Tamarind shell derived N-doped carbon for capacitive deionization (CDI) studies

Renewable biomass waste derived porous carbon materials are widely accepted due to their low cost, eco-friendliness, and sustainability. Herein, a two dimensional (2D) nitrogen (N) -doped porous carbon nanosheets were prepared via a facile and cost-effective pyrolysis method using potassium hydroxide (KOH) activated Tamarind shell biomass waste and urea as the precursors. With the synergetic effect of N-doping, graphitic nature, 2D morphology, hierarchical pores, large specific surface area (410 m² g⁻¹) and high electrical conductivity, the as-obtained N-doped carbon nanosheets showed many favorable features to be an excellent electrode material for effective capacitive deionization (CDI) process. Furthermore, the presence of nitrogen heteroatom contributes to an increase in polarity of the carbon material, which is crucial for improving the wettability of the electrode in the CDI process. The electrochemical analysis showed that the N-doped carbon nanosheets have a better electrochemical double layer (EDL) characteristic, and it possess a specific capacitance of 174.5 F g⁻¹ in 10 mV s⁻¹ than undoped carbon nanosheets (70.6 F g⁻¹). Besides, in the deionization test, the N-doped carbon nanosheets exhibit a maximum salt adsorption capacity (SAC) of 18.8 mg g⁻¹ in 600 mg L⁻¹ NaCl solution at 1.2 V, which is significantly higher than that of undoped carbon nanosheets (11.1 mg g⁻¹). Thus, N-doping is proposed to be an effective method in not only improving the electrical conductivity and wettability of the carbon but also played a crucial role in enhancing the electrosorption performance. As such, the low-cost biomass waste tamarind shell derived N-doped carbon nanosheets developed in this work present offers a promising electrode material for conventional high-performance symmetric CDI applications.