Date Palm Fronds and Chicken Manure Biochar with Carbon Nanotubes for Capacitive Deionization

In this work, three biochars were synthesized from a mixture of an abundant agricultural waste (date palm fronds) and an animal biomass (chicken manure) at pyrolysis temperatures of 700 °C (B-700), 800 °C (B-800), and 900 °C (B-900), respectively. These biochars were characterized and used as electrode materials in a capacitive deionization (CDI) process to remove salts from saline water. The CDI results show that the B-700 electrode displayed the highest desalination efficiency of 10.2% with 100 ppm NaCl. Further mixing the B-700 with 10% and 20% of multi-walled carbon nanotubes (CNT) revealed an enhanced desalination performance. For instance, a biochar-20%CNT electrode achieved a salt adsorption capacity (SAC) of 11.32 mg/g at 200 ppm NaCl, which is 7.6 times higher than that of B-700 alone. The performance enhancement is attributed to carbon nanotubes acting as conductive channels between biochar particles, thereby improving electrical conductivity and electrochemical properties of the CDI electrode. Additionally, the presence of well-known hydrophilic functional groups on CNT surfaces enhances hydrophilicity, providing a highly porous surface area. The results suggest that the CDI method with biochar–CNT electrodes offers opportunities for energy-efficient, low-cost freshwater production, with significant scaling up potential for the treatment of brackish and wastewater.