Interface-involved Functional Applications Based On Cellulose Nanofibers

Inspired by the surface/interface phenomenon in nature,the two-phase interface-involved functional application has gradually become a hot research topic.In previous studies,the liquid-liquid two-phase interface was fully and effectively applied to green chemical synthesis by building the Pickering emulsion catalytic system.Simultaneously,the gas-liquid interface plays a significant role in enhancing the performance of solar evaporator.Based on liquid-liquid and gas-liquid interfaces,Pickering emulsions decorated with various noble metal nanoparticles were prepared to study their applicability in continuous flow catalysis,and Janus solar evaporator was assembled for generating steam from undrinkable water resources.The research contents are displayed as following:(1)By using Ag-anchored cellulose nanofibers(Ag/ACNF)as emulsifier,Pickering emulsion catalytic system was obtained by regulating the electrostatic interaction between Ag/ACNF and the oil-water interface.Due to hydrogen bonding and intermolecular forces,the nanofibers are entangled together to form a firm interface layer to lock the emulsion droplets and enhance the stability of Pickering emulsion.The reduction of organic molecules(4-nitrophenol(4-NP),methylene blue(MB),and methyl orange(MO))was selected as a model reaction to test the reliability of the Pickering emulsion in continuous flow catalysis,which demonstrated very high conversion rates for 4-NP(>98%,50 h),MB(>99%,30 h),and MO(>96%,40 h).This work paves the way for the application of Pickering emulsion into continuous flow catalysis towards green chemical synthesis.(2)Pickering emulsion can be formed by using aldehyde eucalyptus cellulose nanofibers,followed by in-situ growing a series of metal nanoparticles(Pd,Au,Pt)on the interfacial nanofiber layer via aldehyde-induced reduction.Pd-decorated Pickering emulsion is applied to carry out continuous flow catalytic reduction reaction by using organic molecules(4-NP,MB,MO)as model reactants,and it can proceed continuously for at least 55 h,23 h,and 50 h with corresponding conversion efficiencies higher than 99.9%,98%,and 99%,respectively.Meanwhile,Au-and Pt-deposited emulsions are also operable in continuous flow catalysis as demonstrated by continuously catalytic reduction of 4-NP for at least 45 h and 50 h with the corresponding catalytic conversions higher than 98%and 99%,respectively.In addition,cotton nanofibers and bacterial cellulose nanofibers with aldehyde groups could also be used to prepare Pd nanoparticle-decorated Pickering emulsions,which verified the generality of the strategy for fabricating metal-anchored Pickering emulsions.This work has laid a solid foundation for the large-scale application of Pickering emulsion-based continuous flow catalysis.(3)A Janus solar evaporator with 2D water path has been constructed by placing the hydrophobic soot-coated cloth/hydrophilic cloth bilayer on hydrophobic polyethylene(PE)-wrapped cellulose aerogel.Such a unique structure not only possesses a much better salt-resisting ability than common hydrophilic solar evaporator with 2D water channel,but also decreases the heat conduction loss compared to the typical flat Janus structure in the direct contact mode.By employing candle soot(CS)as light absorber,the resultant solar evaporator(SE-CS)was proved to strongly inhibit salt deposition and efficiently produce steam from 3.5or 20 wt%Na Cl solution under 1.0 sun irradiation.Furthermore,SE-CS could be utilized to generate steam from methyl orange(MO)solution(0.01 M)and heavy metal solution(Ni²⁺,Cu²⁺,Zn²⁺,and Pb²⁺with concentration of 1000 mg/L).Besides,kerosene soot(KS)could also result in the efficient steam generation from 3.5wt%Na Cl solution over the resultant solar evaporator(SE-KS)under 1.0 sun illumination.This work strongly promotes practical application of solar-driven evaporation into wastewater purification and seawater desalination.