Preparation Of Phosphoric Acid Modified Magnetic Material And Its Application In The Analysis Of Trace Metal Oxide Nanoparticles

Substantial production and wide applications of engineered nanoparticles（ENMs）have raised great concerns over their potential impact on the environment and humans.However,even in countries with the maximum production and usage of ENMs,such as the United States and China,there is still a lack of regulation on products containing ENPs.TiO₂ NPs and CeO₂ NPs are typical representatives of metal oxide nanoparticles（NPs）,whose toxic/beneficial effects are generally related to their composition,concentration,size and form of existence.Therefore,the development of methods with strong selectivity,high sensitivity,and simple operation to detect the concentration and size of metal oxide NPs is very important for the monitoring of metal oxide NPs in the environment.Inductively coupled plasma mass spectrometry（ICP-MS）is a powerful trace metal element analysis method with wide linear range,fast analysis speed,high sensitivity,and simultaneous multi-element analysis.However,when it is directly used for the analysis of metal oxide NPs in real samples,the analysts would run into some difficulties.For example,the target analyte content is below the instrumental detection limit,ICP-MS cannot distinguish metal oxide NPs from their corresponding metal ions,and conventional measurement mode can’t afford information on the size distribution of NPs.Therefore,before performing ICP-MS detection,a suitable pretreatment technique is needed to separate the matrix and enrich the target analyte;at the same time,it is also necessary to give the size distribution information of NPs by using a suitable separation technique.Magnetic solid phase extraction（MSPE）is a widely used pretreatment method,with the advantages of simple operation,fast analysis speed,high enrichment factor and no need of organic solvents.The development of magnetic materials with high selectivity and large adsorption capacity is the key to improve the performance of relevant methodologies.According to the theory of hard-soft-acid-base,a stable complex can be formed between phosphoric acid and high-valent metals.Therefore,functionalization of magnetic material with phosphoric acid is beneficial to improve the selectivity of the method.The purpose of this paper is to prepare phosphoric acid functionalized materials based on the affinity between phosphoric acid and Ti（Ⅳ）/Ce（Ⅳ）,establish a new MSPE-hollow fiber flow field flow fractionation（HF5）-ICP-MS method,and apply it to the analysis of metal oxide NPs in environmental water.The research content of this paper mainly includes:（1）The phosphoric acid functionalized superparamagnetic iron oxide（Fe₃O₄@SiO₂@GMA-PO₄）was prepared and its adsorption performance for TiO₂ NPs and titanium ions was investigated.According to the different adsorption behavior of TiO₂ NPs and titanium ions on it,MSPE-ICP-MS method was established for the selective quantification of trace TiO₂ NPs in environmental water.Subsequently,the adsorption mechanism was discussed using dispersion-corrected density functional theory（DFT-D）.At low pH,Fe₃O₄@SiO₂@GMA-PO₄ has a good adsorption effect on TiO₂ NPs;with the increase of pH,OH^-will be preferentially adsorbed on the surface of TiO₂ NPs in solution,which makes the adsorption efficiency drop significantly.Under the optimal experimental conditions,the limit of detection for TiO₂ NPs was 17 ng/L with an enrichment factor of 400 and the adsorption capacity was 462 mg/g（25 nm TiO₂ NPs）.The developed MSPE-ICP-MS method was applied to the detection of trace TiO₂ NPs in the Yangtze River and the East Lake water.Subμg/L level of TiO₂ NPs was found in the tested water samples,and recoveries of 91-110%and 90-110%were obtained for TiO₂ NPs at three concentration levels in spiked water samples,respectively.（2）To further increase the grafted amount of phosphoric acid,functionalized magnetic adsorbent（Fe₃O₄@SiO₂@KH550-PA）was synthesized using phytic acid（PA）as the phosphorus source,and the adsorption behavior of CeO₂ NPs on it was investigated.The results showed that CeO₂ NPs were quantitatively adsorbed in the range of pH 1-4.The developed method had simple operation and fast analysis speed（20 min）.We found that the adsorption of CeO₂ NPs on Fe₃O₄@SiO₂@KH550-PA conformed to the Langmuir adsorption model,with a maximum adsorption capacity of 4.18 g/g.Under the optimal experimental conditions,this method exhibited good resistance to matrix interference and a large enrichment factor（200 times）,which enabled the analysis of ppt-level CeO₂ NPs in the environment.HF5 has the advantages of low cost,low mobile phase consumption,and fast analysis speed.It is easy to be online hyphenated with ICP-MS and provide NPs size information.Herein,HF5 separation conditions were optimized for the separation of CeO₂ NPs with different particle size,but the separation was seriously affected by the NPs aggregation and the sample matrix.The hyphenation of HF5-ICP-MS and MSPE will be further optimized by using other hollow fiber and mobile phase composition.