Study On Preparation And Properties Of Graphite Carbon Nitride-Based Photocatalytic Materials And Its Self-Cleaning Application On Cement Surface

Photocatalysis has been worldwide focused on as one of the most promising route to resolve environmental crisis and energy shortage.Graphite phase carbon nitride（g-C₃N₄）,possesses the merits of visible-light absorption,high stability,facile synthesis as well as recyclable,making it superior photocatalysis prospects in the applications of hydrogen production,organics degradation and so forth.The photocatalytic activity of g-C₃N₄has been somehow unfortunately limited owing to the rapid recombination of photogenic charge carrier.As the most widely used building materials in civil engineering infrastructure,self-cleaning cement founded on visible-light catalysis has far-reaching significance for economic and social development and human physiological and psychological health.However,self-cleaning cement is mainly based on titanium dioxide only excited by ultraviolet light.Meanwhile,researches on g-C₃N₄-based self-cleaning cement-based materials are still immature,and the existing studies reveal that g-C₃N₄has weak photocatalytic performance,poor compatibility with cement matrix as well as complex layer structure design and other defects.In this study,g-C₃N₄/Al₂O₃,g-C₃N₄/Bi VO₄heterogeneous materials and g-C₃N₄homogeneous materials were synthetized.The structure,morphology and properties of g-C₃N₄homogeneous materials were investigated under the conditions of reaction atmosphere,reaction temperature,the ratio of composite precursors and p H via X-ray diffractometer,scanning electron microscope and X-ray photoelectron spectrometer,so as to achieve the separation of carriers and enhance the photocatalytic activity.Taking nano-Si O₂as the basement layer,the constructing manner and loading amount were adjusted,which will obtain the high-efficiency visible-light degradation and long-term service efficiency of cement-based materials for organic pollutants.g-C₃N₄homogeneous materials were prepared via calcining composite precursors of thiourea and urea.Results showed that the structure,morphology and properties of g-C₃N₄homogeneous materials were affected by the reaction atmosphere,reaction temperature and the ratio of composite precursor.The g-C₃N₄homogeneous material prepared in Ar atmosphere has higher crystallinity and photocatalytic activity.Higher temperature resulted in increased crystallinity.Meanwhile,the morphology of the g-C₃N₄homogeneous material was small and dispersed,and then large and aggregated.Specially,the homogeneous material obtained at 550°C has small and uniform morphology,showing the best degradation performance for Rh B.In addition,the carrier recombination of g-C₃N₄was effectively suppressed by adjusting the ratio of precursor,but the effect on the specific surface was relatively complex.The remarkable enhancement in degradation of Rh B was achieved when the mass fraction of thiourea in the precursor was 50%（CN-50）.g-C₃N₄/Al₂O₃and g-C₃N₄/Bi VO₄heterogeneous materials were synthesized via homogeneous precipitation method and ultrasonic composite method respectively.Results showed that the crystallinity of g-C₃N₄/Al₂O₃heterostructures prepared under different p H conditions is improved while the carrier recombination rate is significantly reduced,which could promote the enhancement of photocatalytic activity.By adjusting the ratio of precursors,the visible-light response range of g-C₃N₄/Al₂O₃and g-C₃N₄/Bi VO₄heterogeneous materials has been effectively expanded.However,the photocatalytic activity of both of them fluctuated due to the specific surface area and surface groups.The photocatalytic activity was the highest when the mass ratio of Bi VO₄to g-C₃N₄was 1/4,and the degradation rate was 7%higher than that of pure g-C₃N₄.According to the structure,morphology and properties of the g-C₃N₄homogeneous and heterogeneous materials,CN-50 was selected as the photocatalyst while nano-Si O₂was used as the base layers to construct self-cleaning cement successfully by surface treatment.Results showed that the introduction of nano-Si O₂promoted the formation of a relatively uniform g-C₃N₄photocatalytic layer,which promoted the visible light degradation of Rh B on self-cleaning cement effectively.The constructing manner is vital for the performance of the as-prepared photocatalysis layer.By constructing the nano-Si O₂substrate layer for 4-24 hours and then introducing g-C₃N₄catalyst,the masking effect of nano-Si O₂on g-C₃N₄was improved,and the best degradation efficiency of Rh B was shown in 12 hours.Furthermore,variation of nano-Si O₂content brought about varying roughness on the surface of cement which promoted the adhesion of photocatalysis on the substrate,and the sample showed the highest degradation rate of 67.2%in 12 h when 0.3125 mg·cm^-2nano-Si O₂was added,meanwhile the minimum reduction value was 5.4%after the simulated rain test.