Ge Song,Xuedong Du,Yang Zheng,Pei Su,Yunping Tang,Minghua Zhou
To promote the reduction of Fe 3+ and improve the mineralization of organic pollutants , a novel electro-Fenton coupled with sulfite (Fe 3+ -EF/sulfite) process was constructed, which was superior to Fe 3+ -EF process in terms of carbamazepine (CBZ) degradation and mineralization with 5.99 times enhancement in degradation rate constant and 15.7 times enhancement on TOC removal. The complexation of Fe 3+ and sulfite prevented the precipitation of Fe 3+ , reduced Fe 3+ to Fe 2+ , and accelerated the iron cycle, so that H 2 O 2 utilization efficiency (0.051 mg TOC mg H2O2 −1 ) was greatly improved and electric energy consumption was greatly reduced (0.081 kWh g −1 TOC). The quenching experiments and EPR test confirmed that the reactive species, such as SO 3 •- , SO 4 •- , • OH, O 2 •- and 1 O 2 were responsible for the degradation of CBZ. This process also expanded the pH application range from 3 to 9 with satisfactory CBZ removal efficiency. This work verified the suitability of the Fe 3+ -EF/sulfite process for different sulfites (sulfite and bisulfite), typical pollutants (atrazine, sulfamethazine, rhodamine B) and real wastewater with 2.1–18.7 folds enhancement in degradation rate. The Fe 3+ -EF/sulfite process can achieve deep mineralization with low cost and simple operation, which has a broad and cost-effective application prospect in removal of refractory organic pollutants.
The reduction behavior of Fe3+ during the preparation of a zero-valent iron cocoanut biochar (ZBC8-3) by the carbothermic reduction method was analyzed. Fe3+ was first converted into Fe3O4, which was subsequently decomposed into FeO, and finally reduced to Fe0. A minor amount of γ-Fe2O3 was produced in the process. The isothermal thermodynamic data for the removal of Cu(II) over ZBC8-3 followed a Langmuir model. The Langmuir equation revealed a maximum removal capacity of 169.49 mg g−1 at pH = 5 for ZBC8-3. The removal of Cu(II) over ZBC8-3 fitted well to a pseudo-first-order equation, which suggested that the rate limiting step of the process was diffusion. The Cu(II) removal mechanism on ZBC8-3 involved the reduction of Cu(II) by Fe0 to produce Cu0 and Cu2O, while CC, C–O–, and –O–H formed a complex with Cu(II).
Nanoscale zerovalent iron synthesized using borohydride (B-NZVI) has been widely applied in environmental remediation in recent decades. However, the contribution of boron in enhancing the inherent reactivity of B-NZVI and its effectiveness in removing hexavalent chromium [Cr(VI)] have not been well recognized and quantified. To the best of our knowledge, herein, a core–shell structure of B-NZVI featuring an Fe–B alloy shell beneath the iron oxide shell is demonstrated for the first time. Alloyed boron can reduce H+, contributing to more than 35.6% of H2 generation during acid digestion of B-NZVIs. In addition, alloyed B provides electrons for Fe3+ reduction during Cr(VI) removal, preventing in situ passivation of the reactive particle surface. Meanwhile, the amorphous oxide shell of B-NZVI exhibits an increased defect density, promoting the release of Fe2+ outside the shell to reduce Cr(VI), forming layer-structured precipitates and intense Fe–O bonds. Consequently, the surface-area-normalized capacity and surface reaction rate of B-NZVI are 6.5 and 6.9 times higher than those of crystalline NZVI, respectively. This study reveals the importance of alloyed B in Cr(VI) removal using B-NZVI and presents a comprehensive approach for investigating electron pathways and mechanisms involved in B-NZVIs for contaminant removal.
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