Flash Reforming Pyrogenic Carbon to Graphene for Boosting Advanced Oxidation Reaction

Abstract

Biomass‐derived pyrogenic carbon is attractive for advanced oxidation processes (AOPs); however, its amorphous structure limits its activation efficiency. Graphene with highly conjugated π structure possesses superior electron transport ability and thus high usefulness. However, bygone strategies are scarcely effective for reforming pyrogenic carbon to graphene. Herein, for the first time, a state‐of‐the‐art flash Joule heating (FJH) technique is showcased for reforming pyrogenic carbon to 2–5‐layer graphene. FJH current‐induced ultrahigh temperature and stress field realize instantaneous (≈10 s) regeneration of pyrogenic carbon via synchronization actions of carbonization, graphitization, and exfoliation. Meanwhile, volatilization of doped N atoms accelerates graphitization but has less of an effect on graphene configuration. Accordingly, tuned oxygen groups at the graphene edge boost peroxydisulfate (PDS) adsorption for finer initiating activation. Subsequently, 2D graphene with excellent electron utilization rate strengthens hydroxyl radical and direct electron transfer pathways in activating PDS for sulfamethoxazole (SMX) degradation. Impressively, the SMX degradation efficiency by fabricated graphene raises ≈8.9‐fold as compared with pristine pyrogenic carbon. Additionally, fabricated graphene is more efficient in PDS activation than commercial metal catalysts. Undoubtedly, this study realizes effective transformation of pyrogenic carbon to graphene for highly efficient metal‐free carbocatalyst.

Understanding the active sites and associated reaction pathways of metal-free carbocatalysts in persulfate activation and pollutant degradation

“…Meanwhile, other structural characteristics of NDs remain almost unvaried. This finding indicates that the discreet thermal treatment can convert the relatively unstable C–O to stable CO groups, 62,74 which provides a useful platform to investigate the role of CO in the catalytic activation of PMS/PDS. Indeed, the ratio of CO to C–O exhibited a positive linear relationship with the reaction rate constant ( k ) of the AOP with the correlation coefficient ( R 2 ) reaching 0.99, which consolidated that CO groups play a vital role in PMS activation toward the degradation of organics, in the case of 4-chlorophenol.…”

“…4a and b. 62 Reduction treatments are effective in increasing the ratio of sp 2 - to sp 3 -hybridized carbon, thus bringing more active sp 2 carbon sites and lowering the inactive sp 3 carbon sites. 61 The free-flowing electrons provided by the conjugated π network can activate PMS/PDS into free radicals based on the following eqn (1) and (2).…”

“…4b). 62 However, the defects and structure transformation induced by excessive edges were unfavorable for achieving efficient PDS-based AOPs given that graphitic degree and conductivity were also reported to be essential in edge-enriched carbocatalysts by promoting electron transportation from pollutants to activated PDS (PDS*) based on a nonradical electron transfer pathway. 37…”

“…First, thermal annealing and flash Joule heating are effective to finely tune the ratio of CO to C–O groups given the different thermal stabilities of CO and C–O. 62,74 Second, the use of reagents to deactivate the specific O groups; for example, hydroxyl (–OH), ketonic carbonyl (CO), and carboxylic groups (–COOH) on the surface of CNTs can be deactivated with benzoic anhydride, phenylhydrazine, and 2-bromo-1-phenylethanone, respectively. 65 Third, the modification of carbocatalyst surface to create or bring more specific O groups ( e.g.…”

“…, graphene and CNTs) and hence lowers the electrical conductivity as well as presents a steric hindrance effect on the interactions with PMS/PDS. 62 Meanwhile, O doping extent, location, and type should be carefully controlled to realize highly efficient O-doped carbon materials. 76…”