Characterization of Drugs with Good Glass Formers in Loaded-Mesoporous Silica and Its Theoretical Value Relevance with Mesopores Surface and Pore-Filling Capacity

The incorporation of a drug into mesoporous silica (MPS) is a promising strategy to stabilize its amorphous form. However, the drug within MPS has shown incomplete release, despite a supersaturated solution being generated. This indicates the determination of maximum drug loading in MPS below what is experimentally necessary to maximize the drug doses in the system. Therefore, this study aimed to characterize the drugs with good glass former loaded-mesoporous silica, determine the maximum drug loading, and compare its theoretical value relevance to monolayer covering the mesoporous (MCM) surface, as well as pore-filling capacity (PFC). Solvent evaporation and melt methods were used to load each drug into MPS. In addition, the glass transition of ritonavir (RTV) and cyclosporine A (CYP), as well as the melting peak of indomethacin (IDM) and saccharin (SAC) in mesoporous silica, were not discovered in the modulated differential scanning calorimetry (MDSC) curve, demonstrating that each drug was successfully incorporated into the mesopores. The amorphization of RTV-loaded MPS (RTV/MPS), CYP-loaded MPS (CYP/MPS), and IDM-loaded MPS (IDM/MPS) were confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the MDSC curve. Additionally, the good glass formers, nanoconfinement effect of MPS and silica surface interaction contributed to the amorphization of RTV, CYP and IDM within MPS. Meanwhile, the crystallization of SAC was observed in SAC-loaded MPS (SAC/MPS) due to its weak silica surface interaction and high recrystallization tendency. The maximum loading amount of RTV/MPS was experimentally close to the theoretical amount of MCM, showing monomolecular adsorption of RTV on the silica surface. On the other hand, the maximum loading amount of CYP/MPS and IDM/MPS was experimentally lower than the theoretical amount of MCM due to the lack of surface interaction. However, neither CYP or IDM occupied the entire silica surface, even though some drugs were adsorbed on the MPS surface. Moreover, the maximum loading amount of SAC/MPS was experimentally close to the theoretical amount of PFC, suggesting the multilayers of SAC within the MPS. Therefore, this study demonstrates that the characterization of drugs within MPS, such as molecular size and interaction of drug-silica surface, affects the loading efficiency of drugs within MPS that influence its relevance with the theoretical value of drugs.

Remedy for Collapse of ZIF Derived Carbon: Micro-Pore Filled Synthesis to Improve ORR Catalytic Property

Zeolitic imidazolate framework (ZIF) derived carbons deliver outstanding performance as oxygen reduction reaction (ORR) catalysts. However, their electrocatalytic activities are limited due to unavoidable collapse of ZIFs upon pyrolysis, which results in degradation of porosity, sintering of metals and loss of active sites. In this work, a micro-pore filling strategy was employed to strength the architecture of ZIF by using size matched cyanamide molecules as fillers. The cyanamide with high nitrogen content shows a triple effect in stabilizing the carbonaceous skeleton, preserving of metal containing active sites and improving the conductivity of matrix. Therefore, the as-prepared Fe, Co co-doped ZIF derived carbon (FeCo@NC-N) delivers a significantly improved electrochemical activity for ORR than its unfilled counterpart, with half-wave potential upshifted by 30 mV (0.84 V vs. RHE). Besides, a promoted power density of home-assembled zinc-air battery is obtained when FeCo@NC-N is applied as cathode catalyst. This work demonstrates a reliable approach to mitigate framework collapse of metal organic framework (MOF), thus may open a new way for fabrication of MOF based catalysts with increased loading of pores and active sites.

Hydrazide- and Diazole-Linked Covalent Organic Frameworks and Their Water Harvesting Properties

We report a retrosynthetic strategy and its implementation to making covalent organic frameworks (COFs) with irreversible hydrazide and diazole (oxadiazole and thiadiozole) linkages. This involved the synthesis of a series of 2D and 3D hydrazine-linked frameworks, followed by their oxidation and dehydrative cyclization. Each linkage synthesis and functional group transformation—hydrazine, hydrazide, oxadiazole, and thiadia-zole—was evidenced by 15N multi-CP-MAS NMR. In addition, the isothermal water uptake profiles of these frameworks were studied, leading to the discovery that one hydrazide-linked COF is suitable for water harvest-ing from air in arid conditions. These COFs displayed characteristic S-shaped water sorption profiles, a steep pore-filling step below 18% relative humidity at 25 °C, and a total uptake capacity of 0.45 g g–1 at P/Psat = 0.95. In addition, a total of ten 2D and 3D structures with various such linkages were studies for their affinity to water. We found that even small changes made on the molecular level can lead to major differences in the water isotherm profiles and therefore pointing to the utility of water sorption analysis as a complementary analytical tool to study linkage transformations.

Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Improved green and sintered density of alumina parts fabricated by binder jetting and subsequent slurry infiltration

Additive Manufacturing (AM) of ceramics is a constantly emerging field of interest both in research and in industry. Binder jetting-based AM of ceramics in particular offers the opportunity to produce large ceramic parts with a high wall thickness at a high throughput. One limitation is that it requires flowable powders, which are generally coarse and thus exhibit only limited sintering activity. The resulting low sintered densities impede the commercial binder jetting-based production of dense oxide ceramics. We present an approach to efficiently increase the green density of binder jetted alumina parts by optimized slurry infiltration, which also leads to a significant increase in the sintered density. In a first step, alumina parts were fabricated via binder jetting, using a 20-µm-sized alumina powder, yielding relative green densities of about 47–49%. Initial sintering studies with powder compacts showed that sintering even above 1900 °C is not sufficient to achieve acceptable densification. Therefore, green samples were infiltrated with a highly filled ceramic slurry to fill the remaining pores (about 2–5 µm in size) with smaller particles and thus increase the packing density. Particle volume content (40–50 vol%), particle size (100–180 nm) and the infiltration procedure were adapted for tests on cuboid samples to achieve a high penetration of the green bodies and a high degree of pore filling. In this way, the relative green density could be increased starting from about 47% after binder jetting, to 73.4% after infiltration and drying. After sintering at 1675 °C densities above 90% could be achieved, yielding three-point bending strengths up to 145 MPa. As a conclusion, this approach can be regarded as a promising route for overcoming the drawbacks of the binder jetting process on the way to denser, mechanically more stable sintered alumina parts.