1. LSRE-LCM Hybrid Magnetic Carbon Nanocomposites
Shaking the present
Shaping the future
Hybrid Magnetic Carbon Nanocomposites
a tool for environmental catalytic applications
Rui S. Ribeiroa,b*, Adrián M.T. Silvab, Joaquim L. Fariab, Helder T. Gomesa
a Associate Laboratory LSRE-LCM, Polytechnic Institute of Bragança, Portugal
b Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Portugal
lsre-lcm.fe.up.pt
Introduction
The development of efficient and economically viable treatment technologies, able to cope with the increasing complexity of industrial wastewaters, is an ongoing challenge for the scientific community. Under this context, the so-called advanced oxidation processes (AOPs) are usually seen as a powerful tool, since they rely on the formation of highly oxidizing hydroxyl radicals (HO•). Catalytic wet peroxide oxidation (CWPO) is an AOP which relies on the catalytic decomposition of hydrogen peroxide via HO• formation. Therefore, catalyst design plays a crucial role in CWPO. Composite materials such as those combining highly active and magnetically separable iron-based catalysts with the easily tuned properties of carbon-based materials already revealed superior performances in CWPO [1]. Bearing this in mind, our work has been focused on the simultaneous incorporation of magnetic materials within carbon frameworks. At the first stages of this study, (i) carbon embedded and (ii) carbon encapsulated composites were prepared and applied in the CWPO of 4-nitrophenol (4-NP) aqueous model systems. On the one hand, (i) it was found that the activity for CWPO is enhanced by the simultaneous incorporation of cobalt and iron species; on the other hand, (ii) the encapsulation of magnetic materials within carbon shells limits the leaching of metals species while also increasing its activity for CWPO. Combining these beneficial features, a bimetallic iron-cobalt hybrid magnetic graphitic nanocomposite (CoFe2O4/MGNC), composed by a cobalt ferrite (CoFe2O4) core and a graphitic shell, was designed and applied in a real-case study implementing magnetic separation of the catalysts.
Results and discussion
Magnetic/metal phase
Carbon embedded
Carbon encapsulated
The role of cobalt in bimetallic iron-cobalt magnetic carbon xerogels developed for catalytic wet peroxide oxidation [2]
Hybrid magnetic graphitic nanocomposites for catalytic
wet peroxide oxidation applications [3]
CoFe2O4 core
Carbon
shell
Simultaneous incorporation of Co and Fe increases the activity in CWPO:
Co species promote a more efficient regeneration of Fe2+ from Fe3+
Co species catalyse the decomposition of H2O2 via HO• formation
The carbon shell:
Enhances the activity in CWPO, due to increased adsorptive interactions
Limits iron leaching, due to the confinement effect +
Bimetallic iron-cobalt hybrid magnetic graphitic nanocomposite (CoFe2O4/MGNC), composed by a CoFe2O4 core and a graphitic shell
Hybrid magnetic graphitic nanocomposites towards catalytic wet peroxide oxidation of the liquid effluent
from a mechanical biological treatment plant for municipal solid waste [4]
Conclusions
The application of a new generation catalyst, resulting from the encapsulation of CoFe2O4 within a graphitic shell, enables the treatment of waste waters with high pollutant loads, such as the liquid effluent from the MBT plant considered in this study. Regardless of the high organic and inorganic content, the biodegradability of the effluent was enhanced during the treatment, as reflected by the 2-fold increase of the BOD5/COD ratio obtained (widely used as an indicator of the biodegradability of liquid effluents). In addition, disinfection of the liquid effluent was achieved and the treated water revealed no toxicity against selected bacteria. The high stability of CoFe2O4/MGNC for CWPO was demonstrated in a series of five CWPO reaction/magnetic separation sequential experiments in the same vessel.
References
[1] R.S. Ribeiro, A.M.T. Silva, J.L. Figueiredo, J.L. Faria, H.T. Gomes, Appl. Catal., B 187 (2016) 428.
[2] R.S. Ribeiro, A.M.T. Silva, J.L. Figueiredo, J.L. Faria, H.T. Gomes, Catal. Today (2017), accepted.
[3] R.S. Ribeiro, A.M.T. Silva, P.B. Tavares, J.L. Figueiredo, J.L. Faria, H.T. Gomes, Catal. Today 280 (2017) 184.
[4] R.S. Ribeiro, R.O. Rodrigues, A.M.T. Silva, P.B. Tavares, A.M.C. Carvalho, J.L. Figueiredo, J.L. Faria, H.T. Gomes, Appl. Catal., B (2017), submitted.
Acknowledgements
This work was financially supported by: Project POCI FEDER – Associate Laboratory LSRE-LCM funded by FEDER through COMPETE Programa Operacional Competitividade e Internacionalização (POCI) – and by national funds through FCT - Fundação para a Ciência e a Tecnologia. R.S. Ribeiro acknowledges the FCT individual Ph.D. grant SFRH/BD/94177/2013, with financing from FCT and the European Social Fund (through POPH and QREN). A.M.T. Silva acknowledges the FCT Investigator 2013 Programme (IF/01501/2013), with financing from the European Social Fund and the Human Potential Operational Programme.