Loading Of Ultrafine Pt Nanoparticles On The Inner Surface Of Hollow Semiconductors And Their Photocatalytic Hydrogen Production Performance

Hydrogen（H₂）has a high energy density and does not cause any pollution to the environment.It is widely regarded as an extremely important alternative to fossil fuels.However,the typical method used in industry to produce H₂has some disadvantages,such as serious pollution,high cost,and large energy consumption.As a carbon-free and pollution-free process,photocatalytic H₂production is a promising method in the field of H₂production.Photocatalysis semiconductors such as cadmium sulfide（Cd S）and titanium dioxide have been extensively studied up to now,but the high recombination rate of photocarriers and the low utilization of sunlight are the disadvantages of most List of semiconductor materials,so they need to be modified,a low cost,high efficiency,and durable photocatalyst were prepared.In this paper,Cd S and Ti O₂semiconductor materials were modified by supporting suitable cocatalyst to enhance their photocatalytic activity and stability.1.A composite photocatalyst（NC/Pt@Ti O₂-x）composed of hollow N-doped carbon（NC）,Pt nanoparticles（2～5nm）,and Ti O₂was prepared by simultaneous high-temperature pre-carbonization of N-containing polymer（polyethyleneimine,PEI）and in-situ reduction of Pt precursor.Its structure and morphology were characterized through the scanning electron microscope,transmission electron microscope,and so on.The effects of pre-carbonization temperature and thickness of the NC layer on the photocatalytic properties were investigated.It was found that with the increasing polymer dosage in a certain range,the photocatalytic activity increased firstly and then decreased,indicating that the optimal performance could not be played by a too thin or too thick carbon layer.During the pre-carbonization process,PEI was transformed into the NC layer,while the Pt precursor adsorbed on PEI was in situ reduced into Pt nanoparticles（Pt NPs）and then uniformly and stably fixed on the inner surface of the catalyst by NC layers.Thanks to the good distribution of Pt nanoparticles and concurrence of both Pt~0and Pt²⁺,the high conductivity of the NC layer,high specific surface area,large pore size,and optimized charge transfer between Pt and NC,the H₂yield of NC/Pt@Ti O₂-900 photocatalysis under UV-light reached up to 23.8 mmol h^-1g^-1,which was62.3 times and 1.43 times higher than that of pure hollow Ti O₂（Ti O₂-HS）and Pt@Ti O₂-HS（1.5 wt.%）prepared by conventional photo-deposition,respectively.At the same time,it was also found that photocatalysis with Pt nanoparticles on the outer surface of Ti O₂-HS had poorer photocatalytic performance than that on the inner surface.In addition,NC/Pt@Ti O₂-900 still had good photocatalytic stability after 40 h cyclic testing due to the strong Pt-N bond between Pt and NC layers.Besides,the modified photocatalyst still improved both the bandgap width and light absorption efficiency.Because of those above,this study highlights the great potential of thin NC layers in the development of novel photocatalysts with excellent properties.2.The hollow composite NC/Pt@Cd S-HS was prepared by depositing Cd S on the outer surface of the hollow NC layer with highly dispersed Pt NPs by a simple hydrothermal method.Under the presence of lactic acid sacrificial agent and visible light,the hydrogen production rate reached 28.2 mmol h^-1g^-1,which was 3.9 times that of Pt@Cd S-HS.So,the advantages of the thin NC layer in the development of new photocatalysts with excellent properties were proved once again.To further improve the hydrogen production performance of photocatalyst,Bimetallic phosphide Ni Co P as cocatalyst was loaded on the outer surface of NC/Pt@Cd S-HS to obtain NC/Pt@Cd S@Ni Co P-HS composite.The photocatalytic hydrogen production capacity of the prepared catalyst was further improved,and the hydrogen production rate reached 42.4 mmol h^-1g^-1and was 1.5 times that of NC/Pt@Cd S-HS.The high hydrogen yield of NC/Pt@Cd S@Ni Co P-HS is caused by the synergistic effect of NC,Pt,and Ni Co P on Cd S.The NC layer provides the good electrical conductivity and large specific surface area and pores diameter;the highly dispersed ultrafine Pt nanoparticles supply reaction activity sites and accelerate the charge transfer and separation,and Ni Co P further affords more reactive sites,and accelerates the electron transfer rate and inhibits the recombination of photogenerated carriers,and reduces the bandgap width of Cd S and promotes the light-absorption;all of these lead to the good performance of visible-light photocatalytic hydrogen production.During the preparation of NC/Pt@Cd S-HS,the ammonia dosage,Ni/Co mole ratio,and Ni Co P loading amount were optimized.It was determined that the photocatalytic performance of the prepared photocatalyst was the best when the amount of ammonia was 3m L,the loading amount of Ni Co P was 9%and the ratio of Co to Ni was0.7:0.3.In addition,the photocatalytic performance of NC/Pt@Cd S@Ni Co P did not decrease significantly after the 20h cycling test,indicating good reusability.