Ming Lei,Yao Tang,Huimin Wang,Lihua Zhu,Guihua Zhang,Yu Zhou,Heqing Tang
It is still very difficult to achieve rapid cleavage of C-Cl bond of highly-chlorinated benzenes by catalytic reduction process under mild conditions. By using pentachlorobenzene (PentaCB) as a representative of highly-chlorinated benzenes, we proposed a strategy to achieve rapid and complete dechlorination of highly-chlorinated benzenes by exploiting palladium with low content deposited g-C 3 N 4 (Pd/g-C 3 N 4 ) as a catalyst with NaBH 4 as a reductant. Under favorable conditions, this strategy yielded a dechlorination efficiency of 100% for PentaCB (0.4 mmol L −1 ) in methanol solution at 30 °C within 20 min, and especially the consumption of NaBH 4 is as low as 10 mmol L −1 with a molar ratio of Cl atoms to NaBH 4 of only 1:5. A hydro-dechlorination pathway was confirmed to dominate the dechlorination of PentaCB, which involves active hydrogen species (H*) as being identified by electron spin resonance (ESR) monitoring and isotope labelling experiments. The dechlorination rate constant value of chlorobenzenes (CBs) was only a little dependent on the number of chlorine atoms and the chlorine atom with smaller steric hindrance was prior to be substituted by H*. A catalytic mechanism that Pd nanoparticles played an important role on both the weakening/breaking of C-Cl bond and the formation of active hydrogen species was further clarified: Pd exerts affinity interaction on chlorine atoms at ortho -position of CBs molecules to form adsorbed state [CBs] ads ; H* was formed on the Pd surface due to its strong ability in H* retainment; subsequently the generated H* attacks the C-Cl bond in [CBs] ads to achieve hydrodechlorination. The new method provides a highly efficient method to remove halogenated pollutants.
Electrocatalytic hydrodehalogenation (ECHD) offers a promising approach for detoxification of the halogenated antibiotics via hydrogenolysis of the C-X bonds (X = F, Cl or Br). Herein we demonstrated that the commercially-available cobalt phthalocyanine (CoPc) molecules with a high-loading of −[Co-N 4 ]- moieties (Co wt%: 10.8 %) were exceptionally active for hydrogenolysis of the C-Cl bonds in florfenicol (FLO). It afforded an impressive mass activity of 6.2 g FLO h −1 g -1 Co , a low Co leaching of 0.34 μg/L and a strong tolerance to interference from impurities in water, significantly surpassing reported Co/Fe/Ni-based particle and single-site counterparts. Mechanistic studies revealed that the ECHD on CoPc underwent a direct electron transfer manner rather than the atomic hydrogen (H*)-mediated indirect way, and the ECHD efficacy was affected by both the electron and proton transfer kinetics. The single-atom Co, with its d orbitals constituting the lowest unoccupied molecular orbitals of CoPc, served as the primary active site. It facilitated both electron and proton transfer, as well as the cleavage of the C-Cl bond but not the C-F bond. In a continuous-flow cell, the CoPc/C-driven ECHD reduced the antibacterial activity of a FLO-contaminated natural lake water sample by 90.8 % with an energy consumption of 0.19 kwh g -1 FLO . This study highlighted great promise of the single-atom metal-bearing molecular catalyst toward the sustainable detoxification of halogenated antibiotics-contaminated water.
Electrocatalytic hydrodechlorination (EHDC) is a promising approach for decomposing chlorinated organic compounds in water treatment. However, the efficiency of EHDC is constrained by kinetic mismatch between C−Cl bond cleavage and atomic hydrogen (H*) utilization. Herein, we develop a heterostructured Pd-H x WO 3 electrocatalyst with Pd nanoparticles (Pd NPs) anchored on H x WO 3 substrate, which can efficiently decompose 2,4-dichlorophenol (2,4-DCP) by taking advantage of the hydrogen spillover effect. Specifically, the resulting Pd-H x WO 3 electrocatalyst exhibits superior dechlorination rate constant ( k = 1.142 h −1 ) and Faradic efficiency (FE = 10.1 %) than monometallic Pd ( k = 0.3600 h −1 , FE = 3.74 %) and bare H x WO 3 ( k = 0.1167 h −1 , FE = 2.11 %), along with exceptional pH adaptability and stability. Electron spin resonance (ESR) and electrochemical and kinetic isotope effect (KIE) measurements indicate that the transport of the H* from H x WO 3 to Pd NPs is the key to enhanced EHDC performance. Theoretical studies reveal that the Volmer step of water dissociation to produce H* is more favorable due to lower transition state (TS) energy (0.344 eV) on H x WO 3 than that on Pd (TS = 0.532 eV). Furthermore, the interfacial electron redistribution in Pd-H x WO 3 lowers the thermodynamic (Δ G = 0.207 eV) and kinetic (Δ G = 0.239 eV) barriers for H* transfer from the internal site of H x WO 3 to interfacial Pd sites, thereby facilitating the proton-coupled electron transfer (PCET)-mediated EHDC on Pd site. This work provides a new proof-in-concept demonstration for designing hydrogen spillover-integrated electrocatalysts to enhance H* generation-transfer-utilization in EHDC for water decontamination.
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