Size Effect of Silica Shell on Gas Uptake Kinetics in Dry Water

Insight to hydrophobic SiO2 encapsulated SiO2 gel: Preparation and application in fire extinguishing

Micron-sized hydrophobic SiO₂ encapsulated SiO₂ gel (HSESG) was prepared successfully by using SiO₂ gel as the solid core and hydrophobic nano-SiO₂ particle as the shell under high-speed shear stirring. The flowability, stability, particle size distribution, bulk density and water repellency of the powder were measured separately, and it was concluded that this type of product can exhibit smaller static angle, larger flow rate and lower bulk density. After the formation of a stable spatial network of SiO₂ gel in its interior, relevant fire extinguishing experiments were carried out and HSESG exhibits higher efficiency in suppressing wood stack fires than that of ordinary dry water (DW) and ABC dry powder. As a high-efficiency fire-extinguishing material, it also exhibits excellent environmental friendliness and non-toxicity, which will make it have the potential to develop a new application market.

Formation Mechanism of Multipurpose Silica Nanocapsules

Core-shell structures containing active materials can be fabricated using almost infinite reactant combinations. A mechanism to describe their formation is therefore useful. In this work, nanoscale all-silica shell capsules with an aqueous core were fabricated by the HCl-catalyzed condensation of tetraethyl orthosilicate (TEOS), using Pickering emulsion templates. Pickering emulsions were fabricated using modified commercial silica (LUDOX TMA) nanoparticles as stabilizers. By following the reaction over a 24 h period, a general mechanism for their formation is suggested. The interfacial activity of the Pickering emulsifiers heavily influenced the final capsule products. Fully stable Pickering emulsion templates with interfacially active particles allowed a highly stable sub-micrometer (500-600 nm) core-shell structure to form. Unstable Pickering emulsions, i.e., where interfacially inactive silica nanoparticles do not adsorb effectively to the interface and produce only partially stable emulsion droplets, resulted in capsule diameter increasing markedly (1+ μm). Scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements revealed the layered silica "colloidosome" structure: a thin yet robust inner silica shell with modified silica nanoparticles anchored to the outer interface. Varying the composition of emulsion phases also affected the size of capsule products, allowing size tuning of the capsules. Silica capsules are promising protective nanocarriers for hydrophilic active materials in applications such as heat storage, sensors, and drug delivery.

Performance of dry water- and porous carbon-based sorbents for carbon dioxide capture

Carbon dioxide is the primary greenhouse gas that has a strong impact on global warming. Several technologies have been developed for capturing CO₂ to mitigate the greenhouse effect. The objective of this research was to investigate the performance of several sorbents based on dry water and porous carbon materials for capturing CO₂. Seven sorbents were prepared and comparatively evaluated for their CO₂ capture capabilities: (i) Conocarpus biochar (CBC); (ii) commercial activated carbon (CAC); (iii) normal dry water (NDW); (iv) K₂CO₃-treated CBC (TCBC); (v) K₂CO₃-modified dry water (MDW); (vi) MDW and 2% TCBC (MDWTCBC); and (vii) MDW and 2% activated carbon (MDWCAC). The sorption process was carried out with initial CO₂ concentration of 5.7%, temperature of 25 °C, feed gas flow rate of 0.5 l min^-1 and a pressure of 1.0 bar. The pure CO₂ was mixed with O₂ or N₂ to achieve the desired inlet concentration of CO₂. The CO₂ adsorption capacity and partition coefficient (PC) of the tested sorbents were evaluated at 5% and 100% breakthrough (BT). The results showed a longer breakthrough and equilibrium adsorption times for CO₂ when mixed with N₂ than with O₂. Among all sorbents, both CAC and CBC showed enhanced CO₂ capture performance with equilibrium (100% BT) adsorption capacities of 239 and 197 mg g^-1, respectively (in terms of PC: 1.0 × 10^-3 and 7.9 × 10^-4 mol kg^-1 Pa^-1, respectively). In contrast, the performance of TCBC and the dry water-based sorbents was far lower than CAC or CBC. The CO₂ adsorption data fitted well to the non-linearized form of the pseudo-first-order kinetic model. The Fourier-transform infrared spectral patterns indicated that the reaction of CO₂ molecules with the hydroxyl groups of sorbents is possible through the formation of chemisorbed CO₂ species. It could be concluded that the activation process did not play a role in increasing the CO₂ capture performance in order to form new active sorption sites. However, Conocarpus biochar can be used as efficient sorbent for CO₂ capture with a better performance than other materials tested previously (e.g., activated carbon).

Methane Hydrate Nucleation within Elastic Confined Spaces: Suitable Spacing and Elasticity Can Accelerate the Nucleation

Elastic materials are candidates for process intensification of gas storage by forming gas hydrate. In this work, molecular dynamics simulations of hydrate nucleation in elastic silica double layers were performed to study the effect of elastic confined spaces on hydrate formation. It is found that in narrow confined spaces, hexagonal rings dominated the hydrogen bond network of water molecules established rapidly by a multisite nucleation mechanism. With molecules added, a bilayer water structure was formed finally because elastic space can adapt the volume expansion. In medium and wide confined spaces, hydrates were formed from a series of "pseudo cages" which are considered as precursors of complete hydrate cages. Moreover, the induction time for nucleation was a minimum when the elasticity of the silica layer changes: nucleation is fastest in the weak-elastic system. When the elasticity increases, it becomes hard to adapt the volume expansion during nucleation and also difficult to nucleate in very weak-elastic systems because of the fluctuation of the layers.