Pyrazole-linked covalent organic polymer is synthesized using an asynchronous double Schiff base from readily available monomers. The one-pot reaction features no metals as a building block or reagent, hence facilitating the structural purity and industrial scalability of the design. Through a single-crystal study on a model compound, the double Schiff base formation is found to follow syn addition, a kinetically favored product, suggesting that reactivity of the amine and carbonyls dictate the order and geometry of the framework building. The highly porous pyrazole polymer COP-214 is chemically resistant in reactive conditions for over two weeks and thermally stable up to 425 °C in air. COP-214 shows well-pronounced gas capture and selectivities, and a high CO₂/N₂ selectivity of 102. The strongly coordinating pyrazole sites show rapid uptake and quantitative selectivity of Pd (II) over several coordinating metals (especially Pt (II)) at all pH points that are tested, a remarkably rare feature that is best explained by detailed analysis as the size-selective strong coordination of Pd onto pyrazoles. Density functional theory (DFT) calculations show energetically favorable Pd binding between the metal and N-sites of COP-214. The polymer is reusable multiple times without loss of activity, providing great incentives for an industrial prospect.

Formic acid is a compelling chemical storage platform for hydrogen gas, but the lack of an efficient dehydrogenation catalyst is preventing its commercial use. In this issue of Matter, Wang et al. report a fine-tuned zirconium metal-organic framework with palladium nanoparticles that effectively dehydrogenates formic acid without degradation.

Activated carbon has been used in a wide range of applications owing to its large specific area, facile synthesis, and low cost. The synthesis of activated carbon mostly relies on potassium hydroxide (KOH)-mediated activation which leads to the formation of micropores (<2 nm) after a washing step with acid. Here we report the preparation of activated carbon with an anomalously large surface area (3288 m2 g−1), obtained by employing an activation process mediated by cesium (Cs) ions. The high affinity of the carbon lattice for Cs ions induces immense interlayer expansion upon complexation of the intercalant Cs ion with the carbon host. Furthermore, the Cs-activation process maintains the nitrogen content of the carbon source by enabling the activation process at low temperature. The large surface area and well-preserved nitrogen content of Cs-activated carbon takes advantage of its enhanced interaction with CO₂ molecules (for superior CO₂ capture) and lithium ions (for improved Li ion storage), respectively. The present investigation unveils a new approach toward tuning the key structural properties of activated carbon; that is, controlling the affinity of the carbon host for the intercalant ion when they engage in complex formation during the activation process.

Metal ion adsorption from industrial wastewater has received increasing attention for the elimination of heavy metals and selective recovery of precious metals. Among the precious metals found in E-waste, gold has attracted considerable attention because of its wide range of practical applications and high economic value. However, the adsorbents used at present for the recovery of precious metals have very low adsorption capacity and poor metal selectivity for commercial uses. Herein, we introduce a new photochemical route for the selective and efficient adsorption of gold ions using bio-inspired metal-philic coatings. Internal surfaces of the mesoporous polymer microspheres were coated with polydopamine via the oxidative polymerization of catecholamines. The polydopamine layer served as a selective photo-active reductant for gold ions. Under 1-sun simulated illumination, the polydopamine layer selectively reduced gold ions to generate metallic gold nuclei. Moreover, once the metallic gold nanostructures were formed, localized surface plasmon further enhanced the reduction of gold ions. The combined effects increased the maximum amount of gold ions adsorbed per unit mass of the adsorbent up to 26 times compared to that in the dark. The adsorbed metallic gold was re-dissolvable in a thiourea solution for the complete recovery of gold ions. The selectivity toward gold ions among various metal ions was demonstrated using a solution mixture containing eight different metal ions that are commonly found in industrial wastewater. Density functional theory calculations revealed that reduction of gold on the polydopamine layer was energetically favorable, while the reduction of other metal ions was not. The dramatic increase in the maximum adsorption capacity and selectivity owing to the combined effect of the photochemical activation and polyphenol chemistry renders this process a promising approach toward urban mining of novel metal ions from electronic wastes.

Effective removal of excess greenhouse gas CO2 necessitates new adsorbents that can overcome the shortcomings of the current capture methods. To achieve that, porous materials are often modified post-synthetically with reactive amine functionalities but suffer from significant surface area losses. Herein, we report a successful amine post-functionalization of a highly porous covalent organic polymer, COP-130, without losing much porosity. By varying the amine substituents, we recorded a remarkable increase in CO2 uptake and selectivity. Ketone functionality, a rarely accessible functional group for porous polymers, was inserted prior to amination and led to covalent tethering of amines. Interestingly, aminated polymers demonstrated relatively low heats of adsorption, which is useful for the rapid recyclability of materials, due to the formation of suspected intramolecular hydrogen bonding.