| As a new type of visible light catalyst,graphite phase carbon nitride?g-C3N4?has such excellent properties as narrow bandwidth,wide available wavelength range of sunlight,no secondary pollution,easy preparation and stable structure.However,g-C3N4 has low photocatalytic efficiency due to its small specific surface area and high photocarrier recombination rate.In view of the above defects,this study modified g-C3N4 with SiO2composite and K doping to improve its photocatalytic activity,and investigated the synergistic effect of SiO2 composite and K doping on improving the photocatalytic activity of g-C3N4.?1?Nano-scale composite SiO2/g-C3N4 was synthesized from melamine and nanometer SiO2 by vapor deposition.SiO2/g-C3N4 composite photocatalyst with optimal photocatalytic activity was obtained by adjusting the ratio of melamine and nano-silica,and the catalyst was characterized.The photocatalytic activity of g-C3N4/SiO2 was evaluated with rhodamine B and tetracycline hydrochloride as the target pollutants.The results showed that the composite SiO2/g-C3N4 was a nano-particle with a diameter of about 40nm,and g-C3N4was coated on the outside of nano-silica with a core-shell structure.Compared with pure g-C3N4,the specific surface area of SiO2/g-C3N4?97.32m2/g?increased by 5.88 times.The composite probability of photogenerated electrons and holes was greatly reduced,showing high catalytic activity for RhB and tetracycline hydrochloride dyes.95.6%RhB and 60.3%tetracycline hydrochloride could be catalyzed to degrade within 60min.The active species in the degradation process were mainly superoxide radicals,followed by holes,and hydroxyl radicals had the least effect.SiO2/g-C3N4 has good stability,and the photocatalytic activity does not decrease significantly after four cycles.?2?K-doped g-C3N4/SiO2?denoted as SiO2/K-CN?was synthesized by high-temperature thermal polymerization with potassium chloride as the potassium source,melamine as the precursor and silica as the silicon source.K-doped g-C3N4/SiO2 was characterized.The photocatalytic activity and stability of K-dopedg-C3N4/SiO2 in visible light were tested with the antibiotic tetracycline hydrochloride as the target pollutant.The results showed that the catalyst activity was highest when the mass ratio of potassium chloride and melamine mixture to silica was 10:1.The specific surface area of K-g-C3N4/SiO2 catalyst was 28.16m2/g.Both K doping and SiO2 composite can reduce the composite probability of photogenerated electrons and holes.The synergistic effect of K doping and SiO2 composite makes K-g-C3N4/SiO2 complex have high catalytic activity,and can catalyze the degradation of 68.57%tetracycline within 120min.In the process of catalytic tetracycline degradation,the active species that play a role are mainly superoxide radicals,followed by holes,and hydroxyl radicals have the least effect.K-g-C3N4/SiO2complex with good stability. |
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