Highlighting the relative effects of surface characteristics and porosity on CO2 capture by adsorbents templated from melamine-based polyaminals

Synthesis and Characterization of Bipyridine-Based Polyaminal Network for CO2 Capture

The response to the high demand for decreasing the amount of CO₂ in the atmosphere, a new polyaminal-based polymer network was designed and successfully prepared through one-pot polycondensation reaction of melamine and [2,2′-Bipyridine]-5,5′-dicarbaldehyde. The formation of the polymer structure was confirmed by FT-IR, solid-state ¹³C NMR, and powder-X-ray diffraction. The porous properties of the polymeric structure were confirmed by field-emission scanning electron microscope and N₂ adsorption–desorption methods at 77 K. The prepared polymer can take up 1.02 mmol/g and 0.71 mmol/g CO₂ at 273 K and 298 K, respectively, despite its relatively modest Brunauer–Emmett–Teller (BET) surface area (160.7 m²/g), due to the existence of superabundant polar groups on the pore surfaces.

Synthesis of Naphthalene-Based Polyaminal-Linked Porous Polymers for Highly Effective Uptake of CO2 and Heavy Metals

Studying the effect of functional groups on the porosity structure and adsorption efficiency of polymer materials is becoming increasingly interesting. In this work, a novel porous polyaminal-linked polymer, based on naphthalene and melamine (PAN-NA) building blocks, was successfully synthesized by a one-pot polycondensation method, and used as an adsorbent for both CO₂ and heavy metals. Fourier transform infrared spectroscopy, solid-state ¹³ C NMR, powder X-ray diffraction, and thermogravimetry were used to characterize the prepared polymer. The porous material structure was established by field-emission scanning electron microscope and N₂ adsorption–desorption methods at 77 K. The polymer exhibited excellent uptake of CO₂, 133 mg/g at 273 K and 1 bar. In addition, the adsorption behavior of PAN-NA for different metal cations, including Pb(II), Cr(III), Cu(II), Cd(II), Ni(II), and Ba(II), was investigated; a significant adsorption selectivity toward the Pb(II) cation was detected. The influence of pH, adsorbent dose, initial concentrations, and contact time was also assessed. Our results prove that the introduction of naphthalene in the polymer network improves the porosity and, thus, CO₂ adsorption, as well as the adsorption of heavy metals.

Activated carbons from biomass-based sources for CO2 capture applications

In an ever-growing attempt to reduce the excessive anthropogenic CO₂ emissions, several CO₂ capture technologies have been developed in recent years. Adsorption using solid carbonaceous materials is one of the many promising examples of these technologies. Carbon-based materials, notably activated carbons, are considered very attractive adsorbents for this purpose given their exceptional thermal stability and excellent adsorption capacities. More importantly, the ability to obtain activated carbons from agricultural wastes and other biomass that are readily available makes them good candidates for several industrial applications ranging from wastewater treatment to CO₂ adsorption, among others. Activated carbons from biomass can be prepared using various techniques, resulting in a range of textual properties. They can also be functionalized by adding nitrogen-based groups to their structure that facilitates faster and more efficient CO₂ capture. This review provides a detailed overview of the recent work reported in this field, highlighting the different preparation methods and their differences and effects on the textual properties such as pore size, surface area, and adsorption performance in terms of the CO₂ adsorption capacity and isosteric heats. The prospect of activated carbon functionalization and its effect on CO₂ capture performance is also included. Finally, the review covers some of the pilot-plant scale processes in which these materials have been tested. Some identified gaps in the field have been highlighted, leading to the perspectives for future work.

Micro- and Ultramicroporous Polyaminals for Highly Efficient Adsorption/Separation of C1-C3 Hydrocarbons and CO2 in Natural Gas

This paper presents a series of micro- and ultramicroporous polyaminals with BET surface areas up to 1304 m² g^-1, which are prepared from two triazine-based tetraamines and three dialdehydes or monoaldehyde through the A₄ + B₂ or A₄ + B₁ aminalization reaction. It is interesting to find that the para-substituted monomers are favorable to force the linking struts apart in the network to generate micropores (1.22 nm), whereas the meta-substituted monomers make the pores in the network squeezed by the twisted linking struts, resulting in the formation of ultramicropores (0.52 nm). Besides, the adsorption behaviors of the major components of natural gas, such as propane (C₃H₈), ethane (C₂H₆), methane (CH₄), and carbon dioxide (CO₂), are significantly different, strongly depending on the polarizabilities, critical temperatures, molecular sizes of gases, porosity parameters of polymers, and the interaction between gases and the polymer skeleton. At 298 K/1 bar, the polymers show high uptake for C₃H₈ (114.5 cm³ g^-1) and C₂H₆ (84.2 cm³ g^-1). Moreover, the adsorption selectivities of C₃H₈/CH₄, C₂H₆/CH₄, C₃H₈/C₂H₆, C₃H₈/CO₂, C₂H₆/CO₂, and CO₂/CH₄ also reach 296.3, 23.1, 9.0, 22.1, 4.1, and 5.0, respectively, exhibiting promising applications in adsorption/separation of C₁-C₃ hydrocarbons and stripping CO₂ gas from natural gas under the ambient condition.