Photocatalytic Reduction of Cr(VI) to Cr(III) and Photocatalytic Degradation of Methylene Blue and Antifungal Activity of Ag/TiO₂ Composites Synthesized via the Template Induced Route

Abstract

Water treatment through photocatalysts has become an important topic regarding environmental protection. In the present study, silver and TiO₂ (Ag/TiO₂) composites for photocatalysts were effectively synthesized by adopting the template induced method. The prepared samples were characterized using XRD, FTIR spectroscopy, SEM, and EDX. The constructed samples’ particle size and shape were evaluated using a SEM, and the XRD patterns showed anatase crystalline phases. Their morphologies were controllable with changing concentration of reactants and calcination temperature. The synthesized composites act as catalyst in the degradation of methylene blue (MB) and reduction of Cr(VI) to Cr(III) under solar irradiation. In both of these activities, the best result has been shown by the 0.01 Ag/TiO₂ composite. Methanol is used as the hole scavenger in the reduction of Cr(VI) to Cr(III). While the pH factor is important in the photocatalytic reduction of Cr(VI) to Cr(III). According to observations, S. macrospora and S. maydis were each subject to 0.01 Ag/TiO₂ nanocomposites maximum antifungal activity, which was 38.4 mm and 34.3 mm, respectively. The outcomes demonstrate that both photocatalytic and antifungal properties are effectively displayed by the constructed material.

1. Introduction

The earth is immensely affected by wastewater management, environmental pollution, and climate change crisis. The major portion of the earth is comprised of water that can be regenerated, disseminated, distributed, and transported. These characteristics collectively add to water’s great value to people [1,2,3]. The groundwater and surface water resources are crucial for a variety of activities, including cattle development, energy generation, forestry, farming, aquaculture, seafaring, recreation, and so forth [4]. It is a remarkable gift from the nature to humanity that must be preserved. However, environmental degradation, particularly water contamination, is regarded as one of the fundamental issues facing the entire planet, significantly affecting our everyday lives [5]. It comprises the introduction of foreign chemicals into the environment, which harms and disturbs the biosphere [6]. These pollutants appear to be either native substances that have surpassed permitted limits or foreign compounds [7,8,9,10]. Unfortunately, pollution is continually rising and is now a severe issue that requires immediate attention [11]. The usage of dyes and their byproducts significantly pollutes the environment. The nature of water is changed by its release of chemicals from potable to non-potable [12]. Furthermore, microorganisms also change the properties of water and cause different diseases. Many nanomaterials have significant properties to control the growth of bacteria [13]. The aquatic center is unscrewed from the dye waste, changing the soil’s composition and water content. In addition, it encourages several illnesses, environmental degradation, and several infectious diseases.

Toxic metal and organic compound-related water contamination is still a significant environmental and societal issue [14]. Additionally, water contamination has grown to be a significant cause of worry and a top priority for most industrial sectors. Water contamination is significantly influenced by dyes used in the paper, food, and textile sectors. Due to their industrial use, dyes and associated hydrocarbons, which are among the most significant and dangerous toxins in water, are linked to population expansion [15]. Because dyes have chromophore groups in their structure, they are utilized in coloring fabrics. These colors may be distinguished from one another by how easily they dissolve in water. Most dyes are categorized according to the fibers they will be imprinted on and their chemical and physical makeup. MB (methylene blue) is used to tone down the hues of silk in addition to dying paper and office supplies [16]. MB poses a significant concern to human health and can have a negative impact on the environment because it is poisonous, carcinogenic, and non-biodegradable [17,18,19]. The health of people can be seriously harmed by color molecules at extremely low concentrations [20]. It can result in eye burns, which may result in both human and animal eyes being permanently damaged. When ingested through the mouth, it generates a burning feeling and may cause vomiting, excessive perspiration [21], methemoglobinemia [22], and mental disorientation [23]. It can also cause short periods of rapid or difficult breathing when inhaled.

Heavy metals also play a vital role in polluting and poisoning the water. In water, the presence of heavy metals even in a very low concentration is considered to be poisonous and the high specific density and atomic weight of the metalloids make them dangerous [24]. Additionally, such contamination can result in several “neurological, cardiovascular, hematological, respiratory and renal problems” that also impact the bladder, lungs, liver, and kidneys [25]. Although there are naturally occurring heavy metals in the ecosystem, man-made sources of heavy metals are the fourth major cause of pollution. Chromium manganese, copper, arsenic, and lead are the examples of heavy metals that are frequently found in water. Further, chromium is frequently employed in many industrial processes, including the production of paint and metal plating [26]. The tanning business utilized between 4.0 and 6.0 thousand tonnes of basic Cr annually, with 20.0 to 40.0% of that amount being disposed of as waste [27]. Cr(VI) is on the list of priority pollutants in the majority of nations due to its high water mobility and acute toxicity [28]. When compared to Cr, Cr(VI) is 100 times more poisonous (III). Compounds made of Cr(VI) are exceedingly toxic and cancer-causing.

The major reason why chromium(VI) is regarded as being particularly dangerous is that it easily interacts with biological molecules [29]. Due to its low membrane permeability, trivalent chromium Cr(III) is mostly safe in the environment. Chromium in hexavalent form is more effective in piercing the cell membrane through openings for isostructural and isoelectric anions such as HPO₄²⁻ and SO₄²⁻channels, and these forms of chromium are then raised through phagocytosis [30]. By the adsorption reduction method Cr(VI) is converted into the less toxic form Cr(III) [31]. Hexavalent chromium (Cr(VI)) is the most toxic heavy metal to living things, and the most potent carcinogen [32]. Dermatitis and recurrent ulcers have been connected to exposure to Cr (VI) [33]. Modern oxidation techniques have proven effective at cleaning industrial effluent [34,35,36].

The use of solar light in photocatalysis, one of many methods for treating water, has drawn a lot of interest because it is environmentally friendly, economical, and effective in reducing pollutants and energy use [37]. Many commonly used techniques, including coagulation, active carbon adsorption, and precipitation can be utilized to treat wastewater that contains hexavalent chromium. The produced hole and OH^• radical are quickly consumed by sacrificial electron donors such as methanol, preventing the electrons and holes from recombining and making the electrons accessible for the reduction of Cr(VI) [38]. AOPs have a lot of potential for treating industrial waste water that contains dyes because they can degrade soluble organic pollutants in liquid wastes [39]. To remove dye molecules, researchers are now concentrating on heterogeneous catalysts. One of the best AOPs for eliminating organic contaminants from both water and the atmosphere is heterogeneous photocatalysis [40]. Essentially, heterogeneous photocatalysis consists of a catalyst that contain a semiconductor which is activated by using the visible and ultraviolet electromagnetic radiation. The elimination of industrial effluents via the photocatalytic degradation method has attracted interest [41]. By breaking molecular bonds with the species around them, extremely reactive free radicals produced by the photocatalysis process can trigger oxidation–reduction processes, which can reduce or oxidize the pollutants [42]. By inducing radiation, electron and hole pairs are produced on their outer most layers and hydroxyl radical (OH^.) and superoxide radical (O^.₂) are produced by the reaction of water and oxygen with the charge carriers. Due to their potential properties, semiconductor metal oxides (MO) such as SnO₂, CuO, ZnO, and TiO₂, are popular study materials [43,44,45,46,47] such as nonlinear optics [48], photonic crystals [49], electro ceramics components [50], solar cells [51], and gas sensors [52].

By the incorporation of the noble metal nanoparticles in semiconductive oxides, the photocatalytic activity of semiconductors is highly increased [53]. All semiconductors’ mechanisms for electron excitation have the potential to lead to electron and hole recombination, which lowers photo-efficiency from the valence band to the conduction band [54]. Noble metals including Au, Ag, Pd, and Pt, can be used to dope TiO₂ because these boost photocatalytic activity by preventing electron–hole pair recombination, which increases photocatalytic activity [55]. Band gap also plays a considerable role in the photocatalytic process [56]. The band gap of the TiO2 is the 3.2 eV. However, when Titina is doped by the noble metal, the band gap decreases. Reduction in the band gap results in an increased photocatalytic degradation and reduction. One of the effective methods to raise TiO₂’s photocatalytic effectiveness is to load it with Ag. For water purification silver is doped on the surface of the TiO₂ which acts as the self-cleaning agent. In this way, Ag contributes to the process of photocatalysis. The silver metal acts as electron sinks, making them efficient co-catalysts for boosting TiO₂ photo reactivity. To capture the electrons that are transported from the TiO₂ conduction band, Ag can operate as an electron trap. At the same time, it produces a surface plasmon resonance (SPR) effect, extending the light absorption to the visible spectrum which result in an increase in the photocatalytic performance of TiO₂ [57]. It was discovered that Ag could increase the rate of photocatalytic degradation, facilitate charge separation, and increase the adsorption of organic pollutants on the TiO₂ surface [58]. Ag/TiO₂ also acts as the electron trapping center that prevents the recombination of electrons/holes pairs caused by the Schottky barrier resulting in an enhanced photocatalytic activity [59]. The synergistic impact of Ag, TiO₂, and biochar allowed to effectively manufacture a series of biochar-coupled Ag–TiO₂ materials, and the findings demonstrated that the degradation performance of Ag-modified TiO₂ was better than the pure TiO₂ [60]. Jiang et al. showed that after two hours of exposure to light, doping TiO₂ with silver demonstrated 100% photodegrade performance [61]. According to Arbiter et al. after sixty minutes, silver titanium oxide shows 85% of dye degradation [62]. According to Avciata et al. after 150 min of irritation, 75% dye degradation is shown by the TiO₂ doped with Ag [63]. Further, the doping of the silver on the TiO₂ also caused the photo reduction of chromium (VI) to the chromium (III). Silver-TiO₂ also acts as the photo catalyst which enhances the reduction of Cr(VI) to Cr(III).

In our continued research work on water pollution, we focus to synthesize the Ag/TiO₂ composites by using the template induce rout for photocatalytic degradation of methylene blue and photocatalytic reduction of Cr (VI) to Cr (III).

2. Experimental Section

2.1. Material and Method

The reactants employed in this investigation included methylene blue (MB), analytical grade sodium carbonate (Na₂CO₃), magnesium chloride (MgCl₂), silver nitrate (AgNO₃), and potassium dichromate (K₂Cr₂O₇). TiO₂ was used as the titania source. X-ray diffraction (XRD) data were obtained employing a Rigaku D-Max 2400 diffractometer operating in reflection mode (Cu-K radiation), and SEM was used to evaluate the produced Ag/TiO₂ composites (FEI Nova Nano SEM 450).

2.2. Preparation of Ag/TiO₂ Composites

The Ag/TiO₂ composites are synthesized by following the template induced route. This is the bottom-up approach for nanotechnology for synthesizing nanomaterials (Figure 1). In this experiment 0.1 M solution of sodium carbonate (Na₂CO₃) and 0.1 M solution of Magnesium chloride (MgCl₂) were combined uniformly in a beaker at 40 °C. The aforementioned combination was then mixed at a 400 rpm stirring rate for 7 min, after which the suspension was kept at 80 °C for 4 h. The obtained Mg₅(CO₃)₄(OH)₂.4H₂O product (MCH) was then filtered off, three times washed with first ethanol and then water after being dried at 60 °C for 12 h. After dispersing 1 g of synthetic MCH template in 80 mL of pure ethyl alcohol, TiO₂ was added. The solution of distilled water and ethanol was continuously stirred for 4 h at 25 °C temperature. Deionized water and ethanol were used to wash the MCH/TiO₂ intermediate in succession before it was dried. In 100 mL of absolute ethyl alcohol, 0.8 g of MCH/TiO₂ intermediate was dispersed. The aforesaid combination was then given an adequate amount of AgNO₃ solution in three different contents (0.01 M, 0.1 M, and 0.5 M), and the mixture was agitated for two hours. The resultant samples were labeled 0.01-Ag/TiO₂, 0.1-Ag/TiO₂, and 0.5-Ag/TiO₂ with varying concentrations of Ag⁺. After bubbling CO₂ gas into the mixture for 30 min to flush out any remaining Mg²⁺ ions, the mixture was once again washed with the buffer solution of CH₃COOH/CH₃COONH_4. This buffer solution is prepared by dissolving 0.1 g ammonium acetate in 10 mL acetic acid. Then the Ag/TiO₂ composites were dried at 60 °C for 12 h. To create Ag/TiO₂ composites, the Ag₂CO₃/TiO₂ precursor was calcined at 550 °C for 4 h.

2.3. Photocatalytic Degradation Experiment

In the photocatalytic degradation experiment, the 0.0006 g methylene blue dye was taken and then added to the 500 mL of water. Afterward, this solution was sonicated for fifteen minutes. Furthermore, three beakers were taken, and 100 mL solution was added to each. About 0.2 g of composite was inserted to every beaker. The solutions were stirred in the absence of light for thirty minutes to achieve adsorption equilibrium. Then, the stired solutions were added to Petri dishes, and 5 mL of the solution was taken as the reference. These Petri dishes were exposed to direct sunlight and 5 mL solution sample was taken at 30, 60, 90, 120, and 150 min respectively. The color of MB faded. The photocatalytic degradation rate can be estimated by using the following equation:

$$\mathrm{P}\mathrm{h}\mathrm{o}\mathrm{t}\mathrm{o}\mathrm{d}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}=Co-Ct/Co\times 100$$

2.4. Photocatalytic Reduction Experiment

In the photocatalytic reduction experiment, 10 ppm solution of anhydrous K₂Cr₂O₇ was prepared and 0.2 g of 0.01, 0.1, and 0.5 Ag/TiO₂ was added to it as a catalyst. Further, 2 ml of methanol was added into the solution which acted as a hole scavenger. The pH of the solution was altered to 1.5 by utilizing NaOH and H₂SO₄. The solution was stirred for thirty minutes to achieve chemical equilibrium. Taking 0-min reading as the reference afterward, the solutions were poured into a Petri dish and exposed to the sunlight. A total of 5 mL solution was taken in a burette after 5, 10, 15, 20, 15, 20, 25, 30, 35, 40, 45, and 50 min respectively. This experiment was performed in the last days of May. The intensity of the sun was 2100 Wm². The removal rate of the chromium can be determined by using the following equation:

$$\mathrm{P}\mathrm{h}\mathrm{o}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{e}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}=Co-Ct/Co\times 100$$

3. Result and Discussion

The FTIR results as shown in Figure 2 revealed that the 3420 cm⁻¹ peak relates to the stretching vibration of the hydroxyl group [64]. However, the peak at 1621 cm⁻¹ originated due to the bending vibration of the water molecule. The O-Ti-O lattice and Ti-O stretching vibration are responsible for the TiO₂ characteristic bands in the range 500–900 cm⁻¹. [Journal of Materials Science: Materials in Electronics (2018) 29:18111–18119].

To analyze the crystallinity of Ag/TiO₂ composites, XRD was used in the fractional angle range of 10° to 80° as shown in Figure 3. The XRD results show that the peak at 0.01 represents peak a, while the other two peaks represent the peaks of 0.1 and 0.5 given the names b and c respectively. The XRD results of 0.5 Ag/TiO₂, 0.1 Ag/TiO₂, and 0.01 Ag/TiO₂ composites are categorized into two sets. In these two sets, one category shows the peaks of the silver, while all the other peaks are matched with the structure of TiO₂ which is present in the rutile phase. The face-centered cube structure of silver is presented by showing 111, 200, 220, and 311 peaks at definite positions [65]. These peaks are present at the 38.11°, 44.20°, 64.44°, and 77.39° positions [PDF: JCPDS 03–065-2871]. While the other peaks 110,101,210,211,220, 301, and 112 represent the rutile structure of TiO₂. Strong diffraction peaks in XRD patterns at 27°, 36°, and 55° indicated that TiO₂ was in the rutile phase [66]. θ values are 27.3°, 36.0°, 41.0° 54.2°, 56.5°, 68.8°, and 70°, which correspond to tetragonal phase and can be indexed to the [PDF JCPDS 88-1175].

Figure 4 depicts the scanning and flask-like electron microscope that was used to analyze the Ag/TiO₂ composites’ morphology. The shapes of the given images are spherical. Due to spherical shapes, these composites enhance their surface area which increases the capabilities of these composites toward different activities. On the other hand, EDS (Figure 5 and

Table 1. The elemental composition of (a) 0.5 Ag/TiO₂ composite; (b) 0.01 Ag/TiO₂ composite; (c) 0.1 Ag/TiO₂ composite.

Composite	Element	Line Type	Apparent Concentration	k Ratio	Wt%	Wt% Sigma	Standard Lable	Factory Standard
(a)	O	K series	10.63	0.0357	25.65	0.52	O2	Yes
	Ti	K series	14.32	0.1432	21.19	0.32	Ti	Yes
	Ag	L series	25.29	0.2529	37.96	0.53	Ag	Yes
	Au	M series	2.42	0.0242	4.03	0.24	Au	Yes
(b)	O	K series	10.69	0.0359	26.53	0.55	O2	Yes
	Ti	K series	17.00	0.1700	25.58	0.33	Ti	Yes
	Ag	L series	22.69	0.2268	34.87	0.46	Ag	Yes
	Au	M series	2.75	0.0275	4.69	0.28	Au	Yes
(c)	O	K series	11.58	0.0389	27.23	0.46	O2	Yes
	Ti	K series	14.57	0.1456	21.34	0.28	Ti	Yes
	Ag	L series	24.79	0.2479	36.89	0.46	Ag	Yes
	Au	M series	2.43	0.0242	4.01	0.21	Au	Yes

) showed the Ag element peaks, which demonstrated that Ag was combined within TiO₂.

The morphology of the Ag/TiO₂ composites was examined by using the scanning and flask-like electron microscope. The shapes of the given images are spherical. Due to spherical shapes, these composites enhance their surface area which increases the capabilities of these composites toward different activities.

The smallest amount of energy needed by an electron to break out from its bound state is known as the band gap in Figure 6. Talc plots were created using absorbance data from UV–VIS spectrophotometry at room temperature to calculate the band gap for manufactured nanoparticles. To do this, relations were used to compute the photon energy “E” and the absorption co-efficient “α” of synthesized samples:

$$E=hv=1240/\lambda$$

$$\alpha =4\pi \left(absorbance\right)/\lambda$$

The absorption coefficient “α” and the energy band gap have the following relation:

$$\left(\alpha hv\right)=B (hv–Hg)1/2$$

The band gap calculated for the 0.5 Ag/TiO₂ composite is 3.6 eV, while for the 0.1 the band gap is 3.4 eV, and for 0.01 Ag/TiO₂ composite 2.7 eV.

After exposure to methylene blue under sunlight, degradation of methylene blue started. The readings taken at different time intervals are shown in the Figure 7. After taking the readings at these intervals, the collected solutions were run in a UV-visible spectrophotometer, and the degradation percentage was recorded. After analysis, it was observed that the 0.5 Ag/TiO₂, 0.1 Ag/TiO₂, and 0.01 Ag/TiO₂ composites degraded at 54%, 68%, and 90% respectively. So, the result shows the composite 0.01 Ag/TiO₂ shows the highest degradation of methylene blue as compared to the others. Because as the Ag loading exceeds 0.06 wt %, the photocatalytic effectiveness steadily declines, which is mostly caused by the shielding effect of the high Ag coverage.

To study the kinetics of the degradation of methylene blue, a graph was plotted between the instantaneous concentration (at radiation time) and the starting concentration of the sample introduced at zero minutes, resulting in a straight line with an R² > 0.95 as shown Figure 8 and

Table 2. Kinetics study of photocatalytic degradation of methylene blue.

Ag/TiO2 Composites	R2	Kapp	Degradation
0.01 Ag/TiO2	0.0090	0.0135	90%
0.1 Ag/TiO2	0.981	0.007	68%
0.5 Ag/TiO2	0.9682	0.0051	54%

. It shows that a first-order reaction was used to quantify the photocatalytic degradation rates for synthesized photocatalysts:

$$-\mathrm{l}\mathrm{n}\frac{{\mathrm{c}}_{\mathrm{o}}}{{\mathrm{c}}_{\mathrm{t}}}=\mathrm{k}\mathrm{t}$$

where c_e is the instantaneous concentration and c_o is the starting concentration of the material being injected at zero minutes (at irradiation of time). While the value of c_t was determined by comparing the Beer–Lamberts Law at zero minutes and at various irradiation times, the value of c_o is known for each photocatalyst.

$$\frac{\mathrm{A}}{\mathrm{c}}=\frac{\epsilon }{1}$$

The UV data, as shown in Figure 9, indicate that 50 min of exposure to the sunlight using the 0.5 Ag/TiO₂ catalyst results in a 50% reduction of Cr (VI) to Cr (III), while using the 0.1 Ag/TiO₂ catalyst shows a 54% reduction of Cr (VI) to Cr (III), and 0.01 Ag/TiO₂ composite as the catalyst shows 75% reduction of the Cr (VI) to Cr (III). The pH affects the photoreduction of the Cr (VI) to Cr (III) as shown in Figure 10. The best result is shown by the Ag/TiO₂ composites at 1.5 pH as compared to the 5 and 3. So all the experiments of photoreduction of the Cr (VI) to Cr (III) were carried out at pH 1.5.

r = −dC/dt = K′C;

In the above equation, K’, with a unit of time-1, is the fictitious first-order rate constant. r represents the reaction rate where the illumination (reaction) time is represented by t. The amount of aqueous Cr (VI) concentration is denoted by C; where Ce represents the level of Cr (VI) at time t and Co represents the starting level of Cr (VI). The relationship between the Cr (VI) concentration and absorbance is linear as shown in Figure 11 and

Table 3. Kinetics study of photocatalytic reduction of Cr(VI) to Cr(III).

Ag/TiO2 Composites	R2	Kapp	Reduction
0.01 Ag/TiO2	0.8965	0.0259	75%
0.1 Ag/TiO2	0.8708	0.014	54%
0.5 Ag/TiO2	0.9243	0.0166	50%

as well.

ln (C_t /C_o) = −K′

The kinetics study indicates the photocatalytic reduction of Cr(VI) to Cr(III) follows the pseudo first-order reaction.

Ag/TiO₂ + hv e⁻_cb + h⁺_vb

(1)

h⁺vb + H₂O HO + H⁺

(2)

HO+ target pollutant degradation product

(3)

h⁺_vb + target pollutant Oxidation Product

(4)

e⁻_cb + O₂ O^.₂

(5)

O^.₂ + target pollutant degradation product

(6)

e⁻_cb + target pollutant reduction product

(7)

The proposed mechanism of removal of photocatalytic pollutants by Ag/TiO₂ composite is shown in Figure 12. The Ag/TiO₂ in an aqueous matrix is exposed to light with an energy level over its band gap (Eg = 2.7 eV), and electrons are produced in the conduction band and holes in the valance band (Equation (1)). Hydroxyl radicals can be created when the adsorbed water reacts with the photogenerated valance band gaps (Equation (2)). Target pollutants can be subjected to a photocatalytic interaction with the generated hydroxyl radicals and the valance band holes (Equations (3) and (4)). On the other hand, the adsorbed molecular oxygen on Ag/TiO₂ can combine with the photogenerated conduction band electrons to make superoxide radical anions (Equation (5)). Moreover, the target pollutants can cause degradation and reduction products by interacting with newly formed superoxide radical anions and conduction band electrons (Equations (6) and (7)) [67].

3.1. Effect of Methanol

Methanol was chosen to serve as a hole scavenger. Methanol radicals are created when the CH₃OH scavenges the h⁺ in the valence band (CH₂OH^.). The hole scavenger produces a radical by removing the hydrogen from the hydroxyl group [68,69]. The valence band receives e- from the formaldehyde radicals created by the oxidation of the methanol radical. The formaldehyde undergoes additional oxidation to generate formic acid before being broken down into CO₂ and H₂O.

CH₃OH + h⁺ CH₂OH

CH₂OH^• CH₂O + H⁺ + e⁻

The conducting band can accept formaldehyde (CH₂O), H⁺, and e⁻ as donations or fill the positively charged vacancies, which slows the rate of e⁻/h⁺ recombination. The produced holes are scavenged by the methanol, which is then oxidized to produce the species that donate electrons. CH₂OH. E^o = 0.95 V (CH₂OH/CH₂O) [70]. When a methanol hole scavenger is employed, the photogenerated holes are not immediately consumed. Instead, the hydroxyl radicals radicalize the CH₃OH, which results in the formation of e⁻ [71].

OH^• + CH₃OH CH₂OH^• + H₂O

3.2. Antifungal Performance

0.01 Ag/TiO₂, 0.1 Ag/TiO₂, and 0.5 Ag/TiO₂ nanocomposites were further tested for their antifungal activity against S. macrospora and S. maydis using the agar well-diffusion method and amphotericin B as a reference. An overview of the findings is shown in

Table 4. Zones of inhibition for the antifungal activity of 0.01 Ag/TiO₂, 0.1 Ag/TiO₂, and 0.5 Ag/TiO₂ nanocomposites were determined using the Agar Well cut diffusion method.

Antifungal Performance
Bacterial Strains	Samples	Blank	Zone of Inhibition (mm)
S. macrospora	0.01 Ag/TiO2	0	38.4
	0.1 Ag/TiO2	0	30.6
	0.5 Ag/TiO2	0	27.8
S. maydis	0.01 Ag/TiO2	0	34.3
	0.1 Ag/TiO2	0	29.4
	0.5 Ag/TiO2	0	27.2

. When compared to 0.1 Ag/TiO₂ and 0.5 Ag/TiO₂ nanocomposites, 0.01 Ag/TiO₂ nanocomposites display stronger toxicity, with zone inhibition values of 38.4 and 34.3 mm, as shown by the antifungal activity data (Table 4). Reduced size and the synergistic interaction of 0.01 Ag/TiO₂ nanocomposites resulted in an increased antifungal effect.

4. Conclusions

The Ag/TiO₂ composites are synthesized by using the template induced method. For the crystallinity of the Ag/TiO₂ composites, the XRD technique is used. In contrast, the Ag/TiO₂ composites’ morphology is determined using the SEM technique. EDS is used for element detection. Moreover, the photocatalytic removal of MB and the photocatalytic reduction of the Cr (VI) to Cr (III) are performed by using the Ag/TiO₂ composites as the catalysis. After performing these activities, it is concluded that 54%, 68%, and 90% methylene blue is degraded by using the 0.5 Ag/TiO₂, 0.1 Ag/TiO₂,and 0.01 Ag/TiO₂ composites respectively. While 50%, 54%, and 75% Cr(III) is reduced to Cr(III) by using the 0.5 Ag/TiO₂, 0.1 Ag/TiO₂, and 0.01 Ag/TiO₂ composites. The kinetics study shows that degradation of methylene blue follows the first-order kinetics and reduction of Cr(VI) to Cr(III) follows the pseudo first-order reaction. In both of these activities (photocatalytic degradation of methylene blue and photocatalytic reduction of Cr(VI) to Cr(III)) the best result is shown by 0.01 Ag/TiO₂ composite after 150 and 50 min respectively of exposure to sunlight.