Research On Photocatalytic Performance Of ZnO Nanowires Modified By Mn²⁺/Co²⁺ Doping And CuS Coupling

With the rapid development of society and modern civilization,environmental problems such as sewage are causing more and more interference to people's lives.Compared with traditional physical and chemical methods,photocatalytic oxidation technology,which has advantages like low cost,low energy consumption,low toxicity,no secondary pollution and high recycling efficiency,has gradually gained more favor in the industrial field.Among various photocatalysts,ZnO has been widely used in the field of wastewater degradation due to its low toxicity,long-term stability,high electron mobility,good biocompatibility and diverse preparation methods.However,the application of ZnO in the field of photocatalytic degradation of wastewater has been limited,which is closely related to its several shortcomings.First of all,due to the wide band gap?3.37 eV?,ZnO has a poor absorption capacity of visible light and can only use about 4%of sunlight.Secondly,the photo-generated carrier pairs of ZnO are easily recombined on the surface,resulting in a decrease in photocatalytic performance.In addition,ZnO will exhibit photo-corrosion during photocatalytic reaction,thus its structure would be easily destroyed,which leads to a decrease in recyclability.In order to expand the application of ZnO in the field of photocatalytic degradation of wastewater,it is imperative to improve the above disadvantages.In general,controlling surface morphology,precious metal modification,ion doping,and construction of heterojunctions are common,effective and convenient modification methods.In this paper,the modification of metal ions doping(Mn²⁺/Co²⁺)and building p-n heterojunction?CuS/ZnO?was carried out owing to their low-cost and convenience.In this paper,a layer of ZnO seed layer is firstly coated on the surface of the silicon wafer by RF magnetron sputtering.Then,a Mn²⁺/Co²⁺doped or pure ZnO nanowire arrays was grown on the substrate by hydrothermal method.By using a series of characterization methods such as SEM,EDS,XRD,XPS and PL,and using methyl orange?MO?solution as organic pollutants,the photocatalytic degradation ability of various samples can be tested.It can be found that Mn²⁺/Co²⁺were successfully doped into ZnO without destroying its original morphology and crystal structure.Its visible light absorption capacity can be effectively improved and the photogenerated carrier recombination rate can be reduced.This is mainly due to the intermediate energy level formed by the doping ions,which can reduce the effective optical gap,thereby improving the visible light absorption capacity.Besides,the doped ions can also combine photogenerated electrons or holes to inhibit the occurrence of the composite process.In addition,Co²⁺doped ZnO nanowires exhibit better visible light absorption and lower photo-generated carrier recombination,and thus exhibit higher photocatalytic efficiency.However,in view of the fact that the improvement of visible light absorption capacity is still relatively limited by using only ion doping modification,this paper further utilizes successive ion layer adsorption reaction?SILAR?method to uniformly modify CuS nanoparticles on the surface of ZnO nanowires to form p-n heterojunctions,and further explored the effect of the amount of modified CuS on the photocatalytic performance of ZnO nanowires.In the CuS/ZnO heterojunction,photogenerated electrons and photogenerated holes can separate into different materials,which means the recombination of photo-excited carrier pairs can be successfully suppressed.The CuS has a band gap of only 2.2 eV and therefore can act as a visible light absorbing material to enhance the overall structure.It was found that the combination of Co²⁺doping and CuS coupling has higher photocatalytic performance for ZnO nanowires than using Co²⁺doping or CuS composite modification alone.The optimum amount of CuS modification was found.The sample ZnO:Co-CuS-10 exhibited 10 times of SILAR cycle exhibited the best performance.