Sustainable N-doped hierarchical porous carbons as efficient CO2 adsorbents and high-performance supercapacitor electrodes

Behavior, mechanisms, and applications of low-concentration CO2 in energy media

This review explores the behavior of low-concentration CO2 (LCC) in various energy media, such as solid adsorbents, liquid absorbents, and catalytic surfaces. It delves into the mechanisms of diffusion, adsorption, and catalytic reactions, while analyzing the potential applications and challenges of these properties in technologies like air separation, compressed gas energy storage, and CO2 catalytic conversion. Given the current lack of comprehensive analyses, especially those encompassing multiscale studies of LCC behavior, this review aims to provide a theoretical foundation and data support for optimizing CO2 capture, storage, and conversion technologies, as well as guidance for the development and application of new materials. By summarizing recent advancements in LCC separation techniques (e.g., cryogenic air separation and direct air carbon capture) and catalytic conversion technologies (including thermal catalysis, electrochemical catalysis, photocatalysis, plasma catalysis, and biocatalysis), this review highlights their importance in achieving carbon neutrality. It also discusses the challenges and future directions of these technologies. The findings emphasize that advancing the efficient utilization of LCC not only enhances CO2 reduction and resource utilization efficiency, promoting the development of clean energy technologies, but also provides an economically and environmentally viable solution for addressing global climate change.

One-pot synthesis of N-doped petroleum coke-based microporous carbon for high-performance CO2 adsorption and supercapacitors

Waste resource utilization of petroleum coke is crucial for achieving global carbon emission reduction. Herein, a series of N-doped microporous carbons were fabricated from petroleum coke using a one-pot synthesis method. The as-prepared samples had a large specific surface area (up to 2512 m2/g), a moderate-high N content (up to 4.82 at.%), and high population (55%) of ultra-micropores (<0.7 nm). Regulating the N content and ultra-microporosity led to efficient CO2 adsorption and separation. At ambient pressure, the optimal N-doped petroleum coke-based microporous carbon exhibited the highest CO2 uptake of 4.25 mmol/g at 25°C and 6.57 mmol/g at 0°C. These values are comparable or even better than those of numerous previously reported adsorbents prepared by multistep synthesis, primarily due to the existence of ultra-micropores. The sample exhibited excellent CO2/N2 selectivity at 25°C owing to the abundant basic pyridinic and pyrrolic N species; and showed superior CO2 adsorption-desorption cycling performance, which was maintained at 97% after 10 cycles at 25°C. Moreover, petroleum coke-based microporous carbon, with a considerably high specific surface area and hierarchical pore structure, exhibited excellent electrochemical performance over the N-doped sample, maintaining a favorable specific capacitance of 233.25 F/g at 0.5 A/g in 6 mol/L KOH aqueous electrolyte. This study provides insight into the influence of N-doping on the porous properties of petroleum coke-based carbon. Furthermore, the as-prepared carbons were found to be promising adsorbents for CO2 adsorption, CO2/N2 separation and electrochemical application.

Mild and Efficient One-Step Synthesis of Nitrogen-Doped Multistage Porous Carbon for High-Performance Supercapacitors

Biomass-derived carbon materials have broad application prospects in energy storage, but still face problems such as complex synthesis paths and the massive use of corrosive activators. In this study, we proposed a mild and efficient pathway to prepare nitrogen-doped porous carbon material (N-YAC) using one-step pyrolysis with solid K2CO3, tobacco straw, and melamine. The optimized material (N-YAC0.5) was not only enriched with nitrogen, but also exhibited a high specific surface area (2367 m2/g) and a reasonable pore size distribution (46.49% mesopores). When utilized in electrodes, N-YAC0.5 exhibited an excellent capacitance performance (338 F/g at 1 A/g) in the three-electrode system, and benefitted from a high mesopore distribution that maintained a capacitance of 85.2% (288 F/g) at high current densities (20 A/g). Furthermore, the composed symmetric capacitor achieved an energy density of 14.78 Wh/kg at a power density of 400 W/kg. In summary, our work provides a novel and eco-friendly approach for converting biomass into high-performance energy-storage materials.

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.

Amine functionalized benzene based hypercrosslinked polymer as an adsorbent for CO2/N2 adsorption

In this work, benzene based hypercrosslinked polymer (HCP) as an adsorbent was modified using amine group to enhance CO₂ uptake capability and selectivity. Based on BET analysis result, the HCP and the modified HCP provide surface area of 806 (m² g^-1) and micropore volume of 453 (m² g^-1) and 0.19 (cm³ g^-1) and 0.14 (cm³ g^-1), respectively. The CO₂ and N₂ gases adsorption were performed in a laboratory scale reactor at a temperature between 298 and 328 K and pressure up to 9 bar. The experimental data were evaluated using isotherm, kinetic and thermodynamic models to identify the absorbent behavior. The maximum CO₂ adsorption capacity at 298 K and 9 bar was obtained 301.67 (mg g^-1) for HCP and 414.41 (mg g^-1) for amine modified HCP. The CO₂ adsorption thermodynamic parameters assessment including enthalpy changes, entropy changes, and Gibbs free energy changes at 298 K were resulted - 14.852 (kJ mol^-1), - 0.024 (kJ mol^-1 K^-1), - 7.597 (kJ mol^-1) for HCP and - 17.498 (kJ mol^-1), - 0.029(kJ mol^-1 K^-1), - 8.9 (kJ mol^-1) for amine functionalized HCP, respectively. Finally, the selectivity of the samples were calculated at a CO₂/N₂ composition of 15:85 (v/v) and 43% enhancement in adsorption selectivity at 298 K was obtained for amine modified HCP.

Sodium Alginate-Based Carbon Aerogel-Supported ZIF-8-Derived Porous Carbon as an Effective Adsorbent for Methane Gas

Adsorption natural gas (ANG) is a technology in which natural gas is stored on the surface of porous materials at relatively low pressures, which are promising candidates for adsorption of natural gas. Adsorbent materials with a large surface area and porous structure plays a significant role in the ANG technology, which holds promise in increasing the storage density for natural gas while decreasing the operating pressure. Here, we demonstrate a facile synthetic method for rational construction of a sodium alginate (SA)/ZIF-8 composite carbon aerogel (AZSCA) by incorporating ZIF-8 particles into SA aerogel through a directional freeze-drying method followed by the carbonization process. The structure characterization shows that AZSCA has a hierarchical porous structure, in which the micropores originated from MOF while the mesopores are derived from the three-dimensional network of the aerogel. The experimental results show that AZSCA achieved high methane adsorption of 181 cm³·g^-1 at 65 bar and 298 K, along with higher isosteric heat of adsorption (Q_st) throughout the adsorption range. Thus, the combination of MOF powders with aerogel can find potential applications in other gas adsorption.

Valorization of orange peel waste to tunable heteroatom-doped hydrochar-derived microporous carbons for selective CO2 adsorption and separation

Constrained by the extortionately expensive carbon sources, low carbon yields, inadequate adsorption capacities, and corrosive chemical activating agents, the commercialization of carbonaceous CO₂ adsorbents remains a challenging task. Herein, potassium oxalate (K₂C₂O₄), an activating agent with less corrosive properties, was used for the synthesis of activated carbons from inexhaustibly available "orange peel biowaste." For the first time, a comprehensive report is presented on the effect of hydrothermal treatment, hydrochar/K₂C₂O₄ ratio, activation temperature, and melamine modification in tailoring the porosity and surface functionalization of activated carbons. The optimized sample, OPMK-900, exhibited large specific surface area ~2130 m²/g; micropore volume ~1.1166 cm³/g, and a high pyrrolic nitrogen content (~ 46.1 %). Notably, melamine played the dual role as a promoter to K₂C₂O₄ porosity generation and a nitrogen dopant, which synergistically led to an efficient CO₂ uptake of ~6.67 mmol/g at 273 K/ 1 bar via micropore-filling mechanism and Lewis acid-base interactions. Moreover, remarkably high IAST CO₂/N₂ selectivity (105 at 273 K and 96 at 298 K) surpasses most of the biomass-derived carbons. Furthermore, the moderately high isosteric heat of adsorption (∆H_ads ~ 38.9 kJ/mol) revealed the physisorption mechanism of adsorption with a limited energy requirement for the regeneration of the spent adsorbents.

Resource utilization of rice husk biomass: Preparation of MgO flake-modified biochar for simultaneous removal of heavy metals from aqueous solution and polluted soil

In general, the remediation performance of heavy metals can be further improved by metal-oxide modified biochar. This work used MgO-modified rice husk biochar (MgO-5%@RHB-450 and MgO-5%@RHB-600) with high surface activity for simultaneous remediation and removal of heavy metals in soil and wastewater. The adsorption of MgO-5%@RHB-450/MgO-5%@RHB-600 for Cd(II), Cu(II), Zn(II) and Cr(VI) followed the pseudo-second order, with the adsorption capacities reaching 91.13/104.68, 166.68/173.22, 80.12/104.38 and 38.88/47.02 mg g^-1, respectively. The addition of 1.0% MgO-5%@RHB-450 and MgO-5%@RHB-600 could effectively decrease the CaCl₂-extractable Cd concentration (CaCl₂-Cd) by 66.2% and 70.0%, respectively. Moreover, MgO-5%@RHB-450 and MgO-5%@RHB-600 facilitated the transformation of exchangeable fractions to carbonate-bound and residual fractions, and reduced the exchangeable fractions by 8.1% and 9.6%, respectively. The mechanisms for the removal of heavy metals from wastewater by MgO-5%@RHB-450 and MgO-5%@RHB-600 mainly included complexation, ion exchange and precipitation, and the immobilization mechanisms in soil may be precipitation, complexation and pore filling. In general, this study provides high-efficiency functional materials for the remediation of heavy metal pollution.

Development of Uniform Porous Carbons From Polycarbazole Phthalonitriles as Durable CO2 Adsorbent and Supercapacitor Electrodes

Advances in new porous materials have recognized great consideration in CO2 capture and electrochemical energy storage (EES) applications. In this study, we reported a synthesis of two nitrogen-enriched KOH-activated porous carbons prepared from polycarbazole phthalonitrile networks through direct pyrolysis protocol. The highest specific surface area of the carbon material prepared by pyrolysis of p-4CzPN polymer reaches 1,279 m2 g-1. Due to the highly rigid and reticular structure of the precursor, the obtained c-4CzPN-KOH carbon material exhibits high surface area, uniform porosity, and shows excellent CO2 capture performance of 19.5 wt% at 0°C. Moreover, the attained porous carbon c-4CzPN-KOH showed high energy storage capacities of up to 451 F g-1 in aqueous electrolytes containing 6.0 M KOH at a current density of 1 A g-1. The prepared carbon material also exhibits excellent charge/discharge cycle stability and retains 95.9% capacity after 2000 cycles, indicating promising electrode materials for supercapacitors.

Valorization of shrimp shell biowaste for environmental remediation: Efficient contender for CO2 adsorption and separation

Over the years, single heteroatom-doped biowaste-derived activated carbons were studied for effective CO₂ adsorption. However, binary or ternary heteroatoms-doping is equally important and could significantly affect the CO₂ adsorption and flue gas (i.e., CO₂/N₂) separation. Herein, for the first time, shrimp shell-derived chitosan was used to design a series of ternary (N, S, O)-doped hierarchically porous carbons. The resultant carbons exhibit a large specific surface area (up to 2095 m²/g), micropore volume (up to 1.2647 cm³/g), and high heteroatoms content i.e., N up to 4.1 at. %, S up to 4.6 at. %, and O up to 13.4 at. %. Consequently, high CO₂ uptake of 236.80 mg/g at 273 K/1 bar and an excellent CO₂/N₂ gas selectivity (84.3) was observed, attributed to the synergistic role of narrow micropores (<1 nm) and optimum heteroatom content. Furthermore, the stable CO₂ adsorption-desorption cyclic behavior under flue gas conditions i.e., 15% CO₂/85% N₂ reveals the physisorption mechanism of CO₂ adsorption and appears to be an energy-efficient regeneration process. Concluding, our work demonstrates a facile route of valorization of biowaste for environmental remediation to combat biowaste accumulation and mitigating atmospheric CO₂ levels, simultaneously.

Synthesis of membrane-type graphene oxide immobilized manganese dioxide adsorbent and its adsorption behavior for lithium ion

Recently, there has been an urgent need to develop new materials and technologies for extracting lithium ions. Herein, the membrane-type adsorbent of manganese dioxide (MnO₂) is prepared by a vacuum filtration method using graphene oxide (GO) as a binder and amino-β-cyclodextrin (amino-β-CD) as an adjuvant. The results of thermogravimetric analysis show that MnO₂ is successfully immobilized on GO layers with a content of about 24 wt%, which enabled rapid adsorb lithium ions from the ionic solution. In addition, the permeation experiment shows the membrane has specific selectivity for lithium ion transport and adsorption, which is manifested in the selectivity ratios of K⁺/Li⁺, Na⁺/Li⁺ and K⁺/Na⁺ to 2.5, 3.2 and 0.8, respectively. Adsorption experiments show that GO-β-CD/MnO₂ membrane has a high adsorption capacity for lithium ions (37.5 mg g^-1). The adsorption kinetic curve indicates that the lithium adsorption process is controlled by the chemical adsorption mechanism. In the enrichment experiment, the concentration of lithium ions from seawater can be enriched to 1.2 mg L^-1 after 100 cycles. The results suggest that the developed GO-β-CD/MnO₂ membrane could effectively extract lithium ions from seawater.

Controlled assembly of nitrogen-doped iron carbide nanoparticles on reduced graphene oxide for electrochemical reduction of carbon dioxide to syngas

The electrocatalytic CO₂ reduction reaction (CO₂RR) decreases the amount of greenhouse gas in the atmosphere while enabling a closed carbon cycle. Herein, iron oleate was used as a precursor to produce oleic acid-coated triiron tetraoxide nanoparticles (Fe₃O₄@OA NPs) by pyrolysis, which was then assembled with reduced graphene oxide (rGO) and doped with dicyandiamide as a nitrogen source to obtain nitrogen-doped iron carbide nanoparticles assembled on rGO (N-Fe₃C/rGO NPs). The catalyst prepared by nitrogen doping at 800 °C with an Fe₃O₄@OA NPs to rGO weight ratio of 20:1 showed good activity and stability for the CO₂RR. At -0.3 to -0.4 V, the H₂/CO ratio of the product from the catalyzed CO₂RR was close to 2; thus, the product can be used for Fischer-Tropsch synthesis. The results of a series of experiments and X-ray photoelectron spectroscopy analysis showed that the synergy between the CN and FeN groups in the catalyst can promote the reduction of CO₂ to CO. This work demonstrates a facile method for improving the catalytic reduction of CO₂.

Design and synthesis of a 3D flexible film electrode based on a sodium carboxymethyl cellulose–polypyrrole@reduced graphene oxide composite for supercapacitors

A novel, environmentally friendly and freestanding 3D flexible film electrode (CMC–PPy@RGO) was prepared by a simple vacuum filtration method.