Construction of Moiré-like Structure to Efficiently Enhance the H₂ Photogeneration

Abstract

Photocatalytic hydrogen production could sustainably and efficiently convert solar energy. However, a low light utilization ratio limits the wide application. Herein, a Moiré-like structure was constructed in the TiO₂ body to improve the light absorption by multiple reflections and suitable light dispersion and diffraction based on similar wavelength and nick. Furthermore, the Moiré-like structure slightly reduces the band gap and accelerates the separation of the photogenerated electrons and holes, and the mass transfer was enhanced by the regular nano-channels and Bernoulli phenomenon. After calcination at 500 °C (M-T500), compared with pure TiO₂, M-T500 achieved a 20% increase in RhB degradation efficiency and a double increase in hydrogen production rate, thus providing a novel design for catalysts and a high catalytic strategy. Moreover, the nearly 100% recovery rate supported environmental protection and sustainable development.

1. Introduction

Hydrogen, as an environmentally friendly energy carrier, due to the advantages of high energy concentration and combustion products being solely water, is regarded as an optimal solution for addressing energy shortages and environmental pollution issues [1,2]. The application of photocatalytic technology to decompose water for hydrogen production shows great development potential in the field of energy conversion and is an effective method to solve energy shortages and convert solar energy into chemical energy [3,4].

Photocatalysts like TiO₂ exhibit significant potential in the field of solar water splitting. However, the efficiency and effectiveness in practical applications are still limited by several constraining factors [5]. The primary issue lies in the wide bandgap (characteristic of TiO₂ approximately 3.2 eV), which results in the main absorption of light energy in the UV region, accounting for only about 5% of the composition of sunlight [6,7]. Furthermore, a low ratio of light utilization, slow separation of photogenerated electrons and holes, and weak mass transfer greatly restrict the application potential of TiO₂ in the efficient conversion of solar energy [8,9]. Although noble metals (such as Pt, Au, and Pd) are often selected as co-catalysts in photocatalytic reactions to get excellent charge separation efficiency, the high cost poses a significant barrier to the widespread application [10,11]. Therefore, in order to overcome the existing limitations of photocatalysts, it is very important to explore reasonable modification strategies to enhance their photocatalytic hydrogen production capacity.

An effective strategy to enhance the efficiency of hydrogen production is to adjust the catalyst structure [12]. Guan et al. [13] have employed laser etching techniques to create defects in anatase TiO₂. The results observed not only an increase in particle size but also the induction of rutile phase formation, along with the generation of oxygen vacancies and Ti³⁺ ion states, which effectively narrowed the bandgap and thereby enhanced the material’s light absorption capability in the visible light range. Moiré-like structure, as a special interference fringe structure, serves to modulate the absorption of light and is capable of diffractively separating visible light [14,15]. By exploiting its characteristic of multiple reflected light, Moiré-like structure can achieve multiple effective utilizations of light [16]. By modulating the morphological structure of the material, a Moiré-like TiO₂ with a structure analogous to the grating in optical devices has been successfully fabricated and exhibits dispersive properties for light [17]. Additionally, Moiré-like structures can induce the formation of oxygen vacancies on the surface, which constitute defect sites, effectively inhibiting their recombination and thereby prolonging the lifetime of the carriers that act as trapping centers for photogenerated carriers. In view of these advantages, catalysts with Moiré-like structures exhibit great potential in the development of efficient and stable photocatalytic materials.

Hence, TiO₂ with novel Moiré-like patterns was simply synthesized via the sol-gel method by using DVD discs as cheap templates. The grating structure, chemical composition, and ability of photogenerated charge carriers and hydrogen production performance in Moiré-like TiO₂ were systematically enhanced. The unique structural design of this Moiré-like TiO₂ not only enhances the efficiency of light capture and utilization but also significantly promotes the mass transfer and the formation of oxygen vacancy defects, thereby improving its photocatalytic activity.

2. Results and Discussion

2.1. Physical Characterizations of M-TiO₂

The scratch structure on the DVD disc and the Moiré-like TiO₂ are shown in Figure 1. A clear scratch structure existed on the DVD disc (Figure 1a), similar to a grating structure, which is identified as a Moiré-like pattern. The optical DVD served as the substrate template, from which a PDMS film with a Moiré-like structure was obtained through template printing, as depicted in Figure 1b. The consistent structure observed in the printed film confirms the experiment’s feasibility. Subsequently, the obtained Moiré-like PDMS film was utilized as the substrate template. Figure 1c displayed TiO₂ obtained by rubbing on a PDMS thin film with Moiré-like patterns, which expressed the same Moiré-like structure, indicating that the desired etching structure has been successfully imprinted on TiO₂. M-TiO₂ was calcined in a system at 500 °C and still exhibited a distinct Moiré-like structure (Figure 1d), proving that the heating and crystallization process of TiO₂ fits the Moiré-like structure, indicating that the Moiré-like structure possesses a certain degree of stability. By comparing Figure 1c,d, it can be found that after sintering at 500 °C, the grains of M-TiO₂ change from a disorderly to an ordered arrangement, with cracks on the surface before calcination and cracks disappearing after calcination. During the preparation process, M-TiO₂ may contain residual organic compounds or solvents. These organic residues decompose gradually during the calcination process. As a result, when M-TiO₂ is dried at room temperature, cracks may form. However, as the calcination temperature increases, the organic compounds decompose completely, leading to a more dense and compact film structure, and the cracks disappear accordingly [18]. Through these TEM images (Figure 1e), the lattice fringes of titanium dioxide (TiO₂) can be observed. These fringes correspond to specific interplanar spacings. The observed interplanar spacing of 0.359 nm confirms the presence of the anatase (101) crystal plane, which would accelerate the photocatalytic hydrogen generation progress [19].

By SEM analysis, the temperature has no effect on the Moiré-like structure, so only Moiré-like TiO₂ calcined at 500 °C was analyzed in the infrared. Figure S1 shows the Fourier Transform Infrared Spectroscopy (FTIR) of M-T500 [20], from which it can be seen that the characteristic peak appearing at 476 cm⁻¹ is caused by the Ti-O stretching vibration, which corresponds to the relative displacement between titanium and oxygen atoms in the crystal structure. Between 1300 cm⁻¹ and 1400 cm⁻¹, there are two absorption peaks whose positions and intensities are related to the intensity of the Ti-O-Ti stretching vibration. The characteristic peaks appearing at 3401 cm⁻¹ are broad spectral bands induced by the -OH stretching vibration, and the spectral bands appearing near 1634 cm⁻¹ are bending vibrational peaks induced by water of crystallization [21,22]. Furthermore, data about the transmittance and absorptivity were calculated to confirm the effective absorption of M-T500. As illustrated in

Table 1. The transmittance and absorptivity of two TiO₂ species by FTIR.

Material	Transmittance	Absorptivity
P-T500	61.5	38.5
M-T500	32.4	67.6

, the absorptivity of M-T500 was much larger than P-T500, which proved the excellent light absorption ability of the Moiré-like pattern.

XRD analysis of M-TiO₂ at different temperatures was carried out to investigate the effect of temperature on its crystallinity [23]. As shown in Figure S2, with the increase in the calcination temperature of the samples, the degree of crystallinity of the Moiré-like TiO₂ becomes higher and higher and changes from the disordered arrangement of the grains to the ordered arrangement [21,24]. At a temperature of 400 °C, the common anatase crystal type of TiO₂ began to form, and it can be seen from the figure that at the calcination temperatures of 400 °C and 450 °C, the crystal type of M-TiO₂ is anatase, and the rutile type has not yet formed. When the calcination temperature is 500 °C, the rutile crystal type of TiO₂ also begins to form, so the calcination temperature is 500 °C and above for sintering. The crystal type of M-TiO₂ is a mixture of anatase and rutile. The synergistic interactions among the components in mixed crystals can effectively regulate the adsorption of reactants and the desorption of products, thereby accelerating the reaction rate and enhancing catalytic efficiency [25]. From

Table 2. Specific surface area of two TiO₂ species.

Material	Specific Surface Area (m2/g)	Average Pore Diameter (nm)
P-T500	42.2	6.1
M-T500	60.4	8.6

, it can be seen that the specific surface area of M-TiO₂ is 1.4 times as much as that of P-TiO₂, indicating that M-TiO₂ possesses more reaction sites [26]. This is because of the special stripe structure of M-TiO₂, which results in more contact area due to the protrusions and depressions within the same horizontal area, thus enhancing the mass transfer and light reflection number.

2.2. Analysis of the Photovoltaic Properties of M-TiO₂

Figure 2a depicts the solid-state UV-visible absorption spectra of different catalysts, showcasing the characteristic absorption curves typical of indirect bandgap semiconductor TiO₂ [21]. As is evident from the spectra, all four types of M-TiO₂ exhibit higher light absorption thresholds and cover a broader range of absorption wavelengths. Utilizing the Kubelka-Munk formula, the bandgap energies of the five catalysts were calculated [27]. Among them, P-T500 has the largest bandgap, with values of 3.11 eV for P-T500 and 2.92 eV for M-T500, as shown in Figure 2b. These values indicate that M-T500 has a narrower bandgap, enabling it to respond to lower frequencies and a wider range of visible light wavelengths [28]. Consequently, compared to P-TiO₂, M-TiO₂ demonstrates superior light absorption capabilities and catalytic performance.

The photocurrent test was carried out to evaluate the recombination ability [28]. As shown in Figure 3a, when visible light irradiation is turned on, the photocurrent density of the two rises rapidly and reaches a relatively stable value quickly, and when the visible light irradiation is turned off, the photocurrent density decreases rapidly and reaches a lower value, and this phenomenon can be repeated continuously, indicating that P-TiO₂ and M-TiO₂ can continuously and stably provide photocatalytic active charge particles under visible light irradiation. The photocurrent density and photocurrent generation rate of M-TiO₂ are higher than those of P-TiO₂, with M-T500 exhibiting the highest photocurrent density. This is attributed to the increased specific surface area, which enhances the separation efficiency of photogenerated electrons and holes and, to a certain extent, suppresses their recombination. Additionally, a larger specific surface area provides more active sites and opportunities for reactions. The greater the specific surface area, the more active sites are available on the catalyst surface, increasing the contact opportunities between reactant molecules and photogenerated electrons [29], thereby enhancing the reaction rate and catalytic performance.

The movement of photogenerated electrons and holes needs to overcome the resistance generated by the samples themselves, so electrochemical impedance spectroscopy (EIS) was carried out to characterize several catalysts [30]. Figure 3b shows the Nyquist plots of M-TiO₂ and P-TiO₂. The diameters of the semicircles in the plots correspond to the charge transfer resistances, and the radius of the semicircle of the semicircle of M-TiO₂ is obviously smaller compared with that of P-TiO₂, which indicates that the charge movement is less resisted in the catalyst. The radius of the semicircle of M-T500 is significantly smaller compared with that of P-T500, indicating that the charge movement in this catalyst is less resisted; the faster the rate of photogenerated electron movement, the earlier the reaction time with the reactants, and the better the efficiency of the reaction in the same period of time, which is in agreement with the results of the photocurrent test. In addition to the participating reactive holes and electrons, there is a portion of electrons and holes that are not able to carry out the photocatalytic reaction, and they recombine to release energy, which is characterized by fluorescence photoluminescence [31]. As depicted in Figure 3c, the fluorescence intensity of M-TiO₂ is lower than that of P-TiO₂, suggesting a relatively weaker recombination capability of electrons and holes in M-TiO₂. Among them, M-T500 exhibits the smallest semicircle radius, which is attributed to the catalyst’s larger specific surface area. This increased surface area provides a greater space for the dispersion of electrons and holes, thereby reducing the likelihood of their encounter and recombination [32]. This dispersion results in a higher concentration of independent electrons and holes, prolonging the reaction time of photogenerated electrons and holes on the catalyst surface and, consequently, enhancing the catalytic effect.

As shown in Figure 3d, the Mott-Schottky curves were analyzed for several catalysts to calculate their flat-band potentials. Among them, M-T500 exhibited the smallest flat-band potential, indicating that the electrons excited to the conduction band upon light irradiation possess a stronger reducing power [33]. These electrons are more likely to react with H⁺ in water to generate H₂, thereby enhancing the photocatalytic hydrogen evolution activity.

2.3. Analysis of Catalytic Experiments

Through the X-ray photoelectron spectroscopy analysis of the samples, the bonding energies of the Ti2p orbitals were analyzed, and the bonding energies of Ti2p_3/2 of Moiré-like TiO₂ calcined at 450 °C, Moiré-like TiO₂ calcined at 500 °C, and Moiré-like TiO₂ calcined at 550 °C were 458.6 eV, 458.5 eV, and 458.6 eV. The binding energy is due to the Coulomb gravitational force between the electrons outside the atomic layer and the nucleus, and the change of the binding energy has a direct relationship with the electron density, and the decrease in the electron density will make the binding energy increase; on the contrary, the decrease in the binding energy is due to the gain of electrons [34,35]. The variation in the binding energy of elements on the catalyst surface indicates the transfer of photogenerated electrons [36,37]. As shown in Figure 4a, the binding energy of Ti2p in M-T500 is reduced compared to the other two samples, suggesting that electrons from other elements have been transferred to Ti2p in M-T500. The minimum binding energy of Ti2p at a calcination temperature of 500 °C typically implies that the structure and electronic distribution of the catalyst have reached an optimal state under this temperature condition [38,39]. Therefore, according to the decrease in binding energy of Ti2p, it can be seen that the density of photogenerated electrons of M-TiO₂ is the largest at the calcination temperature of 500 °C, and then it can be seen that the catalytic effect of the catalyst is the best at the calcination temperature of 500 °C.

After the SEM and XRD analysis of the samples, it can be seen that the crystallinity and crystal shape of M-TiO₂ at different temperatures are different, so RhB catalytic degradation experiments were carried out on P-TiO₂ at different temperatures and M-TiO₂ at different temperatures. An initial 30 min dark reaction was conducted, with results indicating negligible effects of the dark treatment. Therefore, Figure 5c,d only detects the degradation rate after 30 min. As depicted in Figure 4b,c, it is noticeable that M-TiO₂ exhibits superior RhB degradation compared to P-TiO₂ at the same temperature, and this trend remains consistent across other temperatures tested. This observation suggests that the unique Moiré-like pattern structure contributes significantly to enhancing the catalytic performance. Furthermore, as the calcination temperature of the catalysts increases, the performance of both catalysts exhibits an upward trend, peaking at a calcination temperature of 500 °C. However, it is noteworthy that the catalytic performance of the catalysts begins to decline when the calcination temperature surpasses 500 °C. This is because the significant increase in temperature leads to excessive crystallization, which increases the grain size, decreases the specific surface area of the catalyst, and reduces the number of active sites, thereby reducing catalytic performance [40]. When the calcination temperature is 500 °C or above, the crystal form of the catalyst is a mixed crystal form of rutile and anatase, while below 500 °C, the crystal form of the catalyst is a single anatase. The degradation diagram shows that the catalytic degradation performance of the mixed crystal form is better than that of a single crystal type [24].

During the experiment, it was found that the catalytic effect of TiO₂ sol varies with different aging times, and it could be observed that the catalyst samples prepared with different aging times not only had M-TiO₂ but also TiO₂ without this morphological structure, and after the catalytic degradation by RhB, as shown in Figure 4d, the M-TiO₂ prepared by TiO₂ sol with an aging time of 36 h was the most effective, and this was because the TiO₂ sol with a mixed crystal type was better than the single anatase type. The effect is the best. This is because the TiO₂ sol, after the end of the water bath, presents a gel-like appearance; after time, slowly aging, the viscosity of the sol gradually decreases until the aging time of 36 h, the viscosity of the sol is just right, and thus the prepared M-TiO₂ content is the largest, and the catalytic performance is the best.

Relying on the special morphology and excellent photovoltaic properties, the photocatalytic hydrogen production ability and furfural conversion ability of M-TiO₂ have been greatly improved. As illustrated in Figure 5a and Figure S4, the catalytic hydrogen production rate of M-T500 can reach nearly 324 μmol g⁻¹ h⁻¹, which is approximately 2 times that of P-T500. As depicted in Figure 5c, M-TiO₂ concurrently engages in the degradation of RhB and the process of water splitting for hydrogen production. These two reactions will mutually promote each other, resulting in a reaction rate better than that of a single catalytic system [41,42]. Upon illumination of the catalyst surface, photogenerated electrons and holes are produced. In the hybrid system, some electrons are channeled towards the reduction of water to produce hydrogen gas, while the holes react with H₂O to generate hydroxyl radicals ·OH, which oxidatively degrade RhB, thereby effectively reducing the recombination of electrons and holes. This separation mechanism effectively retards the rapid recombination of electrons and holes, thus enhancing the efficiency of both reaction processes [43]. After 4 cycles, compared with P-T500, the photocatalytic hydrogen production rate and degradation rate of M-T500 remained essentially unchanged (Figure 5b,d), indicating that M-T500 is capable of independently maintaining a stable photocatalytic cycle, demonstrating a certain degree of stability. The high light absorption ability of M-TiO₂ enables it to utilize more light energy, and the photogenerated charges can be quickly separated and transferred to the catalyst surface. Furthermore, a larger surface area can facilitate an increase in the number of active sites, thereby enhancing the reaction rate.

In the detection of free radicals, the fluorescence intensity of 7-hydroxycoumarin and the UV absorbance of NBT were measured under light irradiation over a period of 1 h. As shown in Figure S3a, the fluorescence intensity of the emission spectrum gradually increased over time, indicating the continuous generation of hydroxyl radicals by M-T500 under illumination. As depicted in Figure S3b, the UV absorbance progressively decreased with time, suggesting that the sustained production of superoxide radicals reacted with NBT. EPR tests were conducted on P-T500 and M-T500 before and M-T500 after, as shown in Figure 6. The g-values of oxygen vacancies for P-T500 and M-T500 were 2.0021 and 2.0010, respectively. Meanwhile, the strength of M-T500 is higher than that of P-T500, indicating that M-T500 has a higher number of oxygen vacancies and thus forms more defects. A greater number of defects can enhance the separation efficiency of photogenerated electrons and holes, thereby improving the photocatalytic performance. As shown in Figure S4, the comparison of curves before and after the reaction also confirms the stability of M-TiO₂, which is consistent with the conclusions drawn from the cyclic experiments.

2.4. Photocatalytic Mechanism of M-TiO₂

Superoxide radical (•O₂⁻) and hydroxyl radical (•OH) are the active species produced during the photocatalytic reaction, and in order to investigate the reaction mechanism of the process, the experiment was carried out by controlling the two radicals as variables. The photogenerated holes and electrons oxidize and reduce water, respectively, to obtain two types of radicals. Their production process can be obtained according to the following equation:

$$T+hv\to h^{+}+e^{-}$$

(1)

$$h^{+}+{OH}^{-}\to •OH$$

(2)

$$O_2+e^{-}\to •{O_2}^{-}$$

(3)

$$•{O_2}^{-}+e^{-}+2H^{+}\to H_2{O}_2$$

(4)

$$H_2{O}_2+e^{-}\to •OH+{OH}^{-}$$

(5)

As indicated by the aforementioned equations, both electrons and holes ultimately generate hydroxyl radicals through their respective reactions. Through experimental investigation, the impact of hydroxyl radical on the degradation of RhB by M-TiO₂ was explored. Through experimental investigations, the impact of hydroxyl radicals on the degradation of RhB by M-TiO₂ was examined. Various radical scavengers were selected for validation: tert-butanol (TBA) as an effective scavenger for hydroxyl radicals and ammonium oxalate (AO) as a scavenger for photogenerated holes. Hydrogen peroxide (H₂O₂) was utilized as a source for the generation of •OH through its decomposition. As depicted in Figure S5, in the presence of the photocatalyst M-TiO₂, hydrogen peroxide can decompose to form hydroxyl radicals, which in turn enhance the degradation rate of RhB. Conversely, in the absence of a catalyst, it is evident that the •OH generated by H₂O₂ decomposition will dissipate rapidly. This observation confirms that •OH indeed plays a significant role in enhancing the degradation efficacy of RhB. The addition of ammonium oxalate resulted in a stronger inhibitory effect on the degradation of RhB compared to the addition of tert-butanol, indicating that holes play a decisive role in the degradation process of RhB.

By combining solid-state UV and Mott-Schottky curve analyses, the specific positions of the valence band and conduction band for M-T500 were determined to be 2.51 eV and −0.41 eV, respectively. For M-T500 with a valence band position of 2.51 eV, the photogenerated holes possess strong oxidizing capabilities, which can oxidize water to generate hydroxyl radicals. Based on the analysis of the above characterization, a photocatalytic mechanism is proposed as shown in Figure 7. Under the irradiation of visible light, the electrons and holes generated by the excitation of M-TiO₂ are free at the two ends of the catalyst surface, and the electrons and holes are not easy to be compounded. In hydrogen production experiments, electrons migrate to the surface of the catalyst and undergo a reduction reaction with protons in water to generate hydrogen gas. In the experiment of degrading RhB, electrons and holes react with oxygen and water molecules to generate highly oxidizing free radicals (•OH and •O₂⁻), thereby degrading RhB. It can be seen by SEM that M-TiO₂ has a micron-structured stripe structure, and it can be seen from Table 1 that M-TiO₂ possesses a larger specific surface area, which in turn possesses more reactive active sites. Secondly, when the electrons and holes have a tendency to be compounded, due to the large surface area and the stripe structure on the surface, the compounding path is difficult, which effectively reduces the compounding rate of the photogenerated electrons and holes, and it is easier to stay on the surface to continue to participate in the catalytic degradation reaction, which improves the degradation efficiency.

3. Experimental Section

3.1. Materials

Tetrabutyl titanate (C₁₆H₃₆O₄Ti) was purchased from Shanghai Bohr Chemical Reagent Co. (Shanghai, China). Anhydrous ethanol (C₂H₅OH) was purchased from Tianjin Tianli Chemical Reagent Co. (Tianjin, China) Rhodamine B (RhB) was purchased from Shanghai McLean Biochemical Technology Co. (Shanghai, China). Cetyltrimethylammonium bromide (C₁₉H₄₂BrN) was purchased from Shanghai McLean Biochemical Technology Co.

3.2. Preparation of Moiré-like PDMS Film

The DVD is peeled off, followed by cleaning with anhydrous ethanol and drying. PDMS and curing agent are mixed in a mass fraction ratio of 10:1 to form a diluted mixture, and then the mixture is sprayed onto the treated DVD disk. The coated DVD disk is quickly placed into a vacuum drying oven at 60 °C and dried for 2 h, resulting in a PDMS film with a Moiré-like structure. In addition, the used DVD discs can be recycled for multiple uses, demonstrating the reproducibility of the Moiré-like structure and the preparation of a template with a Moiré-like structure.

3.3. Preparation of Moiré-like TiO₂ by Sol-Gel Method

The strategy of preparing Moiré-like TiO₂ follows the scheme in Figure 8. Preparation of TiO₂ thin films by reference sol-gel method [44]: 10 mL of tetrabutyl titanate was dispersed in a mixture of 5 mL of acetic acid and 40 mL of ethanol, followed by the addition of a certain amount of a mixture of 10 mL of anhydrous ethanol, 10 mL of deionized water, and 2 mL of hydrochloric acid to obtain TiO₂ sol. The Moiré-like PDMS film was submerged in TiO₂ sol and then quickly dried for several hours at a temperature of 40 °C. After drying, the sample was peeled off, resulting in Moiré-like TiO₂ named M-TiO₂. In the process of the preparation and use of the M-TiO₂, only anhydrous ethanol was used as a solvent, and the DVD disks could be recycled after cleaning. Throughout the process, the recycling of M-TiO₂ and DVD disks replaces the use of environmentally harmful solvents and strong alkaline solvents and prevents the release of hazardous substances during the sintering process. This demonstrates excellent environmental value and cost-effectiveness.

3.4. Characterizations

Scanning electron microscope (SEM, JSM-7500F) was used to obtain the microstructure of the Moiré-like pattern. X-ray diffraction (XRD, D8 Advance) was used to determine the crystalline form of Moiré-like TiO₂ formed at different calcination temperatures. A UV-visible spectrophotometer (UV-Cary100) was used to measure the absorbance and concentration standard curves to study the band gap energies and the degradation performance of Moiré-like TiO₂. Fourier Transform Infrared Spectrometer (FT-IR, Nicolet is50) was used to study the chemical composition of Moiré-like TiO₂. The sample preparation process is as follows: Weigh a small amount of sample and mix it with potassium bromide (KBr) powder. Grind the mixture thoroughly in a mortar until uniform, then place it in a pellet mold and press it into thin sheets. After drying in an oven, it can be tested. The surface elemental composition, chemical state, and electronic structure of Moiré-like TiO₂ at different temperatures were obtained by X-ray photoelectron spectroscopy (XPS). The photocurrent and impedance were obtained by an electrochemical workstation (EW, CHI-660E). The catalysts’ photoelectron and hole separation performance were studied by fluorescence spectrometer (PL, LS55) to get the fluorescence intensity of catalysts.

3.5. Catalysis Performances

As shown in Figure S6 (Supporting Information), the degradation rate of RhB within 1 h was tested with varying amounts of catalyst. The performance was found to be optimal at 50 mg of catalyst. Excessive amounts of catalyst can lead to aggregation among the catalyst particles, thereby reducing the effective surface area available for the reaction. This reduction in surface area decreases the number of active sites accessible for the photocatalytic degradation process, consequently diminishing the overall degradation efficiency. Therefore, 50 mg was selected as the catalyst mass for the degradation of RhB. In the experiment, a 300 W xenon lamp was employed as the light source in conjunction with an FGS900-A filter. To prepare an RhB solution with a concentration of 10 mg/L, measure out 50 mL of RhB solution and place it in a 250 mL beaker. Next, weigh 50 mg of the catalyst sample and add it to the RhB solution in the beaker. Stir the mixture for 15 min to ensure thorough dispersion of the catalyst within the solution. Prior to initiating the reaction, allow the system to undergo a 30 min dark reaction period. After commencing the reaction, periodically withdraw small aliquots of the supernatant every 10 min, centrifuge the samples, and subsequently analyze the liquid via UV spectroscopy.

In the experiment, a 300 W xenon lamp was used as the light source, combined with 310–400 nm and 400–700 nm filters. A 500 mg sample of the catalyst was placed into a 500 mL quartz reactor. A mixture of 270 mL of water and 30 mL of triethanolamine was then added to the reactor, which was subsequently sealed. The xenon lamp was switched on to initiate the reaction, and the hydrogen production was measured hourly using gas chromatography (GC) connected to the system.

In photocatalytic degradation reactions, hydroxyl radicals and superoxide radicals are important reactive species, and their detection is a standard for evaluating the oxidative capabilities of different photocatalysts. Coumarin can react with hydroxyl radicals to form 7-hydroxycoumarin, which exhibits fluorescence. In this study, 0.05 g of the catalyst was added to 50 mL of a 0.002 mol L⁻¹ coumarin solution, and the mixture was stirred in the dark for 10 min. Subsequently, the solution was irradiated for 1 h, with the supernatant being sampled every 20 min for fluorescence detection. The excitation wavelength was set at 380 nm, and the fluorescence intensity was measured. Consistent with this principle, superoxide radicals are capable of reacting with nitroblue tetrazolium (NBT), thereby reducing the absorbance intensity of NBT at 259 nm. The concentration of superoxide radicals can be inferred by quantitatively assessing the changes in UV absorbance at this wavelength.

4. Conclusions

In this study, Moiré-like titanium dioxide (M-TiO₂) was prepared using the sol-gel dip-coating method, and the structure and photoelectric properties of M-TiO₂ were systematically investigated. M-TiO₂ exhibits excellent photocatalytic performance, with a significant enhancement in photocatalytic activity compared to pure TiO₂. The RhB degradation efficiency of Moiré-like TiO₂ is improved by 20% compared with pure TiO₂. Notably, M-TiO₂ achieves a hydrogen production rate of 324 μmol g⁻¹h ⁻¹, which is 2 times higher than that of pure TiO₂. The grating structure is the key to the enhanced catalytic performance of M-TiO₂. Overall, this research establishes a simple and sustainable approach, demonstrating the outstanding potential of the Moiré-like structure in photocatalysis.