【作者】 叶燕珠；

【导师】 林深；

【作者基本信息】 福建师范大学 ， 物理化学， 2022， 博士

【摘要】 当前,环境污染与能源危机已成为困扰人类发展的两大问题。因此,开发洁净的、可持续的能源显得尤为重要。氢能是一种洁净、高效的能源,地球上有丰富的太阳能资源,通过光催化分解水制氢将太阳能转化为氢能,有望成为解决能源危机的有效途径之一。虽然太阳能是一种取之不尽的理想能源,但是由于其有限的利用率和能量转化率限制了其实际的应用。因此开发高活性的可见光响应型光催化剂是实现太阳能有效利用的重要途径。半导体光催化剂因其独特的物理化学性能,在材料科学、化学、环境科学等众多领域得到了广泛的应用。金属硫化物固溶体是一类半导体光催化剂材料,可通过整体改变其能带结构,实现对其禁带宽度和能带电位的精确调控,使材料的光吸收能力和氧化还原电位达到最佳平衡。近年来,金属硫化物固溶体在光解水制氢方面受到越来越多的关注,已成为该领域的研究热点之一。基于单一组份的Zn_xCd_1-xS固溶体存在光生载流子容易复合、催化性能不稳定、产氢效率不高等系列问题。本论文通过构筑异质结、添加第二组份助催化剂等途径合成了Zn WO₄/Zn_0.4Cd_0.6S、Co₃O₄/Zn_0.4Cd_0.6S、CoP₃/Zn_0.4Cd_0.6S和Ni CoP/Zn_0.4Cd_0.6S四种Zn_xCd_1-xS固溶体基复合光催化剂,通过XRD、XPS、ICP、SEM、TEM、HRTEM、UV-Vis、BET等多种表征手段分析了其组成、结构、形貌和价态,并对其在光解水制氢中的催化活性和光催化机理进行了系统的研究。研究结果表明:这四种复合物均对可见光响应,第二组份的添加有效促进了光生载流子的迁移和分离,且明显增加了光催化分解水制氢反应的活性位点,从而提升了Zn_xCd_1-xS固溶体的光催化活性。实验研究成果如下::（1）通过溶剂热法合成了一系列不同Zn和Cd组份比的Zn_xCd_1-xS（0≤x≤1）,探讨了Zn和Cd组份比对其光解水制氢活性的影响,遴选出了催化活性最佳的Zn_0.4Cd_0.6S固溶体。在此基础上,通过水热法将Zn WO₄原位负载于Zn_0.4Cd_0.6S固溶体上,构筑p-n型Zn WO₄/Zn_0.4Cd_0.6S异质结光催化剂。进一步通过调节Zn WO₄和Zn_0.4Cd_0.6S的组份比,测试不同Zn WO₄负载量对复合物光催化活性的影响。研究结果显示:相对于单一的Zn_0.4Cd_0.6S固溶体,Zn WO₄/Zn_0.4Cd_0.6S复合物的光催化活性有较大的提升,且Zn WO₄的负载量对复合物的催化活性有较大的影响。当Zn WO₄的负载量为60 wt%时,复合物的光催化活性最高,光解水制氢速率可达39.12 mmol g^-1h^-1,是单纯Zn_0.4Cd_0.6S固溶体的4.7倍,优于许多类似的复合物,该复合物在420 nm下的表观量子产率（AQE）为14.79%。而且,实验结果表明,复合物的催化稳定性明显优于单一组份的Zn_0.4Cd_0.6S固溶体。光催化作用机理研究结果表明,Zn WO₄/Zn_0.4Cd_0.6S复合物的光催化活性和稳定性的增强主要是由于Zn WO₄和Zn_0.4Cd_0.6S之间形成了p-n型异质结,光生载流子在内建电场的作用下加速了迁移和分离,从而使得其光催化性能显著提升。（2）通过简单的溶剂热法构筑了Co₃O₄/Zn_0.4Cd_0.6S p-n型异质结光催化剂,研究了一系列不同Co₃O₄负载量的复合物在可见光（λ≥420 nm）照射下的光催化活性。当Co₃O₄的添加量为4 wt%时,Co₃O₄/Zn_0.4Cd_0.6S具有最佳的光催化活性,光解水制氢的速率高达56.63 mmol g^-1h^-1（AQE为21.86%）,是Zn_0.4Cd_0.6S固溶体的6.8倍,且具有良好的稳定性,其光催化性能优于贵金属修饰的复合物(Pt@Co₃O₄/Ti O₂:19.2mmol h^-1g^-1)。p-n型异质结的构筑,有效促进了Co₃O₄/Zn_0.4Cd_0.6S复合物表面光生电子和光生空穴的分离和迁移,因此其光催化活性和稳定性显著增强。（3）采用溶剂热法合成了一系列不同CoP₃负载量的CoP₃/Zn_0.4Cd_0.6S复合光催化剂。探讨了不同组份比例的CoP₃/Zn_0.4Cd_0.6S复合物在光解水制氢中的催化性能,研究结果表明:引入CoP₃后,CoP₃/Zn_0.4Cd_0.6S复合物的光催化活性和稳定性均显著增强,且CoP₃的用量对CoP₃/Zn_0.4Cd_0.6S复合物的催化活性有很大的影响,1.0wt%-CoP₃/Zn_0.4Cd_0.6S复合物具有最高的光催化活性,其光解水制氢速率高达63.91mmol g^-1h^-1,是单纯Zn_0.4Cd_0.6S固溶体的7.6倍,是1.0 wt%-Pt/Zn_0.4Cd_0.6S(19.72 mmol g^-1h^-1)光解水制氢速率的3.2倍,该复合物在420 nm下的表观量子产率（AQE）达到26.03%。复合物的光催化活性明显优于许多磷化钴修饰的复合光催化剂,有望替代贵金属,成为价格低廉的非贵金属光催化剂广泛应用于光催化领域。CoP₃/Zn_0.4Cd_0.6S复合物催化性能的提升主要归因于助催化剂CoP₃的引入,为光解水制氢反应提供了更多的活性位点,同时可加速光生载流子向CoP₃迁移,有效提升光生载流子的分离效率并抑制光解水制氢的逆反应,进而提升其光解水制氢活性。（4）通过焙烧法合成了双金属磷化物Ni CoP修饰的Ni CoP/Zn_0.4Cd_0.6S复合光催化剂,以期通过Ni和Co的协同作用进一步提升复合物的光催化性能。实验结果表明,引入Ni CoP后,复合物的光催化活性有明显的提升。当Ni CoP的负载量为1wt%时,复合物的催化活性最高,光解水制氢速率可达48.87 mmol g^-1h^-1（AQE为16.10%）,是单纯Zn_0.4Cd_0.6S固溶体的5.8倍。与许多磷化钴镍修饰的复合光催化剂相比,该复合物具有较高的光催化活性和稳定性。更多还原

【Abstract】 At present,environmental pollution and energy crisis have become two major problems that perplex mankind.Therefore,it is particularly important to develop clean and renewable energy.Among many energy materials,hydrogen energy as a clean and efficient energy has attracted much attention.There are abundant solar energy resources on earth,and photocatalytic H₂evolution from water splitting with solar energy is expected to be an effective method to solve the energy crisis.Although solar energy is an ideal energy source,its practical application is limited by its low utilization and conversion rate.Therefore,the development of highly active and visible-light-sensitive photocatalysts is an important way to realize the effective utilization of solar energy.Due to the unique physicochemical properties,semiconductor photocatalysts have attracted much attention in many fields such as material science,chemistry and environmental science.Among them,metal sulphide solid solution is a promising semiconductor photocatalyst.The band gap width and band potential can be precisely regulated through the whole change of the band structure,resulting in the optimized balance of the light absorption ability and the redox potential in the material.In recent years,the application of metal sulphide solid solution in photocatalytic H₂evolution from water splitting has aroused a great deal of interest,becoming one of the research hotspots in this field.Based on a series of problems such as easy recombination of photogenerated carriers,poor photostability and low H₂evolution efficiency of single-component Zn_xCd_1-xS solid solution,four kinds of Zn_xCd_1-xS solid solution based composite photocatalysts,namely,Zn WO₄/Zn_0.4Cd_0.6S,Co₃O₄/Zn_0.4Cd_0.6S,CoP₃/Zn_0.4Cd_0.6S and Ni CoP/Zn_0.4Cd_0.6S were synthesized by the construction of heterojunction and loading co-catalyst.The composition,structure,morphology and valence state were analyzed by XRD,XPS,ICP,SEM,TEM,HRTEM,UV-VIS,BET and other analytical techniques.The photocatalytic activity and the photocatalytic mechanism of H₂evolution from water splitting on these composites were systematically studied.The results show that the four composites are all visible-light-sensitive photocatalysts,the enhanced photocatalytic activity of H₂evolution from water splitting maybe due to the significantly increased active sites and the efficient separation of photogenerating electrons and holes.The experimental research contents are as follows:（1）In the first part,a series of Zn_xCd_1-xS（0≤x≤1）with different Zn and Cd component ratio were synthesized by simple solvothermal method.The influence of Zn and Cd component ratio on the activity of photocatalytic H₂evolution from water splitting was discussed,and Zn_0.4Cd_0.6S was identified as the solid solution with the best photocatalytic activity.On this basis,Zn WO₄was loaded on Zn_0.4Cd_0.6S solid solution by in-situ hydrothermal method to construct Zn WO₄/Zn_0.4Cd_0.6S p-n heterojunction photocatalyst.The influence of different Zn WO₄loading content on photocatalytic H₂evolution from water splitting was tested by adjusting the composition ratio of Zn WO₄and Zn_0.4Cd_0.6S.The results show that the photocatalytic activity of Zn WO₄/Zn_0.4Cd_0.6S composite is significantly enhanced compared with single-component Zn_0.4Cd_0.6S solid solution,and the loading content of Zn WO₄effectively enhanced the photocatalytic activity of the composite..It was confirmed that when the loading content of Zn WO₄was60 wt%of the composite,the composite exhibits the optimal photocatalytic H₂evolution rate of 39.12 mmol g^-1h^-1（with a 14.79%apparent quantum efficiency at 420 nm）,which is 4.7 times higher than that of the single-component Zn_0.4Cd_0.6S solid solution.The photocatalytic activity of the composite is superior to that of many similar compounds.Moreover,the durability of Zn WO₄/Zn_0.4Cd_0.6S composite for photocatalytic H₂evolution from water splitting is significantly superior to that of Zn_0.4Cd_0.6S.Through the discussion of catalytic mechanism,it can be concluded that the enhancement of photocatalytic activity and durability of Zn WO₄/Zn_0.4Cd_0.6S composite is due to the formation of p-n heterojunction between Zn WO₄and Zn_0.4Cd_0.6S.The accelerated migration and separation of photon-generated carriers under the driving of built-in electric field can significantly improve the photocatalytic performance of Zn WO₄/Zn_0.4Cd_0.6S composite.（2）In the second part,Co₃O₄/Zn_0.4Cd_0.6S p-n heterojunction photocatalysts were constructed by simple solvothermal method.The photocatalytic activity of a series of composites with different Co₃O₄loading content was tested under visible light irradiation.When the loading content of Co₃O₄was 4 wt%of the composite,the extremely high H₂evolution rate of 56.63 mmol g^-1h^-1was obtained（with a 21.86%apparent quantum efficiency at 420 nm）,which was 6.8 times higher than that of the single-component Zn_0.4Cd_0.6S solid solution,and it exhibits excellent stability in photocatalytic H₂evolution from water splitting.The photocatalytic performance of the composite is superior to that of the noble metal modified composite(Pt@Co₃O₄/Ti O₂:19.2 mmol g^-1h^-1).The construction of p-n heterojunction effectively promoted the separation and migration of photogenerated electrons and holes on the surface of Co₃O₄/Zn_0.4Cd_0.6S,resulting in the significantly enhanced activity and stability of the composite in photocatalytic H₂evolution from water splitting.（3）In the third part,a series of CoP₃/Zn_0.4Cd_0.6S composite photocatalysts with different CoP₃content were synthesized by one-step solvothermal method,and the influence of CoP₃content on the catalytic performance of the composite was studied in photocatalytic H₂evolution from water splitting.The results of photocatalytic performance test shows that the catalytic activity and durability of the CoP₃/Zn_0.4Cd_0.6S composite are significantly superior to the single-component Zn_0.4Cd_0.6S solid solution,and the loading content of CoP₃significantly enhanced the photocatalytic activity of the composite.The composite with 1.0 wt%CoP₃loading content presents amazing photocatalytic H₂evolution rate of 63.91 mmol g^-1h^-1（with a 26.03%apparent quantum efficiency at 420 nm）,which is 7.6 times higher than that of single-content Zn_0.4Cd_0.6S solid solution and 3.2 times higher than that of 1.0 wt%-Pt/Zn_0.4Cd_0.6S(19.72 mmol g^-1h^-1).The catalytic activity of this composite is significantly better than that of many cobalt phosphide modified composite photocatalysts.It is expected to replace precious metals and become cost-effective noble metal-free photocatalysts widely used in the field of photocatalysis.The improved catalytic performance of the CoP₃/Zn_0.4Cd_0.6S composite is mainly due to the loading of CoP₃as co-catalyst on Zn_0.4Cd_0.6S solid solution surface,which can accelerate the migration of photogenerated carriers to CoP₃,effectively improve the separation efficiency of photogenerated carriers and inhibit the reverse reaction of H₂evolution from water splitting,resulting in the significantly enhanced activity and stability for H₂evolution reaction.（4）In the final part,Ni CoP/Zn_0.4Cd_0.6S composite modified by Ni CoP co-catalyst were synthesized by simple calcination method.The composite is expected to further enhance the photocatalytic activity by the synergistic effect of Ni and Co.Experimental results show that the photocatalytic activity of the composite was significantly improved by the introduction of Ni CoP.The composite modified by 1 wt%Ni CoP as co-catalyst exhibits an optimal H₂evolution rate of 48.87 mmol g^-1h^-1（with a 16.10%apparent quantum efficiency at 420 nm）,which is 5.8 times higher than that of pure Zn_0.4Cd_0.6S solid solution.Compared with many cobalt-nickel phosphide modified composite photocatalysts,Ni CoP/Zn_0.4Cd_0.6S has higher photocatalytic activity and stability..更多还原