Journal of Nanomaterials
Volume 2018 (2018), Article ID 3091970, 10 pages
https://doi.org/10.1155/2018/3091970

Research Article

TiO₂-Intercalated Graphene Oxides with Highly Efficient Photocatalytic Degradation for Methylene Blue

Lirong Yao,¹ Li Dong,¹ Xiaojuan Li,² Sijun Xu,¹ Guangyu Zhang,¹ and Qilong Sun¹

¹National & Local Joint Engineering Research Center of Technical Fiber Composites for Safety and Protection, Nantong University, Nantong 226019, China
²Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan

Correspondence should be addressed to Sijun Xu; xusijunwork@hotmail.com

Received 30 May 2018; Revised 23 September 2018; Accepted 30 September 2018; Published 19 December 2018

Academic Editor: Nageh K. Allam

Copyright © 2018 Lirong Yao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The low photocatalytic decomposition activity of TiO₂ toward industrial pollutants at room temperature is one of the main obstacles for its practical application. TiO₂-intercalated graphene oxide (GO) composites were prepared by in situ hydrolysis of butyl titanate in a GO aqueous solution, followed by hydrothermal reaction to improve their photoelectron separation efficiency. The in situ generated TiO₂ nanocrystals could grow and adhere to the GO walls, thereby greatly improving the contact area and binding strength among them and resulting in low photoelectron transfer resistance. The photocatalytic activities of the as-prepared catalyst were evaluated via photodegradation of methylene blue (MB). The TiO₂-intercalated GOs displayed much higher catalytic activity than GO, TiO₂, and TiO₂-adsorbed GOs. The degradation efficiency of MB by TiO₂-intercalated GOs increased with increasing bath ratio of TiO₂-intercalated GOs to MB solution, but it decreased with increasing initial concentration of MB. Degradation of MB by UV light was much faster than by simulated sunlight. The degradation time by sunlight was only 5% of degradation time by UV light. Cyclic catalytic experiments indicated that TiO₂-intercalated GO maintained 99.97% degradation activity after repeated degradation (five times), thereby indicating the good decomposition durability.

1. Introduction

Solar energy has been used for 2.4 billion years. Plants, including algae, can generate carbohydrate using water, carbon dioxide, and sunlight. Photosynthesis has become a complex and efficient biochemical reaction that translates solar energy into organic matter. However, solar energy can also be transformed by many semiconductors, such as silicon, CdS, CdTe, GaAs, titanium oxide, zinc oxide, and perovskite. Among them, titanium oxide (TiO₂) is one of the most promising materials due to its advantages of low-cost, nontoxic, high physicochemical stability and transparency [1–5]. TiO₂ nanomaterials are widely used in organic wastewater treatment because of their excellent photocatalytic activity [6–17]. However, the high rate of electron-hole recombination is one of the main drawbacks of TiO₂ in photodegradation applications [18, 19].

To improve the photocatalytic efficiency, several methods, such as modification of TiO₂ nanoparticles with conductive organic materials, metal nanoparticles, and carbon materials, were developed to prevent electron-hole pair recombination [4, 20–24]. The integration of TiO₂ and graphene (GR) is intensively investigated, and advancement in this technology is obvious in recent studies because of the super photoelectric properties of GR. For example, TiO₂-GR nanocomposites have been prepared via a facile hydrothermal reaction of graphene oxide (GO) and TiO₂ in an ethanol-water solvent. Such TiO₂-GR nanocomposites exhibited much higher photocatalytic activity and stability toward benzene gas, which is a volatile aromatic pollutant in air, than bare TiO₂ [25]. Wen et al. prepared TiO₂-Ag-GR nanocomposites that showed significantly increased visible light absorption and photocatalytic activity compared with Ag-TiO₂ and TiO₂-GR nanocomposites [26]. Fan et al. compared TiO₂-reduced GO nanocomposites prepared by UV, hydrazine, and hydrothermal reductions. TiO₂-reduced GO composites prepared by the hydrothermal method exhibited optimal photocatalytic performance [27]. Nanakkal and Alexander developed graphene/BiVO₄/TiO₂ ternary nanocomposites through a facile, ultrasonic wave-assisted one-pot hydrothermal method. The as-prepared composite exhibited enhanced photocatalytic degradation of methylene blue (MB) under visible light irradiation [28].

However, the photocatalytic efficiency of TiO₂-GR/TiO₂-GR is still limited because of the high contact resistance and low binding strength between prefabricated TiO₂ nanocrystals due to their large morphology mismatch and lack of chemical interactions that lead to low contact area [29]. To solve this problem, we synthesized closely integrated TiO₂-intercalated GO (TiO₂-GO-TiO₂ sandwich-like) composite nanosheets. TiO₂ could grow in situ on GOs and form the sandwich-like TiO₂-intercalated GO nanosheets by following hydrothermal reaction, when the hydrolysis and condensation of tetrabutyl titanate (TBOT) in GO solution is carefully controlled. The contact resistance and contact strength of TiO₂ nanocrystals can be greatly improved, because they grow by adhering to the GO surfaces [29]. The resultant TiO₂-intercalated GOs possessed a sandwich-like structure with an ultrathin nature and highly crystallized TiO₂ nanocrystals. Most importantly, the TiO₂-GO-TiO₂ nanosheets provide high photodecomposition efficiency and durability for the model dye, MB, compared with TiO₂ and TiO₂-adsorbed GOs [30–37].

2. Experimental

2.1. Materials and Reagents

The natural flake graphite (mesh = 1000) was purchased from Qingdao Jintao Graphite Co. Ltd. (China), and the TiO₂ was purchased from Jinan Jiyu Titanium Chemical Co. Ltd. (China). The concentrated sulfuric acid, potassium permanganate, hydrogen peroxide, hydrochloric acid, butyl titanate, and MB were purchased from Sinopharm Chemical Reagent Co. Ltd. (China) and were of analytical grade.

2.2. Synthesis of GOs, TiO₂-Intercalated GOs, and TiO₂-Adsorbed GOs

GOs were prepared from purified natural graphite by the modified Hummers method [38]. A total of 20 g of graphite and 460 mL of H₂SO₄ were mixed in a beaker container at 0°C under vigorous stirring. Then, 60 g of KMnO₄ was added to the suspension sample, maintaining a temperature of below 5°C. After addition of KMnO₄, the rising temperature should be maintained below 30°C for 30 min. The mixture was diluted with 1000 mL of DI water and heated to 95°C, maintaining this temperature for 15 min. Finally, 3000 mL of DI water and 100 mL of H₂O₂ were added to the mixture to terminate the reaction. The resultant mixture was washed with 10% of HCl aqueous solution, ultrasonicated for 30 min, and stored overnight. The suspension mixture was finally filtered, washed by DI water several times, and dried in a dry oven at 60°C.

The schematic of the preparation of TiO₂-intercalated GOs is presented in Figure 1. A 0.1 g of GOs was dissolved in 30 mL of DI water, sealed by a hydrothermal reactor (50 mL), and hydrothermally reacted at 135°C for 6 h. Then, the GO aqueous solution was ultrasonicated for 30 min, filtered, dried at 60°C, and then dissolved in tetrahydrofuran with ultrasound treatment for three to four hours. Subsequently, 10–50 mL of butyl titanate was added into the GO solution and ultrasonicated for 30 min. The mixture was added into a hydrothermal reactor and crystallized at 180°C for 12 h. Finally, the resultant TiO₂-intercalated GO powder was filtered, washed, and finally dried at 60°C.

Figure 1: Scheme of the preparation of TiO₂-intercalated GOs.

To synthesize TiO₂-adsorbed GOs (control), 40 mL of butyl titanate was added to 100 mL of absolute ethanol solution, after which 5 g of GOs was added. TiO₂-adsorbed GO solution was prepared by stirring for 5 h and then crystallized in a hydrothermal reactor at 180°C for 12 h. The obtained solution was centrifuged and dried at 60°C.

2.3. Characterizations

To identify the crystalline phase of synthesized samples, all samples were subjected to X-ray diffractometer (XRD; Shimata XD-D1, Japan) experiments at a scan speed of 2°/m⁻¹. The morphology of TiO₂ nanoparticles and GO sheets was observed by an S-3400N scanning electron microscope (SEM; Hitachi, Japan) and JEOL 2100F transmission electron microscope (TEM; JEOL, Japan) that operate at 200 kV accelerating voltage. The diffuse reflectance spectra were recorded on a TU-1901 ultraviolet-visible (UV-vis) spectrophotometer (PG Scientific, USA). Fourier transform infrared (FTIR) spectra were obtained on a Thermo Nicolet AVATAR 370 FTIR spectrometer (Bruker, Germany). The X-ray photoelectron spectra (XPS) were studied by the ESCALAB 250 XI X-ray photoelectron spectroscopy (Thermo Scientific, USA).

2.4. Photocatalytic Degradation of MB

The samples were added into 50 mL of the MB solutions and stored in the dark for 24 hours to reach the adsorption equilibrium. The obtained mixtures were placed onto a XPA-4 photochemical reactor (Xujiang Electromechanical Plant, China) with a 300 W UV light type mercury lamp and/or a 350 W solar-simulated xenon lamp. All light sources were located at 15 cm above the reaction solution. In the catalytic decomposition, 1 mL mixture was sampled and centrifuged at regular intervals. The supernatants were obtained and measured using a UV-vis spectrophotometer at a maximum absorption wavelength () of 664 nm to detect the MB concentration. To study the photocatalytic degradation of TiO₂-intercalated GOs toward MB in aqueous solution, we examined the initial MB concentration (ranging from 100–300 mg/L), the bath ratio between TiO₂-intercalated GOs and MB solution (1 : 50, 1 : 100, and 1 : 200), and the light source (without light, UV light, and simulated sunlight). The catalytic performances of the controls, TiO₂, GOs, and TiO₂-adsorbed GOs (prepared by adsorption of TiO₂ to GOs), were studied by following the experimental method.

The concentration (mg/L) and the degradation rate (%) were calculated according to the standard curve of MB. The calculation formula is as follows (1):

where is the initial concentration of MB, and is the concentration of MB at time .

3. Results and Discussion

The integration of TiO₂ and GOs may influence the adsorption band of TiO₂ because of the special electrochemical properties of GOs. The UV-vis absorption spectra in Figure 2 showed that the light absorption edge of TiO₂-intercalated GOs extended to about 426 nm while that of TiO₂ was only about 394 nm. The redshifts into the visible regions demonstrated the significant influence of GOs on the optical characteristics in which the adding of GOs narrowed the bandgap of TiO₂ owing to the formation of Ti–O–C chemical bonding in their interface [39, 40].

Figure 2: UV-vis spectra of TiO₂ and TiO₂-intercalated GOs.

The FTIR spectra of graphite, GOs, and TiO₂-intercalated GOs are shown in Figure 3. The FTIR spectra of the natural flake graphite show a very smooth curve, indicating its poor infrared activity. A broad absorption band, which is a characteristic of the hydroxyl groups in GOs, can be observed at approximately 3430 cm⁻¹. In particular, 3500–3800 cm⁻¹ exhibited a wide range of absorption peaks, which can be attributed to the absorbed water by GOs [41]. In addition, due to the hydroxyl groups in GOs, the FTIR spectra exhibited an absorption band in the vicinity of 1634 cm⁻¹, corresponding to the absorption peak for the bending vibration of O-H [42]. Furthermore, the band at the vicinity of 1720 cm⁻¹ is attributed to the absorption of carboxylic acid and/or the carbonyl stretching vibration of C=O, which is attributed by –COOH and C=O in the surface and/or edge and of the GOs. The band observed at 1380 cm⁻¹ is the stretching vibration of the epoxy groups (C-O-C) and carboxyl C-O in GOs [43]. The band in the vicinity of 1045 cm⁻¹ is generated by the C-OH stretching vibration of GOs. All these absorption bands derived from the oxygen-containing groups in GO nanosheets. This indicates that graphite was fully oxidized and it generated abundant hydrophilic oxygen-containing groups. Hydrogen bonds were readily formed with water molecules because the GO surfaces contain these polar functional groups, thereby explaining the hydrophilic nature of GOs after the oxidation. For TiO₂-intercalated GOs, the absorption band near 3430 and 1634 cm⁻¹, representing the OH stretching and blending vibrations of GOs, respectively, weakened, whereas the C-O adsorption at approximately 1045 cm⁻¹ broadened. The OH groups in GOs were likely to form Ti-O-C during the hydrothermal reaction [29], suggesting the possible chemical interactions between TiO₂ and GOs.

Figure 3: FTIR images of graphite, GOs, and TiO₂-intercalated GOs.

The photocatalytic capability of TiO₂-intercalated GOs was derived from TiO₂ nanocrystals, which were mainly influenced by their crystal form, degree, and morphology. Figure 4 shows the XRD patterns of the natural flake graphite, GOs, and TiO₂-intercalated GOs. The characteristic diffraction peak was located at 2 = 30° for the natural flake graphite. The XRD pattern of GO showed diffraction peaks at 2 = 10°, with lattice spacing of 0.887 nm. However, for TiO₂-intercalated GOs, several new peaks were detected at approximately 2 = 24.8°, 2 = 37.7°, 2 = 48.0°, 2 = 53.8°, 2 = 54.8°, 2 = 62.5°, 2 = 68.2°, 2 = 70.0°, and 2 = 74.8°, corresponding to the diffractions from the (101), (004), (200), (105), (211), (204), (116), (220), and (215) crystal planes of anatase TiO₂ (JCPDS card 21-1272), respectively [44]. In addition, the XRD signals of TiO₂ nanocrystals were extremely strong that the GO signals were completely concealed, thereby suggesting the high content of well-crystallized TiO₂ nanoparticles.

Figure 4: XRD patterns of graphite, GOs, and TiO₂-intercalated GOs.

To examine the chemical composition and binding states of the samples, XPS spectra were collected, as displayed in Figure 5. All binding energies in the XPS experiments are trued by referring to the C1 (284.6 eV) peak. Figure 5(a) presents the wide-scan XPS spectra of GOs and TiO₂-intercalated GOs. TiO₂-intercalated GOs showed three strong peaks at 530.1, 454.8, and 284.1 eV, corresponding to O1s, Ti2p, and C1s [5, 45], respectively. However, only O1 and C1 signals were detected for GOs, indicating that Ti was successfully combined to GO surfaces. Figure 5(b) shows the C1 XPS spectra of TiO₂-intercalated GOs. The C1 XPS spectrum of TiO₂-intercalated GOs could be deconvoluted into three peaks, which were ascribed to sp² bonded carbon (C-C, 284.6 eV), epoxy/hydroxyls (C-O, 286.5 eV), and carboxyl (O=C-O, 288 eV) in line with GOs before the reaction [46, 47]. Therefore, GOs maintained their chemical construction after the hydrothermal reaction [48].

(a)

(b)

Figure 5: (a) XPS spectra and (b) C1s XPS spectra of GOs and TiO₂-intercalated GOs.

The distribution state of TiO₂ on/in the GO-GO surfaces and interlayers is significant for the catalytic activity of TiO₂ nanocrystals. The severe agglomeration of TiO₂ not only leads to low specific surface area but also to low contact efficiency of GO surfaces, thereby greatly influencing the electron-hole separation efficiency. The surface morphology and microscopic structure of the GOs and as-prepared TiO₂-intercalated GOs are initially observed by SEM (Figure 6). GOs were loosely stacked to form microsized layers (Figure 5(a)). Such loose structure was mainly caused by strong electrostatic repulsion among GOs due to the negatively charged oxygen-containing functional groups such as -OH and -COOH in GOs. After the reaction, as shown in Figure 5(b), the as-prepared TiO₂-intercalated GOs had abundant wrinkles and slight curling, indicating good flexibility. Most importantly, TiO₂ nanocrystals were almost uniformly monodispersed on the GO surfaces because these TiO₂ nanocrystals grow on OH, COOH-containing defect sites in the GO nanosheets, restricting their self-agglomeration. Such well-dispersed TiO₂ nanocrystals improved the photocatalytic efficiency of TiO₂-intercalated GO nanosheets by facilitating the generation and separation of electron-hole pairs.

(a)

(b)

Figure 6: SEM images of (a) GOs and (b) TiO₂-intercalated GOs.

The TiO₂ nanocrystals were not only attached to the GO surfaces but also to their interlamination. As shown in Figure 7(b), dense TiO₂ nanocrystals were found on and/or in the GOs, thereby suggesting that TiO₂ has good affinity to GOs [49]. To analyze the detailed hierarchical structure, the GO edge was observed in detail by HRTEM. As shown in Figure 6(a), two GO nanosheets were clearly observed. The nanosheets consisted of 8–10 one-atom thick GOs (arrows 1 and 2 in Figure 7(a)). Such multilayered GO nanosheets preserved certain conductivity and rigidity after oxidation. Notably, TiO₂ nanocrystals were found not only on the outer surface of GOs but also in the interlamination. As shown in box 1, these TiO₂ nanocrystals have relatively clear lattice fringes, indicating that they are on the upper surface of GOs. Interlaminar TiO₂ could be distinguished through careful confirmation of the relative space position between TiO₂ and GO nanosheets. As shown in the circle, TiO₂ nanocrystals were clamped by two GO nanosheets, evidencing the sandwich structure. Similarly, as shown in box 2, the TiO₂ nanocrystals covered by bottomed GOs proved that they are on the lower GO surfaces.

Figure 7: TEM images of TiO₂-intercalated GOs.

3.1. Photocatalytic Degradation of MB

The photocatalytic activities of TiO₂-intercalated GOs, TiO₂-adsorbed GOs, GOs, and TiO₂ for MB were evaluated. As shown in Figure 8(a), GOs and TiO₂ showed relatively weak photocatalytic activity toward MB. For TiO₂-adsorbed GOs, only ~60% of MB was decomposed after 1 h UV radiation. On the contrary, the TiO₂-intercalated GOs exhibited much higher photocatalytic degradation efficiency than other catalysts (TiO₂-intercalated GOs > TiO₂-adsorbed GOs > GOs > TiO₂). They could degrade nearly 99.9% of MB within 18 min under the UV light which was much faster than reported literature [25, 33, 50–53]. Because of in situ growth of TiO₂ nanocrystals by adhering to GO surfaces and/or GO-GO interfaces, the contact resistance between TiO₂ and GOs was significantly reduced. As a result, the photoelectron generated by TiO₂ could be efficiently led away by GOs, thereby greatly improving the separation of electron-hole pairs on TiO₂ surfaces. In addition, GO nanosheets could help TiO₂ to adsorb MB organic molecules due to their huge surface area and abundant anionic OH and COOH groups.

(a)

(b)

(c)

(d)

Figure 8: (a) Photocatalytic degradation of MB over TiO₂, GOs, TiO₂-adsorbed GOs, and TiO₂-intercalated GOs (experimental conditions: initial MB concentration of 100 mg/L, bath ratio of 1 : 50, and light source (UV light)). (b) Effect of MB concentration on the TiO₂-intercalated GO degradation of MB (experimental conditions: bath ratio (1 : 50) and light condition (UV light)). (c) Effect of bath ratio on the photodegradation rate of MB (experimental conditions: initial MB concentration (100 mg/L) and light condition (UV light)). (d) Effect of light conditions on the TiO₂-intercalated GO degradation of MB (experimental conditions: initial MB concentration (100 mg/L) and bath ratio (1 : 50)).

To study the effect of MB initial concentration on the photocatalytic degradation efficiency, the photocatalytic degradation experiments were conducted with MB concentrations that range from 100 mg/L to 300 mg/L, while maintaining other parameters constant. As shown in Figure 8(b), TiO₂-intercalated GOs nearly completely degraded MB when MB concentration even reached up to 300 mg/L, indicating their high catalytic capacity. The complete degradation time for 100–300 mg/L of MB was 18, 30, and 60 min, suggesting the high catalytic efficiency of TiO₂-intercalated GOs. The calculated photodegradation efficiency of TiO₂-intercalated GOs showed significant decrease with increase in MB concentration because of the incident of UV light depth which became shallower with increasing MB concentration, thereby greatly reducing the photodegradation efficiency in the low solution.

To study the effect of the bath ratio between the TiO₂-intercalated GO catalyst and MB solution on the photocatalytic degradation performance, 0.5–2 g TiO₂-intercalated GOs was added into 100 g of 100 mg/L MB solution, while maintaining the other parameters constant. As presented in Figure 8(c), although the photodegradation ratio of MB changed with increasing bath ratio, the corresponding photodegradation rate of TiO₂-intercalated GOs toward MB increased. The nearly complete photodegradation time for MB stretched from 18 min to 23 min and then to 32 min. Thus, the increase in the mass of TiO₂-intercalated GOs could improve the photodegradation efficiency toward MB.

We varied the light conditions (simulated sunlight and UV light) to test their influence on the photocatalytic degradation of MB. As shown in Figure 8(d), 99.99% of MB was degraded by TiO₂-intercalated GOs for only 18 min under UV light, whereas only 99.89% degradation efficiency was obtained under 360 min sunlight irradiation. The degradation time under UV light is only 5% of that under simulated sunlight. The low degradation efficiency is caused by the UV light, which only accounts for a small fraction (3%–5%) of the sunlight, whereas the TiO₂-intercalated GOs only showed photocatalytic degradation activity in the UV band. However, the TiO₂-intercalated GOs could degrade 99.89% of MB under 360 min (<6 h) simulated sunlight irradiation, still indicating their good applicability.

Figure 9 showed MB with and without UV radiation in the presence of TiO₂-intercalated GOs. The color of MB with UV radiation soon became shallow and finally colorless, whereas that without UV radiation showed no obvious change after 20 min magnetic stirring in the dark. This indicates that physical adsorption by GOs was negligible during short UV irradiation probably because a number of OH and COOH groups reacted with TiO₂ to form Ti-O-C groups. The high treatment efficiency for MB should mainly attribute to the high photodegradation of TiO₂-intercalated GOs.

(a)

(b)

Figure 9: MB (a) with and (b) without UV radiation in the presence of TiO₂-intercalated GOs (experimental conditions: initial MB concentration of 100 mg/L, bath ratio of 1 : 50, and light source (UV light)).

To further demonstrate the decomposition durability, the circulating runs of the TiO₂-intercalated GO catalyst in the photocatalytic degradation of MB were carried out. After the complete photodegradation of MB every time, TiO₂-intercalated GO catalyst was collected, washed, dried at 60°C, and used for the next photodegradation cycle. As shown in Figure 10, the TiO₂-intercalated GO catalyst did not exhibit evident significant loss of photocatalytic activity after four runs of MB degradation. The photodegradation rate of MB reached up to 99.98%, 99.98%, 99.99%, and 99.97% after two to four times of circulation. The relative degradation time was 24, 32, 41, and 70 min. Nevertheless, after five times of circulation photodegradation, the TiO₂-intercalated GOs obtained only 55.47% photodegradation rate even after 330 min UV light irradiation. The results indicated that the optimal cycle time of TiO₂-intercalated GOs was four times. To examine the possible damage for the chemical structure of TiO₂-intercalated GOs during prolonged exposure to UV light, FTIR spectra of TiO₂-intercalated GOs before and after six-cycle UV irradiation were measured (Figure 11). The adsorption intensity of OH groups for TiO₂-intercalated GOs slightly weakened after six time cycles while the chemical construction remained unchanged, indicating the high chemical stability. The decrease in hydroxyl, small molecular contamination, and interlayer blocking may be responsible for the weakened photocatalytic performance after five time cycles.

Figure 10: Decomposition durability of TiO₂-intercalated GOs (experimental conditions: initial MB concentration of 100 mg/L, bath ratio of 1 : 50, and light source (UV light)).

Figure 11: FTIR spectra of TiO₂-intercalated GOs with (a) zero and (b) six runs of MB degradation.

4. Conclusion

In summary, we demonstrate a synthesis strategy of sandwich-like TiO₂-intercalated GO nanosheets to improve the contact area between TiO₂ and GOs. Our FIIR, XPS, and XRD measurements showed that the as-prepared TiO₂-intercalated GOs maintained the inherent chemical construction of GOs and generated high content and high crystallized TiO₂ nanoparticles after the hydrothermal reaction. The SEM and TEM results indicated that TiO₂ nanocrystals were uniformly dispersed on and in GO nanosheets, forming an independent sandwich-like structure. Notably, GOs consisted of 8–10 layered one-atom thick GOs. Such structure was beneficial to maintain certain electric conductivity of GOs. In addition, the photocatalytic activities of the as-prepared catalyst were further studied using methylene blue as a degradation sample. The results indicated that the catalytic activity of the TiO₂-intercalated GOs was much stronger than pure TiO₂ and TiO₂-adsorbed GOs. Moreover, decreasing the initial concentration of MB and increasing the bath ratio of TiO₂-intercalated GOs could increase the degradation efficiency of MB. The contrast tests further indicated that the degradation of MB by UV light was much faster than that by simulated sunlight. The final cyclic photodegradation test showed that the TiO₂-intercalated GOs maintained 99.97% degradation activity after four times of repeated degradation, indicating good decomposition durability.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that they have no competing interests.

Acknowledgments

The authors acknowledge the financial support of the National Natural Science Foundation of China (Young Foundation) (no. 51703098 and no. 51503105) and Jiangsu Qing Lan Project.

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