Next Article in Journal
ANCUT1, a Fungal Cutinase MgCl2-Activated by a Non-Essential Activation Mechanism for Poly(ethylene terephthalate) Hydrolysis
Previous Article in Journal
Tribocatalytic Degradation of Organic Dyes by Disk-Shaped PTFE and Titanium: A Powder-Free Catalytic Technology for Wastewater Treatment
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 15
Issue 8
10.3390/catal15080755
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Controllable Preparation of TiO2/SiO2@Blast Furnace Slag Fiber Composites Based on Solid Waste Carriers and Study on Mechanism of Photocatalytic Degradation of Urban Sewage

by
Xinwen Luo
1,
Jinhu Wu
2,
Guangqian Zhu
1,
Xinyu Han
1,
Junjian Zhao
1,
Yaqiang Li
1,*,
Yingying Li
1 and
Shaopeng Gu
2,3,*
1
Department of Automotive Engineering, Hebei Vocational University of Technology and Engineering, Xingtai 054000, China
2
College of Metallurgy and Energy, North China University of Science and Technology, Tangshan 063009, China
3
Hebei Iron and Steel Laboratory, North China University of Science and Technology, Tangshan 063210, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(8), 755; https://doi.org/10.3390/catal15080755
Submission received: 21 July 2025 / Revised: 2 August 2025 / Accepted: 4 August 2025 / Published: 7 August 2025
(This article belongs to the Special Issue Enhanced Photocatalytic Activity over Ti, Zn, or Sn-Based Catalysts)
Browse Figures
Versions Notes

Abstract

Photocatalytic composite materials (TiO2/SiO2/BFSF) were first fabricated using the sol–gel method of loading SiO2 and TiO2 on blast furnace slag fibers (BFSFs) in sequence and using them as a new carrier. Then, TG-DTA, XRD, BET, SEM-EDS, and UV-Vis absorption spectra, as well as spectrophotometric measurements, were employed to analyze the physicochemical properties of TiO2. The influence of SiO2 coating, the number of impregnations in TiO2 sol, the calcination temperature, and the number of repeated usages on the activity of TiO2/SiO2/BFSF was researched by analyzing the degradation of methylene blue (MB) aqueous solution. The results show that SiO2 could increase the load of TiO2, impede the growth of TiO2 grains, and inhibit the recombination of electron–hole pairs, ultimately enhancing the photocatalytic activity of samples. The activity of TiO2/SiO2/BFSF first quickly increased and then slowly decreased with an increase in the loading times of TiO2 sol and calcination temperature. After three impregnations in TiO2 sol and calcining at 450 °C for 2.5 h, a uniform and compact anatase TiO2 thin film was deposited on the surface of TiO2/SiO2/BFSF, showing the strongest activity. When this sample was used to degrade MB aqueous solution for 180 min under ultraviolet light irradiation, the degradation proportion reached a maximum of 96%. After four reuses, the degradation ratio could still reach 67%. In addition, three potential photocatalytic mechanisms were proposed. Finally, the high-value-added application of blast furnace slag for preparing photocatalytic composite materials was achieved, successfully turning solid waste into “treasure”.

1. Introduction

Blast furnace slags (BFSs) are important by-products manufactured in the iron making process. They are the most productive slags in the metallurgical industry, accounting for about 50% of solid wastes in the iron and steel industry. Generally, 300~350 kg of BFS can be produced while 1 t of pig iron is smelted. According to this ratio, an annual output of more than 250 million tons of BFS has been achieved in Chinese iron and steel enterprises [1,2]. At present, BFS is mostly treated by using a wet process; that is, a certain pressure of water is adopted to impact high-temperature molten slags to break them into droplets and quickly cool them to form solid slag particles (i.e., water-quenched slags). In terms of composition, water-quenched slags from silicate solid wastes are highly similar to building materials; thus, they are mostly used to produce cement and concrete.
Before the water-quenching process, BFSs are in a liquid state with a high temperature of 1500 °C, with very high thermal energy. The sensible heat contained in each ton of slags is more than 1.8 GJ. Consequently, in order to utilize energy and BFS solid waste with high quality and efficiency, specialized technology has been developed for the preparation of slag wool fibers using BFSs, which can not only fully utilize the energy of high-temperature BFSs but also help in transforming BFS solid waste into a new product (blast furnace slag fibers—BFSFs). This new product exhibits a small bulk density, stable chemical properties, fire resistance, shock resistance, non-toxicity, good electrical insulation, no corrosion of metals, a large specific surface area, a low cost, and other properties. This product can be used as an insulation material in the field of construction, a filling material in internal partition walls and suspended ceilings for indoor buildings for sound insulation and absorption, or an insulation material in industrial pipelines and industrial furnace kilns, among other uses [3,4]. The features of a low cost and large specific surface area for BFSF should be noted as being important; based on previous experience, materials with these characteristics can serve as good carrier materials, thereby further broadening the application field of blast furnace slags and improving the added value of products.
In recent years, photocatalytic materials have shown broad application prospects in the fields of air purification [5,6], sewage treatment [7,8,9,10], solar cells [11], the photolysis of water to produce hydrogen [12,13], and the preparation of antibacterial self-cleaning products [14,15]. Currently, TiO2 is widely recognized as one of the most ideal photocatalysts. It possesses many excellent properties such as high chemical stability, non-toxicity, non-selectivity to organic pollutants, and a long catalytic life, and it does not contribute to any secondary pollution [16,17,18,19]. However, TiO2 powders are aggregated especially easily during use, which results in a decrease in their photocatalytic degradation ability and a severe problem in terms of recycling and reuse [7,20]. Based on this dilemma, an effective method involves loading TiO2 on a carrier material, which can effectively improve the dispersibility and recyclability of TiO2 particles [21]. Therefore, the selection of carrier materials has been placed under the spotlight for further studies, attracting significant attention from researchers.
According to different usage scenarios, many materials have been used so far as TiO2 carriers, including silica glass fibers [22], basalt fibers [23], carbon fibers [24,25], diatomaceous earth [26], fly ashes [27], mineral slags [28,29,30], and so on. Gong et al. [23] prepared photocatalytic composite materials using basalt fibers as the carrier and evaluated the photocatalytic degradation ability and reusability of samples. Ren et al. [27] designed a novel nano-TiO2/epoxy resin composite and researched its application in alkali-activated slag/fly ash pastes. They clarified that the composite’s mechanical properties, such as its compressive and flexural bending strengths, and porous structures were enhanced, ultimately leading to an improvement in photocatalytic performance. Shao et al. [28] used steel slag-derived calcium silicate hydrate to adsorb heavy metal ions and degrade organic pollutants. They found that the material displayed a tremendous absorption ability and that it could deal with organic pollutants under visible light. Malekhosseini et al. [29] prepared nano-ZnFe2O4 photocatalytic materials using copper slags as carriers and characterized their photocatalytic degradation ability on a p-Xylene aqueous solution. They pointed out that the photocatalytic materials did not pollute the environment, were easy to control, and had a low cost, and they showed that the maximum degradation ratio could reach 95.40%. Song et al. [30] supported TiO2 on BFS to prepare hydrotalcite-like composite materials and degrade tetracycline in aqueous solution. They observed that the wavelength of light that excites TiO2 to produce electron–hole pairs was induced to expand to the visible region, and the photo-degradation ratio of tetracycline was increased. It could be concluded that the employment of carriers could effectively enhance the performance of photocatalysts. However, all of the above photocatalytic materials have rarely been used so far due to a variety of reasons, such as the insufficiency of the carrier source, the high cost, and the weak performance of prepared photocatalytic materials. In view of these problems, combined with the above characteristics of BFSFs, solid waste blast furnace slags can be used as an ideal carrier material for preparing photocatalytic materials. This not only involves utilizing blast furnace slag solid wastes but also improves the photocatalytic activity of titanium dioxide.
Therefore, in this study, the photocatalytic composite materials of TiO2/BFSF and TiO2/SiO2/BFSF were prepared through a two-step sol impregnation loading method to load SiO2 and TiO2 on BFSF in sequence, adopting BFSFs as carrier materials. Then, the photocatalytic activity of the composite materials and the corresponding influence factors were evaluated through the photocatalytic degradation of methylene blue (MB) aqueous solution under ultraviolet light (thus simulating the organic pollutants in urban wastewater; it is used as a benchmark pollutant for evaluating photocatalytic activity by the international academic community, but its representativeness of real urban wastewater is hindered by significant limitations, such as insufficient pollutant diversity and an inadequate toxicity assessment of degradation products). Finally, recycling performance was systematically evaluated, and the mechanism of photocatalytic degradation was elucidated.

2. Results and Discussion

2.1. TG-DTA Analysis

Figure 1 displays the crystal transformation history of TiO2 during the preparation process. The stages of a large quality loss and a small quality loss can be seen on the TG curve. The first stage between 0 °C and 260 °C was caused by the heating of volatile components such as solvent and water, for which the weight loss rate was 18.5%. It should be noted that there is indeed a weak exothermic peak near 264 °C, which is the exothermic peak of the thermal decomposition of organic matter. Then, 270 °C~480 °C captured the second weight loss, mainly due to the carbonization behavior of organic compounds. Then, from 490 °C to 950 °C, there was no obvious weight loss on the TG curve, indicating that the residual components were basically removed. An obvious endothermic peak was formed at 115 °C, indicating the volatilization of solvent and water. An exothermic peak occurred near 415 °C, representing the decomposition and combustion behavior of organic matter. After 415 °C, the samples showed slow exothermic behavior. Combined with the weight loss behavior on the TG curve at the same temperature stage, the transformation process of the titanium dioxide crystal structure from the anatase phase to the rutile phase was gradually completed.

2.2. XRD and BET Analysis

Figure 2 lists the XRD results of the TiO2 powder prepared at different calcination temperatures. It can be observed that all the crystal phases of the calcination products were anatase TiO2, and the intensity of the diffraction peak characterizing the purity of the TiO2 crystal gradually increased as the calcination temperature increased from 350 °C to 500 °C. As the samples were calcined at 600 °C, the obtained products include two types of TiO2 crystals: anatase phase and rutile phase. When the calcination temperature increased to 800 °C, the products were transformed into rutile TiO2. The average grain size (calculated according to the XRD data) and the BET analysis are shown in Table 1 (the experimental values obtained are the average values of three experiments). It can be seen that the average grain size of TiO2 increased with the calcination temperature. Contrarily, the average specific surface area decreased with calcination temperature. The average pore volume and average pore size first increased and then decreased. This is because the high temperature provided more energy, enabling more ions to move and accelerating the migration rate of ions, which ultimately increased the grain size and subsequently decreased the average specific surface area of TiO2.

2.3. SEM-EDS Analysis

Figure 3 shows the microstructure of the original BFSF and the prepared photocatalytic samples. It can be found in Figure 3a that the exterior of the original BFSF was very smooth and clean. The inset in the upper right corner is a diameter distribution map of the BFSF, indicating that the diameter of BFSF was in the range of 1–10 um, with an average diameter of 7 um. The EDS data in Figure 3h shows that only the composition of BFSF was found, with no information on TiO2. Figure 3b shows the BFSF that was loaded with silica sol (SiO2/BFSF). It shows that the exterior of the BFSF was covered with a thin SiO2 coating and became rough. Based on the inset image in the lower left corner, the SiO2 particles were nearly spherical. The inset in the upper right corner shows the distribution range of the grain size for SiO2 particles, indicating that the grain size ranged from 10 to 25 nm, and SiO2 with a grain size of 16 nm accounted for 33.7% of the sample. Figure 3c shows a sample prepared by directly loading TiO2 sol on the BFSF three times (TiO2/BFSF). A uniform and highly dense thin film covered the exterior of the BFSF, and the size of TiO2 particles ranged from 10 to 20 nm. The EDS results in Figure 3i further proved that the particle was TiO2. Figure 3d–f show samples prepared by first loading silica sol on the BFSF (SiO2/BFSF) and then loading TiO2 sol on SiO2/BFSF one, three, and six times, respectively (TiO2/SiO2/BFSF). It can be found in Figure 3d that the surface of SiO2/BFSF was not covered completely with TiO2 particles, suggesting that there were many voids between the adjacent TiO2 particles. However, as shown in Figure 3f, the surface of SiO2/BFSF is fairly rough, and the TiO2 particles on the samples show obvious accumulation, agglomeration, and even shedding behavior. As shown in Figure 3e, all of the samples’ surfaces are wrapped with a TiO2 coating, more uniform and denser than that of the samples’ surfaces in Figure 3c, and the particle size of TiO2 decreased. This could also be confirmed by the diffraction peak intensity of Ti shown in Figure 3i,j in the EDS results. In addition, in the EDS test, Mg, Al, Ca, and Si, among other elements, were also detected. These are the components of the blast furnace slag carrier. Blast furnace slag is the raw material used to prepare BFSF. Figure 3g comprehensively evaluates the sample size, showing a more intuitive comparison. The grain size of the TiO2 coating on the SiO2 thin film was smaller than that of TiO2 directly coating the BFSF, meaning that SiO2 could reduce the grain size of TiO2. The results are similar to those in a previous work [30].

2.4. UV-Vis-NIR Absorption Spectrum

The UV-Vis-NIR absorption spectrum of the prepared TiO2/SiO2/BFSF sample is displayed in Figure 4. It can be clearly observed that there was no absorption of light in the region of visible light or near-infrared light. However, while the wavelength of light was shifted to the UV region—in particular, the wavelength measured less than 350 nm—a sharply increase in light absorption behavior occurred, directly indicating that titanium dioxide film coated the exterior of the BFSF. It is generally recognized that titanium dioxide can absorb ultraviolet light [31]. This also verifies the SEM results well.

2.5. Photocatalytic Activity Evaluation

2.5.1. Effect of SiO2 on Photocatalytic Activity

Figure 5 exhibits the influence of SiO2 on the activity of photocatalytic composite materials. In the first 20 min of the photocatalytic experiment, the UV lamp was turned off, and the sample and methylene blue were fully mixed under the action of high-speed magnetic stirring to maximize the adsorption of methylene blue by titanium dioxide. It can be observed that the photocatalytic degradation ratio of the two samples were very low, at around 4%. This is because the titanium dioxide on the surface of the samples did not absorb ultraviolet light and could not play a role in photocatalytic degradation. After 20 min, the UV light was turned on, and methylene blue’s ability to be degraded by TiO2/SiO2/BFSF was always greater than that for TiO2/BFSF throughout the experiment. Moreover, the degradation ratio at 180 min for TiO2/SiO2/BFSF was about 96%, which is much larger than that for TiO2/BFSF at about 65%. This suggests that the photocatalytic degradation ability of TiO2/SiO2/BFSF was considerably stronger than that of TiO2/BFSF. This is because the SiO2 coating made the surface of BFSF rough and contained a mass of hydroxyl groups that could link with the hydroxyl groups on the external of titanium dioxide, thus enhancing the adhesion of TiO2 and making the loaded TiO2 coating more uniform, firm, and dense, thereby increasing the amount of titanium dioxide supported on the exterior of SiO2/BFSF and ultimately improving the photocatalytic activity [32]. In addition, Si4+ ions might enter the TiO2 lattice to replace some of the Ti4+ ions, causing the lattice distortion of TiO2 [33]. The greater the lattice distortion, the stronger the formed stress field, which could prevent the movement of the grain boundary, thereby inhibiting the growth of TiO2 grains [34]. The Ti-O-Si bridging oxygen structure would be formed with an additional SiO2, and this network structure increases the stabilization of titanium dioxide and improves the crystal form transition temperature of TiO2, ultimately impeding the conversion of titanium dioxide from the anatase phase to the rutile phase [35]. As is known, the small crystal grain and the greater anatase phase were beneficial in heightening the activity of the photocatalyst. Most importantly, the addition of SiO2 could be used as a kernel load to effectively prevent TiO2 agglomeration, boost the disjunction and quantum efficiency of semiconductor electron–hole pairs, and further promote the photocatalytic degradation ability [36].

2.5.2. Effect of Loading Times of TiO2 Sol on Photocatalytic Activity

Figure 6 shows the influence of titanium dioxide sol supporting times on the photocatalytic ability of TiO2/SiO2/BFSF. It could be found that as the number of TiO2 sol supports increased, the degradation ability of methylene blue increased rapidly and then decreased slowly. When the TiO2 sol was supported three times, the degradation ability of methylene blue was obviously stronger than that of the others. When the BFSF did not load TiO2 sol (i.e., the 0th time), the degradation ratio of methylene blue was a constant 0%. The degradation ratio has an important relationship with the number of effective electron–hole pairs produced by titanium dioxide and the utilization ratio of TiO2 to ultraviolet light. The surface of the original BFSF was not loaded with TiO2, resulting in electron–hole pairs not forming under ultraviolet light; thus, MB could not be degraded. The loading amount of titanium dioxide was small as it was loaded once for the titanium dioxide sol, leading to a decrease in the number of photoelectrons, followed by a low degradation ratio. When the TiO2 sol was loaded six times, the agglomeration and superposition phenomenon of TiO2 occurred on the SiO2/BFSF surface, leading to a reduction in surface flatness. In addition, the micropores generated through decomposing organic matter in the surface’s thin film increased, which amplified the scattering behavior of light and then resulted in the low utilization of ultraviolet light energy.
In addition, the further spreading behavior of methylene blue inside the TiO2 film could be prevented using heavy film. Meanwhile, the migrating behavior of the photoelectrons and holes from the inside of the film to the surface of the film could also be suppressed. Moreover, during the migration process, this behavior was enhanced due to the recombination probability of photoexcited carriers [6]. All of these factors decreased the degradation ability of the photocatalyst. With three supports, a homogenic and compact titanium dioxide film covered the external surface of SiO2/BFSF (seen in Figure 3e), accordingly generating strong photocatalytic degradation ability.

2.5.3. Effect of Calcination Temperature on Photocatalytic Activity

Figure 7 shows the degradation ratio for methylene blue through photocatalytic oxidation with TiO2/SiO2/BFSF calcined at different temperatures. It can be seen in Figure 7 that the degradation ratio of methylene blue first exhibited an increasing trend and then a decreasing trend with an increase in the calcination temperature in the range of 350–800 °C. The strongest degradation ability for methylene blue was found with TiO2/SiO2/BFSF samples calcined at 450 °C, and the largest degradation ratio of MB was 95% after the photocatalytic degradation behavior lasted for 180 min. The weakest photocatalytic degradation ability was observed with the TiO2/SiO2/BFSF photocatalyst calcined at 350 °C, and the degradation ratio for methylene blue at 180 min only reached 44%.
Physical and chemical factors such as the crystal phase, grain size, and specific surface area of the photocatalysts strongly influence photocatalytic degradation ability. According to Figure 2 and Table 1, the crystalline phase of titanium dioxide was all the anatase phase when the calcination temperature was between 350 °C and 500 °C. However, the degree of crystallinity of TiO2 calcined at 350 °C was extremely low, leading to poor photocatalytic activity. As the temperature rose to 450 °C and 500 °C, the crystallinity of titanium dioxide increased significantly. Meanwhile, with the crystal size of titanium dioxide calcined at 500 °C (32.6 nm) being considerably larger than that calcined at 450 °C (19.8 nm) and the specific surface area of titanium dioxide calcined at 450 °C being 101.34 m2·g−1, which is much larger than that calcined at 500 °C (67.12 m2·g−1), the photocatalytic ability of the photocatalytic material prepared at 450 °C was eventually determined to be greater than that calcined at 500 °C. After the temperature continued to increase to 500 °C, the crystal phase of TiO2 included both the anatase and rutile phases or included only the rutile phase. Additionally, the crystal grain size and specific surface gradually increased and gradually decreased, respectively. Therefore, the activity of photocatalytic materials gradually decreased.

2.5.4. Photocatalysis Mechanism Research

Figure 8 shows a diagrammatic sketch of the composite materials’ photocatalytic degradation mechanism for methylene blue. The mechanism of photocatalytic degradation technology is based on the ability of semiconductor materials to absorb suitable wavelengths of light to excite electron–hole pairs, which provides strong oxidation ability that could degrade the specific pollutants in wastewater. In the electronic band structure of titanium dioxide, there is a valence band (VB) that is full of electrons and a vacant conduction band (CB) without electrons. There is also a special region between the valence band and the conduction band, called the forbidden band, and the width of this region is called the forbidden band width (Eg). It reflects the energy barrier of electrons in the process of radiation [5,37].
While the TiO2 semiconductor absorbs sufficient energy photons, the electrons in the valence band could bridge the energy barrier and be excited to the conduction band, producing an equal number of holes behind in the valence band, as seen in Equation (1). Thus, electron–hole pairs are formed and would transfer to the exterior surface of the titanium dioxide. The reactivity of the holes (h+) is very large and has strong oxidizing ability. They could react with electron donors on the outer surface of the photocatalyst, such as H2O and OH−, and then form hydroxyl radicals (•OH). Electrons (e−) are good reducing agents. They can easily react with electron acceptors to generate superoxide ions (•O2−), as seen in Equations (2) and (4). When these •O2− and •OH are separated from the surface of titanium dioxide and turned into mobile ions, reactive oxygen species (ROSs), which have a strong oxidation ability, can be produced. Subsequently, the ROSs could further react to generate other ROSs, as shown in Equations (5)–(9). The radicals and ROSs, representatively including •OH, •O2−, •HO2, and H2O2, degrade methylene blue into inorganic substances such as water and carbon dioxide. Comprehensively, for the photocatalytic treatment of methylene blue in wastewater, three potential mechanisms can be found.
Table 2 shows the degradation ratio of MB when adding different scavengers. TBA is one of the most common scavengers for •OH, usually being added to eliminate •OH effects. BQ and AO can eliminate the effects of •O2− and h+ on the photocatalytic oxidation reaction, respectively. It can be found that the degradation ratio of MB decreases with the addition of BTA, BQ, and AO. When the photocatalytic degradation of methylene blue occurs for 3 h, the degradation ratios of MB are 51%, 70%, and 82%, respectively. The addition of BTA shows the strongest inhibition on the photocatalytic reaction. This further suggests that •OH plays a leading role in the photocatalytic degradation process, followed by superoxide ions and finally holes. At the same time, it can be concluded that the three oxidants all play an oxidative role in the entire photocatalytic degradation process of MB.
Nevertheless, the recombination phenomenon of •OH and e− could also exist during the process of transferring •OH and e− to the outer surface of titanium dioxide, and it also includes the titanium dioxides already on the outer surface of the samples. All of these factors significantly affect the photocatalytic degradation ability of titanium dioxide. This is closely related to the chosen carrier material. In this study, the SiO2 coating effectively prevented the recombination of electron–hole pairs and then elevated photocatalytic activity.
T i O 2 + h v → h + + e −
H 2 O + h + → • O H + H +
O H − + h + → • O H
O 2 + e − → • O 2 −
• O 2 − + H + → H O 2 •
H O 2 • → H 2 O 2 + O 2
H O 2 • + H 2 O + e − → H 2 O 2 + O H −
• O H + • O H → H 2 O 2
H 2 O 2 + e − → • O H + O H −

2.5.5. Recycling Property

A recycling experiment was employed to evaluate the influence of repeated use times on the photocatalytic activity of the photocatalytic composite materials (Figure 9). The photocatalytic activity of composite materials showed a downward trend as the times of repeated use increased. When the samples were reused once, the degradation ratio of methylene blue was 97%, and it decreased to 67% when it was reused for the fourth time. This is because some TiO2 particles fall off from the surface of the samples under the intense stirring of the magnetic stirrer during the experiment process, and some inevitable factors during sample handling could also cause the fall of titanium dioxide particles. These include many operations carried out on the composite materials, such as high-speed centrifugation, ultrasonic cleaning, and low-temperature drying for reuse, reducing the photocatalytic degradation ability of TiO2/SiO2/BFSF. In addition, certain special photocatalytic active sites were damaged by some stable and difficult-to-desorb substances formed during the photocatalytic degradation process, resulting in a decrease in the photocatalytic degradation ability of TiO2/SiO2/BFSF.

2.5.6. Evaluation of Photocatalytic Activity of Different Photocatalytic Materials

Table 3 shows the degradation rate of methylene blue treated by photocatalytic materials prepared by titanium dioxide loaded on different types of carrier materials. It can be found that the degradation rates of methylene blue treated with different photocatalytic materials are almost close to 95%. It is worth noting that the degradation times are different. The longest degradation time reached 6 h, while the shortest was only 70 min (Fe2O3/TiO2). Fe2O3/TiO2 composite materials are prepared by modifying TiO2 using Fe2O3, enhancing its photocatalytic ability. The same situation is seen for Fe-TiO2 composite materials. Compared with glass fiber carrier materials and steel tissue carrier materials, BFSF has stronger photocatalytic ability.

3. Experimental Section

3.1. Raw Materials and Reagents

Tetrabutyl titanate (C16H36O4Ti), absolute ethanol (CH3CH2OH), acetylacetone (CH3COCH2COCH3), concentrated hydrochloric acid (HCl, 37%, wt%), methylene blue (MB), silica sol (SiO2·nH2O, 30%, wt%), and deionized water were acquired. All of the chemicals’ reagents except deionized water (prepared during the experiment) were analytically pure grade. In addition, the BFSFs were produced during the experiment. (The preparation process mainly includes two parts: Firstly, the high-temperature melting and homogenization treatment of blast furnace slag were conducted, and secondly, BFSFs were thrown out using high-speed centrifugation after melting. Finally, the prepared BFSFs were collected for use). The main chemical compositions and physicochemical parameters of the BFSF are listed in Table 4 [3,4].

3.2. Material Preparation

The cleaning of BFSFs: BFSFs were first placed in a glass beaker containing anhydrous ethanol solution, ultrasonically cleaned for 20 min, filtered out, and then calcined at 100 °C for 3 h in a muffle furnace. Subsequently, the clean BFSFs were placed back into deionized water, and the above procedures were repeated.
SiO2/BFSF: First, silica sol was diluted with deionized water at a volume ratio of 10:1 and stirred evenly. Then, the clean BFSFs were immersed in the diluted silica sol for 20 min, filtered with a vacuum, dried in an oven at 100 °C, and calcined at 450 °C for 2.5 h in a muffle furnace. SiO2/BFSF was obtained.
TiO2 sol: First, 28 mL of absolute ethanol was placed into beaker A. Then, 4 mL of tetrabutyl titanate and 0.3 mL of acetylacetone were placed into beaker A in turn with a pipet and mixed fully in a magnetic stirrer to obtain solution A. After that, an additional 14 milliliters of absolute ethanol was placed into beaker B, and then 2.0 milliliters of deionized water and 1 milliliter of concentrated hydrochloric acid were placed into beaker B separately and mixed well via magnetic stirring to obtain solution B. Finally, under strong stirring conditions, solution B was added dropwise to solution A at a set speed, finally obtaining TiO2 sol.
TiO2/BFSF and TiO2/SiO2/BFSF: BFSF and SiO2/BFSF were soaked in titanium dioxide sol for 3 min, vacuum-filtered, and dried at 100 °C for 2 h. Then, the above process was repeated to complete the multiple-load process. A schematic of the preparation process is displayed in Figure 10. Finally, the prepared samples were calcined in a muffle furnace at a set temperature for 2.5 h to obtain the TiO2/BFSF and TiO2/SiO2/BFSF photocatalytic composite materials. The final steps involved aging the remaining titanium dioxide sol into gel, drying it into dry gel at 100 °C, grinding it into powder, and calcining it in a muffle furnace at the designated temperature for 2.5 h to obtain titanium dioxide powder.

3.3. Characterization

A high-temperature comprehensive thermal analyzer being manufactured by Beijing Hengjiu Experimental Equipment Co., Ltd. (TG-DTA) (HCT-4, Beijing, China) was adopted to consider the physicochemical change characteristics of titanium dioxide during the preparation process. The sample was heated in a muffle furnace at a rate of 10 °C per minute to 1000 °C in air.
An X-ray diffractometer (XRD) was employed using a DMAX-2500PC X-ray powder diffractometer (Tokyo, Japan) with Cu Kα radiation (λ = 0.154059 nm) at a voltage of 40 kV and current of 30 mA to identify the crystal phase of TiO2 powder. The 2-theta scanning range of the XRD experiment was set between 10° and 80° at a scanning rate of 2° per minute and increments of 0.02°. In addition, based on XRD diffraction spectra, the Scherrer formula was considered to obtain the average particle size of TiO2 grains [18].
The morphologies of the samples were examined using a scanning electron microscope (SEM) (S-4800C, Toshojima, Japan). The working distance was between 8 mm and 12 mm, and the accelerating voltage was 20 kV.
A nitrogen adsorption–desorption apparatus (QDS-MP-30, FL, USA) was set up to research the specific surface area of titanium dioxide powder. The principle of the test is the Brunauer–Emmett–Teller (BET) method. A UV-Vis-NIR Spectrophotometer (UV3600, Kyoto, Japan) was selected to recorded UV-Vis absorption spectra.

3.4. Photocatalytic Activity

The activity of photocatalytic materials was evaluated through the photocatalytic decolorization of methylene blue aqueous solution at room temperature. The specific experimental procedures were as follows: First, 50 mL of 10 mg per liter methylene blue solution, 0.3 g samples, and a rotor of the magnetic stirrer were placed into a quartz tube. The quartz tube was placed in the photocatalytic reactor (YZ-GHX-A, Shanghai, China). Then, the mixed solutions were stirred vigorously for 30 min. After that, the samples were irradiated with a 500 W UV light (LYZD, Shanghai, China, 358.78 W/m2, 27,883 lm, no filters) with a radiation peak at 365 nm and placed 100 mm above the reaction test tube for 3 h in the photocatalytic reactor. During the experiment process, 10 mL samples were taken every half hour and placed in a high-speed centrifuge at a speed of 8000 revolutions per minute for 10 min. The upper liquid was taken and placed in a 723N-type UV–Vis spectrophotometer to test its absorption of light with a wavelength of 664 nm to characterize the degradation ratio of methylene blue according to the Lambert–Beer Law [29]:
D = ( A 0 − A t ) / A 0 = ( C 0 − C t ) / C 0 × 100 %
where C0 is the initial concentration of reactants, and Ct is the concentration of reactants after photocatalytic oxidation time t.
Ultimately, the samples were cleaned via ultrasound, centrifuged, dried, and calcined at 300 °C, and then the above photocatalytic reaction experiment was repeated to assess the reuse effect.

3.5. Photocatalytic Activity Mechanism Research

Tert-butyl alcohol (TBA), benzoquinone (BQ), and ammonium oxalate (AO) were employed to verify the mechanism of the photocatalytic material degradation of methylene blue. In addition, these could also characterize the contribution of different types of oxidants to the degradation of methylene blue.

4. Conclusions

TiO2/BFSF and TiO2/SiO2/BFSF photocatalytic composite materials were prepared through the sol–gel method, and blast furnace slag fibers were selected as the carrier. Photocatalytic activity was systematically evaluated, and the effects of SiO2 coating, the loading times of TiO2 sol, the calcination temperature, and the recycling times on the photocatalytic degradation ability of these photocatalytic composite materials were analyzed in depth. Finally, the photocatalytic degradation mechanism of methylene blue was systematically investigated. This study’s main conclusions are as follows:
(1) The crystalline phase of titanium dioxide was all anatase when the calcination temperature increased within the range of 350 °C to 500 °C. Meanwhile, the photocatalytic degradation ability of TiO2/SiO2/BFSF first increased and then decreased. This is because with the increase in calcination temperature, the crystal grain size of TiO2 increased, and the specific surface area of TiO2 decreased. When the calcined temperature reached 450 °C, TiO2/SiO2/BFSF possessed the strongest photocatalytic activity. When the calcination temperature continued to rise to 600 °C and 800 °C, the crystalline phases of titanium dioxide could be divided into two categories, one containing both the anatase phase and rutile phase and the other containing only the rutile phase. Correspondingly, the photocatalytic degradation ability also weakened.
(2) The loading of SiO2 facilitated the loading amount of TiO2, reduced the crystal grain size of titanium dioxide, and suppressed the probability of electron–hole pair recombination, thus improving the photocatalytic degradation ability of composite materials. The photocatalytic degradation rate of methylene blue obtained through the degradation of TiO2/SiO2/BFSF for 180 min was 96%, which is much larger than that of 65% obtained through the degradation of TiO2/BFSF for 180 min.
(3) The photocatalytic degradation rate of methylene blue first rapidly increased and then decreased slowly with an increase in the number of titanium dioxide sol loadings. When titanium dioxide sol was loaded three times, the samples presented the strongest photocatalytic degradation ability. The maximum value of the methylene blue degradation ratio reached 96% after a photocatalytic reaction for 180 min under ultraviolet radiation.
(4) The photocatalytic degradation ability of TiO2/SiO2/BFSF gradually weakened as the number of repeated uses continued to increase. When the samples were reused four times, and the photocatalytic oxidation of methylene blue lasted for 180 min, the photocatalytic degradation rate could still reach 67%.
(5) There were three potential mechanisms for the degradation of methylene blue with titanium dioxide photocatalytic composite materials. Electron–hole pairs (•OH and e−), superoxide ions and hydroxyl radicals (•O2− and •OH), and reactive oxygen species (•OH, •O2−, •HO2, and H2O2) could simultaneously degrade the organic and inorganic pollutants in wastewater.

Author Contributions

X.L.: Methodology, Investigation, and Formal analysis; J.W.: Writing—review and editing; G.Z.: Data curation and Supervision; X.H.: Formal analysis; J.Z.: Formal analysis, Data curation, and Validation; Y.L. (Yaqiang Li): Conceptualization, Methodology, and Formal analysis; Y.L. (Yingying Li): Formal analysis, Supervision, and Validation; S.G.: Writing—review and editing, Conceptualization, and Investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the National Key Research and Development Program Project (No. 2022YFB3705200, 2022YFB3705201); Tangshan Science and Technology Plan Project (No. 22130212H); Hebei Province Higher Education Science and Technology Research Project (No. QN2024193); Shijiazhuang Basic Research Program Project (No. 241790857A) and Yanzhao Steel Laboratory Regional Innovation Capacity Enhancement Project (No. YZISL2024031).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Acknowledgments

The authors thank North China University of Science and Technology for its support with the analyses.

Conflicts of Interest

The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Wu, J.J.; Wang, H.; Zhu, X.; Liao, Q.; Ding, B. Centrifugal granulation performance of liquid with various viscosities for heat recovery of blast furnace slag. Appl. Therm. Eng. 2015, 89, 494–504. [Google Scholar] [CrossRef]
  2. Ren, Q.Q.; Zhang, Y.Z.; Long, Y.; Zou, Z.S.; Pei, J.J. Crystallisation behaviour of blast furnace slag modified by adding fly ash. Ceram. Int. 2018, 44, 11628–11634. [Google Scholar] [CrossRef]
  3. Li, J.; Liu, W.; Zhang, Y.; Yang, A.; Zhao, K. Research on modifying blast furnace slag as a raw material of slag fiber. Mater. Manuf. Process. 2015, 30, 374–380. [Google Scholar] [CrossRef]
  4. Zhang, Z.Q.; Zhang, Y.Z.; Yang, A.M.; Xing, H.W.; Tian, T.L.; Li, Z.H. Preparation and properties of slag wool board using modified polyvinyl alcohol as binder. Mater. Manuf. Process. 2015, 31, 168–172. [Google Scholar] [CrossRef]
  5. Ren, H.; Koshy, P.; Chen, W.F.; Qi, S.; Sorrell, C.C. Photocatalytic materials and technologies for air purification. J. Hazard. Mater. 2017, 325, 340–366. [Google Scholar] [CrossRef]
  6. Chen, S.F.; Zhang, H.Y.; Yu, X.L.; Liu, W.; Wang, J.E.; Liu, Q.C.; Chen, L. Preparation, characterization and activity evaluation of heterojunction ZrTi2O6/TiO2 photocatalyst. Mater. Chem. Phys. 2010, 124, 1057–1064. [Google Scholar] [CrossRef]
  7. Perović, K.; dela Rosa, F.M.; Kovačić, M.; Kušić, H.; Štangar, U.L.; Fresno, F.; Dionysiou, D.D.; Loncaric Bozic, A. Recent achievements in development of tio2-based composite photocatalytic materials for solar driven water purification and water splitting. Materials 2020, 13, 1338. [Google Scholar] [CrossRef]
  8. Shen, S.; Kronawitter, C.; Kiriakidis, G. An overview of photocatalytic materials. J. Mater. 2017, 3, 1–2. [Google Scholar] [CrossRef]
  9. Hu, X.; Hu, X.; Peng, Q.; Zhou, L.; Tan, X.; Jiang, L.; Tang, C.; Wang, H.; Liu, S.; Wang, Y.; et al. Mechanisms underlying the photocatalytic degradation pathway of ciprofloxacin with heterogeneous TiO2. Chem. Eng. J. 2020, 380, 122366. [Google Scholar] [CrossRef]
  10. Rosa, D.; D’Agostino, F.; Bavasso, I.; Palma, L.D. An innovative and easy method for iron-doped titania synthesis. Chem. Eng. Trans. 2023, 101, 13–18. [Google Scholar] [CrossRef]
  11. Bashiri, R.; Samsudin, M.F.R.; Mohamed, N.M.; Suhaimi, N.A.; Ling, L.Y.; Sufian, S.; Kait, C.F. Influence of growth time on photoelectrical characteristics and photocatalytic hydrogen production of decorated Fe2O3 on TiO2 nanorod in photoelectrochemical cell. Appl. Surf. Sci. 2020, 510, 145482. [Google Scholar] [CrossRef]
  12. Wang, S.; Wang, Y.; Zang, S.Q.; Lou, X.W. Hierarchical hollow heterostructures for photocatalytic CO2 reduction and water splitting. Small Methods 2019, 4, 1900586. [Google Scholar] [CrossRef]
  13. Fu, J.; Jiang, K.; Qiu, X.; Yu, J.; Liu, M. Product selectivity of photocatalytic CO2 reduction reactions. Mater. Today 2020, 32, 222–243. [Google Scholar] [CrossRef]
  14. Pakdel, E.; Wang, J.; Kashi, S.; Sun, L.; Wang, X. Advances in photocatalytic self-cleaning, superhydrophobic and electromagnetic interference shielding textile treatments. Adv. Colloid Interface Sci. 2020, 277, 102116. [Google Scholar] [CrossRef]
  15. Vélez-Peña, E.; Pérez-Obando, J.; Pais-Ospina, D.; Marín-Silva, D.A.; Pinotti, A.; Cánneva, A.; Donadelli, J.A.; Damonte, L.; Pizzio, L.R.; Osorio-Vargas, P.; et al. Self-cleaning and antimicrobial photo-induced properties under indoor lighting irradiation of chitosan films containing melon/TiO2 composites. Appl. Surf. Sci. 2020, 508, 144895. [Google Scholar] [CrossRef]
  16. Kosco, J.; Bidwell, M.; Cha, H.; Martin, T.; Howells, C.T.; Sachs, M.; Anjum, D.H.; Lopez, S.G.; Zou, L.; Wadsworth, A.; et al. Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles. Nat. Mater. 2020, 19, 559–565. [Google Scholar] [CrossRef]
  17. Gholami, P.; Khataee, A.; Soltani, R.D.C.; Dinpazhoh, L.; Bhatnagar, A. Photocatalytic degradation of gemifloxacin antibiotic using zn-co-ldh@biochar nanocomposite. J. Hazard. Mater. 2020, 382, 121070. [Google Scholar] [CrossRef]
  18. Wu, S.; Hu, H.; Lin, Y.; Zhang, J.; Hu, Y.H. Visible light photocatalytic degradation of tetracycline over TiO2. Chem. Eng. J. 2020, 382, 122842. [Google Scholar] [CrossRef]
  19. Ya, J.; Yang, N.; Hu, F.; Liu, Z.; Lei, E. Preparation and activity evaluation of TiO2/Cu-TiO2 composite catalysts. J. Sol-Gel Sci. Technol. 2014, 73, 322–331. [Google Scholar] [CrossRef]
  20. Tsang, C.H.A.; Li, K.; Zeng, Y.; Zhao, W.; Zhang, T.; Zhan, Y.; Xie, R.; Leung, D.Y.C.; Huang, H. Titanium oxide based photocatalytic materials development and their role of in the air pollutants degradation: Overview and forecast. Environ. Int. 2019, 125, 200–228. [Google Scholar] [CrossRef]
  21. Seo, J.H.; Yoon, H.N.; Kim, S.H.; Bae, S.J.; Jang, D.I.; Kil, T.G.; Park, S.M.; Lee, H.K. An overview on the physicochemical properties and photocatalytic pollutant removal performances of TiO2-incorporated cementitious composites. Korean Soc. Compos. Mater. 2020, 33, 68–75. [Google Scholar] [CrossRef]
  22. Löffler, F.B.; Altermann, F.J.; Bucharsky, E.C.; Schell, K.G.; Vera, M.L.; Traid, H.; Dwojak, A.; Litter, M.I. Morphological characterization and photocatalytic efficiency measurements of pure silica transparent open-cell sponges coated with TiO2. Int. J. Appl. Ceram. Technol. 2020, 17, 1930–1939. [Google Scholar] [CrossRef]
  23. Gong, Y.; Song, J.; Bi, H.; Tian, Z. Optimization design of the mix ratio of a nano-TiO2/CaCO3-basalt fiber composite modified asphalt mixture based on response surface methodology. Appl. Sci. 2020, 10, 4596. [Google Scholar] [CrossRef]
  24. Kusiak-Nejman, E.; Czyzewski, A.; Wanag, A.; Dubicki, M.; Sadlowski, M.; Wrobel, R.J.; Morawski, A.W. Photocatalytic oxidation of nitric oxide over AgNPs/TiO2-loaded carbon fiber cloths. J. Env. Manag. 2020, 262, 110343. [Google Scholar] [CrossRef]
  25. Zhang, Y.; Duoerkun, G.; Shi, Z.; Cao, W.; Liu, T.; Liu, J.; Zhang, L.; Li, M.; Chen, Z. Construction of TiO2/Ag3PO4 nanojunctions on carbon fiber cloth for photocatalytically removing various organic pollutants in static or flowing wastewater. J. Colloid Interface Sci. 2020, 571, 213–221. [Google Scholar] [CrossRef]
  26. Zhao, W.; Yang, X.; Liu, C.; Qian, X.; Wen, Y.; Yang, Q.; Sun, T.; Chang, W.; Liu, X.; Chen, Z. Facile construction of all-solid-state z-scheme g-C3N4/TiO2 thin film for the efficient visible-light degradation of organic pollutant. Nanomaterials 2020, 10, 600. [Google Scholar] [CrossRef]
  27. Ren, J.; Guo, S.Y.; Zhao, T.J.; Chen, J.Z.; Nicolas, R.S.; Zhang, L.H. Constructing a novel nano-TiO2/epoxy resin composite and its application in alkali-activated slag/fly ash pastes. Constr. Build. Mater. 2020, 232, 117218. [Google Scholar] [CrossRef]
  28. Shao, N.; Li, S.; Yan, F.; Su, Y.; Liu, F.; Zhang, Z. An all-in-one strategy for the adsorption of heavy metal ions and photodegradation of organic pollutants using steel slag-derived calcium silicate hydrate. J. Hazard. Mater. 2020, 382, 121120. [Google Scholar] [CrossRef]
  29. Malekhosseini, H.; Khosravi, M.; Mahanpoor, K.; Motiee, F. Preparation and characterization of nano ZnFe2O4 supported on copper slag and its effects on the degradation of p-xylene aqueous solution. J. Appl. Chem. Res. 2020, 14, 57–71. [Google Scholar]
  30. Song, Z.; Gao, H.; Zhang, W.; Wang, D. Reinforce of hydrotalcite-like loaded TiO2 composite material prepared by ti-bearing blast furnace slag for photo-degradation of tetracycline. J. Water Process Eng. 2020, 36, 101399. [Google Scholar] [CrossRef]
  31. Yu, J.G.; Liu, W.; Yu, H.G. A one-pot approach to hierarchically nanoporous titania hollow microspheres with high photocatalytic activity. Cryst. Growth Des. 2007, 8, 930–934. [Google Scholar] [CrossRef]
  32. Kwon, C.H.; Kim, J.H.; Jung, I.S.; Shin, H.; Yoon, K.H. Preparation and characterization of TiO2-SiO2 nano-composite thin films. Ceram. Int. 2003, 29, 851–856. [Google Scholar] [CrossRef]
  33. Saravanan, S.; Dubey, R.S.; Subbarao, P.S. Optical investigation of sol–gel-synthesized and spin-coated SiO2/TiO2 multilayers. Nanomater. Energy 2023, 12, 44–48. [Google Scholar] [CrossRef]
  34. Kermadi, S.; Agoudjil, N.; Sali, S.; Boumaour, M.; Bourgeois, S.M.C.; de Lucas, M. Sol-gel synthesis of xTiO2 (100-x) SiO2 nanocomposite thin films: Structure, optical and antireflection properties. Thin Solid Films 2014, 564, 170–178. [Google Scholar] [CrossRef]
  35. Kermadi, S.; Agoudjil, N.; Sali, S.; Zougar, L.; Boumaour, M.; Broch, L.; En Naciri, A.; Placido, F. Microstructure and optical dispersion characterization of nanocomposite sol-gel TiO2-SiO2 thin films with different compositions. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2015, 145, 145–154. [Google Scholar] [CrossRef]
  36. Rasalingam, S.; Peng, R.; Koodali, R.T. Removal of hazardous pollutants from wastewaters: Applications of TiO2-SiO2 mixed oxide materials. J. Nanomater. 2014, 2014, 617405. [Google Scholar] [CrossRef]
  37. Yang, L.; Wang, C.; Liu, Z.; Liu, X.; Song, Y.; Feng, X.; Zhang, B. Functionalizing slag wool fibers with photocatalytic activity by anatase TiO2 and ctab modification. Ceram. Int. 2018, 44, 5842–5847. [Google Scholar] [CrossRef]
  38. Ahmed, M.A.; El-Katori, E.E.; Gharni, Z.H. Photocatalytic degradation of methylene blue dye using Fe2O3/TiO2 nanoparticles prepared by sol-gel method. J. Alloys Compd. 2013, 553, 19–29. [Google Scholar] [CrossRef]
  39. Anwar, D.I.; Mulyadi, D. Synthesis of Fe-TiO2 composite as a photocatalyst for degradation of methylene blue. Procedia Chem. 2015, 17, 49–54. [Google Scholar] [CrossRef]
  40. Schnabel, T.; Jautzus, N.; Mehling, S.; Springer, C.; Londong, J. Photocatalytic degradation of hydrocarbons and methylene blue using floatable titanium dioxide catalysts in contaminated water. Water Reuse 2021, 11, 224–235. [Google Scholar] [CrossRef]
Catalysts 15 00755 g001
Figure 1. TG-DTA analysis of TiO2 xerogel.
Figure 1. TG-DTA analysis of TiO2 xerogel.
Catalysts 15 00755 g001
Catalysts 15 00755 g002
Figure 2. XRD analysis of TiO2 powder prepared at distinct calcination temperatures.
Figure 2. XRD analysis of TiO2 powder prepared at distinct calcination temperatures.
Catalysts 15 00755 g002
Catalysts 15 00755 g003aCatalysts 15 00755 g003b
Figure 3. SEM images and EDS results of BFSF with and without loading SiO2 and TiO2. (a) BFSF, upper right graph shows BFSF size distribution range; (b) SiO2/BFSF, upper right graph shows SiO2 grain size distribution range; (c) TiO2/BFSF sample (supporting TiO2 sol three times, calcining at 450 °C); (d) TiO2/SiO2/BFSF (loading TiO2 sol one time, calcined at 450 °C); (e) TiO2/SiO2/BFSF (loading TiO2 sol three times, calcined at 450 °C); (f) TiO2/SiO2/BFSF (loading TiO2 sol six times, calcined at 450 °C); (g) size distribution range of all samples; (h) EDS data of Figure 3a; (i) EDS data of Figure 3c; (j) EDS data of Figure 3e (inset in each image shows partially enlarged detail).
Figure 3. SEM images and EDS results of BFSF with and without loading SiO2 and TiO2. (a) BFSF, upper right graph shows BFSF size distribution range; (b) SiO2/BFSF, upper right graph shows SiO2 grain size distribution range; (c) TiO2/BFSF sample (supporting TiO2 sol three times, calcining at 450 °C); (d) TiO2/SiO2/BFSF (loading TiO2 sol one time, calcined at 450 °C); (e) TiO2/SiO2/BFSF (loading TiO2 sol three times, calcined at 450 °C); (f) TiO2/SiO2/BFSF (loading TiO2 sol six times, calcined at 450 °C); (g) size distribution range of all samples; (h) EDS data of Figure 3a; (i) EDS data of Figure 3c; (j) EDS data of Figure 3e (inset in each image shows partially enlarged detail).
Catalysts 15 00755 g003aCatalysts 15 00755 g003b
Catalysts 15 00755 g004
Figure 4. UV-Vis-NIR absorption spectrum result.
Figure 4. UV-Vis-NIR absorption spectrum result.
Catalysts 15 00755 g004
Catalysts 15 00755 g005
Figure 5. Effect of SiO2 on activity of photocatalytic composite materials (calcined at 450 °C).
Figure 5. Effect of SiO2 on activity of photocatalytic composite materials (calcined at 450 °C).
Catalysts 15 00755 g005
Catalysts 15 00755 g006
Figure 6. Effect of loading times on photocatalytic degradation ability of TiO2/SiO2/BFSF (calcined at 450 °C).
Figure 6. Effect of loading times on photocatalytic degradation ability of TiO2/SiO2/BFSF (calcined at 450 °C).
Catalysts 15 00755 g006
Catalysts 15 00755 g007
Figure 7. The influence of calcination temperature on the photocatalytic degradation ability of TiO2/SiO2/BFSF (loading TiO2 sol three times).
Figure 7. The influence of calcination temperature on the photocatalytic degradation ability of TiO2/SiO2/BFSF (loading TiO2 sol three times).
Catalysts 15 00755 g007
Catalysts 15 00755 g008
Figure 8. A schematic of the photocatalytic degradation mechanism of the prepared photocatalytic composites under UV conditions.
Figure 8. A schematic of the photocatalytic degradation mechanism of the prepared photocatalytic composites under UV conditions.
Catalysts 15 00755 g008
Catalysts 15 00755 g009
Figure 9. Effect of recycling times on photocatalytic degradation ability of TiO2/SiO2/BFSF.
Figure 9. Effect of recycling times on photocatalytic degradation ability of TiO2/SiO2/BFSF.
Catalysts 15 00755 g009
Catalysts 15 00755 g010
Figure 10. A schematic illustration of the preparation process of photocatalytic composites.
Figure 10. A schematic illustration of the preparation process of photocatalytic composites.
Catalysts 15 00755 g010
Table 1. TiO2 grain size and specific surface area at different calcination temperatures.
Table 1. TiO2 grain size and specific surface area at different calcination temperatures.
Calcination Temperature/°CAverage Grain Size of TiO2/nmAverage Specific Surface Area/m2·g−1Average Pore Volume/cm3/gAverage Pore Size/nm
35012.4114.160.349.5
45019.6102.340.6222.3
50032.467.130.5318.2
60097.349.240.4111.1
800200.415.670.388.4
Table 2. The degradation rate of MB with different photocatalytic composite materials.
Table 2. The degradation rate of MB with different photocatalytic composite materials.
Photocatalytic MaterialsTiO2/SiO2@ BFSFTiO2/SiO2@ BFSF + BTATiO2/SiO2@ BFSF + BQTiO2/SiO2@ BFSF + AO
1 h32%17%22%27%
2 h78%36%51%64%
3 h96%51%70%82%
Table 3. The degradation rate of MB treated by different photocatalytic composite materials.
Table 3. The degradation rate of MB treated by different photocatalytic composite materials.
Photocatalytic MaterialsFe2O3/TiO2BFSF with TiO2Fe-TiO2Glass Fiber with TiO2Steel Tissue with TiO2
Degradation time70 min3 h3 h4 h6 h
Degradation ratio94.2%96%98.5%96.6%98.1%
Ref.[38]--[39][40][40]
Table 4. Main chemical compositions and physicochemical parameters of BFSF (wt%).
Table 4. Main chemical compositions and physicochemical parameters of BFSF (wt%).
SiO2Al2O3CaOMgOFe2O3SAcidity CoefficientDiameter/um
37.715.433.65.94.81.281.27–14
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Luo, X.; Wu, J.; Zhu, G.; Han, X.; Zhao, J.; Li, Y.; Li, Y.; Gu, S. Controllable Preparation of TiO2/SiO2@Blast Furnace Slag Fiber Composites Based on Solid Waste Carriers and Study on Mechanism of Photocatalytic Degradation of Urban Sewage. Catalysts 2025, 15, 755. https://doi.org/10.3390/catal15080755

AMA Style

Luo X, Wu J, Zhu G, Han X, Zhao J, Li Y, Li Y, Gu S. Controllable Preparation of TiO2/SiO2@Blast Furnace Slag Fiber Composites Based on Solid Waste Carriers and Study on Mechanism of Photocatalytic Degradation of Urban Sewage. Catalysts. 2025; 15(8):755. https://doi.org/10.3390/catal15080755

Chicago/Turabian Style

Luo, Xinwen, Jinhu Wu, Guangqian Zhu, Xinyu Han, Junjian Zhao, Yaqiang Li, Yingying Li, and Shaopeng Gu. 2025. "Controllable Preparation of TiO2/SiO2@Blast Furnace Slag Fiber Composites Based on Solid Waste Carriers and Study on Mechanism of Photocatalytic Degradation of Urban Sewage" Catalysts 15, no. 8: 755. https://doi.org/10.3390/catal15080755

APA Style

Luo, X., Wu, J., Zhu, G., Han, X., Zhao, J., Li, Y., Li, Y., & Gu, S. (2025). Controllable Preparation of TiO2/SiO2@Blast Furnace Slag Fiber Composites Based on Solid Waste Carriers and Study on Mechanism of Photocatalytic Degradation of Urban Sewage. Catalysts, 15(8), 755. https://doi.org/10.3390/catal15080755

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop