Thanh-Dinh Nguyen

Mesoporous nitrogen-doped carbon from nanocrystalline chitin assemblies

Nanocrystalline chitin has been used both as a soft template and as the carbon and nitrogen sources for preparing mesoporous nitrogen-doped carbon materials with a layered structure. The chitin nanorods prepared by sequential deacetylation and hydrolysis of fibrils isolated from king crab shells organized into a nematic liquid-crystalline phase. Silica/chitin composites obtained by sol–gel condensation of silica in the presence of liquid-crystalline chitin were carbonized and etched to yield mesoporous nitrogen-doped carbon films that replicate the layered nematic organization of the nanocrystalline chitin films. The high degree of mesoporosity and nitrogen doping in the liquid-crystalline biopolymer-derived carbon replicas allows them to function as efficient supercapacitor electrode materials. Films embedded with tin oxide nanoparticles displayed superior performance for supercapacitor electrodes.

Mesoporous Silica and Organosilica Films Templated by Nanocrystalline Chitin

Liquid crystalline phases can be used to impart order into inorganic solids, creating materials that mimic natural architectures. Herein, mesoporous silica and organosilica films with layered structures and high surface areas have been templated by nanocrystalline chitin. Aqueous suspensions of spindle-shaped chitin nanocrystals were prepared by sequential deacetylation and hydrolysis of chitin fibrils isolated from king crab shells. The nanocrystalline chitin self-assembles into a nematic liquid-crystalline phase that has been used to template silica and organosilica composites. Removal of the chitin template by either calcination or sulfuric-acid-catalyzed hydrolysis gave mesoporous silica and ethylene-bridged organosilica films. The large, crack-free mesoporous films have layered structures with features that originate from the nematic organization of the nanocrystalline chitin.

Chiroptical luminescent nanostructured cellulose films

In this work we report a straightforward and scalable method to fabricate luminescent and iridescent chiral nanomaterials with potential metal ion sensing capacity for environmental and biological applications. Nitrogen-doped carbon dots (N-CDs) were synthesized by a hydrothermal reaction of D-glucose and melamine. New free-standing chiral nematic composite materials with randomly distributed nanoparticles were prepared after N-CD co-assembled with CNCs via evaporation-induced self-assembly (EISA). The left-handed twisted, layered structure of chiral CNC composites remains intact for all the studied compositions, providing both iridescent and photoluminescent properties to our films. Structural, thermal, morphological and photophysical properties of the films were further explored. Overall, our experimental findings reveal that hydrothermal synthesis of melamine and D-glucose is an effective approach to obtain luminescent materials that can be combined with CNCs to obtain photonic films that retain long-range chiral nematic organization. These new functional materials have potential application as luminescent sensors for metal ions or bioimaging purposes.

Chiroptical, morphological and conducting properties of chiral nematic mesoporous cellulose/polypyrrole composite films

In this work, we describe novel conducting chiral nematic composites prepared via in situ oxidative chemical polymerization of pyrrole onto modified chiral nematic cellulose nanocrystal (CNC) films. The surface of free-standing iridescent CNC films was modified by four different approaches including TEMPO-oxidation, acetylation, desulfation and cationization after the fabrication of sulfated CNC films by evaporation-induced self-assembly (EISA). Structural, thermal, optical and morphological features of the modified films were further evaluated. The modified CNC films show enhanced thermal stability of more than 95 °C relative to the acid form of the CNCs. The chiroptical properties could be customized to yield vibrant iridescent colors ranging from cyan-green to red by the surface treatments. Moreover, our experimental findings reveal that the surface modification approach allows the swelling behavior of the iridescent CNC films to be tailored, a property with potential for the fabrication of novel security devices. Conductive CNC/PPy composite films were prepared by in situ oxidative polymerization of pyrrole onto CNC surfaces using FeCl3 and HCl as oxidizing agent and dopant, respectively. PPy was also polymerized onto chiral nematic mesoporous cellulose (CNMC) structures obtained through a concomitant assembly of CNCs and condensation of tetramethoxysilane (TMOS) to fabricate porous structures with enhanced specific charge capacity. Results reveal that the chiral nematic structure of CNCs could be replicated by the PPy coating. Furthermore, it was found that the electrochemical performance of CNC/PPy composites was improved after the development of mesoporous structures. These new, easily prepared materials are attractive candidates for environmentally friendly sensors and energy storage devices.

Aerogel templating on functionalized fibers of nanocellulose networks

We present novel spaghetti-like gel fibers of gelatin-functionalized cellulose nanocrystals (gCNCs) and aerogel templating of semiconductors on the gCNC scaffolds. An injection method is first used to make CNC aerogel fibers by crosslinking with gelatin (GE). The gelation of the injectable fibers can be conducted by manipulating interactions between CNCs and GE to preserve the chiral nematic order. The gCNC fibers are then used as templates to make porous TiO2/gCNC aerogel composites with structural organization imparted by the chiral arrangement and hierarchical organization of the gCNC fibers. The uniqueness of this templating concept lies in its ability to truly replicate spindle-shaped features of CNCs in freestanding TiO2 nanofibrillar aerogels. The affinity of functional groups of gelatin on the CNC aerogels with metal-based precursors causes the attachment of TiO2 nanoparticles around cellulose nanorods to form core–shell-like aerogel composites. The uniform integration of these components leads to the retention of TiO2 aerogel fibers after thermal removal of the gCNC template. To further demonstrate the use of gCNC fibers for templating, they are used to fabricate polypyrrole composites that retain the chiral structure of the aerogel. These new templated fibers are promising materials for supercapacitor electrodes, sensors, catalysts, and dye-sensitized solar cells. The results described here demonstrate a new and generalizable method to construct mesoporous materials with an open-network structure through helicoidal aerogel templating at the nanoscale.

Biocompatible Chitosan-Functionalized Upconverting Nanocomposites

Simultaneous integration of photon emission and biocompatibility into nanoparticles is an interesting strategy to develop applications of advanced optical materials. In this work, we present the synthesis of biocompatible optical nanocomposites from the combination of near-infrared luminescent lanthanide nanoparticles and water-soluble chitosan. NaYF4:Yb,Er upconverting nanocrystal guests and water-soluble chitosan hosts are prepared and integrated together into biofunctional optical composites. The control of aqueous dissolution, gelation, assembly, and drying of NaYF4:Yb,Er nanocolloids and chitosan liquids allowed us to design novel optical structures of spongelike aerogels and beadlike microspheres. Well-defined shape and near-infrared response lead upconverting nanocrystals to serve as photon converters to couple with plasmonic gold (Au) nanoparticles. Biocompatible chitosan-stabilized Au/NaYF4:Yb,Er nanocomposites are prepared to show their potential use in biomedicine as we find them exhibiting a half-maximal effective concentration (EC50) of 0.58 mg mL–1 for chitosan-stabilized Au/NaYF4:Yb,Er nanorods versus 0.24 mg mL–1 for chitosan-stabilized NaYF4:Yb,Er after 24 h. As a result of their low cytotoxicity and upconverting response, these novel materials hold promise to be interesting for biomedicine, analytical sensing, and other applications.