BC article

Overview of Carbon Capture, Utilization, and Sequestration (CCUS)

• Global Context and Climate Objective: Carbon dioxide ($CO_2$) is the primary component of greenhouse gases contributing to global warming. As of recent observations, atmospheric concentrations have reached approximately $400\,\text{ppm}$ and continue to rise. This has resulted in severe environmental hazards, including the melting and disappearance of polar icebergs.

• The Chemical Nature of CO2: $CO_2$ is characterized by its inert and stabilizing properties, attributed to the covalent double bonds between carbon and oxygen atoms ($O=C=O$). These double bonds render the molecule thermodynamically stable and unreactive, creating a significant hurdle for its conversion into value-added products.

• Carbon Sequestration Framework: Carbon sequestration is a systematic engineering approach integrating three critical phases:

  • Capture: Removing $CO_2$ from emission sources like power plants or directly from the air.

  • Utilization: Converting captured carbon into chemicals, fuels, and materials.

  • Storage (Storage/Sequestration): Injecting captured gas into deep geological formations for permanent isolation.

• The Role of Materials: The establishment of a secure CCS infrastructure relies on selecting appropriate materials. Adsorbents and catalysts represent the core of this technology, with current research focusing on capacity, selectivity, impurity tolerance, and regeneration capabilities.

Classification and Preparation of Cellulose-Based Materials

• General Advantages of Cellulose: Cellulose is a prolific, renewable, and degradable natural polymer. It serves effectively as a matrix or filler for paper, films, aerogels, and hydrogels. Its structure contains abundant hydroxyl ($OH$) groups (three in each glucose unit) which facilitate hydrogen bonding and provide sites for chemical modification.

• Nanocellulose: Defined as cellulosic nanoparticles with high stiffness/strength and large surface areas ($SSA$). They are categorized into three types based on morphology and preparation:

  • Cellulose Nanocrystals (CNC): Prepared via acid or enzymatic hydrolysis to minimize dimensions. They exist as rigid rods with high crystallinity.

    • Diameter: $3\text{--}10\,\text{nm}$.

    • Length: $100\text{--}500\,\text{nm}$.

  • Cellulose Nanofibers (CNF): Synthesized primarily through mechanical and pretreatment methods. They form an interwoven network with high aspect ratios.

    • Diameter: $2\text{--}60\,\text{nm}$.

    • Length: $1\text{--}100\,\mu\text{m}$.

  • Bacterial Cellulose (BC): A microorganism-derived nanomaterial featuring a 3D network of fine ribbons. It is noted for superior water retention, biocompatibility, and high tensile strength.

    • Individual fiber diameter: $10\text{--}100\,\text{nm}$.

• Cellulose Derivatives: Produced through esterification or etherification of the linear polysaccharide chains ($\beta-1,4-d\text{-glycosidic}$ bonds). Common derivatives include:

  • Carboxymethyl cellulose (CMC): Most widely used anionic cellulose ether (alkylation).

  • Methyl cellulose (MC) and Ethyl cellulose.

  • Hydroxypropyl cellulose (HPMC).

  • Cellulose acetate (CA), Nitrocellulose.

Application of Cellulose-Based Materials in Carbon Capture

1. Cellulose-Based Composite Films

• Mixed Matrix Membranes (MMMs): Luo et al. combined 2D MXene nanosheets with branched CMC to create self-supporting membranes for flue gas separation.

  • Performance: At an MXene concentration of $1.5\,\text{mg/mL}$, the membrane achieved a $CO_2$ permeability of $521\,\text{GPU}$ and a $CO_2/N_2\text{ selectivity}$ of $40.1$.

• Modified Cellulose Acetate (CA): Nikolaeva et al. incorporated ionic liquid-like pendants (e.g., 1-methylimidazole, HEDMA) onto CA backbones. These thin film composite (TFC) membranes showed that while permeability decreased with higher HEDMA content, $CO_2/N_2$ selectivity could be tuned.

2. Cellulose-Based Composite Aerogels

• Hybrid MOF-Cellulose Aerogels: Yu et al. integrated metal-organic frameworks (e.g., $HP\text{-UIO-66-NH}_2$) into cellulose matrices. By using monocarboxylic acids (MA) with four carbon atoms as modifiers, they achieved a $CO_2$ adsorption capacity of $1.90\,\text{mmol/g}$ at $298\,\text{K}$ and $1\,\text{bar}$.

• Silica/Cellulose Whiskers: Zhou et al. synthesized composite aerogels via sol-gel process using tetraethyl orthosilicate (TEOS). When loaded with $70\%\,\text{tetraethylenepentamine (TEPA)}$, the aerogel reached a maximum capacity of $2.25\,\text{mmol/g}$.

• Bacterial Cellulose (BC) and ZIFs: Ma et al. grew amino-functionalized $ZIF-8$ ($ZIF-8\text{-NH}_2$) crystals in situ on BC. The chelation between zinc ions ($Zn^{2+}$) and cellulose hydroxyl groups provided an interfacial affinity, resulting in a capacity of $1.63\,\text{mmol/g}$.

• Typha Orientalis (TO) Carbon Aerogels: Cheng et al. used acid treatment and freeze-drying to create a 3D network from TO cellulose. After $KOH$ activation, this material achieved a massive $CO_2$ adsorption capacity of $16\,\text{mmol/g}$ at $298\,\text{K}$ and $30\,\text{bar}$.

• Polyethyleneimine (PEI) Grafting: An et al. grafted PEI onto carbon aerogels ($PEI-CPCa$), achieving an adsorption of $5.58\,\text{mmol/g}$ at $313\,\text{K}$ with a separation factor of $113.1$ for simulated flue gas ($15\%\,CO_2, 85\%\,N_2$).

3. Solid Adsorbents

• High-Temperature CaO Sorbents: Chen et al. developed core-shell pellets using cellulose as a pore-making template. Pellets with $40\,\text{wt}\%$ cellulose in the shell allowed better gas access to the active $Ca(OH)_2$ core, yielding a capacity of $0.144\,\text{g/g}$.

• Solar-Triggered Bionic Fibers (CNF-TBFA): Lu et al. integrated PNIPAm (thermal switch), graphene oxide (photothermal switch), and PEI ($CO_2\text{ site}$) onto CNF. This material captured $6.52\,\text{mmol/g}$ of $CO_2$ and regenerated using solar energy.

• Thermosensitive Nanoamines (TRCNF/PEIA): Liu et al. grafted NIPAm onto CNF. The transition at the lower critical solution temperature (LCST) triggers polymer chain contraction, facilitating desorption at lower temperatures ($6.74\,\text{mmol/g}$ capacity).

• Hydrophobic Carbon Coatings: Yu et al. used carbonylated CNF as a binder with activated carbon and $MTMS$ (hydrophobic modifier). The resulting SAC-6-1.0 adsorbent showed $39.4\,\text{mg/g}$ adsorption in dry flue gas, maintaining $97\%$ capacity after 10 cycles.

Cellulose-Based Composite Materials for Carbon Conversion

1. Hydrogenation to Formic Acid and Methanol

• Ru Catalysts on Cellulose-Phytate (CPC): Wang et al. complexed Ru(III) with cellulose-derived supports. The selectivity for formic acid reached $99\%$, with an initial production rate of $15.21\,\text{mol}\,g^{-1}\,h^{-1}$ at $120^{\circ}\text{C}$.

• Photocatalytic Methanol Production: Getahun et al. created $CuO/ZnO\text{-Den-TOCNF}$ films. Amine groups in the polymer act as adsorption sites while $CuO/ZnO$ functions as the photocatalyst. This system converts gaseous $CO_2$ to methanol ($2.16\,\text{mmol/g}$ maximum yield).

2. Conversion to Carbonates

• Mineralized Cellulose Materials (MCM): Reyes et al. created organic-inorganic systems where mineralized cellulose converts captured $CO_2$ into calcium carbonate ($CaCO_3$), usable in building materials and artificial coral stone.

• Cycloaddition with Epoxides: Hu et al. immobilized Co(III)-Salen on CNCs to catalyze the reaction of $CO_2$ and epoxides. Aggrawal et al. used copper oxide nanosheets on a paper matrix to achieve nearly $100\%$ yield of cyclic carbonates after $20\,\text{h}$ under low pressure.

• Biocatalytic Vaterite Formation: Zhang et al. used carboxymethyl cellulose (CMC) and carbonic anhydrase to catalyze $CO_2$ conversion into porous $CaCO_3$ particles, which serve as carriers for bioactive pigments like astaxanthin.

3. Reduction to Carbon Monoxide (CO)

• Electrocatalytic Electrodes: Zhou et al. grew $CuO/Cu$ nanocomposites on BC structures. At $490\,\text{mV}$, the electrode produced $CO$ with a far-potential efficiency of $53\%$, maintaining activity for $40\,\text{h}$.

• Photocatalytic ZnO Catalysts: Shi et al. used cellulose fiber templates to create porous $ZnO$. The $Cu\text{-ZnO}$ catalyst achieved a $CO$ generation rate of $30.17\,\mu\text{m}\,\text{mol}\cdot\text{g}^{-1}\text{h}^{-1}$, outperforming $CuO\text{-ZnO}$ ($8.61\,\mu\text{m}\,\text{mol}\cdot\text{g}^{-1}\text{h}^{-1}$) due to Surface Plasmon Resonance (SPR) effects.

Future Challenges and Strategic Problems

• Adsorption Capacity Gaps: While eco-friendly and low-cost, cellulose-based porous carbons generally possess lower adsorption capacities compared to zeolites or MOFs. Improvements require introducing ultra-micropores and heteroatoms.

• Reaction Path Optimization: There is a need to select optimal reaction paths that balance market demand with chemical technology to promote product diversification.

• Photocatalytic Efficiency: Further exploration is required to use cellulose as a primary photocatalyst carrier to exploit solar energy potential.

• Large-Scale Gas Source Applications: Research must expand usage of cellulose membranes to capture $CO_2$ from diverse sources, including flue gas, biogas, natural gas, and landfill gas to reduce abatement costs.