Naked-eye detection of lead(II) in aqueous solution by silica gel coated with 1-(2-pyridylazo)-2-naphthol

Abstract

Silica gel coated with colorimetric ligand (1-(2-pyridylazo)-2-napthol or PAN) was prepared for Pb(II) naked-eye detection. The stirring time, amount of silica gel and concentration of PAN for coating PAN onto silica gel were optimized. Si-PAN product was characterized by DR-UV-vis spectrophotometry. Si-PAN coated with 5 mM PAN solution was able to extract Pb(II) at pH 4.5-5.5 with 90% extraction within 10 min. After Pb(II) extraction, the color of Si-PAN obviously changed from orange to pink. The concentration of PAN for coating PAN onto silica gel was optimized to detect the lowest concentration of Pb(II) for naked-eye detection. The results showed that the limit of Pb(II) naked-eye detection with Si-PAN coated with 0.5 mM PAN solution was 0.8 mg/L. Si-PAN showed high selectivity towards Pb(II) in comparison with Na⁺, K⁺, Mg²⁺ and Ca²⁺. No color change of Si-PAN in the presence of alkali and alkaline earth was observed while Cu(II), Fe(III) and Zn(II) affected to the color of Si-PAN after extraction. Moreover, it was found that Si-PAN was used as an efficient naked-eye sensor for Pb(II) up to 12 weeks. The determination of Pb(II) in drinking water by naked-eye detection using Si-PAN coated with 0.5 mM PAN solution under the optimum extraction conditions was achieved.