Valorization of Citrus Fruit Waste Into Schiff Base Chromogenic Chemosensor for Detection of Cu ⁺² Ions: An Experimental Study

Abstract In the present study, a Schiff base chromogenic chemosensor [methyl (E)‐2‐((2‐methyl‐5‐(prop‐1‐en‐2‐yl)cyclohex‐2‐en‐1‐ylidene)amino)‐3‐phenylpropanoate] was synthesized from D‐limonene extracted from citrus fruit‐waste biomass. The catalytically oxidized D‐limonene was reacted with phenylalanine methyl ester to form Schiff base (85% yield) as characterized by 1 H‐NMR, FTIR, GCMS (65% purity) and LCMS (67% purity). The obtained Schiff base was tested for detecting heavy metals in contaminated water samples which was found to be highly selective for Cu +2 . An immediate color change from colorless to blue was observed with a high intensity absorption band, indicating its selective chelation with Cu +2 ions. The binding stoichiometry was found to be 2:1 proportion and a decrease in sensing ability was found with an increase in its equivalents, causing a hypsochromic shift ( λ max = 252–241 nm). The optimum pH for detecting Cu +2 was close to neutral (pH = 7.2) without causing any interference with the other metal ions in the same solution. The limit of detection and binding constant were calculated as 20.42 µM and 4.52×10 4 M −1 respectively. The synthesized chemosensor followed pseudo‐first order kinetics ( k = 0.03 s −1 ) which revealed its performance and complex stability upon sensing Cu +2 ions and its reversible nature was confirmed by performing EDTA titration. Thus, the present investigation provides a sustainable, cost‐effective and environmentally benign pathway to synthesize chromogenic chemosensor for detecting Cu +2 ions.