Molten salt-assisted synthesis of carbon polyhedra with self-grown carbon nanotubes on the surface for boosting peroxymonosulfate activation

Highlight • A facile method was used to synthesize surface autocatalytic growth of 1D carbon nanotubes and Co, N-doped 3D carbon polyhedra serve as PMS activation catalysts. • NaCl served as the constraining template in preparation, which prevents nitrogen loss and promotes graphitization simultaneously. • The OTC enhanced degradation surely because nonradical mechanisms (1O2, surface electron transfer) interact with radical routes (OH, SO4−, O2−) in the CNT@CoNC-5 + PMS system. Despite attempts made to use carbon nanotubes (CNTs) as metal-free catalysts for peroxymonosulfate (PMS) activation recently, the challenge remains in the preparation of carbon nanotubes by an in-situ method. In this paper, basing a novel molten salt-assisted method with heat treatment, cobalt (Co) and nitrogen (N) co-doped carbonaceous polyhedrons with self-catalyzed-grown CNTs on the surface (CNT@CoNC-x) were synthesized and employed to activate PMS to degradation oxytetracycline (OTC) in the aqueous phase. Such a unique structure, the three-dimensional carbon matrix with Co and N co-doped in the CNT@CoNC-x, not only confirmed the control of the active sites by the simple method, but also promoted the interaction between metal nanoparticles and CNTs. It is beneficial to accelerate the decomposition of PMS, which in turn improves the degradation efficiency of OTC. A two-stage kinetics of OTC degradation was studied and the apparent rate constant (k0∼5min) of the CNT@CoNC-5 catalyst is 66.97 L/g min−1, which increased 25.46 times greater than that of the CoNC catalyst obtained by calcining ZIF-67 directly. CNT@CoNC-5 catalysts exhibited good environmental resistance and recyclability.