| Heavy metals pollution has seriously threatened the safety of aquatic eeosystems,drinking water,food,and public health due to its toxicity,bioaccumulation,and non-biodegradation.Therefore,the monitoring of heavy metals in environmental water is particularlly significant.However,metal concentations in the biological,environmental,pharmaceutical and food samples are low and their determination are severely interfered by the matrix.Hence,sample pretreatment,especially for the separation and preconcnetration,is essential for the analysis of trace elements.As sample pretreatment methods and sample introduction system,the advantages of photo-redox technology on the improvement of analytical performance and environment-friendly are outstanding.Nano-TiO2 are widely used for solid-phase extraction and photocatalysis because of its large surface area,high chemical stability,non-toxicity,and large number of surfave active points(OH-,O2-and Ti4+).However,the applications of TiO2 have been limited by its band-gaps of approximately 3.0-3.2 eV and the difficulty of its separation and reusing.In this paper,cellulose filter paper for its low cost and abundance is used to immobilize nano-TiO2 and denoted as TiO2/cellulose paper(TCP).Simultaneously,TCP is surface modified by hydroxyl groups on the surface of TiO2,and used for metal analyisis in natural water.The conclusions of this study are shown as follows.(1)Nano-TiO2 is firmly immobilized onto cellulose filter paper by sol-gel methods and then the trouble of its separetion and reusing is overcome.TCP is used as adsorbent with high adsorption capacity,i.e.,more than 259 ?g and 254 ?g for Cd and Pb,respectively.Under the optimum adsorption conditions(i.e.,the pH value of the system 8.0,adsorption time of 3 h,and 25?),the best adsorption ratios of Cd and Pb are more than 94.4%and 95.5%,respectively.The preconcentration of Cd and Pb could not be affected by the coexistence of other metals and humic acid.The concentrations of Cd and Pb are directly quantified by X-ray fluorescence(XRF).The linear calibration curves for Cd and Pb are both in the range of 1.0-50.0 ?g L-1.The correlation coefficients(R2)of Cd and Pb are 0.9980 and 0.9976,respectively,and the detection limits(3?,n=11)for Cd and Pb are 0.51 ?g L-1 and 0.69 ?g L-1,respectively.This proposed method has been successfully applied for the detection of Cd and Pb in drinking water and river water with a preconcentration factor of 103 for 1.0 L of water samples and the results are in agreement with ICP-MS method.(2)As a cheap and abundant porous material,cellulose filter paper was used to immobilize nano-TiO2 and denoted as TiO2/cellulose paper(TCP).With high adsorption capacity for Cu(?)(more than 1.65 mg),TCP was used as adsorbent,photocatalyst,and colorimetric sensor at the same time.Under the optimum adsorption conditions(i.e.,pH 6.5 and 25?),the adsorption ratio of Cu(?)was higher than 96.1%.Humic substances from the matrix could be enriched onto TCP but the interference of their colors on colorimetric detection could be eliminated by the photodegradation.In the precence of hydedylamine,neocuproine as a selective indicator was add onto TCP,a visual color change from white to orange was generated.The concentration of Cu(?)was quantified by the color intensity images,using an image processing software..This fully-integrated visual analysis system was successfully applied for detection of Cu(?)in 10.0 L of drinking water and seawater with a preconcentration factor of 104.Log-linear calibration curve for Cu(?)was in the range of 0.5-50.0 ?g L-1 with a determination coefficient(R2)of 0.985 and its detection limit was 0.5?gL-1.(3)Based on the adsorption for preconcnetration of Cr(?)and photocatalytical reduction for the transformation of Cr(?)into Cr(?)and determination with XRF,a novel method is developed for the determination of total chromium on-line in water samples.Surface modification of TiO2 with Acid Violet 43(TCP-A)could give a more negative surface charge for TCP and expand the response range of UV-vis wavelength from 375 nm to 750 nm.With adsorption capacity of more than 4.66 ?g for Cr(?),TCP-A is used as photocatalyst and adsorbent.Under the optimum experimental conditions(i.e.,pH 6.5,3 h,and 25?),when TCP is replaced by TCP-A,the adsorption ratio of Cr(?)(1.5 mg L-1)is increaseed from 89.4%to 92.7%with more than 0.96 times of reaction rate constant,the absorption ratio of Cr(?)(1.5 mg L-1)is increased from 8.4%to 22.5%;meanwhile,the transformation ratio of Cr(?)(1.5 mg L-1)can increase from 77.9%to 96.0%by photoreduction.When the concentration of Cr(?)is below 2.0 mg L-1,Cr(?)can be photoreduction-induced transformed into Cr(?),its transformation ratio is more than 90%,and then Cr(?)in the sample and from the transformation of Cr(?)is adsorbed onto TCP.The concentration of total chromium is quantitied by XRP.With enrichment factor of 250 and detection limit(3a,n=11)of 0.59 ?g L-1,this proposed method has been successfully analyzed total chromium in real water samples. |
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