| The rapid consumption of fossil fuels and the increasing environmental pollution greatly promote the development of renewable clean Energy.The use of sunlight to drive water splitting to produce hydrogen is considered as a promising process for the preparation of renewable and clean Energy.Among them,the semiconductor is the core of the photocatalytic system.The current research on this aspect is dedicated to the development of a low-cost,stable,reliable,environmentally friendly,and efficient semiconductor catalytic system.Up to now,few photocatalysts can be commercially applied,and TiO2 ranks among the best in this field,becoming the leader in commercial applications in extensive research.Limited by the intrinsic large bandgap of TiO2,which only harvests ultraviolet light to drive the photocatalytic reaction,the total photoelectric conversion efficiency is relatively low.Therefore,the development of photocatalytic materials with high catalytic efficiency responsive to visible light has gradually emerged and has become a new demand in this field.Polymeric carbon nitride(PCN),as a non-metal semiconductor,is a visible light-responsive material.It is non-toxic,resistant to acid and alkali corrosion,and has good thermal stability.In addition,it has the advantages of low preparation cost and a wide range of source materials.As one of the most promising photocatalysts,it has been applied in many fields,including photocatalytic hydrogen production,degradation,and exhaust gas treatment.PCN has a suitable Energy band structure,but the rapid recombination efficiency of the electron-hole pairs becomes a constraint on its photocatalytic performance.In this paper,PCN is modified by optimizing the synthesis process to improve its photocatalytic hydrogen production performance.(1)Etching-induced highly porous polymeric carbon nitride with enhanced photocatalytic hydrogen evolutionThe cyanamide aqueous solution and concentrated sulfuric acid are employed as the precursors,and a direct calcination process is performed to obtain modified carbon nitride.The nitrogen adsorption and desorption experiments show that the specific surface area of modified carbon nitride(CN-0.25H)is increased to 60.42 m2·g-1,which is about 10 times higher than the original CN.The optical and electrochemical properties and explore the effects of light absorption,separation,and transfer of photo-generated carriers on the photocatalytic performance of the catalysts are further characterized.On the basis of loading platinum,the photocatalytic hydrogen production performance of CN and CN-xH was discussed through a photocatalytic hydrogen production system.Among them,CN-0.25 h has the highest hydrogen production performance,reaching 1255.4 μmol·h-1·g-1,which is about 5 times that of the original CN.It was tested with a 420nm monochromatic filter.Its apparent quantum efficiency is 6.7%.By comparing the photon absorption rate(Jabs),photocurrent response,electrochemical impedance spectroscopy,and Mott-Schottky curve,it is proved that the separation and rapid transfer of photo-generated charge are the key factors to improve the photocatalytic activity of CN-0.25H.The new strategy of directly calcining CY to prepare high-porosity CN can improve the photocatalytic activity driven by sunlight,which provides an effective idea for the design of the CN synthesis process.(2)Preparation and photocatalytic performance of trace Pt supported polymeric carbon nitrideThe admixture solution was used as the precursor:add a certain amount of concentrated sulfuric acid and chloroplatinic acid to the cyanamide solution,ultrasonically make them uniform and directly calcinate to obtain Pt-doped modified carbon nitride.The content of Pt was detected by ICP-MS,which is 0.07%,0.23%,and 0.31%,respectively,and the morphology and element distribution of the catalyst was characterized on HAADF-STEM.The optical and electrochemical properties of the catalyst were fu rther tested,and it was proved that the increase in catalyst activity was mainly due to the enhancement of sunlight absorption and the enhancement of the separation and transfer of photo-generated carriers.The photocatalytic activity of the catalyst was evaluated by the hydrogen production performance,and the hydrogen production rate of the catalyst was measuremented under the same conditions.Among them,CN-0.23%Pt has the best performance,with an apparent quantum efficiency of 2.8%at 420 nm.In addition,the differences in the performance of hydrogen production by in-situ platinum loading method and photodeposition method,reducing agent reduction method,and pyrolysis method were also studied.The highest hydrogen production performance of CN-0.23%Pt is 1127.4 μmol·h-1·g-1,which are 10 times,5.7 times,and 5 times higher than them,respectively. |
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