Microbial assisted biogenic synthesis of titanium dioxide nanoparticles for enhanced methylene blue removal from aqueous solutions

This study investigates the synthesis, characterisation, and application of titanium dioxide nanoparticles (TNP) as an adsorbent for effectively removing Methylene Blue (MB) dye from aqueous solutions. The TNP was synthesised through a biogenic route using Pseudomonas aeruginosa as a bio-reducing and stabilising agent. The synthesised nanoparticles were characterised using various analytical techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The UV–visible spectrophotometer was used to monitor nanoparticle formation at a wavelength of 393 nm. Results from the study showed that XRD confirmed the nanostructured and amorphous nature of TNP, while SEM–EDX analysis indicated a coarse and rough surface of the nanoparticles. TEM analysis revealed their uniform spherical morphology, and FTIR spectroscopy identified the presence of O–H, C-O, and N–H functional groups likely responsible for MB adsorption. The adsorption experiments examined factors such as initial dye concentration, adsorbent dosage, contact time, solution pH, and temperature via batch adsorption methods. Kinetic studies demonstrated that the pseudo-second-order model accurately described the complex dynamics of the adsorption process. The Langmuir isotherm model was found to be the best fit for the experimental data, indicating monolayer adsorption on the TNP surface. Thermodynamic studies provided insights into the energetics of the adsorption process, with positive ∆H (12.75 kJ) indicating an endothermic reaction, while positive ∆S (62.27 J/mol) suggested increased disorderliness between adsorbent and adsorbate. Negative values of ∆G (− 8.522 and − 13.967 kJ/mol) confirmed the feasibility and spontaneity of the adsorption system, demonstrating a strong affinity for MB. After five cycles of adsorption and desorption, the regeneration study revealed that TNP maintained an MB removal capacity of over 80%. Highlights from this research underscore the excellent potential of green-synthesised TNP as a promising adsorbent for the efficient removal of MB dye from aqueous solutions and for potential application in other wastewater treatments.