Catalytic activity and mechanism of F- and Cl-doped graphene for peroxymonosulfate activation to remove tetracycline hydrochloride.

Highly active catalysts with salt and acid/alkali resistance are desired in peroxymonosulfate (PMS) activation processes and marine environment applications. F- and Cl-doped graphene (F-GN and Cl-GN) were prepared via electronegative and atom radius adjustment for tetracycline hydrochloride (TCH) pollution removal to satisfy these requirements. The introduction of special F and Cl functionalities into graphene exhibits superior electron transfer properties for PMS activation, considering the experimental and density functional theory (DFT) calculation results. The TCH degradation efficiency reached up to 80% under various pH and salt disturbance conditions with F-GN and Cl-GN. Cl-GN exhibited an activity superior to F-GN due to the higher electron polarization effect of C atoms adjacent to Cl atoms. The presence of more positive charged C sites in Cl-GN (around Cl doping) is more favorable for PMS attachment and sequence radical generation than F-GN. In addition, the main active species functionalized during reaction included ·OH and SO4-·, and the stability of F-GN and Cl-GN was confirmed to be over 60% by recycle test. Final research results provide an effective strategy for designing and preparing PMS activators resistant to salt, acid, and alkali, thereby expanding their application potential.

Elucidating the roles of Ni ions and crosslinking heteroatoms in Ni3(BHT)2/2GO as electron shuttles for electrocatalytic oxidation of tetracycline hydrochloride.

As a hot candidate for marine pollution control, electrocatalytic oxidation strongly depends on the characteristics of anode materials. Even though emerging 2D metal-organic frameworks (2D-MOFs)/graphene oxide (GO) complex has satisfied the conductive and tunable requirements of anode, electrocatalytic efficiency still needs to be improved by maximizing the electron carriers or shuttles. Herein, we capitalized upon crosslinking heteroatoms as pointcut to adjust the electron distribution, mobility, and transfer orientation in 2D-MOFs/GO. As a result, Ni3(BHT)2/2GO (metal centers: Ni; crosslinking heteroatoms: S), which was much higher than materials with metal centers of Cu or crosslinking heteroatoms of N, achieved superior conductivity and 100% tetracycline hydrochloride removal within 12 min. In Ni3(BHT)2/2GO, Ni ions and S atoms cooperated as electron shutters rather than isolated active center and granted accelerated electron transfer from 2D-MOFs to GO layers. Furthermore, Ni sites and S crosslinking heteroatoms exhibited superior activity for ⋅O2- and ⋅OH generation, whereas 1O2 depended more on C and O substrates. All experiments, theory calculations, and application expanding approved the practice feasibility of 2D-MOFs/GO in electrocatalytic oxidation by adjusting crosslinking heteroatoms. All these results provided new perspectives on the micro-molecular regulation for improving electrocatalytic efficiency.

Modulating Cu valence state in Cu and graphene oxide composites for electrocatalytic tetracycline hydrochloride degradation.

Cu and graphene oxide composites (Cu-GO) were designed by anchoring Cu+ via oxygen groups in GO based on the heavy co-relationships of copper (Cu) anode electrocatalytic activity with Cu valence state. With the consumption of oxygen groups under various pyrolysis temperatures, the Cu valence state changed from Cu ions (as CuCl2 and CuCl) to Cu oxide (CuO and Cu2O) and the final metallic Cu. In which the Cu+ in CuCl was more favorable for electrocatalytic oxidation than other Cu valence states. Due to the dramatic contribution of 1O2 and active chlorine, 100% degradation efficiency was achieved using tetracycline hydrochloride (TCH) as the target pollutant. Cu+ showed a selective preference for 1O2 and active chlorine triggering, rather than metallic Cu. Under the attack of 1O2 and active chlorine, the degradation intermediates of TCH were then provided by LC-MS results. The final results not only prove the feasibility of the Cu-GO/electrocatalysis system for pollution control but also shed light on the anode design via Cu valence state modulation.