| It has been about 40 years since the photocatalysis technology was raised to the actual product application.Because it can convert reactions that occur under harsh conditions into mild conditions,it has the application prospect in the field of major problems faced by human beings.Therefore,it is one of the most active parts in the international research field in recent years.However,the current photocatalytic technology still has problems such as low photon yield,difficulty in carrier separation and movement,and difficulty in catalyst recovery.So its industrial application still has great challenges.Graphitic carbon nitride?g-C3N4?,as a newly developed photocatalytic semiconductor material,is a special conjugated polymer,which has attracted the attention of many researchers due to its advantages of stability,non-toxicity and simple preparation.In this paper,urea was selected as the main raw material to study the influence of various factors on the performance of g-C3N4 prepared by urea.By forming a heterojunction with other substances,a composite photocatalytic material with better catalytic performance was obtained.The specific research contents and results are as follows:1.Using urea as raw material,g-C3N4 was prepared by thermal polymerization method at a heating rate of 10?/min,a reaction temperature of 550?,and a reaction time of 4h.The prepared g-C3N4 was characterized by XRD,SEM,BET,Uv-vis and FTIR.It was found that g-C3N4 showed a flaky shape.With the increase of heat polymerization temperature,the purity of g-C3N4 product was higher and higher,and the crystallinity was getting better.Due to the quantum size effect,g-C3N4 shows a band gap of 2.81eV.After increasing the reaction temperature and extending the reaction time,the specific surface area of g-C3N4 can be as high as 292m2/g.Different reaction temperatures,reaction times and reactant materials all have an impact on the photocatalytic performance of the prepared g-C3N4 products.The results show that the photocatalytic degradation of Rhodamine B by g-C3N4 will increase with the increase of thermopolymerization temperature and the prolongation of thermopolymerization time.The g-C3N4 prepared from urea has better adsorption and photocatalytic ability,but the yield is very low;the g-C3N4 prepared from thiourea shows good adsorption and photocatalytic ability,and the yield is also low;although the yield of g-C3N4 prepared from melamine is high,its adsorption and photocatalytic effects are poor For dyes with different surface electric properties,g-C3N4 is more likely to adsorb and degrade positively charged Rhodamine B and methylene blue,but hardly degrade negatively charged methyl orange.2.The flake tungsten oxide?WO3?was prepared by using sodium tungstate,hydrochloric acid and oxalic acid as raw materials by precipitation method.The WO3/g-C3N4 composite photocatalyst was prepared by mixing WO3 and g-C3N4 in a certain ratio and then heat-treating.Through SEM and TEM observation,it was found that WO3 nanosheet was uniformly loaded on g-C3N4 surface with a size of about 200nm.Rhodamine B was used as a simulated pollutant to study the photocatalytic capacity of WO3/g-C3N4 composite photocatalyst.The results show that the photocatalytic performance of WO3/g-C3N4 is better,and the WO3/g-C3N4- 20 composite photocatalyst shows the best degradation efficiency.WO3/g-C3N4-20 is more likely to adsorb and degrade positively charged Rhodamine B,while negatively charged methyl orange is more difficult to degrade.Repeatability and stability experiments show that there is no accidental improvement in the photocatalytic performance of WO3/g-C3N4-20,and the photocatalytic performance of the photocatalyst remains above 90%after 5 cycles.The capture agent experiment proved that the active particles in the photocatalytic process were mainly O2/·O2-and·OH,combined with the ultraviolet visible diffuse reflection spectrum and the empirical formula,it was concluded that the photocatalytic mechanism of the composite material belongs to the Z-type heterojunction.3.Tungsten oxide monohydrate?WO3·H2O?was prepared by precipitation,and WO3·H2O/g-C3N4 composite was prepared by ultrasonic assisted precipitation.It was found by SEM and TEM that WO3·H2O nanosheets with a size of about 200nm were uniformly dispersed on the surface of g-C3N4,and a relatively tight bond based on van der Waals force was formed.With Rhodamine B as the degradation dye,WO3·H2O/g-C3N4 composites show better photocatalytic performance,among which WO3·H2O/g-C3N4-20 has more excellent photocatalytic properties.The stability experiment further demonstrates that the photocatalytic performance of WO3·H2O/g-C3N4 retains its performance after repeated catalysis.Through the capture agent experiment,the main active material of the composite material in the photocatalytic process is·O2-,and in the process of adding the hole trapping agent,WO3·H2O/g-C3N4-20 exhibits more excellent catalytic performance.Combined with the Mote Schottky curves and XPS valence band spectrum analysis,the photocatalytic mechanism of WO3·H2O/g-C3N4-20 also belongs to the Z mechanism heterojunction. |
PDF Full Text Request