Preparation Of Black Phosphorus Polycrystalline Nanosheets And Their Photocatalytic Applications

With the aggravation of the earth's energy crisis,photocatalytic water splitting technology is considered as an effective way to solve the global energy problem.Photocatalyst is the basis of photocatalytic reaction for hydrogen production.Various photo-responsive catalysts of hydrogen production have been developed during the past years.The traditional metal-based semiconductor photocatalysts are suffering from a series of problems,such as high cost,complexity of preparation process and poor photoconversion ability.Therefore,researchers have turned their attention to non-metal-based photocatalysts.Up to data,a series of non-metal-based photocatalytic materials like silicon,boron,sulfur,and red phosphorus-based photocatalysts have been developed.As a novel semiconductor material,black phosphorus?BP?is a two-dimensional material with a band gap of 0.3-2 eV that can be hydrolyzed to produce hydrogen under ultraviolet-visible light irradiation.BP has excellent optical,electrical,thermal and mechanical properties,and possess a wide range of applications in the optical field.Among all the reported non-metal-based photocatalysts,BP is considered as a promising material.In this study,the preparation and photocatalytic application of black phosphorus polycrystals were investigated.We prepared different BP matrix composites to improve hydrogen production performances of BP as a photocatalyst matrix.Specific studies are listed as follows:1.BP polycrystalline nano-plates were used as photocatalyst to produce hydrogen under ultraviolet-visible light irradiation.BP polycrystalline nanomaterials were prepared by one-step hydrothermal method.The analysis of photocatalytic property showed that BP nanomaterial has high photocatalytic activity,electron transfer ability,and excellent photocatalytic hydrogen production ability.The outstanding performance is mainly due to the layered polycrystalline structure of BP nano-sheet.Experimental results displayed that the hydrogen production rate of BP polycrystals is 290.2 umolh^-1g^-1.It is proved that BP nanomaterial has good photocatalytic property and excellent chemical stability,which can replace traditional photocatalysts and develop a new kind of low cost,stable and efficient photocatalyst matrix.2.A co-catalyst was prepared on BP nanosheets by high-temperature hydrothermal method for photocatalytic hydrogen production.The well-dispersed Ti O₂ nanospheres were synthesized by hydrothermal reduction,finally,BP-TiF₃ composite was prepared with RP under high temperature and high pressure.The results showed that BP-TiF₃exhibited a higher hydrogen production rate than the matrix BP and TiO₂,which is mainly due to the large surface charge attracted by the cocatalyst TiF₃,the separation rate of electron holes was accelerated,and the electron reduction ability was enhanced.The results displayed that the maximum rate of hydrogen production rate is 612.0umolh^-1g^-1 when the content of TiO₂ is 0.1 g,so the composite exhibited high photocatalytic performance and excellent stability.The photocatalytic hydrogen production rate of BP-TiF₃ composite under ultraviolet-visible light irradiation for 4 h was significantly higher than that of individual BP(290.2 umolh^-1g^-1)and TiO₂(283.9umolh^-1g^-1).Experiments showed that BP-TiF₃ composite has more application potential than individual components,and it also provides a new way to prepare cocatalyst conveniently.3.The BP polycrystals and molybdenum disulfide?MoS₂?nanosheets were selected as the matrix,and BP-MoS₂ composites were prepared by one-step hydrothermal method after MoS₂ nanosheets were prepared by liquid ultrasonic stripping method.And a two-dimensional heterojunction intercalation structure was constructed,which effectively improved the photocatalytic performance of BP.The test of photocatalytic hydrogen production showed that the BP-MOS₂ heterojunction has faster electron transfer ability and better photocatalytic performance than BP and Mo S₂,and the improvement of its photochemical performance is due to the synergistic effect of BP and MOS₂,and the heterojunction can greatly improve the photocarrier migration rate.The photocatalytic hydrogen production rates of BP-MoS₂ heterostructures,BP,and MoS₂ were 543.2 umolh^-1g^-1,230.6 umolh^-1g^-1 and 226.9 umolh^-1g^-1,respectively.The results displayed that the two kinds of nano-plates formed intercalation heterostructures,and their photocatalytic properties were the best.The results above further prove that BP can be used as the matrix photocatalyst in the photocatalysis reaction,which leads the development of the photocatalyst to the direction of high efficiency,stability and low cost.