Synthesis and characterization of surface engineered nanomaterials via catechol derivatives

Department of Chemical EngineeringAll nanomaterials exhibit large surface to volume ratio in common and their surfaces have great influence with physicochemical properties of them. Therefore, surface engineering of nanomaterials is key to the utilization of unique nanomaterials properties and flexible strategies for deign of advanced materials. In this respect, catechol based nanocoating have been significantly attracted for application of nanocrystals and functionalization of substrates because of its adaptability to universal surface and high affinity in harsh condition. This dissertation demonstrates fabrication and characterization of nanocoating through amine mediated redox modulation of catechol. Synthetic mechanism of the nanocoating was suggested and surface engineering of metal oxide nanoparticles by the coating method have been studied. In addition, compact, biocompatible, and charge modulated iron oxide nanoparticles were synthesized and its bio-application was reported. First, conformal nanocoatings to nanostructured materials was achieved through amine-mediated redox control of a catechol system by separating catechol and amine, which effectively suppress cohesion and enhance a adhesion to yield an optimized nanocoating. The amine-assisted catechol nanocoating exhibits roughness of <0.358 nm and thickness of 1.69 nm on flat substratesthe hydrodynamic diameter of coated iron oxide nanoparticles is less than 20 nm. Surface characterization, density functional theory calculations, and effect of separated amine were investigated to elucidate the coating mechanism. Three key roles of separated amine in the catechol-based nanocoating were suggested as follows, adhesion promotion, suppression of polymerization, and additional stabilization through an in-situ generated, newly designed catechol-amine adduct. Second, multidentate catechol based polyethylene glycol random copolymer ligands was synthesized by reverse addition and fragmentation transfer polymerization. Compact, biocompatible and colloidal stable iron oxide nanoparticles have been synthesized by the ligands via the amine assisted catechol nanocoating method and applied into in vivo magnetic resonance contrast agents. High resolution magnetic resonance angiography with long circulation time was reported. Finally, charge modulated metal oxide nanoparticles were synthesized by surface engineering with multidentate catechol based polymeric ligands. The charged iron oxide nanoparticles exhibit different behavior in vitro cell experiments and gene delivery into cell by positive charged nanoparticles was demonstrated.clos

Facile Method to Prepare for the Ni2P Nanostructures with Controlled Crystallinity and Morphology as Anode Materials of Lithium-Ion Batteries

Conversion reaction materials (transition metal oxides, sulfides, phosphides, etc.) are attractive in the field of lithium-ion batteries because of their high theoretical capacity and low cost. However, the realization of these materials in lithium-ion batteries is impeded by large voltage hysteresis, high polarization, inferior cycle stability, rate capability, irreversible capacity loss in first cycling, and dramatic volume change during redox reactions. One method to overcome these problems is the introduction of amorphous materials. This work introduces a facile method to synthesize amorphous and crystalline dinickel phosphide (Ni2P) nanoparticle clusters with identical morphology and presents a direct comparison of the two materials as anode materials for rechargeable lithium-ion batteries. To assess the effect of crystallinity and hierarchical structure of nanomaterials, it is crucial to conserve other factors including size, morphology, and ligand of nanoparticles. Although it is rarely studied about synthetic methods of well-controlled Ni2P nanomaterials to meet the above criteria, we synthesized amorphous, crystalline Ni2P, and self-assembled Ni2P nanoparticle clusters via thermal decomposition of nickel-surfactant complex. Interestingly, simple modulation of the quantity of nickel acetylacetonate produced amorphous, crystalline, and self-assembled Ni2P nanoparticles. A 0.357 M nickel-trioctylphosphine (TOP) solution leads to a reaction temperature limitation (similar to 315 degrees C) by the nickel precursor, and crystalline Ni2P (c-Ni2P) nanoparticles clusters are generated. On the contrary, a lower concentration (0.1 M) does not accompany a temperature limitation and hence high reaction temperature (330 degrees C) can be exploited for the self-assembly of Ni2P (s-Ni2P) nanoparticle clusters. Amorphous Ni2P (a-Ni2P) nanoparticle clusters are generated with a high concentration (0.714 M) of nickel-TOP solution and a temperature limitation (similar to 290 degrees C). The a-Ni2P nanoparticle cluster electrode exhibits higher capacities and Coulombic efficiency than the electrode based on c-Ni2P nanoparticle clusters. In addition, the amorphous structure of Ni2P can reduce irreversible capacity and voltage hysteresis upon cycling. The amorphous morphology of Ni2P also improves the rate capability, resulting in superior performance to those of c-Ni2P nanoparticle clusters in terms of electrode performance

Eco-Friendly Synthesis of Water-Glass-Based Silica Aerogels via Catechol-Based Modifier

Silica aerogels have attracted much attention owing to their excellent thermal insulation properties. However, the conventional synthesis of silica aerogels involves the use of expensive and toxic alkoxide precursors and surface modifiers such as trimethylchlorosilane. In this study, cost-effective water-glass silica aerogels were synthesized using an eco-friendly catechol derivative surface modifier instead of trimethylchlorosilane. Polydopamine was introduced to increase adhesion to the SiO2 surface. The addition of 4-tert-butyl catechol and hexylamine imparted hydrophobicity to the surface and suppressed the polymerization of the polydopamine. After an ambient pressure drying process, catechol-modified aerogel exhibited a specific surface area of 377 m(2)/g and an average pore diameter of approximately 21 nm. To investigate their thermal conductivities, glass wool sheets were impregnated with catechol-modified aerogel. The thermal conductivity was 40.4 mWm(-1)K(-1), which is lower than that of xerogel at 48.7 mWm(-1)K(-1). Thus, by precisely controlling the catechol coating in the mesoporous framework, an eco-friendly synthetic method for aerogel preparation is proposed

Bio-Inspired Catecholamine-Derived Surface Modifier for Graphene-Based Organic Solar Cells

Owing to the growing interest in next-generation solar cells as a clean and renewable energy source, the demand for alternative transparent conducting electrodes (TCEs) has also increased. Although indium tin oxide (ITO) has been widely used as the standard TCE, its chemical and mechanical instabilities limit its widespread use in emerging photovoltaics. Graphene has attracted much attention as a potential alternative TCE owing to its excellent physical, optical, and electrical properties. However, owing to the inert nature of graphene with a hydrophobic surface, a significant amount of research has been devoted to resolve the nonwetting issue of charge-transporting materials on graphene. In this study, a thin layer of norepinephrine, an amphiphilic catecholamine derivative, was applied to graphene as a hydrophilic surface modifier to enable efficient surface modification without significantly decreasing the optical transmittance or the electrical conductivity. This modification allowed a commonly used hole-transporting material to be applied uniformly to the surface. Thus, the power conversion efficiency (PCE) of organic solar cells (OSCs) fabricated with this poly(norepinephrine)-coated graphene electrode was 7.93%, which is approaching close to that of the ITO-based reference device with a PCE of 8.73%. This work represents the first demonstration of an adhesive biomaterial as an efficient surface modifier for chemically inert graphene and its successful application in OSCs, which shows promise for the future development of bio-inspired graphene systems for applications to various optoelectronic devices

Superparamagnetic NiO-doped mesoporous silica flower-like microspheres with high nickel content

Morphology oriented synthesis of metal oxide doped silica structures have fascinating properties which needed to be explored extensively. In this work, NiO doped silica microsphere with beautiful flower-like morphology has been achieved by adopting a facile surfactant-assisted synthetic route using CTAB-ammonia in H2O???ethanol mixed solvent media. The sol???gel synthesis with effective variations of Ni/Si ratios up to 7.0, followed by a simple hydrothermal treatment and subsequent calcination leads to the formation of NiO???silica mesostructures with high nickel content. Detailed structural and elemental characterizations by using powder X-ray analysis (XRD), scanning electron (SEM) and transmission electron microscopy (TEM), N2 adsorption???desorption, X-ray photoelectron spectroscopy (XPS) revealed that single cubic phase NiO doped mesoporous silica microspheres (for Ni/Si = 5:1 and 7:1) with good surface area (169 and 205 m2 g???1 for sample with Ni/Si = 7:1 and 5:1, respectively) and pore width 3???5 nm, have been formed with 3D flower-like shape and 500???600 nm particle size. These NiO???silica microspheres containing high Ni content up to 76 wt% have shown excellent paramagnetic properties at room temperature. ?? 201

Graphene Oxide Assisted Synthesis of Self-assembled Zinc Oxide for Lithium-Ion-Battery anode

A simple method for the synthesis of a hierarchically self-assembled zinc oxide is presented, in which graphene oxide is used to assist in the assembly of the structure and improve the electrical conductivity of the ZnO. The self-assembled ZnO formed on graphene oxide exhibits a high specific capacity, while also demonstrating good rate performance and cycling stability due to the advantages of using both nanoparticles and a secondary structure.clos

Decoupling of mechanical properties and ionic conductivity in a low molecular weight polymer nanocomposites with highly connected particle aggregates

Hypothesis: High molecular weight polymer nanocomposites (PNCs) with good thermal stability and elevated mechanical strengths can serve as composite polymer electrolytes (CPEs) and thus have been considered as an alternative to conventional liquid electrolytes. However, resolving low ionic conductivity issues of CPEs arising from the low chain mobility derived from a long polymer chain remains challenging.Experiments: Here, we introduce PNCs for use in CPEs which show 1.4 x 10-4 S/cm of ionic conductivity at room temperature with a high shear modulus of 107 Pa using a low molecular weight poly(ethylene glycol) (PEG) matrix and dopamine-modified PEG brush polymer grafted-silica nanoparticles.Findings: We found that densely interconnected supramolecular particle networks can decouple the mechanical strength and ionic conductivity, as the Li-doped interfacial polymer layer supports a direct lithium-ion transport pathway. The extensive structural and rheological studies characterized by small-angle X-ray scattering and oscillatory rheometry experiments revealed that particle connections through interfacial polymer layers play an important role in supporting the elevated mechanical and electrochemical properties with a good thermal stability of PNCs

Seed-mediated synthesis of ultra-long copper nanowires and their application as transparent conducting electrodes

Owing to a recent push toward one-dimensional nanomaterials, in this study, we report a seed-mediated synthetic strategy for copper nanowires (Cu NWs) production involving thermal decomposition of metal-surfactant complexes in an organic medium. Ultra-long Cu NWs with a high aspect ratio and uniform diameter were obtained by separating nucleation and growth steps. The underlying mechanism for nanowire formation was investigated, in addition, properties of the obtained Cu NWs were also characterized using diverse analysis techniques. The performance of resulting Cu NWs as transparent electrodes was demonstrated for potential application. This article can provide information on both new synthetic pathway and potential use of Cu NWs

Enhanced Mechanical Property of Polymer Nanocomposites Using Dopamine-Modified Polymers at Nanoparticle Surfaces

The mechanical reinforcement of polymer nanocomposites (PNCs) relies on the microscopic details, typically the particle dispersion in polymer matrix. While chemical grafting method is common, and usually considered to effectively control particle dispersion, this method requires intricate grafting chemistry and experimentally expensive. Here, we report the improved mechanical property of unentangled poly(ethylene glycol) (PEG) can be obtained by employing the dopamine-derived PEG (DOPA-PEG) brush polymers. The DOPA-PEG is easily adsorbed onto silica nanoparticles via strong H-bonding, increasing the effective size of particles in PEG matrix. The microstructure and rheological properties of particles are strongly influenced by the surface coverage density of DOPA-PEG. One intriguing result is that the shear modulus of PNC with DOPA-PEG can be enhanced by 105 times, compared to the PNCs without DOPA-PEGs. The detailed microstructure and rheology are studied by small angle X-ray scattering (SAXS) and oscillatory rheological experiments

Control of Particle Dispersion with Autophobic Dewetting in Polymer Nanocomposites

Good particle dispersion in polymer nanocomposites (PNCs) is often hampered by autophobic dewetting where the matrix polymers are expelled from the grafted polymer, generally believed to result in increased particle aggregation and enhanced mechanical properties in dilute particle regime. However, we found that autophobic dewetting with highly extended short-chain polymers improves/disrupts particle dispersity, strongly dependent on particle volume fraction. Under strong autophobic condition given with the highmolecular-weight ratio between the matrix, P, and grafted polymer, N, (P/N &gt;&gt; 1), silica nanoparticles grafted with dopamine-modified poly(ethylene glycol) (DOPA-mPEG) brush polymer are dispersed in the PEG matrix by varying the surface grafting rate. In the dilute particle regime, we found that increasing grafting rate ironically improves particle dispersion and reduces the shear modulus as dewetted polymers cannot bridge the particles. In the concentrated particle regime, on the contrary, particles become more aggregated and the corresponding mechanical strength increases with grafting rate as a denser particle network is formed by depletion attractions. Investigating the microstructures, dynamics, and rheological properties of PNCs with small-angle X-ray scattering, time-domain proton NMR, and oscillatory rheometry experiments, respectively, this study provides additional design guidelines for controlling the detailed structure and properties of PNCs