Nanoconfinement-enhanced cerium@carbon nanotubes composites for adsorption of fluoride

The selective removal of fluoride (F^-) from water is of great necessity because excessive F^- in water can cause symptoms such as skeletal fluorosis and nerve damage, which poses a serious threat to human health. Cerium hydroxide (Ce(OH)₃) nanoadsorbents offer a promising strategy for F^- removal, which have limits such as aging-induced phase transition, easy deactivation, and aggregation. This study reports a cerium-loaded carbon nanotube (CNTs) composite (Ce@C_10/80/150) to overcome the intrinsic defects and enhance the selective adsorption capacity for F^- removal from water. Ce@C_10/80/150 was synthesized via nitric acid pre-treatment of CNTs with different pore sizes (10, 80, and 150 nm), followed by in-situ growth of Ce(OH)₃ nanoparticles via the hydrothermal method under nanoconfinement. The structural evolution and fluoride removal performance of bulk Ce(OH)₃ and Ce@C_10/80/150 at different aging times were systematically investigated. Batch experiments demonstrated that Ce@C₁₀ retained a considerable adsorption capacity of 11.94 ± 0.59 mg F g^-1 Ce, which was 2.56-fold higher than that of bulk Ce(OH)₃ after 48 h of aging (4.66 ± 0.24 mg F g^-1 Ce). The composite exhibits wide pH applicability and excellent resistance to interfering ions. XRD, HR-TEM, and SAED characterizations demonstrate that Ce@C_10/80/150 in the nanoconfined system exhibits excellent anti-aging capability. The bulk Ce(OH)₃ had completely transformed into CeO₂ after aging, whereas Ce@C_10/80/150 within the nanoconfined system retained an intermediate transition state. This work provides a facile nanoconfinement strategy to improve the anti-aging performance of cerium-based adsorbents, offering new insights for the design of high-stability adsorbents for practical industrial fluoride wastewater treatment.