Co-catalyst Modification Of Mn_xCd_1-xS And Its Photocatalytic Hydrogen Production Performance

The development and utilization of clean and renewable energy is the key to solve the two significant issues of energy crisis and environmental pollution.Hydrogen energy is known as the most prospective green energy in the 21st century because of its high combustion calorific value,high energy density,clean and non-polluting advantages.The semiconductor photocatalytic hydrogen evolution technology is an effective approach to convert solar energy into hydrogen energy,which is considered to be the most ideal way to develop hydrogen energy,matching the modern industrial needs and the concept of sustainable development.The core of this technology is the semiconductor photocatalyst,but most of the developed semiconductor photocatalysts have narrow light absorption range,high photogenerated carrier recombination rate and low quantum yield,etc.MnxCd1-xS solid solution can respond to visible light,meanwhile,its forbidden band width and energy band potential are tunable,which has attracted much attention in the field of photocatalytic hydrogen production.In the present study,MnxCd1-xS solid solutions with cauliflower-like nanosphere morphology were synthesized by morphology controlling,then Ni2P and ReS2 were loaded on the surface of MnxCd1-xS by co-catalyst modification.The Ni2P/Mn0.2Cd0.8S and ReS2/Mn0.2Cd0.2S composite photocatalysts were prepared to improve the photocatalytic hydrogen production performance of MnxCd1-xS by enhancing the separation efficiency of photogenerated charges and providing sufficient active sites for hydrogen production reactions.In a related study,the materials were thoroughly characterized and the photocatalytic hydrogen production activities were evaluated.At last,its photogenerated carrier separation mechanism and photocatalytic hydrogen production mechanism were explored.The specific works are shown below.In part one,a series of MnxCd1-xS solid solutions with cauliflower-like nanosphere morphology were prepared via a simple hydrothermal method,and the influence of the Mn/Cd ratio of the solid solutions on their photocatalytic hydrogen production activity was investigated.The results indicated that Mn0.2Cd0.8S has the best photocatalytic hydrogen production performance with a hydrogen production rate of 1.71 mmol g-1 h-1,which was approximately a 4-fold improvement over that of CdS.In the second part,using Mn0.2Cd0.8S solid solution with the highest hydrogen production activity as the substrate,novel Ni2P/Mn0.2Cd0.8S composite photocatalysts were obtained by means of in-situ loading Ni2P co-catalysts onto the surface of Mn0.2Cd0.8S via a facile hydrothermal method,and their hydrogen production performance under visible light(λ≥420 nm)was evaluated.The results confirmed that the hydrogen production performance of the cauliflower-like Mn0.2Cd0.8S nanospheres loaded with different amounts of Ni2O nanoparticles was significantly enhanced,in which the 3 wt%Ni2P/Mn0 2Cd0.8S composite had the highest hydrogen production rate(14.20 mmol g-1 h-1),which was approximately a 8.3-fold improvement over that of the pure Mno2Cd0.8S nanospheres.Furthermore,the hydrogen production activity of Ni2P/Mn0.2Cd0.8S composite was higher than the Mn0.2Cd0.8S respectively loaded with Ni,Ni2S,Ni(OH)2,NiB,NiSe2,etc.as co-catalysts.The photoelectrochemical analysis showed that using Ni2P as a co-catalyst was beneficial to promote the separation of photogenerated charges as well as provide sufficient active sites for the hydrogen production reaction,thus enhancing the hydrogen production activity of the composites.In the third part,using the Mn0.2Cd0.8S solid solution with the highest hydrogen production activity as the substrate,a novel ReS2/M0.2Cd0.8S composite was obtained by in-situ loading ReS2 as co-catalyst onto the surface of Mn0.2Cd0.8S via a simple hydrothermal method.The catalyst was evaluated for its hydrogen production performance under visible light(λ≥ 420 nm).The results confirmed that the 5 wt%ReS2/Mn0.2Cd0.8S composite had the highest hydrogen production rate(17.31 mmol g-1 h-1),which was approximately a 10-fold improvement over that of pure Mn0.2Cd0.8S nanospheres.The significantly enhanced hydrogen production activity of the composite photocatalyst could be attributed to the modification of the ReS2 co-catalyst,and the loading of ReS2 nanosheets with a two-dimensional layered structure onto the surface of cauliflower-like Mn0.2Cd0.8S nanospheres can enhance the light absorption of the semiconductors.It can also promote the separation of photogenerated charges and provide sufficient actiye sites for the hydrogen production reaction,finally greatly improving the photocatalytic hydrogen production performance of Mn0.2Cd0.8S nanospheres.