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    Janus amphiphilic carbon nanotubes as Pickering interfacial catalysts for the treatment of oily wastewater by selective oxidation with hydrogen peroxide

    Year: 2020

    Journal: Catal. Today, Volume 356, OCT 1, page 205–215

    Authors: Diaz de Tuesta, Jose L.; Machado, Bruno F.; Serp, Philippe; Silva, Adrian M. T.; Faria, Joaquim L.; Gomes, Helder T.

    Organizations: FCTPortuguese Foundation for Science and TechnologyEuropean Commission [POCI-01-0145-FEDER-031439, IF/00301/2015]; European Regional Development Fund (ERDF)European Commission; Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through ERDF [NORTE-01-0145-FEDER-000006]; national funds through FCT/MCTES (PIDDAC) [UID/EQU/50020/2019]; FCT/MCTES through national funds (PIDDAC)

    Keywords: Janus; Carbon nanotubes; Oily wastewater; Amphiphilic catalysts; CWPO; Biphasic oxidation; Lipophilic pollutant

    Janus-like amphiphilic carbon nanotubes (CNTs) were tested as catalysts in the oxidation of 2-nitrophenol (2-NP) with hydrogen peroxide. A biphasic oil-water medium was used to simulate oily wastewater contaminated with the lipophilic model pollutant 2-NP. The CNTs were synthesized by sequentially feeding ethylene and/or acetonitrile, used as carbon and carbon/nitrogen precursors, respectively. The results obtained for 2-NP removal using biphasic systems were compared with those obtained by CWPO using aqueous solutions. The most active catalyst in the CWPO of 2-NP in aqueous solution was the CNT synthesized only with ethylene. This was explained by its high lipophilic character, allowing the complete removal of 2NP after 24 h of reaction at 50 degrees C, pH(0) = 3, C-cat = 0.25 g L-1, C-2- NP,C-0 = 0.5 g L-1 and the stoichiometric quantity of H2O2 needed for the total mineralization of 2-NP. For the oxidation of 2-NP in biphasic medium, only the Janus-like amphiphilic CNTs (containing a lipophilic undoped section synthetized from ethylene and a hydrophilic N-doped section synthetized from acetonitrile) revealed catalytic activity for the removal of 2-NP. The conversion of 2NP reached in biphasic oxidation conditions was 76.7% after 24 h of reaction at 50 degrees C, considering pH(0) = 3, C-cat = 2.27 g L-1 of total volume (water/oil ratio of 16:50 v/v) and C-2- NP,C-oil,C-0 = 5 g L-1. This removal was ascribed to the formation of Pickering emulsions, by maximizing the interfacial area through an increased contact between the catalyst and both liquid phases. A kinetic model is proposed to accurately predict the experimental data and evaluate the rate constants of the process and its variation with the prepared CNTs.
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