| Photocatalytic technology can convert low-density solar energy into high-density chemical energy,or directly use solar energy to degrade various organic pollutants in water and air.It is an ideal technology for environmental pollution control and clean energy production,which has been rapidly developed in recent years.At present,the conventional semiconductor catalysts can only function under the condition of light,and when the light source is turned off,the catalyst is in a "deactivated" state.The "catalytic memory" material can store and release photogenerated electrons through changes in the valence state of the electron acceptor in the catalyst.Thus the material is also catalytically active in the absence of light,thereby prolonging the time of the catalytic reaction.Therefore,the photocatalyst with"catalytic memory"is constructed and prepared,so that the photocatalyst can maintain a certain catalytic activity in the absence of light,which has great significance in medical and wastewater treatment.For this reason,WO3/g-C3N4 composites were prepared by WO3 and g-C3N4 with earth-abundant nature,simple preparation,good stability and ideal valence band position.Meanwhile the photocatalytic properties and catalytic memory effects were studied.The main content of the paper and the results achieved are as follows:(1)The g-C3N4 was prepared by a simple thermal polycondensation method.On the basis of this,the WO3/g-C3N4 heterojunction composite was prepared by hydrothermal method.Sodium tungstate was used as raw material with oxalic acid,citric acid,acetic acid and salicylic acid-mediated.XRD results showed that the WO3 samples were hexagonal with the four acid-mediated.The morphology presented a multi-stage structure assembled by nanorods,which was uneven distribution on the layer of g-C3N4 to form a heterostructure.Among the four acid-mediated complexes,oxalic acid-mediated complex had the best photocatalytic activity.It may be due to oxalic acid as a capping agent,forming strong hydrogen bond with(WOn)-,had a certain influence on its photocatalytic activity.When the concentration of oxalic acid was 1 mol/L,the photocatalytic degradation of RhB was the best than pure WO3 and pure g-C3N4,which significantly enhanced the photocatalytic performance It indicated that the formation of the heterojunction was beneficial to the separation of photogenerated carriers and effectively enhanced the photocatalytic performance(2)Different ratios of WO3/9-C3N4 had different catalytic properties.The WG1:1 prepared by the oxalic acid concentration of lmol/L had the highest degradation rate of RhB within 210 min,which was as high as 97.46%.Its degradation effect was obvious higher than pure g-C3N4 and pure WO3.In addition,the kinetic constant of WG1:1 was 0.0052/min,which was 4 times and 3.25 times that of pure g-C3N4(0.0013/mim)and WO3(0.0016/min)respectively.After four cycles,the catalytic activity of WO3/9-C3N4 was not significantly decreased,indicating that the catalyst had high stability.Free radical trap experiments demonstrated that the reactive groups such·as O2-,h+,·OH played important roles.It is speculated that the WO3/9-C3N4 conforms to the Z-scheme mechanism(3)The "catalytic memory" activity of WO3/g-C3N4 was confirmed for the first time With 3 h pre-illumination,nearly 42.33%RhB was removed in the dark by WO3/9-C3N4 via its nearly 8 h "memory" photocatalytic activity.Among the complexes with different WO3 content,the WG19:1 had the best "catalytic memory".With the increase of the WO3 content,the more electrons were excited under illumination,and the more electrons were stored.Then the more electrons were released under dark conditions,which had an obvious,catalytic memory" effect.The "catalytic memory,function is attributed to the fact that tungsten can store photogenerated electrons(W6+?W5+)under illumination.When the light source is turned off,the stored electrons are released(W5+?W6+)).ESR characterization demonstrated that WO3/9-C3N4 can produce·O2-and ·OH radicals in the dark.The research of the catalytic memory material will overcome the weakness of the traditional catalysts,prolong the working time of the photocatalyst,and expand the application range of the photocatalyst. |
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