Photothermal halloysite nanotube hybrids with CoO/carbon layers for enhanced pollutant degradation and solar-powered water purification

Advanced environmental governance techniques using photothermal nanomaterials for pollutant removal and water recycling are highly regarded. Here, we incorporated CoO nanospecies onto halloysite nanotubes via in-situ polymerization of tannic acid coordinated with Co ions and carbonization. The resulting halloysite nanotube hybrids with CoO/carbon layer (HNTs@CoO/C) afford great exposure of CoO nanospecies onto the N-doping carbon layer modified halloysite. Compared to composites without a carbon layer, optimized Co(II)/Co(III) redox cycles are achieved. More pyridine nitrogen species on the carbon layer enhance the catalyst's surface affinity for polar contaminants. HNTs@CoO/C has nearly 8.6 fold higher catalytic degradation efficiency for norfloxacin (0.164 min −1 versus 0.019 min −1 for HNTs@CoO). Quenching experiments show that co-existing multiple active species ( SO₄ − , OH, O₂ − , and 1 O₂) play important roles in norfloxacin (NFX) degradation, among which 1 O₂ is dominant. The optimal HNTs@CoO/C also effectively removes other contaminants like sulfadiazine (SDZ), tetracycline (TC), oxytetracycline (OTC), and carbamazepine (CBZ). Moreover, anchoring HNTs@CoO/C on a used cotton towel forms a 2D evaporator. Under the simulated sunlight, it has a good photothermal conversion ability, heating from 19.9 °C to 40.3 °C in 8 min. As a floatable system, it efficiently evaporates water and degrades contaminants in the presence of PMS. These results indicate the potential of this approach for water treatment and resource utilization.