Synthesis and Characterization of a Fluorinated Schiff Base from Benzimidazole and Its Metal Complexes for Antimicrobial and UV-Protective Cotton Fabrics

Abstract

Due to the lack of UV-protective properties for cotton textiles and the potential of cotton textiles to cause microbes to their users, we synthesized benzimidazole Schiff base derivative (BZI) namely N-((1H-benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methanimine and their V(III), Fe(III), Co(II), Ni(II), and Cu(II) complexes as UV protection and antimicrobial agents for cotton textile. Several techniques investigated these compounds: ¹H, ¹³C NMR, IR, UV–Vis, elemental analysis, DTA, and TGA. The Schiff base ligand behaved as a bidentate ligand. The prepared ligand and its complexes are used to treat the cotton fabrics (CFs) by immersing the fabric in the solution of the samples under ultrasonic. The treated cotton fabrics were investigated using IR and SEM-EDX analysis. The UPF values of the treated cotton fabric were obtained. The results showed that the cotton fabric treated with Fe(III) and Cu(II) complexes had excellent UV protection with UPF values of 50+. The disc diffusion method evaluated the treated cotton fabric’s antimicrobial activity. The antifungal activities of the treated CFs demonstrated that the Co(II)-BZI-CF was active on C. albicans with an inhibition zone of 12 mm, while the other samples were inactive on C. albicans and A. flavus. The V(III)-BZI-CF and Fe(III)-BZI-CF had no activity against S. aureus and E. coli bacteria while the other samples gave an inhibition zone of between 10 to 17 mm. Unlike previous studies that primarily focused on either UV protection or antimicrobial properties of metal complexes separately, this research integrates both functionalities by synthesizing benzimidazole Schiff base metal complexes and applying them to cotton textiles, demonstrating enhanced UV protection and selective antimicrobial activity.

1. Introduction

Despite cotton’s importance, it may be exposed to microbe attacks due to its ability to absorb an immense amount of moisture. It may act as a nutrient under specific humidity and temperature conditions, making it a convenient environment for the growth of bacteria and fungi [1,2,3]. Making and studying a fluorinated Schiff base from benzimidazole and its metal complexes for cotton fabrics that are antimicrobial and protect against UV light has been performed [3,4,5]. A lot of research has been conducted on adding antimicrobial agents to cotton fabrics and seeing what happens to the textiles after they are treated. Quaternary ammonium salts, N-halimane compounds [6], chitosan derivatives [7], and Schiff bases and their metal complexes based on aniline derivatives [8], pyridine acetohydrazide derivatives [9], and pyrimidinethione hydrazide derivatives [10], are some examples of these agents. Moreover, in the field of nanoparticles (NPs), for instance, graphene oxide NPs [11], silver NPs [3,12], and metal oxide NPs such as ZnO [12], CuO [13], and TiO₂ [14] were also used as antimicrobial agents.

Sun UV radiation provides some benefits to human health, e.g., the natural synthesis of vitamin D in human skin [15], and is used in the treatment of numerous skin diseases. It also has a role in reducing blood pressure and improving cardiovascular health [16]. Conversely, overexposure to UV radiation may cause harmful effects on the skin and eyes and DNA damage [17,18]. The ozone layer absorbs all UV-C and approximately 95% of UV-B radiation. Around 95% of the UV-A and only 5% of the UV-B radiation reaches the Earth’s surface and affects human skin. The harmful effects that result from UVR radiation on humans can be divided into chronic and acute effects [19]. UV-A radiation leads to skin aging, wrinkling, scaling, dryness, and chloasma and causes sun tanning and sunburn [20]. UV-B radiation causes sun tanning, erythema, blistering, photoaging, as well as photo carcinogenesis, which may raise the risk factor for melanoma or cause various skin cancers. Additionally, it may lead to damage to DNA and the eye, photokeratitis, and cataracts [20,21]. Therefore, protecting the skin from excessive exposure to UV radiation is crucial. Avoiding exposure to sunlight during peak UVR, which is in the midday period, and using sunglasses, sunscreen, and UV protection clothing are UV protection measures that are recommended [22]. Thus, the researchers have paid a lot of attention to improving the UV protection properties of textiles [23]. These properties depend on many factors: fiber type, surface of fabric, porosity, density, type of dyestuff and its concentrations, and finishing processes [21,24]. To classify textiles as having excellent UV protection, the value of the ultraviolet protection factor (UPF) should be higher than 40 [21]. Cotton fibers are considered one of the most fashionable clothing textiles in the summer due to their excellent properties such as breathability, softness, and comfort for the user. The UPF of cotton fibers is weak [22]. Therefore, the researchers have focused on modifying the cotton fabric surface using UV-blocking agents such as metal oxide nanoparticles ZnO [25] and TiO₂ [26], TiO₂/SiO₂ nanocomposites [27], azobenzene Schiff base derivatives [28], benzotriazole derivatives [29], and metal complexes based on aniline Schiff base derivatives [8], pyridine acetohydrazide derivatives [30], and pyrimidinethione hydrazide derivatives [10].

Schiff bases are important organic compounds resulting from the condensation of primary amines with carbonyl compounds (aldehydes or ketones). The Schiff base ligands are one of the most widely used ligands due to their simplicity of formation, remarkable diversity, and ability to form stable complexes with the majority of the transition metals [31,32]. They form complexes by donating the lone pair of electrons that are present on the nitrogen atom of the azomethine group(-C=N-) to the metal ion [33]. Benzimidazole moiety exhibits numerous biological activities including antimicrobial [34], antitumor [35], antidepressant [36], anti-inflammatory [37], anticonvulsant [38], anti-HIV [36], analgesic [39], antimalarial [40], antiviral [41], and antidiabetic [42]. Moreover, it is considered a significant pharmacophore in modern drug discovery. The analysis in this report [43] has mentioned the U.S. Food and Drug Administration (FDA) approved drugs, which reveals that 59% of small-molecule drugs contain nitrogen heterocycle. Benzimidazole is one of the top 25 most frequently appearing nitrogen heterocycles in small-molecule drugs. [43,44]. Some drugs that benzimidazole-based compounds are commercially available including Omeprazole and Rabeprazole (anti-ulcer), Benoxaprofen Analog (anti-inflammatory), Pantoprazole (antacid), Bendamustine Hydrochloride, and Veliparib (anti-cancer), Enviradine (anti-viral), Astemizole (antihistamine), Mebendazole and Albendazole (anthelmintic), Thiabendazole (anti-fungal and anthelmintic), Candesartan (anti-hypertensive) [45,46,47]. Furthermore, several metal complexes based on benzimidazole derivatives have been reported as antimicrobial agents [48,49]. Moreover, benzimidazole derivatives were used as UV-protective agents [50].

Previous studies used Schiff bases and their metal complexes in the finishing of textiles. Benzyl vanillin Schiff base (SB) was used as an antimicrobial, UV resistance, and good fragrance properties for polyester fabric [51]. In another study, lyocell fiber was modified with 4-Amino-benzenesulfonic acid monosodium salt Schiff base ligand and then complexed with copper ions for imparted antibacterial activity [52].

To the best of our knowledge, no work has yet been completed on the treatment of cotton fabric with N-((1H-benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methanimine. The considerations mentioned above prompted us to impart antimicrobial properties and UV protective agents to cotton fabric using a novel Schiff base, namely N-((1H-benzo[d]imidazol-2-yl) methyl)-1-(4-fluorophenyl) methanimine (BZI) and its metal complexes. In our study, five metal ions, namely V(III), Fe (III), Co (II), Ni (II), and Cu (II) are used. Several techniques investigated the BZI and its metal complexes: ¹H and ¹³C NMR, IR, UV–Vis, elemental analysis, and thermal analysis (DTA and TGA). The treated cotton fabrics (CFs) were characterized by IR and SEM-EDX analysis. The UPF values of the treated CFs were obtained. In addition, the antimicrobial activity of the treated CFs was also investigated.

2. Experimental Section

2.1. Materials

Pure bleached 100% cotton fabric (138 g·m⁻²) was purchased from Misr for Spinning and Weaving Company at Mehalla El-Kobra, Egypt.

2.2. Chemicals

4-fluorobenzaldehyde, DMSO, DMF, ethanol, and VCl₃ salt were purchased from Sigma Aldrich (MO, USA), while the other metal salts were obtained from Loba Chemie (Mumbai, India). 1H-benzo[d]imidazol-2-yl)methanamine was provided from BOC Sciences (WA, USA).

2.3. Instruments

Fourier transform infrared (FT-IR) spectra were recorded using an Agilent Cary 600 FTIR spectrometer (Santa Clara, CA, USA) across a wavenumber range of 4000–400 cm⁻¹. Ultraviolet–visible (UV–Vis) spectra for the ligand and metal complexes in the DMSO solution were measured with a Shimadzu UV-1800 spectrophotometer (Duisburg, Germany) over a wavelength range of 200–1100 nm. Proton (¹H) and carbon (¹³C) nuclear magnetic resonance (NMR) spectra were acquired on a Bruker Avance 400 MHz NMR spectrometer using DMSO-d6 as the solvent, with tetramethylsilane (TMS) as the internal reference. X-ray diffraction (XRD) patterns of the ligand and metal complexes were obtained using a Rigaku Ultima-IV diffractometer (Tokyo, Japan) operating at 40 kV and 40 mA, with Cu Kα radiation (λ = 1.54180 Å). Data were collected over a 2θ range of 10–90° with a step size of 0.02°.

The molar conductivity (Λm) of DMF solutions of the metal complexes, at a concentration of 1 × 10⁻³ M, was measured at 25 °C using the Session+ MM374 conductivity meter (Hach, Loveland, CO, USA). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the metal complexes were performed using a Shimadzu DTG-60AH system (Kyoto, Japan) under nitrogen flow at a heating rate of 10 °C/min, in the temperature range of 21–550 °C, with aluminum oxide (Al₂O₃) as the reference material for DTA. The melting points of the synthesized compounds were determined using a Stuart SMP-30 apparatus (Staffordshire, UK). Magnetic susceptibility measurements of the metal complexes were carried out at 25 °C using an Auto magnetic susceptibility balance from Sherwood Scientific (Cambridge, UK). Scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDX) analysis was performed using a TESCAN Vega III system (Brno, Czech Republic) equipped with EDX spectroscopy.

2.4. Preparation of N-((1H-Benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methenamine Ligand: (BZI) (1)

To synthesize the Schiff base ligand, a solution of 4-fluorobenzaldehyde (124.11 mg, 1 mmol) was prepared in 10 mL of ethanol. This solution was then combined with a solution of 1H-benzo[d]imidazol-2-yl)methenamine (147.18 mg, 1 mmol) in 10 mL of ethanol. The mixture was stirred continuously for 6 h to ensure thorough reaction. As the reaction progressed, a yellowish-orange precipitate formed, indicating the formation of the Schiff base ligand. This precipitate was collected by filtration and washed multiple times with ethanol to remove any impurities. Finally, the purified precipitate was allowed to dry, resulting in the desired Schiff base ligand (Scheme 1).

The synthesized Schiff base ligand was obtained with a yield of 68%, and it exhibited a yellowish-orange color. The melting point of the compound was determined to be 125 °C.

Elemental Analysis (E.A.): The experimental elemental analysis results for the compound C15H12FN3 (molecular weight: 253.28 g/mole) were found to be in good agreement with the calculated values. The measured percentages were 71.48% for carbon (calculated: 71.13%), 5.06% for hydrogen (calculated: 4.78%), and 16.78% for nitrogen (calculated: 16.59%).

FT-IR Spectroscopy: The FT-IR spectrum of the compound showed characteristic absorption bands. The band at 3330 cm⁻¹ corresponds to the stretching vibration of the NH group. Weak bands at 2970 cm⁻¹ and 2874 cm⁻¹ are attributed to the C-H stretching vibrations. The strong bands at 1683 cm⁻¹ and 1599 cm⁻¹ are indicative of the C=N stretching vibrations, confirming the formation of the Schiff base. Additionally, the band at 1153 cm⁻¹ is associated with the C-F stretching vibration.

1H-NMR (400 MHz, DMSO-d6): The ¹H-NMR spectrum displayed a singlet at δ 12.18 ppm, corresponding to the NH proton. Another singlet at δ 8.8 ppm was assigned to the N=CH proton. The aromatic protons appeared as a multiplet in the range of δ 7.63–7.16 ppm, integrating for 8 protons.

¹³CNMR (400 MHz, DMSO-d6) (δ, ppm): The ¹³CNMR (400 MHz, DMSO-d6) spectrum showed signals at δ 166.85 ppm (C16), 161.15 ppm (C12), and 142.31 ppm (C8), which are characteristic of the imine and aromatic carbons. The aromatic carbon signals were observed in the range of δ 135.92–115.18 ppm. Additionally, a signal at δ 50.59 ppm was attributed to C10.

These analytical results confirm the successful synthesis and characterization of the Schiff base ligand.

2.5. Preparation of Metal Complexes

To synthesize the metal complexes, 2 mmol of various metal chloride salts ((VCl₃, FeCl₃·6H₂O, CoCl₂·6H₂O, NiCl₂·6H₂O, or CuCl₂·2H₂O) were each dissolved in 10 mL of ethanol. Separately, 2 mmol of the Schiff base ligand N-((1H-benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methanimine (BZI) (253 mg) was also dissolved in 10 mL of ethanol.

The metal chloride solution was then mixed with the BZI solution, and the resulting mixture was subjected to reflux for a period of 4 to 6 h, depending on the specific metal salt used. Refluxing ensures that the reaction mixture is heated to the boiling point of ethanol, allowing the reaction to proceed efficiently while preventing the solvent from evaporating.

As the reaction progressed, the formation of the metal complexes was indicated by the appearance of a precipitate. The resulting complexes were isolated by filtration, washed several times with hot ethanol to remove any unreacted starting materials or impurities, and then dried under vacuum over CaCl₂ to ensure complete removal of any residual solvent.

This methodical approach to synthesizing metal complexes ensures high purity and yield of the desired products, which can then be further characterized and studied for their chemical properties and potential applications.

2.5.1. V(III)-Complex (2)

Yield (60%), color: brown, m.p. = 278 °C, Ʌ_m = 13.45 (Ω⁻¹mol⁻¹cm⁻²), μ_eff = 2.82 BM. E.A. of [V(BZI)(Cl)₃(H₂O)]·2H₂O, C₁₅H₁₈Cl₃FN₃O₃V, (464.62 g·mol⁻¹): Found (calcd.) %C 39.07 (38.78), %H 4.21 (3.91), %N 9.26 (9.04), %Cl 23.11 (22.89), %V 11.17 (10.96). FT-IR (cm⁻¹), 3528–2767 ν(H₂O), 2961w, 2850w ν(C-H), 1679 and 1597 ν(C=N), 593 ν(N→V), 505 ν(N→V), 412 ν(M-Cl).

2.5.2. Fe(III)-Complex (3)

Yield (78%), m.p. > 300 °C, color: reddish brown, Ʌ_m = 12.39 (Ω⁻¹mol⁻¹cm⁻²), μ_eff = 5.67 BM. E.A. of [Fe(BZI)(Cl)₃(H₂O)]·H₂O, C₁₅H₁₆Cl₃FFeN₃O₂, (451.51 g·mol⁻¹): Found (calcd.)%C 40.27 (39.90), %H 4.19 (3.75), %N 9.54 (9.31), %Cl 23.72 (23.55), %Fe 12.48 (12.37). FT-IR(cm⁻¹), 3293–3087 ν(H₂O), 2978w, 2888w ν(C-H), 1601 and 1536 ν(C=N), 548 ν(N→Fe), 533 ν(N→Fe), 421 ν(M-Cl).

2.5.3. Co(II)-Complex (4)

Yield (59%), m.p. > 300 °C, color: olive green, Ʌ_m = 2.55 (Ω⁻¹mol⁻¹cm⁻² ), μ_eff = 4.83 BM. E.A. of [Co(BZI)(Cl)₂(H₂O)₂]·H₂O, C₁₅H₁₈Cl₂CoFN₃O₃, (437.16 g·mol⁻¹): Found (calcd.) %C 41.53 (41.21), %H 4.77 (4.51), %N 9.74 (9.61), %Cl 16.48 (16.22), %Co 13.65 (13.48). FT-IR (cm⁻¹), 3684–3257 ν(H₂O), 2981w, 2884w ν(C-H), 1601 and 1575 ν(C=N), 577 ν(N→Co), 527 ν(N→Co), 417 ν(M-Cl).

2.5.4. Ni(II)-Complex (5)

Yield (81%), m.p. = 283 °C, color: burgundy, Ʌ_m = 13.20 (Ω⁻¹mol⁻¹cm⁻²), μ_eff = 2.91 BM. E.A. of [Ni(BZI)(Cl)₂(H₂O)₂]·3H₂O, C₁₅H₂₂Cl₂FN₃NiO₅, (472.95 g·mol⁻¹): Found (calcd.) %C 37.89 (38.09), %H 4.47 (4.69), %N 8.59 (8.88), %Cl 14.69 (14.99), %Ni 12.33 (12.41). FT-IR(cm⁻¹), 3634–2514 ν(H₂O), 2965w, 2865w ν(C-H), 1673 and 1597 ν(C=N), 595 ν(N→Ni), 517 ν(N→Ni), 427 ν(M-Cl).

2.5.5. Cu(II)-Complex (6)

Yield (70%), m.p. > 300 °C, color: olive green, Ʌ_m = 14.52 (Ω⁻¹mol⁻¹cm⁻²), μ_eff = 1.69 BM. E.A. of [Cu(BZI)(Cl)₂(H₂O)₂]·H₂O, C₁₅H₁₈C_l2CuFN₃O₃, (441.77 g·mol⁻¹): Found (calcd.) %C 40.91 (40.78), %H 4.36 (4.11), %N 9.73 (9.51), %Cl 16.13 (16.05), %Cu 14.47 (14.38). FT-IR (cm⁻¹), 3382–2780 ν(H₂O), 2960w, 2884w ν(C-H), 1711 and 1633 ν(C=N), 543 ν(N→Cu), 531 ν(N→Cu), 436 ν(M-Cl).

2.6. Treatment of Cotton Fabric by Prepared Ligand and Its M-Complexes

To prepare the treated cotton fabrics, the Schiff base ligand (BZI) or its metal complex (M-complex) was first dissolved in 30 mL of ethanol (EtOH). This solution was then subjected to sonication at 50 °C for 5 min. Sonication helps to ensure that the compound is thoroughly dissolved and evenly distributed in the solvent by using ultrasonic waves to agitate the particles.

Next, 1 g of cotton fabric was immersed in the prepared ethanolic solution. The fabric was then sonicated for an additional 20 min at 50 °C. This step allows the compound to penetrate the fabric fibers more effectively, ensuring a uniform treatment.

After sonication, the treated fabric samples were dried at 50 °C for 10 min. This drying step helps to remove the bulk of the ethanol solvent. Finally, the samples were washed repeatedly with deionized water to remove any unbound or excess compound and then dried again to ensure that the fabric was free of any residual moisture.

This method ensures that the cotton fabric is uniformly treated with the ligand or metal complex, potentially imparting new properties to the fabric, such as enhanced durability, antimicrobial activity, or other desired characteristics.

2.7. Ultraviolet Protection Factor (UPF)

The UPF of the treated cotton fabrics was measured using a Shimadzu UV-3101 spectrophotometer (company of Shimadzu in Kyoto from Japan). This instrument operates in the wavelength range of 200–400 nm, which encompasses the ultraviolet (UV) spectrum. The UPF value indicates how effectively the fabric can block UV radiation, providing a measure of its protective capability against harmful UV rays.

2.8. In Vitro Antimicrobial

The antimicrobial properties of the treated fabric samples were assessed using the disc diffusion method. This method involves placing discs of the treated fabric on agar plates inoculated with specific microorganisms. The microorganisms tested included:

• Gram-positive bacteria “Staphylococcus aureus (S. aureus) (AATCC12600)”
• Gram-negative bacteria “Escherichia coli (E. coli) (ATCC11775)”
• Fungi “Candida albicans (C. albicans) (ATCC 7102)” and Aspergillus flavus (A. flavus) (ATCC 9643)

The antimicrobial activity is determined by measuring the zone of inhibition around the fabric discs, which indicates the effectiveness of the treatment in preventing microbial growth. This method provides a clear and quantifiable way to evaluate the antimicrobial properties of the treated fabrics against a range of pathogenic microorganisms.

3. Results and Discussion

3.1. Chemistry

Schiff base ligands have garnered significant attention in coordination chemistry due to their versatile binding properties and potential applications in various fields, including catalysis, material science, and medicinal chemistry. In this study, we focus on the synthesis and characterization of a Schiff base ligand, N-((1H-benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methanimine (BZI), and its metal complexes.

The Schiff base ligand (BZI) was synthesized through a condensation reaction between 4-fluorobenzaldehyde and 1H-benzo[d]imidazol-2-yl)methenamine. This reaction results in the formation of a ligand with both imine and aromatic functionalities, which are known to coordinate effectively with various metal ions.

To explore the coordination chemistry of BZI, it was reacted with different metal chloride salts, including (VCl₃, FeCl₃·6H₂O, CoCl₂·6H₂O, NiCl₂·6H₂O, or CuCl₂·2H₂O). The resulting metal complexes were subjected to a comprehensive suite of analytical techniques to elucidate their structures and properties. These techniques included UV–Vis spectroscopy, FT-IR spectroscopy, elemental analysis, X-ray diffraction (XRD) powder analysis, and thermal analyses (TGA and DTA).

Elemental analysis revealed that the metal salts interacted with the ligand in a 1:1 molar ratio (1 metal: 1 ligand), as depicted in Figure 1. The general formula for the V(III) and Fe(III) complexes was determined to be [M(BZI)(Cl)₃(H₂O)]·nH₂O, n = 2, n = 1, for V(III) and (n = 1) for Fe(III). For the Co(II), Ni(II), and Cu(II) complexes, the general formula was [M(BZI)(Cl)₂(H₂O)₂]·nH₂O, where n = 1, n = 3, n = 1, with (n = 1) for Co(II), (n = 3) for Ni(II), and (n = 1) for Cu(II).

The Supplementary Materials provide detailed information on the physical properties and the results of FT-IR, XRD, and thermal analyses (TGA and DTA) for both the ligand and its metal complexes. These analyses confirm the successful synthesis of the metal complexes and provide insights into their structural and thermal stability, which are crucial for their potential applications in various domains.

UV–Visible Spectra and Magnetic Susceptibility

The UV–Visible spectra of the BZI ligand and its M-complexes were studied in DMSO at 200–1100 nm (Figure 2a,b), and their data were recorded in

Table 1. UV–Vis spectral data of the ligand and its M-complexes.

Comp. No.	Compounds	λmax (nm)	ν (cm−1)	Electronic Transitions
1	BZI	421 358 301	24,272 27,933 33,223	n → π* π → π* π → π*
2	V(III) comp.	719 424 351 297	13,908 24,096 28,490 33,670	3T1g (F) → 3T2g (F) n→ π* π → π* π → π*
3	Fe(III) comp.	655 554 437 327 294	15,267 18,050 22,883 30,581 34,014	6A1g → 4T2g (G) 6A1g → 4T1g (G) n → π* π → π* π → π*
4	Co(II) comp.	705 622 519 449 349 292	14,184 16,077 19,268 22,272 28,653 34,247	4T1g (F) → 4T2g (F) 4T1g (F) → 4A2g (F) 4T1g (F) → 4T1g (P) n → π* π → π* π → π*
5	Ni(II) comp.	500 466 327 289	20,000 21,459 30,581 34,602	3A2g (F) → 3T1g (P) n → π* π → π* π → π*
6	Cu(II) comp.	989 707 513 440 352 300	10,111 14,144 19,493 22,727 28,409 33,333	2B1g → 2A1g 2B1g → 2B2g 2B1g → 2Eg n → π* π → π* π → π*

. As observed in the UV–Vis spectrum of the BZI ligand, three distinct absorption bands are present. The band with the maximum energy, which is observed at 301 nm, can be attributed to the transition of the benzene ring from π to π*. On the other hand, the band appearing at 358 nm is associated with the transition of the imine group from π to π*. It is believed that the n → π* transition of the imine group is responsible for making the lowest energy band appear at a wavelength of 421 nm [53]. There was a bathochromic shift of the n → π* transition in all complexes when compared with the ligand, which is proof of the participation of imine nitrogen in chelation with metallic ions. This shift occurred as a result of the coordination process [54]. A broad absorption band at 719 nm is observed in the visible spectra of the V(III) complex, as depicted in Figure 2b. This band is attributed to the transition from ³T_1g to ³T_2g (F), which suggests that the V(III) complex possesses an octahedral (Oh) organization. There is a correlation between the d² electronic structure of V(III) complexes in an Oh geometry and the magnetic moment value of the V(III) complex, which is 2.52 BM [55]. A pair of absorption bands may be observed in the visible spectra of the Fe(III) complex. These bands are located at 655 and 554 nm, and they are attributed to the transitions from ⁶A_1g to ⁴T_2g (G) and ⁶A_1g to ⁴T_1g (G), respectively. In accordance with the Oh geometry of the Fe(III) ion, these transitions manifest themselves. There is a high spin Fe(III) configuration (d⁵) that is compatible with the μeff value of the Fe(III) complex, which is 5.67 BM [56]. There are three transitions that can be found in the visible spectrum of the Co(II) complex. These transitions are located at 705, 622, and 519 nm. These transitions are described as follows: ⁴T_1g (F) → ⁴T_2g (F), ⁴T_1g (F) → ⁴A_2g (F), and ⁴T_1g (F) → ⁴T_1g (P), respectively. These transitions indicate the octahedral geometry around the Co(II) ion [54,57,58]. The Co(II) complex has a magnetic moment of 4.83 BM, which corresponds with high spin octahedral Co(II) ion (d⁷) [59]. In the case of the Ni(II) complex visible spectrum, there is one absorption band present at 500 nm, which is assigned to ³A_2g (F) → ³T_1g (P) transition and that proves that the Ni(II) complex has an octahedral structure [60]. The μ_eff value of the Ni(II) complex is equal to 2.91 BM, which is compatible with the d⁸ electronic structure of Ni(II) complexes in the geometry of an Oh [61]. In the visible spectrum of the Cu(II) complex, there are three absorption bands that may be observed at 989, 707, and 513 nm. These bands are attributed to the transitions of ²B_1g → ²A_1g, ²B_1g → ²B_2g, and ²B_1g → ²E_g, which occur sequentially. A tetragonal distorted octahedral geometry is confirmed by the fact that the magnetic moment value of the Cu(II) complex is 1.69 BM. This indicates that the Cu(II) complex follows this geometry [62].

3.2. Characterization of the Treated Cotton Fabric

In the realm of textile engineering, the characterization of treated cotton fabrics is pivotal for understanding their enhanced properties and potential applications. This study employs a comprehensive suite of analytical techniques to evaluate the modifications imparted to the cotton substrates. The treated cotton fabrics were meticulously analyzed using the following methodologies:

3.2.1. FTIR Spectra

The IR spectra of the blank CF and treated CFs were obtained and depicted in Figure 3. In the blank cotton fabric spectrum, the peaks characteristic of the cellulose structure were observed. The band around 3315 cm⁻¹ is attributed to the stretching vibration of the OH group [63]. It was found that the stretching and bending vibrations of C-H caused the weak peaks that were observed at 2898 cm⁻¹ and 1369 cm⁻¹, respectively [30]. Vibrations in the range of 1500–800 cm⁻¹ are referred to as O-H vibrations, C–O vibrations, and C–O–C vibrations, respectively [64]. After treatment of the CFs with BZI and its M-complexes, it is observed that all the treated samples exhibited the characteristic peaks of the cellulose structure. Furthermore, the appearance of peaks at 1658 cm⁻¹ and 1641 cm⁻¹ in the infrared spectra of BZI-CF is found. These peaks are associated with the stretching vibration of the C=N groups of the azomethine and benzimidazole rings, respectively [65]. After complexation process, C=N bands (azomethine and benzimidazole ring) shifted to lower wavenumber by (1647 and 1635 cm⁻¹) for V(III) complex, (1650 and 1637 cm⁻¹) for Fe(III) complex, (1643 and 1631 cm⁻¹) for Co(II) complex, (1645 and 1633 cm⁻¹) for Ni(II) complex, and (1647 and 1635 cm⁻¹) for Cu(II) complex. These types of bonding are confirmed by the appearance of a peak near 592–530 cm⁻¹ in all IR spectra of M-BZI-CF which corresponds to the vibration of (M-N) [66]. Moreover, a new peak presents near 437–410 cm⁻¹ in all IR spectra of M-BZI-CF, which can be referred to as the vibration of (M-Cl) [67]. The broadband that appears in the IR spectra of the treated CFs at 3550–3112 cm⁻¹ may be attributed to the hydrogen bonding that forms between the NH of the benzimidazole ring and OH groups of the cellulose CF (Scheme 2) [63]. These results indicate the success of adsorption of the BZI and M-BZI complexes on the cellulose surface of CFs.

The supposed mechanism of the treated CFs by BZI and its complexes is demonstrated in Scheme 2. The BZI ligand bonded to the cellulose molecule of the cotton fabric by the formation of hydrogen bonding between NH of the benzimidazole ring and the OH moiety of the cellulose. After the complexation process, the OH moieties of the cellulose chains bonded to metal ions via coordinated bond, forming a stable complex.

3.2.2. SEM/EDX Analysis

The SEM study was performed to investigate the surface morphology of cotton fabric both before and after it was treated with BZI or its metal complexes V(III), Fe(III), Co(II), Ni(II), or Cu(II). (Figure 4). As illustrated in this figure, the surface morphology of the blank cotton fabric is smooth. After the treatment process, it was observed that the surface morphology of all treated cotton fabrics was completely different from the untreated fabric. They have irregular and rough surfaces, as shown in Figure 4b–g, which indicates the success of the treatment process. The EDX analysis of the blank CF, BZI-CF, and M-BZI-CF (M is V(III), Fe(III), Co(II), Ni(II), or Cu(II)) was also applied, which provided important information that supported the SEM results (Figure 4). The EDX result of the blank CF (Figure 5a) demonstrates that there are only oxygen and carbon elements with atomic percentages of 49.18% and 50.82%, respectively. The appearance of new peaks belonging to fluorine and nitrogen elements in the EDX spectrum of BZI-CF (Figure 5b) indicates the success of the treatment process of cotton fabric with BZI. As illustrated in Figure 5c–g, the existence of new peaks corresponding to chlorine element and V(III), Fe(III), Co(II), Ni(II), or Cu(II) metal, respectively, confirm the successful processing of the cotton fabric by the BZI metal complexes.

3.2.3. Ultraviolet Protection Properties

Table 2. The ultraviolet protection values of treated cotton fabrics.

Sample	Value of UPF	UV Protection Category
Blank CF	3.7	Non rating
BZI-CF	18.9	Good
V(III)-BZI-CF	30.3	Very good
Fe(III)-BZI-CF	57.7	Excellent
Co(II)-BZI-CF	34.4	Very good
Ni(II)-BZI-CF	28.7	Very good
Cu(II)-BZI-CF	51.8	Excellent

displays the results of the determination of the UPF values for both the blank CF and the treated CF. A total of three categories were established by the Australian and New Zealand Standard AS/NZS 4399 (AS/NZS 4399: 1996) for the ultraviolet protection factor (UPF) of sun protective fabrics, apparel, and personal wear (such as headwear) that are worn near the skin. A good UPF value falls between 15 and 24; a very good UPF value falls between 25 and 39; and an excellent UPF value falls between 40 and 50 or higher [68]. Based on this standard, the blank CF provided insufficient protection, with UPF value equal to 3.7. The UPF value of BZI-CF was 18.9, which offered good protection. After the coordination process, it was observed that the UPF values increased depending on the metal ion used. The Ni(II)-BZI-CF, V(III)-BZI-CF, and Co(II)-BZI-CF had very good protection with UPF values of 28.7, 30.3, and 34.4, respectively. Both Cu(II)-BZI-CF and Fe(III)-BZI-CF showed the highest protection (UPF value of 50+), which is classified as an excellent protection level. Conjugated imine bonds with aromatic rings in BZI-CF and its metal complex increase UV absorbance by assisting electron transfer from π and n orbitals to π* orbitals or intramolecular proton transfer in the excited state [69]. The Fe(III) and Cu(II) showed the highest UPF value this may be due to the high absorbance of UV radiation due to the d-d transition and charge transfer, which facilitate the absorption of UV radiation and so the UPF increase.

Based on these results, it was observed that the treated CFs provided higher protection than the blank CF. These high UPF values may be related to the π-π* conjugated system and n-π* transitions of the BZI ligand and its metal complexes [30].

3.2.4. Antimicrobial Properties

The disc diffusion method was used to test the antibacterial activity of the treated and blank cotton fabrics against the pathogen’s G+ and G− bacteria, respectively. Also tested were the samples against Candida albicans and Aspergillus flavus, two kinds of fungus.

Table 3. The inhibition zone diameter of the blank CF and treated samples.

Sample	Inhibition Zone Diameter (mm/cm Sample)
	Bacterial Species	Fungal Species
	S. aureus (G+)	E. coli (G−)	C. albicans	A. flavus
Blank CF	0	0	0	0
BZI-CF	13	12	0	0
V(III)-BZI-CF	0	0	0	0
Fe(III)-BZI-CF	0	0	0	0
Co(II)-BZI-CF	17	15	12	0
Ni(II)-BZI-CF	15	13	0	0
Cu(II)-BZI-CF	14	13	0	0

shows the documented inhibitory zones. The samples of BZI-CF, Co(II)-BZI-CF, Ni(II)-BZI-CF, and Cu(II)-BZI-CF exhibited antibacterial activity against S. aureus and E. coli, with inhibition zones ranging from 10 to 17 mm, according to the results of the antibacterial activity test. Additionally, it was observed that the tested samples exhibited higher antibacterial activity against S. aureus (G+) compared to E. coli (G−), potentially due to the differences in their cell membranes [10]. The antibacterial activity of these M-complexes was greater than that of their ligand, BZI-CF. The chelation theory proposed by Tweedy and Overtone may shed light on this finding. Overtone proposed the idea of cell permeability, which states that because cellular membranes are lipid-based, only molecules that are soluble in lipids are allowed to flow through them. Consequently, the antibacterial activity is controlled by liposolubility, an important component. The strong polarity of metallic cations makes it difficult for them to pass through cell membranes [70,71]. The overlap of the orbitals of the ligand and metallic ion significantly reduces the metal polarity after chelating the ligand with metallic ions. As a result, the donor groups can partially neutralize the positive charge on the metal. Furthermore, it heightens the lipophilicity of the M-complexes and the delocalization of π-electrons throughout the entire chelating ring. Because of this, the M-complex can cross lipid cell membranes and block microbial enzymes from attaching to metals [72,73]. The antifungal activity results of the samples demonstrated that all the samples were inactive against A. flavus and C. albicans except the Co-BZI-CF, which was active only against C. albicans.

Finally, the suggested order of activity for the compounds indicates that Co(II)-BZI-CF exhibits the highest antimicrobial activity, particularly against S. aureus, E. coli, and C. albicans, while V(III)-BZI-CF and Fe(III)-BZI-CF show no activity at all.

4. Conclusions

This study effectively synthesized a novel Schiff base ligand, N-((1H-benzo[d]imidazol-2-yl)methyl)-1-(4-fluorophenyl)methanimine, as well as complexes with V(III), Fe(III), Co(II), Ni(II), and Cu(II). Various physical and spectral investigations were used to characterize these substances. The findings show that the M-complexes were non-electrolytic and produced at a molar ratio of 1:1. While Ni(II) exhibited a hexagonal crystal structure, the ligand and V(III) combination exhibited a tetragonal one, according to the XRD results. Complexes with iron(III) and copper(II) have monoclinic and triclinic crystal structures, respectively.

The SEM results demonstrated that all the treated samples had deposited on the CF surface. The UPF of the treated CF sample’s findings show that the samples have a UV protection efficiency range from good to excellent. Among them, the Cu(II) -BZI-CF and Fe(III) -BZI-CF have excellent UV protection with a UPF value of 50+. The antimicrobial activities of the treated CFs were investigated. The Co(II)-BZI-CF was effective against C. albicans with an inhibition zone of 15 mm, whereas the other treated samples were inactive on A. flavus and C. albicans. The BZI-CF, Co(II)-BZI-CF, Ni(II)-BZI-CF, and Cu(II)-BZI-CF had inhibition zones varied between 10 to 17 mm on S. aureus and E. coli. Here is the organized list of the results: Co(II)-BZI-CF > Ni(II)-BZI-CF > Cu(II)-BZI-CF > BZI-CF. These findings show that the complexation process enhanced the antibacterial efficiency of the treated CF. On the other hand, the V(III)-BZI-CF and Fe(III)-BZI-CF were non-active on S. aureus and E. coli.