light environments, as well as provides a useful reference for the photocatalytic degradation of automotive exhaust fumes in the road domain, broadening the application scenarios and raising the potential for timely application.

2. Materials and Methods

2.1. Materials

The dispersing agent (99%, Beijing Mairuida Technology Co., Ltd., Beijing, China), talcum powder (Beijing Mairuida Technology Co., Ltd.), titanium dioxide (TiO2, 99%, Beijing Mairuida Technology Co., Ltd.), epoxy resin diluent (98%, Shanghai McLean Biochemical Technology Co., Ltd., Shanghai, China), calcium carbonate (CaCO3, 98%, Shanghai McLean Biochemical Technology Co., Ltd.), coalescent (C12H24O3, 98%, Shanghai McLean Biochemical Technology Co., Ltd.), SrAl2O4: Eu2+, Dy3+: SrCO3 (55%), Al2O3 (42%), Eu2O3 (1%), Dy2O3 (1%), and H3BO3 (1%) (Chuangrong Chemical Industry Technology Co., Ltd., Guangzhou, China), melamine (C3H6N6, 99%, Shanghai Dibai Biotechnology Co., Ltd., Shanghai, China), epoxy resin (Beijing Honghu United Chemical Products Co., Ltd., Beijing, China), antifoaming agent (C3H6Cl2, Beijing Puxitang Biotechnology Co., Ltd., Beijing, China), silane coupling agent (98%, Sinopharm, Beijing, China), fumed silica (99%, Beijing Hanlongda Technology Development Co., Ltd., Beijing, China), and epoxy resin curing agent (98%, Beijing China Ocean Co., Ltd., Beijing, China) were used as received from the vendors without further processing.

2.2. Preparation of g-C3N4/TiO2 Composite Photocatalyst

Melamine (C3H6N6) is the most common precursor, chosen as the precursor for g-C3N4 due to its low synthesis cost and ease of operation [34]. C3H6N6 and TiO2 were weighted as a mass ratio of 1:1 [35], ground, and blended until a homogeneous mixture was achieved. The resulting powder sample should then be transferred carefully to a ceramic crucible, covered, and placed in a muffle furnace. For the calcination process, it is advisable to keep the crucible cover semi-closed and set the temperature control system of the muffle furnace to 550 °C. After two hours of calcination, stop heating and open the oven door. It is important to allow the crucible to cool naturally to room temperature before removing it from the furnace for further grinding.

2.3. Preparation of Long-Afterglow Vehicle Exhaust Degradation Coatings

The materials used to create a long-lasting coating for vehicle exhaust degradation included epoxy resin, epoxy resin diluent, defoamer, dispersant, silane coupling agent, talcum powder, calcium carbonate, fumed silica, SrAl2O4: Eu2+, Dy3+, g-C3N4/TiO2 composite photocatalyst, film-forming assistant alcohol ester XII, and epoxy resin curing agent. Firstly, 20 g of epoxy resin, 10 g of epoxy resin diluent, 0.5 g of defoaming agent, 3 g of dispersant, and 6 g of silane coupling agent were weighed and stirred for 9 min at a speed of 110 r/min. Next, 2.5 g talcum powder and 2.5 g calcium carbonate were added and stirred for 12 min at a speed of 180 r/min. Then, 0.5 g of anti-settling agent fumed silica was added, with a total mass of 35 g, to the phosphor powder and composite photocatalyst with mass ratios of 1:1, 1:2, 1:3, 2:1, and 3:1, respectively, as well as 9 g of film-forming aid alcohol ester dodecyl and 10 g of epoxy resin curing agent. We commenced stirring at a speed of 105 r/min for 15 min. Finally, a long-afterglow automobile exhaust purification coating was obtained after adding 1 g of antifoaming agent and stirring for 5 min at a speed of 130 r/min.

2.4. Evaluation of Basic Properties of Coatings

For an accurate assessment of the coating’s condition and appearance, it is recommended to conduct a visual inspection. The rutted plate specimen should be evenly coated with a g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ solution of 2 kg/m2 and then cured at room temperature. Once cured, the specimen should be placed outside to absorb light fully. At night, observe the specimen’s luminous effect, from its initial stimulation to the minimum brightness visible to the human eye (0.32 mcd/m2) until it is no longer visible (<0.32 mcd/m2). Keep a record of the afterglow duration. The coating has a solid content of 45.5%, ensuring robust stability with no indication of caking or delamination after storage. Its drying time is relatively short, only about 30 min. When exposed to light, the coating’s afterglow duration is about 8 h before the light complete fades away, gradually decreasing in intensity over time. Therefore, this coating can provide a potential and feasible solution for automotive exhaust photocatalytic degradation under low light or even in a no-light environment.

2.4.1. Anti-Slip Properties

The asphalt mixture underwent rigorous evaluation, focusing on its friction coefficient and surface texture depth. In accordance with the Field Test Methods of Highway Subgrade and Pavement [36], the friction coefficient was measured using a pendulum friction meter. Furthermore, the surface texture depth was precisely determined by adhering to the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering [37]. This approach ensured that the asphalt mixture met the required standards for friction and texture depth.

2.4.2. Adhesion

The adhesion strength of the paint was assessed through the implementation of the scratch test for paint and varnish films [38]. The evaluation procedure involved applying the paint to a plate specimen and subsequently dividing it into a grid pattern using a cutter. The cutter was required to make cuts deep enough to penetrate the coating, resulting in a total of 6 horizontal and 6 vertical splits. The detached coating blocks that were scattered from the specimen were counted, and the percentage of detachment was used to determine the adhesion index. The index was then evaluated based on the percentage of detachment obtained.

2.4.3. Water Resistance

In compliance with the technical specifications outlined in Pavement Marking Coatings [39], the coating should endure a duration of 24 h of water soaking without exhibiting any irregularities. To determine the coating’s resistance to water, an immersion test was conducted in accordance with determination of resistance to water of films [40]. This entailed the following procedures: (1) A Marshall specimen coated with a heat-reflective coating was placed face down in a container. (2) The container was filled with deionized water until the Marshall specimen was submerged by two-thirds. (3) Following the 24 h soaking period, the test piece was removed and any residual moisture was absorbed using filter paper. The coated specimen was then inspected for any signs of discoloration, blistering, peeling, folding, rust, loss of reflectivity, or any other abnormalities.

2.4.4. Abrasion Resistance

The determination of coating wear resistance is achieved via the Rotary Wear Resistance Test, adhering strictly to the protocol outlined in the national standard [41]. This procedure involves employing a specifically designed hard rubber friction wheel, embedded with emery abrasive, to abrade the coating surface under precise testing conditions, including the maintenance of a constant load on the pressurizing arm. The wear resistance is then determined by calculating the mean value of the coating’s mass loss after undergoing a specified number of grinding rotations.

2.5. Evaluation of Exhaust Degradation Effect

We weighed 40 g of a ternary composite photocatalytic coating, which was evenly applied to the rutted board. The vehicle exhaust was introduced to the reaction chamber, surrounded by tinfoil paper to achieve a good shading effect. The rutted plate specimen was placed in the closed reaction chamber, with the light source placed inside the reaction chamber for standby use. The gas outlet of the reaction chamber was connected to a vehicle exhaust analyzer, and the recorded values were monitored until the concentration stabilized, as shown in Figure 1.
The calculation formula is as follows:
μ1 = (A1 − A2)/A1 × 100%
μ2 = (B1 − B2)/B1 × 100%
μ3 = (C1 − C2)/C1 × 100%
The CO concentration value A1, the NO concentration value B1, the CH concentration value C1, and time were recorded. The light source was turned on, and three different light intensities were set, with the strong light being 800 W/m2, the weak light being 400 W/m2, and no light being 0 W/m2. After the degradation process began, when the exhaust concentration in the reaction chamber decreased and once again stabilized, the CO concentration value A2, the NO concentration value B2, and the CH concentration value C2 were recorded. The degradation efficiencies μ1, μ2, and μ3 of the coating under different light conditions were calculated from A1, B1, C1 and A2, B2, C2.

2.6. Characterization and Analysis of Microscopic Experimental Materials

XRD is a valuable technique that is utilized to analyze the elemental composition and morphology of a sample. FT-IR is a highly efficient method for obtaining molecular structure and chemical bond information on samples by measuring and analyzing their infrared spectra. XPS is employed to deeply determine the elemental composition and chemical bonding state of materials, contributing to a comprehensive understanding of their properties. TG-DSC is a crucial tool to study the thermal stability of materials by measuring the mass changes and thermal effects of the test sample. These microscopic experiments have been used to analyze the structure and morphology of ternary photodegradable composite coatings.

3. Results and Discussion

3.1. Evaluation of Basic Performance of Coating

After comprehensive testing, the long-lasting vehicle exhaust degradation coating displayed remarkable properties. It remained free from clumping in the container, ensuring smooth mixing. Following a period of static storage, there was no observable clumping or stratification, maintaining a consistent and uniform distribution, thereby indicating its reliable storage stability. We analyzed the adhesion index in correlation with the degree of detachment. The testing revealed that 11% of the entire coating area consisted of scattered coating blocks, which corresponded to an evaluation level of 2, indicating a favorable condition. This coating’s resistance to water was also thoroughly tested, confirming its durability without experiencing any discoloration, bubbling, peeling, wrinkling, rusting, loss of gloss, or any other phenomena outlined in Section 2.4.3.
In accordance with the procedure outlined in Section 2.4.4, the wear resistance of the coating was subjected to rigorous testing, and the findings are presented in Figure 2. Wear resistance is an important consideration factor for coatings in practical applications [42]. The data indicate that the coating exhibited a favorable relative wear resistance and a moderate level of wear.

3.2. Evaluation and Comparative Analysis of Exhaust Degradation Performance

The degradation efficiency of vehicle exhaust fumes under no-light conditions with varying mass ratios of the composite photocatalyst g-C3N4/TiO2, and the extended afterglow materials was shown in Figure 3. As the mass ratio of the composite photocatalyst g-C3N4/TiO2 to the long-afterglow materials was gradually reduced, the visible photocatalytic efficiency of the three main components in the exhaust fumes showed a tendency to increase at first and then decrease. From the change curve of the mass ratio from 1:1 to 1:3, we can surmise that when the content of g-C3N4/TiO2 composite photocatalyst was high, the low degradation efficiency of the g-C3N4/TiO2 composite photocatalyst under the no-light condition affected the degradation effect of the whole long-afterglow vehicle exhaust degradation coating, and when the content of the long-afterglow materials was high, the degradation performance of the overall long-afterglow vehicle exhaust degradation coating was not possible due to its low content of g-C3N4/TiO2 photocatalyst. Therefore, the optimum mass ratio of g-C3N4/TiO2 composite photocatalyst to the long-afterglow materials is 1:1.
Figure 4, Figure 5 and Figure 6 show the efficiency of coatings with or without long-afterglow materials SrAl2O4: Eu2+, Dy3+ in degrading NOx, CH, and CO under different lighting conditions. For all coatings with long-afterglow materials, in these experiments, the mass ratio of the g-C3N4/TiO2 composite photocatalyst to the long-afterglow materials was 1:1. From the strong light decomposition curve, it is clear that the catalytic reaction of the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ vehicle exhaust decomposition coating and the g-C3N4/TiO2 composite photocatalytic converter is relatively rapid when the light source is switched on. During the photocatalytic process, each product shows mainly a concave curve, which indicates that after a period of degradation, the degradation products produced by each gas will hinder the contact between the polluted gas and the photocatalytic materials to a certain extent. This leads to a gradual decrease in the visible photocatalytic performance of the sample, which is in line with the experimental results mentioned above. Under a strong-light environment (800 W/m2), the degradation effect of the g-C3N4/TiO2 composite photocatalyst is higher than that of the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ vehicle exhaust degradation coating. This is because the formation of the coating will have a slight negative impact on the original degradation effect. Moreover, the presence of SrAl2O4: Eu2+, Dy3+ will to some extent hinder the full contact between exhaust fumes and g-C3N4/TiO2, leaving it unable to demonstrate its advantages in strong-light environments.
In a weak-light environment (400 W/m2), the g-C3N4/TiO2 photocatalyst demonstrated significant reductions in pollutant concentrations after four hours. Specifically, it achieved a decrease in NOx concentration of 26 ppm and a reduction in CH concentration of 59 ppm. However, with the introduction of long-afterglow materials, these improvements were further enhanced. Within the same four-hour period, the concentration of NOx decreased by an additional 34 ppm, while the concentration of CH decreased by a remarkable 98 ppm. The degradation effect of the long-afterglow automotive exhaust emission control coatings was higher than that of the g-C3N4/TiO2 composite photocatalyst. This is due to the fact that the light intensity is an important factor that affects the degradation effect of the g-C3N4/TiO2 photocatalyst. The lower the light intensity, the worse the degradation efficiency, but the long-afterglow materials can compensate for the light intensity, leading to a slightly greater degradation efficiency. However, the difference between the two is not significant, and the weak-light condition is not sufficient to prove the advantages of the long-afterglow coatings for vehicle exhaust degradation.
In a dark environment (0 W/m2), the g-C3N4/TiO2 photocatalyst showed a decrease in NOx degradation from 68 ppm to 55 ppm within 4 h, with a concentration difference of 13 ppm. The degradation of CH decreased from 769 ppm to 710 ppm, with a concentration difference of 59 ppm. However, after the introduction of long-afterglow materials, the photocatalyst showed significant photocatalytic activity within the same time period, reducing the degradation of NOx from 68 ppm to 34 ppm, with a concentration difference of 34 ppm. The degradation of CH correspondingly decreased from 784 ppm to 686 ppm, with a concentration difference of 98 ppm. That is, the g-C3N4/TiO2 composite photocatalyst showed a weak degradation effect, while the long-afterglow automotive exhaust degradation coating still maintained a good degradation efficiency.
The advantages of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ ternary composite photocatalysts in the degradation of NOx, CH, and CO could not be reflected under strong-light conditions of 800 W/m2. However, in low-light conditions of 400 W/m2, the ternary composite coating showed a 30.8% increase in NOx degradation efficiency and a 66.1% increase in CH degradation efficiency compared to g-C3N4/TiO2. Under no-light conditions of 0 W/m2, the improvement was more significant; we noted that the incorporation of long-afterglow materials led to a significant increase in the degradation rate of NOx, which was 2.6 times higher compared to g-C3N4/TiO2, and likewise for CH, for which its rate was 1.7 times greater than that of g-C3N4/TiO2.
As shown in Figure 6, the results indicated an overall decrease in CO concentration. However, compared to g-C3N4/TiO2, under the low-light and no-light conditions, the improvement of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ in CO degradation rate was too small to show regular changes. The reason for this phenomenon may be that a reversible reaction occurs between CO and CO2 when the catalyst is irradiated with light [43]. The two are both reactants and products, and after a certain period of time, their concentrations reach a relative equilibrium state. However, due to the influence of physical adsorption, the concentration of CO will still show a slight downward trend. When we considering all three lighting conditions, it was apparent that the photocatalyst’s degradation efficiency exceeded that of g-C3N4/TiO2 when long-afterglow materials SrAl2O4: Eu2+, Dy3+ were integrated.

3.3. Microscopic Experimental Results

3.3.1. XRD

Figure 7 shows two distinct peaks, with one at around 27.5°and the other at approximately 13°. The g-C3N4 sample exhibits two standard peaks at 12.87° and 27.45°, which correspond to the planes of (100) and (002), respectively (JCPDS 87–1526). The peak at 27.45° is attributed to the conjugated aromatic structure of g-C3N4, while the faint peak at 12.87° is a result of the in-planar structure. It is noteworthy that the peak at 27.45° is relatively more intense than the peak at 12.87°, which highlights the importance of the conjugated aromatic structure in the sample [44]. The above two peaks indicate that g-C3N4 was successfully prepared [45]. The peaks at around 2θ = 25.3°, 37.8°, 53.9°, 55.1°, 62.7°, and 68.8° are attributed to the (101), (004), (105), (211), (204), and (116) crystal planes of rutile TiO2 [46]. Meanwhile, when the long-afterglow materials were added, the typical characteristic peaks of TiO2 and g-C3N4 could still be observed, which further confirmed that the addition of the long-afterglow materials did not damage the structure of the g-C3N4/TiO2 composite catalyst.

3.3.2. FT-IR

The presence of characteristic peaks in the vibrational spectrum of a material can provide useful information about the properties of the materials. Figure 8 exhibits a clearly defined peak at 808 cm−1, which corresponds to the breathing vibration of the g-C3N4 triazine structure [47]. The region between 1240 cm−1 and 1640 cm−1 shows several characteristic peaks. These include peaks at 1240 cm−1, 1329 cm−1, 1430 cm−1, and 1635 cm−1, which are attributed to the C-N and C=N stretching vibrations of g-C3N4 [6]. Finally, the broad absorption peak in the range of 3000–3300 cm−1 is attributed to the presence of N-H and N=H bonds remaining from incomplete condensation of melamine during the heating process [48]. In a comparison between scenarios with and without long-afterglow materials added, the shapes of the two plots are largely consistent, indicating that the addition of the long-afterglow materials did not destroy the structure of the original g-C3N4/TiO2, and also reflecting the successful composite of the three after the addition of the long-afterglow materials. These observations are expected to facilitate its use in a range of applications, including photocatalysis, sensing, and energy conversion, as they provide useful insights into the structural and functional properties of the materials.

3.3.3. XPS

The chemical binding states of each element in g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ and g-C3N4/TiO2 were characterized through XPS analysis. As we can see from Figure 9a, all elements including C, N, O, and Ti were detected in the survey spectra of g-C3N4/TiO2, and additional Sr, Al, Eu, and Dy were in g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+. The C1s spectrum shows three peaks at 284.8 eV, 286.2 eV, and 288.3 eV. The peak at 284.8 eV corresponds to a surface unstable C-C group, originating from pure graphitic carbon from the XPS instrument itself; the peak at 286.2 eV corresponds to the C-O group of g-C3N4; and the peak at 288.3 eV corresponds to the C-N or N=C-N2 group of g-C3N4 [49]. The N1s spectrum shows three peaks at 398.4 eV, 399.1 eV, and 400.2 eV, assigned to the C=N-C group, C≡C group, and N-H group [50]. The O1s spectrum shows two peaks at 530.9 eV and 532.9 eV depicted in g-C3N4/TiO2, representing the Ti-O band and -OH group, respectively, and an additional peak at 531.5 eV in g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ representing the Al-O band. Within the spectrum of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+, a slight shift of the -OH peak to a higher binding energy position is observed, potentially attributed to the introduction of long-afterglow materials. Both samples showed peaks at around 455.4 and 461.2 eV, which we identified as the 2p3/2 and 2p1/2 peaks, indicating the presence of Ti4+ in both samples. No other peaks related to Ti2+ or Ti3+ were found. In Figure 9f, there is only one fitted peak for the Al 2p oxidation state, originating from SrAl2O4 (at 73.8 eV). The high-resolution scan of Sr 3d reveals two distinct peaks corresponding to Sr3d5/2 (133.0 eV) and Sr3d3/2 (134.8 eV), which are associated with the Sr from the two sites in SrAl2O4 [51]. In addition, there are Eu3d5/2 (1110.1~1179.9 eV) and Dy3d5/2 (1280.1~1349.4 eV) in g-C3N4/TiO2/SrAl2O4 from the XPS survey; however, their contents are relatively low and it is difficult to further analyze the characteristic peaks. The XPS results indicate that a combination of chemical bonds in the form of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ is preferable, instead of physically mixing separate g-C3N4, TiO2, and SrAl2O4: Eu2+, Dy3+.

3.3.4. TG-DSC

Figure 10 is a thermal analysis diagram of the ternary composite photocatalyst. In the TG curve, there is a 3.8% mass loss step between 100 and 250°, which can be attributed to the desorption of water adsorbed by the relevant materials [52]. Between 250 and 400 °C, the mass of the compound undergoes a 28.4% decline. This may correspond to the decomposition of g-C3N4 in composite materials. The decomposition temperature of the composite material is lower than that of pure g-C3N4, which may be attributed to the distribution of TiO2 on the curved surface of g-C3N4, reducing the van der Waals force of g-C3N4 [53]. Organic solvents or additives are used in the preparation process of long-afterglow materials, which may decompose or evaporate in the temperature range of 250–400 °C and may also cause quality loss. The final mass loss between 400 and 600 °C can be attributed to the thermal decomposition of Sr2CO3 [54]. Based on the DSC curve depicted in Figure 10, the ternary composite material exhibits consistent heat absorption within the range of 30–600°, with no particularly prominent exothermic peaks.

4. Conclusions

This research study was conducted to develop and evaluate a composite photocatalyst coating composed of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ and compare its properties with those of g-C3N4/TiO2. This study aimed to determine whether the addition of SrAl2O4: Eu2+, Dy3+ could enhance the photocatalytic performance of the ternary composite photocatalyst under varying lighting conditions. The key findings of this research are as follows.
Firstly, we evaluated the anti-slip properties, adhesion, water resistance, and abrasion resistance of the ternary compound coating and found that it exhibited a good basic performance, and that the afterglow luminescence process lasted for more than 8 h in a dark environment. Secondly, this study demonstrated that the degradation efficiency of the ternary composite photocatalyst was slightly lower than that of g-C3N4/TiO2 when exposed to intense light. However, it was significantly improved in the absence of light. Lastly, microscopic experiments revealed that the introduction of SrAl2O4: Eu2+, Dy3+ cannot damage the original structure and stability of g-C3N4/TiO2.
This study presents a composite photocatalyst, consisting of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+, which has demonstrated great promise in efficiently degrading pollutants in automotive exhaust fumes in all-weather conditions. This composite photocatalyst offers a potential solution to the growing environmental concern about automotive emissions, with the ability to be practically implemented in engineering applications. However, further research is required to fully understand the specific mechanisms behind the photocatalyst’s remarkable ability to degrade pollutants in exhaust fumes. To gain a deeper understanding, future studies may employ theoretical calculations to reveal objective reaction laws from experimental phenomena, which will aid in the development of more directional and forward-looking materials. Overall, this study offers hope for the development of practical and effective solutions to mitigate the harmful effects of automotive emissions on the environment.

Author Contributions

B.Z.: Writing—Review and Editing, Supervision, Funding Acquisition, Project Administration; H.L.: Investigation, Data Curation, Writing—Original Draft; A.C.: Methodology, Resources, Validation; D.W., Writing—Review and Editing; F.G.: Writing—Review and Editing; C.W.: Conceptualization, Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the “Beijing Municipal Education Commission”, grant number KM202310005002, and the “Transportation Science and Technology Research Project of Hebei Province”, grant number 202206.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The funders had no role in the design of this study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

NOxnitrogen oxides
COcarbon monoxide
CHhydrocarbons
TiO2titanium dioxide
g-C3N4graphite carbon nitride
CO2carbon dioxide
SrAl2O4: Eu2+, Dy3+a kind of long-afterglow material
XRDX-ray diffraction
FT-IRFourier transform infrared spectroscopy
XPSX-ray photoelectron spectroscopy
TG-DSCthermogravimetric and differential scanning calorimetry
C3H6N6melamine
μdegradation efficiency
ACO concentration value
BNO concentration value
CCH concentration value

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Figure 1. Schematic diagram of photocatalytic degradation for vehicle exhaust.
Figure 1. Schematic diagram of photocatalytic degradation for vehicle exhaust.
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Figure 2. Abrasion test results of g-C3N4/TiO2/SrAl2O4 coating.
Figure 2. Abrasion test results of g-C3N4/TiO2/SrAl2O4 coating.
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Figure 3. Degradation efficiency of g-C3N4/TiO2 and long-afterglow materials with different mass ratios on exhaust fumes’ different gases: (a) CH, (b) CO, (c) NOx.
Figure 3. Degradation efficiency of g-C3N4/TiO2 and long-afterglow materials with different mass ratios on exhaust fumes’ different gases: (a) CH, (b) CO, (c) NOx.
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Figure 4. Degradation efficiency results of NOx with and without long-afterglow materials SrAl2O4: Eu2+, Dy3+ under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
Figure 4. Degradation efficiency results of NOx with and without long-afterglow materials SrAl2O4: Eu2+, Dy3+ under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
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Figure 5. Degradation efficiency results of CH with and without long-afterglow materials under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
Figure 5. Degradation efficiency results of CH with and without long-afterglow materials under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
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Figure 6. Degradation efficiency results of CO with and without long-afterglow materials SrAl2O4: Eu2+, Dy3+ under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
Figure 6. Degradation efficiency results of CO with and without long-afterglow materials SrAl2O4: Eu2+, Dy3+ under different light intensities: (a) 800 W/m2, (b) 400 W/m2, (c) 0 W/m2.
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Figure 7. Comparison of XRD patterns of g-C3N4/TiO2 doped with or without long-afterglow materials.
Figure 7. Comparison of XRD patterns of g-C3N4/TiO2 doped with or without long-afterglow materials.
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Figure 8. Infrared spectrogram with and without long-afterglow materials, evaluating the stability of the structure of the original g-C3N4/TiO2.
Figure 8. Infrared spectrogram with and without long-afterglow materials, evaluating the stability of the structure of the original g-C3N4/TiO2.
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Figure 9. XPS spectra of g-C3N4/TiO2 and g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+: (a) survey and deconvoluted (b) C1s, (c) N1s, (d) O1s, (e) Ti 2p, (f) Al 2p, (g) Sr 3d.
Figure 9. XPS spectra of g-C3N4/TiO2 and g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+: (a) survey and deconvoluted (b) C1s, (c) N1s, (d) O1s, (e) Ti 2p, (f) Al 2p, (g) Sr 3d.
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Figure 10. TG-DSC curves of thermal decomposition of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ under a nitrogen atmosphere.
Figure 10. TG-DSC curves of thermal decomposition of g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ under a nitrogen atmosphere.
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MDPI and ACS Style

Zhou, B.; Li, H.; Cui, A.; Wang, D.; Guo, F.; Wang, C. Implementing All-Weather Photocatalysis of Exhaust Fumes Based on the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ Ternary Composite Coating. Buildings 2024, 14, 1743. https://doi.org/10.3390/buildings14061743

AMA Style

Zhou B, Li H, Cui A, Wang D, Guo F, Wang C. Implementing All-Weather Photocatalysis of Exhaust Fumes Based on the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ Ternary Composite Coating. Buildings. 2024; 14(6):1743. https://doi.org/10.3390/buildings14061743

Chicago/Turabian Style

Zhou, Bochao, Hailong Li, Ao Cui, Di Wang, Fucheng Guo, and Chao Wang. 2024. "Implementing All-Weather Photocatalysis of Exhaust Fumes Based on the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ Ternary Composite Coating" Buildings 14, no. 6: 1743. https://doi.org/10.3390/buildings14061743

APA Style

Zhou, B., Li, H., Cui, A., Wang, D., Guo, F., & Wang, C. (2024). Implementing All-Weather Photocatalysis of Exhaust Fumes Based on the g-C3N4/TiO2/SrAl2O4: Eu2+, Dy3+ Ternary Composite Coating. Buildings, 14(6), 1743. https://doi.org/10.3390/buildings14061743

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