Evaluation of Photothermal and Rb220 Dye Decolorization Potential of Biosynthesized Cobalt Oxide Nanoparticles from an Endophytic Fungus Aspergillus Nidulans

Abstract

Endophytes are well known for producing biochemical molecules and bioactive metabolites. In addition, they have the capability to synthesize nanoparticles, whose properties are better than the chemical synthesized counterparts. Their potential of synthesizing nanoparticles in a greener way is relatively untapped. Nothapodytes foetida is a medicinal plant, which houses innumerable tolerant endophytic organisms. Various nanoparticles have been used for various applications. Metallic oxide nanoparticles have profound applications in electrochemical devices, supercapacitors, biosensors, and batteries. Though four fungi were isolated from Nothapodytes foetida, Aspergillus nidulans were found to be suitable for the synthesis of cobalt oxide nanoparticles, as it has proficient tolerance towards metal under study. The broth containing precursor solution and organism Aspergillus nidulans had changed from pink to orange indicating the formation of nanoparticles. Characterization by x-ray diffraction analysis (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive x-ray analysis (EDX) confirmed the formation of spinel cobalt oxide nanoparticles at an average size of 34 nm in spherical shape with sulfurbearing proteins acting as a capping agent for the synthesized nanoparticles. The study was a greener attempt to synthesize cobalt oxide nanoparticles using endophytic fungus. The extracellular synthesis makes the process simple. Dielectric constant and dielectric loss values of Co3O4 nanoparticles were measured at room temperature and frequency up to 1 MHz. They are plotted against frequency and these plots show dispersion at frequencies. Frequency dependence of the dielectric constant is found to increase with an increase in the frequency. Through Liquid Chromatography-Mass Spectrometry (LC-MS) analysis, phytochelatins are identified to be involved in the biosynthesis of Co3O4 nanoparticles. Solar energy absorption is a process of capturing solar energy radiated from natural sunlight and converted to some other useful forms by appropriate methods.In this way, a nanofluid based absorption system can provide a substitute for traditional solar collectors for the confinement of solar energy. This work proposes and validates a novel idea of using cobalt oxide nanofluids (Co3O4) to enhance solar thermal conversion efficiency. Experimental results reveal that Co3O4 nanofluids have a good specific absorption rate (SAR) and better photo-thermal conversion efficiency than water. Nanofluid exhibited a greater temperature gradient than pure water, which is desired. Thus the good absorption capability of Co3O4 nanofluids for solar energy indicated that it is suitable for direct absorption solar thermal energy systems. The photocatalytic activity of the biosynthesized cobalt oxide (Co3O4) nanoparticle is investigated using a textile dye Reactive Blue 220 (RB220) and decolorization (%) was monitored using UV-Vis spectrophotometer. The photocatalytic activity has been observed maximum at alkaline pH of 9, nanoparticle dosage of 250 mg/L, and reaction time of 270 min. In the presence of UV light irradiation, a maximum dye concentration of 10 mg/L was treated effectively using 150 mg/L nanoparticle, and 67% decolorization was achieved. Reaction kinetics has been analyzed and the reaction followed the pseudo kinetics model.