Controllable Synthesis And Photocatalytic Properties Of Quaternary Cu-Ga-Zn-S Nanocrystals

Copper-based chalcogenides have an adjustable absorption band gap and diverse structures as well as environmental friendliness,which makes them have a very wide application prospect in the fields of optoelectronic devices and photocatalysis.At present,photocatalytic water decomposition technology is one of the most promising new energy solutions,and the characteristics of copper-based chalcogenides make them of great potential value in photocatalytic applications.Previous studies have shown that the quaternary Cu-Ga-Zn-S nanocrystals have considerable photocatalytic properties,but there is a lack of in-depth research on them.In the thesis,controlled-synthesis of quaternary Cu-Ga-Zn-S nanocrystals with different phases and morphologies was studied in detail,and the photocatalytic hydrogen evolution was studied.Besides,the photocatalytic oxygen evolution was also explored.The specific research contents are as follows:Firstly,the quaternary Cu-Ga-Zn-S nanocrystals with the wurtzite structure were sytnehsized,and then the effects of different Ga/Zn ratios on the morphology owere studied.Then the effects of the Zn content on the photocatalytic hydrogen evolution performance were studied,and the results showed that the best photocatalytic performance of the sample was obtained at a Ga/Zn ratio of 7:1.It was found that ternary Cu-Ga-S nanocrystals had low photocatalytic performance due to the presence of Cu vacancies energy level,which had a negative effect on the photocatalytic properties,and the Cu vacancies could be vanished with the incorporation of of Zn elements.However,high Zn content could reduce the optical absorption band gap,which made against for the photocatalytic performance.Therefore,fonly a moderate Zn content could lead to an optimized photocatalytic performance of Cu-Ga-Zn-S nanocrystals.Finally,the quaternary Cu-Ga-Zn-S nanocrystal was presumed to have the ability of photocatalytic oxygen production according to its energy level structure,and the oxygen evolution experiment supported the deduction.Secondly,the morphology and phase of quaternary Cu-Ga-Zn-S nanocrystals was regulated by tuning the types of anions in copper precursors,solvents and Cu contents.In terms of morphology regulation,the introduction of different anions made the morphology vary from rod-like,hexagonal-like to triangular particles.Moreover,the crystal phase could be regulated by varying the content of Cu precursor,and the samples with different crystal phases including blende,wurtzite and digenite were synthesized,respectively.The results showed that the formation process of nanocrystals could be divided into three stages: precursor decomposition,nucleation and growth.The different Cu contents could directly affect the crystal structure in the nucleation and growth stages.In addition,the change of the types of anions in Cu precursors could also affect the precursor decomposition stage and thus affected the tuing of the crystal structure.Finally,the photocatalytic hydrogen evolution properties of the Cu-Ga-Zn-S nanocrystals with different crystal phases were compared,and the results showed that the Cu-Ga-Zn-S nanocrystals with blende structure had better performance.