Green synthesis of ammonium nitrate (NH₄NO₃) fertiliser: production via plasma water/ice interaction with air and NH₃ plasma

This study introduces a green and sustainable method for synthesising ammonium nitrate (NH₄NO₃) using plasma activated water (PAW). Nitrate ions (${\mathrm{NO}}_3^{-}$) were generated via air plasma treatment, and ammonium ions (${\mathrm{NH}}_4^{+}$) were introduced using low pressure ammonia (NH₃) plasma exposure to nitrate-rich PAW in frozen form to produce NH₄NO₃. Results demonstrated that process parameters, including NH₃ gas pressure, applied voltage, and treatment time, significantly influenced PAW properties, with NH₃ plasma treatment time showing the most substantial impact. Extending the treatment time from 0.5-1.5 hours increased ${\mathrm{NH}}_4^{+}$ ion concentration by 134.2%, achieving a maximum of 168.2 mg L^-¹ with an energy consumption of 74.8 mg ${\mathrm{NH}}_4^{+}$ ions kWh^-¹. The ${\mathrm{NO}}_3^{-}$ ion concentration reached 63.5 mg L^-¹ with an energy yield of 222 mg ${\mathrm{NO}}_3^{-}$ ions kWh^-¹. This method achieved a total yield of 27.6 mg NH₄NO₃ kWh^-¹ and produced a neutral to slightly basic PAW suitable for agricultural applications, offering a promising alternative to traditional NH₄NO₃ production processes.