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.
Although sulfide is effective for heavy metal immobilization, it rarely exists in pristine pyrogenic biochar and easily undergoes intensive hydrolysis. In this work, carbothermal reduction of sulfate for on-site sulfide formation and simultaneous carbon layer encapsulation was developed to synthesize sulfide (CaS) modified biochar for enhancing heavy metal immobilization capacity. The initial reaction temperature for this carbothermal reduction was 700 °C. Increasing the pyrolysis temperature, modifier electron accepting ability and loading content could facilitate carbothermal reduction as further partly confirmed by on-site MS of pyrolysis gas and S 2p XPS of biochar analysis. The formed CaS on biochar could be greatly inhibited from hydrolysis due to the encapsulation effect of carbon layer and reached nearly 100% utilization efficiency in Cd2+ fast immobilization. TEM line scan and XRD of post-adsorbed biochar indicated that high heavy metal immobilization capacity was mainly attributed to the coprecipitation reaction governed by the formation of metal-sulfur bond. Compared with reported absorbents, CaS-modified biochar via carbothermal reduction with on-site encapsulation exhibited an excellent stability and outstanding immobilization capacity for various heavy metal ions (such as Cd2+, Pb2+, Cu2+, Zn2+, Ag+). Graphical Abstract
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