Study On The Fabrication Of One-dimensional Cadmium Sulphide Based Heterostructures And Their Properties Of Hydrogen Generation From Photolycatalytic Water Splitting

The excessive exploitation and consumption of traditional fossil fuels have led to serious energy crisis and environmental pollution.Therefore,the development of environmental friendly renewable new energy instead of non-renewable energy has become a major focus of global attention.Scientists have found that photocatalytic hydrogen evolution from water splitting can be realized on some semiconductors.Solar energy can be converted into high-calorific value and clean hydrogen energy,which is expected to solve the two major problems of energy and environment simultaneously,so it has a very important significance.With special energy band structure and photogenerated carrier transport properties,semiconductor heterojunction materials can effectively improve separation of photogenerated electron-hole pairs,thus improving the quantum efficiency,which have become the focus of photocatalytic materials.Cadmium sulfide?CdS?is a highly effective visible light responsive semiconductor due to its negative conduction band position and narrow band gap,which has attracted great attention in the field of solar energy conversion.However,because of its direct band gap,CdS is to take photogenerated electron-hole pairs recombination and photocorrosion easily.Therefore,it is urgent to improve the activity and stability of photocatalytic hydrogen evolution of CdS.On the basis of the inherent structural advantages of one-dimensional CdS nanowires,different kinds of transition metal sulfide catalysts were constructed on the surface of CdS to form nanoheterostructure composite materials.By regulating the kind and loading content of the cocatalyst,the mechanism of enhancing the performance of the synthesized composite catalyst was analyzed from the perspective of crystal structure and optical propert using various characterization technologies.In addition,the hydrogen evolution behavior of employing different biomass?i.e.,glucose,lignin,cellulose?as sacrifice reagent was preliminarily explored.Hydrogen evolution are combined effectively by photocatalytic water splitting and photocatalytic biomass reforming,which provides a new idea for obtaining economic and environmental sustainable energy.The specific content mainly includes the following aspects:Firstly,two-dimensional MoS₂ was fabricated in situ on the surface of one-dimensional CdS nanowires by two-step method.The properties of nanocomposites are strongly depended on the MoS₂ content.The optimal amount of MoS₂?5%mol of MoS₂ loading?results in the most enhanced photoelectrochemical?PEC?and photocatalytic hydrogen evolution reaction?HER?.Compared with pure CdS NWs,the the5%-MoS₂/CdS nanocomposite shows 5.5 times enhancement in photocurrent intensity and86.3 times increase in the glucose and lactic acid as hole scavengers.The enhancement of the PEC and HER properties of the MoS₂/CdS nanocomposite can be attributed to the close contact between the MoS₂ and the CdS at its interface,thus forming heterojunction and promoting the separation of charge carrier.In addition,transient absorption spectroscopy was used to probe the charge carrier dynamics in the catalyst,which further revealed the mechanism of PEC and HER performance enhancement of the composite catalyst.Secondly,uniform one-dimensional NiS/CdS nanocomposites using NiS nanoparticles loaded on the surface of CdS nanowires were constructed by two-step solvothermal synthesis.The synergistic interaction between CdS and NiS at the interface through close contact effectively enhanced the separation of photogenerated charge carriers.At the same time,NiS,as a non-noble metal cocatalyst,provided more reactive sites for HER.Therefore,compared with bare CdS nanowires,one-dimensional NiS/CdS nanocomposites exhibited stronger hydrogen evolution activity under visible light driven.When lactic acid and lignin were used together as sacrifice reagents,the photoactivity of 0.2-NiS/CdS was5041 times that of the pure CdS,and its apparent quantum efficiency was as high as 44.9%.In addition,the transient femtosecond absorption spectroscopy?TA?technique was used to detect the dynamic of charge carriers in the prepared catalyst.The results reveal the mechanism of enhanced photocatalytic activity of NiS/CdS composites.The results showed when the molar ratio of NiS/CdS is 0.2,the average carrier life of CdS nanowires by 97 times,indicating that there was an efficient charge separation and transfer process in0.2-NiS/CdS structure.However,further increase NiS amount reversely promoted the recombination of photogenerated electron-hole pairs,which resulted in the shorter lifetime of photogenerated carriers.It was mainly attributed to the serious aggregation of excessive NiS nanoparticles on CdS surface,which turned into the recombination center of photogenerated electron-hole pairs.In addition,the results of TA obtained by transient absorption spectrometry are consistent with the variation tendency of hydrogen evolution,indicating that longer carrier life can make better the of hydrogen evolution performance.This work demonstrates a simple and controllable method to synthesize well-shaped one-dimensional nanocomposite photocatalyst,which provides reference for visible-light-driven energy conversion,particularly involving the use of biomass.Thirdly,Ni₃S₂/CdS nanocomposites were synthesized by two-step method with one-dimensional CdS nanowires as the matrix.Under visible light irradiation???400 nm?,Ni₃S₂/CdS nanocomposites show higher photocatalytic hydrogen evolution performance than pure CdS nanowires or Ni₃S₂ nanoparticles.The photochemical and photocatalytic properties of Ni₃S₂/CdS nanocomposites were studied as a function of the molar ratio between Ni₃S₂ and CdS.In addition,ultrafast transient absorption?TA?spectroscopy was used to study the charge carrier dynamics in 10%-Ni₃S₂/CdS,and the time was 4 times shorter than that of pure CdS NWs.These results indicate there is effective charge transfer between CdS and Ni₃S₂ on the interface,which enhances its photochemical and photocatalytic proterties of the composite catalysts.Fourthly,1D NiCo₂S₄/CdS nanocomposites have been successfully synthesized using a two-step hydrothermal strategy.The morphology,structure,optical properties and photochemical response of prepared samples are systematically analyzed.These results reveal that metallic NiCo₂S₄ NPs and CdS NWs form Schottky junction in their interface.Besides,with the unique intrinsic properties,NiCo₂S₄,as cocatalysts,can simultaneously enhance the visible-light harvest and improve the water reduction.By carefully regulating NiCo₂S₄ content,we conclude that 10%-NiCo₂S₄/CdS nanocomposite exhibits the highest H₂ evolution rate(20.0 mmol·h^-1·g^-1),which is hundreds of times higher than that of pristine CdS NWs,and Hydrogen evolution was also observed in aqueous solution of cellulose.The strategy developed in this work can provide useful reference for other visible-light-driven photocatalysis systems to construct noble-metal-free nanocomposites.