Fabrication And Adsorption Properties Of Cellulose-based Adsorbent With Hyperbranch-mesostructure System

Based on nano-scale mesostructure,functional mesoporous silica is a hybrid porous material modified by organic reagents,which possesses large specific surface area,high pore volume,fast mass transfer rate,adjustable structure,high hydrothermal stability and facile surface functionalization,exhibiting great advantages and potential in various fields such as protein separation,catalyst carrier,drug carrier,nano reactor and adsorbent materials.Hyperbranched polymer is a dendrimer macromolecular with quasi spherical structure,which has been widely investigated on applications of additives,macromolecular building blocks,interface induction and adsorption owing to its low viscosity,few molecular chain entanglement and functional groups with high density,being a excellent surface modifier.Cellulose fiber is biomass material with macromolecular chains that is abundant in nature,which has good hydrophilicity,biocompatibility,renewability,biodegradability and accessibility for modification.As a result,as an excellent biosorbent,cellulose fiber can be also employed to fabricate functional composite adsorbent materials by providing mechanical support as base component.In this study,carboxyl-functional SBA-15 mesoporous silica?SBA-CAR?was synthesized by using 2-Cyanoethyltriethoxysilane?CTES?and tetraethoxysilane?TEOS?.Then multi-amino hyperbranched polymer?HBP?was introduced onto mesostructure surface of SBA-CAR,fabricating a highly-efficiency and versatile hybrid adsorbent with a hyperbranched-substrate adsorption nanonetwork.Subsequently,its adsorption properties and mechanism were investigated,and the feasibility of covalently forming efficient adsorption structure by HBP and carboxylic meso-substrate was further confirmed.In order to integrating functionalized mesoporous silica onto cellulose fiber in a homogeneous and stable way,carboxyl-functional mesoporous silica nanoparticles?CA-MSN?were synthesized through one-pot co-condensation by Carboxyethylsilanetriol sodium salt?CES?and TEOS.And effect of CES/TEOS molar ratio on nanoparticles morphology was discussed to select an optimal route.Then self-assembled mesoporous silica/cotton fiber composite adsorbent?AM-cotton?and in-situ functionalized mesoporous silica adsorbent based on cellulose?HIM-cotton?were fabricated through different integration routes,and their morphology,structure and adsorption properties were measured and analyzed.Based on the research experiences and results,the combination mode between CA-MSNs and fibers was explored and improved,and finally,cellulose-based composite adsorbent with a stable hyperbranch-mesostructure system?HM-cotton?was developed by using HBP as mediate,inducing a self-assembly of CA-MSN onto anion-modified cotton fiber and forming a dot-plane structure.The resultant product was characterized for morphology and structure,and its adsorption capacities for cationic dye methylene blue?MB?,anionic dye congo red?CR?,heavy metal ion Cu²⁺and Fe³⁺from aqueous medium were further studied,as well as its adsorption mechanism and recyclability property.The results show that the functionalized structure of SBA-HBP is ordered as 2D hexagonal?P6mm?mesostructure,which was to some extent affected by the co-condensation process,and its BET surface area,pore volume and average pore size are80 m²/g,0.15 m³/g and 5.8 nm,respectively.SBA-HBP exhibits excellent adsorption capacities for anionic and cationic dyes as well as heavy metal ions from aqueous medium,and the corresponding adsorption equilibriums were reached within about 2 h and 3 h.Besides,after 5 regenerations,about 90%adsorption capacities was retained.Adsorption mechanism studies show that the adsorption process obeys the pseudo-second-order kinetics model and Langmuir isotherm model.CA-MSN was synthesized by using CES as functional silica source.The resultant product exhibits stable and monodisperse nanomorphology with 50 nm quasi-sphere nanoparticle,wormhole-type mesopore and narrow distribution of pore size when moral ratio of CES/TEOS is 1:10.Its BET surface area,pore volume and average pore size are379 m²/g,0.58 m³/g and 3.37 nm,respectively.AMSN,obtained by grafting HBP onto CA-MSN,was incorporated to cotton fiber via electrostatic self-assembly,fabricating AM-cotton.The study results show that AM-cotton surface is covered by substantial polymer-wrapped AMSNs which exhibits the similar mesostructure with CA-MSN.As a result,AM-cotton shows good adsorption capacities for organic dye pollutants from aqueous medium,and the adsorption equilibriums were reached within about 3 h and 4 h.Through in-situ synthesis route,CES and TEOS were introduced simultaneously to cotton fiber surface and functionalized by HBP,obtaining HIM-cotton.The study results indicate that abundant mesoporous silica particles with diameter ranging from 171.6 nm and 578.3 nm are distributed on the HIM-cotton surface by in-situ growth,which are wrapped by hyperbranched polymer.Owing to the positively charged surface with Zeta potential of+12.2 mV,HIM-cotton is considered to have potential adsorption effect,and it shows good adsorption capacities for CR and MB from aqueous medium in saturated adsorption experiments.HBP-cotton was fabricated by chemically graft of HBP on AN-cotton.Under the induction of its HBP layer,CA-MSN was evenly integrated onto the HBP-cotton surface in dot and monolayer ways by electrostatic self-assembly and steric hindrance effect,and then immobilized by chemical bonds,obtaining HM-cotton.The adsorption properties of HM-cotton is largely affected by initial pH of pollutant solutions,and the adsorption equilibriums were reached within about 3 h and 2.5 h for dyes and heavy metal ions from aqueous medium,respectively.For regeneration experiments,average about 80%of maximum adsorption capacities was still retained after 5 cycles.And the adsorption process obeys the pseudo-second-order kinetics model and Langmuir isotherm model.