Bon Heun Koo

A hybrid cationic system comprising bio-based chitosan and synthetic branched polyethyleneimine (BPEI) was employed to facilitate the flame-retardant deposition of halloysite nanotubes (HNTs) onto cotton fabrics through a layer-by-layer (LbL) assembly process. The FTIR results revealed new peaks of O-H stretching and Si-O-Si groups on halloysite nanoclay at the respective positions of 3699.84 cm⁻¹, 3625.60 cm⁻¹, and 527.57 cm⁻¹, which suggests successful layering of the anionic species. From surface microstructural analysis, bridging features between adjacent fibers of coatings were found; however, an increase in homogeneity and randomness was also observed as the number of layers increased. Thermogravimetric analysis further exposed that the incorporation of nanoclay tubes engenders substantial char residue at 700 °C up to 32.98%, while the decomposition rate decreased from 0.235% to 0.149%. Additionally, the flame-retardant properties were rigorously assessed using a vertical flame test: self-extinguishment behavior emerged in the C-25 and C-30 coated samples, while the other samples effectively resisted flame propagation. The results confirm the effectiveness of hybrid flame-retardant coating and offer a sustainable strategy for eliminating reliance on hazardous chemical additives.

In this work, poly(acrylic acid)-based layers were injected to form a sandwich layer between the cationic and anionic species for a compact and effective fire-retardant coating on cotton fabric using the layer-by-layer coating technique. From the SEM analysis, as the number of tri-layers increases, the attachment intensity increases, as can be seen for poly(acrylic acid) chitosan and bentonite clay PCB-5TL (the highest tri-layers), while in the case of halloysite-based coatings, as the number of tri-layers increases, instead of attachment, the agglomeration increases due to the high surface area of halloysite nanoclay tubes. FTIR and UV confirmed the finding from the new peak entry and an increase in thickness. The highest thermal residue, ~18%, was obtained for poly(acrylic acid) chitosan and halloysite nanoclay PCH-5TL with a maximum degradation peak intensity at ~389 °C. From the flammability and after-burning SEM investigation test, it was observed that the halloysite-based coating with a higher number of layers offered higher resistance against the flame spread and ignition and, thus, produced a higher amount of char.

The multifunctional attributes of SmFeO₃ make it a promising candidate for the current diverse technological applications. Therefore, in this work, we investigated the effect of synthesis temperature on the magnetic, optical and electrochemical properties of SmFeO₃ nanoparticles at room temperature (SFO-RT) and 50 °C (SFO-50) when prepared through the co-precipitation method. The XRD analysis revealed two distinct phases: SmFeO₃ and Sm₂O₃ as secondary with SmFeO₃ emerging as the primary phase (88–93%). The FESEM images showed the amalgamated morphology of the nanoparticles indicating the enhanced thermal kinetics of the solution which not only limited the particle growth but also facilitated their coalition. The band gap energy was found to be 2.2 and 2.3 eV for SFO-RT and SFO-50, respectively, while the values of saturation magnetization noted were 2.14 and 1.53 emu/g for SFO-RT and SFO-50, respectively. The XPS analysis revealed Sm to be in a +3 oxidation state, while Fe was in a mixed (+3/+2) oxidation state showing an increase in the ionic concentration in SFO-50. From the electrochemical measurements, the highest specific capacitance was observed for SFO-50 (65.8 F/g) as compared to SFO-RT (49.3 F/g). The results indicate a clear effect of synthesis temperature on the properties of SmFeO₃. Here, two factors played a prominent role: one was the morphology, shaped through the particle growth, and the other was the secondary phase. The decrease in the size of the agglomerated particles and phase fraction of the secondary phase brought about necessary changes in the structural attributes to reduce the saturation magnetization and enhance the specific capacitance of SFO-50. Overall, this study shows that the synthesis temperature affects the crystalline structure and phase fractions leading to the modulation of electronic structure, band gap, magnetic interactions and specific capacitance.

The traditional acid-based production method was often utilized to produce flame-retardant material, which is environmentally hazardous and adversely affects the intrinsic properties of the substrates. To address these critical challenges, this work was carried out to develop a pioneer flame-retardant composite material based on cotton and biocompatible hybrid cationic/anionic species deposited through the Layer-by-Layer deposition method. The FTIR results unveil the peaks reflected by coated elements, confirm the successful deposition of coating materials on the cotton substrate. The microstructure and uniform deposition of the coating were analyzed through scanning electron microscopy. The thermal stability of the composites is enhanced with higher coating layers due to the formation of a protective char layer. Flame retardancy of the investigated samples is measured through the vertical flame test and micro-combustion calorimetry method, exhibiting remarkable reduction in peak heat release rate and total heat released rate by 47.30% and 34%, respectively. The acquired results acknowledge the suitability of the production method to produce green fire-retardant materials with excellent thermal stability and flame retardancy to utilize in the fire-resistant industry.

Oxidation of graphite layers is a crucial intermediate step during the chemical exfoliation of graphene, directly influencing the layer thickness, defect density, and functional group distribution. However, the mechanism governing structural and chemical changes in this stage remains insufficiently understood. In this work, graphene oxide (GO) was synthesized via the modified Hummer's method with controlled oxidation times of 6, 12, and 24 h, labeled as GO-T1, GO-T2, and GO-T3, respectively. XRD results showed nearly constant interlayer spacing but notable variations in crystallite size, indicating a time-dependent structural reorganization. FTIR and XPS analyses revealed that the overall oxygen content (C/O ratio) remained relatively stable, while the functional group distribution varied with oxidation time. Raman spectroscopy demonstrated a steady increase in the defect density over prolonged oxidation. Based on these findings, a time-dependent oxidation mechanism was proposed, offering a pathway to systematically understand and fine-tune GO properties through a controlled reaction time for practical applications.

Elemental substitution is an effective way to modify the physical properties of a material by introducing a heteroatom to tune the structural, electronic, and magnetic properties of the primary compound. In this context, this work aims to study the effect of transition metal dopants (T = Fe, V) on structural and magnetic properties of the prepared Mn_2−xT_xO₃ particles. The Rietveld refined X‐ray diffraction patterns reveal the expansion in unit cell volume on incorporating Fe and V into the Mn₂O₃ lattice. The fitted XPS spectra indicate the multivalent nature of constituents Mn/Fe/V. Each sample exhibits an antiferromagnetic (AFM) nature with a Néel temperature (T_N) close to 80 K. The Fe‐doped sample demonstrates enhanced magnetization strength ascribed to the ferromagnetic (FM) nature of Fe. Whereas, the V‐doped specimen showcases the strong AFM‐FM interaction between the AFM‐Mn₂O₃ and uncompensated FM surface spins initiated by oxygen vacancies. The resultant FM‐AFM coupling induces unidirectional anisotropy, leading to a complete shift of the hysteresis loop. The present work helps to understand the root cause of exchange bias development in AFM/uncompensated FM spin nanostructures.

Schematic representation of the rearrangement of magnetic spins at specific points of the hysteresis loops due to the AFM/FIM coupling, resulting in shifted ZFC–FC hysteresis loops, i.e., exchange bias (EB).

Fire hazards are an increasing concern in several high-tech industries of public importance, particularly where textile fabrics are used in abundance. In this study, a novel layer by layer deposition method was utilized to develop a fire-retardant coating on cotton fabric. The method involves a hybrid cationic solution consisting of chitosan and branched polyethyleneimine, while bentonite clay was used as the anionic species. The treated fabric was characterized using SEM, VFT, and attenuated total reflection Fourier transform infrared spectroscopy (FTIR). SEM and EDS profiling confirmed the successful deposition of the (BPEI/CH + BNT) species on the surface of the cotton fabrics. FTIR analysis shows changes in chemical composition between the uncoated and coated samples, as confirmed by modifications in peaks at 3621 cm⁻¹, 1023.3 cm⁻¹, 1631 cm⁻¹, and 614.8 cm⁻¹. Finally, the thermal degradation behavior of pre-coated and post-coated samples was evaluated using thermogravimetric (TGA) analysis within a temperature range of 25 °C~700 °C, where the highest residue of ~19.83% was observed at 700 °C for the D-BPCB-30BL sample, signifying highly improved thermal stability compared to uncoated cotton.