| With the rapid progress of world economy, the number of chemical product increase constantly, and the excess emission of industrial waste water, waste gas and residue have caused the serious problems of environmental pollution. Environmental protection and pollution control were the essential means of carrying out sustainable development, and won wide acclaim from the governments of all countries in the world. The methods of waste water control presently consisted of physical method, chemical method and biological method, etc. All these means had their own characteristics. The drawbacks to these approach were inefficient, limited applied range and contamination was not completely mineralized. The photocatalysis technology of titanium dioxide, which was presented to avoid the disadvantages above, was one of the most important advanced oxidation technologies. Titanium dioxide photocatalysis was the research hotspot in environmental scenice field, due to its capability in photochemical transformation of many organic or inorganic pollutants. Application superiority of titanium dioxide was stability, low toxicy and inexpensive. There were two types of titanium dioxide used for research in this experiment. One was 100% rutile titanium dioxide (TiO2), the other was 80% rutile and 20% anatase P25 titanium dioxide (P25). Cyclodextrin (CD) is a class of cyclic oligosaccharides consisting of six or more D-glucose units by a-1,4-glucose bonds linkages. The most common CD comprise a-CD (6 D-glucose units),β-CD (7 D-glucose units) and y-CD (8 D-glucose units). The cavity of the CD ring is covered by the D-glucose hydrogen atoms and is hydrophobic, while the exterior surface of the CD is hydrophilic by hydroxyl groups coverage. The CD formed a noncovalently bonded inclusion complex within a wide variety of appropriate size guest molecules, which composed principally of inorganic ions, organic compound and radicals. The CD capacity of selective inclusion complexation between host and guest is called molecular recognition, and the selective encapsulation of CD to enantiomers is called chiral recognition. The CD cavity restrictions can change physical and chemical properties of guest molecules in inclusion compound. The CD gains increasing attention of many science domain with the development of CD research. Based on the studies of titanium dioxide,β-CD and our previous reseach, we embodied both titanium dioxide modification and p-CD for enhancing adsorption capacity and selective photodegradation of bare titanium dioxide in this paper.(1) The adsorption experiment ofβ-CD in two kinds of titanium dioxide suspension indicated:the adsorption isotherm presented a good fit to Langmuir model; adsorption kinetics could be used to simulate by pseudo second order model. Time of equilibrium adsorption was 30min under our experiment conditions. With the increase of dosage of titanium dioxide, the adsorption removal efficiency rise due to more active site of adsorption. The rate constant of pseudo second order model of P-CD in two titanium dioxide were increased with the higher initial concentrations ofβ-CD. The adsorption amount ofβ-CD exhibited a maximum capacity at pH of isoelectric point on the surface of titanium dioxide, while the adsorption capacity of P-CD was decreased as solution pH changed.With the increase of initial concentration, the adsorption removal efficiency rise. The photodegradation experiment ofβ-CD in two kinds of titanium dioxide suspension showed:the photodegredation process ofβ-CD was described by Langmuir-Hinshelwood equation (L-H) in the initial stage of the reaction. The L-H rate constant inβ-CD/P25 system was 1.55 times as that inβ-CD/TiO2 system due to mixed crystal effect of P25. The presence of oxygen led to higher apparent kinetic rate in two kinds of titanium dioxide suspension, which resulted from adsorbed oxygen molecule trapped electrons to cause extension of recombination time of electronhole pairs.(2) Theβ-cyclodextrin (β-CD) modified titanium dioxide composites nanoparticle have been successfully synthesized through cross-linking. There were two types of linking agent used for preparation of modified titanium dioxide. One was 3-glycidoxypropyltrimethoxysilane (S1), the other was 3-chloropropyltriethoxysilane (S2). The modified nanoparticle were characterized with XRD, BET, TEM, PLS, UV-DRS, PL, IR and TOC methods. The analytical results indicated modification had no effect on crystal lattice of titanium dioxide; particle size becomed big; BET surface area decreased; size distributions increased; absorptivity of UV-Vis unchanged; excitation spectrum becomed weaker; proved immobilizing P-cyclodextrin on the surface of titanium dioxide; measure content ofβ-cyclodextrin in modified nanoparticle. The results of showed that the accelerating adsorption effect of 2,4-dinitrophenol on modified nanoparticle was the best in controal adsorption experiment of modified nanoparticle to 2,4-dinitrophenol (DNP), bisphenol A (BPA) and rhodamine B (RhB). This is because molecular recognition property ofβ-cyclodextrin on the titanium dioxide surface. The adsorption experiment of BPA in two kinds of modified titanium dioxide (TiO2-S1-CD and P25-S1-CD) suspension indicated:the adsorption isotherm presented a good fit to Langmuir model; adsorption kinetics could be used to simulate by pseudo second order model. Time of equilibrium adsorption was 300min under our experiment conditions. The rate constant of pseudo second order model ofβ-CD in TiO2-S1-CD or P25-S1-CD were increased with the higher initial concentrations of BPA. The adsorption amount of BPA exhibited a maximum capacity at pH of isoelectric point on the surface of titanium dioxide, while the adsorption capacity of BPA was decreased as solution pH changed.With the increase of BPA initial concentration, the adsorption removal efficiency rise. The modification ofβ-CD enhanced adsorption of two titanium dioxides as a result ofβ-CD complex inclusiont.(3) Combining with the photodegradation activities of three kinds of contaminant, such as dye, phenol compound and heavy metal ions, on P25-S1-CD surface, we conclude that P25-S1-CD was found to be selective of photodegradation. For dye, which photodegradation mechanism of dye is photosensitization, P25-S1-CD increase the adsorption capacity of dye while enhance photodegradation of dye. For phenol compound and heavy metal ions, which photochemical degradition mechanism of dye is Photocatalysis, P25-S1-CD inhibited photodegradation of phenol compound and heavy metal ions. Studies also show that the kinetic of the degradation of OrangeⅡ/P25-S1-CD can be expressed by the Langmiur-Hinshelwood model, and the reaction rate constant kre.=3.87μM-1. min,the observed adsorption equilibrium constant Kads.=0.0228 L/μM. The L-H rate constant in OrangeⅡ/P25-S1-CD system was 8.41 times as that in OrangeⅡ/P25 system due to high absorbability of P25-S1-CD. The observe rate constants of Orange II in P25-S1-CD suspension were increased with the higher initial concentrations of Orange II. With the increase of dosage of P25-S1-CD, The observe rate constants of Orange II rise. The observe rate constants of Orange II increased while pH decrease. The result of adding scavenger experiment was called to provet that hydroxyl radical is important active substance for attracting Orange II.(4) Simultaneously photocatalytic oxidation of BPA and reduction Cr(VI) was investigated in TiO2 or TiO2-S1-CD suspension. The result showed TiO2 had advantage over the TiO2-S1-CD for simultaneously photocatalytic BPA and Cr(VI). The cause of inhibition of photocatalysis degradation of TiO2-S1-CD was thatβ-CD reacted with active radical on TiO2 surface. The observe rate constants of BPA and Cr(VI) in TiO2 or TiO2-S1-CD suspension were increased with the higher dosage of catalyst and lower pH. The mechanism photoreduction Cr(VI) was that Cr undergo a chemical reaction with photo-induced electron, and The mechanism photo oxidation of BPA was that BPA was attacked by photo-induced hole and singlet oxygen... |
