EBT anchored SiO2 3-D microarray: a simultaneous entrapper of two different metal centers at high and low oxidation states using its highest occupied and lowest unoccupied molecular orbital, respectively

Abstract

A quick and facile synthesis of a mesoporous (pore diameter = 46.2–47.1 nm) material (FSG-EBT) through the immobilization of azo dye (EBT) on functionalized silica gel (FSG) has been achieved. FSG-EBT simultaneously binds two different metal centers, Zr(IV) and Tl(I) at their high and low oxidation states, respectively. Highest occupied molecular orbital (HOMO) of the extractor binds Zr(IV) with a breakthrough capacity (BTC) of 490 μmol g⁻¹ and its lowest unoccupied molecular orbital (LUMO) extracts Tl(I) (BTC = 120 μmol g⁻¹). The LUMO has thus enhances the BTC of the resin as a whole. This binding mode sequence differs from earlier existing mode of binding where extractors bind metals using HOMO and LUMO operative on the same metal centre only. HOMO/LUMO value (μmol g⁻¹) reiterates itself as a definite quantum mechanical descriptor of BTC, and BTC is a definite descriptor of the state of metal (monomer/polymer) sorbed. The synthesis needs no stringent reaction condition such as refluxing. Its corresponding nanomaterial has been well assessed (composition: [Si(OSi)₃(OH)·xH₂O]_n[–Si(CH₃)₂–NH–C₆H₄–NN–EBT]₄; structure: tetrahedral) and is reiterated by density functional theory (DFT) calculation. Along with its good extractor qualities [high pore volume, PV = 0.3747 cm³ g⁻¹; surface area, SA = 330.97 m² g⁻¹; BTC (Q₀ = 476.7 μmol g⁻¹); column efficiency, CE = 296 and preconcentration factor, PF = 120.20 ± 0.04; reusability > 1000 cycles; and faster rate of sorption–desorption], FSG-EBT possesses well demarcated spatial placement of HOMO–LUMO with a substantial band gap (η = 7.1471 eV). This makes charge recombination by mixing difficult and thus shows its potential applicability as a good donor–acceptor organic electronic device.