Preparation And Surface Functionalization Modification Of Larch Wood-based Porous Foam Materials

Woody biomass is a cheap and easily available renewable resource,and the wood liquefactiontechnology can transform the macromolecular components of the difficult-to-melt woody material into small molecules rich in active reaction sites.In this paper,larch wood chips were used as raw material,phenol as liquefying agent and mixed acid of concentrated sulfuric acid and concentrated phosphoric acid as catalyst,and the reaction of the obtained liquefied material and formaldehyde to obtain larch lignin-based phenolic resin was studied,and the surface-modified porous foam materials were prepared by surface coating,grafting or soft templating agent modification method with lignin-based phenolic resin as the base material.Initially,the larch wood-based porous foam materials were realized for the controlled separation and recovery of oil-water mixture and used as electrode materials for supercapacitors.It mainly includes:non-responsive porous foam materials,alkali-responsive with decanoic acid modified Ti O2 coating,acid-responsive with P4vp grafting and wet-responsive with fully cross-linked chitosan coating for controlled oil-water separation and recovery,and F127 soft template method micro/medium/macroporous foam carbon supercapacitor electrode materials.The main studies are as follows:（1）Foam resin（LLB-PF）and foam carbon（LLB-CF）with three-dimensional connected porous honeycomb structure were prepared by obtaining liquefied material precursors from larch wood chips.The results showed that the three-dimensional connected porous honeycomb structure of LLB-PF was formed during the self-foaming process and remained intact in the charred LLB-CF,and the pore bubble diameter of LLB-PF ranged from 300-450μm and the pore diameter ranged from 1.0-3.5μm,while the overall size of LLB-CF shrank and the pore bubble diameter ranged from 225-375μm and the pore diameter remained unchanged The overall size of LLB-CF shrank and the pore diameter was between 225-375μm with no change in pore diameter,maintaining between 1.0-3.5μm.The WCA of LLB-PF and LLB-CF were 144.6°and105.6°,respectively,and these two ultra-light foams had excellent selective absorption of oil-water mixture.The absorption capacity of tetrachloromethane and epoxidized soybean oil reached 88 and 153 times of their own weight,respectively.The cycling test showed that LLB-PF and LLB-CF still showed excellent absorption ability even after 5 cycles,showing the ability of recycling to recover organic solvents.（2）The porous foam materials with alkali-responsive surface wettability were prepared by surface coating modification with LLB-PF as the base material and decanoic acid-modified Ti O2as the alkali-responsive group.The results showed that the pore bubble size of the alkali-responsive porous foam（PF-DA）was in the range of 300-450μm,and the pore diameter was in the range of 1.0-3.5μm.The obtained PF-DA exhibited hydrophobicity（water contact angle,WCA=122°）and superoleophilicity（oil contact angle,OCA=0°）in a neutral environment,making it selectively permeable to oil and organic solvents,and used for oil-water separation to allow oil to permeate through while blocking aqueous solutions from the outside of the foam.When PF-DA is placed in an alkaline aqueous solution or ammonia atmosphere,its surface wettability switches from hydrophobic to superhydrophobic（WCA=0°）and submerged superoleophobic（OCA=152°）,selectively allowing water to permeate through while keeping oil and organic solvents out of the foam,resulting in controlled oil/water separation.Thus,this switchable water/oil permeability gives PF-DA the ability to perform oil-water separation in complex situations.（3）Acid-responsive foam carbon（CF-P4vp）with switchable wettability was prepared by surface grafting modification with larch liquefaction（LLS）and 4-vinylpyridine（4vp）as the acid-responsive group.The results showed that CF-P4vp has a three-dimensional reticular porous structure with a basic skeleton diameter ranging from 50-200μm and a ligament diameter of about 5μm.After grafting poly（4-vinylpyridine）（P4vp）,the protonation and deprotonation of the pyridine moiety in different p H environments allowed CF-P4vp to obtain acid-responsive switchable surface wettability with p H=1 water droplets and p H=7 droplets with a WCA of 0°and 136.1°,respectively.CF-P4vp can absorb 15-35 its own weight of oil or organic solvent in a neutral aqueous solution at p H=7 and desorb all the absorbed material within 40 s after immersion in the aqueous solution at p H=1.After 15 repetitions,there was only about 2.8%reduction in the organic（chloroform）uptake rate.（4）Two wet-responsive foams with surface switchable wettability,RF-CS and LLS-MF-CS,were prepared by surface coating modification with LLS as the raw material and fully cross-linked chitosan（CS/GA）as the wet-responsive group.results showed that RF-CS was a three-dimensional porous foam-like structure with pore bubble sizes ranging from 300-400μm and pore When in air,RF-CS and LLS-MF-CS are bi-superphilic with static water contact angle and static oil contact angle of 0°,and when in aqueous solution,the wet response CS coating makes the surfaces of RF-CS and LLS-MF-CS change to oleophobic,where RF-CS can still maintain good and stable oleophobicity in aqueous solutions with p H 1-13 and high concentration of saline solutions,and the static oil contact angle is maintained between 128.8 and 141.8°,RF-CS and LLS-MF-CS5 have good absorption ability to organic solvents containing common functional groups,which can reach 4.1-13.8 times and 4.9-19.0 times of their own weight,respectively.（5）The foam carbon electrode material（LLS-CF）was prepared by one-step carbonization activation surface pore structure modification using LLS as raw material and F127 as soft template agent.The results show that LLS-CF is a three-dimensional mesh skeleton structure,and the skeleton size collapses and shrinks with the increase of carbonization temperature,and the skeleton size of LLS-CF₁₀₀₀ at 1000℃is between 50-200μm,and the ligament diameter is about 4μm.The average pore size of mesopores was about 3.82 nm,and the specific surface area was 331.55 m2/g.The percentage of microporous specific surface area increased significantly from 3.68%to 41.88%in LLS-CF₃₅₀.In the three-electrode electrochemical test with 6 M KOH electrolyte system,the specific capacitance of LLS-CF₁₀₀₀ reached 81.4 F/g at a current density of 0.5 A/g,and the capacitance was maintained at 93.1%after more than 6000cycles of charging and discharging at a current density of 5 A/g.