Preparation And Photocatalytic Propertiesof Sulfide-based Composite Photocatalyst

The consumption of fossil fuels will not only trigger an energy crisis,but also cause environmental pollution problems.Therefore,looking for a clean,renewable energy source is an urgent problem in nowadays society.In recent years,photocatalytic water splitting for hydrogen evolution technology can directly convert solar energy into hydrogen energy.The key to photocatalytic water splitting for hydrogen evolution is the design of photocatalysts,if novel photocatalysts with visible light response can be utilized for water splitting for hydrogen evolution by using solar energy,the energy crisis and environmental problems will be solved.At present,the photocatalytic hydrogen production activity and stability of most photocatalysts under visible light irradiation are still low,and they could not meet the requirements for industrial production.Therefore,it is of great significance to develop an efficient and stable photocatalyst with visible light respose for photocatalytic water splitting for hydrogen evolution.In this dissertation,the preparation and photocatalytic properties of the Bi₂MoO₆/Mn_0.2Cd_0.8S,UT-MoS₂/Mn_0.2Cd_0.8S and CdLa₂S₄/ZnIn₂S₄ composite photocatalysts were systematically studied also.The detailed research contents are shown as follows:?1?A series of Mn_xCd_1-x-x S?x=0-1?solid solution photocatalysts were synthesized via a co-precipitation followed by a hydrothermal method.The results show that the optimal decomposition water for hydrogen evolution rate of 1633?mol·g^-1·h^-11 was achieved when the value of x is 0.2 in Mn_xCd_1-x-x S composites,which is about 3.2 times higher than of that blank CdS.Subsequently,Bi₂MoO₆/Mn_0.2Cd_0.8S composites with different mass ratio of Bi₂MoO₆ to Mn_0.2Cd_0.8S were synthesized via a hydrothermal method.The composition,structure and light absorption properties of theobtainedsampleswerecharacterizedbyX-raydiffraction?XRD?,ultraviolet-visible diffuse reflection spectroscopy?UV-vis DRS?,scanning electron microscope?SEM?,transmission electron microscopy?TEM?,high-resolution transmission microscopy?HRTEM?,X-ray photoelectron spectroscopy?XPS?and photoluminescence?PL?emission spectrum,respectively.The effects of different mass ratio of Bi₂MoO₆ on photocatalytic activity for hydrogen production from aqueous solution containing Na₂S and Na₂SO₃ as sacrificial reagents under visible light??>420 nm?irradiation were researched.The experimental results show that the highest photocatalytic hydrogen production rate of 4700?mol·g^-1·h^-11 in Bi₂MoO₆/Mn_0.2Cd_0.8S composite was achieved when the weight ratio of Bi₂MoO₆ is5%of Mn_0.2Cd_0.8S,which was 2.9 times higher than that of pure Mn_0.2Cd_0.8S under the same experimental condition.The enhanced photocatalytic activity of composites might be attributed to the well-matched band structure of Bi₂MoO₆ and Mn_0.2Cd_0.8S.Meanwhile,the Bi₂MoO₆/Mn_0.2Cd_0.8S composites showed good stability during the process of hydrogen production from water.?2?Mn_0.2Cd_0.8S nanoparticles decorated with ultrathin?UT?MoS₂ nanosheets were synthesized by a ultrasonic exfoliation assisted hydrothermal method.The composition,structure and light absorption properties of the as-prepared samples were characterized by XRD,FE-SEM,TEM,HRTEM,XPS,BET,UV-vis DRS,and PL,respectively,and their photocatalytic activities of hydrogen evolution from water was analyzed.The experimental results show that the UT-MoS₂/Mn_0.2Cd_0.8S composites exhibit higher photocatalytic hydrogen evolution activity than pure Mn_0.2Cd_0.8S from aqueous solution,when Na₂S and Na₂SO₃ were used as sacrificial reagents and with visible light??>420 nm?irradiation.The optimal weight ratio of UT-MoS₂ was 6%of Mn_0.2Cd_0.8S in UT-MoS₂/Mn_0.2Cd_0.8S composites,and the corresponding photocatalytic hydrogen production rate was 13187?mol·g^-1·h^-1,which was 8.1 and2.3 times higher than that of pristine Mn_0.2Cd_0.8S and Pt?1wt.%?/Mn_0.2Cd_0.8S under the same experimental condition,respectively.Moreover,the UT-MoS₂/Mn_0.2Cd_0.8S composites displayed good stability during the process of photocatalyticr hydrogen evolution from water.The possible photocatalytic mechanism is as follows:the UT-MoS₂ was used a cocatalyst to provide more active sites for photo-generated electrons,which can effectively promoted the separation of photo-generated electron andholepairs,thephotocatalytichydrogenevolutionactivityof UT-MoS₂/Mn_0.2Cd_0.8S composites has been significantly improved.?3?A series of CdLa₂S₄/ZnIn₂S₄ heterojunction photocatalysts with different weight ratio of CdLa₂S₄ to ZnIn₂S₄ were prepared by a solvothermal method.The composition,structure and light absorption property of the as-prepared samples were characterized by XRD,FE-SEM,TEM,HRTEM,XPS,UV-vis DRS,and PL,respectively,and their photocatalytic activities of hydrogen evolution from water was analyzed.The experimental results show that the photocatalytic hydrogen production activity of CdLa₂S₄/ZnIn₂S₄ heterojunction photocatalysts is significantly improved under visible light irradiation comparing with pure CdLa₂S₄ and ZnIn₂S₄.The maximum photocatalytic hydrogen evolution rate of CdLa₂S₄/ZnIn₂S₄ heterojunction photocatalyst was achieved to be around 1181?mol·g^-1·h^-11 when the weight ratio of CdLa₂S₄ to ZnIn₂S₄ was 15%,which was 5.1 and 4.3 times higher than that of blank CdLa₂S₄ and ZnIn₂S₄ under the same experimental condition.Meanwhile,the CdLa₂S₄/ZnIn₂S₄heterojunctionphotocatalystsexhibitedgoodstabilityof photocatalytic hydrogen production.The heterojunction photocatalyst with a staggered band gap and a close contact interface can promote the separation of photo-generated electron and hole pairs to same extents,which will enhance their photocatalytic hydrogen evolution activity accordingly.