Hummers’ and Brodie’s graphene oxides as photocatalysts for phenol degradation
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PhotocatalysisGraphene oxideMetal-freeSurface chemistryPhotoluminescence
Pedrosa, M., Da Silva, E. S., Pastrana-Martínez, L. M., Drazic, G., Falaras, P., Faria, J. L., ... & Silva, A. M. (2020). Hummers’ and Brodie’s graphene oxides as photocatalysts for phenol degradation. Journal of Colloid and Interface Science, 567, 243-255.
SponsorshipThis work was financially supported by project NORTE-01- 0145-FEDER-031049 (InSpeCt) funded by FEDER funds through NORTE 2020 - Programa Operacional Regional do NORTE and by national funds (PIDDAC) through FCT/MCTES (PTDC/EAMAMB/ 31049/2017). We would also like to thank the scientific collaboration under project ‘‘AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020” (NORTE-01-0145-FEDER-000006, NORTE 2020, Portugal 2020 Partnership Agreement, through FEDER), project ‘‘Associate Laboratory LSRE-LCM” (UID/EQU/50020/2019 - FCT/ MCTES – PIDDAC) and project 2DMAT4FUEL (POCI-01-0145- FEDER-029600 - COMPETE2020 – FCT/MCTES - PIDDAC). MP acknowledges the PhD research grant from FCT (Ref. SFRH/ BD/102086/2014). LMPM acknowledges the Spanish Ministry of Economy and Competitiveness (MINECO) and the European Social Fund for a Ramon y Cajal research contract (RYC-2016-19347). GD acknowledges the Slovenian Research Agency (P2-0393). PF acknowledges support from Prince Sultan Bin Abdulaziz International Prize for Water–Alternative Water Resources Prize 2014
Undoped metal-free graphene oxide (GO) materials prepared by either a modified Hummers’ (GO-H) or a Brodie’s (GO-B) method were tested as photocatalysts in aqueous solution for the oxidative conversion of phenol. In the dark, the adsorptive capacity of GO-B towards phenol (~35%) was higher than that of GO-H (~15%). Upon near-UV/Vis irradiation, GO-H was able to remove 21% of phenol after 180 min, mostly through adsorption. On the other hand, by using less energetic visible irradiation, GO-B removed as much as 95% in just 90 min. By thorough characterization of the prepared materials (SEM, HRTEM, TGA, TPD, Raman, XRD, XPS and photoluminescence) the observed performances could be explained in terms of their different surface chemistries. The GO-B presents the lower concentration of oxygen functional groups (in particular carbonyl groups as revealed by XPS) and it has a considerably higher photocatalytic activity compared to GO-H. Photoluminescence (PL) of liquid dispersions and XRD analysis of powders showed lower PL intensity and smaller interlayer distance for GO-B relative to GO-H, respectively: this suggests lower electron-hole recombination and enhanced electron transfer in GO-B, in support of its boosted photocatalytic activity. Reusability tests showed no efficiency loss after a second usage cycle and over three runs under visible irradiation, which was in line with the similarity of the XPS spectra of the fresh and used GO-B materials. Moreover, scavenging studies revealed that holes and hydroxyl radicals were the main reactive species in play during the photocatalytic process. The obtained results, establish for the first time, that GO prepared by Brodie’s method is an active and stable undoped metal-free photocatalyst for phenol degradation in aqueous solutions, opening new paths for the application of more sustainable and metal-free materials for water treatment solutions.