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Article

Ag/AgCl-Decorated Layered Lanthanum/Niobium Oxide Microparticles as Efficient Photocatalysts for Azo Dye Remediation and Cancer Cell Inactivation

by
Elmuez Dawi
1,* and
Mohsen Padervand
2,*
1
Department of Mathematics and Science, College of Humanities and Sciences, Ajman P.O. Box 346, United Arab Emirates
2
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh P.O. Box 55181-83111, Iran
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(7), 638; https://doi.org/10.3390/catal15070638
Submission received: 20 May 2025 / Revised: 25 June 2025 / Accepted: 27 June 2025 / Published: 30 June 2025
(This article belongs to the Special Issue Remediation of Natural Waters by Photocatalysis)
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Abstract

Ag/AgCl-decorated layered lanthanum oxide (La2O3) and niobium pentoxide (Nb2O5) plasmonic photocatalysts are fabricated through an ionic liquid-mediated co-precipitation method. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques were used to illustrate the physicochemical properties of the materials. The photoactivity was evaluated for the degradation of Acid Blue 92 (AB92) azo dye, a typical organic contaminant from the textile industry, and U251 cancer cell inactivation. According to the results, Nb2O5–Ag/AgCl was able to remove >99% of AB92 solution in 35 min with the rate constant of 0.12 min−1, 2.4 times higher than that of La2O3–Ag/AgCl. A pH of 3 and a catalyst dosage of 0.02 g were determined as the optimized factors to reach the highest degradation efficiency under solar energy at noon, which was opted to have the highest sunlight intensity over the reactor. Also, 0.02 mg/mL of Nb2O5–Ag/AgCl was determined to be of great potential to reduce cancer cell viability by more than 50%, revealed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and mitochondrial membrane potential (MMP) examinations. The mechanism of degradation was also discussed, considering the key role of Ag0 nanoparticles in inducing a plasmonic effect and improving the charge separation. This work provides helpful insights to opt for an efficient rare metal oxide with good biocompatibility as support for the plasmonic photocatalysts with the goal of environmental purification under sunlight.

1. Introduction

Environmental pollution is a serious global issue with significant outcomes adversely affecting human health and the quality of life of all creatures on Earth. With the growing population and increasing demands for higher levels of industrial activities, various organic, inorganic, and biological contaminants have been entering the ecosystem, which are of great potential to endanger the future of food and living security [1]. Dye compounds are from the organic pollutants family, with major applications in textile industries for coloring products. The existence of a variety of functional groups in the chemical structures of these compounds alongside the unsaturated bonds make them hazardous industrial effluents in water bodies, potentially convertible to secondary pollutants with higher toxicity for the ecosystem and human beings [2]. Depending upon their chemical, thermal, and photostability under outdoor conditions, dye compounds possess different lifetimes and environmental persistence, requiring appropriate strategies for being efficiently treated with the minimum possibility of secondary pollution generation [3]. Several types of techniques have been served to remove dye pollutants from the aqueous environment, among which adsorption onto solid surfaces [4], electrochemical approaches [5], biological methods [6], conventional chemical treatments [7], coagulation/flocculation [8], and photocatalytic technologies [9] have been extensively examined. Inappropriate disposal of biological waste is another problematic environmental issue in the current century that causes soil and water contamination as well as disease outbreaks [10]. Among them, cancer cells, which are the main targets of plenty of academic and hospital research activities, could produce a significant level of metabolic waste in the environment [11]. The rapid growth of the adverse ingredients of such waste materials leads to toxic effects on both human and animal body systems through influencing the quality of drinking water [12]. As a result, huge efforts have been recently made to develop efficient strategies for essential management of the corresponding effluents, among which photocatalytic technology is sorted as a promising candidate due to the green aspects and sustainability.
Photocatalysis, in particular, visible-light-driven systems, has shown promising performance in purifying polluted water bodies with such hazards [13,14]. Under sunlight, a lasting and easy-to-obtain energy source, semiconducting solid particles absorb photons to generate electron–hole pairs and trigger the chain radical formation reactions. Also, the photogenerated charge carriers could directly oxidize/reduce the contaminant structures and decompose them. To benefit from this occurrence during photocatalysis, specific efforts should be made to prolong the charge carriers’ durability under ambient conditions. Doping metal and non-metal impurities [15], defect engineering [16], heterojunction construction [17], and plasmonic nanoparticle deposition on the surface [18] are among the most versatile strategies to enhance the photoactivity of semiconducting materials aimed at promoting various applications including environmental purification from hazards and energy saving and production. In this regard, silver/silver halide nanoparticles have been extensively explored to reach highly efficient photocatalysts [18]. Ag/AgX (X is a halide) nanoparticles showed prominent potential for removing microbial pollutants from an aqueous environment [19]. When coupled with other semiconductors, these compounds result in altered morphology and the systematic construction of advanced photocatalytic schemes with significant improvement in photocatalytic performance [20]. Lei et al. studied the capacity of peroxymonosulfate-activated ZnFe2O4 coupled with Ag/AgCl nanoparticles for the removal of arsenic wastewater under visible light [21]. Peroxymonosulfate activation in this system was assigned to the loop conversion of Ag0/Ag+ on the surface. Metal–organic framework-derived AgCl/Ag-containing plasmonic photocatalysts have been recently reported for the removal of antibiotics and toxic chromium ions [22]. The improved photocatalytic performance was attributed to the amelioration of light-harvesting features caused by the surface plasmon resonance of silver nanoparticles, as well as the facilitated interfacial charge transfer between the junctions. Several other kinds of supports have been used to fabricate Ag/AgX-based photocatalytic materials, among which layered double hydroxide (LDH) materials [23,24], titanate perovskites [25,26,27], carbon nitride [28,29], metal oxides [30,31,32], and graphene oxides [33] have indicated wide applications due to their low cost, facile preparation, and environmental friendliness. Due to the electronic nature of the support materials and their unique morphologies (1D, 2D, and/or 3D), they could be differently affected by the Ag/AgX nanoparticles loading in terms of light-harvesting properties and photoactivity. The use of photoactive semiconducting materials has also gained increasing attention for purifying hospital wastewater, as well as the biological hazards released from corresponding academic activities [34,35]. This is mostly due to the challenging management of biomedical waste, especially in developing countries, which causes health hazards and imposes significant toxicity on the environment [36]. Benefiting from the facilitated generation of reactive oxygen species under sunlight by the semiconducting metal oxide powders, alongside the intrinsic antimicrobial features of the plasmonic agents (such as Ag and Au), the resulting coupled constructions are interesting candidates for biological waste treatment [34,37].
In this work, we used niobium pentoxide and lanthanum oxide as two types of rare oxide materials as support for Ag/AgCl nanoparticles through an ionic liquid-mediated approach. The crystalline phases, morphology, chemical nature, and electronic features of the photocatalysts were investigated using different techniques. The photocatalytic activity was evaluated for the removal of azo dye pollution and glioblastoma multiforme cancer cell (U251) inactivation under visible light at ambient conditions. The results were compared to understand which oxide material could efficiently function as a visible-light-driven photocatalyst aimed at environmental purification of wastewater.

2. Results and Discussion

2.1. Characterization of the Materials

XRD analysis was carried out to explore the crystalline phases of the prepared photocatalysts. All diffraction peaks for the support in the XRD pattern of the Nb2O5–Ag/AgCl sample could be indexed to the orthorhombic niobium pentoxide crystalline phase (JCPDS card No. 30-0873). The characteristic peaks and as-related crystal planes of the major phases are exhibited in Figure 1 [38,39]. The Ag and AgCl characteristic peaks are also obvious in both patterns [40], which were in the similar 2 theta degrees since the photocatalytic materials were fabricated using the same method. The sharp peaks assigned to the crystal phase of La2O3 are also demonstrated in Figure 1, which are well in agreement with card no. JCPDS 04–0856 for the lanthanum oxide structure. The results of XRD obviously confirmed the successful modification of both oxide supports with plasmonic Ag and AgCl nanoparticles to reach highly efficient photocatalysts.
SEM images were provided to demonstrate the morphological features of the obtained structures. From Figure 2 and Figure 3, both samples show a 2D morphology in the background covered with small nanoparticles on the surface, which could be attributed to the presence of Ag/AgCl nanoparticles. The dual-phase micrographs of Nb2O5–Ag/AgCl and La2O3–Ag/AgCl suggest the rapid growth of plasmonic AgCl nanoparticles in the attachment region of ionic liquid close to the sheet-like support particles where metallic Ag° could also aggregate in the surrounding area. This could favorably affect the surface area and porosity as well as catalytic active sites, which is of great significance in improving the photocatalytic performance.
More importantly, as clearly indicated in the SEM images of the photocatalytic La2O3–Ag/AgCl structure (Figure 3), the average particle (Ag/AgCl) size on the surface is estimated to be lower than 50 nm. The support nanosheets were also shown to be more effectively aggregated in this sample, which could be due to the stronger interactions of the templating agent (ionic liquid) in the interfacial regions of the lanthanum oxide nanosheets compared to the niobium oxide case.
EDX analysis was performed to describe the elemental percentage of the photocatalytic constructions on the surface. The obtained results for the Nb2O5–Ag/AgCl and La2O3-Ag/AgCl structures are shown in Figure 4 and Figure 5, containing the quantitative data in the tables inside. From Figure 4, the key elements of the first sample, as expected, include Nb, Ag, Cl, and O. The weight percentage of Ag is also around 9%, thrice that of Cl, contributing to both Ag and AgCl formation in the structures. The element with the highest abundance is oxygen, which could easily be anticipated from the stoichiometry of the support material, Nb2O5.
The obtained EDX results for the La2O3–Ag/AgCl sample are indicated in Figure 5. The abundance of oxygen in this sample is lower compared to the previous one, Nb2O5–Ag/AgCl, originating from the La2O3 stoichiometry. Although the weight percentages of silver and chlorine are also lower compared to that of Nb2O5–Ag/AgCl, the population of Ag is still 2.4-fold that of Cl, manifesting the likely existence of silver in two forms, Ag and AgCl, on the surface.
The FT-IR spectra of the fabricated photocatalysts are shown in Figure 6. This analysis was conducted to explore the chemical bond features of the constructions to better understand the surface functionality. The peaks at around 3450 and 1629 cm−1 (remarked as blue squares) could be attributed to the stretching and bending vibration modes of OH groups on the surface arising from the adsorbed water molecules. The obvious bands at 423 and 660 cm−1 in the FTIR of La2O3–Ag/AgCl (black asterisks) originate from the La-O stretching vibration [41,42]. The obvious band at 1470 cm−1 (yellow triangular symbols) in the FTIR spectrum of the La2O3-based sample could be due to the presence of carbonate in the crystalline structure of lanthanum oxide [43]. The pattern of Nb2O5–Ag/AgCl is obviously different from that of the other photocatalyst, except for the bands assigned to the adsorbed moisture on the surface. The characteristic band corresponding to the stretching vibration mode of Nb–O–Nb in the pattern of Nb2O5–Ag/AgCl appears at 640 cm−1 (red circle) [44]. The other sharp band at 853 cm−1 (red circles) is attributed to the asymmetric stretching vibration mode of Nb=O, verifying the crystalline nature of niobium pentoxide as the support [44,45].
DRS analysis was performed to explore the bandgap values of the prepared photocatalysts and compare them with each other and with the pure support. The solid-state UV–Vis spectra of the photocatalysts are indicated in Figure 7a, implying the improvement in light-harvesting properties with the surface modification strategy benefiting from the Ag/AgCl nanoparticle decoration. Furthermore, the Nb2O5–Ag/AgCl sample is expected to possess better visible-light photoactivity from its higher blue shift amount compared to the La2O3-based construction. Figure 7b exhibits the bandgap estimation curves of the samples according to the Tauc equation [46]. As shown in Figure 7b, the bandgap values are evaluated to be 2.89 and 3.12 eV for the Nb2O5–Ag/AgCl and La2O3–Ag/AgCl structures, respectively, manifesting the higher visible-light photoactivity of the Nb2O5-based sample. This factor, alongside the better morphological features of Nb2O5–Ag/AgCl, referring to its suitable particulate texture properties from the SEM images, makes it more likely to be introduced as a promising candidate for environmental purposes.

2.2. Photocatalytic Performance of the Constructions

2.2.1. Dye Contaminant Removal

The photocatalytic activity of the constructions was examined for the removal of Acid Blue 92 azo dye, a target aqueous contaminant from the textile industry, under visible irradiation. Figure 8 and Figure 9 demonstrate the obtained results, exhibiting the photocatalytic performance of the prepared photocatalysts. From Figure 8, the absorbance is dramatically reduced across all wavelengths in the presence of Nb2O5–Ag/AgCl, implying high photoactivity of the photocatalyst toward mineralizing the organic pollutant under visible light. The kinetics of the reaction were also examined by plotting Ln (A0/A) against reaction time at the maximum absorption wavelength of AB92 (574 nm) and finding the slope, resulting in a rate constant of 0.12 min−1 for this first-order reaction. Undoubtedly, these efficiency and kinetics data are significantly affected by changing the experimental conditions of the reaction and could be improved by altering and optimizing the operational factors.
The obtained results for the La2O3–Ag/AgCl sample, Figure 9, implied the lower photoactivity of this sample compared to the former case, Nb2O5–Ag/AgCl. Although the photocatalytic performance is still high, the rate constant for this sample was estimated to be 0.05, less than half of that of Nb2O5–Ag/AgCl. Different factors could contribute to this observation, among which morphology, porosity, and light-harvesting properties are the most important ones. The lower energy bandgap of Nb2O5–Ag/AgCl could enhance the visible-light activity to efficiently degrade the chromophores of the azo dye compound in an aqueous medium. From the SEM images, the more suitable texture of the photocatalyst’s surface and pore pattern for Nb2O5–Ag/AgCl is another desirable factor to ameliorate the photocatalytic performance of this material.
The PL spectra of the two photocatalysts were recorded to compare the charge separation efficiency over them. From Figure 10, the lower intensity of Nb2O5–Ag/AgCl’s emission spectrum in the excitation wavelength compared to that of La2O3–Ag/AgCl implies a longer lifetime of the photogenerated charge carriers and its lower recombination rate in this construction [47,48]. Thereby, a higher photocatalytic activity for dye degradation reaction could be expected for the Nb2O5–Ag/AgCl photocatalyst, as its lower bandgap and exterior surface morphology make this material a better candidate for photocatalytic purposes.
Further tests were conducted in the presence of Nb2O5–Ag/AgCl, as the prior photocatalyst, to achieve better photocatalytic performance by examining the pH, catalyst powder dosage, and sunlight irradiation source. By altering the solution pH, the photocatalyst surface indicates a variety of capacities for AB92 molecule adsorption and its efficient degradation under illumination [49]. The results shown in Figure 11a indicate that the highest photocatalytic efficiency was achieved at pH 3 for AB92 degradation over Nb2O5–Ag/AgCl, compared to the neutral medium and pH 8. Since the target pollutant is an anionic dye, the surrounding conditions making the photocatalyst surface more positive (acidic conditions) are rationally suitable to promote the adsorption steps effectively [50,51]. While the higher concentration of hydroxyl anions (under the basic condition) could facilitate the formation of OH radicals aimed at efficient removal of the organic contaminant from aqueous medium, in our case, the stronger interactions between the dye molecules and the positive surface of the photocatalyst during the adsorption steps is introduced as the most likely evidence for its better photocatalytic performance [52].
As frequently reported in the literature, the powder dosage could significantly affect the photodegradation efficiency over different materials [53]. The photodegradation rate was explored in the presence of three doses of the photocatalyst. A dosage of 0.02 g was found to be the best to achieve the highest photoactivity of Nb2O5–Ag/AgCl (Figure 11b). Lower doses correspond to a smaller number of catalytic active sites on the photocatalyst, which is the rational explanation for the weaker photocatalytic performance under such conditions. However, higher doses could tarnish the limpid aqueous reaction medium, which opposes the facile incidence of light photons on the surface of the solid and hinders the degradation reaction [54]. Moreover, solid particles in the presence of nearby water molecules could simply coagulate, resulting in a decrease in surface area and waste of catalytic active sites, thereby reducing the photocatalytic efficiency [55].
After finding the optimized powder dosage and pH, the irradiation source was switched to sunlight. These tests were carried out at noon in non-cloudy weather to have the highest intensity of solar energy. From Figure 11c, 75% of the dye could be removed over the aforementioned photocatalyst under sunlight and the optimist operation factors, manifesting the promising performance of the photocatalytic material with the goal of practical application. This observation is of significant importance since all attempts aim at minimizing the utilization costs of photocatalytic technologies in real-world applications [56]. Replacing artificial irradiating lights with a natural solar energy source is one of the most attractive strategies in the field.
The stability of the Nb2O5–Ag/AgCl construction after multiple uses under photocatalytic conditions was explored through recycling experiments. The obtained results shown in Figure 12a indicate that the photocatalytic activity is still desirable (81.2%) after four repeated uses, suggesting that the surface/bulk structure of the material is chemically stable for practical uses in real-world applications. The XRD analysis was conducted to provide instrumental evidence supporting the above-mentioned statement. From Figure 12b, the crystal phases of Nb2O5–Ag/AgCl kept almost unchanged with partial decreases in the intensity of some characteristic peaks assigned to both support and AgCl peaks on the surface, implying the structural stability of the plasmonic construction for being introduced as a promising photocatalyst toward environmental purification from organic wastewater and biological hazards under ambient circumstances. Figure 12c exhibits the surface morphology of the photocatalytic powder sample before and after multiple experimental tests. It implies the generation of obvious alterations in morphology texture as the surface functionality of the Nb2O5–Ag/AgCl powder (benefiting from Ag/AgCl nanoparticles) changed to the bare layered sheet-like structure of the support, Nb2O5. From this examination, the aggregation of the support layers is also intensified with repeated exposure to the aqueous solution of the pollutant, which could adversely influence the catalytic active sites. These findings could serve as essential evidence for the decrease in AB92 photocatalytic degradation efficiency from 91.0 to 81.4% under visible light.
The 2D layered texture of the support could facilitate the adsorption of the AB92 dye molecules on the surface to be sensitized toward chromophore bond dissociation and pollutant mineralization [57]. Upon light photon absorption on the surface, Ag nanoparticle photoexcitation occurred, leading to the generation of the surface plasmon resonance effect [58]. Thereafter, the photogenerated electrons transformed to the conduction band of Nb2O5 to convert molecular oxygen into superoxide reactive species. Photoexcited holes, on the other hand, accumulate in the valence band of AgCl, where water molecules could be oxidized to generate OH radicals. The high concentration of oxidizing holes in this region could also be directly triggered to decolorize the dye solution through chromophore bond dissociation [59]. Researchers have also suggested the formation of Cl0 species on the surface as a result of the incessant migration of photoexcited holes to the valence band of AgCl [58]. Cl0 is expected to be highly unstable and able to rapidly capture an electron from the AB92 molecules, thereby directly decomposing the pollutant’s molecular structure. The aforementioned photogenerated species are all extremely reactive and could efficiently promote the mineralization of AB92 organic pollution in aqueous media (Figure 13). A few quenching experiments were also performed to find the most effective species promoting the contaminant degradation process. Isopropyl alcohol, triethanolamine, and para-benzoquinone were expected to act as a hydroxyl scavenger, a hole scavenger, and a superoxide radical scavenger, respectively. According to the results, the degradation efficiency decreased to 39.5, 63.6, and 45.8%, respectively, for the corresponding chemical quenchers, illustrating that the positive holes and superoxide ion radicals play a major role in degrading AB92 over Nb2O5–Ag/AgCl under visible irradiation.
To highlight the photocatalytic effectiveness of the prepared materials, various types of La2O3- and Nb2O5-based photocatalysts are explored, and their key information is represented in Table 1. As shown in this collection, depending upon the construction design and modification strategies, La2O3 and Nb2O5 composite materials are of good potential to be promising candidates for environmental remediation. Also, the content of this table implies that the optimized plasmonic Nb2O5–Ag/AgCl photocatalyst in this work indicates an exterior photocatalytic performance towards dye contaminants mineralization under visible light compared to similar photoactive materials reported by now. This could be due to the unique morphology of the structures along with the simultaneous action of silver plasmonic effect and silver chloride existence on the surface, which ameliorated the light-harvesting properties. To reach the highest mineralization percentage, the structural stability of the pollutant under irradiation plays a key role. While some chromophores in the chemical structure of the dye compounds could be easily degraded by the photogenerated radicals in the aqueous medium, some others demand stronger photocatalytic conditions and longer treatment times to achieve the highest efficiency.

2.2.2. Anticancer Activity of the Materials

The prepared materials were explored to assess their biological activity against U251 glioblastoma cancer cells, a widely used cell line in the academic community. As the waste from such activities is released into the environment and has considerable potential to adversely affect human health and food security, attention has been focused on finding suitable approaches for their inactivation under solar light [72,73]. The MTT assay was carried out to obtain a quantitative description of the anticancer activity of the materials. According to the obtained results (Figure 14a), cell viability decreased more drastically when treated with Nb2O5–Ag/AgCl compared to pure Nb2O5, demonstrating the vital role of Ag/AgCl nanoparticles on the surface in making the microparticles strong anticancer candidates. From Figure 14a, the decrease in cell viability showed a remarkable concentration dependency for both pristine Nb2O5 and Nb2O5–Ag/AgCl. One can also observe that the rate of decrease in cell viability in the latter case (red pattern) was significantly higher than in the former case (green pattern). Based on the results, 0.02 mg/mL of the Nb2O5–Ag/AgCl powder was able to kill >50% of the cancer cell population meaningfully, while this level of antiproliferative activity for the pure support was achieved at 0.08 mg/mL of dosage, illustrating the stronger anticancer performance of the plasmonic photocatalytic material against U251 cancer cells. In fact, at this dosage of the catalyst, a sufficient amount of charge carriers and reactive oxygen species such as hydroxide and superoxide could be produced to attack the cancer cell walls and damage them, leading to cell death. The anticancer activity of these materials was also explored in dark conditions to highlight the effect of light presence in improving the performance (Figure 14b). From Figure 14b, the anticancer activity under dark conditions was significantly lower than under light conditions. In fact, the absence of light clearly hindered the efficient production of ROS, which are in charge of degrading the cell walls and decreasing cell viability. This revealed that the prepared materials are essentially visible-light active, promoting biological waste purification under ambient conditions.
The results of the MMP test for Nb2O5-Ag/AgCl and pure Nb2O5 are exhibited in Figure 15. The ratio of red to green light intensity in this pattern implies the anticancer performance of the construction, where a lower red-to-green intensity ratio indicates higher anticancer activity and vice versa. The photocatalytic structure benefits from Ag/AgCl nanoparticles on the surface, which were most frequently revealed as potent agents against pathogenic microorganisms [74]. Also, the anticancer activity of silver-containing nanomaterials has been recently reported [75,76]. The reactive oxygen species generated after light exposure of the silver/silver halide-containing materials could promote cell wall damage through different mechanisms reported in the literature [77]. Moreover, when the cancer cells come into close contact with the photocatalytic particles, the Ag/AgCl nanoparticles on the surface can efficiently interfere with normal cell-feeding phenomena through effective electronic interactions and silver ions leaching into the reaction medium [78,79], leading to inactivation of the cancer cells.
The findings of this study clearly demonstrate that the prepared materials could effectively serve as anticancer agents as well as reliable heterogeneous systems for the removal of dye compound contaminants from water resources under sunlight at normal conditions.

3. Materials and Methods

3.1. Chemical Reagents

Lanthanum oxide and niobium pentoxide powders were purchased from Shanghai Maclin Biochemical Technology and Shanghai Aladdin Bio-Chem Technology Co., Ltd., both in Shanghai, China, respectively. Silver nitrate and the 1-hexyl-3-methylimidazolium chloride ionic liquid were bought from Sigma–Aldrich Co., LLC. (Burlington, MA, USA) Double-distilled water and pure ethanol were used during the material preparation and photocatalytic tests. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and dimethyl sulfoxide (DMSO) were provided by Sigma–Aldrich Co., LLC. DMEM medium cell culture and phosphate-buffered saline (PBS) were purchased from Gibco-Thermo Fisher Scientific, Germany.

3.2. Preparation of the Constructions

Pre-determined amounts of the support material powders were well-dispersed in 55 mL of distilled water following sonication (frequency of 50 kHz and power of 70 W) for 30 min. A volume of 1.2 mL of the ionic liquid was then poured into the aforementioned suspensions under magnetic stirring at 298 K. A total of 25 mL of 0.1 M AgNO3 solution was gradually added to the vessel drop by drop, and the temperature was maintained at 50 °C for 130 min. After completion of the fabrication reaction, the obtained dark blue precipitates were centrifuged, washed with ethanol and distilled water several times, and dried at 70 °C for 18 h. The product was denoted as X–Ag/AgCl (X = Nb2O5, La2O3).

3.3. Photocatalytic Tests

All the photocatalytic experiments were performed in a double-jacket Pyrex reactor surrounded by cooling tap water to keep the temperature at 298 K. The illumination source was a 125 W mercury lamp. Further details on the experimental conditions and the light intensity of the irradiation source are provided elsewhere [80]. A volume of 2 mL of the dye solution containing the catalyst powder was taken at various time intervals and subjected to the UV–Vis spectrophotometer to assess the AB92 removal efficiency percentage according to the equation [(A0 − A)/A0] × 100 (where A0 and A are the initial absorbance and absorbance at different time intervals, respectively). The reaction rate was also explored by fitting the obtained concentrations in the first-order rate equation (ln(C0/C) vs. time) to find the rate constants.
The cancer cell treatment examinations were conducted according to the instructions reported elsewhere [12].

4. Conclusions

Layered La2O3 and Nb2O5 microparticles were decorated with Ag/AgCl nanoparticles using an ionic liquid as a templating agent to make efficient plasmonic photocatalysts. The XRD patterns obviously implied the formation of Ag0 and AgCl crystallite phases as well as the presence of the support’s characteristic peaks. SEM images demonstrate the layered shape morphology of the materials containing small nanoparticles on the surface, where the superior porosity structure could be proposed for the Nb2O5–based material. DRS revealed that the light absorption band edge of Nb2O5 moved to the visible region with Ag/AgCl loading more effectively. This could be attributed to the stronger interfacial interactions of the Nb2O5 layers and AgCl nanoparticles in the heterojunction system, enhancing the structural photostability. Accordingly, Nb2O5 acted as a better support for light-sensitive Ag/AgCl nanoparticles, where ~100% of AB92 contaminant was removed with the rate constant of 0.12 min−1 over Nb2O5–Ag/AgCl in 40 min. Also, the lower intensity of the PL emission spectrum revealed the lower recombination rate of photogenerated electron–hole pairs over Nb2O5–Ag/AgCl. This construction was able to degrade 75% of the dye solution within the same reaction time at pH 3 and 0.02 g of the catalyst powder under sunlight. Based on the results of MTT, the U251 cell viability was reduced by >50% with 0.02 mg/mL of Nb2O5–Ag/AgCl, as supported by the fluorescence microscopy images for MMP. As a whole, our findings support the idea that the biocompatible Nb2O5 material is superior to La2O3 for making plasmonic photocatalysts aimed at dye pollution and cancer cell degradation in practical applications.

Author Contributions

Conceptualization, formal analysis, data curation, funding acquisition, writing—original draft preparation, writing—review and editing, E.D. Methodology, validation, resources, writing—original draft preparation, M.P. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to gratefully acknowledge the partial funding of Ajman University, Grant ID: DRG Ref. 2024-IRG-HBS-01.

Data Availability Statement

The datasets generated during this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. XRD patterns of the prepared photocatalysts (blue pattern: Nb2O5–Ag/AgCl; orange pattern: La2O3-Ag/AgCl). L refers to lanthanum oxide, and N refers to niobium pentoxide.
Figure 1. XRD patterns of the prepared photocatalysts (blue pattern: Nb2O5–Ag/AgCl; orange pattern: La2O3-Ag/AgCl). L refers to lanthanum oxide, and N refers to niobium pentoxide.
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Figure 2. SEM images of the photocatalytic Nb2O5-Ag/AgCl powder.
Figure 2. SEM images of the photocatalytic Nb2O5-Ag/AgCl powder.
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Figure 3. SEM micrographs of the La2O3–Ag/AgCl photocatalyst.
Figure 3. SEM micrographs of the La2O3–Ag/AgCl photocatalyst.
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Catalysts 15 00638 g004aCatalysts 15 00638 g004b
Figure 4. The EDX analysis results (sample: Nb2O5–Ag/AgCl powder).
Figure 4. The EDX analysis results (sample: Nb2O5–Ag/AgCl powder).
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Figure 5. The EDX analysis results (sample: La2O3-Ag/AgCl powder).
Figure 5. The EDX analysis results (sample: La2O3-Ag/AgCl powder).
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Figure 6. FTIR spectra of the photocatalysts (blue spectrum: Nb2O5–Ag/AgCl; orange spectrum: La2O3–Ag/AgCl).
Figure 6. FTIR spectra of the photocatalysts (blue spectrum: Nb2O5–Ag/AgCl; orange spectrum: La2O3–Ag/AgCl).
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Figure 7. UV–Vis absorption spectra (a) and the corresponding Tauc plots (b) of the prepared photocatalysts.
Figure 7. UV–Vis absorption spectra (a) and the corresponding Tauc plots (b) of the prepared photocatalysts.
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Figure 8. UV–Vis spectra of the AB92 solution (a) and rate constant estimation plot (b) for the degradation tests over Nb2O5–Ag/AgCl (dye concentration: 15 ppm, room temperature, neutral pH).
Figure 8. UV–Vis spectra of the AB92 solution (a) and rate constant estimation plot (b) for the degradation tests over Nb2O5–Ag/AgCl (dye concentration: 15 ppm, room temperature, neutral pH).
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Figure 9. UV–Vis spectra of the AB92 solution (a) and rate constant estimation plot (b) for the degradation tests over La2O3–Ag/AgCl (dye concentration: 15 ppm, room temperature, neutral pH).
Figure 9. UV–Vis spectra of the AB92 solution (a) and rate constant estimation plot (b) for the degradation tests over La2O3–Ag/AgCl (dye concentration: 15 ppm, room temperature, neutral pH).
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Figure 10. The PL spectra of the prepared photocatalysts.
Figure 10. The PL spectra of the prepared photocatalysts.
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Figure 11. Optimizing the experimental conditions toward higher efficiency. (a) pH effect, (b) powder dosage effect, and (c) degradation under sunlight at the optimized pH and powder dosage values.
Figure 11. Optimizing the experimental conditions toward higher efficiency. (a) pH effect, (b) powder dosage effect, and (c) degradation under sunlight at the optimized pH and powder dosage values.
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Figure 12. The results of recycling tests (a), the XRD patterns of the photocatalyst powder before and after repeated use (b), and the SEM micrographs of the powder before and after multiple tests (c).
Figure 12. The results of recycling tests (a), the XRD patterns of the photocatalyst powder before and after repeated use (b), and the SEM micrographs of the powder before and after multiple tests (c).
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Catalysts 15 00638 g013
Figure 13. A schematic diagram for the mechanism of AB92 photocatalytic degradation over Nb2O5–Ag/AgCl.
Figure 13. A schematic diagram for the mechanism of AB92 photocatalytic degradation over Nb2O5–Ag/AgCl.
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Figure 14. The cell viability test (MTT) results under irradiation (a) and dark conditions (b) (green: pure Nb2O5; red: Nb2O5–Ag/AgCl).
Figure 14. The cell viability test (MTT) results under irradiation (a) and dark conditions (b) (green: pure Nb2O5; red: Nb2O5–Ag/AgCl).
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Figure 15. The results of MMP tests for (a) Nb2O5 and (b) Nb2O5-Ag/AgCl.
Figure 15. The results of MMP tests for (a) Nb2O5 and (b) Nb2O5-Ag/AgCl.
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Table 1. Comparison of the photocatalytic performance of the current construction with previously reported works in the literature.
Table 1. Comparison of the photocatalytic performance of the current construction with previously reported works in the literature.
StructurePollutantIrradiation SourceEfficiency (%)/Time (Min)Ref.
Nb2O5/rGOMethylene blueSolar irradiation 99.5/60[60]
Ag3PO4/Nb2O5Methyl orangeFluorescence lamp (23 W)96/60[61]
Nb2O5Rhodamine BUVC illumination98.99/60[62]
g-C3N4/Nb2O5Rhodamine B300 W xenon lamp98.1/120[63]
Nb2O5/Nb2CTxRhodamine BVisible light91.2/120[64]
Nb2O5/BiOClRhodamine BVisible light96.7/120[65]
La2O3–ZnOMethylene blueVisible light99/120[66]
Gd2O3–La2O3Methylene blueUV light84.8/120[67]
La2O3–CuOCrystal violetSunlight irradiation97.05/135[68]
OG/La2O3/ZrO2Fast green dyeVisible light irradiation89/90[69]
La2O3/SnO2Methylene blueUV light83/70[70]
La2O3/C3N4Methyl orange Visible light (λ > 420 nm)100/120[71]
Nb2O5–Ag/AgClAcid blue 92125 W mercury visible lamp>99/35this work
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MDPI and ACS Style

Dawi, E.; Padervand, M. Ag/AgCl-Decorated Layered Lanthanum/Niobium Oxide Microparticles as Efficient Photocatalysts for Azo Dye Remediation and Cancer Cell Inactivation. Catalysts 2025, 15, 638. https://doi.org/10.3390/catal15070638

AMA Style

Dawi E, Padervand M. Ag/AgCl-Decorated Layered Lanthanum/Niobium Oxide Microparticles as Efficient Photocatalysts for Azo Dye Remediation and Cancer Cell Inactivation. Catalysts. 2025; 15(7):638. https://doi.org/10.3390/catal15070638

Chicago/Turabian Style

Dawi, Elmuez, and Mohsen Padervand. 2025. "Ag/AgCl-Decorated Layered Lanthanum/Niobium Oxide Microparticles as Efficient Photocatalysts for Azo Dye Remediation and Cancer Cell Inactivation" Catalysts 15, no. 7: 638. https://doi.org/10.3390/catal15070638

APA Style

Dawi, E., & Padervand, M. (2025). Ag/AgCl-Decorated Layered Lanthanum/Niobium Oxide Microparticles as Efficient Photocatalysts for Azo Dye Remediation and Cancer Cell Inactivation. Catalysts, 15(7), 638. https://doi.org/10.3390/catal15070638

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