Kristina T. Constantopoulos

Benzene carboxylic acid derivatized graphene oxide nanosheets on natural zeolites as effective adsorbents for cationic dye removal.

Graphene oxide (GO) nanosheets were grafted to acid-treated natural clinoptilolite-rich zeolite powders followed by a coupling reaction with a diazonium salt (4-carboxybenzenediazoniumtetrafluoroborate) to the GO surface. Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) revealed successful grafting of GO nanosheets onto the zeolite surface. The application of the adsorbents for the adsorption of rhodamine B from aqueous solutions was then demonstrated. After reaching adsorption equilibrium the maximum adsorption capacities were shown to be 50.25, 55.56 and 67.56 mg g(-1) for pristine natural zeolite, GO grafted zeolite (GO-zeolite) and benzene carboxylic acid derivatized GO-zeolite powders, respectively. The adsorption behavior was fitted to a Langmuir isotherm and shown to follow a pseudo-second-order reaction model. Further, a relationship between surface functional groups, pH and adsorption efficiency was established. Results indicate that benzene carboxylic acid derivatized GO-zeolite powders are environmentally favorable adsorbents for the removal of cationic dyes from aqueous solutions.

Carbon Nanotubes Anchored to Silicon for Device Fabrication

This report highlights recent progress in the fabrication of vertically aligned carbon nanotubes (VA-CNTs) on silicon-based materials. Research into these nanostructured composite materials is spurred by the importance of silicon as a basis for most current devices and the disruptive properties of CNTs. Various CNT attachments methods of covalent and adsorptive nature are critically compared. Selected examples of device applications where the VA-CNT on silicon assemblies are showing particular promise are discussed. These applications include field emitters, filtration membranes, dry adhesives, sensors and scaffolds for biointerfaces.

Chiral self-assembly of designed amphiphiles: influences on aggregate morphology.

A series of novel amphiphiles were designed for self-assembly into chiral morphologies, the amphiphiles consisting of a glutamic acid (Glu) headgroup connected through an 11-carbon alkoxy chain to a diphenyldiazenyl (Azo) group and terminated with a variable length alkyl chain (R-Azo-11-Glu, where R denotes the number of carbons in the distal chain). TEM imaging of amphiphile aggregates self-assembled from heated, methanolic, aqueous solution showed that chiral order, expressed as twisted ribbons, helical ribbons, and helically based nanotubes, increased progressively up to a distal chain length containing eight carbons, and then decreased with further increases in distal chain length. TEM and CD showed that the chiral aggregations of single enantiomers were influenced by the molecular chirality of the headgroup. However, the assembly of D,L-10-Azo-11-Glu into nanotubes demonstrated that chiral symmetry breaking effected by the azo group was also relevant to the chiral organization of the amphiphiles. The chiral order of aggregate morphologies was additionally affected by the temperature and solvent composition of assembly in a manner correlated to the mechanism driving assembly; i.e., D,L-10-Azo-11-Glu was sensitive to the temperature of assembly but less so to solvent composition, while L-14-Azo-11-Glu was sensitive to solvent composition and not to temperature. FTIR and UV-vis spectroscopic investigations into the organization of the head and azo groups, in chiral and achiral structures, illustrated that a balance of the influences of the hydrophilic and hydrophobic components on self-assembly was required for the optimization of the chiral organization of the self-assembled structures.

A versatile approach to grafting biofouling resistant coatings from polymeric membrane surfaces using an adhesive macroinitiator

Biofouling is a serious problem for any wetted structure, having a negative influence on applications as diverse as marine transport, implanted medical devices and water treatment. Here, we address this issue by creating a polydopamine-based coating on desalination reverse osmosis membranes incorporating a bromo-macroinitiator for subsequent polymerisation of sulfobetaine monomers into anti-biofouling polymer brushes. Surface characterisation using attenuated total reflectance-Fourier transform infrared spectroscopy and the water contact angle demonstrated the attachment of the polysulfobetaine brushes and that the hydrophilicity increased for the coated membranes. Using a macroinitiator formation time of ten minutes followed by polyzwitterion coating of one hour resulted in a 17% increase in water flux without significant effect on the salt rejection performance. These membranes also exhibited substantial suppression of protein and bacterial attachment of 69% and 88% respectively compared to unmodified membranes.

Preparation and characterisation of vertically aligned single-walled carbon nanotube arrays on porous silicon

Vertically aligning carbon nanotubes (VACNTs) onto 2D porous materials is advantageous for many conceivable electronic applications but also for investigating the unique water transport properties of CNTs and the molecular separation of molecules during fluid transport through their inner shell. Here we report a wet chemical technique to produce vertically-aligned single walled CNT arrays on porous silicon (pSi). The nanotubes were first acid treated to produce carboxylic acid functionalities on the single-walled CNT. The carboxy-functional nanotubes were then covalently immobilised on a pSi surface that had been either ozone treated or silanated with aminopropyl triethoxysilane (APTES). The VACNT surfaces were analysed with atomic force microscopy (AFM), confocal Raman spectral imaging and Fourier transform infrared (FTIR) spectroscopy. Dense arrays of VACNTs were observed with the obtained CNT orientation and surface coverage depending upon attachment method and attachment reaction time.

Preparation and characterization of multiwalled carbon nanotube (MWCNT)/polymer nanostructured materials

Here, we report on a novel method of incorporating carbon nanotubes into a polymer matrix by using carbon nanotubes as a chain transfer agent (CTA) in Reversible Addition-Fragmentation chain Transfer (RAFT) polymerisations. The dithioester RAFT agents were covalently linked to multi-walled carbon nanotubes (MWCNTs) via a method, which involved the reaction of acyl halide MWCNTs with a magnesium chloride dithiopropanoate salt. Polystyrene (PSt) was subsequently grafted from the MWCNT surface via the core-first technique, which implies an outward growth of polymer chains from the core, using the R-group approach. The structure and morphology of the hybrid nanomaterials were investigated using FTIR, NMR, thrmogravimetric analysis (TGA) and atomic force microscopy (AFM) techniques. The results showed that the MWCNT chain transfer agent could be successfully used to mediate the growth of polystyrene polymer from the MWCNT surface via the living radical polymerisation approach.