Study On Separation/Enrichment Of Heavy Metals In Environment By Nanoscale TiO₂ Solid Phase Extraction Combine With Spectroscopy

Heavy metal pollution is a threat to the ecological environment and human health with great toxicity and harmfulness.Since the complexity of environmental samples and the property of super-lower concentration of heavy metal in environmental samples, heavy metal ions cannot be analyzed directly through equipment.It can be analyzed only after process of pretreatment,enrichment,separation,purification,etc.Recenely, solid-phase extraction(SPE)technique has become increasingly popular,because it is experienced with several major advantages:(â…°)the fast,simple and direct sample application in very small size(micro liter volume)without any sample loss;(â…±)higher preconcentration factor;(â…²)rapid phase separation;(â…³)the ability of combination with different detection techniques in the form of on-line or off-line mode;(â…´)time and cost saving.The absorption property of metal ions on nano TiO₂ or loaded nano TiO₂,main influence factor and absorption capability etc,was studied systematically and detected by flame atomic absorption spectrometry(FAAS)/inductively coupled plasma atomic emission spectrometry(ICP-AES).The method was applied to the separation/enrichment and speciation analysis of trace elements.The major contents are as follows:(1)A new method was proposed for the separation and enrichment of Cu,Mn andNi using nanometer sized TiO₂ as solid phase extractor and detected by ICP-AES. The major factors influence on the process of separation and enrichment,the interference of co-existing ions and the possible sorption mechanism were studied.The capacity of absorption was investigated.Under optimum conditions,the detection limits were 26μg·L^-1with relative standard deviation(RSD)of 2.5%for Cu,20μg·L^-1with RSD of 1.6%for Mn and 91μg·L^-1with RSD of 3.8%for Ni,respectively.It was found that the present method used in the article had many advantages including high selectivity,good stability and good perfermence of absorption and desorption.The result showed that the method suit for the analysis of environmental samples.(2)The absorption behavior of nano TiO₂ towards Zn(â…¡)and Cu(â…¡)was studied by FAAS.The major factors Influence on the absorption and desorption,the interference of co-existing ions and the capacity of absorption were investigated.The result showed that the sorption rate was more than 98%at pH 8～9.The quantitative Zn(â…¡)and Cu(â…¡) adsorbed by TiO₂ were eluted by 2.0mol/L HCl.The detection limits,RSD and static adsorption capacities of Zn(â…¡)and Cu(â…¡)were 39μg·L^-1and 23μg·L^-1,3.4%and 2.7%,12000μg·g^-1and 7400μg·g^-1,respectively.Under optimum conditions,the contents of Cu and Zn in Yangtze River water and Seawater were determinated,and the recovery of standard addition was 93%～102.4%.(3)The absorption behavior of nano TiO₂(rutile type)towards Cr(â…¥)/Cr(â…¢)using FAAS was studied.The possible absorption mechanism was investigated and applied to the speciation analysis of Cr in water samples.The result showed that the detection limits under little acid condition(pH=6.5)were 57μg·L^-1for Cr(â…¥)and 41μg·L^-1for Cr(â…¢),respectively.Cr(â…¥)and Cr(â…¢)showed a good linear relationship at range of 0～9.0 and 0.1～10mg·L^-1,and RSD were 2.6%and 3.4%(2.0mg·L^-1Cr,n=6), respectively.The method was simple,rapid and highly selective.It was applied to the speciation analysis of Cr in industrial wastewater and surface water,and satisfactory results were obtained.(4)A new method was proposed for the separation and enrichment of molybdate anion using nano TiO₂ as solid phase extractor and detected by FAAS.The major factors influence on the sorption and desorption were studied.The result showed that the sorption rate of nanometer sized TiO₂ towards Mo was more than 90%under the conditon of pH 1.2,TiO₂ 100mg,surging time 10min and standing time 30min.The quantitative Mo adsorbed by TiO₂ was eluted by 10 mL 0.5mol/L NaOH at normal temperature.Under optimum conditions,the detection limit of Mo(â…¥)was 12.0μg·L^-1 and RSD was 2.9%(5.0mg·L^-1Mo,n-6).(5)The absorption behavior of nano TiO₂ loading on silica gel to Cd²⁺and Cu²⁺ was studied and detected by FAAS.Major factor influencing its absorption and desorption,influence of coexistence ions was discussed.The absorption capability of loaded TiO₂ to Cd²⁺and Cu²⁺was also investigated.Under the condition of pH 8, sorbent 0.020 g,surging time 5 min,standing time 3 h,the adsorption rate of loaded nano titania to Cd²⁺and Cu²⁺could amount to 100%;take nitric acid(10mL 4mol/L)as strippant,surging time 5 min,standing time 3 h,Cd²⁺and Cu²⁺could desorpt rationally from loaded nano titania.Results show that the enrichment factor is 5,detection limit 0.026mg.L^-1,relative standard deviation 2.93%.(6)Nano TiO₂ loading on silica gel was prepared by sol-gel method.The absorption behavior of it towards Cr³⁺and Mn²⁺was investigated.It was found that the adsorption percentages of the metal ions studied were over 90%in pH 8.0～9.0,and 0.5mol/L HNO₃ was sufficient for complete elution.The adsorption capacity of supported nano TiO₂ for Cr³⁺and Mn²⁺was found to be 13.5 and 6.1mg·g,respectively. A method using supported nano TiO₂ as adsorbent has been developed for the separation/enrichment and determination of Cr³⁺and Mn²⁺in environmental sample. The RSD and the recovery of standard addition was 2.0～2.5 and 93%～102.4%, respectively.During the process of heavy metals enrichment and separation,nano titania could be used as sorbents for solid phase extraction of Cu²⁺,Mn²⁺,Ni²⁺,Cr(â…¥),Cr³⁺,Cd^2+, Mo(â…¥),Zn²⁺,which could be dected rationally and analyzed formly via the technology of FAAS combined with AES.Take the absorption property of titania,we prepared selective loaded-sorbent(e.g.diacetyldioxime/nano titania)by loading some special ligand on the surface of titania for enrichment,separation and dection of special ions (e.g.Ni²⁺).