Aiming to a Smart Agriculture through the Electrochemical Impedance of a Chitosan-Molybdate Membrane as a Function of Available Phosphate Species

Abstract The identification and quantification of nutrients in the soil is of great importance in agriculture because plants depend on their presence in the soil or their supply as fertilizer to grow properly. However, there is currently no well-defined method for quantifying macronutrients in the field. Therefore, chitosan membranes that have been developed are biocompatible and biodegradable and are applied to stainless steel and carbon inks whose function is to adsorb phosphorus (P) species present in cultivated soils. Studies on Z-potential were carried out on chitosan solutions, varying the pH to measure the surface charge. It was found that as the pH of the solution increased, from 2 to 10, the surface charge decreased until a negative surface charge (from 59.9mV to -5mV). The chitosan/chitosan molybdate membranes were also examined by atomic force microscope (AFM) to observe their roughness and morphology. The chitosan membrane has a smoother appearance than the chitosan-molybdate membrane, confirmed by roughness at the micrometric scale. Electrochemical characterization included electrochemical impedance spectroscopy (EIS) measurements in solutions containing hydrogen phosphide ions HPO4= to determine the changes in resistance of the chitosan/chitosan-molybdate membranes. As the ion concentration in the solution increased, the charge transfer resistance (Rtc) decreased. However, when ammonium molybdate was added to the chitosan membrane, it acted as a promoter for the uptake of HPO4= by the membrane. Thus, based on their characterization, chitosan biosensors have shown that they are capable of attracting anionic species, which contributes to the minimization of preference zones on the surface of a sensing electrode.