Principles governing control of aggregation and dispersion of aqueous graphene oxide

Abstract Controlling the structure of graphene oxide (GO) phases and their smaller analogues, graphene (oxide) quantum dots (GOQDs), is vitally important for any of their widespread intended applications: highly ordered arrangements of nanoparticles for thin-film or membrane applications of GO, disp...

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Autores principales:	James L. Suter, Peter V. Coveney
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/4d84dad5830644fbb635b53600c18e79
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spelling	oai:doaj.org-article:4d84dad5830644fbb635b53600c18e792021-11-21T12:18:11ZPrinciples governing control of aggregation and dispersion of aqueous graphene oxide10.1038/s41598-021-01626-32045-2322https://doaj.org/article/4d84dad5830644fbb635b53600c18e792021-11-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-01626-3https://doaj.org/toc/2045-2322Abstract Controlling the structure of graphene oxide (GO) phases and their smaller analogues, graphene (oxide) quantum dots (GOQDs), is vitally important for any of their widespread intended applications: highly ordered arrangements of nanoparticles for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials and three-dimensional porous arrangements for hydrogels. In aqueous environments, it is not only the chemical composition of the GO flakes that determines their morphologies; external factors such as pH and the coexisting cations also influence the structures formed. By using accurate models of GO that capture the heterogeneity of surface oxidation and very large-scale coarse-grained molecular dynamics that can simulate the behaviour of GO at realistic sizes of GOQDs, the driving forces that lead to the various morphologies in aqueous solution are resolved. We find the morphologies are determined by a complex interplay between electrostatic, $${\pi }$$ π – $${\pi }$$ π and hydrogen bonding interactions. Assembled morphologies can be controlled by changing the degree of oxidation and the pH. In acidic aqueous solution, the GO flakes vary from fully aggregated over graphitic domains to partial aggregation via hydrogen bonding between hydroxylated domains, leading to the formation of planar extended flakes at high oxidation ratios and stacks at low oxidation ratios. At high pH, where the edge carboxylic acid groups are deprotonated, electrostatic repulsion leads to more dispersion, but a variety of aggregation behaviour is surprisingly still observed: over graphitic regions, via hydrogen bonding and “face-edge” interactions. Calcium ions cause additional aggregation, with a greater number of “face-face” and “edge-edge” aggregation mechanisms, leading to irregular aggregated structures. “Face-face” aggregation mechanisms are enhanced by the GO flakes possessing distinct domains of hydroxylated and graphitic regions, with $${\pi }$$ π – $${\pi }$$ π and hydrogen bonding interactions prevalent between these regions on aggregated flakes respectively. These findings furnish explanations for the aggregation characteristics of GO and GOQDs, and provide computational methods to design directed synthesis routes for self-assembled and associated applications.James L. SuterPeter V. CoveneyNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-11 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q James L. Suter Peter V. Coveney Principles governing control of aggregation and dispersion of aqueous graphene oxide
description	Abstract Controlling the structure of graphene oxide (GO) phases and their smaller analogues, graphene (oxide) quantum dots (GOQDs), is vitally important for any of their widespread intended applications: highly ordered arrangements of nanoparticles for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials and three-dimensional porous arrangements for hydrogels. In aqueous environments, it is not only the chemical composition of the GO flakes that determines their morphologies; external factors such as pH and the coexisting cations also influence the structures formed. By using accurate models of GO that capture the heterogeneity of surface oxidation and very large-scale coarse-grained molecular dynamics that can simulate the behaviour of GO at realistic sizes of GOQDs, the driving forces that lead to the various morphologies in aqueous solution are resolved. We find the morphologies are determined by a complex interplay between electrostatic, $${\pi }$$ π – $${\pi }$$ π and hydrogen bonding interactions. Assembled morphologies can be controlled by changing the degree of oxidation and the pH. In acidic aqueous solution, the GO flakes vary from fully aggregated over graphitic domains to partial aggregation via hydrogen bonding between hydroxylated domains, leading to the formation of planar extended flakes at high oxidation ratios and stacks at low oxidation ratios. At high pH, where the edge carboxylic acid groups are deprotonated, electrostatic repulsion leads to more dispersion, but a variety of aggregation behaviour is surprisingly still observed: over graphitic regions, via hydrogen bonding and “face-edge” interactions. Calcium ions cause additional aggregation, with a greater number of “face-face” and “edge-edge” aggregation mechanisms, leading to irregular aggregated structures. “Face-face” aggregation mechanisms are enhanced by the GO flakes possessing distinct domains of hydroxylated and graphitic regions, with $${\pi }$$ π – $${\pi }$$ π and hydrogen bonding interactions prevalent between these regions on aggregated flakes respectively. These findings furnish explanations for the aggregation characteristics of GO and GOQDs, and provide computational methods to design directed synthesis routes for self-assembled and associated applications.
format	article
author	James L. Suter Peter V. Coveney
author_facet	James L. Suter Peter V. Coveney
author_sort	James L. Suter
title	Principles governing control of aggregation and dispersion of aqueous graphene oxide
title_short	Principles governing control of aggregation and dispersion of aqueous graphene oxide
title_full	Principles governing control of aggregation and dispersion of aqueous graphene oxide
title_fullStr	Principles governing control of aggregation and dispersion of aqueous graphene oxide
title_full_unstemmed	Principles governing control of aggregation and dispersion of aqueous graphene oxide
title_sort	principles governing control of aggregation and dispersion of aqueous graphene oxide
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/4d84dad5830644fbb635b53600c18e79
work_keys_str_mv	AT jameslsuter principlesgoverningcontrolofaggregationanddispersionofaqueousgrapheneoxide AT petervcoveney principlesgoverningcontrolofaggregationanddispersionofaqueousgrapheneoxide
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Principles governing control of aggregation and dispersion of aqueous graphene oxide

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