Preparation And Properties Of The Ternary MoSSe And Its Heterojunction Photocatalysts

In recent years,the problem of water pollution in the environment has become a growing problem as a consequence of the abuse and random discharge of antibiotics.Among these coping strategies,semiconductor-based photocatalytic degradation technology is favored for its green,sustainable and low-cost.The structure of ternary MoSSe is similar to that of MoS₂ and MoSe₂,while its internal dipole perpendicular to the plane can induce an internal electric field and the lattice distortion caused by the coexistence of internal S and Se atoms can also enhance its binding energy,resulting in higher separation efficiency of internal carriers,photocatalytic activity,and stability than the MoS₂ and MoSe₂.In this paper,based on the structural similarity of MoSSe,MoS₂,and MoSe₂,a new preparation scheme of MoSSe was developed,and the photocatalytic degradation activity of levofloxacin and photoelectrochemical performance of MoSSe were investigated.Subsequently,in view of the relatively limited separation efficiency of the internal carriers of a single MoSSe material and its inability to produce hydroxyl radicals directly,then MoSSe was modified by constructing the S-scheme heterojunction based on semiconductor coupling to optimize the transport path of its internal carriers and preserve the original redox activity.Then the photoelectrochemical activity and degradation efficiency of tetracycline hydrochloride for the composites were systematically investigated.The main research contents of this paper are as follows:（1）The MoSSe nanosheets with tunable bandgap were prepared by a hydrothermal method,which based on the adjustment of the proportion of sulfur and selenium.Among them,the photocurrent response and photocatalytic levofloxacin degradation rate constant of the MSS1 sample were higher than those of the MoS₂ and MoSe₂,which was 2.5 times and 6.6 times higher than that of the MoS₂,respectively.（2）MoSSe/Bi₂WO₆ S-scheme heterojunction composites with different Bi∶Moratios were constructed by coupling the Bi₂WO₆ with wide bandgap（2.88 e V）with the aforementioned MoSSe with the best performance.Among them,the photocurrent response（13.72μA/cm²）and photocatalytic tetracycline hydrochloride degradation rate constant(0.03593 min^-1)of the MSSB3 sample were 4.4 times and 1.4 times higher than those of the original MoSSe,respectively.（3）The MoSSe/Co₃O₄ S-scheme heterojunction photocatalytic materials with different Co∶Moratios were synthesized based on a hydrothermal method of growing Co₃O₄ nanoparticles（band gap of 1.96 e V）on the MoSSe nanosheets.Among them,the photocurrent response（35.98μA/cm²）of the MSCO2 sample was 6.8 times higher than that of the original MoSSe,and also exhibited a high reaction rate constant(0.02576 min^-1)in the degraded tetracycline hydrochloride.Among them,the high catalytic performance of the MoSSe nanosheets could be attributed to the presence of the built-in electric field,which facilitated the separation and transmission of internal carriers,thus producing a lot of catalytic active substances for the degradation of levofloxacin.Besides,the S-scheme heterojunction composites constructed based on the pristine MoSSe all exhibited enhanced photocurrent response and photocatalytic degradation activity of tetracycline hydrochloride,which could be attributed to the following three reasons:Firstly,the addition of Bi₂WO₆ and Co₃O₄ all effectively promoted the increase of the specific surface area of the composites,which could provide more exposed active sites.Secondly,the energy band bending structure and the built-in electric field formed during the construction of the S-scheme heterojunction greatly facilitated the separation and transport of carriers.Finally,both Bi₂WO₆ and Co₃O₄ formed the S-scheme heterojunction structure with MoSSe,which optimized the transmission pathway of internal carriers,broadened the range of visible-light absorption,and preserved the excellent redox activity.Meanwhile,the different S-scheme heterojunction systems based on MoSSe were different in terms of increase in specific surface area,performance enhancement,and degradation pathway of tetracycline hydrochloride.Obviously,the MoSSe/Bi₂WO₆ S-scheme heterojunction system exhibited the highest enhancement in photocatalytic degradation performance,which could be attributed to the incorporated Bi₂WO₆ material with a wide bandgap,positive valence band potential,and oxidation activity.The MoSSe/Co₃O₄ S-scheme heterojunction system showed the best enhancement of photoelectrochemical performance,which could be attributed to the incorporated Co₃O₄ material with a narrow bandgap,and the relatively higher utilization rate of visible light.