Jung Hyeun Kim

A bimetallic AuCu/TiO₂ catalyst was synthesized via photo deposition for the selective oxidation of lignin-derived vanillin to vanillic acid. To compensate for Cu loss arising from galvanic replacement during sequential deposition, the precursor input ratio was optimized to Au:Cu = 2:2 to achieve a target molar composition of 3:1. TEM analysis revealed uniformly dispersed bimetallic nanoparticles with a mean diameter of 7.0 nm ± 2.1 nm, and XPS confirmed zerovalent deposition of both metals on TiO2 surface. Also, ESR analysis detected Ti3+ and additionally detected interfacial Cu2+ paramagnetic species that were undetectable by XPS, supporting the electronic metal-support interaction between the metal nanoparticles and TiO2. O₂-TPD measurements demonstrated a synergistic downshift in the atomic oxygen radical anion (O⁻) desorption temperature from 434.8 °C (Au/TiO₂) to 391.4 °C in AuCu/TiO₂, attributed to a sequential cooperative mechanism in which Cu facilitates primary O₂ activation to superoxide (O₂⁻), followed by further conversion to reactive O⁻ at Au–TiO₂ interfaces. Finally, HPLC analysis of the vanillin oxidation confirmed that the bimetallic AuCu/TiO₂ catalyst exhibited the highest catalytic performance, achieving a vanillin conversion of 81.34 %, vanillic acid yield of 74.01 %, reaction rate of 2.77 molg⁻¹h⁻¹, and the effects of various reaction conditions on the vanillin oxidation behavior were further investigated.

A sequential two-step strategy was developed to enhance the sound absorption performance of polyurethane (PU) foams. In the first step, ethyl cellulose surface-treated with a silane coupling agent (GPTMS) was incorporated to regulate cellular morphology, reducing cavity size, pore size, and open porosity to promote a pore structure favorable for sound absorption. The optimized foam containing 0.4 wt% treated ethyl cellulose (T0.4) exhibited the highest acoustic performance among the ethyl cellulose series. In the second step, polyurethane-imide (PUI) precursors were introduced into T0.4 at solid contents of 4–20 wt%, forming spherical PUI-derived structures on the PU struts that induced additional multidirectional diffuse scattering of sound waves. The optimal sample, T0.4/PUI-12, achieved an average sound absorption coefficient of 0.851, a 32.8% improvement over pristine PU foam. TGA analysis showed that PUI incorporation increased the onset decomposition temperature from 334 °C (T0.4) to 352 °C (T0.4/PUI-20), and DMA results revealed significant increases in both storage modulus and loss modulus. These results demonstrate that the combined use of GPTMS-treated ethyl cellulose and PUI provides an effective pathway toward multifunctional PU foams with simultaneously improved sound absorption, thermal stability, and dynamic mechanical performance.

A hollow TiO2/Cu2O composite photocatalyst was synthesized via a carbon sphere-templated method combined with a copper precipitation–reduction process. HRTEM confirmed a well-defined heterointerface between anatase/rutile TiO2 and crystalline Cu2O, while XPS verified the exclusive Cu+ oxidation state and revealed a Cu loading-dependent shift in Cu–O binding energy reflecting a transition from dispersed interfacial Cu species to bulk-like Cu2O domains. UV–vis DRS and PL analyses demonstrated that Cu2O incorporation extended visible-light absorption and suppressed charge carrier recombination. Under simulated solar irradiation with methanol as a sacrificial reagent, the optimal HTC5 composite (5 mol% Cu) achieved a hydrogen evolution rate of 1100 μmol g−1·h−1, approximately 23 times higher than that of pristine hollow TiO2, with stable activity retained over four consecutive cycles. XPS valence band and Mott–Schottky analyses confirmed the formation of a Type-II p–n heterojunction, enabling spatial separation of photogenerated charge carriers and facilitating efficient proton reduction. These results demonstrate that the synergistic combination of a hollow light-harvesting architecture and a Type-II heterojunction provides a rational design strategy for efficient, low-cost photocatalysts for solar-driven hydrogen production.

Photoelectrochemical (PEC) water splitting offers a promising route for sustainable hydrogen production, but BiVO₄ photoanodes remain limited by poor charge transport, severe recombination, and sluggish surface oxygen evolution kinetics. Here, a Zn-doped BiVO₄ photoanode was modified through electrochemical defect engineering and FeNi-layered double hydroxide (FeNi-LDH) cocatalyst deposition to enhance PEC performance. XPS analysis revealed partial reduction of V⁵⁺ to V⁴⁺ upon electrochemical treatment, indicating defect-related self-doping, while LDH deposition increased surface oxygen-related species. Under AM 1.5G illumination, the optimized LEB photoanode achieved a photocurrent density of 3.60 mA cm⁻² at 1.23 V vs. RHE—2.07-fold higher than the pristine BiVO₄ photoanode—along with the lowest charge-transfer resistance (233 Ω), shortest interfacial time constant (0.62 ms), and highest ABPE (0.95%). LEB also delivered a practical H₂ production rate of 32.7 μmol h⁻¹ cm⁻² with a Faradaic efficiency of 55.6%. These results demonstrate that the synergistic combination of electrochemical defect modulation and FeNi-LDH cocatalyst deposition effectively enhances charge separation, interfacial charge transfer, and hydrogen-production performance in BiVO₄-based PEC systems.