| With the increasing complexity of wastewater systems and the strengthening of environmental protection regulatory standards,society’s requirements for water treatment technologies have been increasing.Flocculation as an important component of water treatment process,the development of multifunctional,efficient and environmentally friendly new flocculants has become a current research hotspot.At present,natural polymers with the advantages of environmental friendliness and biodegradability have attracted much attention from researchers,but they have the disadvantages of few active sites,poor solubility and unsatisfactory flocculation effect,while the traditional organic synthetic flocculants have excellent flocculation effect but single performance and residual monomers are toxic,so many researchers have grafted organic monomers on natural materials to expand the application scope and improve flocculation performance.Therefore,many researchers have grafted organic monomers on natural materials to expand the range of applications and improve flocculation performance.In addition,it has been shown that the size distribution and the sequence structure within the molecule of flocculants have an effect on the flocculation performance.Based on the above,this study firstly prepared nano chitosan(NCS)particles as the grafting backbone by ionic cross-linking reaction,selected acrylamide(AM)and cationic surface active monomer(methacryloyloxyethyl dimethyl benzyl ammonium chloride,DML)as the grafting side chains,and combined with UV-template polymerization technique to prepare a new chitosan-based polymer flocculant with surface active monomer block distribution(NCSg-TPAD).The addition of nano-chitosan improved the adsorption enrichment and biodegradability of the flocculants,while the sequentially distributed DML monomers exhibited stronger electro-neutralization and hydrophobic association ability during flocculation,and the flocculation performance was further enhanced.On this basis,the optimal synthesis conditions of NCS-g-TPAD flocculants were optimized,the kinetics of the template polymerization reaction was explored,and the composition and structural characteristics of the products were analyzed using various characterization tools.In addition,the flocculants were applied to turbidity removal of kaolin suspensions and municipal sludge dewatering,and the flocculation mechanism of NCS-g-TPAD was also explored in combination with modern characterization tools.The main research contents and conclusions are as follows:(1)Optimization of NCS-g-TPAD preparation.The synthesis conditions were optimized by single-factor experiments and response surface analysis with the characteristic viscosity and conversion rate as the optimization indexes.The optimum polymerization products were obtained under the conditions of m(AM):m(CS)= 10:1,n(AM):n(DML)=10:1,n(DML):n(NaPAA)= 1:1,initiator VA-044 concentration 1.75 wt ‰,reaction system pH 5,and light time 3.5 h.The characteristic viscosity and conversion rate were 10.68 and98.9%,respectively.d L/g,98.9%.The order of significance effects were:n(DML):n(NaPAA)> m(AM):m(CS)> VA-044 mass concentration > pH(2)Kinetic analysis of the template polymerization reaction.The results showed that the template polymerization was carried out by the type I ZIP reaction mechanism;about 80%of the DML monomer was adsorbed on the template molecular chain before polymerization;the chain termination reaction was dominated by double base termination and single base termination was also present.(3)Characterization of physicochemical properties of NCS-g-TPAD.The results of infrared spectroscopy(FTIR)and X-ray diffraction(XRD)showed that AM and DML monomers were successfully grafted onto chitosan nanoparticles,and the polymerized product exhibited an amorphous structure;the results of nuclear magnetic resonance hydrogen spectroscopy(1H NMR)showed that the interference peaks on the DML unit of NCS-g-TPAD were significantly reduced compared with the non-template polymerized product.The NMR results showed that the interference peaks from other monomers on the DML unit were significantly weaker compared with the non-template polymerization product,indicating that the chemical environment of DML was close to homopolymerization,which proved the generation of the block structure.The results of thermogravimetric analysis(TGA)not only showed the good thermal stability of the polymerized product,but also the three heat absorption peaks in the decomposition stage of the main chain further proved the sequence distribution of DML monomers;the SEM results showed that the template polymerized product had a more irregular and rough surface;the results of particle size analysis showed that the median particle size of the graft polymerized product was 71.64 nm,which was consistent with the nanometer size.(4)Municipal sludge dewatering performance evaluation.The effect of different flocculation conditions on sludge dewatering performance was investigated,and the results showed that the dewatering effect was optimal at 40 mg/L and pH=6.Compared with the non-template polymer,the surface of the NCS-g-TPAD-conditioned sludge floc was rougher and the settling performance was better,and the block distribution of DML monomer greatly enhanced the removal of PN from the extracellular polymer.The three mechanisms of adsorption bridging,electrical patching and hydrophobic association during sludge dewatering acted synergistically to improve the flocculation performance.(5)Investigation of flocculation performance of kaolin suspensions.The effects of different factors on turbidity removal rate and floc size were investigated,and the composition structure of flocs was analyzed by XPS and SEM characterization techniques.Compared with the commercially available flocculants,NCS-g-TPAD showed excellent turbidity removal effect at low dosing rate and the median particle size was 97.5% and1061.906 μm,respectively;The block structure of DML enhanced the interaction force between micro flocs and showed better regeneration performance and larger median particle size value;in addition,the SEM analysis of flocs showed that nano-chitosan played an adsorption and enrichment role,and the flocs showed rough and irregular surface;the XPS analysis of flocs showed that the electric neutralization in flocculation was mainly contributed by amino and quaternary ammonium groups. |
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