Preparation Of Tubular Carbon Nitride Based Photocatalyst And Its Properties For Dye Degradation And Hydrogen Production By Water Splitting

The massive burning of fossil fuels has led to energy crisis and environmental damage.Photocatalytic technology not only provides a cost-effective way to cope with the energy crisis by preparing clean renewable energy such as hydrogen energy through solar energy conversion,but also degrades toxic and harmful water pollutants for environmental purification.Among many photocatalysts,graphitic carbon nitride（g-C₃N₄）has received widespread attention since it was first discovered to be used for photocatalytic hydrogen production due to its advantages of abundant elemental reserves on earth,easy preparation,appropriate energy band structure,and high chemical and thermal stability.However,the narrow visible light response range,slow charge transfer rate and low specific surface area greatly limit the improvement of its photocatalytic performance.It is shown that constructing hollow porous structures with special morphology can accelerate the carrier transfer process and generate more active sites,thus obtaining better photocatalytic activity.In this paper,hollow porous tubular g-C₃N₄（CNPCx）,rolled brush tubular g-C₃N₄（CNC-x）and Covalent organic framework（COF）heterojunction type photocatalysts were constructed by a simple molecular self-assembly method,and the different catalysts were tested for photocatalytic hydrogen production and rhodamine B degradation performance,respectively.The mechanism of photocatalytic performance enhancement was investigated in combination with the characterization analysis.The main research works are as follows:（1）Hollow porous g-C₃N₄ nanotubes photocatalysts were obtained from melamine and phenylphosphonic acid by a facile self-assembly method without any template.A series of characterization and photoelectrochemical tests demonstrated the hollow porous tubular structure and the faster photoinduced carrier migration rate,the synergistic effect of which led to a significant improvement in photocatalytic performance.The photocatalytic activity of the prepared g-C₃N₄nanotubes was investigated by photocatalytic hydrogen precipitation rate and Rh B degradation experiments under visible light,and the hydrogen precipitation rate reached 865μmol h^-1 g^-1 and the degradation efficiency reached 99.5%within 120 min.（2）The brush-like g-C₃N₄ photocatalysts with bridge unit modification were synthesized by a combination of molecular self-assembly and thermal polycondensation.By characterizing the composition and morphology of the materials,it was demonstrated that the catalysts have a special brush-like structure with a bridge unit consisting of C-C=O that has been incorporated into the CN framework,which not only acts as an electronic bridge in the framework to facilitate charge transfer,but also enhances the light absorption ability and narrows the band gap.In addition,the brush-like structure provides more reaction sites and shortens the diffusion path of the carrier.The synergistic effect of the brush-like morphology and the bridge unit enabled CNC-x to exhibit excellent photocatalytic H₂ production rate(1459μmol h^-1 g^-1)and Rh B degradation performance with a degradation rate constant 8.75 times higher than that of CN.（3）The COF nanosheets were successfully loaded on g-C₃N₄ tubular structures using a simple ultrasonic method to form COF/g-C₃N₄（FCNPx）heterojunction composite photocatalysts.It was also characterized in detail by SEM,TEM,XPS,XRD,PL spectroscopy,etc.COF was successfully loaded on the surface of CNP to form heterojunctions.The formation of the heterojunction was beneficial to the increase of the photoinduced carrier migration rate,and the degradation efficiency of Rh B reached 97.7%and the hydrogen precipitation rate reached 3874μmol h^-1 g^-1 in 60 min time,and finally,the photocatalytic mechanism was discussed.