Electrochemical Detection Of As(?) Over Single-Atom Catalysts And The Study On Catalytic Mechanism

Water pollution problems related to heavy metal ions(HMIs),such as As(?),continue to appear,which poses a huge threat to the ecological environment and public health.The design of ultra-sensitive electrochemical sensors to achieve efficient,accurate,and sensitive detection of HMIs,like As(?),in the water environment has always been the pursuit of analytical chemists.However,it is worth noting that the design of electrochemical sensors still relies on empiricism,and the nanomaterials with good electrical conductivity,high porosity,and large specific surface area are always selected as electrode modifiers.However,the catalytic ability of the sensing materials and the corresponding electrocatalytic detection mechanism were ignored and remained largely unexplored,which greatly limits the further improvement of electrochemical performance.In fact,the high-energy active components of the nanomaterials can affect the electronic structure,catalytic activity,electron transfer rate,and adsorption capacity of the sensor interfaces,thereby further influencing the electrochemical reduction/deposition or oxidation/stripping behavior of HMIs.In this thesis,the electrochemical sensors based on the single-atom catalysts with simple coordination and stable structure are designed.Besides,the influence of the catalytic ability of the sensing materials on the electrochemical behavior toward As(?)and the corresponding catalytic detection mechanism are deeply explored.(1)Defect engineering strategy was adopted to fix Pt single atoms on the defective MoS2 nanosheets,and the high-sensitive and-stable detection of As(?)were achieved by adjusting the loading amount of Pt atoms(1 wt%,4 wt%,12 wt%).X-ray absorption fine structure spectroscopy(XAFS)and theoretical calculations revealed that Pt single-atoms were stably fixed by four S atoms,and activated the adjacent S atoms.Then Pt and S atoms synergistically interacted with O and As atoms,respectively,and transferred some electrons to H3ASO3,which change the rate-determining step of H3ASO3 reduction and reduce reaction energy barriers,thereby promote rapid and efficient accumulation for As(0).Compared with Pt nanoparticles,the weaker interaction between arsenic species and Pt1/MoS2 enabled the effortless regeneration and cyclic utilization of active centers,which is more favorable for the oxidation of As(0).(2)Coordinated design strategy was used to anchor highly active Co single atoms on a nitrogen-doped porous carbon substrate(Co SAC),and the exceptional sensing interface was constructed with Co SAC,successfully achieving ultra-sensitive and high-selective electrochemical detection toward As(?).Combining XAFS,density functional theory(DFT)calculation and reaction kinetics simulation,we demonstrated that Co single atoms stabilized in N2C2 support serve as active sites to catalyse H3AsO3 reduction and transfer electrons via the formation of Co-O hybridization bond,leading to a lower energy barrier,promoting the breakage of As-O bonds.Importantly,the first electron transfer is the rate-limiting step of arsenic reduction and is found to be more favorable on Co SAC both thermodynamically and kinetically.In addition,compared with the detection results of Cd(?),Cu(?),Zn(?),and Hg(?),Co SAC exhibited excellent selectivity for As(?),which is also due to the formation of Co-O hybrid bond,as there are no specific interaction sites between Co single atoms and ordinary divalent HMIs that without oxygen anions.(3)We compared the electrochemical behavior difference of two kinds of Fe single-atom catalysts with different coordination structures(FeN2C2,FeN3P)toward As(?),and studied the corresponding catalytic detection mechanism.It was found that under natural water pH conditions(pH 8.0),FeN3P can achieve high-sensitive detection for As(?),and the detection sensitivity(3.90 ?A ppb-1)is 20 times higher than that of FeN2C2.Even in the coexistence of Cu(?),FeN3P can also exhibit the highly selective and accurate detection of As(?).While for FeN2C2,the presence of Cu(?)significantly enhanced the response signals of As(?).XAFS fitting and DFT calculation revealed that the different interaction ways of FeN2C2 and FeN3P with H3AsO3 molecules is the main reason for their different electrochemical behaviors.The P and Fe atoms on FeN3P had strong affinities for the O and As atoms in H3ASO3,respectively,causing H3AsO3 breaking a As-O bond and transforming into H2AsO2 and OH during the adsorption process.Meanwhile,the electrons of FeN3P were transferred to H2ASsO2 and OH,decreasing the oxidation state of As(?)and accelerating its further electrochemical accumulation reduction process.In addition,the coexistence of Cu(?)did not compete with As(?)for active sites on FeN3P,and not affect the interaction mode between FeN3P and As(?),which is the reason for the excellent anti-Cu interference detection of As(?)on FeN3P.