Application Of Nano-TiO₂ And Its Surface Modified Compounds On The Determination Of Trace Organic Pollutants

Because of high recovery of the analyte, removing interference components, using less or no organic solvents, handling small sample size, simple operation, saving time, automated in the pretreatment, solid phase extraction was growing attenion in the analysis of trace substances.The characteristics of organic pollutants in water were retention in a long time, existence in a wide range, low concentration and great harm. Printing and dye wastewater and phenol wastewater were large industrial wastewater discharge. They are difficult to degrade organic pollutants inclusive of the benzene ring with three inducing effects (carcinogenic, mutagenic, teratogenic). They can be harm for people and environment by bioaccumulation and food chain. Addition to the pollution seriously water, organic pollutants are all in trace levels. The analysis, adsorption and photocatalytic degradation for organic pollutants need solid phase adsorbents whose characteristic were large specific surface area, high adsorption capacity, strong affinity with benzene ring pollutants, and so on.Nano-TiO2 could be widely applied in preconcentration of trace elements because of its advantages of large specific surface area, non-toxicity, high adsorption capacity, low cost, and long service life. The usage of Nano-TiO2 was limited by its strong polar, high surface free energy and easily reunitation, and the effective action area of nano-TiO2 was decreased because nano-TiO2 was not easy to disperse in water and organic media. Meanwhile, the extreme low surface coverage of organic pollutants on the TiO2 was the key factor that resulted in the low adsorption. The surface of Nano-TiO2 should be modified to improve its treatment effect.The conclusions of this study were:(1) Use the new surface modifier (1-hydroxy-2-naphthoic acid)Applied group established a new surface modification technology-chemical adsorption. Nano-TiO2 was modified by 1-hydroxy-2-naphthoic acid as new solid phase extraction agent. The advantages of nanometer size titanium dioxide surface modified with 1-hydroxy-2-naphthoic acid were: a. Enhancing the wettability of nano-TiO2 powder surface; b. Good dispersive capacity in polar and non-polar solvent; c. Enhancing the surface coverage of benzenoid pollutants on TiO2 through phenyl group interaction.(2)A new solid phase extractant was provided for the enrichment of trace amounts of salicylic acid. The salicylic acid contains both a phenol hydroxyl (?OH) and a carboxyl (?COOH) group and their reaction with the–OH groups on TiO2 surface to form an ester with stabile six-membered ring could facilitate the esterification between salicylic acid and TiO2. Under the adsorption conditions of the pH value of solution 3.0, adsorption time 15 min, adsorbent dosage of TiO2 1.8 mg mL-1, and the adsorptive capacity of TiO2 less than 11.1μg g-1, the adsorption ratio of SA achieved was higher than 98%. The adsorbed SA could be eluted by 5 mL of 0.5 mol L-1 NaOH and the elution percentage was higher than 99%. This method gave a concentration factor of 50 for a 250 mL sample. Detection limit (3σ, n=11) of 30.8μg L-1 was obtained.(3) A new method was established to determination of trace Alizarin violet 3B and 1-hydroxy 2-naphthoic acid. Alizarin violet 3B and 1-hydroxy 2-naphthoic acid both contain a phenol hydroxyl (?OH) or a carboxyl (?COOH), and their reaction with the–OH groups on TiO2 surface to form an ester with stabile membered ring. Under the adsorption conditions of the pH value of solution 3.0, adsorption time 40 min, adsorbent dosage of TiO2 2.0 mg mL-1, the adsorption ratio of Alizarin violet 3B(adsorptive capacity≤5.54μg mg-1) and 1-hydroxy 2-naphthoic acid (adsorptive capacity≤12.5mg/mg ) achieved were higher than 88% and 98.9%. The adsorbed 1-hydroxy 2-naphthoic acid could be eluted by 5 mL of 3 mol L-1 NaOH and the elution percentage was higher than 91.2%. The adsorbed Alizarin violet 3B could be eluted by 5 mL of 5 mol L-1 5-sulfosalicylic acid at the temperature of 50℃and the elution percentage was higher than 91.8% This method gave a concentration factor of 50 for a 250 mL sample. Detection limit (3σ, n=11) of 19.7μg L-1 and 20.3mg L-1was obtained.(4) A new method was established to determination of trace phenolic pollutants. Comparing with the enrichment effects of p-nitrophenol (p-NP) on nano-TiO2 and nano-TiO2 surface modified with 1-hydroxy-2-naphthoic acid (HNA-TiO2) with the same experimental conditions.The adsorption rate on HNA-TiO2 was all higher than nano-TiO2. The adsorption ratio of p-NP was higher than 98 % under the optimum adsorption conditions as follows: the solution acidity 0.5 mol L-1 [H+], adsorption time 15 min, adsorbent dosage of HNA-TiO2 1.6 mg mL-1, and the adsorptive capacity of HNA-TiO2 less than 4.69μg mg-1. The adsorbed p-NP could be eluted by 5 mL of 2 mol L-1 NaOH and the elution percentage was higher than 92 %. This method gave a concentration enhancement of 50 for 250 mL sample. Detection limit (3σ, n=11) of 25.4μg L-1 was obtained.Therefore, nano-TiO2 could be solid-phase extractant for organic pollutants which contains a phenol hydroxyl (?OH) or a carboxyl (?COOH). Through simple surface modification, enhance the surface coverage of benzenoid pollutants on TiO2 through phenyl group interaction.