Preparation Of Functional Biomass Composites And Their Removal Performance Of Methylene Blue In Aqueous Phase

Biomass is abundant species,wide sources,developed pore structure and abundant surface functional groups,so it is easy to composite modified and used as adsorbent in water treatment.Methylene Blue（MB）is a widely used cationic dye.Due to its strong toxicity,high chromaticity and high organic content,it has great harm to the ecological environment.Therefore,it is beneficial to develop new adsorbents with biomass as raw material from the perspective of environmental friendliness and sustainable development.In this paper,three functional biomass composites were prepared using orange peel,bamboo leaves and durian shell as raw materials to explore the adsorption properties and possible adsorption mechanisms of these three materials on methylene blue in aqueous solution.The specific research methods and conclusions are as follows:（1）Biochar was prepared from orange peel by pyrolysis.Mg/Al-LDHs were in-situ grown on the surface of biochar by hydrothermal method to obtain Biochar@Mg/Al-LDHs composites（BC@Mg/Al-LDHs）.The materials were characterized by SEM,TEM,BET,XRD and XPS,and the results showed that Mg/Al-LDHs is regular hexagonal structures.The poor dispersion of Mg/Al-LDHs in aqueous solution can be effectively overcome by using BC as the substrate.Adsorption isotherm study showed that the adsorption process of BC@Mg/Al-LDHs for MB was more in line with the Langmuir adsorption isotherm model,and the adsorption kinetics showed that the adsorption process was more in line with the pseudo-second-order kinetic model.Adsorption experiments showed that Mg/Al-LDHs loading improve the adsorption capacity of the material.At 45°C,the maximum adsorption capacity of BC@Mg/Al-LDHs for MB was 75.79mg/g.BC@Mg/Al-LDHs can be used as an effective adsorbent to remove PO₄^3-and organic pollutants（TOC）in aqueous solution,and the removal rates of PO₄^3-and TOC are 61.69%and47.62%,respectively.（2）In order to solve the problem that powder adsorbents are easy to agglomerate in solution,improve the reaction activity and increase the adsorption capacity.Using bamboo leaves as raw materials to extract fibers by Na OH/urea method to prepare cellulose aerogels.Three-dimensional aerogel@ZIF-8 composites（CA@ZIF-8）was prepared by stepwise method.The SEM test shows that ZIF-8 is a regular twelve-sided cube structure.In situ growth of ZIF-8 on aerogels can effectively overcome the problem of insufficient dispersion and easy agglomeration of ZIF-8 in solution.The adsorption experiment results showed 25°C and the dosage of 0.2 g/L,the maximum adsorption capacity of CA@ZIF-8 for MB was 90.18 mg/g.Adsorption isotherm study showed that the adsorption process of CA@ZIF-8 for MB conformed to Freundich adsorption isotherm model,and adsorption kinetics showed that the adsorption process conformed to pseudo-second-order kinetic model.（3）In order to realize the rapid separation and recovery of adsorbent after adsorption,the fiber was extracted from durian shell by referring to the extraction method of bamboo leaf fiber.Magnetic Fe₃O₄ nanoparticles were grown on its surface by one-step hydrothermal method,and durian shell fiber-Fe₃O₄-MOF composites（DFM）were prepared by self-assembly method.The adsorption experiment results showed that DFM-10 had the strongest adsorption capacity for MB.BET test showed that the specific surface area of DFM-10 increased about 3.7 times after 10 cycles compared with DFM-0.The adsorption isotherm was more in line with the Langmuir adsorption isotherm model,and the maximum adsorption capacity of MB was 53.31 mg/g at 45°C.The adsorption cycle experiment showed that DFM-10 as a magnetic material,could be completely separated from the aqueous solution within 30 s under the action of an external magnetic field.After five adsorption-desorption cycles,the MB removal rate remained 83.15%.The study on the treatment effect of adsorbent on actual wastewater showed that DFM-10 had good removal effect on TOC in actual wastewater,and the removal rate reached 91.44%.In summary,the three functional biomass composites prepared in this paper have good removal effects on MB in aqueous phase.After adsorption,they can be quickly separated and recovered from aqueous solution by using their own structural characteristics,and have good recycling performance,which can provide reference for the practical application of biomass composites in the removal of MB in wastewater.