Study On Activity Of Coated Z-scheme Photocatalyst With Core-shell Structure And Photoconversion Property

In order to supply the necessary energy for human production activities,the exploitation of traditional fossil fuel has increased rapidly,which has caused the global energy crisis.In addition,the vigorous development of the printing and dyeing industry has led to environmental pollution that can not be ignored.Therefore,sustainable energy supply and environmental protection have become two main challenges in the process of social development.As a non-polluting renewable source,hydrogen is expected to replace traditional fossil energy.Photocatalytic decomposition of water for hydrogen production is one of the most promising hydrogen production technologies.However,for a single photocatalyst combined with solar energy,it is very difficult to produce hydrogen through photocatalytic water splitting.If some substances with strong reducibility are used as sacrificial agents,especially organic pollutants in dye wastewater,high-efficient hydrogen production and purification of the wastewater can both be achieved.At present,many semiconductor materials have been widely applied for photocatalytic reactions,but there are still some problems,such as low utilization rate of sunlight and easy recombination of photo-generated carriers.It is an effective way to enhance the photocatalytic activity by combining two or more monomer photocatalysts with matching band gaps to construct a Z-scheme photocatalytic system.Furthermore,after appropriate modification,Z-scheme photocatalyst can not only broaden the light response range,but also make the photocatalysts synchronously have strong oxidation and reduction capacities,achieving efficient removal of organic pollutants and hydrogen production.Thus,it is of great significance to develop a Z-scheme photocatalyst with low recombination rate of electron-hole pairs and full utilization of sunlight.In this study,a novel coated Z-scheme Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd@Ni O photocatalyst with core-shell structure is prepared by hydrothermal,coprecipitation and calcination methods.In this Z-scheme photocatalyst,Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺as an excellent up-conversion luminescence agent can convert low-energy infrared light into high-energy visible light,broadening Cd S light response range.The introduced Pd nanorods act as conductive channels and co-catalysts,leading to successful construction of a coated Z-scheme photocatalytic system with core-shell structure.Core-shell structure increases contact area between two monomer photocatalysts,promoting the transfer of photo-generated electrons.It also provides a large oxidation surface for organic pollutant degradation.The performance of prepared photocatalyst is assessed by Congo red degradation and simultaneous hydrogen production.Some affecting factors such as Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd and Ni O mass ratio,sunlight irradiation time,pollutant initial concentration and photocatalyst used times are studied.The emission light spectrum and energy conversion mechanism of Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺are also investigated.The possible mechanism of CR degradation with synchronous hydrogen production caused by Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd@Ni O photocatalyst is discussed.The results prove that the coated Z-scheme Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd@Ni O photocatalyst with core-shell structure(3:1 mass ratio of Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd and Ni O)has a preeminent photocatalytic activity.Congo red degradation ratio and hydrogen production amount reach 92.48%and653.06μmol/g,respectively,under sunlight irradiation for 180 min.Moreover,this photocatalyst shows excellent stability in five cycles.It can be considered that the coated Z-scheme Na Gd F₄:Nd³⁺,Yb³⁺,Tm³⁺@Cd S-Pd@Ni O photocatalyst with core-shell structure in this research may have broad application spaces in the treatment of organic pollutant wastewater using solar energy and the production of clean energy.