Porous inorganic/organic hybrid monolith-based solid sensor for the colorimetric analysis of Cu2+ ions

Abstract

In this article, we demonstrate the fabrication and application of a naked eye–responsive solid-state Cu2+ opto-chemosensor for the detection and recovery of Cu2+ from various environmental water samples. The colorimetric ion sensor is fabricated by physically anchoring a 4-hexyl-6-(quinolin-8-yldiazenyl) benzene-1,3-diol (HQDB) chelating probe, onto the indigenously designed silica-polymer hybrid monolith host template, and is systematically characterized. The inimitable macroporous backbone with the continuous interconnected mesoporous web structure of the monolith template offers greater immobilization of the ligand molecules onto its surface. The porous hybrid monolithic framework provides better accessibility towards the probe chelating sites for the Cu2+, thereby offering a faster visual response within 2 min of contact time. The sensor enables a unique visible color transition from yellowish orange to dark brown due to the formation of stable 1:1 [Cu2+-HQDB] (λmax 480 nm) charge-transfer complexes. The solid sensor exhibits high efficiency of sensing at pH 8.0, with a limit of detection (LOD) and quantification (LOQ) values of 0.45 and 1.5 ppb, respectively. Moreover, the solid sensor proffers remarkable selectivity towards Cu2+, which makes it more useful for real-time analysis, within a short analysis time. The porous monolithic sensor is reusable for eight cycles of sensing applications with greater data reproducibility when applied to real water samples.