Carbonous materials were found to catalyze the dechlorination of trichloroethylene (TCE) by green rust (GR), but the catalytic mechanism was not fully understood. We have developed a facile ball milling method to synthesize N-doped graphene (NG) with various N species, catalyzing fast dechlorination of TCE to acetylene by GR with the highest acetylene production rate of ~0.1 d −1 . The adsorption of TCE onto NG is mainly derived from the graphene region of NG, and high pyridinic N is essential for the enhanced TCE reduction by GR. Oxygen species did not enhance the TCE reduction in GR/NG system. High dechlorination rates are correlated to a high amount of defect in NG and a high electron conductivity of NG. Pyridinic N has the highest adsorption energy for TCE among all the N species, which leads to the highest catalytic performance. High electrochemically active surface area resulted from the high content of pyridinic N facilitate the NG-catalyzed dechlorination. The acetylene production rate in real groundwater is still around one-third of that in ultrapure water. This work not only reveals the catalytic mechanism of NG-catalyzed dechlorination by GR, but also provide a feasible approach for practical remediations of TCE-contaminated groundwater using GR-NG mixture.
The influence of intercalated anions on the structure and composition of green rusts supplies a theoretical possibility for the investigation of the structural modification of Fe II /Fe III (oxyhydr)oxide materials. β-Cyclodextrin was intercalated into the mixed-valent iron-based hydroxide layers to synthesize new green rust materials (β-CD GRs), pursuing high-capacity uranium VI (U VI ) sorption . The molar ratios of Fe II to Fe III and the molar ratios of β-CD GR to Fe II + Fe III had a significant effect on the synthesis of β-CD GRs. The synthesis process was further optimized by the quadric predictor and desirability function in a central composite design in combination. Both strong acidity and alkalinity were harmful to the adsorption of β-CD GRs towards U VI . The pseudo-first-order kinetic model and Langmuir isotherm model were appropriate in fitting the whole adsorption process. The maximum monolayer adsorption capacity of β-CD GRs was 2548.61 mg/g. The presence of mimic groundwater constituents explicitly deteriorated the interaction between β-CD GR and U VI species. Nanoscale nodules and particles were formed on the β-CD GR after the adsorption experiments. The peaks at 1159 and 609 cm −1 vanished with the band at 1103 cm −1 being left-shifted to 1117 cm −1 in the FTIR spectra of β-CD GR during the heterogeneous process. The intercalation of β-CD brought obvious enhancement of U VI species sorption to the GR material, which was combinedly driven by several reaction pathways and different from the unmodified GRs.
Qingchan Li,Wenjing Yao,Jinhua Zhang,Zhen Li,Wenhao Wang,Jiahao Du,Jinxiang Li
Green rust (GR) is an interlayer anion-containing Fe(II)/Fe(III) mineral material that is versatile in removing a series of ionic contaminants in water. Taking SeO 4 2- (Se(VI)) as the target contaminant, this study identified that the removal processes of Se(VI) by GR could be divided into three stages: initial rapid interlayer exchange, followed by a rebound, and finally slow removal. In addition, as the percentage of SO 4 2- in GR interlayer increased, the Se(VI) removal by GR gradually decreased. To mediate the SO 4 2- -induced rebound of Se(VI), the coupling of GR with iron nanoparticles (nFe 0 @GR) was proposed in this study and it was found that the removal efficiency of Se(VI) by nFe 0 @GR was 3.53 folds greater than that of GR. This study further revealed that the enhanced reactivity of nFe 0 @GR with Se(VI) could be attributed to the re-equilibration of SO 4 2- driven by the formed GR in situ . Since it had a weaker electrostatic repulsion with interlayer SeO 4 2- than pristine GR, the Se(VI) could be quickly removed by nFe 0 @GR without the rebound. Moreover, the nFe 0 @GR was demonstrated to be effective in immobilizing Se(VI) from simulated groundwater and has a great potential to reduce the risk of Se(VI) re-release into the environment.
The Schikorr reaction 3Fe(OH) 2 → Fe 3 O 4 + H 2 + 2H 2 O, has been proposed for nearly 100 years. Although it has shown great potential application value in steel corrosion, recovery of ferrous waste liquid, and other fields, the reaction catalyst itself is still unclear. We confirmed that Cu(II) ions were essentially converted into the oriented CuO nanosheets as a catalyst during a low-temperature hydrothermal process. Moreover, this catalytic reaction required the participation of hydroxide ions without relationship to sulfate ions and trace dissolved oxygen molecules in the solution. The growth process tracing experiment found that green rust was the reaction intermediate, and the reaction stage from green rust to Fe 3 O 4 was the reaction rate control stage. Finally, the reaction rate was clearly defined by using the FWHM of the XRD diffraction peak of the (3,1,1) crystal plane of Fe 3 O 4 , and the activation energy was calculated as 79.46 ± 5.05 kJ mol −1 .
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