Application of PAR Modified Fish Scale's for Adsorption and Colorimetric Detection of Heavy Metals in Water Samples

4-(2-pyridylazo) resorcinol (PAR) modified fish scales of Barbonymus gonionotus (PARFS) were simply prepared and used for metal ion adsorption and detection study. The experimental conditions were optimized based on pH, contact time, and initial metal ion concentration. The PARFS responded selectively to Cu (II), Ni (II), and Zn (II) with a color change using naked-eye detection. The adsorption isotherm and kinetics were investigated in the batch system and the results showed that the Freundlich isotherm and the pseudo-second-order model were the best models to present adsorption mechanisms. The adsorption capacity of PARFS for Cu (II), Ni (II), and Zn (II) at 10 mg/L (pH 6.4) for 24 h were 0.201, 0.157, and 0.356 mg/g, respectively. The PARFS showed high sensitivity and selectivity toward the detection of Cu (II) at pH 1.0 for 15 sec, and the naked-eye detection limit can be obtained at 500 μg/L. The colorimetric analysis was conducted using a scanner for digital images of PARFS pellets and the ImageJ program for RGB measurement. The relationship between Cu (II) concentration and ∆ RGB intensity was linear in the range from 100 to 1000 μg/L. A calibration curve obtained from ∆ Green intensity vs concentration exhibited the highest R² and slope with the limit of detection (LOD) of 43 μg/L and limit of quantification (LOQ) of 130 μg/L. This method was successfully applied to real water samples with the percentage of recovery from 85.8 to 99.4 and the percent relative standard deviation (%RSD) from 5 to 10.