Preparation Of TiO₂ And Chitosan Sulfate Microspheres By Microwave Assisted Method And Study On Decoloration Of Dyes

Nowadays,the rapid development of industry causes the problem of energy shortage and environmental pollution.And dyeing and finishing wastewater has become a prominent issue of water pollution.One of the ways to solve the energy shortage problem is to adopt microwave heating to take place of traditional one.There are chemical degradation and physical adsorption methods to deal with water pollution.Titanium dioxide is chosen to degrade the dyes as semiconductor photocatalysis and chitosan-based adsorbent is chosen to adsorb dyes and heavy metal ions.This thesis contains five chapters:the first chapter is the literature review;the second one is the preparation of titanium dioxide?TiO₂?microsphere and its photocatalytic properties;the third one is the preparation of hollow TiO₂ microsphere and its photocatalytic properties;the fourth one is the preparation of chitosan sulfate microsphere and its adsorption properties and the last one is the conclusion of the studies.In the second chapter,flower-shaped TiO₂ nanopheres were prepared using ammonium hexafluorotitanate??NH₄?₂TiF₆?and boric acid?H₃BO₃?as precusors at low temperature?<100°C?by microwave-assisted method in open system.The effects of different reaction conditions?including temperature and time of microwave heating and the concentration and molar ratio of precursors?on the morphology and photocatalytic activity of TiO₂ microspheres were studied.And the growth mechanism of TiO₂ microspheres was researched.The hydrolysis rate of[TiF₆]^2-in the solution increased with the assistance of microwave heating.And the reaction between F^-and H₃BO₃ could be accelerated to form stable BF₄^-which drove the hydrolysis of?NH₄?₂TiF₆.The results showed that the reaction conditions had a little effect on the crystal form of TiO₂ but had a great influence on the morphology of TiO₂ the crystal structures.The formation mechanism of TiO₂ flower-like microspheres was aggregation and growth,that is to say,?NH₄?₂TiF₆ was hydrolyzed to form TiO₂ flake particles?primary particles?,and then the primary particles aggregated together to form secondary particles,and finally the secondary particles adsorbed the primary particles layer by layer to form the flower-like microspheres.The anatase TiO₂ with good crystallinity could also be prepared even at a low concentration of?NH₄?₂TiF₆(1.5×10^-3mol/L)and short heating time?15 min?with the microwave-assisted method.Rhodamine B was degraded under UV light by TiO₂ prepared under different conditions,and the decolorization rate could reach above 94%after irradiation for 3hours.Moreover,the photocatalytic performance was better than that of commercial P25-TiO₂.TiO₂ particles obtained by microwave heating at 90°C for 45 min with?NH₄?₂TiF₆ concentration of 0.02 mol/L and precusors ratio of?NH₄?₂TiF₆:H₃BO₃ at1:2 were modified under different conditions.The effects of acid,alkali and H₂O₂ on the growth,morphology,crystal form and photocatalytic activity of TiO₂ were studied.Results showed that when the boric acid was replaced by sodium borate or ammonium borate,the reaction rate and the yield of TiO₂ particles both increased.Although the product was still anatase type TiO₂,the product had a low degree of crystallinity and a high degree of agglomeration.However,when citric acid or sodium citrate was added during the preparetion of TiO_2,the reaction rate and the yield decreased.And the addition had a great influence on the morphology of TiO₂,but had no significant effect on crystal form.However,the crystallinity decreased and the yield of TiO₂ also decreased.This was due to that citrate ions were adsorbed to the surface of newly formed TiO₂ during the reaction,inhibiting or slowing the growth and affecting the nucleation of TiO₂.The product was used as photocatalyst to degrade Rhodamine B,and the lower the photocatalytic activity of the prepared TiO₂was,the greater the addition amount of citric acid or sodium citrate during the hydrolysis of?NH₄?₂TiF₆ was.However,with the increasing amount of citric acid or sodium citrate,the photocatalytic activity of TiO₂ decreased.When adding other organic acids?such as glutaric acid,adipic acid and 1,2,3,4-butanetetracarboxylic acid?BTCA??,the morphology of TiO₂ was not affected much,but its photocatalytic activity could be improved.H₂O₂ modified TiO₂ was prepared by microwave heating to improve the photocatalytic activity under the visible light.The reaction between H₂O₂ and TiO₂ can generate a light yellow titanium peroxide complex which could absorb visible light and thereby increased the utilization of TiO₂ for the visible light.The results showed that the morphology and crystal form of the product had no change,but the specific surface area increased and the product could absorb the visible light which resulted in the improvement of photocatalytic activity under visible-ultraviolet light.In order to improve the photocatalytic properties of TiO₂,the hollow TiO₂microspheres were prepared using carbon microspheres as the templates in the third chapter.Compared with the traditional hydrothermal method,microwave-assisted heating had advantages of low temperature,rapid heating rate and atmospheric pressure.In this research,glucose was chosen as the carbon source and hydrochloric acidasthedehydratingagent,respectively.Undertheconditionof microwave-assisted heating,the glucose was heated at 90°C for 30 min to obtain finely dispersed carbon microspheres with uniform particle size around 340 nm.The growth mechanism of carbon microspheres with the help of microwave heating accorded with La Mer model.Using the carbon microspheres as templates,a core-shell structure with TiO₂ as the shell and a carbon sphere as the core was prepared.The effects of the concentration of?NH₄?₂TiF₆,heating time,temperature and the ratio of titanium source and boron source on the morphology of the core-shell structure were investigated.The results showed that the core-shell structure could be obtained when the usage of template spheres was 0.08 g,concentration of?NH₄?₂TiF₆ was 1.5×10^-3mol/L,molar ratio of Ti and B was 1:2,and microwave heating at 90°C for 50 min and 60 min for the first and second step,respectively.Then after calcination,hollow microspheres with uniform particle size about 270 nm were obtained.The prepared hollow spheres were used as photocatalysts to degrade rhodamine B under UV irradiation.The decolorization rate of hollow TiO₂ microspheres reached 97.7%within 60 min,which was much efficient than that of P25-TiO₂.This was due to that the large specific surface area of hollow TiO₂ helped to improve the adsorption capacity of TiO₂ to rhodamine B,and the hollow structure could improve the utilization of ultraviolet light.In order to improve the reusability,chitosan was modified to make it insoluble.In the fourth chapter,chitosan sulfate microspheres were prepared using chitosan and sulfuric as raw materials by microwave-assisted method.The effects of reaction conditions?including concentration of H₂SO₄,temperature and time of microwave heating?on morphology and properties of products were studied.Moreover,the reaction mechanism was also investigated.The results showed that the free amino groups of chitosan were protonated to form amino salt?NH₃⁺?in H₂SO₄ solution,and NH₃⁺ions were reacted with the SO₄^2-ions in the solution to generate the chitosan sulfate by electrostatic adsorption.The reaction conditions had a great influence on the morphology.And the multilayer microspheres?CSS-30?with oblate and hollow shape could be obtained when the concentration of H₂SO₄ was 1.2 mol/L and microwave heating temperature was 90°C.The cross-linking reaction between H₂SO₄and chitosan could be completed within 30 min.The product was used to adsorb Cr?VI?,methyl orange and weakl acid blue 5R.The results showed that CSS-30 had excellent adsorption properties for all three pollutants and its adsorption efficient was much higher than that of non-crosslinked chitosan.When the initial concentration of Cr?VI?was 100 mg/L,the adsorption reached saturation within only 9 min and the adsorption capacity was as high as 112 mg/g.At an initial methyl orange concentration of 50 mg/L,the adsorption reached saturation within 15 min,and its adsorption capacity was as high as 187 mg/g.When the initial concentration of weak acid blue 5R was 200 mg/L,the adsorption reached saturation suing 3h and the maximum adsorption capacity was 660 mg/g.