# Fungi-Templated Silver Nanoparticle Composite: Synthesis, Characterization, and Its Applications
## 3 Results and Discussion
### Photocatalytic Degradation of Methylene Blue  
Several industries such as textile, plastic, and paper are known to generate streams of waste effluents containing substantial amounts of organic dyes which are eventually released into water bodies. These industrial effluents, when released into water bodies without any prior treatment, cause severe damage to both aquatic plants and animals. Recently, it is seen that conventional water treatment methods are replaced by advanced oxidation processes such as the Fenton method, photolysis, ozonolysis, and photocatalysis. In photocatalysis, using a suitable catalyst, degradation of organic pollutants present in wastewater is carried out in the presence of UV radiation associated with sunlight. Methylene blue (MB) is an aromatic heterocyclic dye which is commonly found in industrial wastewater that causes calamitous effects on the environment [25]. It is a carcinogenic thiazine pollutant which upon ingestion poses serious threats to human health, and it is known to cause severe damage to the nervous system. Nausea, breathing difficulties, and gastric infections are the other ailments associated with the ingestion of methylene blue. Methylene blue shows an intense absorbance at 655 nm. The FH-AgNPs prove to be effective in the degradation of methylene blue in the presence of visible light. A catalyst load of 30 mg was used for the degradation studies. The fungal biomass is known to degrade dye by a mechanism known as biosorption. Biosorption includes various physico-chemical interactions such as adsorption, deposition, electrostatic interactions, and ion exchange that trigger the dye degradation [26]. The functional groups present in the fungal cell wall serve as the binding sites for the dye molecules. The amino, carboxylic acid, phosphate groups and lipids are prominent binding sites. Pre-treatment of the fungal biomass is found to increase the adsorption capacity of the fungi. Bio-templating AgNPs on the fungal hyphae increases the adsorption capacity and the catalytic activity. A percentage degradation of 67.86% was obtained within 60 min (Figure 4b), which highlights the potent catalytic activity of FH-AgNPs in dye degradation. A UV-Visible spectrophotometer was used to monitor the extent of degradation of MB. There was a significant reduction in the absorption band of MB with an increase in time (Figure 4a) that indicates degradation of MB catalysed by FH-AgNPs The FH-AgNPs stand out as potent catalysts due to the combined effect of the fungi and the AgNPs. Figure 3: XRD analysis of AgNPs and FH-AgNPs. The possible mechanism for the photocatalytic degradation of methylene blue by the FH-AgNPs composite occurs via a series of photochemical reactions. The synthesized composite material possesses combined properties of both the fungi and the nanoparticle, thereby exhibiting an enhanced catalytic activity when compared to activity exhibited when they are present individually. The enhanced surface area provided by the fungi and the unique surface plasmon resonance phenomenon [27] of AgNPs are believed to be the reasons for the enhanced catalytic activity exhibited by the composite. When the surface of the nanoparticles is irradiated with high-energy photons, a collective oscillation of electrons occurs from the outermost band to a higher energy state. Later, molecular oxygen present in water undergoes plasmonic excitation of the surface electrons and becomes converted to the free radical species O2*. This is followed by an electron capture process by the holes generated in the nanoparticles, wherein electrons are captured from methylene blue adsorbed on the surface of the nanoparticles. This results in the oxidation of methylene blue, and the free radical (O2*) generated reacts with H+ and forms other active radicals such as OH* and OH2*. These free radicals are responsible for the degradation of methylene blue into various azo dye intermediates.