Self-Assembly of Janus Nanoparticles into Transformable Suprastructures

One of the greatest challenges in colloidal self-assembly is to obtain multiple distinct but transformable suprastructures from the same particles in monophasic solvent. Here, we combined deformable and rigid lobes in snowman-shaped amphiphilic Janus nanoparticles (JNPs). These JNPs exhibited excellent ability to self-assemble into micelles, worms, mini-capsules, giant- and elongated-vesicles. This rich suprastructural diversity was obtained by kinetic manipulation of the self-assembly conditions. The suprastructures consist of four to thousands of highly oriented JNPs with dimensions ranging from 500-nanometer to 30-μm. Moreover, the suprastructures can be transformed into one another or dissembled into individual particles. These features make colloidal assembly highly comparable to that of amphiphilic molecules, however, key differences were discovered

Molecular-Weight Determination of Polymer Brushes Generated by SI-ATRP on Flat Surfaces

A new type of photolabile, surface-initiated, atom-transfer radical polymerization (SI-ATRP) initiator 3-(2-bromo-2-methylpropanamido)-3-(2-nitrophenyl)­propanoic acid was synthesized, and immobilized via an aminosilane linker onto a flat silicon surface. Poly­(lauryl methacrylate) and polystyrene brushes were grown from the surface via SI-ATRP, and the surface-tethered polymer chains cleaved off under UV irradiation. The kinetics of the cleavage process were investigated, and an apparent effect of osmotic forces within the polymer brush could be observed. The molecular weight of the cleaved polymers could be readily determined by means of size-exclusion chromatography

Efficient Adsorption of Acetylene over CO₂ in Bioinspired Covalent Organic Frameworks

Rational design of covalent organic frameworks (COFs) to broaden their diversity is highly desirable but challenging due to the limited, expensive, and complex building blocks, especially compared with other easily available porous materials. In this work, we fabricated two novel bioinspired COFs, namely, NUS-71 and NUS-72, using reticular chemistry with ellagic acid and triboronic acid-based building blocks. Both COFs with AB stacking mode exhibit high acetylene (C2H2) adsorption capacity and excellent separation performance for C2H2/CO2 mixtures, which is significant but rarely explored using COFs. The impressive affinities for C2H2 appear to be related to the sandwich structure formed by C2H2 and the host framework via multiple host–guest interactions. This work not only represents a new avenue for the construction of low-cost COFs but also expands the variety of the COF family using natural biochemicals as building blocks for broad application

Tunable Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks Triggered by CO₂ Sorption

Two-dimensional covalent organic frameworks (2D COFs) have been widely viewed as rigid porous materials with smooth and reversible gas sorption isotherms. In the present study, we report an unusual hysteresis step in the CO2 adsorption isotherm of a 2D COF, TAPB-OMeTA. In situ powder X-ray diffraction (PXRD) measurements, computational modeling, and Pawley refinement indicate that TAPB-OMeTA experiences slight interlayer shifting during the CO2 adsorption process, resulting in a new structure that is similar but not identical to the AA stacking structure, namely, a quasi-AA stacking structure. This interlayer shifting is responsible for the step in its CO2 adsorption isotherm. We attribute the interlayer shifting to the interactions between COF and CO2, which weaken the attraction strength between adjacent COF layers. Notably, the repulsion force between the methoxy groups on the backbone of TAPB-OMeTA is essential in facilitating the interlayer shifting process. After further increasing the size of side groups by grafting poly(N-isopropylacrylamide) oligomers to the TAPB-OMeTA backbone via surface-initiated atom transfer radical polymerization (SI-ATRP), we observed a second interlayer shifting and two adsorption steps in the CO2 adsorption isotherm, suggesting tunability of the interlayer shifting process. Density functional theory (DFT) calculations confirm that the quasi-AA stacking structure is energetically preferred over AA stacking under a CO2 atmosphere. These findings demonstrate that 2D COFs can be “soft” porous materials when interacting with gases, providing new opportunities for 2D COFs in gas storage and separation

Tunable Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks Triggered by CO₂ Sorption

Two-dimensional covalent organic frameworks (2D COFs) have been widely viewed as rigid porous materials with smooth and reversible gas sorption isotherms. In the present study, we report an unusual hysteresis step in the CO2 adsorption isotherm of a 2D COF, TAPB-OMeTA. In situ powder X-ray diffraction (PXRD) measurements, computational modeling, and Pawley refinement indicate that TAPB-OMeTA experiences slight interlayer shifting during the CO2 adsorption process, resulting in a new structure that is similar but not identical to the AA stacking structure, namely, a quasi-AA stacking structure. This interlayer shifting is responsible for the step in its CO2 adsorption isotherm. We attribute the interlayer shifting to the interactions between COF and CO2, which weaken the attraction strength between adjacent COF layers. Notably, the repulsion force between the methoxy groups on the backbone of TAPB-OMeTA is essential in facilitating the interlayer shifting process. After further increasing the size of side groups by grafting poly(N-isopropylacrylamide) oligomers to the TAPB-OMeTA backbone via surface-initiated atom transfer radical polymerization (SI-ATRP), we observed a second interlayer shifting and two adsorption steps in the CO2 adsorption isotherm, suggesting tunability of the interlayer shifting process. Density functional theory (DFT) calculations confirm that the quasi-AA stacking structure is energetically preferred over AA stacking under a CO2 atmosphere. These findings demonstrate that 2D COFs can be “soft” porous materials when interacting with gases, providing new opportunities for 2D COFs in gas storage and separation

Aggregated Structures of Two-Dimensional Covalent Organic Frameworks

Covalent organic frameworks (COFs) have found wide applications due to their crystalline structures. However, it is still challenging to quantify crystalline phases in a COF sample. This is because COFs, especially 2D ones, are usually obtained as mixtures of polycrystalline powders. Therefore, the understanding of the aggregated structures of 2D COFs is of significant importance for their efficient utilization. Here we report the study of the aggregated structures of 2D COFs using 13C solid-state nuclear magnetic resonance (13C SSNMR). We find that 13C SSNMR can distinguish different aggregated structures in a 2D COF because COF layer stacking creates confined spaces that enable intimate interactions between atoms/groups from adjacent layers. Subsequently, the chemical environments of these atoms/groups are changed compared with those of the nonstacking structures. Such a change in the chemical environment is significant enough to be captured by 13C SSNMR. After analyzing four 2D COFs, we find it particularly useful for 13C SSNMR to quantitatively distinguish the AA stacking structure from other aggregated structures. Additionally, 13C SSNMR data suggest the existence of offset stacking structures in 2D COFs. These offset stacking structures are not long-range-ordered and are eluded from X-ray-based detections, and thus they have not been reported before. In addition to the dried state, the aggregated structures of solvated 2D COFs are also studied by 13C SSNMR, showing that 2D COFs have different aggregated structures in dried versus solvated states. These results represent the first quantitative study on the aggregated structures of 2D COFs, deepen our understanding of the structures of 2D COFs, and further their applications

Evaluation of Schiff-Base Covalent Organic Frameworks for CO₂ Capture: Structure–Performance Relationships, Stability, and Performance under Wet Conditions

Covalent organic frameworks (COFs) have been considered promising adsorbent materials for postcombustion CO2 capture due to their high porosity, tunable functionalities, and excellent framework stability. Nevertheless, few research studies have systematically investigated the structure–performance relationships and the effect of moisture on CO2 capture performance of COFs. In this study, a series of Schiff-base COFs with different functionalities, pore sizes, and framework dimensions are prepared and evaluated for potential applications in postcombustion CO2 capture. Gas sorption isotherms and ideal CO2/N2 sorption selectivity calculations reveal the following: (1) COFs undergoing enol-to-keto transformations outperform other studied COFs with imine functionalities and similar pore sizes. (2) CO2 uptake capacity of a COF is not necessarily a function of its pore aperture and specific surface area. TpPa-1 with keto-enamine moieties exhibits an impressive CO2 uptake of 0.6 mmol g–1 and a CO2/N2 sorption selectivity of 114. Dynamic breakthrough experiments of wet CO2/N2 mixed gas (17% relative humidity) indicate that both keto-COFs studied, NUS-2 and TpPa-1, retain about 70% of their dry CO2 adsorption capacities, which can be attributed to the moderately hydrophobic pore environment of the COFs. Considering the noticeable cost of flue gas desiccation, our study suggests that COFs with moderate hydrophobicity would be promising adsorbent candidates for practical postcombustion CO2 capture

Multivariate Polycrystalline Metal–Organic Framework Membranes for CO₂/CH₄ Separation

Membrane technology is attractive for natural gas separation (removing CO2, H2O, and hydrocarbons from CH4) because of membranes’ low energy consumption and small environmental footprint. Compared to polymeric membranes, microporous inorganic membranes such as silicoaluminophosphate-34 (SAPO-34) membrane can retain their separation performance under conditions close to industrial requirements. However, moisture and hydrocarbons in natural gas can be strongly adsorbed in the pores of those membranes, thereby reducing the membrane separation performance. Herein, we report the fabrication of a polycrystalline MIL-160 membrane on an Al2O3 substrate by in situ hydrothermal synthesis. The MIL-160 membrane with a thickness of ca. 3 μm shows a remarkable molecular sieving effect in gas separation. Besides, the pore size and environment of the MIL-160 membrane can be precisely controlled using reticular chemistry by regulating the size and functionality of the ligand. Interestingly, the more polar fluorine-functionalized multivariate MIL-160/CAU-10-F membrane exhibits a 10.7% increase in selectivity for CO2/CH4 separation and a 31.2% increase in CO2 permeance compared to those of the MIL-160 membrane. In addition, hydrophobic MIL-160 membranes and MIL-160/CAU-10-F membranes are more resistant to water vapor and hydrocarbons than the hydrophilic SAPO-34 membranes

Exclusive Recognition of CO₂ from Hydrocarbons by Aluminum Formate with Hydrogen-Confined Pore Cavities

Exclusive capture of carbon dioxide (CO2) from hydrocarbons via adsorptive separation is an important technology in the petrochemical industry, especially for acetylene (C2H2) production. However, the physicochemical similarities between CO2 and C2H2 hamper the development of CO2-preferential sorbents, and CO2 is mainly discerned via C recognition with low efficiency. Here, we report that the ultramicroporous material Al­(HCOO)3, ALF, can exclusively capture CO2 from hydrocarbon mixtures, including those containing C2H2 and CH4. ALF shows a remarkable CO2 capacity of 86.2 cm3 g–1 and record-high CO2/C2H2 and CO2/CH4 uptake ratios. The inverse CO2/C2H2 separation and exclusive CO2 capture performance from hydrocarbons are validated via adsorption isotherms and dynamic breakthrough experiments. Notably, the hydrogen-confined pore cavities with appropriate dimensional size provide an ideal pore chemistry to specifically match CO2 via a hydrogen bonding mechanism, with all hydrocarbons rejected. This molecular recognition mechanism is unveiled by in situ Fourier-transform infrared spectroscopy, X-ray diffraction studies, and molecular simulations