Functionalized silica nanotubes with azo-chromophore for enhanced Pd2+ and Co2+ ions monitoring in E-wastes

Abstract Silica nanotubes (SNTs) were utilized as a scaffold for designing a novel solid chemical sensor. The optical nanosensor was designed by direct immobilization of novel azo-chromophore with two carboxylic acid groups called (Z)-2-((2-hydroxynaphthalen-1-yl)diazenyl)terephthalic acid (azo-HNTA) onto the SNTs. Beer's law was obeyed in the ranges of 5–240 and 5–150 ppb for Pd2+ and Co2+ ions, with linear correlation coefficients of 0.999 and 0.971, respectively. The novel nanosensor presented high sensitivity for very low concentrations up to 1.10 × 10−7 mol L−1 (11.7 ppb for Pd2+). The proficiency of this chemosensor for utilizing as an adsorber was tested. The (azo-HNTA) sensor presented a very quick adsorption property for the elimination of Pd2+ and Co2+ ions without preconcentration. The capacities of adsorption were 69.83 and 161.03 mg/g for Pd2+ and Co2+ ions, respectively. Additionally, this nanosensor has efficient recognition and selective recovery of Pd2+ and Co2+ ions in E-wastes.