Jong Wan Ko

Bio-inspired mineralization of CO2 gas to hollow CaCO3 microspheres and bone hydroxyapatite/polymer composites

We present the utilization of gaseous carbon dioxide (CO2) with increased mineralization rate in the presence of dopamine, a biomimetic molecule of adhesive foot protein secreted from mussels, to synthesize hollow calcium carbonate (CaCO3) microspheres and their composites with biodegradable polymer fibers. This CO2-consuming route was applied to the development of highly porous electrospun polycaprolactone scaffold hybridized with CaCO3 vaterite crystals that were readily transformed to bone hydroxyapatite minerals in a simulated body fluid.

Synthesis of visible light-active CeO2 sheets via mussel-inspired CaCO3 mineralization

Visible light-active, nano-grained CeO2 sheets are successfully synthesized using polydopamine-induced CaCO3 vaterite microspheres. The nano-grained CeO2 sheets exhibited a distinct polycrystalline sheet-like structure with grains, with a red-shift in the UV-visible absorption spectrum and a much narrower bandgap (2.71–2.83 eV). Visible light-responsive photocatalytic activity was observed with nano-grained CeO2 sheets at a rate constant that was much higher than that of CeO2 nanoparticles.

Synthesis of Ni-based co-catalyst functionalized W:BiVO4 nanofibers for solar water oxidation

We report on the synthesis of highly porous, 1-D tungsten-doped BiVO4 nanofibers (W:BiVO4 NFs). To facilitate photocatalysis, we introduced nickel nanoparticles (NiOx NPs) as co-catalysts on the surface of W:BiVO4 NFs. The outstanding water oxidation performance of the NiOx NP-functionalized W:BiVO4 NFs was obtained through (i) the control of polymers/precursors to achieve porous W:BiVO4 NFs (for highly increased surface area), (ii) the control of the tungsten-doping level (for fast charge transfer), and (iii) the optimization of the loading amounts of NiOx NPs (for efficient charge pathway suppression of charge recombination).

Enzymatic photosynthesis of formate from carbon dioxide coupled with highly efficient photoelectrochemical regeneration of nicotinamide cofactors

We present the photoelectrochemical (PEC) regeneration of nicotinamide cofactors (NADH) coupled with the enzymatic synthesis of formate from CO2 towards mimicking natural photosynthesis. The water oxidation-driven PEC platform exhibited high yield and the rate of NADH regeneration was compared to many other homogeneous, photochemical systems. We successfully coupled solar-assisted NADH reduction with enzymatic CO2 reduction to formate under continuous CO2 injection.

Photoactive g-C3 N4 Nanosheets for Light-Induced Suppression of Alzheimer's β-Amyloid Aggregation and Toxicity.

Graphitic carbon nitride (g-C3 N4 ) has a suppressive capability toward Alzheimers Aβ aggregation under light-illumination. Photoinduced electrons of g-C3 N4 generate reactive oxygen resulting in photooxidation of amyloid peptides that blocks Aβ aggregation. Fe doping of g-C3 N4 frameworks results in enhanced optical properties and even stronger inhibition of Aβ aggregation.

Carboxymethyl cellulose-templated synthesis of hierarchically structured metal oxides

The synthesis of hierarchically structured metal oxides has been intensively pursued over many years for diverse industrial applications. Here, we report a simple but green approach for the synthesis of metal oxide fibers using carboxymethyl cellulose fibers (CMC). We synthesized 1D hierarchical metal oxides using CMC fibers as a sacrificial template. The electrostatic interaction between metal ions and carboxyl groups in CMC induced the formation of hierarchical structures of binary (e.g., CeO2, ZnO) and tertiary (e.g., CaMn2O4) metal oxide fibers.

Human Urine-Fueled Light-Driven NADH Regeneration for Redox Biocatalysis.

Human urine is considered as an alternative source of hydrogen and electricity owing to its abundance and high energy density. Here we show the utility of human urine as a chemical fuel for driving redox biocatalysis in a photoelectrochemical cell. Ni(OH)2 -modified α-Fe2 O3 is selected as a photoanode for the oxidation of urea in human urine and black silicon (bSi) is used as a photocathode material for nicotinamide cofactor (NADH: hydrogenated nicotinamide adenine dinucleotide) regeneration. The electrons extracted from human urine are used for the regeneration of NADH, an essential hydride mediator that is required for numerous redox biocatalytic reactions. The catalytic reactions at both the photoanode and the photocathode were significantly enhanced by light energy that lowered the overpotential and generated high currents in the full cell system.

Self-Assembled Peptide-Carbon Nitride Hydrogel as a Light-Responsive Scaffold Material

Peptide self-assembly is a facile route to the development of bioorganic hybrid materials that have sophisticated nanostructures toward diverse applications. Here, we report the synthesis of self-assembled peptide (Fmoc-diphenylalanine, Fmoc-FF)/graphitic carbon nitride (g-C3N4) hydrogels for light harvesting and biomimetic photosynthesis through noncovalent interactions between aromatic rings in Fmoc-FF nanofibers and tris-s-triazine in g-C3N4 nanosheets. According to our analysis, the photocurrent density of the Fmoc-FF/g-C3N4 hydrogel was 1.8× higher (0.82 μA cm-1) than that of the pristine g-C3N4. This is attributed to effective exfoliation of g-C3N4 nanosheets in the Fmoc-FF/g-C3N4 network, facilitating photoinduced electron transfers. The Fmoc-FF/g-C3N4 hydrogel reduced NAD+ to enzymatically active NADH under light illumination at a high rate of 0.130 mol g-1 h-1 and drove light-responsive redox biocatalysis. Moreover, the Fmoc-FF/g-C3N4 scaffold could well-encapsulate key photosynthetic components, such as electron mediators, cofactors, and enzymes, without noticeable leakage, while retaining their functions within the hydrogel. The prominent activity of the Fmoc-FF/g-C3N4 hydrogel for biomimetic photosynthesis resulted from the easy transfer of photoexcited electrons from electron donors to NAD+ via g-C3N4 and electron mediators as well as the hybridization of key photosynthetic components in a confined space of the nanofiber network.

Nature-inspired Synthesis of Nanostructured Electrocatalysts through Mineralization of Calcium Carbonate

Biomineralization is a biogenic process that produces elaborate inorganic and organic hybrid materials in nature. Inspired by the natural process, this study explored a new mineralization approach to create nanostructured CaCO3 films composed of amorphous CaCO3 hemispheres by using catechol-rich polydopamine (PDA) as a biomimetic mediator. The thus synthesized biomimetic CaCO3 was successfully transformed to nanostructured films of metal-oxide minerals, such as FeOOH, CoCO3 , NiCO3 , and MnOOH, through a simple procedure. The CaCO3 -templated metal-oxide minerals functioned as efficient electrocatalysts; a CaCO3 -templated cobalt phosphate (nanoCoPi) film exhibited high stability as a water-oxidation electrocatalyst with a current density of 1.5 mA cm-2 . The nanostructure of nanoCoPi, consisting of individual nanoparticles (≈70 nm) and numerous internal pores (BET surface area: 3.17 m2  g-1 ), facilitated an additional charge-transfer pathway from the electrode to individual active sites of the catalyst. This work demonstrates a plausible strategy for facile and green synthesis of nanostructured electrocatalysts through biomimetic CaCO3 mineralization.

Alzheimer Therapy: Photoactive g‐C3N4 Nanosheets for Light‐Induced Suppression of Alzheimer's β‐Amyloid Aggregation and Toxicity (Adv. Healthcare Mater. 13/2016)

The accumulation of β-amyloid peptides and their aggregation in brain is a hallmark of Alzheimers disease. On page 1560 C. B. Park and co-workers describe a strong suppression effect of graphitic carbon nitride (g-C3 N4 ) toward β-amyloid aggregation under light-illumination. Photoexcited g-C3 N4 generates reactive oxygen species and blocks further β-amyloid aggregation by impacting conformational structure of β-amyloid, rendering it a promising material for Alzheimer therapy.