Adsorption of methylene blue and metachromasy over analcime zeolites synthesized by using different Al precursors

Abstract

Pure crystalline Analcime (ANA) zeolite samples were successfully synthesized using various aluminum precursors such as aluminum nitrate (ANA-nit), aluminum sulfate (ANA-sul), aluminum isopropoxide (ANA-isop), sodium aluminate (ANA-sodalu) and aluminum chloride (ANA-chl) to study the influence of various anions on the physicochemical properties of ANA zeolite structure. The physicochemical properties of the samples have been studied using elemental analysis, X-ray diffraction, Fourier-transformed infrared spectroscopy, scanning electron microscope, N2-physisorption, X-ray photon spectroscopy, and diffuse reflectance UV–vis measurements. The synthesized analcime samples exhibited highly crystalline ANA structure; however, the anions present in the Al precursor influenced the crystallite and particle sizes. All the samples possessed a band gap energy of around 3.8 eV. The metachromasy phenomenon of methylene blue (MB) over synthesized Analcime samples was investigated under UV irradiation. The UV–vis absorption spectra of MB solution show a transformation from mono-MB to H-aggregated MB species due to the metachromasy phenomenon occurring over the surface of synthesized analcime samples. The formation of H-aggregated MB species differs for the synthesized ANA samples, which depends on the presence of active species on the ANA surface. The ANA-nit sample exhibited a fast metachromatic phenomenon due to more surface basic sites (e.g., O2−, O−) distributed over different (micro-, meso- and macro-) pores.