Solving two environmental problems simultaneously：Microporous carbon derived from mixed plastic waste for CO2 capture

Conversion of plastic waste into porous carbon for CO2 capture is an attractive approach to solve the carbon emission and plastic pollution problems, simultaneously. However, the previous studies are limited to the utilization of single PET plastic. The conversion of mixed plastic waste (MPW), which is of more practical significance, is seldom reported. In this study, mixed plastic waste was converted into porous carbon materials for CO2 capture through cascading autogenic pressure carbonization (APC) and chemical activation. The carbon yield of 56% was achieved through APC of MPW. The activator (KOH) dosage had significant effects on the structure and properties of the prepared porous carbons. Porous carbon prepared with KOH/C ratio of 4 had the largest micropore area and the maximum CO2 adsorption was 2.7 mmol g-1 at 298 K and 1 bar. The experimental data were well fitted to the pesudo first-order kinetic model. The MPW derived porous carbon exhibited not only high CO2 uptake capacity, but also fast adsorption rate, good selectivity of CO2 over N2 and good cyclic stability, which could be regarded as a promising adsorbent for CO2 adsorption.

The role of surface chemistry on CO2 adsorption in biomass-derived porous carbons by experimental results and molecular dynamics simulations

Biomass-derived porous carbons have been considered one of the most effective adsorbents for CO2 capture, due to their porous structure and high specific surface area. In this study, we successfully synthesized porous carbon from celery biomass and examined the effect of external adsorption parameters including time, temperature, and pressure on CO2 uptake in experimental and molecular dynamics (MD) simulations. Furthermore, the influence of carbon's surface chemistry (carboxyl and hydroxyl functionalities) and nitrogen type on CO2 capture were investigated utilizing MD simulations. The results showed that pyridinic nitrogen has a greater tendency to adsorb CO2 than graphitic. It was found that the simultaneous presence of these two types of nitrogen has a greater effect on the CO2 sorption than the individual presence of each in the structure. It was also revealed that the addition of carboxyl groups (O=C-OH) to the carbon matrix enhances CO2 capture by about 10%. Additionally, by increasing the simulation time and the size of the simulation box, the average absolute relative error for simulation results of optimal structure declined to 16%, which is an acceptable value and makes the simulation process reliable to predict adsorption capacity under various conditions.

Activated Carbon from Palm Date Seeds for CO2 Capture

The process of carbon dioxide capture and storage is seen as a critical strategy to mitigate the so-called greenhouse effect and the planetary climate changes associated with it. In this study, we investigated the CO₂ adsorption capacity of various microporous carbon materials originating from palm date seeds (PDS) using green chemistry synthesis. The PDS was used as a precursor for the hydrochar and activated carbon (AC). Typically, by using the hydrothermal carbonization (HTC) process, we obtained a powder that was then subjected to an activation step using KOH, H₃PO₄ or CO₂, thereby producing the activated HTC-PDS samples. Beyond their morphological and textural characteristics, we investigated the chemical composition and lattice ordering. Most PDS-derived powders have a high surface area (>1000 m² g⁻¹) and large micropore volume (>0.5 cm³ g⁻¹). However, the defining characteristic for the maximal CO₂ uptake (5.44 mmol g⁻¹, by one of the alkaline activated samples) was the lattice restructuring that occurred. This work highlights the need to conduct structural and elemental analysis of carbon powders used as gas adsorbents and activated with chemicals that can produce graphite intercalation compounds.

Preparation of Nitrogen-Doped Cellulose-Based Porous Carbon and Its Carbon Dioxide Adsorption Properties

Nitrogen-doped cellulose-based porous carbon materials were obtained by hydrothermal method and KOH chemical activation together with melamine as a nitrogen-doping precursor. The effects of hydrothermal temperature on the microstructure and surface morphology of the products were mainly studied. Also, the carbon dioxide adsorption capacity of the prepared porous carbon was investigated. It was found that when the hydrothermal carbonization temperature was 270 °C and the mass ratio of cellulose and melamine was 1:1, the largest micropore specific surface area of 1703 m²·g^-1 and micropore volume of 0.65 cm³·g^-1 were obtained, with a nitrogen-doping composition of 1.68 atom %. At the temperature of 25 °C and under the pressure of 0.1, 0.2, 0.3, and 0.4 MPa, the adsorption amount of CO₂ was 1.56, 3.79, 5.42, and 7.34 mmol·g^-1, respectively. Also, the adsorption process of CO₂ was in good accordance with the Freundlich isotherm model.

Evaluation of kinetics and mechanism properties of CO2 adsorption onto the palm kernel shell activated carbon

The volumetric adsorption kinetics of carbon dioxide (CO₂) onto the synthesized palm kernel shell activated carbon via single-stage CO₂ activation and commercial Norit® activated carbon were carried out at an initial pressure of approximately 1 bar at three different temperatures of 25, 50, and 100 °C. The experimental kinetics data were modelled by using the Lagergren's pseudo-first-order model and pseudo-second-order model. Comparing these two, the non-linear pseudo-second-order kinetics model presented a better fit towards CO₂ adsorption for both adsorbents, owing to its closer coefficient of determination (R²) to unity, irrespective of the adsorption temperature. In addition, kinetics analysis showed that the corresponding kinetics coefficient (rate of adsorption) of both activated carbons increased with respect to adsorption temperature, and thereby, it indicated higher mobility of CO₂ adsorbates at an elevated temperature. Nevertheless, CO₂ adsorption capacity of both activated carbons reduced at elevated temperatures, which signified exothermic and physical adsorption (physisorption) behaviour. Besides, process exothermicity of both carbonaceous adsorbents can be corroborated through activation energy (E_a) value, which was deduced from the Arrhenius plot. E_a values that were in range of 32-38 kJ/mol validated exothermic adsorption at low pressure and temperature range of 25-100 °C. To gain an insight into the CO₂ adsorption process, experimental data were fitted to intra-particle diffusion model and Boyd's diffusion model, and findings revealed an involvement of both film diffusion and intra-particle diffusion during CO₂ adsorption process onto the synthesized activated carbon and commercial activated carbon.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

Lignocellulose-based adsorbents: A spotlight review of the effective parameters on carbon dioxide capture process

The increasing demand for energy all around the world has led to a rise in greenhouse gases (GHGs), of which carbon dioxide (CO₂) is the most important. CO₂ is largely responsible for global warming and climate change. Processes such as carbon dioxide capture and storage (CCS), which have an effective role in climate mitigation, seem to be promising. In recent years, porous carbons, particularly activated carbons (ACs), have rapidly emerged as one of the most effective adsorbents of CO₂. However, the implementation of pristine ACs in the real world is still hindered due to their physical and weak adsorption, which makes these adsorbents sensitive to temperature and relatively poor in selectivity. Hence, the surface modification of ACs is essential in order to improve their surface area, pore structure and alkalinity. Numerous studies have reported lignocellulose-based ACs as very promising adsorbents of CO₂. In this review, the sources, health and environmental effects of CO₂, and the abatement methods of GHGs are described. In addition, the capture and separation of CO₂ from gas stream using various types of lignocellulose-based ACs are summarized. Furthermore, the key factors controlling the adsorption of CO₂ by ACs (characteristics of adsorbents, preparation conditions, as well as adsorption conditions) are comprehensively and critically discussed. Finally, future research needs and prospective research challenges are summarized.

Facile synthesis of tetraphenylethene-based conjugated microporous polymers as adsorbents for CO2 and organic vapor uptake

We present three novel conjugated microporous polymers (CMP@1–3), which were formed by an imidization reaction between tetra-(4-aminophenyl)ethylene and anhydrides.

Performance of dry water- and porous carbon-based sorbents for carbon dioxide capture

Carbon dioxide is the primary greenhouse gas that has a strong impact on global warming. Several technologies have been developed for capturing CO₂ to mitigate the greenhouse effect. The objective of this research was to investigate the performance of several sorbents based on dry water and porous carbon materials for capturing CO₂. Seven sorbents were prepared and comparatively evaluated for their CO₂ capture capabilities: (i) Conocarpus biochar (CBC); (ii) commercial activated carbon (CAC); (iii) normal dry water (NDW); (iv) K₂CO₃-treated CBC (TCBC); (v) K₂CO₃-modified dry water (MDW); (vi) MDW and 2% TCBC (MDWTCBC); and (vii) MDW and 2% activated carbon (MDWCAC). The sorption process was carried out with initial CO₂ concentration of 5.7%, temperature of 25 °C, feed gas flow rate of 0.5 l min^-1 and a pressure of 1.0 bar. The pure CO₂ was mixed with O₂ or N₂ to achieve the desired inlet concentration of CO₂. The CO₂ adsorption capacity and partition coefficient (PC) of the tested sorbents were evaluated at 5% and 100% breakthrough (BT). The results showed a longer breakthrough and equilibrium adsorption times for CO₂ when mixed with N₂ than with O₂. Among all sorbents, both CAC and CBC showed enhanced CO₂ capture performance with equilibrium (100% BT) adsorption capacities of 239 and 197 mg g^-1, respectively (in terms of PC: 1.0 × 10^-3 and 7.9 × 10^-4 mol kg^-1 Pa^-1, respectively). In contrast, the performance of TCBC and the dry water-based sorbents was far lower than CAC or CBC. The CO₂ adsorption data fitted well to the non-linearized form of the pseudo-first-order kinetic model. The Fourier-transform infrared spectral patterns indicated that the reaction of CO₂ molecules with the hydroxyl groups of sorbents is possible through the formation of chemisorbed CO₂ species. It could be concluded that the activation process did not play a role in increasing the CO₂ capture performance in order to form new active sorption sites. However, Conocarpus biochar can be used as efficient sorbent for CO₂ capture with a better performance than other materials tested previously (e.g., activated carbon).

Role of Surface Phenolic-OH Groups in N-Rich Porous Organic Polymers for Enhancing the CO2 Uptake and CO2/N2 Selectivity: Experimental and Computational Studies

Design and successful synthesis of phenolic-OH and amine-functionalized porous organic polymers as adsorbent for postcombustion CO₂ uptake from flue gas mixtures along with high CO₂/N₂ selectivity is a very demanding research area in the context of developing a suitable adsorbent to mitigate greenhouse gases. Herein, we report three triazine-based porous organic polymers TrzPOP-1, -2, and -3 through the polycondensation of two triazine rings containing tetraamine and three dialdehydes. These porous organic polymers possess high Brunauer-Emmett-Teller (BET) surface areas of 995, 868, and 772 m² g^-1, respectively. Out of the three materials, TrzPOP-2 and TrzPOP-3 contain additional phenolic-OH groups along with triazine moiety and secondary amine linkages. At 273 K, TrzPOP-1, -2, and -3 displayed CO₂ uptake capacities of 6.19, 7.51, and 8.54 mmol g^-1, respectively, up to 1 bar pressure, which are considerably high among all porous polymers reported till date. Despite the lower BET surface area, TrzPOP-2 and TrzPOP-3 containing phenolic-OH groups showed higher CO₂ uptakes. To understand the CO₂ adsorption mechanism, we have further performed the quantum chemical studies to analyze noncovalent interactions between CO₂ molecules and different polar functionalities present in these porous polymers. TrzPOP-1, -2, and -3 have the capability of selective CO₂ uptake over that of N₂ at 273 K with the selectivity of 61:1, 117:1, and 142:1 by using the initial slope comparing method, along with 108.4, 140.6, and 167.4 by using ideal adsorbed solution theory (IAST) method, respectively. On the other hand, at 298 K, the calculated CO₂/N₂ selectivities in the initial slope comparing method for TrzPOP-1, -2, and -3 are 27:1, 72:1, and 96:1, whereas those using IAST method are 42.1, 75.7, and 94.5, respectively. Cost effective and scalable synthesis of these porous polymeric materials reported herein for selective CO₂ capture has a very promising future for environmental clean-up.