Novel Molecular Sieves Based on Yttrium Silicates: Potential Materials for Environmental Remediation by Adsorption of Hazardous Inorganic Metals

Human activities have introduced numerous potential hazardous trace elements into the environment since the industrial growth. The intensive use of waste water irrigation, sewage sludge, pesticide and emissions from vehicle exhausts, mining, smelting and the rapid development of industries without effective control has resulted in a large accumulation of inorganic heavy metals in the environment. Heavy metal pollution of soils and water is an increasingly urgent problem all over the world, and worsening the situation heavy metals, unlike organic contaminants, are generally immutable, not degradable and persistent in soils. This study reports the synthesis and characterization of a crystalline yttrium silicate and its ion exchanged derivatives with Ba²⁺, Sr²⁺, Cd²⁺ and Pb²⁺ . The new material has a monoclinic unit cell, with parameters a = 13,26 Å ; b = 9,25 Å ; c = 12,37 Å ;and β = 114,76°. SEM data revealed the material morphology is built by germinated plates which resemble closely tetragonal structures,. The plates width vary from 2 µm, to 20 µm. ²⁹Si-MAS-NMR data indicated 9 different chemical shifts at -83, -84, -92, -97, -98, -99, -101, -106 and -107 ppm;which is an indication of a disordered structure. ⁸⁹Y-MAS-NMR of the as made yttrium silicate mainly composed by 4 chemical shifts environment at 220, 160, 142 and 89ppm. The material is highly selective for Pb²⁺ and Cd²⁺ with adsorption of 30% (Cd²⁺) and 25% ( Pb²⁺). Ion exchange with the inorganic cations have also induced structural changes in the crystallographic as indicated by the XRD and NMR-MAS data.