Construction Of Heterogeneous Photocatalyst For The Photocatalytic Performance And Mechanism Research Under Visible Light

Environmental pollution and energy crisis have become two main problems on the road of social sustainable development.It has become the primary goal of the present to effectively solve these problems.The semiconductor photocatalysis technique is a low energy consumption,green technology without causing secondary pollution,which could effectively control the water contamination of environment and preparation of new clean energy?hydrogen?.So far,a lot of semiconductor photocatalysts have been developed and utilized,but the low photocatalytic performance and other problems have greatly restricted the applications,which mainly due to the traditional wide band gap semiconductors were unable to effectively utilize light energy as well as the single semiconductors with higher composite probability of photoelectric charge.Construction of the heterogeneous structure is an effective measure by forming space electric potential difference between two or more semiconductor materials to improve electronic-hole on the separation efficiency and light energy utilization,thus largely promoting the photocatalytic activity.In this work,the vanadate and carbon materials were chosen as the basal construction of heterojunction semiconductor,and some methods were used for characterizing the structure,morphology and photoelectric performance.The mechanism of photocatalytic reaction was also explored by studying the transfer mechanism of charge during photochemical reaction of heterogeneous photocatalyst.The primary study contents are listed below:?1?Construction of monoclinic-tetragonal BiVO₄ heterojunctions photocatalysts for the degradation performance and mechanism research of tetracycline under visible lightThe monoclinic-tetragonal BiVO₄(M-T BiVO₄)heterojunction photocatalysts have been resoundingly prepared through the method of microwave,and the crystalline phases of monoclinic scheelite?M-phase?,tetragonal zircon?T-phase?products were controlled by switching the organic additives.The photocatalytic performance of as-prepared photocatalysts were assessed by the degradation of tetracycline?TC?with visible-light illumination.Compared with the single crystal BiVO₄ samples,the monoclinic-tetragonal BiVO₄ exhibited a higher photodegradation ratio of 80.5%in 1.0h.By the further investigation of PL spectrum and active species trapping experiments,we considered that the improved activity may be due to the construction of heterostructure,which greatly promoting charge's separation effiviency and improving the photocatalytic performance.?2?Construction of Ag₃VO₄-based heterojunctions photocatalysts for the degradation performance and mechanism research of pollutant under visible light?1?A novel Ag₃VO₄/WO₃ heterojunction photocatalyst has been successfully synthesied by the methods of hydrothermal and precipitation reaction.Under visible-light irradiation for 30 minutes,the 10%Ag₃VO₄/WO₃ sample showed an excellent photocatalytic performance?71.2%?,which was about 3.1 and 4.6 times higher than that of single Ag₃VO₄ and WO_3,respectively.On the basis of the active species trapping experiment and ESR,we also proposed the photocatalytic mechanism of heterojunction.The improved photocatalytic activity should be owing to the construction of heterojunction,thus leading to an effective separation of the photogenerated electron-hole pair's.?2?The novel visible light driven Ag₃VO₄/BiVO₄ heterojunction has been successfully fabricated via a hydrothermal process and a facile precipitation reaction.The composite ratio of BiVO₄ and Ag₃VO₄ had great influences on the photocatalytic performance,and we also found that the as-synthetic sample at 10:1 mole ratio of Ag₃VO₄/10BiVO₄ performed the highest photocatalytic activity.The RhB was completely degraded?95.9%?under visible light irradiation in 20 min,which was 10times and 3.4 times higher than that of the pristine BiVO₄ and Ag₃VO₄,respectively.Furthermore,the Ag₃VO₄/10BiVO₄ sample also showed a superior degradation activity on the other organic dyes such as methyl blue?MB?and methyl violet?MV?.We considerd that the enhanced photocatalytic property could be due to the construction of heterojunction,leading to an effective separation of the photogenerated charges carriers.On the basis of the active species trapping experiment and ESR test,we also proposed the photocatalytic reaction mechanism.?3?Construction of carbon quantum dots-based multicomponent heterojunctions photocatalysts for the photocatalytic performance and mechanism research under visible light?1?Novel p-n junction photocatalysts nitrogen doped graphene quantum dots?NGQDs?-BiOI/MnNb₂O₆ have been prepared via the hydrothermal method for the environmental remediation.We selected different antibiotics of tetracycline?TC?,oxytetracyline,ciprofloxacin and doxycycline as the targeted pollutants to study the photocatalytic performance of different samples.Compared with MnNb₂O₆ and BiOI samples,the hybrid materials?NGQDs-BiOI/MnNb₂O₆?could significantly enhance photocatalytic activity.The optimum photocatalytic efficiency of 5%NGQDs-BiOI/MnNb₂O₆ sample for the degradation of TC was 87.2%within 60 min.Based on the experiment conclusions,we found that the ratio of BiOI/MnNb₂O₆ and the content of NGQDs both had an important impact on the degradation activity.By the further studies of ESR,trapping experiments and electrochemical test,we considered that the high charge carrier mobility of NGQDs and the p-n junction photocatalytic systems were the main reasons to improve the photocatalytic property,leading to an effective separation of the photogenerated charges carriers.?2?Through the hydrothermal and calcine synthetic method,we successfully prepared nitrogen doped graphene quantum dots?NGQDs?-BiVO₄/g-C₃N₄ Z-scheme heterojunction,and some antibiotics?tetracycline?TC?,oxytertracyline?OTC?and ciprofloxacin?CIP??were chosen as target pollutants to explore the photocatalytic performance.Results showed that when the mole ratio of BiVO₄:g-C₃N₄ was 1:2 and the NGQDs addition amount is 5 wt%,the corresponding 5%NGQDs-BiVO₄/2g-C₃N₄sample performed the highest photocatalytic efficiency?91.5%in 30 min with TC?,which was much higher than that of the single BiVO₄ and g-C₃N₄.In addition,the 5%NGQDs-BiVO₄/g-C₃N₄ sample also exhibited a high light stability.By the further studies,we believed that the enhanced photocatalytic property could be ascribed to the Z-scheme photocatalytic systems,which could accelerate the separation of the charge carriers.And after introducing NGQDs,it can improve the rate of electron transfer.?3?The nitrogen doped graphene quantum dots?NGQDs?-ZnNb₂O₆/g-C₃N₄heterostructures were successfully prepared and showed highly efficient photocatalytic performance for water splitting into hydrogen.Results showed that both the ZnNb₂O₆/g-C₃N₄ mole ratio and the amount of NGQDs displayed important influence for H₂ production.Moreover,the optimum synthesis conditions of the ZnNb₂O₆/g-C₃N₄mole ratio?1/7?and the amount of NGQDs?5%?were both obtained,and the corresponding 5%NGQDs-ZnNb₂O₆/7g-C₃N₄ sample performed a much higher hydrogen-evolution rate of 340.9?mol?g^-1?h^-1.By the further studies of photocurrent,impedance and fluorescence test,we found that the heterojunction system and the NGQDs were the major causes for the improvement of the photocatalytic activity,leading to an enhanced absorption of visible light and a rapid mobility of charge carrier.At last,the activity of photocatalytic water splitting was enhanced.