Al–Sr metal oxides and Al–Cd layered double hydroxides for the removal of Acridine orange dye in visible light exposure

This study involves the preparation and utilization of Al-based catalysts for the photo-catalytic degradation of acridine orange (AO) dye. Al–Sr and Al–Cd were developed in metal oxides nanoparticles and layered double hydroxides (LDH) morphology respectively. The LDH nature of Al–Cd catalyst was confirmed via X-ray diffraction (XRD) spectrum with the characteristic peak at 2θ =11.8º. Sheet like morphology was adopted by both the catalysts as analyzed through field emission scanning electron microscope. The Al–Cd-LDH sheets were assembled above each other. The crystal phase and functional groups of the catalysts were studied through XRD and Fourier transformed infrared spectroscopy respectively. The thermo gravimetric analysis showed the greater stability for Al–Cd-LDH as compared to Al–Sr metal oxides. A band gap of 2.85 eV and 2.6 eV was calculated for Al–Sr metal oxides and Al–Cd-LDH respectively by utilizing diffuse reflectance spectroscopy. The Nitrogen adsorption/desorption isotherms indicated 62.83 m²/g surface area for Al–Cd-LDH and 24.63 m²/g for Al–Sr metal oxides. Similarly, the total pore volume and average pore sizes were 0.933 mL/g and 0.9685 nm for Al–Cd-LDH and 0.0437 mL/g and 1.0393 nm for Al–Sr metal oxides. Both catalysts showed prominent and effective results for the degradation of AO dye. Under UV–Vis light irradiation, the Al–Sr metal oxides showed approximately 90% degradation in 90 min, while Al–Cd-LDH showed less than 50% efficiency. However, with the increase of irradiation time, the degradation rate of Al–Cd-LDH was enhanced to approximately 90% after 240 min. The Al–Cd-LDH showed 29% of acridine orange dye adsorption after 240 min while Al–Sr metal oxides showed 26% adsorption after 90 min. The low catalytic performance of Al–Cd-LDH could be attributed towards the LDH nature which probably interfered the electronic moments for free radical formation. Furthermore, the effect of various parameters such as dye concentration, pH, catalyst amount and different scavengers were also evaluated. Both catalysts showed good recyclability and hence better stability.