Photocatalytic Degradation Of Organic Pollutants On Graphitic Carbon Nitride With Nitrogen Vacancies

Photocatalytic oxidation technology based on graphite phase carbonitride?g-C3N4?for degradation various organic pollutants is a hot research topic.Traditional g-C₃N₄ is considered to be a chemically stable non-metallic photocatalyst,but it also faces the problems of all photocatalysts:high electron-hole recombination probability and low visible light utilization efficiency.Therefore,we believe that g-C3N4modification is effective method to improve its photocatalytic activity.At the same time,the development of a new and efficient catalytic activation system based on g-C₃N₄ photocatalytic system will further improve the degradation efficiency of pollutants.In this paper,we introduce nitrogen vacancies in situ on g-C₃N₄ to construct a p-n homojunction structure,which promoted the separation of photo-generated carriers and achieve efficient degradation of pollutants.Then we use nitrogen vacancies modified g-C₃N₄ photocatalytic activated sulfite to produce sulfite radicals for the degradation of organic contaminants.The research work carried out in this thesis is as follows.?1?An innovative method was developed for preparing g-C₃N₄ p-n homojunction and the prepared PN-x homojunction as photocataltsts for degradation of several organic pollutants were investigated.Under the given conditions(catalyst load 0.5 g L^-1,initial pH 7.0),the degradation efficiency of PN-x homojunction to above pollutants is over 95%.The apparent degradation rate constants of these organic contaminants were increased by 3-7.3 times compared to g-C₃N₄ which was not subjected to secondary calcination,indicating that its photocatalytic performance was significantly enhanced.Free radical quenching experiments and electron paramagnetic resonance spectroscopy indicated that the main active species of PN-x homojunction catalysts for degrading pollutants were superoxide radicals(O₂^·-)and photogenerated holes?h⁺?.The synergistic mechanism of PN-x homojunction is that the introduction of nitrogen vacancies in n-type g-C3N4 leads to the conversion of surface conductivity types to p-n type,which improves the separation efficiency of photogenerated electrons and holes,promotes free radicals,and ultimately accelerats the degradation of pollutants.?2?A g-C₃N₄ photocatalytic activated sulfite system for the efficient degradation of organic pollutants was constructed.To further improve its activation efficiency,g-C₃N₄ containing plentiful nitrogen vacancies was used as an activator.It was found that graphite carbon nitride with nitrogen vacancies?NV-g-C₃N₄?can be prepared by calcining melamine under nitrogen gas stream.In the presence of Na₂SO₃(20 mmol L^-1),carbamazepine could be completely degraded in 120min.Free radical quenching experiments and electron paramagnetic resonance spectroscopy indicated that the main active species in the NV-g-C₃N₄/Sulfite system were photogenerated holes?h⁺?and sulfite radicals(SO₃^·-).Based on the experimental results and discussion,we believe that nitrogen vacancies can capture electrons,and accelerate the separation of electrons and holes,resulting more holes activate sulfite to produce SO₃^·-,which leads to rapid degradation of pollutants.