Eco-Friendly Synthesis of Al₂O₃ Nanoparticles: Comprehensive Characterization Properties, Mechanics, and Photocatalytic Dye Adsorption Study

Abstract

Metal and metal oxide nanoparticles are gaining traction in inorganic catalysis and photocatalysis, driving the development of eco-friendly methods. This study introduces an eco-friendly and cost-effective approach for synthesizing Al₂O₃ nanoparticles (NPs) using extracts derived from the leaves of Calligonum comosum L. The primary objective of this investigation is to assess the photocatalytic efficacy of the synthesized catalyst in addressing organic pollutants. The Al₂O₃ NPs exhibit a spherical morphology with crystalline arrangements, as evidenced by an average crystallite size of 25.1 nm in the XRD analysis. The band gap energy of the Al₂O₃ NPs is determined to be 2.86 eV. In terms of mechanical properties, the Al₂O₃ NPs show significant potential in enhancing both flexural and compressive properties, thereby making them a viable choice for improving the mechanical performance of composites. Notably, the Young’s modulus of the hybrid composite (comprising plant material and Al₂O₃ NPs) exhibits a remarkable increase of 34.4% in flexion and 78.3% in compression compared to the plant material alone. The catalytic performance of the Al₂O₃ NPs is evaluated using methylene blue (MB) as a cationic dye and Rose Bengal (RB) as an anionic dye. Impressively, the Al₂O₃ NPs demonstrate degradation efficiencies of 98.2% for MB and 90.5% for RB. The degradation processes occur under solar light irradiation, with a contact time of 120 m, a maintained pH of 7, and a temperature of 25 °C. This study found that Al₂O₃ nanoparticles are a promising, cost-effective, and environmentally friendly option for water treatment.

1. Introduction

Water, often referred to as the lifeblood of all living organisms, comprises a substantial fraction of their body mass [1]. In the contemporary era, however, industrial activities have significantly compromised this vital resource, particularly in the context of potable water and aquatic ecosystems. The extensive use of a variety of chemicals, notably dye contaminants from industries such as leather, textiles, pharmaceuticals, and cosmetics, has transformed water bodies into reservoirs of pollution. Effluents from textile industries, which are replete with a combination of organic, inorganic, polymeric, and elemental pollutants, pose a severe threat to water quality, aquatic biodiversity, soil fertility, and ecosystems at large [2,3,4,5]. In the face of these daunting challenges, nanotechnology has emerged as a promising solution, offering advanced catalytic processes to effectively mitigate water pollution. Although several wastewater treatment methods are currently in use, including flocculation, oxidation, and reverse osmosis, many of these techniques are hindered by lengthy procedures, high operational costs, and limited efficiency [6]. In stark contrast, photodegradation, especially when facilitated by photocatalysis, offers a rapid, cost-effective, and efficient alternative for water treatment [7]. Al₂O₃ NPs have demonstrated robust adsorption activity for heavy metals, thereby showing promise for water purification applications [8]. The escalating global challenge of providing clean and fresh water, particularly in the context of a growing population, is a pressing issue, with over 0.78 billion people lacking access to safe water resources [9]. Elevated concentrations of heavy metals such as lead and cadmium in water can lead to severe health issues [10,11]. Al₂O₃ NPs, with their impressive mechanical strength, including flexural, compressive, and tensile strengths, emerge as robust and versatile materials [12]; their large specific surface area and high adsorption capacity make them particularly advantageous for adsorption processes, especially at low temperatures [13]. Recent research indicates that plant extracts could potentially serve as a viable, eco-friendly option for the synthesis of nanomaterials. The active constituents present in plant extracts, including enzymes, polyphenols, phenolics, carbohydrates, and proteins, have demonstrated the ability to efficiently reduce, stabilize, and encapsulate metal ions, leading to the creation of metal nanoparticles [14]. Notably, nanoparticles produced from plant sources exhibit greater stability and uniformity in both shape and size compared to those produced by conventional chemical approaches [15]. Several studies have investigated the effect of Al₂O₃ NPs on the adsorption of cationic dyes, further highlighting their potential in addressing water pollution, for instance, Ali et al.’s work [16]. The synthesis of γ-alumina (Al₂O₃) nanoparticles involves the use of formamide and Tween-80. A_l2O₃ NPs proved effective in adsorbing methylene blue dye from water, with capacity increasing from 490 to 2210 mg g⁻¹ as initial concentration rose from 50 to 400 mg L⁻¹ under pH 9, 10 min reaction time, and 60 °C conditions. Manikandan et al. [17] synthesized green-treated (Al₂O₃ NPs) using a bio-reduction method, assessing pH’s impact on particle size. A Prunus × yedoensis leaf extract (PYLE) was used for green synthesis, exhibiting Al₂O₃ NPs’ nitrate removal (94%). The authors suggest optimizing pH and nanoparticle size for enhanced catalytic activity.

This research tackles an urgent environmental issue by synthesizing non-toxic Al₂O₃ NPs using extracts from the readily accessible and non-hazardous plant species Calligonum comosum L. The detailed analysis of these nanoparticles emphasizes their importance in fulfilling the needs of industrial applications, which demand a fine equilibrium between flexural strength, stiffness, high compressive strength, and resistance to deformation. The outcomes not only demonstrate the adaptability of this approach but also underscore its effectiveness in removing organic pollutants from water-based solutions. Additionally, the evaluation of their photocatalytic efficiency against standard organic dyes under sunlight is intended to provide useful information. The expected results suggest that the nanocomposite could serve as a sustainable and efficient solution in light industries and for tackling water pollution.

2. Materials and Methods

2.1. Materials

Leaves of Calligonum comosum L. and Arachis hypogaea L. were collected from El Oued, Algeria (coordinates: 33°22′06″ N, 6°52′03″ E). Aluminum nitrate nonahydrate (Al(NO₃)₃·9H₂O, 99%), sodium hydroxide (NaOH, 97%), Methyl blue (MB, C₁₆H₁₈C_lN₃S) and Rose Bengal (RB, C₂₀H₄₄I₄N₄O₁₃S) dyes, both with purity greater than 99%. All chemicals were procured from Biochem Chemopharama, Karlsruhe, Germany. Deionized water, which is free of minerals, was used as the solvent for all experiments.

2.2. Preparation of Plant Extract

First, fresh Calligonum comosum L. leaves were meticulously washed with distilled water to remove any contaminants. These leaves were then left to air-dry in a shaded area at room temperature, ensuring that all moisture evaporated naturally.

To prepare the extract, 10 g of the dried leaves was combined with 150 mL of deionized water. This mixture was heated to 65 °C and allowed to simmer for two hours. As the process progressed, the solution turned a light brown hue, indicating the extraction of essential compounds.

The next step involved filtering this brown solution through Whatman N°. 1 filter paper to remove any solid particles. The filtered extract was then carefully stored in a refrigerator, preserving its properties for future experiments [18].

2.3. Synthesis of Al₂O₃ NPs

To synthesize Al₂O₃ nanoparticles using a Calligonum comosum L. leaf extract, a specific protocol was followed. First, 50 mL of the leaf extract was combined with 100 mL of a 0.1 M Al(NO₃)₃·9H₂O solution. This mixture was continuously stirred at 70 °C for 2 h. During the stirring process, a 2 M NaOH solution was gradually added drop by drop. The appearance of a light yellow color in the solution indicated the formation of Al₂O₃ nanoparticles.

The resulting precipitate was separated from the reaction mixture through centrifugation at 3000 rpm for 10 min, which helped remove impurities. After centrifugation, the precipitate was dried at 80 °C for 24 h. Finally, it was calcined at 900 °C for 6 h. The end product of this synthesis was white Al₂O₃ nanoparticles [19].

2.4. The Prepared Al₂O₃ NPs for Mechanical Properties

In the synthesis of the prepared Al₂O₃ NPs for mechanical properties, we combine 10 g (70%) of the plant leaves of Calligonum comosum L. with 4.3 g (30%) of Al₂O₃ NPs, followed by the addition of a specific quantity of resin. The mixture is thoroughly blended; placed in a mold having dimensions of 30 cm by 30 cm and a thickness of 4 mm, using a vacuum method; and left to dry for 48 h. This process results in the formation of a composite material, Al₂O₃ NPs, suitable for flexural and compression tests (Figure 1).

2.5. Characterization

To determine the morphology of the Al₂O₃ nanoparticles (NPs), we employed a scanning electron microscope (SEM, Leo Supra 55, Zeiss Inc., Oberkochen, Germany), operating at 10 kV. This technique allowed us to visualize the shape and surface structure of the nanoparticles. For crystal structure verification, we performed an X-ray diffraction (XRD) analysis using a Rigaku Miniflex 600 diffractometer (Rigaku, Tokyo, Japan) with Cu-Kα radiation (λ = 1.5406 Å). The analysis covered 2θ angles ranging from 10° to 80°, providing detailed insights into the structural characteristics and grain size of the nanoparticles. To identify the functional groups present in the prepared compounds, Fourier transform infrared (FTIR) spectroscopy was conducted. We utilized a Perkin-Elmer Corporation device (Series 1725X, Norwalk, CT, USA) for this purpose. The band gap energy (Eg) of the Al₂O₃ NPs was determined using the Tauc relationship: (hv) = A (h − Eg)ⁿ. Absorption spectra were recorded with a Shimadzu UV-Vis apparatus (UV-2450, Shimadzu, Duisburg, Germany). For this measurement, samples were dispersed in distilled water, maintaining a concentration of 0.1 mg of nanoparticles in 2 mL of water.

2.6. Mechanical Properties of the Prepared Al₂O₃ NPs

Following the fabrication of the Al₂O₃ NP material, mechanical tests, specifically flexural and compression tests, were conducted on both the plant material alone and the combination of plant material with Al₂O₃ NPs. Flexural examinations utilized the Zwick Z 2.5 machine, featuring a 2 kN sensor. Conversely, compression tests were carried out using the Zwick/Roell Z10 machine (Ulm, Germany), controlled by Test Xpert software version 12.0 and equipped with a precise 10 kN force sensor. To enable a comprehensive comparison of the mechanical performance of each sample, these assessments were executed under consistent conditions, including ambient temperature and a testing speed of 5 mm/min.

2.7. Photocatalytic Degradation of RB and MB

The use of Al₂O₃ nanoparticles (NPs) in photocatalysis has proven to be highly effective in degrading hazardous AZO dyes, like methylene blue (MB) and Rose Bengal (RB), present in wastewater. This method leverages sunlight to activate the nanoparticles, leading to the formation of reactive species that can decompose the dyes. As a result, this process not only breaks down the dyes but also fully mineralizes them, presenting an eco-friendly and efficient solution for wastewater treatment [20].

To evaluate the catalytic activity of the samples, the photodegradation of MB and RB dyes in aqueous solutions under sunlight was observed. The dye solutions were prepared at a concentration of 2.5 × 10⁻⁵ M, with 5.0 mg of a dye catalyst per 5.0 mg of Al₂O₃ nanoparticles. After thoroughly mixing the samples, they were exposed to direct sunlight. The reaction’s progress was tracked using a UV-Vis spectrometer at specified intervals of 5, 15, 30, 45, 60, 75, 90, 105, and 120 min. To stop the degradation process, the solution was centrifuged at 3000 rpm for 5 min. The absorbance of MB and RB dyes was measured at wavelengths of 663 nm and 542 nm, respectively, using a UV-Vis spectrophotometer.

To evaluate the extent of adsorption, the dye concentrations (MB and RB) were monitored by comparing the initial aqueous solution with the solution post-photodegradation test [21].

$$\mathrm{q}\mathrm{e}=\frac{\left({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{e}}\right)\mathrm{v}}{\mathrm{m}}$$

(1)

The quantity of dye absorbed by the adsorbent at equilibrium is symbolized as qe (mg·g⁻¹). The dye solution’s initial concentration is noted as C₀ (mg·L⁻¹), and its concentration at equilibrium is indicated as C_t (mg·L⁻¹). In this context, “m” refers to the mass of Al₂O₃ nanoparticles utilized (g), while “V” stands for the volume of the dye solution (L). The reaction’s progress is tracked through UV-Vis spectroscopy. When Al₂O₃ NPs are added to the reaction mixture, they catalyze the reduction in the dye. The efficiency of the photodegradation of the dye (MB and RB) is determined using Equation (2) [22].

$$\mathrm{D}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o} (\%)=\frac{({\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{t}})}{{\mathrm{C}}_0}\times 100$$

(2)

3. Result and Discussion

3.1. UV–Vis Spectroscopy

Figure 2a shows UV-Vis spectra of the Calligonum comosum L. extract, revealing peaks at 211 nm (condensed tannins) [23], 232 nm (flavonoids) [24], and 276 nm (potential polyphenols) known for antioxidant properties [25,26]. In green synthesis, a solution with metal salts and a plant extract rich in tannins, flavonoids, or polyphenols is used. These compounds reduce Al³⁺ ions, leading to nanoparticle formation. The stabilizing properties of the compounds prevent nanoparticle agglomeration [27].

Figure 2b depicts the UV-Vis spectra of Al₂O₃ NPs, revealing a peak at 359 nm, and the absorption spectrum of Al₂O₃ NPs. These findings were compared to prior reports indicating an absorption peak for the biogenesis of Al₂O₃ NPs at 322 nm [28], 345 nm [29], and 382 nm [30]. Figure 2c illustrates the band gap energies of Al₂O₃ NPs, determined to be 2.86 eV. The distinct UV bands exhibited by Al₂O₃ NPs in the UV range indicate a narrow nanoparticle distribution and suggest potential applications in photocatalysis [31]. Previous studies reported varying optical band gaps for Al₂O₃ NPs produced in different solvent systems [17].

3.2. FTIR Spectroscopy Analysis

To determine the functional groups present in the leaf extract and Al₂O₃ nanoparticles (NPs), Fourier transform infrared (FTIR) spectroscopy was employed. Various peaks were observed in the FTIR spectrum of Al₂O₃ NPs at wavenumbers 3430, 2341, 1676, 1488, 1070, 828, and 586 cm⁻¹ (Figure 3). The broad peak at 3430 cm⁻¹ is indicative of the O–H vibration, typically from water molecules [32]. At 2341 cm⁻¹, a weak band appears, which corresponds to the C-H bond stretching in methyl groups [32].

In the 1676 cm⁻¹ region, bands signifying the presence of the O=C bond were detected [33]. The peak at 1488 cm⁻¹ is associated with the Al-OH bonding mode [29]. The peaks at 1070 cm⁻¹ and 828 cm⁻¹ are attributed to the symmetric bending of Al–O–H and the Al–O stretching mode in the tetrahedral structure, respectively [34]. Finally, a strong absorption band at 586 cm⁻¹ confirms the presence of the Al-O bond stretching vibration, thereby validating the formation of Al₂O₃ NPs [35].

3.3. X-ray Diffraction

Figure 4 illustrates the XRD analysis of Al₂O₃ nanoparticles, revealing the presence of gamma (γ) and delta (δ) phases. The diffraction pattern matches the standard JCPDS patterns for γ-Al₂O₃ (JCPDS 10-0425) and δ-Al₂O₃ (JCPDS 00-016-0394). The crystal characteristics are as follows: γ-Al₂O₃ adopts a cubic structure with dimensions a = 7.9000 Å, b = 7.9000 Å, c = 7.9000 Å, α = 90°, β = 90°, and γ = 90°, while δ-Al₂O₃ exhibits a tetragonal structure with dimensions a = 7.9430 Å, b = 7.9430 Å, c = 23.5000 Å, α = 90°, β = 90°, and γ = 90°. Notably, the XRD peaks used for crystallite size calculation correspond specifically to γ-Al₂O₃ nanoparticles.

Distinct diffraction peaks are observed at specific 2θ values for γ-Al₂O₃ nanoparticles, 18.14°, 31.61°, 37.71°, and 45.08°, corresponding to crystal planes (111), (220), (311), and (400), respectively. Similarly, for δ-Al₂O₃ nanoparticles, peaks appear at 16.72°, 20.40°, 29.19°, 32.34°, 33.60°, 36.42°, 40.55°, 42.96°, 52.74°, 57.00°, and 62.24°, corresponding to crystal planes (103), (114), (107), (222), (118), (312), (226), (1110), (2210), (2212), and (4010), respectively. The absence of impurity peaks in the XRD spectra underscores the high purity of the Al₂O₃ nanoparticle samples [36].

Using the Debye–Scherrer equation, the average particle size was determined.

d = kλ/βcosθ

(3)

The standalone pure Al₂O₃ nanoparticles were analyzed for crystallite size using X-ray diffraction. The crystallite size (d) was determined to be 25.1 nm, where θ represents Bragg’s angle, λ denotes the wavelength of X-ray radiation (1.5406 Å), and β represents the full width at half maximum (FWHM) of the diffraction peak. In the equation d = kλ/β, the constant k is 0.94.

3.4. Morphological and Elemental Analysis

SEM images revealed that the Al₂O₃ NPs exhibit an almost spherical shape with irregularities, displaying agglomeration and density, as shown in Figure 5a [29]. The nanoparticles also demonstrate a uniform size distribution, ranging from 30 to 40 nm, with an average size of 33 nm.

The EDX spectra of the Al₂O₃ NPs validate their purity. Both aluminum (Al) and oxygen (O) are present in the sample, constituting weight percentages of 41.36% and 58.64%, respectively. The atomic percentages indicate 32.96% for aluminum and 67.04% for oxygen, affirming that the prepared Al₂O₃ NPs are essentially free from impurities.

3.5. Mechanical Properties of the Prepared Al₂O₃ NPs

3.5.1. Flexion Test

In Figure 6a,b, the flexural test, the plant sample derived from Calligonum comosum L. leaves exhibits notable stiffness with a Young’s modulus of 347.87 MPa. The composite sample (plant + Al₂O₃ NPs) outperforms this with an impressive Young’s modulus of 530.32 MPa (

Table 1. Young’s Modulus from Flexural Test for Plant-based Samples with and without Al₂O₃ NPs.

Samples	Plant
Young’s modulus (MPa)	347.87
Samples	Plant + Al2O3 NPs
Young’s modulus (MPa)	530.32

). The Young’s modulus of the hybrid composite (plant and Al₂O₃ NPs) showed a remarkable 34.4% increase in flexion. This highlights the enhanced stiffness achieved through the incorporation of Al₂O₃ NPs, offering valuable insights for applications prioritizing flexural strength and rigidity.

3.5.2. Compression Test

In Figure 6c,d, the compression testing, the plant sample shows strong inherent strength with a Young’s modulus of 1139.23 MPa. However, the composite sample (plant + Al₂O₃ NPs), treated with aluminum oxide, exhibits remarkable improvement with a Young’s modulus of 5242.88 MPa (

Table 2. Young’s Modulus from Compressive Test for Plant-based Samples with and without Al₂O₃ NPs.

Sample	Plant
Young’s modulus (MPa)	1139.23
Sample	Plant + Al2O3 NPs
Young’s modulus (MPa)	5242.88

). The Young’s modulus of the hybrid composite (plant and Al₂O₃ NPs) showed a remarkable 78.3% increase in compression. This underscores the significant enhancement in compressive properties achieved through the strategic incorporation of aluminum oxide, valuable for applications requiring high compressive strength and resistance to deformation.

3.6. Photocatalytic Degradation of Methylene Blue and Rose Bengal

The degradation mechanism of methylene blue (MB) and Rose Bengal (RB) via pure Al₂O₃ nanoparticles under solar irradiation is driven by a sophisticated interplay of photochemical reactions. These reactions, triggered by the intrinsic semiconductor properties of Al₂O₃ NPs upon exposure to solar light, initiate a sequence of events crucial for breaking down organic dye molecules. Initially, solar photons are absorbed by the Al₂O₃ NPs, generating electron–hole pairs within the semiconductor material.

These photoinduced electron–hole pairs migrate to the surface of the photocatalyst, where they participate in redox reactions with the adsorbed dye molecules. Specifically, electrons in the conduction band (CB) of Al₂O₃ NPs reduce the dye molecules, while holes in the valence band (VB) are involved in water oxidation. This process yields reactive oxygen species (ROS) such as hydroxyl radicals (^•OH) and superoxide radicals (O₂^•−), which act as potent oxidizing agents. These ROS initiate degradation by attacking the adsorbed MB and RB molecules, thereby initiating the breakdown process (see Equations (4)–(9)) [21,22,23,26] (Figure 7).

The degradation itself involves the cleavage of chemical bonds and chromophoric groups within the dye molecules, transforming them into smaller, less chromatic fragments. The presence of Al₂O₃ NPs significantly influences the overall efficiency of the photocatalytic process under solar light irradiation.

In summary, the photocatalytic degradation of MB and RB using pure Al₂O₃ NPs under solar light is governed by the absorption of photons, leading to the generation of electron–hole pairs, which in turn drive redox reactions with the dyes on the nanoparticle surface. This cascade of events culminates in the breakdown of the dye molecules into less complex fragments, highlighting the pivotal role of Al₂O₃ NPs in enhancing the efficiency of this photocatalytic procedure.

Al₂O₃ + hv → e⁻_(CB) + h⁺_(VB)

(4)

h⁺_(VB) + H₂O → H⁺→ OH^∙

(5)

e⁻_(CB) + O₂→ O^.∙−2

(6)

h⁺_(CB) + OH ⁻→ OH∙

(7)

OH^∙ + MB or RB (dye) → CO₂ + H₂O + other degradation products

(8)

O^∙−2 + MB or RB (dye) → CO₂ + H₂O + other degradation products

(9)

The degradation of methylene blue (MB) and Rose Bengal (RB) under solar light using pure Al₂O₃ nanoparticles is visually depicted in Figure 8a–d. Initially, distinctive absorption peaks are observed at approximately 663 nm for MB and 542 nm for RB. These peaks gradually diminish as the reaction proceeds, indicating a continuous degradation process over an extended period. Figure 8 illustrates the absorption spectra, demonstrating a visible decrease in peak intensities for both dyes, accompanied by a fading of their vibrant colors over time.

The evaluation of photocatalytic activity shows that Al₂O₃ nanoparticles achieve degradation efficiencies of 98.2% and 90.5% for MB and RB, respectively, within 120 min. Notably, RB exhibits enhanced decomposition efficiency over time, consistent with findings reported in previous studies [28,31,37]. These results underscore the effective dye removal capability of Al₂O₃ nanoparticles (

Table 3. Comparison of Photocatalytic Degradation efficiency results for Al₂O₃ NPs compared to this work.

Metal NPs	Method of Synthesis	The Particle Size (nm)	Organic Pollutants	Time (min)	Dye Removal (%)	Ref.
Al2O3	green method	28	MB	150	89.1	[28]
α-Al2O3	sol–gel	42	MB	4 h	85	[37]
γ-Al2O3	precipitation	36	MB	4 h	91.6	[37]
Al2O3	sol–gel	/	MB	30	95.9	[31]
Al2O3	green method	50–100	nitrate in aqueous solution	105	94	[17]
Al2O3	chemical precipitation	/	ciprofloxacin	1–5 h	90	[38]
Al2O3	green method	25.1	MB	120	98.2	This work
			Rose Bengal		90.5

).

3.7. Recyclability and Stability

Researchers conducted experiments to evaluate the recyclability of δ-Al₂O₃ and γ-Al₂O₃ nanoparticles as photocatalysts for water purification, focusing on their ability to be separated and reused effectively. Each cycle involved drying the used photocatalysts for subsequent reuse under identical conditions as the initial cycle [39,40,41].

The results of five consecutive cycles of photocatalyst recycling are illustrated in Figure 9a,c. These findings demonstrate that δ-Al₂O₃ and γ-Al₂O₃ nanoparticles maintained high effectiveness and reusability in degrading Rose Bengal (RB) and methylene blue (MB) dyes through photodegradation. Figure 9b,d indicate a slight decrease in photocatalyst efficiency, reducing from 98.2% to 87.36% after five cycles for MB degradation, and from 90.5% to 80.32% after five cycles for RB degradation.

This decline is attributed to the inevitable loss of photocatalyst material during recycling processes such as the washing, centrifugation, or adsorption of intermediate species generated during photocatalysis [42,43]. X-ray diffraction (XRD) data in Figure 9e show consistent diffraction peaks of the Al₂O₃ nanoparticles’ photocatalyst before and after the photodegradation process across the five cycles. This stability underscores the suitability of Al₂O₃ nanoparticles for repeated use in water remediation applications [44,45].

It is worth noting that the slight decrease in decomposition efficiency over the cycles could potentially be mitigated with improved methods of catalyst recovery and reuse. Furthermore, the stability of the Al₂O₃ NPs’ photocatalyst, as evidenced by the consistent XRD diffraction peaks, is a promising indicator of their long-term viability for water remediation applications. However, further research may be needed to fully understand the long-term effects of repeated use and potential strategies for maintaining optimal performance [46,47]. It would also be interesting to explore the performance of these photocatalysts under different conditions and with different types of pollutants. This could provide a more comprehensive understanding of their potential applications in water remediation [48,49,50].

4. Conclusions

In this research, the successful synthesis of Al₂O₃ NPs using an extract from Calligonum comosum L. yielded spherical-shaped particles with a crystal structure, boasting a crystallite size of 25.1 nm. The determined band gap energy for these Al₂O₃ NPs stood at 2.86 eV. These findings underscore the importance of integrating Al₂O₃ NPs for targeted treatments of plant-derived materials. This study provides valuable insights applicable across diverse scenarios, particularly in applications requiring a delicate balance between flexural strength, rigidity, high compressive strength, and resistance to deformation. Notably, the Young’s modulus of the hybrid composite (plant and Al₂O₃ NPs) exhibited a significant 34.4% increase in flexion and a remarkable 78.3% increase in compression compared to the plant material alone. Such results not only emphasize the versatility of this innovative methodology but also highlight its potential impact on the materials industry. Furthermore, the incorporation of Al₂O₃ NPs emerges as a promising avenue for enhancing the performance of composites, with a specific focus on lightweight and high-performance materials. Notably, these biosynthesized Al₂O₃ NPs demonstrated exceptional efficacy in the removal of organic dyes. Under specific conditions, namely, a contact time of 120 min, pH = 7, and a solution temperature of 25 °C, the decomposition coefficients reached 98.2% for methylene blue (MB) and 90.5% for Rose Bengal (RB). These findings also suggest that Al₂O₃ NPs exhibit considerable potential as effective agents for wastewater treatment, particularly in the degradation of dyes. The successful synthesis and remarkable catalytic performance of these nanoparticles contribute valuable insights to the advancement of efficient and sustainable approaches for water treatment and pollution control.