Preparation Of Photocatalytic Materials Of CdS And Mn-Cd-S Solid Solutions And Their Application In Photocatalytic Hydrogen Production

The energy given by nature like oil and natural gas is consumed faster than expected and will be used up in the next 50 years.The massive use of these energy sources has caused tens of thousands of pollution,and it has also caused some damage to the environment.We need clean renewable energy and excellent technology to protect the environment.Hydrogen energy is considered to be an ideal solution to this big problem because of its clean,pollution-free,wide source,and high combustion calorific value.Its product is water after burning,which does not have any bad influence on the environment and meets our needs.Therefore,the development of hydrogen energy,has a significant impact not only in China but also in the world today.Cadmium sulfide?CdS?materials,due to their proper conduction band position,have strong reducing ability and can catalyze the hydrogen production under visible light irradiation.By modifying the crystal structure,composition and morphology of the CdS,the electronic energy level structure and position of the conduction band and valence band can be slightly adjusted to improve the hydrogen production efficiency.In this paper,CdS and Mn_xCd_1-x-x S photocatalysts were synthesized by hydrothermal method.Using photocatalytic water splitting as a reaction model,their visible light photocatalytic properties were investigated.In addition,X-ray powder diffractometry,scanning electron microscopy,transmission electron microscopy,ultraviolet-visible diffuse reflectance spectroscopy,X-ray photoelectron spectroscopy,fluorescence spectroscopy,N₂ adsorption-desorption,etc.,are used to test the composition,structure,and absorption edge of the catalyst,photoresponse,the chemical state of surface elements,specific surface area and band structure were characterized in detail.The results show that:1.The results indicated that hexagonal branched dendritic structure CdS?S-TA?could be produced in TA solution and showed the highest HER activity due to the branched 1D structure,the smallest interfacial electron transfer resistance and the most negative conduction band bottom(E_cb).Whereas in TAA,spherical CdS?S-TAA?with a mixed phase of hexagonal and cubic was obtained.The mixed phase structure and the more positive E_cbb of S-TAA lead to a considerably lower HER activity than that of S-TA.Low crystallized hexagonal CdS nanoparticles?S-Cys?were prepared in L-Cys and showed the lowest HER performance as its E_cbb is very near to H⁺reduction potential.Thus,compared to T-AA and L-Cys,TA is a more suitable sulfur source for hydrothermal preparation of highly active CdS for HER.2.The results indicated that TA and L-Cys favor the formation of the hexagonal phase MCS and the end-members?i.e.CdS and MnS?,while TAA benefits their formation in the cubic phase.Compared to TA and L-Cys,TAA is the preferred sulfur source for the preparation of highly active MCS.The consolidation of cubic?-MnS into cubic CdS results in the formation of MCS.The activity of MCS is significantly improved with the increase of Mn content from x=0 to 0.6.MCS with x=0.6 shows the highest HER performance.The enhanced activity can be attributed to the improved separation efficiency of photo-induced charge carriers and the negative-shift of E_cb,which are induced by the introduction of Mn.A segregation of inert?-MnS from MCS is occurred when Mn content is larger than 0.6,resulting in a decay of the HER activity.Besides,with the incorporation of MnS into CdS,a change of the semiconductivity from n-type to bipolar type is found in MCS.It should be caused by the uneven sulfidation of Mn in MCS.This study shows that sulfur sources have an important influence on the structure and properties of sulfide-based photocatalytic materials,and that sufficient attention should be given to the preparation of such visible light photocatalytic materials.The relevant conclusions obtained by the research institute can be the theoretical basis and experimental reference for the development of efficient sulfide-based photocatalytic materials.