Of Tio <sub>, 2 </ Sub> Photocatalytic Degradation Of Typical Heterocyclic Compounds In Coking Wastewater

Coked wastewater, containing a large quantities of phenolic compounds, various aromatics as well as heterocyclic species, is a typical hardly-degradable organic pollutant derived from industry. Its complicate composition and considerable discharge cause serious contamination to the environment. Therefore, environmental investigators'concern about treatment of coked wastewater has become focal one of a worldwide spot. Of the method to treat hardly degradable organic wastewater, photocatalystic oxidation is one of the techniques with brilliant prospects.The paper characterizes the structure of manometer TiO₂ material embedded by Zn atom, by means of X-ray diffraction(XRD), difference thermal analysis, and infrared spectrum(IR). The results show that synthetic TiO₂ is a manometer-level material. Its powder and one with 1%Zn embedded have a mean particle diameter of 19nm and 21.5nm respectively. Calcined at 360℃, non-crystalline TiO₂ is converted into anatase one, whereas crystalline transition occurs in TiO₂ embedded by 1%Zn at 500℃. In addition, a strong thermal absorption peak survives at 545℃. IR detects the change of TiO₂ structure by SO42- entity in TiO₂ embedded by 1%Zn.With quinoline and pyridine as precursors and TiO₂ embedded by 1%Zn as a photocatalyst, and Under the ultraviolet radiation, the initial concentration of heterocyclic species, treatment duration, calcine temperature of TiO₂, Zn quantities embedded in TiO₂, the amount of TiO₂, initial pH value of the solution, the extra amount of hydrogen peroxide, are considered to effect on percent degradation on heterocyclic compounds. The experiment indicates that TiO₂ is the most photocatalytically active when 1%Zn is embedded; the temperature to calcine TiO₂ has a significant effect on catalytic activity, i.e., highest catalytical activity at 500℃in TiO₂ embedded by Zn; longer photocatalytic oxidation time corresponds to appreciable percent degradation on heterocyclic species, namely, 6h is demanded to reach 81% degradation and 51% TOC removal for quinoline and, whereas 92% degradation and 58% TOC removal for pyridine; large initial concentration of heterocyclic compounds is comparable to small degradable rate if the concentration lies between 10 and 50 mg/L, whose dynamic equation is the first-order; highest degradation on quinoline occurs at addition of 0.6g/L catalyst, whereas pyridine at 0.8gl ; 6-8 pH value corresponds to highest percent degradation on heterocyclic compounds; the percent degradation increases as addition of hydrogen peroxide, but excessive hydrogen peroxide decreases percent degradation, e.g., the removal percentage for quinoline reaches 65% from original 35% in 3h if 6ml/L H2O2 is added, while the percentage for pyridine reaches 74% from original 53%.The simulation wastewater is available if 1:1(w:w) ratio of quinoline to pyridine is mixed in aqueous solution. The degradation regulation is studied under ultraviolet radiation. The experiment reveals that the percent degradation on quinoline and pyridine increases with duration increasing. The result brings out parallel tendency to degradation of single organic component system. The pyridine is more susceptible to photodegradation instead. Addition of 0.8g /L TiO₂ results in highest TOC removal in the mixture; however, the optimal addition quantities are 0.8g/L TiO₂. Excessive catalyst corresponds to poor TOC removal. The percent degradation-time relation does not follow zeroth- or first- order dynamic equation stringently. Nevertheless, the TOC removal-time relation follows the first-order dynamic equation.