Heterogeneous Fenton oxidation of catechol and 4-chlorocatechol catalyzed by nano-Fe3O4: Role of the interface

Abstract

h i g h l i g h t sCatechol or 4-chlorocatechol was removed within 3 h in nano-Fe 3 O 4 /H 2 O 2 system. 4-Chlorocatechol was removed faster than catechol, with a minor mineralization. The oxidation of (chloro-)catechols obeyed Eley-Rideal mechanism. Carboxyl acids and ethers or dimers were generated and also adsorbed on nano-Fe 3 O 4 . a r t i c l e i n f o /g. Almost all the catechol or 4-chlorocatechol was oxidized within 3 h after the addition of H 2 O 2 , while about only 10% of the parent compounds adsorbed onto nano-Fe 3 O 4 without H 2 O 2 . And the oxidation curves followed the pseudo-second order kinetic model. 4-Chlorocatechol was oxidized faster than catechol, but with only 40% of mineralization. The contribution of homogeneous reaction induced by the leaching iron was limited. The surface generated reactive oxygen species were Å OH and HO Å 2 =O ÅÀ 2 , which were further reacted to generate oxygen-centered radicals in both systems, and carbon-centered radicals only in catechol system. In-situ flow-cell ATR-FTIR spectroscopy further confirmed that the adsorbed catechol or 4-chlorocatechol remained on the nano-Fe 3 O 4 surface, indicating an EleyRideal mechanism. Meanwhile, the generated carboxyl acids and some intermediates like ethers or dimers were also adsorbed. Accordingly, schematic diagrams of oxidation mechanisms of catechol and 4-chlorocatechol in nano-Fe 3 O 4 /H 2 O 2 system were proposed.

Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe 3 O 4 : Inhibitor or stabilizer?

“…The strong band at 1261 cm −1 was assigned to ν(CO) of adsorbed catechol species, and the band at 1275 cm −1 was assigned to the combination of an ether C-O-C stretch between aromatic rings and the O-H bending vibration (Dubey et al, 1998;Lana-Villarreal et al, 2005), suggesting the formation of polymeric catechol species during the oxidation. The IR results were consistent with the results from previous work in which the formation of carboxylates, alcohols and dimers of catecholate species, such as 2-furanglycolic acid, 1,2-benzendicarboxylic acid and formic acid, oxalic acid, maleic acid and succinic acid, was identified for the oxidation of catechol by Fe 3 O 4 -H 2 O 2 , by GC-MS (Gas Chromatography-Mass Spectrometer), ESI-Q-TOF-MS and ion chromatography analysis (He et al, 2014).…”

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review

“…Nevertheless, other researchers propose that the surface-generated ROS mainly oxidize the organic compounds in solution, especially for unadsorbed organic compounds (Furman et al, 2009;Liang et al, 2012), i.e., an Eley-Rideal mechanism. He et al (2014) directly observed that adsorbed catechol or 4-chlorocatechol remained on the nano-Fe 3 O 4 surface during the oxidation by in-situ flow-cell ATR-FTIR experiments. Hence, ROS was hypothesized to predominantly attack the unadsorbed parent compounds near the interface region.…”

“…Meanwhile, the activity of Fe 3 O 4 MNPs decreased gradually during consecutive runs, probably due to the leached iron and other factors, like the poisoning of the active catalytic sites by adsorbed organic species or oxidation of the surface (He et al, 2014) etc.…”

EDTA enhanced heterogeneous Fenton oxidation of dimethyl phthalate catalyzed by Fe 3 O 4 : Kinetics and interface mechanism

“…The preparation of the Fe 3 O 4 film was prepared as our previous work [28]. The FTIR Spectra were acquired using the Nicolet 8700 FTIR spectrometer (Thermo, USA) equipped with a DTGS detector and ATR accessory, and were recorded by averaging 32 scans at a resolution of 4 cm −1 .…”