Synthesis of Highly Porous Coordination Polymers with Open Metal Sites for Enhanced Gas Uptake and Separation

Metal-containing amorphous microporous polymers are an emerging class of functional porous materials in which the surface properties and functions of polymers are dictated by the nature of the metal ions incorporated into the framework. In an effort to introduce coordinatively unsaturated metal sites into the porous polymers, we demonstrate herein an aqueous-phase synthesis of porous coordination polymers (PCPs) incorporating bis­(<i>o</i>-diiminobenzosemiquinonato)-Cu­(II) or -Ni­(II) bridges by simply reacting hexaminotriptycene with CuSO₄·5H₂O [Cu­(II)-PCP] or NiCl₂·6H₂O [Ni­(II)-PCP] in H₂O. The resulting polymers showed surface areas of up to 489 m² g^–1 along with a narrow pore size distribution. The presence of open metal sites significantly improved the gas affinity of these frameworks, leading to an exceptional isosteric heat of adsorption of 10.3 kJ·mol^–1 for H₂ at zero coverage. The high affinities of Cu­(II)- and Ni­(II)-PCPs toward CO₂ prompted us to investigate the removal of CO₂ from natural and landfill gas conditions. We found that the higher affinity of Cu­(II)-PCP compared to that of Ni­(II)-PCP not only allowed for the tuning of the affinity of CO₂ molecules toward the sorbent, but also led to an exceptional CO₂/CH₄ selectivity of 35.1 for landfill gas and 20.7 for natural gas at 298 K. These high selectivities were further verified by breakthrough measurements under the simulated natural and landfill gas conditions, in which both Cu­(II)- and Ni­(II)-PCPs showed complete removal of CO₂. These results clearly demonstrate the promising attributes of metal-containing porous polymers for gas storage and separation applications

Lightweight and Highly Conductive Aerogel-like Carbon from Sugarcane with Superior Mechanical and EMI Shielding Properties

Aerogel-like carbon (ALC) based on sugarcane was prepared by a hydrothermal carbonization (HTC) and postpyrolysis process. The ALC prepared from sugarcane exhibits a typical cellular structure with low density, high specific surface area, and excellent electrical conductivity. Although with low density, the specific elastic modulus of ALC can reach 484.7 MPa·cm³/g, based on our knowledge, this is the strongest aerogel-like carbon ever reported. The average electromagnetic interference (EMI) shielding effectiveness of ALC in X band is 51.0 dB with an absorption-dominant shielding feature. More importantly, the specific surface area of ALC, which has subtle influence on the properties of ALC, can be fined tuned by the HTC process. Considering the chemical-free fabrication process with sustainable raw materials, adjustable structure, excellent mechanical properties, the lightweight and highly conductive ALCs are postulated to have promising potential applications in sensor, energy conversion and storage, and EMI shielding

Selective Surfaces: Quaternary Co(Ni)MoS-Based Chalcogels with Divalent (Pb²⁺, Cd²⁺, Pd²⁺) and Trivalent (Cr³⁺, Bi³⁺) Metals for Gas Separation

Porous chalcogels with tunable compositions of Co_<i>x</i>M_1<i>–x</i>MoS₄ and Ni_<i>x</i>M_1–<i>x</i>MoS₄, where M = Pd²⁺, Pb²⁺, Cd²⁺, Bi³⁺, or Cr³⁺ and <i>x</i> = 0.3–0.7, were synthesized by metathesis reactions between the metal ions and MoS₄^2–. Solvent exchange, counterion removal and CO₂ supercritical drying led to the formation of aerogels. All chalcogels exhibited high surface areas (170–510 m²/g) and pore volumes in the 0.56–1.50 cm³/g range. Electron microscopy coupled with nitrogen adsorption measurements suggest the presence of both mesoporosity (2 nm < <i>d</i> < 50 nm) and macroporosity (<i>d</i> > 50 nm, where <i>d</i> is the average pore size). Pyridine adsorption corroborated for the acid character of the aerogels. We present X-ray photoelectron spectroscopic and X-ray scattering evidence that the [MoS₄]^2– unit does not stay intact when bound to the metals in the chalcogel structure. The Mo⁶⁺ species undergoes redox reactions during network assembly, giving rise to Mo^4+/5+-containing species where the Mo is bound to sulfide and polysulfide ligands. The chalcogels exhibit high adsorption selectivities for CO₂ and C₂H₆ over H₂, N₂, and CH₄ whereas specific compositions exhibited among the highest CO₂ enthalpy of adsorption reported so far for a porous material (up to 47 kJ/mol). The Co-Pb-MoS₄ and Co-Cr-MoS₄ chalcogels exhibited a 2-fold to 4-fold increase in CO₂/H₂ selectivity compared to ternary CoMoS₄ chalcogels

Carbon Aerogel from Winter Melon for Highly Efficient and Recyclable Oils and Organic Solvents Absorption

Direct conversion of biomass to carbon aerogel provides a promising approach to developing absorbent materials for spilled oils and organic solvents recovery. In this work, three-dimensional carbon aerogels were fabricated via a hydrothermal and post-pyrolysis process using winter melon as the only raw materials. The winter melon carbon aerogel (WCA) prepared shows a low density of 0.048 g/cm³, excellent hydrophobicity with a water contact angle of 135°, and selective absorption for organic solvents and oils. The absorption capacity of WCA for organic solvents and oils can be 16–50 times its own weight. Moreover, distillation can be employed to recover WCA and harvest the pollutants. Over five absorption–harvesting cycles, the absorption capacity of WCA to organic solvents and low boiling point oils can recover almost 100% of its starting capacity. With a combination of low-cost biomass as raw materials, green preparation process, low density, and excellent hydrophobicity, WCA as an absorber has great potential in application of spilled oil recovery and environmental protection

Water–Gas Shift Reaction on Pt/Ce_1–<i>x</i>Ti_<i>x</i>O_2−δ: The Effect of Ce/Ti Ratio

Pt nanoparticles (1.2–2.0 nm size) supported on Ce_1–<i>x</i>Ti_<i>x</i>O_2−δ (<i>x</i> = 0, 0.2, 0.5, 0.8, and 1.0) carriers synthesized by the citrate sol–gel method were tested toward the water–gas shift (WGS) reaction in the 200–350 °C range. A deep insight into the effect of two structural parameters, the chemical composition of support (Ce/Ti atom ratio), and the Pt particle size on the catalytic performance of Pt-loaded catalysts was realized after employing in situ X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and HAADF/STEM, scanning electron microscopy (SEM), in situ Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies under different gas atmospheres, H₂ temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption (NH₃-TPD and CO₂-TPD) techniques. The 0.5 wt % Pt/Ce_0.8Ti_0.2O_2−δ solid (<i>d</i>_Pt = 1.7 nm) was found to be by far the best catalyst among all the other solids investigated. In particular, at 250 °C the CO conversion over Pt/Ce_0.8Ti_0.2O_2−δ was increased by a factor of 2.5 and 1.9 compared to Pt/TiO₂ and Pt/CeO₂, respectively. The catalytic superiority of the Pt/Ce_0.8Ti_0.2O_2−δ solid is the result of the support’s (i) robust morphology preserved during the WGS reaction, (ii) moderate acidity and basicity, and (iii) better reducibility at lower temperatures and the significant reduction of “coking” on the Pt surface and of carbonate accumulation on the Ce_0.8Ti_0.2O_2−δ support. Several of these properties largely influenced the reactivity of sites (<i>k</i>, s^–1) at the Pt–support interface. In particular, the specific WGS reaction rate at 200 °C expressed per length of the Pt–support interface (μmol CO cm^–1 s^–1) was found to be 2.2 and 4.6 times larger on Pt supported on Ce_0.8Ti_0.2O_2−δ (Ti⁴⁺-doped CeO₂) compared to TiO₂ and CeO₂ alone, respectively

Influence of Graphene Reduction and Polymer Cross-Linking on Improving the Interfacial Properties of Multilayer Thin Films

Graphene is a versatile composite reinforcement candidate due to its strong mechanical, tunable electrical and optical properties, and chemical stability. However, one drawback is the weak interfacial bonding, which results in weak adhesion to substrates. This could be overcome by adding polymer layers to have stronger adherence to the substrate and between graphene sheets. These multilayer thin films were found to have lower resistance to lateral scratch forces when compared to other reinforcements such as polymer/clay nanocomposites. Two additional processing steps are suggested to improve the scratch resistance of these films: graphene reduction and polymer cross-linking. Graphene<b>/</b>polymer nanocomposites consisting of polyvinylamine (PVAm) and graphene oxide (GO) were fabricated using the layer-by-layer assembly (LbL) technique. The reduced elastic modulus and hardness of PVAm/GO films were measured using nanoindentation. Reducing GO enhances mechanical properties by 60–70% while polymer cross-linking maintains this enhancement. Both graphene reduction and polymer cross-linking show significant improvement to scratch resistance. Particularly, polymer cross-linking leads to films with higher elastic recovery, 50% lower adhesive and plowing friction coefficient, 140 and 50% higher adhesive and shear strength values, respectively, and lower material pileup and scratch width/depth

Nanoporous Polymers Incorporating Sterically Confined <i>N</i>‑Heterocyclic Carbenes for Simultaneous CO₂ Capture and Conversion at Ambient Pressure

Postcombustion CO₂ capture and the conversion of captured CO₂ into value added chemicals are integral part of today’s energy industry mainly due to their economic and environmental benefits arising from the direct utilization of CO₂ as a sustainable source. Sterically confined <i>N</i>-heterocyclic carbenes (NHCs) have played a significant role in organocatalysis due to their air-stability, super basic nature, and strong ability to activate and convert CO₂ gas. Here, we report a new class of nanoporous polymer incorporating sterically confined <i>N</i>-heterocyclic carbenes (NP-NHCs) that exhibit exceptional CO₂ capture fixation efficiency of 97% at room temperature, which is the highest ever reported for carbene based materials measured in the solid state. The NP-NHC can also function as a highly active, selective, and recyclable heterogeneous nanoporous organocatalyst for the conversion of CO₂ into cyclic carbonates at atmospheric pressure with excellent yields up to 98% along with 100% product selectivity through an atom economy reaction by using epoxides. Narrow pore size distribution of NP-NHC also allowed us to introduce a unique substrate selectivity based on size, just like enzymes, for the corresponding epoxides. This metal-free two in one approach for the CO₂ gas fixation/release and conversion provides a new direction for the cost-effective, CO₂ capture and conversion processes

Mid-temperature CO₂ Adsorption over Different Alkaline Sorbents Dispersed over Mesoporous Al₂O₃

CO2 adsorbents comprising various alkaline sorption active phases supported on mesoporous Al2O3 were prepared. The materials were tested regarding their CO2 adsorption behavior in the mid-temperature range, i.e., around 300 °C, as well as characterized via XRD, N2 physisorption, CO2-TPD and TEM. It was found that the Na2O sorption active phase supported on Al2O3 (originated following NaNO3 impregnation) led to the highest CO2 adsorption capacity due to the presence of CO2-philic interfacial Al–O––Na+ sites, and the optimum active phase load was shown to be 12 wt % (0.22 Na/Al molar ratio). Additional adsorbents were prepared by dispersing Na2O over different metal oxide supports (ZrO2, TiO2, CeO2 and SiO2), showing an inferior performance than that of Na2O/Al2O3. The kinetics and thermodynamics of CO2 adsorption were also investigated at various temperatures, showing that CO2 adsorption over the best-performing Na2O/Al2O3 material is exothermic and follows the Avrami model, while tests under varying CO2 partial pressures revealed that the Langmuir isotherm best fits the adsorption data. Lastly, Na2O/Al2O3 was tested under multiple CO2 adsorption–desorption cycles at 300 and 500 °C, respectively. The material was found to maintain its CO2 adsorption capacity with no detrimental effects on its nanostructure, porosity and surface basic sites, thereby rendering it suitable as a reversible CO2 chemisorbent or as a support for the preparation of dual-function materials

Chalcogen-Based Aerogels As Sorbents for Radionuclide Remediation

The efficient capture of radionuclides with long half-lives such as technetium-99 (⁹⁹Tc), uranium-238 (²³⁸U), and iodine-129 (¹²⁹I) is pivotal to prevent their transport into groundwater and/or release into the atmosphere. While different sorbents have been considered for capturing each of them, in the current work, nanostructured chalcogen-based aerogels called chalcogels are shown to be very effective at capturing ionic forms of ⁹⁹Tc and ²³⁸U, as well as nonradioactive gaseous iodine (i.e., a surrogate for ¹²⁹I₂), irrespective of the sorbent polarity. The chalcogel chemistries studied were Co_0.7Bi_0.3MoS₄, Co_0.7Cr_0.3MoS₄, Co_0.5Ni_0.5MoS₄, PtGe₂S₅, and Sn₂S₃. The PtGe₂S₅ sorbent performed the best overall with capture efficiencies of 98.0% and 99.4% for ⁹⁹Tc and ²³⁸U, respectively, and >99.0% for I₂(g) over the duration of the experiment. The capture efficiencies for ⁹⁹Tc and ²³⁸U varied between the different sorbents, ranging from 57.3–98.0% and 68.1–99.4%, respectively. All chalcogels showed >99.0% capture efficiency for iodine over the test duration. This versatile nature of chalcogels can provide an attractive option for the environmental remediation of the radionuclides associated with legacy wastes from nuclear weapons production as well as wastes generated during nuclear power production or nuclear fuel reprocessing