Study On The Modification Of Cadmiun,Bismuth Based Semiconductor Nanomaterials And Its Photocatalytic Performance

Since the industrial revolution,the exploitation and utilization of coal,oil and,oil and natural gas have greatly promoted the development of human society,but the problems of environmental pollution caused by excessive use of fossil energy,global greenhouse effect and energy depletion have become increasingly serious.The emergence of these problems has prompted people to increase their efforts to research and develop new green energy.Solar energy has the advantages of clean and inexhaustible,so the technology that can effectively utilize solar energy is considered as a feasible solution to solve the energy crisis and alleviate environmental pollution.Among the emerging technologies using solar energy,photocatalytic technology stands out.Photocatalysis is a green technology that converts solar energy into chemical energy under light conditions using semiconductor photocatalysts.In recent years,in addition to wastewater treatment,it has also been widely studied in water spiliting to produce hydrogen and oxygen,as well as nitrogen fixation,carbon dioxide conversion to carbon monoxide,methane and other available chemicals.The preparation of semiconductor photocatalysts is a key factor in the application of this technology.Traditional photocatalyst,such as:TiO₂,Bi₂WO₆,BiVO₄,CdS,etc.,have low photocatalytic performance due to some problems.?1?Large band gap such as TiO₂,ZnO makes their limited use of visible light and they can only respond in the ultraviolet region.Therefore,improving the utilization of sunlight is one of the problems to be solved.?2?The photocatalysts,represented by CdS and Cu₂O have good visible light utilization,but they are not very stable and are prone to photocorrosion.Furthermore,the recombination of photo-generated electrons and holes is also very serious.Therefore,avoiding carrier recombination and improving the separation efficiency of electrons and holes is another subject to be solved.This article selects cadmium sulfide and bismuth tungstate as the main research materials,exploring several semiconductor modification methods to achieve the efficient separation of photo-generated carriers,thereby promoting its photocatalytic performance:1.Introduce built-in electric field and CoP cocatalyst by one-step method to promote photocatalytic hydrogen production performance of CdS nanorodsThis chapter mainly introduces the gradient doping of P and loading the co-catalyst CoP in cadmium sulfide nanorods by one step.The introduction of P gradient doping successfully builds a built-in electric field causing the directional movement of electrons,which promotes the efficient separation of carriers in the cadmium sulfide nanorods.Meanwhile,loading CoP forms Schottky barrier allowing the separated electrons transferred to the cocatalyst again,further realizing the separation of photogenerated carriers.Through testing,it was found that the 7%CoP/CdS-P₆ photocatalyst produce hydrogen from water was as high as 22.95 mmol·h^-1·g^-1,which was 3.17 times and 18.36 times higher than that of CdS-P₆ and CdS alone.The enhanced performance of the final sample is mainly due to the efficient separation of carriers in the cadmium sulfide nanorods.2.Build?-FeOOH/CdS heterojunction to improve photocatalytic water oxidation and nitrogen fixation performanceThis work mainly introduces the construction of heterostructures to improve the photocatalytic performance of nano-semiconductor materials.CdS nanoparticles were grown on a pre-formed shuttle-shape?-FeOOH nanomaterial through a simple and mild one-step wet-chemical method,and thus type-II heterojunction?-FeOOH/CdS nanocomposite was successfully constructed.Thanks to excellent interface contact and energy band matching,?-FeOOH/CdS nanocomposites not only achieve efficient separation of carriers,but also differ from half of the carrier recombination consumption in Z-type heterojunctions.The reaction realizes the efficient use of carriers and improves the efficient use of solar energy.The photocatalytic experiments showed that the performance of the optimal ratio composite material?-FeOOH/CdS-1 was 785?mol h^-11 g^-1,which are 5.16 times and 20.66 times higher than that of pure?-FeOOH and CdS samples.At the same time,the nitrogen-fixing performance of?-FeOOH/CdS-1 samples under the full spectrum is 215.56?mol·h^-1·g^-1,which is 19.8 times and6.29 times than that of pure?-FeOOH and CdS samples.3.Regulate morphology to achieve electron-hole transfer to different crystal planes and improve the photocatalytic performance of Bi₂WO₆This chapter mainly introduces the morphology of Bi₂WO₆ can be adjusted from the assembled balls of nanosheets to the dispersed nanosheets of different thickness by adjusting the pH value of the reaction solution.Electrons and holes are transferred to different crystal planes on the nanosheets respectively,which promotes the separation of carriers in space.At the same time,as the thickness changes,the twist and asymmetry of the W-O bond in the[WO₄]^2-octahedron increases,and the local built-in electric field is enhanced correspondingly,which improves the separation ability of photo-generated electron-hole pairs and the photocatalytic performance.The prepared Bi₂WO₆ nanomaterials show high photocatalytic oxygen generation activity under visible light irradiation,and also achieve hydrogen production activity under full spectrum irradiation.