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Article

La-Doped ZnO/SBA-15 for Rapid and Recyclable Photodegradation of Rhodamine B Under Visible Light

by
Ziyang Zhou
1,
Weiye Yang
1,2,
Jiuming Zhong
1,*,
Hongyan Peng
1,2 and
Shihua Zhao
1,2,*
1
College of Physics and Electronic Engineering, Hainan Normal University, Haikou 571158, China
2
The Innovation Platform for Academicians of Hainan Province, Haikou 571158, China
*
Authors to whom correspondence should be addressed.
Molecules 2025, 30(24), 4800; https://doi.org/10.3390/molecules30244800
Submission received: 31 October 2025 / Revised: 12 December 2025 / Accepted: 15 December 2025 / Published: 16 December 2025
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Abstract

La-doped ZnO nanoclusters confined within mesoporous SBA-15 were synthesized using an impregnation–calcination method and evaluated for their visible-light-driven photocatalytic degradation of Rhodamine B (RhB). Small-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the preservation of the 2D hexagonal mesostructure of SBA-15 post-loading. In contrast, wide-angle XRD and Fourier-transform infrared spectroscopy (FT-IR) analyses revealed that the incorporated ZnO existed predominantly as highly dispersed amorphous or ultrafine clusters within the mesopores. N2 adsorption–desorption measurements exhibited Type IV isotherms with H1 hysteresis loops. Compared to pristine SBA-15, the specific surface area and pore volume of the composites decreased from 729.35 m2 g−1 to 521.32 m2 g−1 and from 1.09 cm3 g−1 to 0.85 cm3 g−1, respectively, accompanied by an apparent increase in the average pore diameter from 5.99 nm to 6.55 nm, attributed to non-uniform pore occupation. Under visible-light irradiation, the photocatalytic performance was highly dependent on the La doping level. Notably, the 5% La-ZnO/SBA-15 sample exhibited superior activity, achieving over 99% RhB removal within 40 min and demonstrating the highest apparent rate constant (k = 0.1152 min−1), surpassing both undoped ZnO/SBA-15 (k = 0.0467 min−1) and other doping levels. Reusability tests over four consecutive cycles showed a consistent degradation efficiency exceeding 93%, with only a ~7 percentage-point decline, indicating excellent structural stability and recyclability. Radical scavenging experiments identified h+, ·OH, and ·O2− as the primary reactive species. Furthermore, photoluminescence (PL) quenching observed at the optimal 5% La doping level suggested suppressed radiative recombination and enhanced charge carrier separation. Collectively, these results underscore the synergistic effect of La doping and mesoporous confinement in achieving fast, efficient, and recyclable photocatalytic degradation of organic pollutants.

1. Introduction

With the acceleration of global industrialization, the effective treatment of organic pollutants, such as dye-contaminated wastewater, has become a significant challenge in environmental science. Within the broad spectrum of wastewater remediation approaches, photocatalytic oxidation is recognized as one of the most promising approaches for water pollution control due to its capacity to utilize solar energy for the thorough mineralization of pollutants, alongside its inherent environmental compatibility and sustainability [1,2]. Among semiconductor photocatalysts, ZnO has attracted considerable attention due to its superior photocatalytic performance, excellent chemical stability, and low cost [3,4]. However, its practical application is hindered by two primary limitations: (i) the rapid recombination of photogenerated e−–h+ pairs, which substantially diminishes quantum efficiency [5], and (ii) the aggregation of nanoscale particles, which significantly impairs the accessibility of active sites and mass transfer kinetics [6].
To address these limitations, a synergistic modification approach that integrates carrier confinement with elemental doping has been developed [7,8,9]. Ordered mesoporous silica SBA-15 is an exemplary support for confining metal oxide nanoparticles due to its highly regular 2D hexagonal pore structure (5–10 nm), exceptionally large surface area (>600 m2 g−1), and significant thermal stability [10,11,12]. This distinctive pore confinement effect not only effectively inhibits the aggregation and leaching of active components but also preserves efficient mass transfer pathways. This strategy has been demonstrated to be effective in various catalytic systems, including TiO2 and Fe2O3 [13,14,15].
Concurrently, doping with rare-earth elements constitutes an effective strategy for modifying the electronic structures of semiconductors. This approach enhances optoelectronic properties by introducing defect energy levels and altering local charge distributions [16]. La, a representative rare-earth element, has been demonstrated to extend the visible-light absorption range of ZnO and inhibit carrier recombination through the formation of electron trapping centers, thereby improving overall photocatalytic efficiency [8,17].
Building upon this foundation, the research synthesized La-ZnO/SBA-15 composite photocatalysts using an impregnation–calcination method to improve light absorption and charge separation by confining La-doped ZnO nanoclusters within the mesopores of SBA-15. Comprehensive characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and N2 adsorption–desorption analysis, were employed alongside Rhodamine B (RhB) degradation experiments, kinetic analyses, and radical trapping studies. These investigations demonstrated that the La doping ratio significantly impacts photocatalytic activity. Importantly, the confined active species (e−, h+, ·OH, and ·O2−) engage in synergistic oxidation pathways during RhB degradation. This study provides a viable design framework for high-performance, recyclable mesopore-confined photocatalysts with significant potential applications in environmental remediation.

2. Results

2.1. Analysis of Structure and Composition via XRD

Figure 1 illustrates the small-angle X-ray diffraction (SAXRD) patterns of the synthesized SBA-15 support, ZnO/SBA-15, and 5% La-doped ZnO/SBA-15 composites. The SBA-15 material exhibits three diffraction peaks at 2θ values of 0.84°, 1.45°, and 1.68°, which correspond to the (100), (110), and (200) reflections characteristic of highly ordered hexagonal mesoporous silica SBA-15 [10]. The SAXRD patterns of both ZnO/SBA-15 and 5% La-doped ZnO/SBA-15 exhibit identical characteristic peaks, confirming that the hexagonal mesostructure remains intact following impregnation and calcination. This observation demonstrates that the incorporation of ZnO and subsequent La doping does not disrupt the 2D hexagonal mesoscopic order, thereby highlighting the excellent thermal stability of SBA-15 as a catalyst support.
Figure 2 depicts the wide-angle XRD (WAXRD) patterns of the SBA-15 support, ZnO/SBA-15, and 5% La-ZnO/SBA-15 composites. All samples exhibit a broad diffraction hump in the 16–33° (2θ) range, characteristic of the amorphous silica framework of SBA-15 [18,19,20,21]. No additional reflections attributable to crystalline ZnO are observed for the composites, even though the Zn(NO3)2 precursor is completely decomposed to ZnO during calcination at 550 °C [22]. This absence of distinct ZnO peaks indicates that the ZnO phase is present as highly dispersed, ultrafine nanoclusters confined within the SBA-15 mesopores, with crystallite sizes below the XRD detection limit (~3–5 nm) and with weak reflections overlapped by the intense amorphous silica [23,24]. Such pore-confined ZnO nanoclusters are often described as “XRD-amorphous” in SBA-15-based systems [25,26].

2.2. HRTEM Analysis

Figure 3 presents high-resolution transmission electron microscopy (HRTEM) images of SBA-15 and 5% La-ZnO/SBA-15. Figure 3a illustrates the TEM image of SBA-15 viewed perpendicular to the pore channels, revealing a highly ordered 2D hexagonal honeycomb pore arrangement. The channels exhibit a regular configuration with long-range periodicity, uniform pore size distribution (~5–7 nm), and structural characteristics typical of SBA-15 mesostructures [27]. Figure 3b depicts the image taken parallel to the pore axis, illustrating straight, parallel channels with consistent spacing and high aspect ratios, thereby further confirming the structural regularity and integrity.
Following the loading of the active component, the 5% La-ZnO/SBA-15 composite preserves the mesoporous structure of SBA-15, in agreement with the SAXRD analysis. In Figure 3c, the composite exhibits a well-defined honeycomb pore arrangement characterized by hexagonal ordering and different channel boundaries. Within certain pores, discrete dark spots are observed, which are likely attributable to the incorporated ZnO species. The image oriented parallel to the pore direction (Figure 3d) shows numerous dispersed dark nanoparticles on the pore walls and within the channels, presumably corresponding to ZnO clusters formed through the impregnation-annealing process.

2.3. FT-IR Analysis

Figure 4 illustrates the FT-IR spectra of SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15. All samples exhibit absorption peaks at approximately 3430 cm−1 and 1633 cm−1, which correspond to the stretching vibration of surface-adsorbed water or silanol groups (Si–OH) and the bending vibration of H–O–H in water molecules, respectively [28,29]. Within the skeletal vibration region (1400–400 cm−1), the broad absorption band near 1080 cm−1 is attributed to the asymmetric stretching vibration of Si–O–Si [30], whereas the peaks at 800 cm−1 and 460 cm−1 are assigned to the symmetric stretching and bending vibrations of Si–O–Si, respectively [18,31]. Additionally, a weak absorption band near 960 cm−1 is observed in all samples, which is typically ascribed to the stretching vibration of Si–O–Si [32].
In the ZnO/SBA-15 and 5% La-ZnO/SBA-15 samples, a broad absorption band ranging from 1020 cm−1 to 1230 cm−1 is observed, with the signal near 1110 cm−1 attributed to the stretching vibration of Zn–O bonds, which is typically characteristic of amorphous or polycrystalline ZnO materials [33]. Notably, no additional different characteristic absorption peaks of ZnO are detected beyond this broad band, suggesting that ZnO is highly dispersed within the SBA-15 support, and likely to exist in an amorphous form or as ultrafine clusters. The weak infrared signal may result from the low ZnO content, which is potentially obscured by the intense Si–O–Si skeletal vibrations of the SBA-15 matrix, or from the high dispersion of ZnO clusters that prevents the formation of well-defined absorption features.

2.4. Sorption Analysis

Figure 5 depicts the N2 adsorption–desorption isotherms for SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15. All samples exhibit Type IV isotherms according to the 2015 IUPAC classification [34], accompanied by H1-type hysteresis loops, which are indicative of materials possessing narrow pore size distributions and uniform cylindrical mesopores [35]. The absence of significant changes in the isotherm type suggests that the ordered mesoporous channels of SBA-15 remain largely preserved during the formation of ZnO clusters, confirming the results obtained from SAXRD and TEM analyses.
In Table 1, the structural parameters exhibit significant changes following ZnO loading. Specifically, the BET surface area (SBET) decreases from 729.35 m2 g−1 for pure SBA-15 to 521.32 m2 g−1, representing a reduction of approximately 29.5%. Similarly, the total pore volume (Vp) decreases from 1.09 cm3 g−1 to 0.85 cm3 g−1, corresponding to a reduction of approximately 22.0%. These results confirm the successful incorporation of ZnO into the SBA-15 framework, with partial occupation of the pore channels resulting in moderate pore blockage.
Despite a reduction in pore volume, the average pore diameter calculated using the BJH method increases from 5.99 nm to 6.55 nm. This observation is further clarified by the BJH pore size distribution curves in Figure 6, which show that the curves following ZnO loading exhibit broadened peaks and decreased intensity. These changes indicate a broader pore size distribution and reduced structural homogeneity. This phenomenon results from the non-uniform deposition of ZnO precursors within the SBA-15 channels: during impregnation and calcination, ZnO nanoparticles preferentially nucleate at constricted sites or pore entrances, thereby blocking smaller channels while leaving larger pores relatively accessible. Consequently, N2 desorption measurements predominantly reflect the larger pores, leading to an “apparent increase” in the average pore diameter. Furthermore, secondary high-temperature calcination may cause localized sintering of the SBA-15 silica framework or minor collapse of pore walls, further contributing to structural disorder.
Integrated analysis of TEM, XRD, FT-IR, and N2 adsorption–desorption data reveals that the synthesized ZnO/SBA-15 nanocomposite retains the ordered hexagonal mesostructure of SBA-15 while confining ZnO clusters in an amorphous state within the mesopores. This pore-confined loading strategy not only suppresses ZnO nanoparticle aggregation—enhancing exposure of active sites—but also preserves high surface area and interconnected pore channels, facilitating reactant diffusion and mass transfer during catalytic processes. Such structural features provide a robust foundation for efficient photocatalytic degradation of organic pollutants in water, aligning with established literature on mesoporous silica-encapsulated metal oxides for environmental catalysis.

3. Discussion

3.1. Comparison of Photocatalytic Activity

Figure 7a illustrates the photocatalytic degradation performance of RhB under visible light irradiation for ZnO/SBA-15 samples with varying La doping ratios. The undoped ZnO/SBA-15 sample achieves approximately 98% RhB degradation within 60 min, indicating favorable intrinsic photocatalytic activity. However, increasing the La doping concentration does not result in a linear improvement in photocatalytic performance: both the 2.5% and 7.5% La-doped ZnO/SBA-15 samples exhibit degradation efficiencies of approximately 95% at 60 min, comparable to the undoped sample. In contrast, the 5% La-doped ZnO/SBA-15 sample demonstrates significantly enhanced activity, achieving near-complete RhB degradation (>99%) within 40 min, thereby significantly outperforming all other samples.
The blank solution, pure SBA-15, pure ZnO, and La-ZnO exhibit nearly identical degradation efficiencies, achieving only ~40% RhB degradation after 60 min of irradiation. In contrast, the 5% La-ZnO/SBA-15 composite achieves near-complete RhB degradation (>99%) within 40 min, exhibiting significantly superior performance compared to all other samples.
Figure 8 depicts the kinetic analysis based on the Langmuir–Hinshelwood model, demonstrating that the photodegradation of RhB adheres to pseudo-first-order kinetics [36]:
In(C0/C) = −kt
where C0 and C represent the initial and instantaneous concentrations of RhB at time t, respectively; k represents the apparent first-order rate constant (min−1); and t represents the reaction time (min).
The fitting results indicate rate constants of 0.1152 min−1 for 5% La-ZnO/SBA-15, 0.0467 min−1 for undoped ZnO/SBA-15, 0.0565 min−1 for 2.5% La-ZnO/SBA-15, and 0.0624 min−1 for 7.5% La-ZnO/SBA-15. These results reveal that 5% La-ZnO/SBA-15 exhibits a significantly higher rate constant, thereby confirming its superior kinetic performance in the photodegradation of RhB.
Figure 9 presents the recyclability test results of 5% La-ZnO/SBA-15 over four consecutive cycles. In the initial run, the catalyst achieved 99% degradation of RhB, indicating excellent initial activity. During the second cycle, the efficiency remained at 94%, demonstrating robust structural stability. The degradation efficiency stabilized at approximately 93% in the third and fourth cycles, with no significant decline, thereby confirming consistent catalytic performance. Although minor deactivation of active sites or slight leaching of active components may have occurred during recycling, the overall performance exhibited no substantial deterioration. After four cycles, efficiency decreased by approximately 7%, underscoring the catalyst’s excellent reusability and operational stability for practical applications. As summarized in Table 2, the photocatalytic performance of the synthesized 5% La-ZnO/SBA-15 composite is compared with various ZnO-based catalysts reported in the literature for dye degradation. The comparison reveals that the 5% La-ZnO/SBA-15 composite achieves a high degradation efficiency (>99%) within a notably shorter time (40 min) under visible light. For instance, the ZnO–SiO2 composite [37] required 60 min to reach a comparable efficiency under UV light, and the flower-like ZnO@SiO2 [38] attained only 85% degradation after 180 min of UV light. These results indicate advantage and potential of the 5% La-ZnO/SBA-15 composite for efficient pollutant degradation under visible light.

3.2. Photocatalytic Mechanism Explained

To elucidate the reaction mechanism underlying the photodegradation of RhB over 5% La-ZnO/SBA-15, 50 mg of photocatalyst was dispersed in 100 mL of RhB solution (20 mg L−1), and systematic radical trapping experiments were performed (Figure 10). The addition of specific scavengers significantly inhibited the degradation efficiency: the ·O2− scavenger BQ decreased the degradation rate to 32%; ·OH and h+ co-scavenger MeOH reduced it to 38%; the h+-specific scavenger EDTA-Na lowered it to 42%; and the e− scavenger KI diminished it to 53%. In contrast, the degradation efficiency exceeded 99% in the absence of scavengers. These results unequivocally demonstrate the synergistic involvement of e−, h+, ·OH, and ·O2− in the photodegradation process.
To elucidate the charge carrier separation behavior underlying the radical trapping experiments, Photoluminescence (PL) spectroscopy was utilized to assess charge separation efficiency. In Figure 11, ZnO/SBA-15 samples with varying La doping concentrations exhibit two characteristic emission bands: a prominent broad peak near 380 nm and a weaker broad peak approximately 480 nm, corresponding to near-band-edge (NBE) radiative recombination and deep-level emission (DLE) associated with oxygen vacancies and Zn interstitial defects, respectively [43,44,45]. With increasing La doping concentration, the overall PL intensity first decreases and then increases: the undoped ZnO/SBA-15 sample shows the highest emission intensity, which decreases progressively at 2.5% and 5% La, and rises again at 7.5% La. The most pronounced fluorescence quenching is observed for the 5% La–ZnO/SBA-15 sample, indicating that this doping level provides an optimal concentration of La-induced defect states and trapping sites to promote the separation and migration of photogenerated e−–h+ pairs while suppressing their radiative recombination [46,47,48]. At higher La loading (7.5%), excessive La-related defects and/or La-rich clusters are likely formed, which act as additional recombination centers and partly offset the beneficial effect of La doping, in agreement with the partial recovery of PL intensity. The optimized charge-carrier separation at 5% La doping allows a larger fraction of photogenerated carriers to participate in surface redox reactions, thereby enhancing the photocatalytic degradation of RhB [49,50].

4. Materials and Methods

4.1. Materials

The following chemicals were utilized in the synthesis of the photocatalyst: La(NO3)3·6H2O (99%, Macklin Biochemical, Shanghai, China) and Zn(NO3)2·6H2O (99%, Macklin Biochemical, Shanghai, China) served as the La and Zn precursors, respectively; deionized water (DI), EO20PO70EO20 (P123, Mn ~5800, Sigma-Aldrich, St. Louis, MO, USA), tetraethyl orthosilicate (TEOS, 99%, Sigma-Aldrich, St. Louis, MO, USA), and HCl (37%, Sinopharm, Shanghai, China) were employed for the preparation of the SBA-15 template; and CH3CH2OH (99%, Sinopharm, Shanghai, China) was also used. All chemicals were utilized as received without further purification.

4.2. Synthesis of SBA-15

SBA-15 mesoporous material was synthesized with minor modifications to a previously established protocol [10]. In brief, 4 g of Pluronic P123 copolymer was added directly to 150 mL of 1.7 mol L−1 HCl solution and stirred in a water bath at 303 K until a colorless, transparent solution was obtained. The temperature of the bath then increased to 312 K, and 9.4 mL of TEOS was slowly added dropwise using a pipette. The mixture was continuously stirred at this temperature for 24 h. Subsequently, the solution was transferred to an autoclave and subjected to hydrothermal crystallization at 373 K for 24 h. Following the reaction, the product was collected via vacuum filtration using a Büchner funnel, and the resulting filter cake was alternately washed with deionized water and CH3CH2OH for three cycles to remove residual HCl and Pluronic P123 template. The solid was subsequently dried at 373 K for 12 h in air, followed by calcination at 823 K for 3 h in air, yielding SBA-15.

4.3. Synthesis of La-ZnO/SBA-15

La-ZnO/SBA-15 composites were synthesized using a post-impregnation technique. SBA-15 was first vacuum-dried at 343 K for 2 h. Subsequently, a predetermined amount of La(NO3)3·6H2O and 0.24 g of Zn(NO3)2·6H2O were dissolved in 10 mL of CH3CH2OH, followed by the addition of 0.2 g of the pre-treated SBA-15. The resulting mixture was uniformly dispersed with ultrasonic assistance and continuously stirred at ambient temperature for 24 h. After stirring, the mixture was dried in air at 333 K for 12 h to ensure complete solvent evaporation, followed by annealing in a tube furnace at 823 K for 2 h. Employing this procedure, a series of La–ZnO/SBA-15 samples with different La-doping levels (0, 2.5, 5.0, and 7.5 at.%) were prepared by adjusting the amount of La(NO3)3 precursor relative to Zn(NO3)2 in the impregnation solution. Here, the La content is expressed as atomic percent (at.%), defined as the molar fraction of La in the total amount of La and Zn. The synthesis route is schematically illustrated in Figure 12.

4.4. Characterization

The surface morphology of the samples was examined using a FEI Tecnai G2 F20 TEM (FEI Company, Hillsboro, OR, USA). The crystal structure and mesostructure were investigated employing a Bruker D8 Advance XRD with Cu Kα radiation (λ = 1.5406 Å). FT-IR spectra were obtained using a Nicolet 6700 spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) using the KBr pellet method, with a resolution of 4 cm−1. N2 adsorption–desorption isotherms were measured using a Micromeritics ASAP 2460 surface area analyzer (Micromeritics Instrument Corporation, Norcross, GA, USA). Prior to analysis, samples were degassed under vacuum at 373 K for 12 h. The specific surface area was calculated by the Brunauer–Emmett–Teller (BET) method. The pore-size distribution was obtained from the desorption branch of the isotherms by applying the Barrett–Joyner–Halenda (BJH) method, which uses the Kelvin equation to relate the relative pressure of capillary condensation to the mesopore radius. PL spectra were recorded with the fluorescence module of a HORIBA micro-Raman spectrometer, employing an excitation wavelength of 325 nm.

4.5. Photocatalytic Evaluation

The photocatalytic degradation of RhB at a concentration of 20 mg L−1 was investigated using La-ZnO/SBA-15 catalysts under irradiation from a 250 W Hg lamp. In the experimental procedure, 50 mg of the photocatalyst was dispersed in 100 mL of the RhB solution, followed by a 30 min dark adsorption period to achieve adsorption equilibrium. Subsequently, at 15 min intervals after the initiation of illumination, 3 mL aliquots were withdrawn and centrifuged to remove catalyst particles. The concentration of RhB was quantified by measuring the absorbance at 553 nm using a Hitachi U-3900 UV-Vis spectrophotometer.
The degradation efficiency was determined as follows:
Degradation (%) = (C0 − Ct)/C0 × 100
To elucidate the active species involved in the photocatalytic process, radical scavenging experiments were conducted using specific quenchers: benzoquinone (BQ, 0.01 mol L−1) to target ·O2−, ethylenediaminetetraacetic acid disodium salt (EDTA-Na, 0.1 mol L−1) for h+, KI (0.1 mol L−1) for surface-bound ·OH and h+, and methanol (MeOH, 0.1 mol L−1) for ·OH [18,19,20,21].

5. Conclusions

La-doped ZnO/SBA-15 mesoporous composites were prepared by an impregnation–calcination route and evaluated as visible-light photocatalysts for RhB degradation. Structural characterization confirms that the ordered 2D hexagonal mesostructure and mesoporosity of SBA-15 are preserved after ZnO and La loading, with ZnO present as amorphous or ultrafine clusters confined within the mesopores.
Photocatalytic tests show that the activity strongly depends on the La content, with the 5% La-ZnO/SBA-15 sample exhibiting the best performance: it achieves nearly complete RhB degradation within 40 min and maintains high efficiency over repeated cycles, indicating good stability. Radical trapping experiments reveal that h+ and ·OH are the main reactive species, with ·O2− also contributing, and that appropriate La doping promotes charge separation and suppresses recombination.
In summary, the combination of mesoporous confinement and optimal rare-earth doping offers a promising strategy for the design of robust photocatalytic systems aimed at the efficient degradation of organic pollutants in aqueous environments.

Author Contributions

Conceptualization, Z.Z. and W.Y.; methodology, Z.Z.; soft-ware, Z.Z.; validation, Z.Z., W.Y. and H.P.; formal analysis, Z.Z.; investigation, Z.Z.; resources, Z.Z.; data curation, Z.Z.; writing—original draft preparation, Z.Z.; writing—review and editing, Z.Z.; visualization, Z.Z.; supervision, H.P.; project administration, S.Z. and J.Z.; funding acquisition, S.Z. and J.Z. All authors have read and agreed to the published version of the manuscript.

Funding

Please add: This research was supported by the National Natural Science Foundation of China (Grant No. U1704145); the Hainan Provincial Natural Science Foundation of China (Grant No. 522MS062); the Special Research Fund of the Innovation Platform for Academicians of Hainan Province (Grant No. YSPTZX202207); and the Nature Science Foundation for High-level Talents in Higher Education of Hainan (Grant No. 422RC667).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molecules 30 04800 g001
Figure 1. SAXRD patterns of the prepared samples.
Figure 1. SAXRD patterns of the prepared samples.
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Figure 2. WAXRD patterns of the prepared samples.
Figure 2. WAXRD patterns of the prepared samples.
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Figure 3. HRTEM images of SBA-15 (a,b) and 5% La-ZnO/SBA-15 (c,d): (a) SBA-15 perpendicular to pore channels; (b) SBA-15 parallel to pore channels; (c) 5% La-ZnO/SBA-15 perpendicular to pore channels; (d) 5% La-ZnO/SBA-15 parallel to pore channels.
Figure 3. HRTEM images of SBA-15 (a,b) and 5% La-ZnO/SBA-15 (c,d): (a) SBA-15 perpendicular to pore channels; (b) SBA-15 parallel to pore channels; (c) 5% La-ZnO/SBA-15 perpendicular to pore channels; (d) 5% La-ZnO/SBA-15 parallel to pore channels.
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Molecules 30 04800 g004
Figure 4. FT-IR spectra of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
Figure 4. FT-IR spectra of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
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Molecules 30 04800 g005
Figure 5. N2 adsorption–desorption isotherms of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
Figure 5. N2 adsorption–desorption isotherms of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
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Figure 6. BJH pore size distribution curves of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
Figure 6. BJH pore size distribution curves of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
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Molecules 30 04800 g007
Figure 7. (a) Photocatalytic degradation of RhB over ZnO/SBA-15 samples with different La doping ratios under visible-light irradiation. (b) Photocatalytic degradation of RhB over blank solution, pure SBA-15, pure ZnO, La-ZnO, and 5% La-ZnO/SBA-15 under visible-light irradiation.
Figure 7. (a) Photocatalytic degradation of RhB over ZnO/SBA-15 samples with different La doping ratios under visible-light irradiation. (b) Photocatalytic degradation of RhB over blank solution, pure SBA-15, pure ZnO, La-ZnO, and 5% La-ZnO/SBA-15 under visible-light irradiation.
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Molecules 30 04800 g008
Figure 8. Pseudo-first-order kinetic fitting curves for RhB photodegradation over ZnO/SBA-15 samples with different La doping concentrations.
Figure 8. Pseudo-first-order kinetic fitting curves for RhB photodegradation over ZnO/SBA-15 samples with different La doping concentrations.
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Figure 9. Cycling degradation of RhB by the 5% La-ZnO/SBA-15 under visible light irradiation.
Figure 9. Cycling degradation of RhB by the 5% La-ZnO/SBA-15 under visible light irradiation.
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Figure 10. The degradation curve of RhB by 5% La-ZnO/SBA-15 photocatalyst under different quenching conditions.
Figure 10. The degradation curve of RhB by 5% La-ZnO/SBA-15 photocatalyst under different quenching conditions.
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Figure 11. PL spectra of La-ZnO/SBA-15 composites.
Figure 11. PL spectra of La-ZnO/SBA-15 composites.
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Figure 12. Schematic illustration of the preparation route of La–ZnO/SBA-15.
Figure 12. Schematic illustration of the preparation route of La–ZnO/SBA-15.
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Table 1. The mesoscopic structure parameters of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
Table 1. The mesoscopic structure parameters of the SBA-15, ZnO/SBA-15, and 5% La-ZnO/SBA-15.
SamplesSBET (m2/g)Pore Volume (cm3/g)Pore Diameter (nm)
SBA-15729.351.095.99
ZnO/SBA-15534.610.906.74
5%La-ZnO/SBA-15521.320.856.55
Table 2. Comparison with various ZnO-based composite photocatalysts.
Table 2. Comparison with various ZnO-based composite photocatalysts.
CatalystLight SourceDye ConcertationPhotocatalyst MassIrradiation Time (min)Efficiency (%)Reference
Y doped V-ZnO NPsVisible LightRhB3 g/L18087.5[9]
ZnO-SiO2UV LightRhB (10 mg/L)0.5 g/L6095[37]
ZnO@SiO2UV LightRhB (20 mg/L)15 g/L18082.5[38]
Ru-induced ZnO/SBA-15UV LightMB (20 mg/L)1 g/L12097.96[39]
La-doped ZnO/SiO2SunlightMG (15 mg/L)0.3 g/L12092.1[40]
ZnO/r-GOVisible LightRhB0.5 g/L150100[41]
SnO2/ZnO@GOVisible LightRhB (15 mg/L)0.2 g/L6098.9[42]
La-Doped ZnO/SBA-15Visible LightRhB (20 mg/L)0.5 g/L4099.71This work
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Zhou, Z.; Yang, W.; Zhong, J.; Peng, H.; Zhao, S. La-Doped ZnO/SBA-15 for Rapid and Recyclable Photodegradation of Rhodamine B Under Visible Light. Molecules 2025, 30, 4800. https://doi.org/10.3390/molecules30244800

AMA Style

Zhou Z, Yang W, Zhong J, Peng H, Zhao S. La-Doped ZnO/SBA-15 for Rapid and Recyclable Photodegradation of Rhodamine B Under Visible Light. Molecules. 2025; 30(24):4800. https://doi.org/10.3390/molecules30244800

Chicago/Turabian Style

Zhou, Ziyang, Weiye Yang, Jiuming Zhong, Hongyan Peng, and Shihua Zhao. 2025. "La-Doped ZnO/SBA-15 for Rapid and Recyclable Photodegradation of Rhodamine B Under Visible Light" Molecules 30, no. 24: 4800. https://doi.org/10.3390/molecules30244800

APA Style

Zhou, Z., Yang, W., Zhong, J., Peng, H., & Zhao, S. (2025). La-Doped ZnO/SBA-15 for Rapid and Recyclable Photodegradation of Rhodamine B Under Visible Light. Molecules, 30(24), 4800. https://doi.org/10.3390/molecules30244800

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