Silanol-rich platelet silica modified with branched amine for efficient CO2 capture

In this work, we report a new route to improve the CO adsorption performance of solid amine adsorbents. Platelet mesoporous silicas with abundant surface silanols were prepared by emulsion synthesis followed by simple solvent extraction. These silanol-rich silica particles were then functionalized with branched polyethyleneimine (BPEI) by grafting or impregnation to prepare CO adsorbents. Silanol-rich silicas grafted with BPEI exhibited 70% higher amine density and 47% higher CO adsorption capacity than its calcined counterpart. The adsorbent achieved a maximum CO adsorption efficiency up to 13.82 mmol CO/g-BPEI. Adsorbed species found in the infrared spectra suggested that silanols may contribute to the enhanced CO adsorption efficiency on grafted amines. Silanol-rich silica functionalized with BPEI retained more porosity than its calcined counterparts, which may account for its superior CO adsorption capacity. Silanol-rich silica impregnated with amines achieved the highest CO adsorption efficiency ever reported (5.65 mmol/g, 526.7 mg/g-BPEI). Adsorption kinetic modeling confirmed that silanol-rich adsorbent provides better CO diffusion pathways. These potential benefits of silanol-amine interaction, coupled with platelet mesoporous structure and branched polyamine chains, opens a new pathway to high-performance adsorbents for CO capture

A new operando surface restructuring pathway via ion-pairing of catalyst and electrolyte for water oxidation

The highly efficient and stable electrolysis needs the rational control of the catalytically active interface during the reactions. Here we report a new operando surface restructuring pathway activated by pairing catalyst and electrolyte ions. Using SrCoO3-δ-based perovskites as model catalysts, we unveil the critical role of matching the catalyst properties with the electrolyte conditions in modulating catalyst ion leaching and steering surface restructuring processes toward efficient oxygen evolution reaction catalysis in both pH-neutral and alkaline electrolytes. Our results regarding multiple perovskites show that the catalyst ion leaching is controlled by catalyst ion solubility and anions of the electrolyte. Only when the electrolyte cations are smaller than catalyst's leaching cations, the formation of an outer amorphous shell can be triggered via backfilling electrolyte cations into the cationic vacancy at the catalyst surface under electrochemical polarization. Consequently, the current density of reconstructed SrCoO3-δ is increased by 21 folds compared to the pristine SrCoO3-δ at 1.75 V vs. reversible hydrogen electrode and outperforms the benchmark IrO2 by 2.1 folds and most state-of-the-art electrocatalysts in the pH-neutral electrolyte. Our work could be a starting point to rationally control the electrocatalyst surface restructuring via matching the compositional chemistry of the catalyst with the electrolyte properties

Design of a viscose based solid amine fiber: effect of its chemical structure on adsorption properties for carbon dioxide

A solid amine fiber VF-AM-TETA was designed with viscose (VF) substrate for efficient CO2 capture, where its hydroxyl groups could serve synergizing effect in CO2-amine reaction. When grafting modification and subsequent amination were applied to VF, effect of structures of grafting monomers as well as amines on its CO2 adsorption properties was taken into account. Amines with different 1 degrees and 2 degrees amine ratios were investigated as amination agents in terms of amine efficiency, so as to afford the fibrous adsorbent with maximum effective reactive amine sites for CO2 capturing. Results suggested that higher content in primary amine can facilitate CO2 adsorption onto the fiber by stronger basicity and smaller steric hindrance. Consequently, optimal chemical structure provided VF-AM-TETA with satisfactory adsorption capacity of 4.08 mmol/g when amine content was 8.74 mmol/g. Constant adsorption behavior within 6 adsorption-desorption cycles indicated its desirable regeneration performance in practical use due to excellent mechanical properties of VF-AM-TETA. (c) 2013 Elsevier Inc. All rights reserved

Simple synthesis of nitrogen-rich polymer network and its further amination with PEI for CO2 adsorption

The nitrogen-rich polymer network (MF/PAM) was synthesized through interpenetration between the molecular chains of melamine-formaldehyde resin(MF) and polyacrylamide (PAM), to which the polyethylene imine (PEI) was grafted to obtain solid amine adsorbent (MF/PAM-g-PEI). Compared with MF, the swelling capacity of MF/PAM was greatly enhanced, it could swell rapidly and directly in water. Although the interpenetration of PAM into MF may reduce the porosity of MF/PAM, the CO capture capacity of the solid amine adsorbents (MF/PAM-g-PEI) could still reach 2.8 mmol/g at 273 K. The adsorbents also exhibited promising adsorption kinetics and regeneration performances. The kinetics observation showed that the Avrami model could better descript the CO adsorption process compared with the pseudo-first-order model and pseudo-second-order model. Meanwhile, the Avrami kinetic orders (n) range from 1.21 to 1.56, displaying that the both physisorption and chemisorption exist in the adsorption process and the PEI have successfully grafted onto the polymer network, which also can be confirmed by the adsorption activation energy value. After 18 adsorption-desorption recycles, the MF/PAM-g-PEI could preserve its initial capacity without any decrease. Our work provides a new method to achieve promising solid amine adsorbents with higher adsorption capacity and better regeneration performance

Preparation of a solid amine adsorbent based on polypropylene fiber and its performance for CO2 capture

A novel kind of solid amine-containing fibrous adsorbent (PP-GMA-TETA) was prepared through irradiation grafting copolymerization with glycidyl methacrylate (GMA) onto polypropylene (PP) fiber, followed by reacting with triethylenetetramine (TETA) to introduce primary and secondary amine groups on its surface. The effects of the reaction conditions, such as the TETA concentration, temperature, and reaction time on amination degree of PP-GMA-TETA, were investigated. Adsorption capacity of PP-GMA-TETA with 77.7% amination degree could reach 4.72 mmol/g. After adsorption, the spent fiber could be completely regenerated at 100 degrees C by steam for 20 min and its adsorption behavior kept almost constant within six recycles. The comparison of adsorption capacities of amine fibers aminated with various aminating agents also demonstrated that fibers with higher content of primary amine would obtain faster adsorption rates and higher adsorption capacities

Defective Carbons Derived from Macadamia Nut Shell Biomass for Efficient Oxygen Reduction and Supercapacitors

Efficient yet cost-effective electrode materials play deciding roles in the widespread application of fuel cells, as precious metals, such as platinum (Pt), remain the main component of the cathodic oxygen reduction reaction (ORR) electrocatalyst. Herein, a type of biomass, macadamia nut shell (MNS), is utilized for synthesizing ORR catalysts, aiming at enhancing the activity and lowering the production cost of the electrode materials. Benefiting from a defective catalysis mechanism, the resulting defective MNS material (D-MNS-A) shows greatly improved ORR performance in alkaline solutions. The onset potential of D-MNS-A is only 29mV more negative than that of the commercial Pt/C. Moreover, the durability of D-MNS-A is superior to that of Pt/C, and it presents excellent tolerance to methanol. In addition, D-MNS-A is an ideal material for supercapacitors. It exhibits a specific capacitance of 155F/g under the current density of 1A/g in 1M NaSO electrolyte, which was further increased to 231F/g after coating with MnO. The defective nature combined with the highly porous structure of D-MNS-A render it a potential material for fuel cell and supercapacitor applications

Fine-tuning the coordinatively unsaturated metal sites of metal–organic frameworks by plasma engraving for enhanced electrocatalytic activity

Metal-organic frameworks (MOFs) have recently emerged as promising electrocatalysts because of their atomically dispersed metal sites and porous structures. The active sites of MOF catalysts largely exist as coordinatively unsaturated metal sites (CUMSs). In this study, facile microwave-induced plasma engraving is applied to fine-tune the CUMSs of cobalt-based MOF (Co-MOF-74) without destroying its phase integrity by controlling the plasma-engraving species, intensity, and duration. The electrochemical activity of the engraved MOF is found to be quantitatively correlated to the coordination geometry of the metal centers corresponding to CUMSs. Specifically, the hydrogen plasma-engraved Co-MOF-74 shows an enhanced catalytic activity of oxygen evolution reaction, which exhibits a low overpotential (337 mV at 15 mA cm), high turnover frequency (0.0219 s), and large mass activity (54.3 A g). The developed CUMS control strategy and the revealed CUMSs activity correlation can inspire the further microstructure tuning of MOFs for various applications

Controlled synthesis and aminating of poly(melamine)-paraformaldehyde mesoporous resin for CO2 adsorption

A series of mesoporous amino resins (MA) with pore diameters of 2.82 to 9.87 nm have been successfully synthesized at low temperature using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123) as surfactant template via HCl catalyzed sol-gel reactions of melamine and paraformaldehyde, followed by ethanol extraction. The mesoporous amino resin MA-P123-3.5 g, prepared at optimal condition by adding 3.5 g P123 as surfactant template, had higher specific surface area of 706.7 m /g and larger pore size of 9.87 nm. After impregnating with polyethylenimine (PEI), the obtained MA-P123-3.5 g-PEI showed the highest CO uptakes of 4.68 mmol/g and amine utilization efficiency of 51.48% at 40 °C, which is higher than the theoretical amine utilization efficiency (35%). The kinetics studies implied that the Avrami model could better describe the CO adsorption process on the MA-PEI adsorbent, indicating the synergistic effect of chemical and physical adsorption mechanisms. The further analysis of CO diffusion model implied that the porous structure of MA is beneficial to the diffusion of CO in the particles. Due to the positive influence to the amine groups of the larger pore diameter in the accessibility and diffusion process, the MA samples impregnated with PEI also showed good regeneration stability after 10 cycles of CO adsorption-desorption. These results are helpful for developing high-performance CO adsorbents