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.

Urban mining of precious metals from electronic waste, such as printed circuit boards (PCB), is not yet feasible because of the lengthy isolation process, health risks, and environmental impact. Although porous polymers are particularly effective toward the capture of metal contaminants, those with porphyrin linkers have not yet been considered for precious metal recovery, despite their potential. Here, we report a porous porphyrin polymer that captures precious metals quantitatively from PCB leachate even in the presence of 63 elements from the Periodic Table. The nanoporous polymer is synthesized in two steps from widely available monomers without the need for costly catalysts and can be scaled up without loss of activity. Through a reductive capture mechanism, gold is recovered with 10 times the theoretical limit, reaching a record 1.62 g/g. With 99% uptake taking place in the first 30 min, the metal adsorbed to the porous polymer can be desorbed rapidly and reused for repetitive batches. Density functional theory (DFT) calculations indicate that energetically favorable multinuclear-Au binding enhances adsorption as clusters, leading to rapid capture, while Pt capture remains predominantly at single porphyrin sites.

Gold recovery from electronic waste could prevent excessive mining with toxic extractants and provide a sustainable path for recycling precious metals. Unfortunately, no viable recycling is practiced, except burning electronic circuit boards in underdeveloped countries, mainly because of the lack of chemical scavengers as adsorbents. Here, we report the synthesis of a family of porphyrin–phenazine-based polymers and their gold-capturing properties as well as application in gold recovery from actual e-waste. The polymers show high selectivity toward gold as well as other precious metals. The Au(III) adsorption isotherms were well-fitted to the Langmuir adsorption model and proportionality between porosity and uptake capacity was observed. Solution pH values and illumination conditions were shown to have influences on the performance of the adsorbents with the highest capacity of 1.354 g/g obtained in acidic pH and under continuous UV irradiation. Such a remarkable capacity of 7 times the theoretical estimate was achieved through photochemical adsorption–reduction mechanism supported by the observed suppressing effect of oxidant on gold-capturing ability. The adsorbents are robust and recyclable, a significant advantage over other emerging materials.