Mechanical Property Modulation And Application Of Poly(vinyl Alcohol) Hydrogel Membrane

Wastewater contaminated by dyes has become a serious global water resource problem.Approaches that can be used to effectively treat dye wastewater are desired.Because of its low cost,high efficiency,and ease of treatment,the adsorption method is popular.Hydrogels are often used as adsorbents due to their non-toxicity,high swelling ratio,and ease of production.In order to increase the specific surface area of the adsorbents,they are usually made into membranes.However,the current membrane-type adsorbents also have shortcomings,which are prominently manifested in two aspects:1)they cannot be re-used after the dye adsorption,causing re-pollution,and 2)the mechanical properties of the membrane are poor,and thereby the membranes are easily damaged during application.In this thesis,by adding dimethyl sulfoxide?DMSO?,nano titanium dioxide?TiO₂?,sodium carbonate?Na₂CO₃?into polyvinyl alcohol?PVA?,PVA-TiO₂ composite hydrogel membrane with high mechanical properties and photocatalytic ability was prepared through the freeze-thaw cycle method.After adsorption,the dye is decomposed by sun light,and the membrane can be re-used for dye wastewater treatment.First,the structure and composition of the hydrogel were characterized,and the mechanism of its high crystallinity and photocatalysis was analyzed.Secondly,the adsorption properties of congo red?CR?and methylene blue?MB?dyes were studied,and the effects of initial dye concentration and adsorption time on adsorption performance were discussed.Further,the treatment ability of the hydrogel membrane to MB under sun light conditions was studied.The effects of TiO₂ content,DMSO ratio and light time on the treatment efficiency were analyzed.Finally,mechanical tensile tests were carried out on the composite hydrogel,and the effects of TiO₂ content,DMSO ratio and the number of freeze-thaw cycles on the tensile strength and tensile modulus were discussed.The results demonstrate that the addition of DMSO to the solvent can effectively improve the crystallinity and transparency of the PVA hydrogel.The maximum adsorption capacity of PVA-TiO₂ composite hydrogel membrane for CR and MB dyes was 791.14 mg/g and 303.83mg/g,respectively,and the adsorption process of the two dyes was in accordance with the Langmuir adsorption isotherm model and pseudo-second-order kinetics model.The degradation of MB dye after 1 h light treatment was 684.7 mg/g.After the dye was completely degraded,the membrane could be reused.The tensile experiment results show that the content of TiO₂,the ratio of DMSO and the number of freeze-thaw cycles have a significant impact on the mechanical properties of the composite hydrogel.By optimizing the raw material ratio and preparation process,the tensile strength of the prepared film reaches 14.3 MPa,which is 12times of that of the PVA hydrogel.The PVA-TiO₂ composite hydrogel membrane prepared here has both high mechanical properties and sustainable treatment of dye pollutant under natural light conditions,and has a promising prospect of industrial application.