Abstract
Two commercial activated carbon were functionalized with nitric acid, sulfuric acid, and ethylenediamine to induce the modification of their surface functional groups and facilitate the stability of corresponding AC-supported iron catalysts (Fe/AC-f). Synthetized Fe/AC-f catalysts were characterized to determine bulk and surface composition (elemental analysis, emission spectroscopy, XPS), textural (N2 isotherms), and structural characteristics (XRD). All the Fe/AC-f catalysts were evaluated in the degradation of phenol in ultrapure water matrix by catalytic wet peroxide oxidation (CWPO). Complete pollutant removal at short reaction times (30–60 min) and high TOC reduction (XTOC = 80 % at ≤ 120 min) were always achieved at the conditions tested (500 mg·L−1 catalyst loading, 100 mg·L−1 phenol concentration, stoichiometric H2O2 dose, pH 3, 50 °C and 200 rpm), improving the results found with bare activated carbon supports. The lability of the interactions of iron with functionalized carbon support jeopardizes the stability of some catalysts. This fact could be associated to modifications of the induced surface chemistry after functionalization as a consequence of the iron immobilization procedure. The reusability was demonstrated by four consecutive CWPO cycles where the activity decreased from 1st to 3rd, to become recovered in the 4th run. Fe/AC-f catalysts were applied to treat two real water matrices: the effluent of a wastewater treatment plant with a membrane biological reactor (WWTP-MBR) and a landfill leachate, opening the opportunity to extend the use of these Fe/AC-f catalysts for complex wastewater matrices remediation. The degradation of phenol spiked WWTP-MBR effluent by CWPO using Fe/AC-f catalysts revealed pH of the reaction medium as a critical parameter to obtain complete elimination of the pollutant, only reached at pH 3. On the contrary, significant TOC removal, naturally found in complex landfill leachate, was obtained at natural pH 9 and half stoichiometric H2O2 dose. This highlights the importance of the water matrix in the optimization of the CWPO operating conditions.
Highlights
Prior to catalytic wet peroxide oxidation (CWPO) runs, for comparison purpose, the evolution of phenol concentration was followed during adsorption and CWPO runs with bare activated carbons (AC) and functionalized AC-f (Table 6)
It it could be concluded that the sequence for TOC reduction by CWPO follows could be concluded that the sequence for TOC reduction by CWPO follows the order: the order: Landfill leachate water, pH 9 > wastewater treatment plants (WWTPs) effluent, pH 3 > ultrapure water, pH 8
All the materials used in the functionalization of activated carbons, preparation of catalysts, and CWPO reaction were provided by Merck (Darmstadt, Germany)
Summary
Additional advantages are desired for the support to provide multifunctional catalysts with added values as adsorption capacity, low metal loading, regeneration of metal species, wide range of operating pH or in situ generation of hydroxyl radical source [13,16,33] In this sense, the use of magnetic supports [34,35], or the presence of immobilized magnetic particles could play the double role of CWPO catalytic site and easy recoverability [1,14,36,37], where the coupling of an electro-magnetic field [2] or microwave [4,16,27] has shown to improve the CWPO performance. Fe/AC-f catalysts to the removal of pollutants from complex effluents by CWPO
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