The Resource Utilization of Poplar Leaves for CO2 Adsorption

Every late autumn, fluttering poplar leaves scatter throughout the campus and city streets. In this work, poplar leaves were used as the raw material, while H3PO4 and KOH were used as activators and urea was used as the nitrogen source to prepare biomass based-activated carbons (ACs) to capture CO2. The pore structures, functional groups and morphology, and desorption performance of the prepared ACs were characterized; the CO2 adsorption, regeneration, and kinetics were also evaluated. The results showed that H3PO4 and urea obviously promoted the development of pore structures and pyrrole nitrogen (N-5), while KOH and urea were more conductive to the formation of hydroxyl (-OH) and ether (C-O) functional groups. At optimal operating conditions, the CO2 adsorption capacity of H3PO4- and KOH-activated poplar leaves after urea treatment reached 4.07 and 3.85 mmol/g, respectively, at room temperature; both showed stable regenerative behaviour after ten adsorption-desorption cycles.

Production of demineralised high quality hierarchical activated carbon from lignite and determination of adsorption performance using methylene blue and p-nitrophenol: The role of surface functionality, accessible pore size and surface area

In the adsorption process, the surface area, pore and particle size distribution and the chemical structure of the solid and the type of adsorbent are of vital importance. Activated carbon (AC) is a very good adsorbent material and its cost is highly dependent on the starting material and production method. The pore size and functional structure of the surface depend on the amount of activation chemical used. Hierarchical ACs were produced from lignite by loading two different amounts of KOH. The impregnation ratio (KOH/lignite) was chosen as 1/1 and 3/1 and the produced ACs were labelled as AC1 and AC3. The surface areas of AC1 and AC3 were determined as 1321.3 and 2421.3 m2/g, and the total pore volumes were 1.079 and 1.425 cm3/g. Methylene blue (MB) and p-nitrophenol (p-NP) were used to determine the adsorption performance of the produced ACs. The adsorption data were evaluated in terms of the Langmuir and Freundlich models. The amounts of MB and p-NP adsorbed on the surface were calculated in mg/g, total and accessible surface area in mg/m2. It was determined that the MB and p-NP adsorbed to the AC1 sample were higher than the AC3 sample per m2 of population. Molecular orientation is possible depending on the solid surface functionality and chemical structure of the molecule to be adsorbed. It was concluded that in addition to the large surface area, the pore width that can be entered and the functional structure of the surface are very significant factors in the adsorption processes.

Development of Low-Cost Porous Carbons through Alkali Activation of Crop Waste for CO2 Capture

To achieve the "double carbon" (carbon peak and carbon neutrality) target, low-cost CO₂ capture at large CO₂ emission points is of great importance, during which the development of low-cost CO₂ sorbents will play a key role. Here, we chose peanut shells (P) from crop waste as the raw material and KOH and K₂CO₃ as activators to prepare porous carbons by a simple one-step activation method. Interestingly, the porous carbon showed a good adsorption capacity of 2.41 mmol/g for 15% CO₂ when the mass ratio of K₂CO₃ to P and the activation time were only 0.5 and 0.5 h, respectively, and the adsorption capacity remained at 98.76% after 10 adsorption-desorption cycle regenerations. The characterization results suggested that the activated peanut shell-based porous carbons were mainly microporous and partly mesoporous, and hydroxyl (O-H), ether (C-O), and pyrrolic nitrogen (N-5) functional groups that promoted CO₂ adsorption were formed during activation. In conclusion, KOH- and K₂CO₃-activated P, especially K₂CO₃-activated P, showed good CO₂ adsorption and regeneration performance. In addition, not only the use of a small amount of the activator but also the raw material of crop waste reduces the sorbent preparation costs and CO₂ capture costs.

Optimization of CO2 Sorption onto Spent Shale with Diethylenetriamine (DETA) and Ethylenediamine (EDA)

A novel technique was employed to optimize the CO₂ sorption performance of spent shale at elevated pressure-temperature (PT) conditions. Four samples of spent shale prepared from the pyrolysis of oil shale under an anoxic condition were further modified with diethylenetriamine (DETA) and ethylenediamine (EDA) through the impregnation technique to investigate the variations in their physicochemical characteristics and sorption performance. The textural and structural properties of the DETA- and EDA- modified samples revealed a decrease in the surface area from tens of m²/g to a unit of m²/g due to the amine group dispersing into the available pores, but the pore sizes drastically increased to macropores and led to the creation of micropores. The N-H and C-N bonds of amine noticed on the modified samples exhibit remarkable affinity for CO₂ sequestration and are confirmed to be thermally stable at higher temperatures by thermogravimetric (TG) analysis. Furthermore, the maximum sorption capacity of the spent shale increased by about 100% with the DETA modification, and the equilibrium isotherm analyses confirmed the sorption performance to support heterogenous sorption in conjunction with both monolayer and multilayer coverage since they agreed with the Sips, Toth, Langmuir, and Freundlich models. The sorption kinetics confirm that the sorption process is not limited to diffusion, and both physisorption and chemisorption have also occurred. Furthermore, the heat of enthalpy reveals an endothermic reaction observed between the CO₂ and amine-modified samples as a result of the chemical bond, which will require more energy to break down. This investigation reveals that optimization of spent shale with amine functional groups can enhance its sorption behavior and the amine-modified spent shale can be a promising sorbent for CO₂ sequestration from impure steams of the natural gas.

The development of activated carbon from corncob for CO2 capture

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO2.