Magnetic carbon nanotube sorbents with macropores formed by salts for oily wastewater treatment

The development of carbon-based sorbents that are simple to fabricate, possess high sorption capacity and are easily collected and reusable has been of great interest for oily wastewater remediation. A magnetic carbon nanotube (CNT) oil sorbent is proposed to cleanup of oily wastewater, offering effortless and complete recovery and enabling reusability. The sorbent, characterized by easy preparation of multi-walled CNT (MWCNT) with -cresol for macronization, is coupled with a space-holder technique that employs salts for open pore formation for oil sorption. Four sorbents were prepared with varying ratios of sodium chloride (NaCl) and monosodium L-glutamate (MSG), resulting in surface open pores corresponding to salt particle sizes. The sorbents formed an extensive macropore network of more than 200 μm while enhancing the specific surface area. Their bulk densities ranged from 126 kg/m to 139 kg/m, indicating CNT powder densification and suitability for wastewater oil absorption. With its elongated rectangle shape, the MSG-prepared sorbent, exhibited the widest specific surface area and diverse macropores, including those larger than 800 μm. The sorbents exhibited sorption capacities of 2.37–13.60 g of oil/g of sorbent and volume gains of 44–123 %, depending on the oil and solvent types. These values were comparable to or exceeded those of previous carbon-based sorbents. The sorption capacities of the sorbents remained consistent over ten sorption-heat treatment cycles, highlighting recyclability. Sorbents of MWCNT grown from iron catalysts exhibited easy recovery by a magnet after oil sorption, with surface magnetism. Despite their promise for oily wastewater treatment, CNT sorbents must address challenges related to capacity improvement, scalability, economic viability, and environmental impact to be practical for widespread application.