Sustainable and Energy-Efficient Capacitive Deionization Enabled Through Upcycled Wheat Straw Biochar via Ammonium Ferric Citrate Modification

Capacitive deionization (CDI) technology represents an emerging and energy-efficient solution for seawater desalination and wastewater treatment. To further enhance its sustainability and economic viability, it is very important to develop high-performance electrodes made from low-cost and renewable raw materials. Herein, a new electrode material is introduced; the material was derived from wheat straw and modified via a simple and green process using ammonium ferric citrate (AFC) as a synergistic activator and modifier. The modification of AFC significantly enhanced the physicochemical properties of biochar. At the optimal AFC concentration of 1 mol·L−1, the specific surface area reached 321.27 m2·g−1, with a specific capacitance of 208.19 F·g−1. In the NaCl desalination experiment, the MWC-1.0 electrode exhibited a desalination capacity of 13.62 mg g−1 under the conditions of 1.2 V voltage and 2 mm electrode spacing in an initial solution concentration of 500 mg L−1. After 20 cycles of adsorption/desorption, the deionization capacity of the material was still retained at 90.5% of its initial capacity, demonstrating excellent regeneration performance. This work provides a sustainable method for preparing efficient and stable biochar electrodes, further highlighting its potential application in energy-saving seawater desalination technology.