Study On Preparation And Application Of Enhanced Bacterial Cellulose/Polyvinyl Alcohol Adsorption Material

Dye wastewater and heavy metal ions from industrial waste discharges will cause serious pollution to the natural environment.It is one of the main killers of serious threats to human health and aquatic life because of its carcinogenic,teratogenic,highly toxic characteristics and its difficulty in degrading under natural conditions.Therefore,wastewater containing harmful chemical molecules and heavy metal ions must be purified before being discharged into the environment,and adsorption technology is considered to be one of the most effective methods.Natural polymers are ideal adsorbents for the removal of environmental contaminants due to their biodegradability,low cost,non-toxicity,and the ability to combine various contaminants through chemical and/or physical interactions.In addition to the various advantages of natural polymers,bacterial cellulose is the purest cellulose in nature and thus become a research hotspot in various fields.In this thesis,bacterial cellulose was prepared by modifying the Hestrin and Schramm medium with Gluconacetobacter xylinum ATCC53582 as the strain.Subsequently,the bacterial cellulose/polyvinyl alcohol was used as the framework material,and the enhanced bacterial cellulose/polyvinyl alcohol adsorption material was prepared by freeze-thaw circulation method through the composite filler graphene oxide and attapulgite.We used Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?,scanning electron microscopy?SEM-EDS?,BET specific surface area test and thermogravimetry?TG-DSC?to characterize the structure,properties and appearance of the prepared materials.In order to investigate its adsorption performance,we conducted experimental tests with Congo red,methylene blue,Cu²⁺and Pb²⁺as adsorption targets.The specific conclusions are as follows:?.The results of FTIR,XRD and TG-DSC analysis showed that hydrogen bonds were formed between the initial components of the adsorbed material,and the thermal stability increased.The SEM results show that the pore structure in the surface of the reinforced material is more in the form of zigzag and wedge structure than the skeleton material,and the surface morphology becomes more irregular.The BET test showed a decrease in the specific surface area of the material and an increase in the pore size.The N₂ adsorption-desorption curve is a typical type-II isotherm and exhibits a H₃ hysteresis loop.?.The optimal pH of the reinforced material for Congo red and methylene blue adsorption are 3 and 8,respectively.The adsorption kinetics is mainly physical process,and the intraparticle diffusion contributes to the adsorption.Corresponding isothermal adsorption is more in line with Freundlich model,and the optimal adsorption capacities are 207.93 mg/g and 211.53 mg/g,respectively.The results of thermodynamic study show that for the adsorption process of Congo red,the?G⁰,?H⁰ and?S⁰ are both negtive,suggesting that the adsorption is spontaneous and exothermic,and the spontaneousness of the adsorption and the randomness of the solid-liquid interface decrease.As the adsorption process advances,the degree of disorder of the solid-liquid interface and the rate of adsorption decrease.For methylene blue,?G⁰<0,?H⁰>0,?S⁰>0,indicating that the adsorption spontaneously proceeds and absorbs heat.The degree of disorder in the solid-liquid interface and the adsorption initiative both increase with the increase of temperature.The optimal adsorption temperatures are30°C and 40°C,respectively.After four cycles of use,the regeneration rates were maintained at above 90%and 88%,respectively.?.The optimal pH for the adsorption of Cu²⁺and Pb²⁺are 6 and 5,respectively.The adsorption kinetics is mainly determined by surface diffusion and intraparticle diffusion.Isothermal adsorption is more consistent with Freundlich model.The optimal adsorption capacities are 150.79 mg/g and 217.8 mg/g,respectively.Results from thermodynamic studies show that the adsorptions of Cu²⁺and Pb²⁺both have negtive?G⁰,?H⁰ and?S⁰,suggesting the process is spontaneous and exothermic.The optimal adsorption temperatures are both 30°C.Reuse performance study shows that the regeneration rate remaines at around 76%and 88%,respectively,after four cycles of use.?.The adsorption performance characterization of the three reinforced materials BPGA1%,BPGA1.5%and BPGA2%was compared and the results show that BPGA2%has the best adsorption capacity for both Congo red,methylene blue,Cu²⁺and Pb²⁺among the three potential materials.Compared with similar adsorbent materials,we prepared adsorbent materials have several significant advantages.Firstly,the entire preparation process of the material is environmentally friendly,there is no environmentally harmful component,and the cost is relatively low.Secondly,it has a high removal capacity for both anionic and cationic dyes and heavy metal ions.Finally,the material exhibits good recycling performance and can be degraded in the environment at the terminal,without secondary pollution.It is expected to be used to remove industrial wastewater that actually contains heavy metal ions and dye molecules.