Janus amphiphilic carbon nanotubes as Pickering interfacial catalysts for the treatment of oily wastewater by selective oxidation with hydrogen peroxide
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 °C,
pH0 = 3, Ccat = 0.25 g L−1, C2-NP,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 °C, considering pH0 = 3, Ccat = 2.27 g L−1 of total volume (water/oil ratio of 16:50 v/v) and C2-NP,oil,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.
This work is a result of the Project “PLASTIC_TO_FUEL&MAT -
Upcycling Waste Plastics into Fuel and Carbon Nanomaterials”, with
the reference POCI-01-0145-FEDER-031439, supported by national
funds through FCT and by the European Regional Development Fund
(ERDF); the Project “AIProcMat@N2020 - Advanced Industrial
Processes and Materials for a Sustainable Northern Region of Portugal
2020″, with the reference NORTE-01-0145-FEDER-000006, supported
by Norte Portugal Regional Operational Programme (NORTE 2020),
under the Portugal 2020 Partnership Agreement, through ERDF; and
the Associate Laboratory LSRE-LCM - UID/EQU/50020/2019 - funded
by national funds through FCT/MCTES (PIDDAC). Bruno F. Machado
acknowledges the financial support of the exploratory project under the
FCT Investigator Programme (ref. IF/00301/2015) with the financial
support of FCT/MCTES through national funds (PIDDAC).
