Highly Sensitive Analysis Of Uranyl Ions Based On Molybdenum Oxide Quantum Dots

The rapid development of nuclear energy has increased the demand for uranium,which has made uranium resources more and more tightly,and on the other hand,nuclear waste,slag and other uranium-containing solids and wastewater have continued to increase,making the problem of uranium pollution increasingly prominent.Traditional uranium analysis methods such as atomic absorption spectroscopy,emission spectroscopy,phosphorescence,mass spectrometry,etc.detect all forms of uranium in the sample.However,in the environment,especially in the aqueous medium,uranium mainly exists in the form of uranyl ions(UO₂²⁺)and participates in the whole process of nuclear fuel processing and waste treatment.Therefore,the study of UO₂²⁺will help predict the behavior of radionuclide in the environment and the monitoring of radionuclides during nuclear waste storage.At the same time,although traditional methods have high sensitivity,they are expensive,complicated to operate,and can only be performed in a laboratory.Therefore,in-situ,online and fast UO₂²⁺detection is full of challenges but still urgently needed.As a typical type of transition metal oxides,molybdenum oxide quantum dots（MoO_x QDs）have been used in the analysis of biological enzymes,drugs,explosives,etc.due to their advantages of simple preparation,excellent optical properties and good environmental compatibility.Based on these,MoO_xQDs is used as a new type of UO₂²⁺fluorescent probe to establish new methods for rapid and sensitive analysis of UO₂²⁺in environmental water samples.The main research contents are as follows:（1）When UO₂²⁺and MoO_x QDs coexist,UO₂²⁺can combine with the oxygen atoms on its surface to form MoO_x QDs-UO₂²⁺complexes,and cause the fluorescence of MoO_x QDs to be quenched.Based on this,this paper uses MoO_x QDs as a new type of UO₂²⁺fluorescent probe to establish a simple and rapid UO₂²⁺detection method.Under the best experimental conditions,when the concentration of UO₂²⁺is 0.13～16.64μmol/L,the fluorescence intensity of MoO_x QDs has a good linear relationship with the content of UO₂²⁺,and the detection limit is 0.09μmol/L（3σ/K）.Under the masking effect of ethylenediaminetetraacetic acid（EDTA）,common metal ions(Cu²⁺,Al³⁺,Th⁴⁺,Ni²⁺,Fe³⁺,Zn²⁺,K⁺,Na⁺,Hg²⁺,Ca²⁺,Mg²⁺,Pb²⁺)in water will not interfere with the detection of UO₂²⁺.The recovery rates of standard addition for natural water and lake water are 99.7%and 100.6%,respectively,and the relative standard deviations are both less than 5%,indicating that the method is accurate.Although this method has the advantages of simplicity,speed and accuracy,it lacks the sensitivity and cannot meet the requirements of direct analysis of environmental water samples.Therefore,it is necessary to introduce more UO₂²⁺coordination functional groups on the surface of MoO_x QDs to improve the sensitivity of UO₂²⁺analysis.（2）Dopamine（DA）is modified on the surface of MoO_x QDs to obtain a new functionalized MoO_x QDs（DA-MoO_x QDs）with rich oxygen-containing and nitrogen-containing functional groups,and then the DA-MoO_x QDs is applied to the highly-sensitive detection of UO₂²⁺in water samples.Compared with MoO_x QDs,the sensitivity of DA-MoO_x QDs to UO₂²⁺is increased substantially.The increased sensitivity can be account for the introducing of a large number of nitrogen-containing and oxygen-containing groups on MoO_x QDs by DA modifying,such as C-NH-C,-NH₂ and-OH,which endows the DA-MoO_x QDs with strong UO₂²⁺coordination ability.When UO₂²⁺is coexisted with DA-MoO_xQDs,the strong coordination of UO₂²⁺and DA-MoO_x QDs leads to the aggregation of DA-MoO_x QDs,and thus the fluorescence quenches.Under the optimal conditions,the fluorescence intensity of DA-MoO_x QDs decreases linearly with the increase of UO₂²⁺content when the concentration of UO₂²⁺is 5.0～1000 nmol/L,and the limit of detection is3.85 nmol/L（3σ/K）which is lower than the UO₂²⁺concentration（130 nmol/L）in drinking water defined by the Environmental Protection Agency of America.Common anions(SO₄^2-,CO₃^2-,NO₃^-,HPO₄^2-,Cl^-,Br^-、F^-)in water samples do not interfere with the UO₂²⁺detection and other metal ions(Mn²⁺、Hg²⁺、Fe³⁺、Cd²⁺、Ca²⁺、Al³⁺、Ni²⁺、Cu²⁺、Pb²⁺)even if their concentration is 100 folds higher do not affect the UO₂²⁺detection in the presence of masking agents.At the same time,the standard addition and recovery experiments on lake and river water also show that the method based on DA-MoO_x QDs is highly accurate,which shows a great promising in online,in-situ and rapid UO₂²⁺analysis and provide technical support for uranium pollution prevention and control.