Preparation Of PLNPs@COFs Composites And Their Photocatalytic Properties

With the industrialisation of human society,more and more energy problems and environmental issues have emerged.Photocatalysis,as a green technology that directly converts solar energy into chemical energy,is considered to be one of the promising and effective means to solve these problems.As one of the typical long afterglow nanomaterials（PLNPs）,Zn₂Ge O₄:Mn²⁺not only has the ability to store light energy and release the stored light energy through afterglow luminescence as PLNPs,but also has the advantages of good redox ability and strong stability.The application in the field of photocatalysis has great potential.To this end we have carried out a two-part work to modify Zn₂Ge O₄:Mn²⁺to improve its performance.The detailed work is as follows:1.Zn_1.99-xGe O₄:Mn_0.01,Li_x（x=0,0.1,0.2,0.3）（ZGO:Mn,Li）series materials co-doped with different concentrations of Li⁺were firstly prepared by a combined hydrothermal-calcination method.The morphological characterisation results show that the synthesised PLNP is a rod-like structure of about 400 nm.The optical characterisation results show that the doping of Li⁺enhances the photoluminescence and afterglow of Zn_1.99Ge O₄:Mn_0.01.Zn_1.79Ge O₄:Mn_0.01/Li_0.2 has the best effect and can produce afterglow for tens of hours after excitation,with the emission light concentrated in the visible region around 530 nm.The photocatalytic degradation experiments and the photocatalytic hydrogen production experiments showed that the doping of Li⁺enhanced the photocatalytic performance of Zn_1.99Ge O₄:Mn_0.01,with Zn_1.79Ge O₄:Mn_0.01/Li_0.2 being the best,and the degradation rate of rhodamine B was 1.8 times higher than that of unmodified.The photocatalytic hydrogen production rate was 0.38 mmol?h^-1?g^-1,which was 1.5 times higher than that of unmodified.2.In order to further broaden the light absorption range and increase the specific surface area of the materials,covalent organic skeletal materials（COFs）with good light absorption and high specific area were selected to form composites with PLNPs.The PLNPs@COFs composites with different mass ratios of core-shell structure were prepared by a two-step hydrothermal method.The morphological characterisation results showed that the two formed a good core-shell structure,with the COFs uniformly wrapped around the surface of the PLNPs and tightly bonded between them.The solid UV absorption test shows that the introduction of COFs compensates for the lack of light trapping ability of PLNPs,and the photocatalytic degradation and hydrogen production experiments show that the photocatalytic degradation performance and hydrogen production performance of the composites with COFs are significantly improved.The composite achieved a maximum degradation rate of 100%for Rh B in 50 minutes.Hydrogen production rates of up to 34.77mmol?h^-1?g^-1 were achieved,compared to 0.38 mmol?h^-1?g^-1 and 26.97 mmol?h^-1?g^-1 for PLNPs and COFs alone,respectively.We provide a method to bind PLNPs to COFs.A stable core-shell heterogeneous structure was formed between the two.The composite combines the advantages of PLNPs and COFs,possesses excellent light absorption,good adsorption,strong redox ability,exhibits excellent photocatalytic degradation performance and photocatalytic hydrogen production performance,and has great potential for photocatalytic applications.