Jungmok You's research while affiliated with Kyung Hee University and other places

Photovoltaic (PV) technology enables the conversion of solar energy into electricity. Si-based PV modules, which currently represent more than 90% of the global PV market, are expected to be in...

With the increase in demand for low-carbon technology, green raw materials, and comfortable heating, academia and industry have paid considerable attention to cellulose-based electrothermal composites. This attention owes to the fact that cellulose is a versatile, abundant, low-cost, and sustainable material with beneficial properties. Here, we develop a novel strategy for fabricating flexible, transparent electrothermal heaters that are composed of both silver nanowire (AgNW)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrothermal composites and a regenerated cellulose (RC) matrix. The AgNWs were spin-coated onto glass substrates and easily transferred onto an RC surface through the coagulation and regeneration of the cellulose solution. PEDOT:PSS was coated onto the AgNW-coated RC matrix to improve the electrical and electrothermal properties of the film heaters. The PEDOT:PSS/AgNW/RC composite films demonstrated an excellent optical transmittance of 73.8% at 550 nm and a low sheet resistance of 11.2 Ω/sq. These composite heaters also exhibited a rapid heating response, uniform heat distribution, excellent heat generation, and robust structural stability. These electrothermal composites made from earth-abundant, low cost, and recyclable materials have great potential for green, flexible, transparent film heaters.

Electrocatalyst engineering from the atomic to macroscopic level of electrocatalysts is one of the most powerful routes to boost the performance of electrochemical devices. However, multi‐scale structure engineering mainly focuses on the range of atomic‐to‐particle scale such as hierarchical porosity engineering, while catalyst engineering at the macroscopic level, such as the arrangement configuration of nanoparticles, is often overlooked. Here, a 2D carbon polyhedron array with a multi‐scale engineered structure via facile chemical etching, ice‐templating induced self‐assembly, and high‐temperature pyrolysis processes is reported. Controlled phytic acid etching of the carbon precursor introduces homogeneous atomic phosphorous and nitrogen doping, as well as a well‐defined mesoporous structure. Subsequent ice‐templated self‐assembly triggers the formation of a 2D particle array superstructure. The atomic‐level doping gives rise to high intrinsic activity, while the well‐engineered porous structure and particle arrangement addresses the mass transport limitations at the microscopic particle level and macroscopic electrode level. As a result, the as‐prepared electrocatalyst delivers outstanding performance toward oxygen reduction reaction in both acidic and alkaline media, which is better than recently reported state‐of‐the‐art metal‐free electrocatalysts. Molecular dynamics simulation together with extensive characterizations indicate that the performance enhancement originates from multi‐scale structural synergy.

Emerging water purification technology, known as interfacial solar steam generation (ISSG), has been rapidly developing in recent years. ISSG offers a promising solution to address both freshwater shortage and energy demand by simultaneously producing freshwater and electricity. This is achieved through the combination of microporous films and highly efficient photothermal materials. In this study, we have developed a composite film using a 2D material, reduced graphene oxide (rGO), and a combination of 1D materials, chitin fiber@multi-walled carbon nanotube (Chiber@CNT). Through a hybrid dimensional design, these materials’ advantages are integrated, resulting in a composite film with a distinct laminar porous structure and excellent broadband absorption. Notably, under 1 kW·m−2 sunlight irradiation, the composite film achieves a water evaporation flux of 2.10 kg·m−2·h−1 with a photothermal conversion efficiency of 75.79%. In addition, by utilizing an energy-harvesting strategy based on natural water evaporation in porous nanomaterials for power generation, the composite film successfully enables the simultaneous production of freshwater and electricity. Its output voltage reaches 0.39 V in a 3.5 wt% NaCl solution. Furthermore, the film’s output voltage varies with the concentration of NaCl, increasing from 0.26 V (in deionized water) to 0.45 V (in the saturated NaCl solution). Molecular dynamic simulation results indicate that the enhanced power generation can be attributed to the difference in interatomic interaction strength between ions and hydrophilic functional groups in chitin fiber (Chiber). This finding provides a deep physical mechanism and opens up possibilities for the film’s application in highly concentrated salt solutions.

Covalent organic frameworks (COFs) with high specific surface area, tailored structure, easy functionalization, and excellent chemical stability have been extensively exploited as fantastic materials in various fields. However, in most cases, COFs prepared in powder form suffer from the disadvantages of tedious operation, strong tendency to agglomerate, and poor recyclability, greatly limiting their practical application in environmental remediation. To tackle these issues, the fabrication of magnetic COFs (MCOFs) has attracted tremendous attention. In this review, several reliable strategies for the fabrication of MCOFs are summarized. In addition, the recent application of MCOFs as outstanding adsorbents for the removal of contaminants including toxic metal ions, dyes, pharmaceuticals and personal care products, and other organic pollutants is discussed. Moreover, in‐depth discussions regarding the structural parameters affecting the practical potential of MCOFs are highlighted in detail. Finally, the current challenges and future prospects of MCOFs in this field are provided with the expectation to boost their practical application.

H2O2 production through solar-driven photocatalytic route has received increasing attention. Herein, a carbon ring incorporated hollow g-C3N4 tubes (CHCN) was successfully fabricated via a novel supramolecular self-assembly strategy, co-inducing by hydrogen bond and covalent bond. The optimum H2O2 yield over the CHCN-0.02 reached up to 1.58 mmol L-1 h-1 (AQE= 28.10%, 420 nm), which was 5.4 times significantly higher than that of bulk g-C3N4 (0.29 mmol L-1 h-1) under visible light irradiation. Experimental and density functional theory (DFT) calculations revealed that the CHCNs not only expedited the charge carrier transfer/separation but also favored molecular oxygen adsorption and regulated bandgap structure under the in-plane electronic field induced by continuous π-conjugated Cring, which boosted the ORR efficiency for photocatalytic H2O2 synthesis. The optimized CHCN catalyst demonstrated adequate hybrid ORR routes, consisting of a dominated selective one-step two-electron ORR pathway and highly efficient two-step single-electron ORR for H2O2 production. Therefore, this work not only provides a new strategy for an efficient H2O2 formation using a g-C3N4-based photocatalyst but also explores the functionary mechanism of the ORR process and enlightens the way to highly efficient H2O2 generation.

Nanocellulose-based materials have attracted significant attention because of their attractive advantages. Particularly, aerogel, a porous nanocellulose material, have been used in diverse applications owing to their unique properties. In this study, short rod-like cellulose nanocrystals (CNCs) and long filament-like cellulose nanofibers (CNFs) were isolated from a eucalyptus pulp source using acidolysis and oxidation/mechanical methods, respectively. Subsequently, two different aerogels were prepared from the CNCs and CNFs using the sol–gel method and their properties were compared. The morphology, chemical structure, chemical composition, shrinkage rate, internal structure, thermal degradation, biophysical properties, and mechanical properties of the as-prepared aerogels were compared. Furthermore, the shrinkage of the CNC and CNF aerogels was effectively controlled using a supercritical CO2 drying process. Additionally, three decomposition regions were observed in the thermogravimetric analysis curves of the aerogels; however, the CNF aerogels exhibited enhanced thermal stability than the CNC aerogels. Further, the CNC and CNF aerogels exhibited a mesoporous structure, and the compressive strength of the CNC and CNF aerogels under 85% strain was 269.5 and 299.5 kPa, respectively. This study provides fundamental knowledge on the fabrication of CNCs, CNFs, and corresponding aerogels from lignocellulosic biomass, and their characteristics. Graphical abstract

With the ever‐growing environmental issues, sulfate radical (SO4•−)‐based advanced oxidation processes (SR‐AOPs) have been attracting widespread attention due to their high selectivity and oxidative potential in water purification. Among various methods generating SO4•−, employing heterogeneous catalysts for activation of peroxymonosulfate or persulfate has been demonstrated as an effective strategy. Therefore, the future advances of SR‐AOPs depend on the development of adequate catalysts with high activity and stability. Metal–organic frameworks (MOFs) with large surface area, ultrahigh porosity, and diversity of material design have been extensively used in heterogeneous catalysts, and more recently, enormous effort has been made to utilize MOFs‐based materials for SR‐AOPs applications. In this work, the state‐of‐the‐art research on pristine MOFs, MOFs composites, and their derivatives, such as oxides, metal/carbon hybrids, and carbon materials for SR‐AOPs, is summarized. The mechanisms, including radical and nonradical pathways, are also detailed in the discussion. This work will hopefully promote the future development of MOFs‐based materials toward SR‐AOPs applications.

Mesoporous metal films can detect biomarkers with high sensitivity. Further coating the mesoporous metal with polymers enhances sensing selectivity by favoring specific biomarkers against other interferents. In the present study, we report the fabrication of a Nafion®-coated mesoporous Pd film to filtrate interferents present in sweat during non-invasive biosensing. By using a Nafion®-coated mesoporous Pd film, lactic acid, a metabolite present in sweat, can be successfully detected with high sensitivity.

Herein, we report the synthesis of gold (Au)-loaded mesoporous iron oxide (Fe2O3) as a catalyst for both CO and NH3 oxidation. The mesoporous Fe2O3 is firstly prepared using polymeric micelles made of an asymmetric triblock copolymer poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG). Owing to its unique porous structure and large surface area (87.0 m² g⁻¹), the as-prepared mesoporous Fe2O3 can be loaded with a considerably higher amount of Au nanoparticles (Au NPs) (7.9 wt%) compared to the commercial Fe2O3 powder (0.8 wt%). Following the Au loading, the mesoporous Fe2O3 structure is still well-retained and Au NPs with varying sizes of 3–10 nm are dispersed throughout the mesoporous support. When evaluated for CO oxidation, the Au-loaded mesoporous Fe2O3 catalyst shows up to 20% higher CO conversion efficiency compared to the commercial Au/Fe2O3 catalyst, especially at lower temperatures (25–150 °C), suggesting the promising potential of this catalyst for low-temperature CO oxidation. Furthermore, the Au-loaded mesoporous Fe2O3 catalyst also displays a higher catalytic activity for NH3 oxidation with a respectable conversion efficiency of 37.4% compared to the commercial Au/Fe2O3 catalyst (15.6%) at 200 °C. The significant enhancement in the catalytic performance of the Au-loaded mesoporous Fe2O3 catalyst for both CO and NH3 oxidation may be attributed to the improved dispersion of the Au NPs and enhanced diffusivity of the reactant molecules due to the presence of mesopores and a higher oxygen activation rate contributed by the increased number of active sites, respectively.