| Water pollution has become one of the most pressing problems in the world.How to efficiently and cheaply treat complex wastewater containing heavy metal ions,oils,dyes and other pollutants has been widely concerned.Lignocellulose has the characteristics of wide sources,abundant reserves,low cost,renewable,good biocompatibility,etc.,and contains multiple functional groups such as hydroxyl and carboxyl groups,and is easy to chemically modify.Paper-based functional materials prepared with lignocellulose as raw materials have shown great application prospects in complex wastewater treatment.In this paper,poplar pulp,softwood pulp,and wheat straw pulp are used as lignocellulosic raw materials,MA,CA,and PEI are used as modifying reagents,combined with papermaking technology,and no organic solvents are used to construct paper-based functional materials.The material has low cost,high wet strength,high heavy metal ion adsorption,dye adsorption and oil-water separation performance.The reaction mechanism in the process of functional modification was explored,the performance of paper-based materials in oil/water separation and adsorption was studied,and the relationship between adsorption mechanism,underwater superhydrophobic surface construction mechanism and material properties was discussed.At the same time,the practical application performance of paper-based materials in complex wastewater was further evaluated.The specific research works are as follows:(1)Low cost and high wet strength paper-based lignocellulosic adsorbents and their heavy metal ion adsorption properties.Paper-based lignocellulosic adsorbents with high wet strength,high adsorption capacity and good for recycling were prepared from polar chemimechanical pulp by simple papermaking and one-step dip coating.The results showed that increasing the concentration of MA increased the crosslinking degree and carboxyl content of wood fibers,which increased the wet strength of paper-based materials and the number of metal ion adsorption sites.The wet strengths reach 35%of their dry strengths.Due to its high surface carboxyl content,paper-based material shows excellent adsorption performance for heavy metal ions.The linear-fitting data showed that the adsorption of metal ions by the material was chemisorption,and the maximum adsorption capacity of Cu(II)and Pb(II)were high up to 35.4 mg/g and 110.0 mg/g,respectively.At the same time,combined with the papermaking process,the theoretical maximum adsorption capacities of Cu(II)and Pb(II)were high up to 56.5 mg/g and 126.6 mg/g by adding porous zeolite filler without greatly reducing the wet strength of the paper-based adsorbent..(2)High adsorption capacity paper-based materials and their continuous removal of solids and heavy metal ions.Paper-based lignocellulosic adsorbents with high wet strength,high adsorption capacity,and good separation and recycling performance were prepared from the polar chemomechanical pulp by simple papermaking and polyatomic acid coating modification.As a highly reactive polybasic acid,citric acid can introduce carboxyl groups on the surface of fibers and form covalent cross-links between fibers.With the increase of beating degree and citric acid dosage,the degree of cross-linking reaction increased,and the wet strength and carboxyl group content increased.The wet strengths reached 40～50%of their dry strengths and the maximum carboxyl content was 0.66 mmol/g.In order to avoid the error between the fitting results and the actual situation,a nonlinear-fitting equation was used to better explore the adsorption process of paper-based materials.The maximum theoretical adsorption capacities of the materials for Cu(II)and Pb(II)were high up to 61.96 and 138.11 mg/g,respectively.Good regeneration stability and more than 90%of its initial adsorption capacity were achieved even after four adsorption-regeneration cycles,and the adsorbents were basically unaffected during the desorption process.The paper-based adsorbents with micron holes can be used in combination with the filter device to adsorb metal ions while effectively blocking and separating particles with particle size greater than50μm,which can realize continuous adsorption.(3)Amphoteric multifunctional paper-based materials and their underwater oil-water separation and heavy metal ion adsorption properties.Paper-based materials were prepared by using softwood pulp as raw materials,citric acid(CA)and polyethyleneimine(PEI)as modified reagents.Two polar groups with different charge characteristics,namely the carboxyl group(negative charge)and amino group(positive charge),were introduced by the modified reagent.The paper-based material obtained has high mechanical strength and good flexibility,the wet strength reached 55%of its dry strength,and the wet burst resistance index was 1.74 k Pa·m~2/g.Due to the multi-level micro-nano rough structure and the high content of hydrophilic functional groups,the paper-based material showed excellent superhydrophilic/underwater superoleophobic properties.Its UOCA to n-hexane,petroleum ether,soybean oil,and other oils were all greater than 150°,and the synergistic effect of amphoteric charges improves the p H stability of the underwater contact angle.Oil-water separation experiments showed that the separation efficiency of paper-based materials for the oil-water mixture was higher than 99%,and for oil-in-water emulsions could reach more than 98%,and the separation efficiency was stable within the p H range of 3-11.At the same time,the theoretical maximum adsorption capacity for Cd(II)and Pb(II)reached 73.29 and 93.75mg/g,respectively.The paper-based material,which has the performance of heavy metal ion adsorption and oil-water separation,can be combined with the filtration equipment simply to achieve a one-step treatment of multiple pollutants in complex wastewater.(4)High porosity paper-based materials and their heavy metal ion adsorption,oil and water separation and dye removal properties.The paper-based material with high porosity,high wet strength and pure water flux was prepared by using straw pulp as raw material,CA as humidifier and modifier and adding calcium citrate particles.Compared with the base paper,the porosity of the paper-based material with the addition of CC pore-making agent increased from 30%to 69%.At the same time,the content of carboxyl group increased to 0.91mmol/g and the wet strength increased from 1.9 to 10.5 Nm/g after CA modification.Because straw pulp has shorter fiber size,larger specific surface area,higher lignin content,and higher porosity and carboxyl content than wood pulp,the theoretical maximum adsorption capacity of this paper-based material for Cd(II),Pb(II)and MB was 136,229 and 128.9 mg/g.In addition,due to the introduction of a large number of highly polar carboxyl groups on the paper substrate surface and the construction of a special multi-stage micro-nano rough structure,the UOCA was up to 165°,the separation efficiency of the emulsion oil was 99.3%,and the membrane flux was up to 2020 L/(m~2·h).The paper-based functional material integrates oil and water separation,dye adsorption,heavy metal ion adsorption and other functions in one.Compared with the traditional adsorption or separation materials,it has the advantages of low cost,green environmental protection,high processing efficiency and easy recycling. |
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