Next Article in Journal
Evaluation of the Impact of Hydrogen Peroxide on ANFO-Based Materials’ Morphology
Next Article in Special Issue
Green Technique for Producing Carbon-Based Catalysts for Cellulose Hydrolysis
Previous Article in Journal
Photocatalytic Degradation of Rhodamine B Using 1D CuO/TiO2 Nanofibers Synthesized via the Electrospinning Method
Previous Article in Special Issue
Agrifood Waste Valorization: Development of Biochar from Peach Kernel or Grape Pits for Cr6+ Removal from Plating Wastewater
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 18
Issue 18
10.3390/ma18184253
materials-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

Photoelectrocatalytic Degradation of Rhodamine B in the Presence of TiO2-BiVO4

by
Anli Sun
1,†,
Chao Kong
1,†,
Jie Wang
1,
Beihai Zhou
1,
Huilun Chen
1,
Rongfang Yuan
1,* and
Zhiming Bai
2
1
Beijing Key Laboratory of Resource-Oriented Treatment of Industrial Pollutants, School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China
2
School of Resources and Safety Engineering, University of Science and Technology Beijing, Beijing 100083, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Materials 2025, 18(18), 4253; https://doi.org/10.3390/ma18184253
Submission received: 11 August 2025 / Revised: 7 September 2025 / Accepted: 9 September 2025 / Published: 11 September 2025
(This article belongs to the Special Issue Carbonaceous Materials: Fabrication, Characterization and Applications—Second Edition)
Browse Figures
Versions Notes

Abstract

The discharge of printing and dyeing wastewater has become a key concern in global water pollution control due to its high pollutant concentration, dark color, refractory biodegradability and toxic characteristics. Photoelectrocatalytic (PEC) technology has gained widespread attention as it can effectively treat refractory organic pollutants. In this study, titanium dioxide (TiO2)–bismuth vanadate (BiVO4) composite materials were synthesized through the sol–gel/solvothermal hybrid method, and layered heterojunction structures were fabricated via sol–gel precursor preparation followed by spin-coating deposition. The PEC degradation efficiency of rhodamine B (RhB) was systematically evaluated under varying operational conditions in the presence of TiO2-BiVO4. The four-layer BiVO4/four-layer TiO2 material showed the optimal catalytic activity among the tested structures, achieving an 80.3% removal of RhB under an applied bias of 4 V and illumination intensity of 14,000 lx. Through the equilibrium adjustment of the Fermi levels, the type Ⅱ heterostructure was formed. Moreover, superoxide radical (O2−) was identified as the predominant reactive oxygen species driving the degradation mechanism. Mechanistic analysis revealed that RhB degradation was accomplished through deethylation, benzene ring cleavage, and subsequent ring-opening mineralization. This study prepared an efficient PEC material, which provides a theoretical basis for the PEC treatment of printing and dyeing wastewater.

Graphical Abstract

1. Introduction

The printing and dyeing industry, a cornerstone of global textile manufacturing, has expanded significantly alongside economic growth and rising living standards. This expansion has correspondingly amplified wastewater discharge containing persistent synthetic dyes. These dyes and auxiliaries demonstrate remarkable persistence, with high salinity impairing biological treatment efficiency and extreme pH values damaging aquatic life and treatment infrastructure [1,2]. Additionally, the diversity of printing and dyeing processes and fiber types creates substantial wastewater quality variability [3]. Rhodamine B (RhB) is a fluorescent xanthene dye with high water/ethanol solubility and exceptional chemical stability [4]. Characterized by its oxygen-bridged aromatic structure, RhB resists degradation while exhibiting toxic effects through bioaccumulation in aquatic ecosystems. Its light absorption characteristics exacerbate water discoloration, which impairs photosynthesis by reducing sunlight penetration. Moreover, its ability to chelate metal ions can induce chronic toxicity in aquatic organisms [5]. Traditional methods like biodegradation and adsorption can partially treat these effluents, but remain challenged by low efficiency, high costs, and secondary pollution risks.
Photoelectrocatalysis (PEC) is an emerging technology that integrates photocatalysis (PC) and electrochemistry (EC). By utilizing semiconductors as electrodes and incorporating light fields into the EC process, PEC achieves synergistic photoelectric catalysis, thereby enhancing photocarrier productivity and facilitating redox reactions [6]. In recent years, PEC technology, as a sustainable and eco-friendly technology, has been widely applied in H2 production, CO2 reduction, and NH3 synthesis [7,8,9]. Additionally, PEC is effective in treating wastewaters with low biodegradability, high complexity, and high concentration of pollutants [10,11].
The selection of photoelectrode materials constitutes a critical determinant in photoelectrocatalytic (PEC) system design. Titanium dioxide (TiO2) and bismuth vanadate (BiVO4) have emerged as two prominent semiconductor candidates with distinct operational characteristics. TiO2 has been extensively employed in pollutant degradation due to its exceptional physicochemical stability and favorable charge transfer properties [12]. Nevertheless, its practical implementation faces two principal constraints. Firstly, rapid recombination of photogenerated electron–hole (e−/h+) pairs substantially diminishes catalytic efficiency [13]. Secondly, its wide bandgap (~3.2 eV) restricts optical absorption to ultraviolet wavelengths (<400 nm), thereby failing to harness the visible light spectrum (400–760 nm), which represents approximately 45% of incident solar energy [14]. In comparison, monoclinic scheelite-phase BiVO4 demonstrates enhanced solar energy conversion capabilities through its narrower 2.4 eV bandgap [15,16]. However, this bismuth-based semiconductor encounters analogous charge carrier limitations, particularly inefficient separation of conduction band e− and valence band h+, compounded by persistent carrier recombination phenomena that collectively degrade its practical catalytic performance [17].
To address these challenges, modification strategies have been developed to synergistically enhance charge separation dynamics and light utilization. Among them, the construction of heterojunction interfaces has emerged as a particularly effective solution. By establishing an interfacial electric field to directionally drive photogenerated e−/h+ separation and broadening the light absorption range, photocatalytic performance is thereby significantly improved [18]. For instance, Adhikari et al. deposited Fe2O3 onto Bi2WO6 to construct heterojunction photoelectrodes for PEC sensing and degradation of tetracycline (TC) [19]. In general, the design and preparation of composite semiconductor materials can be achieved by selecting components, optimizing interface properties, and adjusting size, among other factors. Currently, photoelectrodes formed from these composite materials are widely employed in the PEC field.
The performance of PEC is significantly influenced by various parameters. In addition to the type of photoelectrode and PEC reactor design, operating conditions, such as the external potential, current density applied to the photoelectrode, and light source intensity, are decisive factors influencing PEC performance [20,21]. In addition, water quality parameters, including solution pH, coexisting ions, and electrolyte concentration, also play a crucial role in PEC performance [22,23,24]. By studying the influence of various factors, the PEC system can be optimized to address the ongoing environmental pollution.
In this study, two distinct TiO2-BiVO4 heterojunction materials were developed. The preparation process of TiO2-BiVO4 materials was optimized based on RhB removal efficiency, with subsequent parameter adjustments under varying operational conditions (e.g., applied bias voltage, light intensity, and electrolyte composition) to maximize catalytic activity. The chemical composition, optical properties, pore structure, and morphology of the synthesized materials were systematically characterized. The recyclability and long-term stability of the materials were rigorously assessed to determine their practical applicability. Additionally, the catalytic mechanism of TiO2-BiVO4 and the degradation pathway of RhB in the PEC system were elucidated through energy band alignment and identification of reactive oxygen species. This work provides basic support for the development of efficient PEC materials for environmental applications.

2. Materials and Methods

2.1. Materials

Glacial acetic acid (CH3COOH), sodium sulfate (Na2SO4) and sodium nitrate (NaNO3) (all AR grade) from MaxScientific Inc. (Beijing, China). Hydrochloric acid (HCl) (AR) from Tianjin Guangfu Technology Development Co., Ltd. (Tianjin, China). Ethanol absolute (C2H5OH) and acetone (C3H6O) (both AR) from Beijing Chemical Works (Beijing, China). Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and ammonium vanadate (NH4VO3) (both AR) from Beijing HongHu LianHe HuaGong ChanPin Co., Ltd. (Beijing, China). Isopropanol (IPA, C3H8O), p-benzoquinone (BQ, C6H4O2) (both AR) and EDTA-2Na (C10H14N2Na2O8, 98%) from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China). RhB (C28H31ClN2O3), tetrabutyl orthotitanate (TBT, C16H36O4Ti), titanium tetraisopropanolate (C12H28O4Ti), nitric acid (HNO3) and sodium hydroxide (NaOH) (all AR) from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

2.2. Preparation of TiO2-BiVO4 Composite and Layered Materials

The TiO2-BiVO4 composite (TiO2-BiVO4-M) and layered (TiO2-BiVO4-L) materials were synthesized through a combination of sol–gel-hydrothermal and spin-coating methods. To prepare BiVO4 precursors, 4.85 g Bi(NO3)3·5H2O was dissolved in 5 mL HNO3 (16 mol·L−1), diluted to 20 mL with deionized water, and stirred for 1 h. Concurrently, 1.17 g NH4VO3 was dissolved in 20 mL NaOH (4 mol·L−1) under 30 min stirring. The two solutions were combined dropwise, and the pH of the mixture was adjusted to 9.0 ± 0.1 using NaOH (2 mol·L−1). Following 1 h of stirring, the mixture underwent hydrothermal treatment at 200 °C for 6 h in a Teflon-lined autoclave. The resultant precipitate was centrifuged, washed with deionized water and ethanol, and dried at 80 °C for 12 h to yield BiVO4 powder.
For the TiO2-BiVO4-M fabrication, 4 mL C12H28O4Ti was blended with 12 mL IPA through 1 h of stirring, followed by the addition of 1 mL glacial acetic acid with subsequent 1 h of mixing. Meanwhile, 0.15 g BiVO4 powder was dispersed in 3.2 mL IPA with 0.3 mL deionized water via ultrasonication for 30 min. The BiVO4 dispersion was incorporated into the TiO2 precursor and stirred for 1 h, and progressively diluted with deionized water until a viscous sol formed. The sol was hydrothermally treated at 200 °C for 2 h. The obtained hydrogel was stirred for 2 h before spin-coating onto a 3 × 3 cm FTO conductive glass using a homogenizer and calcined at 550 °C for 2 h to obtain the TiO2-BiVO4-M.
In synthesizing TiO2-BiVO4 layered material (TiO2-BiVO4-L), BiVO4 precursor preparation excluded hydrothermal crystallization. The TiO2 sol was formulated by introducing 10 mL C16H36O4Ti into a mixture of 16 mL ethanol and 4 mL glacial acetic acid under continuous agitation. An 80% (v/v) ethanol solution was incrementally added, with the mixture aged for 24 h to stabilize. The TiO2 sol was spin-coated onto cleaned FTO glass, dried at 180 °C, and calcined at 550 °C for 2 h. The BiVO4 sol layer was then spin-coated onto the TiO2 film, finalized through 550 °C calcination for 2 h.
In the spin-coating process, 0.25 mL of precursor solution was dropped onto FTO glass and allowed to stand for several minutes to ensure sufficient adsorption. The substrate was then rotated in two stages: first at 500 r/s for 10–15 s to spread the solution uniformly, followed by 3000 r/s for 30 s to expel most of the water. This process yielded a reproducible thin film, with the final thickness determined primarily by the number of spin-coating cycles.

2.3. Characterization of TiO2-BiVO4

The morphological characteristics of the prepared materials were observed by the FEI XL 30 ESEM FEG scanning electron microscopy (Hillsboro Field Electron and Ion Company, Hillsboro, OR, USA). The crystalline structure of the prepared materials was characterized by Bruker D8 Advance X-ray diffraction (Berlin Bruker Corporation, Berlin, Germany) with Cu Kα (λ 0.15406 nm) radiation in the range of 10–80° and a scan rate of 0.02°·min−1. The element component, chemical state, and valence band binding energy were analyzed by the Thermo Scientific ESCA-LAB 250 X-ray photoelectron spectroscopy (Massachusetts Thermo Fisher Scientific Inc., Waltham, MA, USA). The optical absorption property of the catalyst was recorded by the Shimadzu UV-1800 UV-vis diffuse reflectance spectroscopy (Kyoto Shimadzu Corporation, Kyoto, Japan). Photocurrent–time curve (I-t) and electrochemical impedance spectroscopy (EIS) of the as-prepared materials were measured by a three-electrode electrochemical workstation system (Chenhua CHI-660E, Shanghai, China) equipped with a saturated calomel electrode as reference electrode, a Pt flake as counter electrode and as-prepared catalysts as working electrode.

2.4. Photoelectrocatalytic Degradation Experiment

The PEC properties of the as-prepared materials were evaluated through the degradation of RhB. In the PEC degradation study of RhB, 500 mL of a 10 mg·L−1 RhB solution was placed in a self-designed quartz reactor. The electric field was applied using an electrochemical workstation, with the voltage set to 2, 4, and 6 V, respectively. Simulated solar light was supplied by a 300 W xenon lamp (Beijing Perfectlight Technology Co., Ltd., Beijing, China, wavelength range 320–780 nm) equipped with a filter to block infrared radiation. The lamp was positioned at distances of 5, 10, or 15 cm from the reactor to adjust the light intensity. The as-prepared material, platinum (Pt) flake, and saturated calomel electrode were used as the working electrode, counter electrode, and reference electrode, respectively. Multiple degradation experiments were performed under various concentrations of RhB (5, 10, and 15 mg·L−1), pH values (about 4, 6, 7, and 9), and electrolyte solutions (Na2SO4 or NaNO3 at concentrations of 0.1, 0.25, 0.5, and 1 M) to determine the optimal conditions for PEC degradation of RhB in the presence of TiO2-BiVO4 and to assess its performance. The RhB solution was stirred for 60 min to ensure adsorption–desorption equilibrium, and samples were taken every 60 min to determine the RhB concentration using a UV-vis absorption spectrometer (Kyoto Shimadzu Corporation, Kyoto, Japan) at 554 nm. In the catalyst recycling experiment, the catalysts were washed several times with a mixture of anhydrous ethanol and ultrapure water UPW after each test, and then dried at 60 °C for 3 h for the next cycle. To minimize errors, all trials were repeated three times.

3. Results and Discussion

3.1. Optimization of Preparation Process of TiO2-BiVO4

3.1.1. TiO2-BiVO4 Composite Material

In the absence of light, TiO2-BiVO4 composite materials with different BiVO4 loading levels (0, 0.10, 0.15, 0.20, and 0.25 g) could reach adsorption equilibrium within 60 min, with the RhB removal efficiency of less than 3.2% (Figure S1). The photocatalytic results (Figure 1a) showed that after the adsorption equilibrium and simulated sunlight irradiation for 360 min, the degradation efficiencies of pure TiO2 and BiVO4 on RhB were 26.6% and 42.9%, respectively. While the degradation efficiency of TiO2-BiVO4 on RhB was obviously increased, and the degradation efficiency on RhB firstly increased and then decreased when the loading amount of BiVO4 in the composites increased from 0 g to 0.25 g, and the photocatalytic activities were as follows: TiO2-BiVO4 (0.15 g) > TiO2-BiVO4 (0.10 g) > TiO2-BiVO4 (0.20 g) > TiO2-BiVO4 (0.25 g), and the degradation efficiencies were 72.1%, 51.6%, 46.2% and 32.9%, respectively. The positive correlation between the degradation rate and the number of active centers of the semiconductor catalyst up to the optimal loading level. An increase in the loading level increases the PEC active centers. However, when the loading level exceeds the optimal value, the catalyst tends to agglomerate, leading to a decline in visible light photocatalytic efficiency [25,26]. Therefore, the optimum loading amount of BiVO4 in TiO2-BiVO4 composites was determined to be 0.15 g.
Calcination temperature is another important factor affecting the properties of TiO2-BiVO4 composite material. The calcination process not only affects the crystal structure and phase purity of the material, but also influences the specific surface area and pore structure of the material [27]. Appropriate calcination temperatures can promote the tight binding between TiO2 and BiVO4, enhance the structural stability of the materials, and optimize the transport and separation of photogenerated charges. The degradation curves of RhB (10 mg·L−1, pH 7, and applied bias voltage of 2 V) under different calcination temperature conditions are shown in Figure 1b. As the calcination temperature increased, the PEC performances were in the order of TiO2-BiVO4 (550 °C) > TiO2-BiVO4 (500 °C) > TiO2-BiVO4 (450 °C) > TiO2-BiVO4 (600 °C), with degradation efficiencies of 76.9%, 63.3%, 60.5%, and 44.3%, respectively. Specifically, incomplete crystalline development at low calcination temperature (450 °C) leads to carrier migration limitation, and the increase in calcination temperature (500–550 °C) promotes the crystallization of the anatase phase and enhances charge separation efficiency [28,29]. At higher calcination temperature (600 °C), the crystal structure changes from anatase to rutile, triggering an intensification of carrier complexation, while grain coarsening leads to a decrease in active sites [30].

3.1.2. TiO2-BiVO4 Layered Material

The layer number of BiVO4 significantly impacts the PEC performance of TiO2-BiVO4 layered structures. By controlling the spin-coating cycles of precursor solutions, the film thickness was precisely regulated, with 3 layers established as the baseline and incrementally increased to 4 and 5 layers for comparative analysis. Experimental results obtained in a pH 7 electrolyte demonstrated that increasing BiVO4 layers from 3 to 4 enhanced the RhB degradation efficiency from 51.3% to 60.3% after 360 min, achieving optimal performance (Figure 1c). This improvement originates from extended light absorption pathways and enhanced photon harvesting capability through appropriate layer stacking [31]. However, further increasing to 5 layers resulted in reduced degradation efficiency (55.1%), attributed to compromised light penetration depth and prolonged carrier migration paths. Excessive BiVO4 thickness restricts photon access to internal active layers, while lengthened charge transport distances promote recombination losses [32]. Although increased layer numbers theoretically provide additional catalytic sites, over-stacking may induce active site shielding effects that diminish effective reaction interfaces. The synergistic effect of the light absorption enhancement and carrier transport efficiency identifies 4-layer BiVO4 as the optimal structural parameter.
The thickness of TiO2 layers plays a pivotal role in governing the PEC performance of TiO2-BiVO4 heterostructures, analogous to the influence of BiVO4 layer optimization. Precise matching of spin-coating cycles between TiO2 and BiVO4 enables spatial modulation of heterojunction interfaces, achieving synergistic effects of broadband light absorption and efficient carrier separation [33]. Experimental results reveal that the 360 min RhB degradation efficiency reached 51.3% when both components were 3-layer structured, consistent with the baseline data from single-variable BiVO4 layer studies. Synchronously increasing both layers to 4 significantly enhanced degradation efficiency to 77.5%, primarily attributed to amplified interface effects (Figure 1d). The optimized layer configuration increased heterojunction interface density, thereby improving spatial charge separation [34]. Nevertheless, expanding the layer count to 5 led to a notable decline in degradation efficiency to 72.7%, which can be attributed to several intertwined factors. Specifically, the extended carrier migration paths hindered the efficient charge transport. Additionally, the heightened interfacial defect density facilitated the recombination of photogenerated e−/h+, thereby reducing the effective charge separation. Furthermore, significant optical shielding effects emerged as the upper TiO2 layers impeded photon penetration into the underlying active regions, limiting the light absorption capacity. This multifactorial interplay resulted in the observed reduction in efficiency [35]. Photon transport losses induced by the light-blocking effect of TiO2 dominate performance degradation beyond critical layer thresholds. Consequently, the dual 4-layer configuration emerges as the optimal architecture, balancing sufficient photon harvesting, effective interfacial charge separation, and minimized transport losses through systematic design optimization.

3.2. Characterization of the Catalysts

3.2.1. Morphological Analysis

The surface morphologies and microstructures of TiO2-BiVO4-M and TiO2-BiVO4-L were investigated via SEM images. It can be seen that TiO2-BiVO4-M (Figure 2a,b) exhibited a granular composition of numerous small particles tightly clustered together. This structure exhibited relatively high porosity, which resulted from the formation of rough, uneven, and irregular surfaces due to the heterogeneous size and distribution of the particles. The voids between these particles were formed by irregular or inconsistent stacking. In contrast, TiO2-BiVO4-L (Figure 2c,d) consisted of numerous sheets forming lamellar structures. These sheets were stacked on top of each other, each maintaining a relatively flat and well-defined boundary, resulting in a smooth and homogeneous appearance.
The adsorption isotherms of both TiO2-BiVO4-M and TiO2 presented the type-I isotherms (Figure 3a). These isotherms showed a rapid increase in the range of P/P0 < 0.1, indicating the presence of microporous structures in TiO2-BiVO4-M. In addition, a type-IV isotherm is typical for mesoporous material, often associated with a hysteresis loop and presents a non-uniform pore structure or irregular pore shape [36]. In the range of 0.2 < P/P0 < 1.0, TiO2-BiVO4-M displayed significant adsorption behavior with a hysteresis loop, consistent with the characteristics of a type IV isotherm. This indicated that TiO2-BiVO4-M possessed both microporous and mesoporous structures. As shown in Figure 3b, the pore structure of TiO2 was relatively stable and narrow, with a pore volume of 0.4467 cm3·g−1. In contrast, TiO2-BiVO4-M exhibited a wider distribution of pore sizes and a slightly smaller pore volume of 0.2011 cm3·g−1. Additionally, the pore structure was more diverse. These features enhanced the light absorption properties of the materials and contributed to improved catalytic activity. It is noteworthy that although TiO2-BiVO4-M possesses a significantly higher specific surface area (159.6 m2·g−1) than TiO2-BiVO4-L (89.0 m2·g−1), it demonstrates inferior PEC activity for RhB degradation. The high surface area of TiO2-BiVO4-M originates from its irregular, porous particulate morphology, which may conversely lead to severe light scattering and tortuous charge transport paths, exacerbating charge recombination [37]. In contrast, the well-ordered layered structure of TiO2-BiVO4-L, while yielding a lower surface area, establishes a more effective heterojunction interface. This architecture significantly enhances the separation and migration of photogenerated charges (Figure 3g,h). Consequently, the overall performance of TiO2-BiVO4-L surpasses that of the composite material.

3.2.2. Crystal Structure Analysis

The phase structures of the four samples were characterized by XRD (Figure 3c). TiO2 presented an anatase-type structure with characteristic diffraction peaks located at 25.3° (101), 37.8° (004), 48.0° (200), 54.4° (105), 55.6° (211), and 62.7° (204) [38]. Similarly, BiVO4 presented a monoclinic scheelite-type structure and showed clear diffraction peaks at angles of 18.9° (101), 28.8° (112), 30.6° (004), 34.5° (200), and 47.1° (204) [39]. Comparing the TiO2-BiVO4-M and TiO2-BiVO4-L to pure TiO2 and BiVO4, obvious diffraction peaks corresponding to the anatase and monoclinic scheelite phases were observed in their XRD diffractograms. This indicated that the heterogeneous structure of TiO2-BiVO4-M and TiO2-BiVO4-L did not affect the crystalline structure of TiO2 and BiVO4. It was worth noting that the characteristic peaks around 25.3° for TiO2-BiVO4-L exhibited obvious weakening and broadening. To quantify any crystallographic changes, the average crystallite size was estimated using the Scherrer equation:
D = Kλ/wcosθ
where D represents the crystallite size; K represents the Scherrer constant (0.89); λ denotes the incident X-ray wavelength, determined by the test conditions; for a copper target, λ = 0.15406; θ represents the diffraction angle (°); w denotes the half-width of the diffraction peak; 2θ and w are measured by XRD.
The calculated crystallite sizes were 23.3 nm (TiO2), 25.7 nm (BiVO4), 23.2 nm (TiO2-BiVO4-M), and 24.1 nm (TiO2-BiVO4-L), respectively. This indicates that the peak broadening is not primarily due to a reduction in crystallite size.
Instead, the broadening is most likely attributed to the introduction of microstrain within the crystal lattice. The formation of a heterojunction between two distinct materials (TiO2 and BiVO4) with different crystal structures can induce significant local lattice distortions and defects at the interfaces. This microstrain, a well-known contributor to XRD peak broadening [40], is particularly pronounced in the layered structure (TiO2-BiVO4-L) due to its extensive and well-defined interfacial contact area. This effect, rather than spatial positioning, is the dominant cause of the observed peak profile changes.

3.2.3. Optical Properties

The UV-vis DRS of several materials is illustrated in Figure 3d. Typically, anatase TiO2 has a band gap of approximately 3.2 eV, resulting in strong absorption predominantly in the UV region, with light absorbed below approximately 380 nm [41]. In contrast, BiVO4 has a relatively narrow bandgap (2.4 eV), allowing it to absorb a larger portion of the visible spectrum, with an absorption edge around 517 nm. TiO2-BiVO4-M exhibited photoresponsivity in both the UV and visible regions, due to the heterojunction structure of the two n-type semiconductors, which facilitates the migration of e− from the conductive band (CB) of one semiconductor to the other, while h+ migrate in the opposite direction [42]. As a result, the absorption edge of TiO2-BiVO4-M shifted to lower energies (longer wavelengths) compared to TiO2 or BiVO4 alone, but the absorption intensity in the visible region was significantly reduced. The TiO2-BiVO4-L consisted of alternating layers of TiO2 and BiVO4, leading to a synergistic effect on the light absorption properties of the two materials. This material demonstrates enhanced absorption in both the UV and visible regions, with the visible light absorption extending beyond the range of BiVO4 alone, resulting in a broader spectral absorption range.
The energy band structure critically determines semiconductor performance, as evidenced by the XPS valence band spectra in Figure 3e. TiO2 exhibited a relatively high valence band potential (EVB, XPS) of 3.03 eV, while BiVO4 exhibited a lower EVB, XPS value of 2.83 eV. The corresponding standard hydrogen electrode (EVB, NHE) can be calculated according to the following formula:
EVB, NHE = φ + EVB, XPS − 4.44
where φ represents the work function of the instrument (4.45 eV) [43]. Thus, the EVB, NHE of TiO2 and BiVO4 is calculated to be 3.04 and 2.84 eV, respectively. According to the formula of the band gap energy (Eg) of the semiconductor:
(αhν)n = k(hν − Eg)
as shown in Figure 3f, the Eg value of TiO2 and BiVO4 is estimated to be 3.46 and 2.26 eV, respectively [44]. The conduction band potential (ECB) of different samples can be calculated according to the empirical formula:
EVB = ECB + Eg
Thus, the ECB of TiO2 and BiVO4 could be confirmed to be −0.42 and 0.58 eV, respectively.
It is worth noting that the measured band gaps (3.46 eV for TiO2 and 2.26 eV for BiVO4) show slight deviations from the commonly reported values (~3.2 eV and ~2.4 eV), which may be attributed to differences in calculation methods and material structural; however, these shifts are within the range observed in prior reports and do not affect the type-II band alignment or the proposed charge transfer mechanism [45,46].

3.2.4. Photoelectrochemical Properties

For assessing the injection and separating efficiency of carriers, the transient photocurrent density and electrochemical impedance spectroscopy (EIS) of these samples were measured. The EIS of the photoelectrode is depicted in Figure 3g. The inset showed the equivalent circuit for fitting Nyquist plots, where Rs represents the solution resistance between the reference electrode and the working electrode; CPE is a constant phase angle component that represents the bilayer capacitance; and Rt denotes the charge transfer resistance of the electrode. Generally speaking, the smaller the diameter of the semicircle in the Nyquist plot, the faster the interfacial charge transfer ability [47]. Although the impedance values of the TiO2 (21.4 Ω) and BiVO4 (18.6 Ω) were much lower than those of the TiO2-BiVO4-M (62 Ω) and TiO2-BiVO4-L (241 Ω), the maximum impedance value of these photoelectrodes was approximately 200 Ω, which was relatively low compared to other photoelectrodes.
The photocurrent–time (I-t) curves for TiO2, BiVO4, TiO2-BiVO4-M and TiO2-BiVO4-L samples with typical on-off cycles of intermittent light irradiation are shown in Figure 3h. Comparing the four materials, the photocurrent of TiO2-BiVO4-L reached 4.1 μA·cm−2, which was higher than that of TiO2-BiVO4-M (3.1 μA·cm−2), BiVO4 (1.9 μA·cm−2), and TiO2 (1.85 μA·cm−2). The rapid enhancement of the photogenerated current in TiO2-BiVO4-L may be attributed to the heterogeneous structure formed by TiO2 and BiVO4, which reduced the band gap and extended the response to the visible region.

3.3. Photoelectrocatalytic Degradation of RhB

3.3.1. Optimization of Photoelectrocatalytic Conditions

The degradation efficiency and reaction kinetic in the presence of as-prepared samples under different systems were investigated by degrading RhB under irradiation for 360 min. As shown in Figure 4a,b, the PEC system exhibited the highest degradation efficiency (74.9% for TiO2-BiVO4-M and 80.3% for TiO2-BiVO4-L), which were 15.1% and 15.7% higher compared to the PC system. In contrast, the EC system also catalyzed RhB degradation, but with the lowest efficiency (18.1% for TiO2-BiVO4-M and 23.8% for TiO2-BiVO4-L). The limited performance of EC alone highlights the critical role of photoexcitation in generating charge carriers, as purely electrochemical processes lack sufficient redox potential or active species to efficiently degrade complex organic molecules [48]. Meanwhile, the applied bias voltage acting as a driving force to effectively separate photogenerated e−/h+, thereby prolonging their lifetime and increasing the availability of reactive species for RhB oxidation [49]. The degradation kinetics of RhB under different catalytic systems followed the Langmuir-Hinshelwood first-order kinetic equation (Figure S2). The degradation rate of RhB in the PEC system were 0.00356 mg·L−1·min−1 (TiO2-BiVO4-M) and 0.00413 mg·L−1·min−1 (TiO2-BiVO4-L), respectively, which were 1.48 and 1.5 times faster than that of the PC system and 6.9 and 6.1 times faster than that of the EC system. These results further demonstrate the higher performance of the PEC system, highlighting the synergistic effect of PC and EC in enhancing the degradation kinetics of RhB compared to standalone photocatalytic or electrochemical methods.
To investigate the effect of applied bias pressure on the PEC degradation performance of RhB (10 mg·L−1, pH 5.8) with the presence of TiO2-BiVO4 materials, three bias voltages of 2 V, 4 V and 6 V were applied (Figure 4c,d). As the applied bias voltage increased from 2 V to 4 V, the degradation efficiency of RhB increased from 51.9% (TiO2-BiVO4-M) and 62.9% (TiO2-BiVO4-L) to 74.9% and 77.6%. However, when the applied bias voltage increased to 6 V, the degradation efficiency decreased to 59.2% and 69.4%, respectively, which was attributed to the limited thickness of the photoelectrode material, where the space charge layer could not exceed the thickness of the semiconductor oxide film. At a fixed light intensity, the number of photogenerated e− reaches an upper limit, so when the applied bias voltage reaches a critical value, the photogenerated carriers have been sufficiently separated, and further voltage increase will not further enhance the catalytic performance [50]. In addition, excessive voltages can lead to certain disadvantages in the charge transfer process, such as electrochemical decomposition of the electrolyte and possible photocorrosion of the composite surfaces [51], as evidenced by reduced stability in recycling tests (Figure 5), which may negatively affect the efficiency of the PEC.
The effect of light intensity in PEC degradation of RhB with the presence of TiO2-BiVO4 materials is presented in Figure 4e,f. For granular TiO2-BiVO4-M (Figure 1b and Figure 2a), though surface morphology-induced light scattering can increase effective photon absorption, weak light intensity was not sufficient to fully stimulate the photocatalytic reaction on the material surface, yielding only 41.2% RhB degradation at 1800 lx. Enhanced light intensity (4000 lx) improved efficiency to 53.3%, indicating activated surface reaction sites through increased photon flux that promoted photogenerated carrier generation and separation [52]. Maximum efficiency (74.3%) was achieved at 14,000 lx with stable kinetics. In comparison, TiO2-BiVO4-L exhibited similar PEC behavior: with increasing light intensity, the degradation efficiency was in the order of 36.4%, 55.4%, and 79.9% (Figure 4f). Under low light intensity, photocarrier recombination dominates interfacial transfer [53]. When the irradiation intensity increased, the layered structure showed higher performance in terms of its ability to capture and convert light energy, with each layer of TiO2-BiVO4-L potentially participating more fully in the PEC reaction, maximizing the light absorption and catalytic potential of the material.
Although TOC removal was not measured in this study, previous reports on TiO2-based and BiVO2-based photoelectrocatalysts have shown that high dye decolorization efficiencies generally correspond to TOC removals in the range of 50–70% under similar conditions [40,54,55], suggesting that the present material can also achieve comparable mineralization performance.

3.3.2. Reutilization Performance of TiO2-BiVO4

The cycling stability of photoanode materials serves as a critical indicator for practical applications, directly determining the long-term operational efficacy of PEC systems. The stability of TiO2-BiVO4 materials was evaluated by investigating their degradation performance over multiple catalytic cycles (Figure 5). After four catalytic cycles, the degradation rate of RhB in the presence of TiO2-BiVO4-M within 360 min decreased from 76.6% to 55.8% (Figure 5a). This decline is likely due to partial detachment and erosion of catalyst particles from the electrode surface under the applied bias potential and vigorous stirring during PEC operation. In addition, the accumulation of refractory intermediates may have contributed to active site fouling.
In contrast, the degradation rate of RhB in the presence of TiO2-BiVO4-L decreased slightly from 78.6% to 70.8% (Figure 5b). Although the degradation efficiency of the materials decreased slightly after each repeated use, the overall decrease in performance was relatively small, sustaining over 70% degradation efficiency after 24 h of continuous operation. This stability can be attributed to its layered architecture, which provides stronger adhesion to the FTO substrate and a more integrated structure that mitigates material loss.
Overall, while TiO2-BiVO4-M demonstrated higher initial activity, its structural robustness remains a challenge for long-term use. In comparison, TiO2-BiVO4-L offers a favorable balance of activity and durability, making it more promising for practical PEC applications.

3.3.3. Effects of Water Quality Factors

Water quality factors, such as initial pollutant concentration, pH value, and electrolyte type and concentration, may significantly affect the reaction kinetics during the PEC process.
Both TiO2-BiVO4-M and TiO2-BiVO4-L reached adsorption equilibrium within 60 min (Figure S3) when the initial concentrations of RhB were 5, 10, and 15 mg·L−1. Optimal adsorption occurred at 10 mg·L−1 of RhB solution, where TiO2-BiVO4-M and TiO2-BiVO4-L exhibited adsorption efficiencies of 7.9% and 6.3%, respectively. After 360 min of irradiation, the degradation efficiencies of different initial concentrations of RhB with the presence of TiO2-BiVO4-M (Figure 6a) were 65.5%, 73.1%, and 43.0%, while those in the presence of TiO2-BiVO4-L (Figure 6b) were 62.7%, 76.2%, and 55.9%, respectively. At lower initial pollutant concentrations, increasing the concentration could enhance the adsorption of pollutant molecules, thereby better utilizing the activation of the photocatalyst [56]. However, when the initial concentration increased to 15 mg·L−1, excessive adsorption of RhB and its intermediates on the catalyst surface led to competition for active sites, reducing the degradation efficiency of PEC [57]. The porous but irregular structure of TiO2-BiVO4-M suffers from active site occlusion at high pollutant loads. While the higher specific surface area of TiO2-BiVO4-L is counterbalanced by its ordered pore structure (Figure 2c,d), which mitigates pore blockage by RhB intermediates.
The pH-dependent PEC degradation of RhB is systematically illustrated in Figure 6c,d. Dark adsorption experiments revealed that both TiO2-BiVO4-M and TiO2-BiVO4-L achieved adsorption equilibrium within 60 min, exhibiting maximum adsorption efficiencies at pH 5.8 (6.55% and 6.97%, respectively) and minimum values at pH 9.2 (3.02% and 3.62%) (Figure S4). In the PEC degradation study of RhB, the degradation rates of RhB under different pH values with the presence of TiO2-BiVO4-M within 360 min followed the order of pH 5.8 (78.4%) > pH 3.6 (43.2%) > pH 7.1 (28.3%) > pH 9.2 (25.2%), while TiO2-BiVO4-L exhibited enhanced efficiencies following the same pH sequence of: pH 5.8 (78.9%) > pH 3.6 (56.2%) > pH 7.1 (34.3%) > pH 9.2 (29.3%). This behavior correlates with the acid-base characteristics of RhB (pKa~3.5–5.0) and the surface charge properties of TiO2-BiVO4. As an amphoteric dye, RhB shows pH-dependent speciation and surface charge characteristics. In acidic conditions, its protonated cationic form dominates due to carboxyl group protonation. In neutral and alkaline environments, deprotonated anionic species are more common [58]. The surface charge of TiO2-BiVO4 materials is also pH-responsive. TiO2 has an isoelectric point around 6.67 [59] and BiVO4 has a lower one [60]. Near pH 5.8, the reduced positive surface charge of the catalyst minimizes electrostatic repulsion with cationic RhB species, enhancing adsorption. This is supported by the maximum dark adsorption efficiencies (Figure S4). Under strongly acidic conditions (pH 3.6), although excessive surface protonation causes electrostatic repulsion with RhB cations, reducing adsorption, the high H+ concentration promotes h+-mediated oxidation and helps generate hydroxyl radical (·OH) through water oxidation [61]. This maintains relatively high degradation efficiency. In neutral and alkaline environments, the intensified electrostatic repulsion between negatively charged catalyst surfaces and anionic RhB molecules greatly limits adsorption. Meanwhile, the elevated pH also suppresses ·OH production via water oxidation pathways [62]. These combined effects account for the sharp decline in degradation efficiency at pH 7.1 and 9.2.
In addition, we explored the effects of two different types of electrolytes (Na2SO4 and NaNO3) and their concentrations (0.1, 0.25, 0.5, and 1 M) on the PEC degradation of RhB with the presence of TiO2-BiVO4 material. The removal rates of RhB in the presence of TiO2-BiVO4-M exhibited an initial increasing trend and a decreasing trend with increasing Na2SO4 concentration. The degradation efficiencies of all concentrations were arranged as follows: 0.5 M Na2SO4 (74.6%) > 0.25 M Na2SO4 (71.6%) > 0.1 M Na2SO4 (64.5%) > 1 M Na2SO4 (54.9%) (Figure 6e), which was similar with the results of the NaNO3 electrolyte system: 0.5 M NaNO3 (56.3%) > 0.25 M NaNO3 (53.9%) > 0.1 M NaNO3 (50.1%) > 1 M NaNO3 (43.3%) (Figure 6f). For TiO2-BiVO4-L, as shown in Figure 6g,h, the PEC degradation results showed a similar trend, but with overall higher efficiency than TiO2-BiVO4-M. The degradation efficiency was the highest at electrolyte concentration of 0.5 M (77.5% for Na2SO4 system and 58.8% for NaNO3 system) and the lowest at 1 M (52.5% for Na2SO4 system and 46.6% for NaNO3 system). This may be due to the weaker charge shielding effect at lower electrolyte concentrations, which promotes the separation and migration of photogenerated carriers, thus enhancing the PEC degradation process. However, at higher electrolyte concentrations, the strong charge shielding effect may inhibit effective carrier separation, reducing degradation efficiency [63]. Overall, the layered structure may exhibit better PEC degradation performance at different electrolyte concentrations due to the provision of more reactive interfaces and improved charge transport pathways.
Additionally, the steady-state photocurrent–concentration curves of the two electrolyte solutions were investigated (Figure S5). Under identical conditions, the photocurrent intensity of TiO2-BiVO4 material in Na2SO4 electrolyte was significantly higher than in NaNO3 electrolyte. In addition, as electrolyte concentration increased, the photocurrent for Na2SO4 rose significantly, while the increase for NaNO3 was minimal. Although higher electrolyte concentrations promoted photocurrent generation, the excessive shielding effect may negatively affect overall PEC performance.
In summary, while steady-state photocurrent intensity is directly proportional to electrolyte concentration, optimal PEC degradation performance depends not only on photocurrent generation but also on its effect on the PEC process. Although high electrolyte concentrations produce higher photocurrents, PEC performance is better at lower concentrations due to the shielding effect. Moreover, different electrolyte types can significantly affect PEC performance, with Na2SO4 outperforming NaNO3 in both photocurrent intensity at the same concentration and PEC degradation under identical conditions. Therefore, considering factors such as degradation efficiency and cost, 0.5 M Na2SO4 was the optimal electrolyte.

3.4. Catalytic Mechanisms of TiO2-BiVO4

3.4.1. Active Species During Photoelectrocatalyzing

To understand the mechanism of BiVO4-TiO2 degradation of RhB, it is important to discover which reactive species play a major role in the photocatalytic removal process. During the PEC degradation of RhB with the presence of BiVO4-TiO2, the h+, ·OH, and ·O2− are eliminated by adding EDTA-2Na, IPA, and BQ as the scavengers, respectively [64,65]. The degradation efficiencies of RhB within 360 min decreased from 74.9% in the absence of scavengers to 71.6%, 64.9%, and 41.6% in the presence of EDTA-2Na, IPA, and BQ, respectively. In the TiO2-BiVO4-L system, the RhB degradation rates decreased from 80.3% to 75.6%, 70.5% and 50.3% when the mentioned quenchers were added, respectively (Figure 7). The degradation rates of RhB in TiO2-BiVO4-M and TiO2-BiVO4-L systems did not decrease significantly with the presence of EDTA-2Na and IPA, suggesting that h+ and·OH played a minor role in the situation. BQ obviously hindered the RhB degradation, implying that ·O2− was the main active species responsible for the PEC degradation of RhB in the presence of TiO2-BiVO4. Further analysis of the generation and intensity of the active species was carried out by electron paramagnetic resonance (EPR) spectra (Figure 7c).
EPR experiments using DMPO as spin-trapping agent for ·OH and ·O2− [66]. When TiO2-BiVO4 is illuminated by a 300 W xenon lamp, the characteristic peaks of ·OH and ·O2− could be easily detected, which confirmed the presence of ·OH and·O2−.

3.4.2. Photoelectrocatalytic Mechanism of TiO2-BiVO4

The highest occupied molecular orbital (HOMO) energy level of RhB is approximately 1.6 V relative to NHE [67], which corresponds to the highest energy state of RhB electrons during electrochemical or photochemical processes. Conversely, the lowest unoccupied molecular orbital (LUMO) energy level of RhB is around −0.6 V (NHE) [68]. This indicates the ability to accept electrons from a molecule, particularly in PEC reactions where electron acceptance is essential for reduction processes.
In terms of the energy levels of the semiconductors, the Fermi energy level (EF) of TiO2 is about 0.1 to 0.2 eV above its ECB [69]. As an intrinsic semiconductor, the EF of BiVO4 is located in the middle of its conduction and valence bands [70]. So, the EF in pure TiO2 and BiVO4 was −0.22 and 1.71 eV, respectively. Upon forming the TiO2-BiVO4 heterostructure, the EF of both materials adjusts to reach equilibrium. The higher EF of BiVO4 shifts downward, while the lower EF of TiO2 shifts upward. This adjustment facilitates the migration of e− from BiVO4 to TiO2, while h+ is accumulated in BiVO4. This anisotropic charge migration not only prolongs the lifetime of e−/h+ but also enhances their participation in redox reactions.
In the TiO2-BiVO4 system, PEC activity is predominantly enabled by the formation of a type II heterojunction between TiO2 and BiVO4. Specifically, the EVB of TiO2 is more positive than the HOMO of RhB [71] and the potentials of the radical ·OH/OH− (2.38 eV, vs. NHE) and ·OH/H2O (2.72 eV, vs. NHE) [72]. This energetic alignment allows photogenerated h+ to directly oxidize RhB or react with water to form ·OH. Additionally, since the ECB of BiVO4 lies lower than that of TiO2, e− can transfer from the conduction band of BiVO4 to that of TiO2, where they are ultimately trapped by oxygen molecules to form ·O2− [73]. These reactive oxygen species further participate in the degradation process. The mismatch in valence and conduction band potentials enhances the separation efficiency of e−/h+, thereby improving the overall photocatalytic performance of the system. The valence band offset in the heterojunction structure effectively minimizes e−/h+ recombination, thereby boosting the generation of reactive oxygen species (Figure 8).

3.5. Degradation Pathways of RhB

In order to investigate the degradation pathway of RhB, we sampled the reaction system of PEC degradation of RhB with the presence of TiO2-BiVO4 at 0, 30, 60, 120 and 180 min, and carried out UV-visible spectrophotometric detection to infer the degradation pathway of RhB based on the absorption peaks of RhB and its intermediate products at different wavelengths.
In the PEC degradation of RhB, the characteristic absorption peak of RhB was mainly located at 554 nm (Figure 9) before the reaction, and the absorption peak continued to decrease with the blue shift phenomenon from the beginning to the end of the PEC reaction in 360 min, which indicated that the structure of RhB was changed during the PEC treatment. At the beginning of the reaction, the absorption peak at 256 nm was also high, and it decreased and blue shifted with the reaction time, which implied that during the PEC degradation of RhB, some side chains of RhB molecules appeared to be stripped of their ethyl groups and certain intermediates were produced. Similarly, Shafaee et al. concluded that the decrease and blue shift in the absorbance of the RhB degradation solution at wavelength 554 nm represent the successive de-ethylation of the RhB molecule and the sequential generation of N,N,N-triethyl rhodamine (539 nm), N,N-diethyl rhodamine (522 nm), N-ethyl RhB (510 nm) and rhodamine (498 nm) [74]. In addition, the degradation of RhB by PEC showed only a decrease in the intensity of the absorption peaks at the late stage of the reaction, and the degradation of RhB was basically completed at 360 min. However, at the later stage, the absorption peaks did not show a blue shift phenomenon, which could be attributed to the breakage of C=C, C=N and C=O in the molecular structure of RhB during the PEC process and the occurrence of ring-opening, which were more conducive to the complete degradation and mineralisation of RhB.
Measurement of UV-Vis absorption spectra was able to demonstrate that intermediate products are produced during the degradation of RhB. In general, the degradation of RhB usually produces a variety of intermediate products, mainly including N-deethylation products, aromatic ring breakage products, carboxylic acids or ammonia, and other nitrogen-containing small molecules. The analysis of reaction intermediates and final products helps to assess the efficiency of the catalytic system and may reveal some details of the reaction process. In order to further explain the degradation pathway of RhB degradation by PEC in the presence of TiO2-BiVO4 materials, experimental detection was carried out by HPLC-MS/MS, and the intermediate products identified by the analysis are shown in Table S1.
As suggested by Horikoshi et al., the PEC degradation of RhB by photoactive substances (e.g., ·OH and h+) can attack the central carbon of RhB, decolourising the dye and further degrading it through the N-deethylation process [75]. In the mass spectra, the main intermediates with m/z values of 443, 415, 387, and 359 were RhB and N-deethylated intermediates, such as N,N-diethyl-N‘-ethyl rhodamine, N,N-diethyl rhodamine, N-ethyl-N’-ethyl rhodamine, N-ethyl rhodamine, N-ethyl rhodamine, and N-ethyl rhodamine. In addition to the N-deethylated intermediates, a number of other intermediates could be identified, i.e., debenzene intermediates and ring-opening intermediates (Figure 10). Ultimately, similar to the literature on the degradation of RhB [76,77,78,79], the oxidation products were mineralised to CO2, H2O, NO3− and NH4+ [80].

4. Conclusions

Against the backdrop of escalating global textile industry emissions, where conventional wastewater treatment methods struggle with persistent organic pollutants due to inefficiency and secondary contamination risks, two distinct TiO2-BiVO4 heterojunction materials were prepared for the degradation of RhB in water. The fundamental structural differences between these two materials are clearly evidenced by our characterization results. The composite material (TiO2-BiVO4-M) features an intimately mixed, granular morphology with a high specific surface area (159.6 m2·g−1) and a porous network comprising both micropores and mesopores. In contrast, the layered material (TiO2-BiVO4-L) exhibits a well-defined, stratified structure with sequential layers of TiO2 and BiVO4, resulting in a smoother surface and a lower specific surface area (89.0 m2·g−1). XRD analysis confirmed that both architectures successfully formed the intended heterojunction without altering the crystalline phases of the individual components, while the notable peak broadening in the layered sample suggests strain induced by the fabrication process.
TiO2-BiVO4-L exhibited higher degradation efficiency compared to TiO2-BiVO4-M, attributed to its ordered multilayered configuration, which enhances light absorption across a broader spectral range and provides directional pathways for charge transport. Enhanced stability was also observed in the layered structure, retaining over 70% efficiency after four cycles, which underscores its practical potential for long-term applications. The catalytic mechanism was primarily driven by the formation of a type II heterojunction, where e− were transferred from the conduction band of BiVO4 to TiO2, while h+ accumulated in BiVO4, facilitating efficient charge separation. ·O2− was identified as the dominant reactive oxygen species responsible for RhB degradation. Degradation pathways of RhB were systematically elucidated, involving sequential deethylation, cleavage of the aromatic chromophore, and subsequent ring-opening mineralization, ultimately leading to the formation of inorganic byproducts such as CO2, H2O, and NH4+. This study provides a robust theoretical foundation for the practical application of TiO2-BiVO4 heterojunctions in treating refractory organic pollutants, highlighting their potential for sustainable wastewater remediation in the printing and dyeing industry. While this study focused on the detailed degradation mechanism of Rhodamine B, future work will expand to include other prevalent dye classes (e.g., azo and reactive dyes) to fully assess the practical potential of the TiO2-BiVO4 photoelectrode in treating diverse industrial wastewaters.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ma18184253/s1, Figure S1: Photoelectroreaction device diagram; Figure S2: Effect of BiVO4 loading amounts in the dark adsorption of RhB with the presence of TiO2-BiVO4-M (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1); Figure S3. Effect of RhB concentrations in the dark adsorption of RhB with the presence of (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1); Figure S4. Effect of RhB concentrations in the dark adsorption of RhB with the presence of (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1); Figure S5. Effect of pH values in the dark adsorption of RhB with the presence of (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1); Figure S6. Steady-state photocurrent of TiO2-BiVO4 materials electrode oxidizing organic matter in different electrolyte solutions: (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L; Figure S7. UV-visible light absorption spectrum during the PEC degradation process of RhB; Table S1: Main degradation intermediates of RhB.

Author Contributions

Conceptualization, A.S. and R.Y.; methodology, A.S. and C.K.; formal analysis, A.S., C.K. and Z.B.; investigation, A.S., C.K. and Z.B.; data curation, A.S. and C.K.; writing—original draft preparation, A.S. and C.K.; writing—review and editing, A.S., J.W. and R.Y.; supervision, B.Z., H.C. and R.Y.; funding acquisition, R.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the “Interdisciplinary Program for Young Teachers” of the University of Science and Technology Beijing (FRF-IDRY-23-040).

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/Supplementary Material. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Zhang, S.; An, X.; Gong, J.; Xu, Z.; Wang, L.; Xia, X.; Zhang, Q. Molecular response of Anoxybacillus sp. PDR2 under azo dye stress: An integrated analysis of proteomics and metabolomics. J. Hazard. Mater. 2022, 438, 129500. [Google Scholar] [CrossRef]
  2. Katheresan, V.; Kansedo, J.; Lau, S.Y. Efficiency of various recent wastewater dye removal methods: A review. J. Environ. Chem. Eng. 2018, 6, 4676–4697. [Google Scholar] [CrossRef]
  3. Samsami, S.; Mohamadizaniani, M.; Sarrafzadeh, M.-H.; Rene, E.R.; Firoozbahr, M. Recent advances in the treatment of dye-containing wastewater from textile industries: Overview and perspectives. Process Saf. Environ. Prot. 2020, 143, 138–163. [Google Scholar] [CrossRef]
  4. Ding, S.; Li, X.; Qiao, X.; Liu, Y.; Wang, H.; Ma, C. Identification and screening of priority pollutants in printing and dyeing industry wastewater and the importance of these pollutants in environmental management in China. Environ. Pollut. 2024, 362, 124938. [Google Scholar] [CrossRef]
  5. Rafii, F.; Hall, J.D.; Cerniglia, C.E. Mutagenicity of azo dyes used in foods, drugs and cosmetics before and after reduction by Clostridium species from the human intestinal tract. Food Chem. Toxicol. 1997, 35, 897–901. [Google Scholar] [CrossRef] [PubMed]
  6. Daghrir, R.; Drogui, P.; Robert, D. Photoelectrocatalytic technologies for environmental applications. J. Photochem. Photobiol. A Chem. 2012, 238, 41–52. [Google Scholar] [CrossRef]
  7. Zanoni, M.V.B.; Guaraldo, T. Photoelectrochemical hydrogen generation and concomitant organic dye oxidation under TiO2 nanotube. ECS Trans. 2013, 50, 63. [Google Scholar] [CrossRef]
  8. Chen, P.; Zhang, Y.; Zhou, Y.; Dong, F. Photoelectrocatalytic carbon dioxide reduction: Fundamental, advances and challenges. Nano Mater. Sci. 2021, 3, 344–367. [Google Scholar] [CrossRef]
  9. Comer, B.M.; Lenk, M.H.; Rajanala, A.P.; Flynn, E.L.; Medford, A.J. Computational study of transition-metal substitutions in rutile TiO2 (110) for photoelectrocatalytic ammonia synthesis. Catal. Lett. 2021, 151, 1142–1154. [Google Scholar] [CrossRef]
  10. Song, R.; Chi, H.; Ma, Q.; Li, D.; Wang, X.; Gao, W.; Wang, H.; Wang, X.; Li, Z.; Li, C. Highly efficient degradation of persistent pollutants with 3D nanocone TiO2-based photoelectrocatalysis. J. Am. Chem. Soc. 2021, 143, 13664–13674. [Google Scholar] [CrossRef]
  11. Bessegato, G.G.; Cardoso, J.C.; Zanoni, M.V.B. Enhanced photoelectrocatalytic degradation of an acid dye with boron-doped TiO2 nanotube anodes. Catal. Today 2015, 240, 100–106. [Google Scholar] [CrossRef]
  12. Garcia-Segura, S.; Brillas, E. Applied photoelectrocatalysis on the degradation of organic pollutants in wastewaters. J. Photochem. Photobiol. C Photochem. Rev. 2017, 31, 1–35. [Google Scholar] [CrossRef]
  13. Ahmadpour, N.; Nowrouzi, M.; Madadi Avargani, V.; Sayadi, M.H.; Zendehboudi, S. Design and optimization of TiO2-based photocatalysts for efficient removal of pharmaceutical pollutants in water: Recent developments and challenges. J. Water Process Eng. 2024, 57, 104597. [Google Scholar] [CrossRef]
  14. Li, D.; Zhang, N.; Yuan, R.; Chen, H.; Wang, F.; Zhou, B. Effect of wavelengths on photocatalytic oxidation mechanism of sulfadiazine and sulfamethoxazole in the presence of TiO2. J. Environ. Chem. Eng. 2021, 9, 106243. [Google Scholar] [CrossRef]
  15. Li, Z.; Luo, W.; Zhang, M.; Feng, J.; Zou, Z. Photoelectrochemical cells for solar hydrogen production: Current state of promising photoelectrodes, methods to improve their properties, and outlook. Energy Environ. Sci. 2013, 6, 347–370. [Google Scholar] [CrossRef]
  16. Moniz, S.J.A.; Shevlin, S.A.; Martin, D.J.; Guo, Z.-X.; Tang, J. Visible-light driven heterojunction photocatalysts for water splitting—A critical review. Energy Environ. Sci. 2015, 8, 731–759. [Google Scholar] [CrossRef]
  17. Tayebi, M.; Lee, B.-K. Recent advances in BiVO4 semiconductor materials for hydrogen production using photoelectrochemical water splitting. Renew. Sustain. Energy Rev. 2019, 111, 332–343. [Google Scholar] [CrossRef]
  18. Low, J.; Yu, J.; Jaroniec, M.; Wageh, S.; Al-Ghamdi, A.A. Heterojunction photocatalysts. Adv. Mater. 2017, 29, 1601694. [Google Scholar] [CrossRef] [PubMed]
  19. Adhikari, S.; Selvaraj, S.; Kim, D.-H. Construction of heterojunction photoelectrode via atomic layer deposition of Fe2O3 on Bi2WO6 for highly efficient photoelectrochemical sensing and degradation of tetracycline. Appl. Catal. B Environ. 2019, 244, 11–24. [Google Scholar] [CrossRef]
  20. Wu, S.; Hu, Y.H. A comprehensive review on catalysts for electrocatalytic and photoelectrocatalytic degradation of antibiotics. Chem. Eng. J. 2021, 409, 127739. [Google Scholar] [CrossRef]
  21. Ye, S.; Chen, Y.; Yao, X.; Zhang, J. Simultaneous removal of organic pollutants and heavy metals in wastewater by photoelectrocatalysis: A review. Chemosphere 2021, 273, 128503. [Google Scholar] [CrossRef] [PubMed]
  22. Zhang, Y.; Ma, H.; Chen, X.; Wang, W.; Li, F.; Qiang, T.; Shen, Y.; Cong, Y. CQDs improved the photoelectrocatalytic performance of plasma assembled WO3/TiO2-NRs for bisphenol A degradation. J. Hazard. Mater. 2023, 443, 130250. [Google Scholar] [CrossRef]
  23. Hu, Y.; Niu, Q.; Wang, Y.; Zhang, Y.; Zhao, G. Highly efficient removal mechanism of dimethyl phthalate over an economical 3D {001}TiO2/Ti photoelectrode with enhanced photoelectrocatalytic activity and long service life. Appl. Catal. B Environ. 2021, 285, 119812. [Google Scholar] [CrossRef]
  24. Yu, J.; Zou, J.; Xu, P.; He, Q. Three-dimensional photoelectrocatalytic degradation of the opaque dye acid fuchsin by Pr and Co co-doped TiO2 particle electrodes. J. Clean. Prod. 2020, 251, 119744. [Google Scholar] [CrossRef]
  25. Gong, Q.; Zhou, Y.; Wang, R.; Jiao, W. Enhanced photocatalytic pure water splitting of porous g-C3N4/CdS composite by the bimetallic phosphide. J. Environ. Chem. Eng. 2022, 10, 108046. [Google Scholar] [CrossRef]
  26. Shen, H.; Ni, D.; Niu, P.; Zhou, Y.; Zhai, T.; Ma, Y. Enhancing photocatalytic H2 evolution from water on CuO-Co3O4/TiO2: The key roles of Co3O4 loading amounts. Int. J. Hydrogen Energy 2017, 42, 30559–30568. [Google Scholar] [CrossRef]
  27. Long, L.; Li, J.; Wu, L.; Li, X. Enhanced photocatalytic performance of platinized CdS/TiO2 by optimizing calcination temperature of TiO2 nanotubes. Mater. Sci. Semicond. Process. 2014, 26, 107–111. [Google Scholar] [CrossRef]
  28. Jiang, D.; Zhao, L.; Shao, Y.; Wang, D. Preparation and characterization of layered LiNi0.9Co0.05Mn0.025Mg0.025O2 cathode material by a sol–gel method for lithium-ion batteries. RSC Adv. 2015, 5, 40779–40784. [Google Scholar] [CrossRef]
  29. Miao, J.; Geng, W.; Alvarez, P.J.J.; Long, M. 2D N-doped porous carbon derived from polydopamine-coated graphitic carbon nitride for efficient nonradical activation of peroxymonosulfate. Environ. Sci. Technol. 2020, 54, 8473–8481. [Google Scholar] [CrossRef] [PubMed]
  30. Wu, X.; Liu, Y. Phase change and crystal growth of TiO2 in metatitanic acid. Ceram. Int. 2023, 49, 4607–4613. [Google Scholar] [CrossRef]
  31. Baek, J.H.; Kim, B.J.; Han, G.S.; Hwang, S.W.; Kim, D.R.; Cho, I.S.; Jung, H.S. BiVO4/WO3/SnO2 double-heterojunction photoanode with enhanced charge separation and visible-transparency for bias-free solar water-splitting with a perovskite solar cell. ACS Appl. Mater. Interfaces 2017, 9, 1479–1487. [Google Scholar] [CrossRef]
  32. Polo, A.; Nomellini, C.; Marra, G.; Selli, E.; Dozzi, M.V. WO3/BiVO4 heterojunction photoanodes: Optimized photoelectrochemical performance in relation to both oxides layer thickness. Catal. Today 2025, 446, 115137. [Google Scholar] [CrossRef]
  33. Hwang, S.W.; Kim, J.U.; Baek, J.H.; Kalanur, S.S.; Jung, H.S.; Seo, H.; Cho, I.S. Solution-processed TiO2/BiVO4/SnO2 triple-layer photoanode with enhanced photoelectrochemical performance. J. Alloys Compd. 2019, 785, 1245–1252. [Google Scholar] [CrossRef]
  34. Qadri, M.A.A.; Nurfani, E. Effect of TiO2:Zn layer thickness on the performance of MAPbI3-based perovskite solar cells fabricated under open-air condition. Next Mater. 2025, 8, 100537. [Google Scholar] [CrossRef]
  35. Izmirli, S.; Cavdar, S. Effect of film thickness on photodiode and photodetector performance of titanium dioxide (TiO2) prepared via solution assisted spin coating method. Appl. Surf. Sci. 2025, 688, 162187. [Google Scholar] [CrossRef]
  36. Mohamed, R.M. UV-assisted photocatalytic synthesis of TiO2-reduced graphene oxide with enhanced photocatalytic activity in decomposition of sarin in gas phase. Desalin. Water Treat. 2012, 50, 147–156. [Google Scholar] [CrossRef]
  37. Hisatomi, T.; Kubota, J.; Domen, K. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting. Chem. Soc. Rev. 2014, 43, 7520–7535. [Google Scholar] [CrossRef]
  38. Huang, L.; Yuan, Y.; Wang, Y.; Yılmaz, M.; Zhang, T.C.; Yuan, S. Visible-light-driven photocatalytic oxidation of H2S by boron-doped TiO2/LDH heterojunction: Synthesis, performance, and reaction mechanism. Chem. Eng. J. 2022, 448, 137607. [Google Scholar] [CrossRef]
  39. Eghbali, S.; Boroujerdnia, M.; Haghighatzadeh, A. Visible-light-active Ag-doped BiVO4 nanostructures: Preparation and optical and photocatalytic studies. Phys. B Condens. Matter 2025, 703, 416990. [Google Scholar] [CrossRef]
  40. Jubeer, E.M.; Manthrammel, M.A.; Subha, P.A.; Shkir, M.; Biju, K.P.; AlFaify, S.A. Defect engineering for enhanced optical and photocatalytic properties of ZnS nanoparticles synthesized by hydrothermal method. Sci. Rep. 2023, 13, 16820. [Google Scholar] [CrossRef]
  41. Kaplan, R.; Erjavec, B.; Dražić, G.; Grdadolnik, J.; Pintar, A. Simple synthesis of anatase/rutile/brookite TiO2 nanocomposite with superior mineralization potential for photocatalytic degradation of water pollutants. Appl. Catal. B Environ. 2016, 181, 465–474. [Google Scholar] [CrossRef]
  42. Zhang, X.; Zhang, X.; Feng, K.; Hu, X.; Fan, J.; Liu, E. A carbon membrane-mediated CdSe and TiO2 nanofiber film for enhanced photoelectrochemical degradation of methylene blue. RSC Adv. 2021, 11, 11872–11881. [Google Scholar] [CrossRef]
  43. Li, X.; Kang, B.; Dong, F.; Zhang, Z.; Luo, X.; Han, L.; Huang, J.; Feng, Z.; Chen, Z.; Xu, J.; et al. Enhanced photocatalytic degradation and H2/H2O2 production performance of S-pCN/WO2.72 S-scheme heterojunction with appropriate surface oxygen vacancies. Nano Energy 2021, 81, 105671. [Google Scholar] [CrossRef]
  44. Kim, Y.I.; Atherton, S.J.; Brigham, E.S.; Mallouk, T.E. Sensitized layered metal oxide semiconductor particles for photochemical hydrogen evolution from nonsacrificial electron donors. J. Phys. Chem. 1993, 97, 11802–11810. [Google Scholar] [CrossRef]
  45. Fidalgo, A.; Letichevsky, S.; Santos, B.F. Assessment of TiO2 band gap from structural parameters using artificial neural networks. J. Photochem. Photobiol. A-Chem. 2021, 405, 112870. [Google Scholar] [CrossRef]
  46. Wang, X.; Huo, P.; Liu, Y.; Xiang, Y.; Jia, C.; Yan, Z. High-throughput screening of ternary vanadate photoanodes for efficient oxygen evolution reactions: A review of band-gap engineering. Appl. Catal. A Gen. 2021, 616, 118073. [Google Scholar] [CrossRef]
  47. Wang, H.; Zhu, Y.; Kumar Joshi, M.; Cheng, Y.; Zhang, P.; Tan, M.; Yu, R.; Mao, Z.; Li, X. In-situ and ex-situ preparation of Bi2S3 on the BiVO4/TiO2 to construct Bi2S3/BiVO4/TiO2 heterojunction for efficient Cr(VI) reduction. Chem. Eng. J. 2024, 500, 156640. [Google Scholar] [CrossRef]
  48. Ma, Q.; Yan, C.; Lv, W.; Mei, Y.; Peng, H.; Du, J.; Zheng, B.; Guo, Y. Coexisting chloride ion for boosting the photoelectrocatalytic degradation efficiency of organic dyes. Catal. Lett. 2023, 153, 378–387. [Google Scholar] [CrossRef]
  49. Xie, G.; Chang, X.; Adhikari, B.R.; Thind, S.S.; Chen, A. Photoelectrochemical degradation of acetaminophen and valacyclovir using nanoporous titanium dioxide. Chin. J. Catal. 2016, 37, 1062–1069. [Google Scholar] [CrossRef]
  50. Zhao, X.; Zhu, Y. Synergetic degradation of rhodamine B at a porous ZnWO4 film electrode by combined electro-oxidation and photocatalysis. Environ. Sci. Technol. 2006, 40, 3367–3372. [Google Scholar] [CrossRef]
  51. Orimolade, B.O.; Zwane, B.N.; Koiki, B.A.; Rivallin, M.; Bechelany, M.; Mabuba, N.; Lesage, G.; Cretin, M.; Arotiba, O.A. Coupling cathodic electro-fenton with anodic photo-electrochemical oxidation: A feasibility study on the mineralization of paracetamol. J. Environ. Chem. Eng. 2020, 8, 104394. [Google Scholar] [CrossRef]
  52. Ma, L.; Zhang, Z.; Duan, J.; Li, J.; Lin, Q.; Jiang, Y.; Zhu, K.; Fang, Z.; Ji, B.; Yang, Z. Optimize the preparation process of m-TiO2@CdS by response surface methodology to enhance the light intensity adaptability of photocatalytic degradation of tetracycline. J. Alloys Compd. 2025, 1010, 177979. [Google Scholar] [CrossRef]
  53. Wang, Z.; Qiao, W.; Yuan, M.; Li, N.; Chen, J. Light-intensity-dependent semiconductor–cocatalyst interfacial electron transfer: A dilemma of sunlight-driven photocatalysis. J. Phys. Chem. Lett. 2020, 11, 2369–2373. [Google Scholar] [CrossRef] [PubMed]
  54. Wang, D.T.; Li, X.; Chen, J.F.; Tao, X. Enhanced Visible-Light Photoelectrocatalytic Degradation of Organic Contaminants at Iodine-Doped Titanium Dioxide Film Electrode. Ind. Eng. Chem. Res. 2012, 51, 218–224. [Google Scholar] [CrossRef]
  55. Jayaraman, V.; Ayappan, C.; Mani, A. Facile preparation of bismuth vanadate-sheet/carbon nitride rod-like interface photocatalyst for efficient degradation of model organic pollutant under direct sunlight irradiation. Chemosphere 2022, 287, 132055. [Google Scholar] [CrossRef]
  56. Gupta, V.K.; Jain, R.; Mittal, A.; Saleh, T.A.; Nayak, A.; Agarwal, S.; Sikarwar, S. Photo-catalytic degradation of toxic dye amaranth on TiO2/UV in aqueous suspensions. Mater. Sci. Eng. C 2012, 32, 12–17. [Google Scholar] [CrossRef]
  57. Leng, H.; Jia, Y.; Lv, Z.; You, H.; Fu, L. Enhanced quinoline degradation by 3D stack Z-scheme photoelectrocatalytic system with Ag-TNTs photoanode and CN-CNWs photocathode. J. Environ. Chem. Eng. 2022, 10, 106826. [Google Scholar] [CrossRef]
  58. Rao, W.; Piliouras, P.; Wang, X.; Guido, A.; Kugler, K.; Sieren, B.; Wang, L.; Lv, G.; Li, Z. Zwitterionic dye rhodamine B (RhB) uptake on different types of clay minerals. Appl. Clay Sci. 2020, 197, 105790. [Google Scholar] [CrossRef]
  59. Chen, X.-Q.; Shen, W.-H. Preparation and properties of stable nanocrystalline anatase TiO2 colloids. Chem. Eng. Technol. 2008, 31, 1277–1281. [Google Scholar] [CrossRef]
  60. Ghazal, N.; Mohamed, S.A.; Hameed, M.F.O.; Obayya, S.S.A.; El Nazer, H.A.; Madkour, M. Surface and optoelectronic impacts of ZnO/BiVO4/MWCNT nanoheterostructure toward photodegradation of water contaminants. Surf. Interfaces 2022, 33, 102278. [Google Scholar] [CrossRef]
  61. Xiang, Q.; Yu, J.; Wong, P.K. Quantitative characterization of hydroxyl radicals produced by various photocatalysts. J. Colloid Interface Sci. 2011, 357, 163–167. [Google Scholar] [CrossRef]
  62. Konstantinou, I.K.; Albanis, T.A. TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: Kinetic and mechanistic investigations: A review. Appl. Catal. B Environ. 2004, 49, 1–14. [Google Scholar] [CrossRef]
  63. Wei, X.-P.; Yang, Y.-T.; Zheng, Z.-Y.; Yuan, W.-B.; Ni, H.-G. A simple preparation method of Ti/TiO2/BiVO4 and implications for enhanced photoelectrocatalytic performance under visible light illumination. Inorg. Chem. Commun. 2025, 171, 113602. [Google Scholar] [CrossRef]
  64. Liang, L.; Gao, S.; Zhu, J.; Wang, L.; Xiong, Y.; Xia, X.; Yang, L. The enhanced photocatalytic performance toward carbamazepine by nitrogen-doped carbon dots decorated on BiOBr/CeO2: Mechanism insight and degradation pathways. Chem. Eng. J. 2020, 391, 123599. [Google Scholar] [CrossRef]
  65. Li, C.; Sun, Z.; Zhang, W.; Yu, C.; Zheng, S. Highly efficient g-C3N4/TiO2/kaolinite composite with novel three-dimensional structure and enhanced visible light responding ability towards ciprofloxacin and S. aureus. Appl. Catal. B Environ. 2018, 220, 272–282. [Google Scholar] [CrossRef]
  66. Zheng, Q.; Liu, X.; Tian, L.; Zhou, Y.; Liao, L.; Lv, G. Mechanism of Fenton catalytic degradation of Rhodamine B induced by microwave and Fe3O4. Chin. Chem. Lett. 2025, 36, 109771. [Google Scholar] [CrossRef]
  67. Hussein, A.; Scholz, M. Dye wastewater treatment by vertical-flow constructed wetlands. Ecol. Eng. 2017, 101, 28–38. [Google Scholar] [CrossRef]
  68. Law, M.; Goldberger, J.; Yang, P. Semiconductor nanowires and nanotubes. Annu. Rev. Mater. Res. 2004, 34, 83–122. [Google Scholar] [CrossRef]
  69. Hu, Y.; Li, D.; Zheng, Y.; Chen, W.; He, Y.; Shao, Y.; Fu, X.; Xiao, G. BiVO4/TiO2 nanocrystalline heterostructure: A wide spectrum responsive photocatalyst towards the highly efficient decomposition of gaseous benzene. Appl. Catal. B Environ. 2011, 104, 30–36. [Google Scholar] [CrossRef]
  70. Tokunaga, S.; Kato, H.; Kudo, A. Selective preparation of monoclinic and tetragonal BiVO4 with scheelite structure and their photocatalytic properties. Chem. Mater. 2001, 13, 4624–4628. [Google Scholar] [CrossRef]
  71. Guang, L.; Hui, W.; Xuejun, Z. Effect of drying temperatures on structural performance and photocatalytic activity of BiOCl synthesized by a soft chemical method. J. Solid State Chem. 2016, 239, 259–264. [Google Scholar] [CrossRef]
  72. Zhang, J.; Ma, Z. Ag3VO4/AgI composites for photocatalytic degradation of dyes and tetracycline hydrochloride under visible light. Mater. Lett. 2018, 216, 216–219. [Google Scholar] [CrossRef]
  73. Wang, Y.; Lu, N.; Luo, M.; Fan, L.; Zhao, K.; Qu, J.; Guan, J.; Yuan, X. Enhancement mechanism of fiddlehead-shaped TiO2-BiVO4 type II heterojunction in SPEC towards RhB degradation and detoxification. Appl. Surf. Sci. 2019, 463, 234–243. [Google Scholar] [CrossRef]
  74. Shafaee, M.; Goharshadi, E.K.; Mashreghi, M.; Sadeghinia, M. TiO2 nanoparticles and TiO2@graphene quantum dots nancomposites as effective visible/solar light photocatalysts. J. Photochem. Photobiol. A Chem. 2018, 357, 90–102. [Google Scholar] [CrossRef]
  75. Horikoshi, S.; Hidaka, H.; Serpone, N. Environmental remediation by an integrated microwave/UV-illumination technique: IV. Non-thermal effects in the microwave-assisted degradation of 2,4-dichlorophenoxyacetic acid in UV-irradiated TiO2/H2O dispersions. J. Photochem. Photobiol. A Chem. 2003, 159, 289–300. [Google Scholar] [CrossRef]
  76. Yu, K.; Yang, S.; He, H.; Sun, C.; Gu, C.; Ju, Y. Visible light-driven photocatalytic degradation of rhodamine B over NaBiO3: Pathways and mechanism. J. Phys. Chem. A 2009, 113, 10024–10032. [Google Scholar] [CrossRef]
  77. He, Z.; Sun, C.; Yang, S.; Ding, Y.; He, H.; Wang, Z. Photocatalytic degradation of rhodamine B by Bi2WO6 with electron accepting agent under microwave irradiation: Mechanism and pathway. J. Hazard. Mater. 2009, 162, 1477–1486. [Google Scholar] [CrossRef] [PubMed]
  78. Sun, M.; Li, D.; Chen, Y.; Chen, W.; Li, W.; He, Y.; Fu, X. Synthesis and photocatalytic activity of calcium antimony oxide hydroxide for the degradation of dyes in water. J. Phys. Chem. C 2009, 113, 13825–13831. [Google Scholar] [CrossRef]
  79. Chen, C.; Li, X.; Ma, W.; Zhao, J.; Hidaka, H.; Serpone, N. Effect of transition metal ions on the TiO2-assisted photodegradation of dyes under visible irradiation:  A probe for the interfacial electron transfer process and reaction mechanism. J. Phys. Chem. B 2002, 106, 318–324. [Google Scholar] [CrossRef]
  80. Natarajan, T.S.; Thomas, M.; Natarajan, K.; Bajaj, H.C.; Tayade, R.J. Study on UV-LED/TiO2 process for degradation of Rhodamine B dye. Chem. Eng. J. 2011, 169, 126–134. [Google Scholar] [CrossRef]
Materials 18 04253 g001
Figure 1. Effects of (a) BiVO4 loading amount and (b) calcination temperature on PEC degradation of RhB in the presence of TiO2-BiVO4-M, and (c) number of BiVO4 layers and (d) TiO2 layers on PEC degradation of RhB in the presence of TiO2-BiVO4-L (CRhB 10 mg·L−1, light intensity 14,000 lx, applied bias voltage 2 V, initial pH 7.0 ± 0.1).
Figure 1. Effects of (a) BiVO4 loading amount and (b) calcination temperature on PEC degradation of RhB in the presence of TiO2-BiVO4-M, and (c) number of BiVO4 layers and (d) TiO2 layers on PEC degradation of RhB in the presence of TiO2-BiVO4-L (CRhB 10 mg·L−1, light intensity 14,000 lx, applied bias voltage 2 V, initial pH 7.0 ± 0.1).
Materials 18 04253 g001
Materials 18 04253 g002
Figure 2. SEM images of (a,b) TiO2-BiVO4-M, and (c,d) TiO2-BiVO4-L.
Figure 2. SEM images of (a,b) TiO2-BiVO4-M, and (c,d) TiO2-BiVO4-L.
Materials 18 04253 g002
Materials 18 04253 g003
Figure 3. (a) N2 adsorption–desorption isotherms and (b) pore size distribution of TiO2 and TiO2-BiVO4-M, (c) XRD patterns and (d) UV-Vis DRS of TiO2, BiVO4, TiO2-BiVO4-M and TiO2-BiVO4-L, (e) XPS valence band spectra and (f) band gaps of TiO2 and BiVO4, (g) EIS plots (The inset is the equivalent circuit diagram) and (h) transient photocurrent spectra of TiO2, BiVO4, TiO2-BiVO4-M and TiO2-BiVO4-L.
Figure 3. (a) N2 adsorption–desorption isotherms and (b) pore size distribution of TiO2 and TiO2-BiVO4-M, (c) XRD patterns and (d) UV-Vis DRS of TiO2, BiVO4, TiO2-BiVO4-M and TiO2-BiVO4-L, (e) XPS valence band spectra and (f) band gaps of TiO2 and BiVO4, (g) EIS plots (The inset is the equivalent circuit diagram) and (h) transient photocurrent spectra of TiO2, BiVO4, TiO2-BiVO4-M and TiO2-BiVO4-L.
Materials 18 04253 g003
Materials 18 04253 g004
Figure 4. Effect of (a,b) degradation systems, (c,d) external bias voltage, and (e,f) light intensity on RhB degradation (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1).
Figure 4. Effect of (a,b) degradation systems, (c,d) external bias voltage, and (e,f) light intensity on RhB degradation (CRhB 10 mg·L−1, initial pH 7.0 ± 0.1).
Materials 18 04253 g004
Materials 18 04253 g005
Figure 5. Removal rates for the RhB degradation in the presence of TiO2-BiVO4 catalysts in four successive cycles: (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L (CRhB 10 mg·L−1, light intensity 14,000 lx, applied bias voltage 2 V, initial pH 7.0 ± 0.1).
Figure 5. Removal rates for the RhB degradation in the presence of TiO2-BiVO4 catalysts in four successive cycles: (a) TiO2-BiVO4-M and (b) TiO2-BiVO4-L (CRhB 10 mg·L−1, light intensity 14,000 lx, applied bias voltage 2 V, initial pH 7.0 ± 0.1).
Materials 18 04253 g005
Materials 18 04253 g006
Figure 6. Effect of (a,b) initial concentrations, (c,d) pH values, and (e–h) Na2SO4 and NaNO3 electrolytes and their concentrations on RhB degradation (light intensity 14,000 lx, applied bias voltage 2 V).
Figure 6. Effect of (a,b) initial concentrations, (c,d) pH values, and (e–h) Na2SO4 and NaNO3 electrolytes and their concentrations on RhB degradation (light intensity 14,000 lx, applied bias voltage 2 V).
Materials 18 04253 g006
Materials 18 04253 g007
Figure 7. Effect of capture agent on PEC degradation of RhB in the presence of: (a) TiO2-BiVO4-M, (b) TiO2-BiVO4-L, and (c) EPR spectra of ·OH and ·O2−.
Figure 7. Effect of capture agent on PEC degradation of RhB in the presence of: (a) TiO2-BiVO4-M, (b) TiO2-BiVO4-L, and (c) EPR spectra of ·OH and ·O2−.
Materials 18 04253 g007
Materials 18 04253 g008
Figure 8. PEC degradation mechanism of RhB in the presence of TiO2-BiVO4 material.
Figure 8. PEC degradation mechanism of RhB in the presence of TiO2-BiVO4 material.
Materials 18 04253 g008
Materials 18 04253 g009
Figure 9. UV-visible light absorption spectrum during the PEC degradation process of RhB.
Figure 9. UV-visible light absorption spectrum during the PEC degradation process of RhB.
Materials 18 04253 g009
Materials 18 04253 g010
Figure 10. Possible PEC degradation pathways of RhB in the presence of TiO2-BiVO4 material.
Figure 10. Possible PEC degradation pathways of RhB in the presence of TiO2-BiVO4 material.
Materials 18 04253 g010
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

Sun, A.; Kong, C.; Wang, J.; Zhou, B.; Chen, H.; Yuan, R.; Bai, Z. Photoelectrocatalytic Degradation of Rhodamine B in the Presence of TiO2-BiVO4. Materials 2025, 18, 4253. https://doi.org/10.3390/ma18184253

AMA Style

Sun A, Kong C, Wang J, Zhou B, Chen H, Yuan R, Bai Z. Photoelectrocatalytic Degradation of Rhodamine B in the Presence of TiO2-BiVO4. Materials. 2025; 18(18):4253. https://doi.org/10.3390/ma18184253

Chicago/Turabian Style

Sun, Anli, Chao Kong, Jie Wang, Beihai Zhou, Huilun Chen, Rongfang Yuan, and Zhiming Bai. 2025. "Photoelectrocatalytic Degradation of Rhodamine B in the Presence of TiO2-BiVO4" Materials 18, no. 18: 4253. https://doi.org/10.3390/ma18184253

APA Style

Sun, A., Kong, C., Wang, J., Zhou, B., Chen, H., Yuan, R., & Bai, Z. (2025). Photoelectrocatalytic Degradation of Rhodamine B in the Presence of TiO2-BiVO4. Materials, 18(18), 4253. https://doi.org/10.3390/ma18184253

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