Synthesis of phosphate-modified zeolite as a modifier in carbon paste electrode for nitrite electrochemical detection

In this work, template-free synthesis of phosphate mordenite zeolites was carried out. Post synthesis impregnation using phosphoric acid was applied to add phosphate group to zeolite framework, i.e. P-loading. Phosphate modification led to disruption of bridging hydroxyl and silanol groups as confirmed by FT-IR spectra. EDX spectra showed that the Si/Al ratio of the zeolite increases with the amount of P-loading and ²⁷ Al NMR revealed the formation of aluminophosphate on mordenite. The modified electrodes of phosphate mordenite zeolite were used for the electrocatalytic oxidation of nitrite, which was investigated by using square wave voltammetry. The effect of different electrolytes and pH values were also investigated and the calibration curve of nitrite oxidation at phosphate mordenite carbon paste electrodes showed a linear dependence.