What is the chemical mechanism at work during the carboxylation of graphene oxides?

The literature describes carboxylation as an efficient technique to increase the ability of graphene oxide to adsorb metals, as it increases the content of carboxylic acids in the material, while decreasing the content of C-O bonds of epoxide and hydroxyl groups [1,2,3]. Basically, a chemical treatment is carried out where acetic acid is used as a source of carboxylic acids, in a basic environment produced by the addition of NaOH (3M). Can anyone please tell me what is the mechanism involved in this carboxylation reaction? Specifically, why is a basic environment necessary for carboxylation and what are the chemical reactions involved?


Thanks


[1] HE, H.; KLINOWSKI, J.; FORSTER, M.; LERF, A. A new structural model for graphite oxide. Chemical Physics Letters, v. 287, n. 1-2, p. 53-56, abr. 1998. Elsevier BV. <http://dx.doi.org/10.1016/s0009-2614(98)00144-4>.


[2] WHITE, R. L.; WHITE, C. M.; TURGUT, H.; MASSOUD, A.; TIAN, Z. R. Comparative studies on copper adsorption by graphene oxide and functionalized graphene oxide nanoparticles. Journal of the Taiwan Institute of Chemical Engineers, v. 85, p. 18-28, abr. 2018. Elsevier BV. <http://dx.doi.org/10.1016/j.jtice.2018.01.036>.


[3] ZHAO, L.; CHEN, J.; XIONG, N.; BAI, Y.; YILIHAMU, A.; MA, Q.; YANG, S.; WU, D.; YANG, S. Carboxylation as an effective approach to improve the adsorption performance of graphene materials for Cu2+ removal. Science of the Total Environment, v. 682, p. 591-600, set. 2019. Elsevier BV. <http://dx.doi.org/10.1016/j.scitotenv.2019.05.190>.


