Fabrication of hierarchical carbon nanosheet-based networks for physical and chemical adsorption of CO2

Natural Products Derived Porous Carbons for CO2 Capture

As it is now established that global warming and climate change are a reality, international investments are pouring in and rightfully so for climate change mitigation. Carbon capture and separation (CCS) is therefore gaining paramount importance as it is considered one of the powerful solutions for global warming. Sorption on porous materials is a promising alternative to traditional carbon dioxide (CO2 ) capture technologies. Owing to their sustainable availability, economic viability, and important recyclability, natural products-derived porous carbons have emerged as favorable and competitive materials for CO2 sorption. Furthermore, the fabrication of high-quality value-added functional porous carbon-based materials using renewable precursors and waste materials is an environmentally friendly approach. This review provides crucial insights and analyses to enhance the understanding of the application of porous carbons in CO2 capture. Various methods for the synthesis of porous carbon, their structural characterization, and parameters that influence their sorption properties are discussed. The review also delves into the utilization of molecular dynamics (MD), Monte Carlo (MC), density functional theory (DFT), and machine learning techniques for simulating adsorption and validating experimental results. Lastly, the review provides future outlook and research directions for progressing the use of natural products-derived porous carbons for CO2 capture.

Nitrogen-doped hydrochar prepared by biomass and nitrogen-containing wastewater for dye adsorption: Effect of nitrogen source in wastewater on the adsorption performance of hydrochar

Dye wastewater has become one of the main risk sources of environmental pollution due to its high toxicity and difficulty in degradation. Hydrochar prepared by hydrothermal carbonization (HTC) of biomass has abundant surface oxygen-containing functional groups, and therefore is used as an adsorbent to remove water pollutants. The adsorption performance of hydrochar can be enhanced after improving its surface characteristics through nitrogen-doping (N-doping). In this study, wastewater rich in nitrogen sources such as urea, melamine and ammonium chloride were selected as the water source for the preparation of HTC feedstock. The N atoms were doped in the hydrochar with a content of 3.87%-5.70%, and mainly in the form of pyridinic-N, pyrrolic-N and graphitic-N, which changed the acidity and basicity of the hydrochar surface. The N-doped hydrochar adsorbed methylene blue (MB) and congo red (CR) in wastewater through pore filling, Lewis acid-base interaction, hydrogen bond, and π-π interaction, and the maximum adsorption capacities of those were obtained with 57.52 mg/g and 62.19 mg/g, respectively. However, the adsorption performance of N-doped hydrochar was considerably affected by the acid-base property of the wastewater. In a basic environment, the surface carboxyl of the hydrochar exhibited a high negative charge and thus an enhanced electrostatic interaction with MB. Whereas, the hydrochar surface was positively charged in an acid environment by binding H⁺, resulting in an enhanced electrostatic interaction with CR. Therefore, the adsorption efficiency of MB and CR by N-doped hydrochar can be tuned by adjusting the nitrogen source and the pH of the wastewater.

Guanidine-Based Covalent Organic Frameworks: Cooperation between Cores and Linkers for Chromic Sensing and Efficient CO2 Conversion

C(sp)-H carboxylation with CO₂ is an attractive route of CO₂ utilization and is traditionally promoted by transition metal catalysts, and organocatalysis for the conversion remains rarely explored and challenging. In this article, triaminoguanidine-derived covalent organic frameworks (COFs) were used as platforms to develop heterogeneous organocatalysts for the reaction. We demonstrated that the COFs with guanidine cores and pyrazine linkers show high catalytic performance as a result of the cooperation between cores and linkers. The core is vitally important, which is deprotonated to the guanidinato group that binds and activates CO₂. The pyrazine linker collaborates with the core to activate the C(sp)-H bond through hydrogen bonding. In addition, the COFs show acid- and base-responsive chromic behaviors thanks to the amphoteric nature of the core and the auxochromic effect of the pyrazine linker. The work opens up new avenues to organocatalysts for C-H carboxylation and chromic materials for sensing and switching applications.

One-Step Synthesis of 3D Pore-Structured Adsorbent by Cross-Linked PEI and Graphene Oxide Sheets and Its Application in CO2 Adsorption

In this study, a one-step method of polyethylenimine (PEI) cross-linking graphene oxide (GO) was used to prepare a 3D pore-structured adsorbent with abundant amine groups for chemisorption of CO₂. The cross-linking of PEI with GO sheets and the vacuum freeze-drying step are the keys to the formation of the 3D pore structure. The results of characterization analysis revealed that the as-prepared adsorbent had a 3D porous structure rich in amine groups. Besides, the adsorption/desorption test showed that the prepared adsorbent has excellent and stable adsorption performance, and the maximum CO₂ adsorption capacity is 2.18 mmol/g at 343 K and 10 vol % CO₂. Moreover, the adsorption kinetics analysis indicated that the adsorption process was dominated by homogeneous adsorption, and the adsorbent had a strong affinity with CO₂. Finally, the correlation analysis shows that the kinetic constants obtained by the Avrami model simulation can be effectively used for the actual CO₂ adsorption process design.

Characterization and Ofloxacin Adsorption Studies of Chemically Modified Activated Carbon from Cassava Stem

Cassava is a type of crop popular in Asian countries. It can be easily cultivated and grows to a mature plant in 9 months. Considering its availability, this work studied activated carbon based on cassava stem. Ofloxacin was chosen as the adsorbate, simulating the wastewater from the pharmaceutical industry. Cassava stem was ground into particles and heated to the activated state, 787 °C. The cassava-stem-activated carbon was further treated with the surface modifier, namely sodium hydroxide and zinc chloride, to study the improvement in ofloxacin adsorption. Prepared adsorbents were characterised using the SEM, FT-IR, XRD, DSC and TGA methods before being evaluated through batch adsorption, thermodynamic, and kinetic studies. The surface area analysis indicates that treatment of the activated carbon with NaOH and ZnCl₂ increases the surface area due to the removal of organic content by the chemicals. Better ofloxacin adsorption of all activated carbon samples can be obtained with solutions at pH 8. An endothermic reaction was predicted, shown by higher ofloxacin adsorption at a higher temperature, supported by a positive value of ΔH° in the thermodynamic studies. The negative values of ΔG° revealed that adsorptions were spontaneous. The higher R² values indicate that the adsorption process follows the pseudo-second-order equation of kinetic study. The maximum adsorption capacities are 42.37, 62.11, 62.89 and 58.82 mg/g for raw cassava stem (RC), cassava-stem-activated carbon (AC), NaOH-modified cassava-stem-activated carbon (NAC), and ZnCl₂ modified cassava-stem-activated carbon (ZAC). The adsorption capacity is good compared to previous works by other researchers, making it a possible alternative material for the pharmaceutical industry’s wastewater treatment.

One-Step Synthesis of a Mn-Doped Fe2O3/GO Core-Shell Nanocomposite and Its Application for the Adsorption of Levofloxacin in Aqueous Solution

This study describes for the first time the synthesis, characterization, and application of a MnFe₂O₃/GO core-shell nanocomposite as an adsorbent for the removal of levofloxacin (Lev) from real water samples. The formation of the proposed nanocomposite was confirmed using various characterization techniques. The structural techniques revealed a 20 nm average particle size of the MnFe₂O₃/GO core-shell nanocomposite, with a surface area of 70.7 m² g^-1, as shown by the BET results. The most influential parameters (adsorbent dosage, stirring rate, and Lev pH) that affected the adsorption process were optimized using the response surface methodology (RSM) based on a central composite design. The optimum conditions were 0.007 g, 2, and 7 for adsorbent dosage, stirring rate, and Lev pH, respectively. The adsorption behavior of Lev on the MnFe₂O₃/GO core-shell nanocomposite was examined using isotherm models, kinetics, and thermodynamics. The kinetic models demonstrated that the adsorption process was controlled by both intraparticle and outer diffusion. Furthermore, the results obtained revealed that the adsorption of Lev on MnFe₂O₃/GO was dominated by electrostatic interactions. Moreover, Dubinin-Radushkevich and Temkin isotherms confirmed that the sorption mechanism was dominated by electrostatic interactions, while Langmuir and Sips models confirmed a monolayer adsorption process. The maximum adsorption capacity of Lev onto the MnFe₂O₃/GO adsorbent was found to be 129.9 mg g^-1. Furthermore, the thermodynamic data revealed that the adsorption system was spontaneous and exothermic. The synthesized MnFe₂O₃/GO core-shell nanocomposite showed significant recyclability and regenerability properties up to five adsorption-desorption cycles. As a proof of concept, the performance of the prepared adsorbent was evaluated for laboratory-scale purification of spiked real water samples. The prepared adsorbent significantly reduced the concentration of Lev in the real water samples and the removal efficiency ranged from 86 to 97%.

Quantifying instant water cleaning efficiency using zinc oxide decorated complex 3D printed porous architectures

Industrialization harms the quality of water; therefore, cleaning and monitoring water sources are essential for sustainable human health and aquatic life. An increase in active surface area and porosity can result in quick and efficient cleaning activity. 3D printing can build porous architecture with controlled porosity and active surface area. Here, catalytically active ZnO nanosheets were grown on the surface of 3D printed architecture (Schwarzites and Weissmuller) with different porosity and surface area. The Weissmuller structure along with ZnO, has shown better catalytic performance due to its higher porosity (~69%) and high active surface area, compared to Schwarzites structure. Synergistic effect of adsorption and photodegradation has resulted in ~95% removal efficiency of mixed dye within 10 min by Weissmuller structure. The dye degradation efficiency was determined using colorimetric measurements with a regular smartphone for real-time quantitative investigation of dye removal efficiency. Most importantly, decorated 3D printed structures exhibit high structural stability without residuals (ZnO nanosheets) in water after performing the recycling experiment. Therefore, the decorated 3D printing structures and colorimetric detection method will offer a user-friendly versatile technique for analysis of removal efficiency of toxic components in different polluted water sources without using high-end sophisticated instruments and complicated procedures.

Preparation of Acid- and Alkali-Modified Biochar for Removal of Methylene Blue Pigment

Walnut shell biochar (WSC) and wood powder biochar (WPC) prepared using the limited oxygen pyrolysis process were used as raw materials, and ZnCl₂, KOH, H₂SO₄, and H₃PO₄ were used to modify them. The evaluation of the liquid-phase adsorption performance using methylene blue (MB) as a pigment model showed that modified biochar prepared from both biomasses had a mesoporous structure, and the pore size of WSC was larger than that of WPC. However, the alkaline modified was more conducive to the formation of pores in the biomass-modified biochar materials; KOH treatment resulted in the highest modified biochar-specific surface area. The isothermal adsorption of MB by the two biomass pyrolysis charcoals conformed to the Freundlich equation, and the adsorption process conformed to the quasi-second-order kinetic equation, which is mainly physical adsorption. The large number of oxygen-containing functional groups on the particle surface provided more adsorption sites for MB adsorption, which was beneficial to the adsorption reactions. The adsorption effects of woody biomass were obviously higher than that of shell biomass, and the adsorption capacities of the two raw materials' pyrolysis charcoal were in the order of WPC > WSC. The adsorption effects of different treatment reagents on MB were in the order ZnCl₂ > KOH > H₃PO₄ > H₂SO₄. The maximum adsorption capacities of the two biomass treatments were 850.9 mg/g for WPC with ZnCl₂ treatment and 701.3 mg/g for WSC with KOH treatment.

Microporous polyimides with high surface area and CO2 selectivity fabricated from cross-linkable linear polyimides

Linear polyimides of intrinsic microporosity have been intensively investigated for gas separation due to their microporous structure and high surface area. The microporous structure in the linear polyimides of intrinsic microporosity comes from their contorted structure. Therefore, most linear polyimides without contorted structure do not have micropores. In this work, the microporous polyimides are constructed through the condensation of a cross-linkable dianhydride monomer with two novel nitrogen-rich diamine monomers and post crosslinking reaction. The linear polyimide precursors without contorted structure have the same main-chain structure. The introduction of crosslinked structure endow the crosslinked polyimides (PI-CLs) with microporous structure. The microporous structure in PI-CLs can be tuned by changing the substituents of the linear polyimide precursors. The PI-CLs have competitive CO₂ uptake capacity (7.3-9.4 wt%) at 273 K and 1 bar. Particularly, the crosslinked polyimide containing trifluoromethyl groups (CF₃-PI-CL) shows high CO₂/N₂ and CO₂/CH₄ selectivity (72 and 22) at 273 K, which are among the best results for reported porous materials. This work reveals that the introduction of crosslinked structure and changing substituents is an efficient method for constructing microporous polyimides with abundant micropores and excellent CO₂ selective adsorption capacity. This method also has great potential for fabricating high-performance microporous polymers based on other linear polymers without rigid contorted structure.

Efficacies of Carbon-Based Adsorbents for Carbon Dioxide Capture

Carbon dioxide (CO2), a major greenhouse gas, capture has recently become a crucial technological solution to reduce atmospheric emissions from fossil fuel burning. Thereafter, many efforts have been put forwarded to reduce the burden on climate change by capturing and separating CO2, especially from larger power plants and from the air through the utilization of different technologies (e.g., membrane, absorption, microbial, cryogenic, chemical looping, and so on). Those technologies have often suffered from high operating costs and huge energy consumption. On the right side, physical process, such as adsorption, is a cost-effective process, which has been widely used to adsorb different contaminants, including CO2. Henceforth, this review covered the overall efficacies of CO2 adsorption from air at 196 K to 343 K and different pressures by the carbon-based materials (CBMs). Subsequently, we also addressed the associated challenges and future opportunities for CBMs. According to this review, the efficacies of various CBMs for CO2 adsorption have followed the order of carbon nanomaterials (i.e., graphene, graphene oxides, carbon nanotubes, and their composites) < mesoporous -microporous or hierarchical porous carbons < biochar and activated biochar < activated carbons.

CuO-modified activated carbon for the improvement of toluene removal in air

We used an impregnation method to prepare CuO/AC (activated carbon) composite materials of different CuO content and characterized them via scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), and Fourier transform infrared spectroscopy (FT-IR). The effect of CuO content on toluene adsorption/desorption was evaluated. We explored the reusability of AC and AC03 (CuO modified AC with CuO loading 0.3 wt.%) adsorbents via toluene adsorption/desorption cycle testing. We used quasi-first- and quasi-second-order models, the Bangham model, and the Weber-Morris model to fit the toluene adsorption data. The introduction of CuO species evidently improved the adsorption performance of activated carbon toward toluene. The CuO content markedly affected the specific surface area, CuO dispersal, the numbers of oxygen-containing functional groups on the surface, and adsorption performance of the prepared composite adsorbents. Low CuO content was not favorable for the formation of active adsorption sites, while high content greatly reduced the specific surface area, and even covered active adsorption sites. The toluene adsorption performance varied in the order AC03 > AC02 > AC05 > AC08 > AC01 (AC03, AC02, AC05, AC08 and AC01 are CuO modifying AC with CuO loading 0.3, 0.2, 0.5 0.8 and 0.1 wt.%, respectively). The breakthrough time and toluene adsorption capacity of the AC03 composite adsorbent were 94 min and 701.8 mg/g, respectively, and the recycling efficiency was 92.8% after thermal desorption at 200°C. The adsorption process was best described by the Bangham model and adsorption could be divided into three stages.

Carbon Dioxide Adsorption on Porous and Functionalized Activated Carbon Fibers

Polyacrylonitrile-based activated carbon fibers (ACFs), modified using potassium hydroxide (KOH) or tetraethylenepentamine (TEPA), were investigated for carbon dioxide (CO2) adsorption, which is one of the promising alleviation approaches for global warming. The CO2 adsorption isotherms were measured, and the values of isosteric heat of adsorption were calculated. The results showed that the KOH-modified ACFs exhibited a great deal of pore volume, and a specific surface area of 1565 m2/g was obtained. KOH activation made nitrogen atoms easily able to escape from the surface of ACFs. On the other hand, the surface area and pore volume of ACFs modified with TEPA were significantly reduced, which can be attributed to the closing or blocking of micropores by the N-groups. The CO2 adsorption on the ACF samples was via exothermic reactions and was a type of physical adsorption, where the CO2 adsorption occurred on heterogeneous surfaces. The CO2 uptakes at 1 atm and 25 °C on KOH-activated ACFs reached 2.74 mmole/g. This study observed that microporosity and surface oxygen functionalities were highly associated with the CO2 uptake, implying the existence of O-C coordination, accompanied with physical adsorption. Well cyclability of the adsorbents for CO2 adsorption was observed, with a performance decay of less than 5% over up to ten adsorption-desorption cycles.