Naked‐eye colorimetric and optical assay of heavy metals based on nano‐architectured prototype of organically functionalized mesoporous titania grafted with 4‐chloro‐2‐(4′‐methyl‐benzothiazol‐2′‐ylazo)‐phenol

Abstract

Heavy metals are extremely toxic, causing harm to aquatic and human life. Thus, this study focused on developing simple, colorimetric, and low‐cost optical sensors for detection of metal ions with high selectivity and sensitivity. Here, a novel benzothiazole azo‐dye, namely, 4‐chloro‐2‐(4′‐methyl‐benzothiazol‐2′‐ylazo)‐phenol (CMBTAP) was synthesized and characterized by Fourier transform infrared spectroscopy (FT‐IR), 1H‐nuclear magnetic resonance (NMR), 13C‐NMR, and mass spectroscopic techniques. This azo‐dye has been anchored into the amino‐functionalized mesoporous TiO2 which synthesized using pluornic123 and cetyltrimethylammonium bromide as templates to yield CMBTAP‐M‐TiO2 (1) and CMBTAP‐M‐TiO2 (2), respectively. The designed nanosensors were characterized by FT‐IR, transmission electron microscopy, nitrogen adsorption–desorption isotherms, X‐ray diffraction, and thermogravimetric analyses. The colorimetric and optical sensing behavior of CMBTAP and its nanosensor analogs toward different metal ions like Ba2+, Fe3+, Co2+, Ni2+, Cu2+, Cd2+, Hg2+, and Al3+ were explored using naked‐eye observations, steady‐state absorption, and emission techniques. Significant changes in colors, the absorption and emission spectra were observed. The action of these nanosensors is reversible where on adding ethylenediaminetetraacetic acid to the formed complexes, the original absorption and emission spectra of the free sensors are restored, demonstrating that the chelation process is reversible. For CMBTAP and the nanosensors, the binding constants of the complexes formed with the used metal ions, and limit of detection (LOD) were calculated. In comparison with CMBTAP, the results revealed that the nanosensors exhibited a stronger binding affinity, selectivity, sensitivity, and lower LODs for the studied metal ions, implying that the sensing efficiency of CMBTAP is improved after loading onto the nanostructured TiO2. Thus, we have successfully converted the hazardous azo dye into an environmentally safe optical sensor for detection of toxic metal ions in wastewater with high sensitivity.