Surface Modification Of Supported Nano-TiO₂ Photocatalysis For Water Quality Analysis And Pollution Control

Photocatalysis is an advanced oxidation technology for sample pre-treatment and pollution control with the characteristics of environmental friendly,high efficiency,low energy consumption,simple operation,mild reaction conditions,wide application range,and no secondary pollution.Solid phase extraction is an increasingly useful sample preparation technique.This technology is used not only to extract traces of the analyte with high recovey but also to remove the interfering components of the complex matrices in order to obtain a cleaner extract containing the analytes of interest.The advantages of this technology are no or a little of organic solvents,small volume of sample,simple operation,saving time,and easy to automation.Titanium dioxide is the most widely used photocatalyst because of its advantages of large specific surface area,non-toxicity,low cost,and long service life.However,the application of TiO₂ was limited by its strong polar,high surface free energy,easily reunitation,and poor dispersive capability.Meanwhile,because of its broad energy gap,the photocatalytic process should be induced by ultraviolet light.The extreme low surface coverage of organic pollutants on the catalyst TiO₂ resulted in the low adsorption and photocatalytic efficiency.Surface modification of nano-TiO₂ could increase the light utilization and the surface coverage of organic pollutants,which were crucial for the photocatalytic activity of heterogeneous photocatalysis.The primary production,the specied distribution,and ecosystem structure in the ocean could be affected by the availability of phosphorus（P）.However,the concentration level of P in surface seawaters in oligotrophic regions is nmol/L.The dissolved organic P（DOP）could be used as an alternative source of inorganic P by marine phytoplankton.Therefore,in order to understand the biogeochemical cycling of P,it is necessary to develop an accurate analytical technique for P,which is operational convenience,low cost,and sensitive for the determination of trace organic and inorganic P.What’s more,this technique can be adopted on shipboard by developing countries.Organophosphorus pesticides（OPs）are one of the most dangerous pollutants.Thus far,several validated methods are currently available for the identification and quantification of OPs,including gas chromatography,liquid chromatography,and chromatographic techniques coupled to mass spectrometry.However,their applications in developing countries and on-field monitoring are limited by the disadvantages,such as expensive instruments,complicated and time-consuming pretreatments,and well trained operators.Therefore,a simple,rapid,and low cost technology for on-filed separation and detection of OPs in water samples is of great practical interest.The safety of drinking water is threatened by microcystins for its high toxicity to mammals’ liver and nervous system.The microcystin cannot be removed effectively bythe conventional drinking water treatment methods,including coagulation and sedimentation,sand filtration,and adsorption,Using activated carbon,the adsorption can remove effectively of microcystins,but their toxic group could not be destroyed and the secondary pollution could not be avoided.The microcystins could be degraded completely by biological methods,but the degradation time is long.After chemical oxidation treatment,the microcystins could be oxidized completely into CO₂,H₂O and other harmless substances,even if only partial oxidation may also improve the biodegradability.However,there are disadvantages of insufficient of oxidative capacity,high processing costs,and producing secondary pollution.So,the developing of a new removing technology for microcystins is important.（1）Base on the preconcentration by lysine surface modified Fe₃O₄@SiO₂@TiO₂,.a new method for the determination of dissolved organic and inorganic phosphorus in seawater at the level of nmol/L is propoded by spectrophotometryFe₃O₄@SiO₂@TiO₂ is surface modified with lysine,and then as solid phase extractant.The adsorption efficiency for soluble phosphate in the seawater is 98.1%,when the adsorbent concentration is 1.2 mg/mL,adsorption time 30 min,and pH 8.3.When the pH value is adjusted by hydrochloric acid to 4.0,the 94.8%of adsorbed P can by eluted and the preconcentration factor is 100.Under dark conditions,inorganic phosphorus is adsorbed selectively.Under UV irradiation,organic phosphorus is degraded into inorganic phosphorus,adsorbed onto the Fe₃O₄@SiO₂@TiO₂ and then the total concentration of total soluble phosphorus could be determined.The content of organic phosphorus is calculated with subtraction.Linear calibration curves for soluble phosphorus are 3.4-1134 nmol/L and the detection limit is 1.33nmol/L.This method has been applied to detect the concentration of dissolved inorganic and organic phosphorus in South China Sea and the Taiwan Channel.Compared with the method of magnesium hydroxide-induced coprecipitation,the results are no significant difference.（2）A fully integrated analysis system is constituted for visual simultaneous detection of organophosphorus pesticides on surface modified TiO₂-thin layer.Titania@polystyrene hybrid micro spheres are surface modified by ascorbic acid（AA-TiO₂@PS）and then used as stationary phase,photocatalyst and colorimetric probe.As the different affinity between AA-TiO₂@PS and OPs,OPs（chlopyrifos,Malathion,parathion,parathion-methyl,and methamidophos）could be separated simultaneously by mobile phase in 12 min at different RF value.All of OPs could be photodegraded into PO43-in 20 min by visible light.Based on chromogenic reaction between PO43-and chromogenic agent（ammonium molybdate and ascorbic acid）,OPs could be quantified by the color intensity of the images using a camera with image processing software.Linear calibration curves for each species of OPs are from 19.3 nmol P L-1 to 2.30 μmol P L-1.With obvious advantages of simple operation,sufficient sensitivity,low cost,rapidity,and on-field monitoring,our proposed method is successfully utilized to detect five species of OPs in water samples.（3）Using 5-sulfosalicylic acid surface modified Fe₃O₄@SiO₂＠TiO₂ as the photocatalyst,a new technology for visible light-driven photocatalytic degradation of microcystin in dring water is developed.The photocatalytic degradation ratio of microcystins is 98.6%,when the optimal catalytic conditions are adopted,including catalyst 1.2 mg/mL,pH 4.0,initial concentration of microcystin 70μg/L,and light irradiate 120 min with 350W xenon.After photodegradation,the water quality standards of our country（i.e.,a maximum concentration of 1.0 μg/L）can be achieved.This method provides a new approach for treatment of microcystins with the advantages of green,economical,efficient,and recyclable photocatalyst.