Materials Science Forum Vol. 1153

Abstract: The study investigates the strength improvement of kaolinite clay soil with the inclusion of various percentages and combinations of silica fume (SF) and cockle shell ash (CKSA). Hence, the mechanical properties of various mix ratios of SF and CKSA are examined through the standard Proctor, unconfined compressive strength (UCS), and consolidated isotropic undrained (CIU) triaxial tests. The samples were treated for 1, 7, 14 and 30 days and examined under the UCS tests. The experimental results show that the strength of the kaolinite clay significantly rises with the inclusion of SF and CKSA at dissimilar mix ratios and curing days. The Field Emission Scanning Electron Microscopy (FESEM) profile has illustrated that the kaolinite clay soil molecules were fused jointly with SF and CKSA to form calcium aluminate hydrates (CAH) and calcium silicate hydrate (CSH), which enhanced the development of strength of the stabilized kaolinite clay. The combination of SF and CKSA resulted in a significant strength increment of the kaolinite clay soil up to 86.99%.

Abstract: Continuous emissions of carbon dioxide (CO₂) into the atmosphere brought several environmental problems. Photoconversion of CO₂ not only can produce value-added products (i.e. methanol) but also aim to reduce the environmental problems caused by CO₂. The present work demonstrates the preparation of N-Bi co-doped carbon quantum dots/titanium dioxide (N-Bi co-doped CQDs/TiO₂) as a visible-light driven photocatalyst for the photoconversion of CO₂ to methanol. Hydrothermal-synthesized N-Bi co-doped CQDs were incorporated into TiO₂ nanoparticles through facile mixing method. The loading of CQDs in TiO₂ matrix resulted in a decrease of band gap to 2.75 and 2.65 eV for N-CQDs and N-Bi CQDs, respectively. Gas chromatography equipped with flame-ionization detection (GC-FID) analysis showed a methanol yield of 17 µmol/gcat from the photoconversion experiment using N-Bi-CQDs/TiO₂ photocatalyst composite. The performance of composite was assigned to the loading of N-Bi co-doped CQDs, which reduced the electron-hole recombination in TiO₂. Doping of N-Bi played an important role in localizing the photogenerated electron-holes, essentially enhancing the electron transfer at the CQDs/TiO₂ interface. Thus, our work could provide insight into the application of CQDs-based photocatalysts in the visible-light driven photocatalytic conversion of CO₂ to value-added products.

Abstract: Extraction of metallic gold from refractory ores is traditionally energy-intensive and most often damaging to the environment. Ethaline DES offers an alternative to dissolve gold using an environmentally benign yet chemically stable process. The study aims to explore the efficiency and mechanisms of gold dissolution of refractory ores using Ethaline DES in a room and at elevated temperatures by investigating the thermodynamic stability of the system. Results from the leaching experiments showed that gold dissolution was significantly higher at an elevated temperature (50°C) compared to room temperature (25°C) in Ethaline DES. It is further confirmed with thermochemical data that the entropy and heat capacity of the system were enhanced at an elevated temperature. Maximum gold dissolution was observed at 56.74% during the 48th hour of the leaching process at elevated temperatures. Meanwhile, leaching at room temperature only yielded 18.56% of gold during the 6th hour but precipitated for the rest of the leaching period. Density functional theory (DFT) simulation and thermodynamic calculations showed that AuCl2[C2H4O2]2-was the most stable complex. With the lowest Gibbs free energy and highest HOMO-LUMO gap, exhibiting superior stability and lower reactivity than the others. This study supports the use of Ethaline DES as a sustainable method for refractory gold extraction, highlighting the critical role of temperature in optimizing its efficiency.

Abstract: Zeolitic-imidazolate frameworks (ZIFs) have shown promise in gas separation through membranes. Nevertheless, the potential of mixed-layer ZIFs to be tailored for targeted gas separation remains largely unexplored. This study aims to fill this research gap through a Molecular Dynamics (MD) study by proposing two molecular models for mixed-layer ZIFs and evaluating their effectiveness in H₂ and CO₂ separation. MD simulations are conducted to validate and assess the diffusion properties of H₂ and CO₂ within the mixed-layered ZIF models. The results demonstrate that H₂ has higher diffusivity than CO₂ within the proposed ZIF models. Mixed-layer ZIF-8/ZIF-7 exhibits higher diffusion coefficients for both H₂ (4.79 × 10^-9 m²/s) and CO₂ (8.13 × 10^-11 m²/s) compared to pure ZIF-8, attributed to increased pore flexibility from the ZIF-7 layer. However, this enhancement in diffusion comes at the cost of reduced selectivity due to broader pore size distribution. In contrast, mixed-layer ZIF-8(Zn)/ZIF-8(Co) demonstrates a substantial increase in H₂ diffusion (5.17 × 10^-9 m²/s) and an exceptional selectivity of 310.00 for H₂ over CO₂, owing to the altered framework flexibility from incorporating different metal ions. The study further explores the effect of different adsorbate molecular models, revealing that the H₂_COMPASS and CO₂_TRAPPE combination yields the highest H₂/CO₂ selectivity. Additionally, increased molecular loading enhances diffusion. These findings underscore the critical role of structural modifications and molecular model selection in optimizing ZIF-based materials for gas separation applications. The proposed models and simulation results offer a foundation for future studies and the development of efficient and sustainable gas capture technologies.