Study On The Coordination Reaction Of Different Structure Fibers And Metal Ions And The Catalytic Performance Of Their Complexes

In the recent years, fiber metal complex as a special polymer metal complex (PMC) based functional materials has caused great attention worldwide owing to its huge development potential and bright future in the sustainable energy, environmental protection and smart materials. Hence, the coordination between alginate fiber as a typical carboxylic fiber and Fe3+ ion and its major effecting factors were firstly investigated in this present study. On the basis of characterization, the resulting alginate fiber Fe complexes were used as the heterogeneous Fenton catalysts for the oxidative degradation of the azo dye in water. The impact of reaction conditions on catalytic activity of the complexes was examined. And the polyacrylic acid grafted polytetrafluoroethylene (PTFE) fiber and polyacrylic acid grafted polypropylene (PP) fiber were prepared as two carboxylic fibers by surface grafting polymerization method. The coordination performance and catalytic activity of Fe complexes were compared with those of alginate fiber at the same conditions. The effect of carboxylic fiber molecular structure and surface properties on the coordination performance of the three carboxylic fibers and catalytic activity of their Fe complexes were emphatically evaluated. The relationship between the coordinating group structure and catalytic activity of fiber metal complex was also investigated by comparing the catalytic activity of four modified polyacrylonitrile (PAN) fiber Fe complexes containing different coordinating groups. In addition, three typical metal ions including two transition metal ions Fe3+ and Cu2+ ion and a rare earth metal ion Ce3+ were used to coordinate with the carboxylic fibers to compare their coordination performance and catalytic activity of their Fe complexes. The promotion effect of Cu2+ ion as assist metal ion on the catalytic activity of obtained fiber metal complexes were investigated.In order to obtain the low cost and high performance fiber metal complex based heterogeneous Fenton reaction catalyst for the dye degradation, the citric acid modified cotton fiber as a new carboxylic fiber ligand was prepared by a commercial pad-dry-cure process and with citric acid as the modified agent. The effects of modification conditions on carboxylic acid content and coordination performance with Fe3+ ions of the resulting fiber ligand were studied. The possibility of citric acid modified cotton fiber Fe complex in the replacement of alginate fiber Fe complex as a heterogeneous Fenton reaction catalyst was discussed by the comparison of catalytic performance and mechanical properties between the two complexes. On the other hand, the amidoximated PAN fiber Fe complex was prepared and used as the heterogeneous Fenton catalyst for the oxidative degradation of 28 typical water-soluble anionic azo dyes. The quantitative structure property relationship (QSPR) model equations between the molecular structure and degradation performance of these azo dyes were developed and applied for predicting the degradation performance of the azo dyes with similar molecular structure. Finally, a heterogeneous Fenton system composed of polyacrylic grafted PTFE fiber Cu-Fe bimetallic complex/H2O2 was applied in the degradation of the reactive dyeing effluents and reused for the coloration of cotton fabrics with three reactive dyes. The reusing possibility of treated effluents was examined by comparing the quality of the dyed fabric with treated effluent as the medium that of the dyed fabric with tap fresh water as the medium.The experimental results including six parts as follows:(i) The carboxyl group of the alginate fiber could coordinate with Fe3+ ions to form the alginate fiber Fe complex. Increasing Fe3+ ion initial concentration, reaction temperature and pH value could give rise to the higher Fe content of complexes. The crystallinity and light absorption properties of alginate fiber were significantly increased after the coordination with Fe3+ ions. Alginate fiber Fe complexes showed high catalytic activity for the degradation and mineralization of azo dye, especially under visible irradiation. The catalytic activity of alginate fiber Fe complex was improved significantly by increasing its Fe content, and reduced in the alkaline environment. Alginate fiber Fe complexes also showed better reuse ability and stability in the presence of inorganic salts during the catalytic degradation of the dye in water.(ii) Compared with alginate fiber, the coordination of polyacrylic acid grafted PTFE fiber and polyacrylic acid grafted PP fiber reacted with Fe3+ ion with difficulty, and the two resulting Fe complexes had lower Fe content and different coordination numbers under the same conditions. This was mainly determined by the great difference in the molecular structure and surface properties between them. The two resulting Fe complexes had the relatively lower catalytic activity than alginate fiber Fe complex, especially under visible irradiation. Although alginate fiber Fe complexes showed better reuse performance than the other two Fe complexes, its mechanical property was more significantly reduced than the two Fe complexes during reuse process. Furthermore, the mixed modified PAN fiber Fe complexes containing more complex coordination group showed higher catalytic activity than the other three modified PAN fiber Fe complexes under the same reaction conditions, which is mainly relative to the nature of their coordination groups and their unsaturated coordination structure.(iii) Three metal ions mentioned above could coordinate with carboxylic acid fiber, respectively to produce corresponding fiber metal complexes. Their coordinating capacities were ranked in the order:Fe3+> Cu2+> Ce3+. While their activation energy showed a reversed trend. Further studies showed that the coordination between them was spontaneous, and could be described using Langmuir or Freundlich isothermal adsorption models, respectively. The catalytic activity of three metal complexes was still arranged in the order described above. Additionally, the introduction of Cu2+ ion could significantly improve the catalytic activity of the PTFE fiber Fe complexes, and had an insignificant effect on the catalytic activity of alginate fiber Fe complexes.(iv) The citric acid modified cotton fiber was synthesized by using citric acid to modify cotton fiber, and then coordinated with Fe3+ ions to prepare the citric acid modified cotton Fe complexes. Fe coordination resulted in a decrease in crystallinity of citric acid modified cotton fiber, but significantly enhanced its visible light absorption properties. Dye degradation was significantly accelerated in the presence of the citric acid modified cotton Fe complexes under visible irradiation. Appropriately increasing the concentrations of citric acid, NaH2PO4 or curing temperature during the modification of cotton fiber enhanced the carboxyl group surface content of the modified fiber as well as Fe content and catalytic activity of its complex. Besides, citric acid modified cotton fiber Fe complexes exhibited more excellent catalytic, reuse ability and mechanical performance than alginate fiber Fe complexes, and it has been regarded as a low cost and high performance heterogeneous Fenton reaction catalyst.(v) 28 typical water-soluble anionic azo dyes with different structures were effectively degraded and mineralized in the presence of amidoximated PAN fiber Fe complex. The QSPR model equations for the dye decoloration and mineralization were successfully developed by using multiple linear regression analysis (MLR), and the number of azo linkages in the dye molecule was evaluated to be the most significant negative or positive effecting factor for the decoloration percentage or total organic carbon (TOC) removal during the dye degradation.(â…µ) Three reactive dyeing effluents could be treated by grafted PTFE fiber Cu-Fe bimetallic complex and H2O2. The treated effluents could be reused as the dyeing medium for the coloration of cotton fabrics. The color strength, color differences and fastness properties of the dyed cotton fabrics using the treated dyeing effluent as the aqueous medium were almost no change significantly, compared with those of the dyed fabric with tap fresh water as the medium.