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

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 Fe3+, Cd2+, Ni2+, Zn2+, Pb2+, Co2+, Hg2+ and Cu2+ with a color change from yellow to orange or purple in alkaline solutions, while it shows a color change only for Cu2+ under strongly acidic conditions. At pH 12.0, this optical sensor has a high sensitivity that makes it possible to detect Cu2+ 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. (C) 2011 Elsevier B.V. All rights reserved.