Molecular imprinting of cellulose cotton fabric/silica materials with a colorimetric dithizone chelation for smartphone-based detection of Zn (II) ions in water samples

Molecularly imprinted materials based on imprinting dithizone-Zn (II) (DTZ-Zn (II)) complexes onto cotton fabric/silica, and the Color Grab application for the OPPO A54 smartphone, were proposed and applied for the first time to detect Zn (II) ions in water samples. The proposed materials were prepared by using cotton fabrics as cellulosic materials, tetraethoxysilane as silica sources and DTZ-Zn (II) as template molecules. The initial concentration of DTZ and Zn (II), the volume of tetraethoxysilane and the reaction time were optimised to obtain the maximum adsorption of the DTZ-Zn (II) complexes in the imprinted materials. The concentration of hydrochloric acid and the extraction time were optimised to obtain the maximum Zn (II) removal. The results found that 10 mL of a solution containing DTZ (0.20 mM) and Zn (II) (0.30 mM), 25 μL of tetraethoxysilane, with 10 minutes reaction time, exhibited the strongest binding of the template complexes. Zn (II) ions were selectively removed from the materials by using 0.1 M hydrochloric acid for 10 minutes. The morphology of the prepared materials was characterised by scanning electron microscopy–energy-dispersive X-ray spectroscopy and attenuated total reflectance–Fourier Transform-infrared spectroscopy. The smartphone measurement based the cotton fabric/silica materials exhibited linear relationship between saturation (%) and Zn (II) concentrations in the range of 0.1 to 1.0 mg/L, with limit of detection of 0.02 mg/L and limit of quantification of 0.06 mg/L. The proposed method was successfully applied to determine Zn (II) in real-water samples with the % recovery ranging from 98% to 115% and an acceptable relative standard deviation of less than 6 (n = 3).