Preparation Of Lignosulfonate Based Composites And Their Application In Wastewater Treatment

Sodium lignosulfonate（SLS）,as a waste by-product of the paper industry,contains a large number of functional groups such as sulfonic acid groups,hydroxyl groups,methoxy groups,and conjugated double bonds that can interact with pollutants such as dyes.At present,it has been reported that it could been made into adsorbent and separation membrane for the removal of pollutants in water.However,due to the limited active site and strength of sodium lignosulfonate,the removal performance of lignosulfonate-based adsorbents and separation membranes for organic dyes in water is not outstanding.Therefore,in this paper,sodium lignosulfonate was aminated and hybridised with hyperbranched polyamide to prepare lignosulfonate-based hybrid hydrogel adsorbent,and its adsorption properties for organic dyes were studied and its adsorption mechanism was explored.Using PVDF microporous membrane and PET fabric as the membrane substrate respectively,a superhydrophilic layer composed of sodium lignosulfonate and hyperbranched polyamide hybrid was constructed on the surface.The separation performance of the hybrid modified separation membrane for dye aqueous solution was studied,and the separation of oil-water emulsion was preliminarily investigated.The following research results were obtained:（1）Sodium lignosulfonate and hyperbranched polyamide hybrid hydrogel adsorbent（HPAS）was prepared by a one-pot reaction using polyethylene glycol diglycidyl ether as a crosslinking agent.The relationship between the adsorbent structure and the dye adsorption behavior was investigated,and the hybrid hydrogel was found to have an ultrahigh adsorption capacity for Congo red（CR）.When the initial concentration of CR is 6000 mg/L,the natural p H,the temperature is 298 K,and the amount of adsorbent HPAS-4 is 0.8 g/L,the actual maximum adsorption capacity of CR can reach 5120 mg/g,which is higher than most other reported literature.At the same time,HPAS-4 also showed strong adsorption performance for Cu（II）;the maximum absorption capacity was 249mg/g（C₀Cu（II）=100 mg/L）.After five adsorption-desorption cycles,HPAS-4 still maintained a high adsorption capacity for CR and Cu（II）.The adsorption of CR and Cu（II）by HPAS is a spontaneous endothermic process,which conforms to the pseudo-second-order kinetic model and the Langmuir adsorption model.The main mechanism of the CR adsorption process is the hydrogen bond interaction caused by abundant N and O atoms in HPAS,accompanied by electrostatic attraction andπ-πinteraction.The adsorption of Cu（II）on HPAS is mainly determined by complexation/chelation,accompanied by the precipitation of copper derivatives on HPAS.（2）Superhydrophilic PVDF membrane（M-HPAS）modified by sodium lentisulfonate and hyperbranched polyamide was prepared by using PVDF microporous membrane as the substrate,which was introduced by double bond through alkalization and surface grafting polymerization of glycidyl methacrylate,and then crosslinked with sodium amine lentisulfonate and hyperbranched polyamide.The separation performance of dye wastewater and oil-water emulsion was investigated.The results show that when the alkalization treatment time was 4 h,the content of GMA in the graft solution was 20%,and the dosage of sodium amylated lentisulfonate and hyperbranched polyamide were 0.1g and 0.3 g,respectively,the M-HPAS membrane showed excellent separation performance for the anion dye solutions such as Congo red,direct red 80 and Titan yellow.The separation fluxes were 3942.53,3904.96 and 2567.17 L·m^-2·h^-1,respectively,and the separation fluxes for CR were higher than those reported in most other literatures.At the same time,the separation efficiency can reach 100%.For low concentration（10 and 20ppm）CR dye solutions,the separation efficiency can still be maintained at 100%after 25cycles of separation.Compared with most reported modified PVDF membranes,M-HPAS has excellent oil/water emulsion separation flux and efficiency.The fluxes of p-toluene emulsion and n-hexane emulsion were 4028.90 L·m^-2·h^-1 and 3152.44 L·m^-2·h^-1,and the separation efficiency was more than 98%.In addition,M-HPAS has good reusability.The separation flux can be restored to more than 96%by simply rinsing the oil and water with deionized water after separation.The excellent separation performance of anionic dyes and oil-water emulsion is attributed to the superhydrophilic gel layer with a three-dimensional network structure containing a large number of functional groups such as amino,sulfonic and hydroxyl groups.The separation of oil and water emulsion was realized by demilsification of amino and hydroxyl groups in the superhydrophilic condensate layer.LA/HP/PEGDGE formed a specific three-dimensional network structure and the synergistic effect of PVDF membrane porous structure provided a favorable channel for the mass transfer of water and increased the separation flux.（3）Superhydrophilic polyester fabric（PET-HPAS）modified by sodium lignosulfonate and hyperbranched polyamide hybrid crosslinking reaction was prepared by grafting polyglycyl methacrylate（PGMA）on the substrate of PET polyester fabric,and its performance in separating dye wastewater and oil-water emulsion was investigated.The results showed that when GMA content was 20%,BP content was 1.0%,UV illumination time was 15 min,and the dosage of LA and HP were 0.15 g and 0.6 g,respectively,the pure water flux of PET-HPAS is 163.10 L·m^-2·h^-1,which is 1.3 times that of the original polyesterfabric(127.54 L·m^-2·h^-1)（under gravity）.PET-HPAS showed excellent separation performance for anionic dye solution and oil-water emulsion,with a separation efficiency of 100%and a separation flux of 125.7 L·m^-2·h^-1 for 10 ppm anionic dye Congo red.The separation efficiency of PET-HPAS for CR reaches 100%when CR concentration is 10,20,30 and 40 ppm.The separation fluxes of p-toluene emulsion,n-hexane emulsion and petroleum ether emulsion were 154.53,139.21 and 83.24 L·m^-2·h^-1,respectively,and the separation efficiency of PET-HPAS was over 98%.It is superior to other reported modified PET fabrics and PET-HPAS has better reusability.Similarly,the excellent separation performance of anionic dye and oil-water emulsion of PET-HPAS is also attributed to the three-dimensional network structure of superhydrophilic gel layer containing a large number of functional groups such as amino,sulfonic acid,hydroxyl and so on.The separation of oil and water emulsion is realized by demilsification of amino and hydroxyl groups in the superhydrophilic condensate layer.LA/HP forms a specific three-dimensional network structure on PET surface and the synergistic effect of porous structure of PET fabric provides a favorable channel for the mass transfer of water and increases the separation flux.