Are carboxylic anhydrides in graphene oxides considered adsorption sites for metals? If so, are they more or less reactive than carboxylic acids?

Question

The literature abundantly addresses the fact that carboxylic acids present in graphene oxides act as efficient adsorption sites for metals in aqueous solutions (e.g., HE et al., 2021; ZHAO et al., 2019; NOVÁCEK et al., 2017; WANG et al., 2018). Wang et al. (2018), for example, showed through DFT measurements that the adsorption energies of the complexes (–COOH)/Co, GO(–OH)/Co, and NGO/Co, where N corresponds to nitrogen-containing functional groups introduced into graphene oxide and Co to cobalt ions, were 44.05 kcal/mol, 16.44 kcal/mol, and 6.33 kcal/mol, in that order. This result was corroborated by the performance of the adsorbents in removing Co(II) from the water (GO (0.74 mmol/g) > NGO (0.46 mmol/g)). However, I have not found anything regarding whether carboxylic anhydrides, which can be identified via potentiometric titration, also capture metals through their complexation and/or via ion exchange. I would like to know if they can and if their reactivity is lower than, equal to, or higher than that of carboxylic acids in the water, present in graphene oxides, for the adsorption of metals. Thanks in advance!

HEA, Lei; WANG, Lei; ZHU, Haomiao; WANG, Zhe; ZHANG, Luxia; YANG, Lutao; DAI, Yong; MO, Hong; ZHANG, Jun; SHEN, Jian. A reusable Fe3O4/GO-COOH nanoadsorbent for Ca2+ and Cu2+ removal from oilfield wastewater. Chemical Engineering Research and Design, v. 166, n. 171, p. 248-258, jan. 2021.

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.

NOVÁČEK, M.; JANKOVSKÝ, O.; LUXA, J.; SEDMIDUBSKÝ, D.; PUMERA, M.; FILA, V.; LHOTKA, M.; KLÍMOVÁ, K.; MATĚJKOVÁ, S.; SOFER, Z. Tuning of graphene oxide composition by multiple oxidations for carbon dioxide storage and capture of toxic metals. Journal of Materials Chemistry A, v. 5, n. 6, p. 2739-2748, 2017. Royal Society of Chemistry (RSC). http://dx.doi.org/10.1039/c6ta03631g.

WANG, X.; LIU, Y.; PANG, H.; YU, S.; AI, Y.; MA, X.; SONG, G.; HAYAT, T.; ALSAEDI, A.; WANG, X. Effect of graphene oxide surface modification on the elimination of Co(II) from aqueous solutions. Chemical Engineering Journal, v. 344, p. 380-390, jul. 2018. Elsevier BV. http://dx.doi.org/10.1016/j.cej.2018.03.107.

Answer 1

There are no surprises that the metal adsorption literature is silent about carboxylic anhydride on carbon surfaces. These groups do exist on carbon surfaces but as you can guess from the name "anhydride" and "water" do not get along very well. This is why I had asked you to clarify your medium? These anhydride groups will enventually hydrolyze to carboxylic acid groups. There is a very nice paper "Formation and chemistry of carboxylic anhydrides at the graphene edge" [RSC Adv., 2015,5, 104198-104202, DOI https://doi.org/10.1039/C5RA23209K], that shows the hydrolysis of carboxylic anhydride in water and in humid air. This process is relatively fast as show in the Supporting File.

In the field of carbons and surfaces, I would advise to read at 12 papers before arriving at a conclusion. Surfaces are very very difficult to analyze chemically and a lot of speculation exists.