Nanoscale
Published on 19 June 2014. Downloaded by North Carolina State University on 31/10/2014 02:19:56.
COMMUNICATION
Cite this: Nanoscale, 2014, 6, 8590
Received 4th March 2014 Accepted 17th June 2014
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Hollow hybrid polymer–graphene oxide nanoparticles via Pickering miniemulsion polymerization† Stuart C. Thickett,*a Noriko Wood,a Yun Hau Ngb and Per B. Zetterlund*a
DOI: 10.1039/c4nr01175a www.rsc.org/nanoscale
The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coating of graphene oxide (GO) is demonstrated. The capsules are prepared by Pickering miniemulsion polymerization, exploiting the surface activity of GO for its use as a colloidal surfactant. This approach represents a simple and convenient route towards hollow carbon nanostructures for a variety of applications. The incorporation of surface-modified TiO2 nanoparticles into the interior of these capsules was also demonstrated.
Hollow carbon-based nanostructures represent an exciting class of nanomaterials with potential applications such as nanoreactors, the delivery of therapeutic payloads, as supercapacitors and as catalytic supports.1 Common routes to the formation of hollow nanostructured carbon include the use of sacricial colloidal templates (e.g. silica, TiO2 or polymer nanoparticles) or deposition techniques such as layer-by-layer (LbL) assembly,2–6 however these approaches either require several synthetic steps or subsequent removal of the templating material. Furthermore, the removal of those hard templates is usually associated with hazardous processes including the use of strong hydrouoric acid.6 One of the most actively researched members of the carbon nanofamily is graphene, a two-dimensional sheet of sp2 hybridized carbon atoms arranged in a hexagonal bonding network.7 The exceptional mechanical, thermal and electrical properties that graphene possesses8 has led to applications ranging from supercapacitors, light energy conversion devices through to biological sensors.9,10 While most graphene-based
a
Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. E-mail: [email protected]; [email protected]; Tel: +61-2-9385-4447; +61-2-9385-4331
b
School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
† Electronic supplementary information (ESI) available: Characterization of GO nanosheets, TEM images of porous polymer particles, polymer conversion vs. time data, particle size data, BET isotherm data. See DOI: 10.1039/c4nr01175a
8590 | Nanoscale, 2014, 6, 8590–8594
materials are designed utilizing its two-dimensional planar structure, the pursuit of the preparation of hollow graphenic scaffolds is relatively less investigated.5,11,12 Graphitic carbon with hollow structures offers a number of advantages in specic applications. For instance, high electron conductivity together with porosity within the graphitic shell of the hollow structures will enable the materials to act as nanoreactors when the void space is decorated with other functional components for drug delivery and catalytic reactions. Graphene sheets have a high tendency to aggregate due to high surface area and strong p–p and van der Waals interactions,13 and are poorly dispersible in many polar and non-polar solvents.14,15 Due to these reasons, graphene oxide (GO), the oxidized form of graphene produced via the oxidation of graphite in the presence of strong acids,16 has been long considered the most convenient synthetic route towards the large-scale production of graphenic materials. Possessing a variety of oxygen-containing functional groups (e.g. hydroxyl, ketone, epoxide and carboxylate17), GO is readily dispersible in polar media18 and can be functionalized with small molecules or polymers for incorporation into organic or inorganic matrices.19,20 Reduction (either via chemical or thermal methods) of GO enables the partial restoration of the original graphenic framework.21 The preparation of hollow GO nanoscaffolds has been reported through the use of techniques such as LbL assembly and capillary molding,22,23 the latter requiring the dispersion of a GO aerosol and a colloidal template into a high temperature furnace. These methods involve driving GO to a solid interface via physical adsorption or electrostatic interactions. An attractive ‘so templating’ alternative involves utilizing the recently reported amphiphilic properties of GO nanosheets, namely that GO possesses surfactant-like properties and can stabilize oil-inwater (o/w) emulsions.24–26 These o/w emulsions are Pickering emulsions,27 whereby the stabilizer is a solid and not a classical surfactant, and are formed by the signicant reduction of interfacial energy by adsorption of the solid at the oil–water interface. Our group has used this phenomenon to demonstrate
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 19 June 2014. Downloaded by North Carolina State University on 31/10/2014 02:19:56.
Communication
the synthesis of polymer nanoparticles ‘armoured’ with a shell of nano-sized GO (with GO sheet size
Published on 19 June 2014. Downloaded by North Carolina State University on 31/10/2014 02:19:56.
COMMUNICATION
Cite this: Nanoscale, 2014, 6, 8590
Received 4th March 2014 Accepted 17th June 2014
View Article Online View Journal | View Issue
Hollow hybrid polymer–graphene oxide nanoparticles via Pickering miniemulsion polymerization† Stuart C. Thickett,*a Noriko Wood,a Yun Hau Ngb and Per B. Zetterlund*a
DOI: 10.1039/c4nr01175a www.rsc.org/nanoscale
The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coating of graphene oxide (GO) is demonstrated. The capsules are prepared by Pickering miniemulsion polymerization, exploiting the surface activity of GO for its use as a colloidal surfactant. This approach represents a simple and convenient route towards hollow carbon nanostructures for a variety of applications. The incorporation of surface-modified TiO2 nanoparticles into the interior of these capsules was also demonstrated.
Hollow carbon-based nanostructures represent an exciting class of nanomaterials with potential applications such as nanoreactors, the delivery of therapeutic payloads, as supercapacitors and as catalytic supports.1 Common routes to the formation of hollow nanostructured carbon include the use of sacricial colloidal templates (e.g. silica, TiO2 or polymer nanoparticles) or deposition techniques such as layer-by-layer (LbL) assembly,2–6 however these approaches either require several synthetic steps or subsequent removal of the templating material. Furthermore, the removal of those hard templates is usually associated with hazardous processes including the use of strong hydrouoric acid.6 One of the most actively researched members of the carbon nanofamily is graphene, a two-dimensional sheet of sp2 hybridized carbon atoms arranged in a hexagonal bonding network.7 The exceptional mechanical, thermal and electrical properties that graphene possesses8 has led to applications ranging from supercapacitors, light energy conversion devices through to biological sensors.9,10 While most graphene-based
a
Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. E-mail: [email protected]; [email protected]; Tel: +61-2-9385-4447; +61-2-9385-4331
b
School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
† Electronic supplementary information (ESI) available: Characterization of GO nanosheets, TEM images of porous polymer particles, polymer conversion vs. time data, particle size data, BET isotherm data. See DOI: 10.1039/c4nr01175a
8590 | Nanoscale, 2014, 6, 8590–8594
materials are designed utilizing its two-dimensional planar structure, the pursuit of the preparation of hollow graphenic scaffolds is relatively less investigated.5,11,12 Graphitic carbon with hollow structures offers a number of advantages in specic applications. For instance, high electron conductivity together with porosity within the graphitic shell of the hollow structures will enable the materials to act as nanoreactors when the void space is decorated with other functional components for drug delivery and catalytic reactions. Graphene sheets have a high tendency to aggregate due to high surface area and strong p–p and van der Waals interactions,13 and are poorly dispersible in many polar and non-polar solvents.14,15 Due to these reasons, graphene oxide (GO), the oxidized form of graphene produced via the oxidation of graphite in the presence of strong acids,16 has been long considered the most convenient synthetic route towards the large-scale production of graphenic materials. Possessing a variety of oxygen-containing functional groups (e.g. hydroxyl, ketone, epoxide and carboxylate17), GO is readily dispersible in polar media18 and can be functionalized with small molecules or polymers for incorporation into organic or inorganic matrices.19,20 Reduction (either via chemical or thermal methods) of GO enables the partial restoration of the original graphenic framework.21 The preparation of hollow GO nanoscaffolds has been reported through the use of techniques such as LbL assembly and capillary molding,22,23 the latter requiring the dispersion of a GO aerosol and a colloidal template into a high temperature furnace. These methods involve driving GO to a solid interface via physical adsorption or electrostatic interactions. An attractive ‘so templating’ alternative involves utilizing the recently reported amphiphilic properties of GO nanosheets, namely that GO possesses surfactant-like properties and can stabilize oil-inwater (o/w) emulsions.24–26 These o/w emulsions are Pickering emulsions,27 whereby the stabilizer is a solid and not a classical surfactant, and are formed by the signicant reduction of interfacial energy by adsorption of the solid at the oil–water interface. Our group has used this phenomenon to demonstrate
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 19 June 2014. Downloaded by North Carolina State University on 31/10/2014 02:19:56.
Communication
the synthesis of polymer nanoparticles ‘armoured’ with a shell of nano-sized GO (with GO sheet size
