An inorganic–organic hybrid optical sensor for heavy metal ion detection based on immobilizing 4-(2-pyridylazo)-resorcinol on functionalized HMS

Abstract A novel and low-cost optical sensor for heavy metal ion detection has been prepared by immobilizing 4-(2-pyridylazo)-resorcinol (PAR) on the functionalized hexagonal mesoporous silica (HMS) via N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC). The successful fabrication of this optical sensor is confirmed by extensive characterizations using FT-IR, low angle X-ray diffraction (XRD), UV–vis spectroscopy and N 2 sorption, meanwhile its colorimetric properties, selectivity, sensitivity and reversibility are also investigated. The optical sensor responds selectively to heavy metal ions, such as Fe 3+ , Cd 2+ , Ni 2+ , Zn 2+ , Pb 2+ , Co 2+ , Hg 2+ and Cu 2+ with a color change from yellow to orange or purple in alkaline solutions, while it shows a color change only for Cu 2+ under strongly acidic conditions. At pH 12.0, this optical sensor has a high sensitivity that makes it possible to detect Cu 2+ in aqueous solution with the detection limit as low as 40 ppb by naked-eye. This optical sensor also shows excellent reversibility and regeneration by treatment with a solution of EDTA.