TY - BOOK
T1 - Surface and Interface Properties of Graphene Oxide From Structure to Applications
AU - Liu, Zilong
PY - 2018
Y1 - 2018
N2 - Graphene oxide (GO) is a two dimensional nanomaterial featuring a variety of chemically reactive
functionalities, such as epoxides, hydroxyls and carboxyls at the edge and on the plane of GO sheets. The understanding of the surface and interface of GO is relevant to precisely control its properties that are important for potential applications, such as environmental remediation, water treatment, sensors and energy fields. The goal of this research was to obtain a deeper understanding of the fundamental interactions and processes that affected the surface and interface of GO, with a couple of scientific approaches-experimental, theoretical and computational.
Although GO has been well studied, the type of oxygen bonding and its spatial distributions on individual GO sheets have not yet been well understood. It was demonstrated that the spatial distribution of C-O and C=O on the single and multilayer GO could be directly determined with AFM-IR, atomic force microscopy coupled with infrared spectroscopy. These oxygen bonding were prefer to situate on areas where graphene was in discrete domains, with folded structures and on edges of GO sheets, with spatial resolution of a few tens of nanometres. Based on the experimental observations, an updated structural model of GO was proposed with C=O on its plane and edge.
After obtaining a clearer picture of atomic composition and bonding on GO, we mimicked sandstone reservoir pore surfaces using GO sheets deposited on flat silicon wafers, where the surface had oxidised to amorphous silica, as a model system. The absolute adhesion and the level of the low salinity (LS) response were consistent with observations on sand grains from oil reservoirs. The results indicated that the LS response was closely correlated with electric double layer repulsion and cation bridging contributed to adhesions of polar or acidic molecules from crude oil. The oxidised graphene surface offered a convincing model for the pore surfaces of reservoir materials, that can be used for systematic testing for developing more effective EOR strategies.
With the presence of various ions in the salt solutions of the second study, we investigated the ion effects on molecular interaction between GO and organic molecules. For experiments with the -COO(H) tips, adhesion decreased in the order: Ba2+ > Ca2+ > Mg2+ > Na+, whereas for the -CH3 tips, ion dependent adhesion was relatively low but followed the same sequence: Ba2+ > Ca2+ > Mg2+ ≈ Na+. It was proposed that ion bridging played a definitive role in the adhesion between -COO(H) tips and GO surfaces, while adhesion of -CH3 tips was a response to the hydrophilic interactions and the ion dependent part was suggested to arise from ion bridging
between the GO surface and slightly negative charged -CH3 tips because few anions absorbed on its surface. High pH had a notable effect on ion bridging and thus on the adhesion of the -COO(H) tip but a negligible effect on the -CH3 tip.
The fourth study shifted the focus from the fundamental perspectives to the applications of GO. It was demonstrated that the readily available GO and graphite nanosheet (GN) could be applied as sensing material to fabricate high performance strain sensors by using a simple synthetic method. With addition of 15 wt% GO, the gauge factor (GF) of GN based strain sensors considerably increased by ~1400% from 10 (without addition of GO) to 153 under 7% stretch deformation. Retaining an excellent linear response, 5 and 10 wt% GO/GN strain sensors had GFs of 30 and 120, with a stretchability of 50 and 15%, respectively. More importantly, a good balance between sensitivity and stretchability was obtained with the presence of GO, which effectively changed the microstructure of conductive network of GN films that was probed by SEM, TEM, Raman, XPS. Applicability of the strain sensors was also demonstrated for various applications ranging from the wearable wireless pedometer to human-machine interfacing.
AB - Graphene oxide (GO) is a two dimensional nanomaterial featuring a variety of chemically reactive
functionalities, such as epoxides, hydroxyls and carboxyls at the edge and on the plane of GO sheets. The understanding of the surface and interface of GO is relevant to precisely control its properties that are important for potential applications, such as environmental remediation, water treatment, sensors and energy fields. The goal of this research was to obtain a deeper understanding of the fundamental interactions and processes that affected the surface and interface of GO, with a couple of scientific approaches-experimental, theoretical and computational.
Although GO has been well studied, the type of oxygen bonding and its spatial distributions on individual GO sheets have not yet been well understood. It was demonstrated that the spatial distribution of C-O and C=O on the single and multilayer GO could be directly determined with AFM-IR, atomic force microscopy coupled with infrared spectroscopy. These oxygen bonding were prefer to situate on areas where graphene was in discrete domains, with folded structures and on edges of GO sheets, with spatial resolution of a few tens of nanometres. Based on the experimental observations, an updated structural model of GO was proposed with C=O on its plane and edge.
After obtaining a clearer picture of atomic composition and bonding on GO, we mimicked sandstone reservoir pore surfaces using GO sheets deposited on flat silicon wafers, where the surface had oxidised to amorphous silica, as a model system. The absolute adhesion and the level of the low salinity (LS) response were consistent with observations on sand grains from oil reservoirs. The results indicated that the LS response was closely correlated with electric double layer repulsion and cation bridging contributed to adhesions of polar or acidic molecules from crude oil. The oxidised graphene surface offered a convincing model for the pore surfaces of reservoir materials, that can be used for systematic testing for developing more effective EOR strategies.
With the presence of various ions in the salt solutions of the second study, we investigated the ion effects on molecular interaction between GO and organic molecules. For experiments with the -COO(H) tips, adhesion decreased in the order: Ba2+ > Ca2+ > Mg2+ > Na+, whereas for the -CH3 tips, ion dependent adhesion was relatively low but followed the same sequence: Ba2+ > Ca2+ > Mg2+ ≈ Na+. It was proposed that ion bridging played a definitive role in the adhesion between -COO(H) tips and GO surfaces, while adhesion of -CH3 tips was a response to the hydrophilic interactions and the ion dependent part was suggested to arise from ion bridging
between the GO surface and slightly negative charged -CH3 tips because few anions absorbed on its surface. High pH had a notable effect on ion bridging and thus on the adhesion of the -COO(H) tip but a negligible effect on the -CH3 tip.
The fourth study shifted the focus from the fundamental perspectives to the applications of GO. It was demonstrated that the readily available GO and graphite nanosheet (GN) could be applied as sensing material to fabricate high performance strain sensors by using a simple synthetic method. With addition of 15 wt% GO, the gauge factor (GF) of GN based strain sensors considerably increased by ~1400% from 10 (without addition of GO) to 153 under 7% stretch deformation. Retaining an excellent linear response, 5 and 10 wt% GO/GN strain sensors had GFs of 30 and 120, with a stretchability of 50 and 15%, respectively. More importantly, a good balance between sensitivity and stretchability was obtained with the presence of GO, which effectively changed the microstructure of conductive network of GN films that was probed by SEM, TEM, Raman, XPS. Applicability of the strain sensors was also demonstrated for various applications ranging from the wearable wireless pedometer to human-machine interfacing.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011935531&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Surface and Interface Properties of Graphene Oxide From Structure to Applications
PB - Department of Chemistry, Faculty of Science, University of Copenhagen
ER -