Recovery Of Alginate From Printing Wastewater And Preparation And Application Of Photocatalytic Composite Material

Sodium alginate（SA）is widely used,especially in printing and dyeing industry as printing paste consumption is huge,so a lot of printing wastewater containing SA is produced.In this paper,SA in simulated printing wastewater is recovered and photocatalytic composite materials are prepared respectively for wastewater decolorization,which can not only provide a certain theoretical basis for the actual printing wastewater SA recovery,but also realize the recycling of pollutants.The main conclusions of this study are as follows:1.The effects of metal ion type,metal salt dosage and standing temperature on alginate recovery were studied.The results showed that the optimum conditions for recovery of sodium alginate were as follows:for SA solution with 0.8wt%,Zn Cl₂ as recovery agent,dosage of 12.5 g/L,stirring speed of 120 r/min,stirring for 3 min,standing temperature of50℃for 50 min,solid content of 86.46%obtained after filtration.2.The modified photocatalytic material ZA-Ti O₂ was prepared by sol-gel method by doping recovered alginate（main component zinc alginate ZA）into 20 m L anhydrous ethanol and 20 m L tetrabutyl titanate solution.The optimum process parameters for the preparation of ZA-Ti O₂ were as follows:ZA addition amount of 0.50 g,heating rate of10℃/min,calcination temperature of 650℃,holding time of 2 h.For the cationic yellow X-GL dye solution with initial concentration of 50 mg/L,ZA-Ti O₂ dosage of 0.70 g/L,photocatalytic degradation of 365 nm 1000 W UV mercury lamp for 75 min,the decolorization rate reached 96.17%.After four cycles of ZA-Ti O₂,the decolorization rate still reached more than 84.07%,indicating that it had good recycling ability.The kinetic curves of cationic yellow X-GL in ZA-Ti O₂ degradation solution accord with the quasi-first order kinetic reaction.XRD,TEM and XPS results show that rutile and anatase phase Ti O₂ coexist to construct rutile/anatase heterostructure during calcination.The C element produced by calcined ZA acts as sensitizer to accelerate electron transport.3.Photocatalytic composites C/Cd S/Ti O₂ were prepared by high temperature calcination using recovered SA as medium,thiourea（CH₄N₂S）,Cd S and Ti O₂ as raw materials.The optimal mass ratio of C/Cd S/Ti O₂ preparation is:CH₄N₂S:recovered SA:Ti O₂=0.75:1:2.The photocatalytic degradation results showed that the decolorization rate reached 97.02%when the initial concentration of cationic yellow X-GL solution was 50mg/L,the dosage of C/Cd S/Ti O₂ was 0.60 g/L,and the lamp source was 365 nm and 1000W ultraviolet mercury lamp was irradiated for 60 min.Free radical capture experiments show that the main effects of C/Cd S/Ti O₂ are·OH and·O^2-;The study on the utilization of cyclic decolorization showed that the decolorization rate of the dye still reached more than80.26%after four cycles,which indicated that the dye had good stability.XRD and TEM showed that Cd S/Ti O₂ heterojunction was successfully constructed on carbon base using SA as medium.On the one hand,SA inhibits the volatilization of CH₄N₂S.On the other hand,the calcined C improved the photocatalytic activity of the material.