Construction And Performance Of Water Purification Materials Based On Bacterial Cellulose

Water shortage is one of the most severe global challenges of the 21st century.As the serious water pollution and the deterioration of the water ecological environment become more prominent,the sustainable development of society and economy has been dramatically restricted.Therefore,it is urgent to design and develop advanced materials and technologies to treat sewage to meet people’s demand for safe and clean water.Bacterial cellulose（BC）is a green biomass regarded as one of the most promising bio-derived nanomaterials,which is environmentally friendly,reproducible,and economical.Undoubtedly,it owns great competitiveness and in-depth research significance in the face of water crisis and the challenge of searching for sustainable materials.In this paper,we have constructed and optimized a series of high-performance water purification materials based on BC nanofibers.Typically,various organic,inorganic,and biological pollutants are utilized to evaluate its feasibility as a high-performance purifier in environmental remediation.We have investigated and analyzed the purification mechanisms involved in the process of adsorption and membrane filtration.Systematically clarified the structure-activity relationship between the structure and properties of pollutant molecules and the performances of materials.Hopefully,the results could provide theoretical basis and technical support for realizing the application of bacterial cellulose resources in water environment control and management.The main contributions of this dissertation are described as follows:1.Preparation and adsorption properties of bacterial cellulose/Ca-montmorillonite compositesBC/Ca-montmorillonite（Ca-MMT）nanocomposites were prepared by integrating soft BC substrate with Ca-MMT.Along with gathering the physicochemical properties and functionalities of organic nanofibers and inorganic mineral clays.Various characterization methods and static adsorption experiments were conducted to explore the structure,morphology,and adsorption properties of the composites.Taking methylene blue and tetracycline as model pollutants,the adsorption behavior of the composites under different conditions was investigated by changing the p H value,initial concentration and adsorption time of the pollutant solution.The results showed that the theoretical equilibrium adsorption capacities of BC/Ca-MMT for methylene blue and tetracycline were 338.8 mg·g^-1 and 230.5 mg·g^-1,respectively.The adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model.Electrostatic attraction,cation exchange and hydrogen bonding interaction were the main involved mechanism.Meanwhile,the material could realize simultaneous purification of methylene blue-tetracycline coexisting system.Furthermore,the sample was ease of regeneration and kept stable reusability through consecutive four recycles.Hence,the BC/Ca-MMT is expected to be a promising biomass adsorbent in sewage treatment.2.Preparation and application of quaternized bacterial cellulose as a multifunctional and efficient water purifierHere,we describe a design of multifunctional water purifier QAC-BC,which has biomass-based structure by grafting polyethylenimine derived quaternary ammonium compounds（QAC）onto three-dimensional BC substrate.The microscopic morphology,chemical structure and physical properties were characterized by various means.The adsorption and antibacterial properties of the material were systematically studied by static adsorption experiment and antibacterial experiment.The results showed that the maximum adsorption capacities of QAC-BC towards Pb²⁺and Congo red were 200 mg·g^-1 and 694 mg·g^-1,respectively.The adsorption process was controlled by mechanisms such as hydrogen bonding,electrostatic attraction and metal chelation.What’s more,QAC-BC could effectively capture other common pollutants such as Cu²⁺,Cr⁶⁺and methyl orange,and possesses much higher adsorption capacities than those similar biomass-based materials in recent studies.Meanwhile,QAC-BC exhibited excellent disinfection efficiency towards both Escherichia coli and Staphylococcus aureus,which are representatives of Gram-negative and Gram-positive bacteria,respectively.Remarkably,this purifier also demonstrated effective removal of the heavy metal ions,dyes and microorganisms simultaneously from both simulated and local polluted water.With more virtues of superior reusability and extreme handy convenience,this multifunctional and high-efficiency water purifier will be more attractive in practical application.3.Preparation and properties of highly permeable and anti-fouling ultrafiltration membrane based on bacterial celluloseWe find a feasible way to use the adhesive polydopamine（PDA）to modify BC in liquid phase,integrating with reduced graphene oxide（RGO）nanosheets to fabricate a highly permeable and anti-fouling ultrafiltration membrane（BC/PDA/RGO）for the separation of dyes and oil-water mixtures.Different characterization methods were utilized and the performances of the ultrafiltration membrane were evaluated.The results showed that the composite membrane exhibited long-term robust pure water flux(>1100 L·m^-2·h^-1)and splendid rejection efficiency for dyes with large molecular weight,large molecular size and more positive charges.During the filtration process,the rejection of molecules was not only governed by a molecular sieving mechanism,but also affected by the electrostatic attraction between solution and solute.Meanwhile,benefiting from the unique superhydrophilicity and underwater superoleophobicity,the BC/PDA/RGO membrane exhibited extraordinary separation performance for the surfactant-stabilized oil-in-water emulsions.Besides,the composite membrane showed superior anti-fouling property and a high flux recovery ratio（～96.9%）in multiple cycling measurements.Taken the advantages of low cost,high efficiency,and easy large-scale production together,this work provides a bright future for the wide application of the BC/PDA/RGO ultrafiltration membrane in water remediation.4.Construction and properties of flexible TEMPO-oxidized BC/ultralong HAP nanowires filtration membraneA highly flexible free-standing composite membrane based on TEMPO-oxidized BC nanofibers and ultralong hydroxyapatite nanowires（HAPNW）with adjustable hydrophilicity and hydrophobicity have been developed under vacuum-assisted suction filtration.The as-prepared TEMPO-BC@HAPNW composite membrane displayed robust mechanical strength,high flexibility,and deformability.Nevertheless,the porous and hierarchical structure,along with intrinsic hydrophilicity endowed the composites with good permeability.In the filtration test of Ti O₂ nanoparticles,the results indicated that the composites showed long-term high water flux(>800 L·m^-2·h^-1)and high rejection efficiency（>99%）.More importantly,the composites exhibited superior filtration and adsorption performance in the removal of methylene blue by the size exclusion and electrostatic interaction.Additionally,the surface wettability of the composites modified by sodium oleate was switched to be hydrophobic and lipophilic,with excellent separation ability for various organic solvents and oils,and easy to recycle.Hereof,the superior separation performances,facile and precisely controllable preparation process,and easy functionalization,which lay a foundation of the TEMPO-BC@HAPNW filtration membrane to realize its large-scale production and commercial application.