Study On The Regulation Of The Electronic Structure And Electro/Photoelectrochemical Sensing Mechanism Of Cobalt-Based Nanomaterials

Pollutants in the water environment have caused serious threats to human health and the ecological environment.It is important to achieve quantitative detection of these pollutants.With the rapid development of chemically modified electrodes and the rise of nanomaterials,electroanalytical techniques have been widely used in the detection of water environmental pollutants.However,many studies still focused on new breakthroughs of sensitivity,ignoring the mechanism behind the electroanalytical results.The understanding of active sites and specific processes of electron transfer at the electrochemical interface during electrocatalysis was still limited,resulting in a lack of guidance for designing highly sensitive and selective sensing interfaces.In our works,the electronic structure of Co-based nanomaterials was regulated by means of constructing composite materials,vacancy engineering and atoms-doping.The electrochemically sensitive interfaces with high activity were constructed to realize the highly sensitive and selective detection of specific pollutants.The sensing mechanisms were analyzed from the electronic structure and the process of electron transfer,including the following contents:(1)Co@Co3O4 was obtained by controlling the oxidation degree of cobalt nanoparticles supported on nitrogen-doped carbon materials,which achieved highly sensitive and selective detection of Pb(Ⅱ)with excellent selectivity,stability and reproducibility.Moreover,it had good practicability and accuracy in detecting Pb(Ⅱ)in actual water samples.The interfacial oxygen atoms build an electron bridge for Co activating Co3O4.Particularly,new energy levels of oxygen atoms were generated and matched with that of Pb(Ⅱ).The strong orbital coupling effect between O and Pb made the Co@Co3O4 sensitive and selective toward Pb(Ⅱ).Comared with Co and Co3O4,Pb(Ⅱ)got more electrons from Co@Co3O4,and longer Pb-O bonds were formed,allowing more Pb(Ⅱ)to be catalyzed and reduced.(2)P-doped orthorhombic CoSe2 with Vse(o-CoSe2-x|P)was obtained,and the electrochemical sensitivity of o-CoSe2-x|P toward As(Ⅲ)was greatly increased with excellent stability,repeatability,selectivity,anti-interference and practicality.Experimental and theoretical DFT calculations found that P doping regulated the electronic structure of the active site on CoSe2.Electrons were transferred from the Co and Se sites to the P sites,making the P sites electron-rich donors.Furthermore,new energy levels were generated that match well with free As atoms,enabling sensitive detection of As(Ⅲ).The P sites have been certified as the really active sites of interaction with As(Ⅲ).(3)High-density Ir single atoms(SAs)were successfully synthesized on the surface of Co3O4 with abundant oxygen vacancies(Vo-Co3O4).In addition to Ir-O bonds,the Ir-O-Co/Ir bonds were also present.The coordination oxygen atoms of Ir-OIr had ultra-high activity,and generated energy levels matching with which of O atoms in H3AsO3.The Ir SAs/Vo-Co3O4 exhibited ultra-high sensitivity to As(Ⅲ),with good stability,repeatability and anti-interference.The research found that coordination oxygen atoms of Ir-O-Ir interacted with-OH in the H3ASO3,and-OH captured the electrons of Ir-coordinated O,further enchaining the ability of O to capture the electrons of Ir,thus increasing the valence state of Ir.Under the synergistic effect of Vo,the breaking energy of-OH in H3ASO3 decreased sharply.In addition,different from other common heavy metal cations,the specific interaction with-OH made Ir SAs/Vo-Co3O4 super-selective for As(Ⅲ).(4)A direct Z-scheme heterojunction of ZnS/Co9S8 with hollow cubic structures was designed,which achievd the highly sensitive and selective detection of chlorpyrifos,through the inhibition to the photoresponse of ZnS/Co9S8 by chlorpyrifos with excellent stability.For sensitivity,the hollow cubic structures of the heterojunction increased the light absorption,and the formation of a direct Z-scheme structure of the photocatalysts greatly improved the spatial separation of the photogenerated charge carriers,thus achieving better photoelectrochemica activity and higher photocurrent response of the heterojunction.In particular,the interaction between ZnS/Co9S8 with N and S of chlorpyrifos created the high selectivity for chlorpyrifos.