Molecular dynamics simulations of hyperbranched poly(ethylene imine)–graphene oxide nanocomposites as dye adsorbents for water purification

Abstract

Atomistically detailed molecular dynamics simulation were employed to study the adsorption capacity of graphene-oxide-based (GO) aqueous systems on the methylene blue (MB) dye, in the presence of branched poly(ethylene imine)...

The Role of Oxidation Pattern and Water Content in the Spatial Arrangement and Dynamics of Oxidized Graphene-Based Aqueous Dispersions

“…To examine whether the flakes of the closely packed arrangement in the EF-based systems actually correspond to stacked configurations and to acquire more detailed information regarding the relative orientation of neighboring flakes at larger distances as well, we calculated the orientational order parameter quantified through the second Legendre polynomial, , where θ is the angle formed by the two vectors which are normal to the examined sheets (one sheet is taken each time as reference) [ 17 ]. This parameter assumes a value of 1 if a perfect alignment of the examined vector is detected with respect to the reference direction, a value of −0.5 when a perpendicular arrangement is detected between the examined vectors, and a value of 0 for a random orientation.…”

“…The second model is a fully oxidized graphene sheet with carboxyl, hydroxyl, and epoxy groups distributed on both surfaces as well as around the edges, according to the Lerf–Klinowski model [ 81 ]. More details, including certain self-assembly characteristics of this model in an aquatic environment but in the presence of other compounds as well, have recently been discussed [ 17 ].…”

“…The degree of hydration and the nature of the interactions among the components play a crucial role in the relative arrangement of the solute molecules and thus in the final structure formed in the dispersion [ 8 , 9 ]. Electrostatic [ 1 ], as well as specific, interactions (such as hydrogen bonding [ 10 , 11 , 12 , 13 ]) between the solute and the water molecules, in conjunction with the degree of hydrophilicity/hydrophobicity [ 13 , 14 , 15 ] of the oxidized carbon components or the presence of functional groups [ 15 , 16 , 17 ], essentially drive the self-assembly process of the carbon-based molecules. In the case of graphene oxide (GO) aqueous systems, the overall degree of oxidation [ 12 , 13 ], the presence or absence of specific oxidized groups (e.g., hydroxyl, epoxy, carboxyl) [ 18 , 19 , 20 ], the oxidation pattern (i.e., the spatial distribution of these groups) [ 12 , 13 , 21 , 22 ], and the charging state of the flakes [ 1 , 3 , 13 ] are directly associated with the self-organization process [ 23 ] and with the morphological features (average size, aggregation number, stacking behavior) of the formed aggregates [ 7 , 24 , 25 ].…”

“…The formation of spatially isolated or interconnected GO aggregates may significantly affect the properties of these systems [ 25 , 26 ], while the details of the inter- and intra-cluster arrangement (i.e., the average separation between the GO sheets belonging in the same or in different aggregates [ 27 , 28 , 29 ]), as well as the diffusional dynamics of entrapped water or ionic moieties within their interior [ 28 , 29 , 30 , 31 ], essentially determine the suitability of these systems as components in several industrial (e.g., in selective gas separation [ 32 , 33 , 34 ], desalination [ 16 , 35 , 36 , 37 ]), environmental (e.g., nanofiltration [ 38 , 39 , 40 ], water purification [ 17 , 39 , 41 , 42 ]), and biomedical (e.g., drug and gene delivery [ 43 ], toxicity assessment [ 44 ]) processes. Controlling these features by obtaining detailed information at the microscopic (or even better at the atomic) level is therefore essential for a rational design of these materials.…”

Construction and application of carbon aerogels in microwave absorption

“…Carbon aerogels, a unique class of porous material constructed with carbon-based materials, demonstrate attractive properties in the fields of energy storage, 15,16 catalysis, 17,18 gas storage 19 and wastewater treatment. 20,21 That is, they benefit from the low density, light weight, high conductivity and ultra-high specific surface area of carbon aerogels. [22][23][24] Significantly, the structural characteristics mentioned above ensure that the aerogel itself is a promising candidate for microwave absorption.…”