| Some scholars pointed out that since entering the 21st century,energy,water resources,food,environment,poverty,war,disease,education,democracy and population are ten major categories of problems that have seriously threatened the survival of human beings.Among them,the energy problem caused by a large number of industrial consumption and uncontrolled development is particularly prominent,and the ensuing environmental problems are also increasingly serious.With the increasing awareness of environmental protection by the government and the public,all kinds of environmental conditions have improved slightly,but the situation of pollution and energy exhaustion is still not optimistic.According to the principle of sustainable development,the use of traditional energy has been unable to meet the requirements of human nature protection.Under the dual pressure of environment and energy problems,it provides an opportunity for the development of renewable energy.In the renewable energy,the most abundant,the most environmentally friendly is solar energy.Therefore,under the natural condition of visible light irradiation can drive organic pollutants ore into CO2,H2O and other inorganic semiconductor photocatalytic oxidation method has received the widespread attention,and is widely used in environmental protection,such as water decomposition hydrogen production,toxic wastewater treatment,air purification,etc.,is currently used in environmental restoration and the development of new energy.In the new field of photocatalytic water treatment,the metal-free graphite-like carbon nitride(g-C3N4)is a kind of visible light photocatalyst with a narrow band gap,which is a later-coming one.It has stable chemical and thermal properties and excellent photochemical properties in water.Conventional thermal fusion method,however,the preparation of block g-C3N4 photocatalytic activity is not ideal,the main constrained factors including but not limited to:light is relatively low,the ability to capture the narrow band gap of 2.7 eV make carrier light composite extremely easily,hierarchical stack state leads to low utilization rate of specific surface area,seriously hindered the research and application in water treatment process of industrialization.To overcome all these shortcomings and improve the photocatalytic performance of g-C3N4 is undoubtedly one of the key targets of water treatment researchers.Based on the above reasons,2D-2D-type-Ⅱ N-doped Bi2O2CO3/porous g-C3N4 heterojunction was successfully prepared by using strong alkali to destroy part of g-C3N4 structure and making full use of the "sacrificial" part of C and N elements in situ as C and N sources.Then,the 0D-2D-2D Ag@N-Bi2O2CO3/porous g-C3N4 ternary composite heterojunction was prepared by photoreductive deposition method.Finally,the 0D-2D Bi-g-C3N4 schottky junction was prepared by simple solvothermal method.Specific research contents are as follows:(1)The porous structure of the massive g-C3N4 was controlled by alkaline low-temperature hydrothermal treatment under hydrothermal conditions.At the same time,the stripped g-C3N4 was used as C source and N source to synchronically self-assemble on the newly exposed surface of g-C3N4,and N-doped Bi2O2CO3 nanosheets were formed in situ,thus N-Bi2O2CO3/porous g-C3N4 composite photocatalyst product was finally obtained.Among them,three different modification methods,such as alkali stripping,N element doping and semiconductor composite,are effectively integrated,and the "trinity" cooperatively improves the structural and characteristic limitations of carbon nitride.The "trinity" synergistically improves the structural and characteristic limitations of carbon nitride.In the visible light simulation device made by the laboratory,the degradation rate of 30 mg/L X-3B aqueous solution by adding 0.05g binary composite material can reach 93%after 90 min,which is 5 times and 8 times that of pure g-C3N4 and Bi2O2CO3,respectively.(2)On the basis of the above binary composites combined with photoinduced reduction deposition method,silver nanoparticles(Ag NPs)were selectively deposited on the surface of N-Bi2O2CO3/porous g-C3N4 composite photocatalyst to prepare Ag@N-Bi2O2CO3/porous g-C3N4 ternary composite photocatalytic material,through the analysis of the DRS can be observed at 500 nm as the center of the obvious,surface plasmon resonance(SPR)peak due to SPR effect,optical electronic can quickly migrated to Ag NPs,and quickly back into super oxygen anion free radical(·O2-),so as to speed up the photoproduction carrier separation and transfer rate and further improve the photocatalytic performance.When the Ag NPs dosage was 10 wt%,the utilization rate of generation carriers was the highest.Under visible light irradiation of 30 mg/L X-3B aqueous solution,the degradation rate of 0.01g ternary composite photocatalytic material can reach 78.2%in 15 min and 97%in 90 min,which are 5.78 times and 29.3 times of pure g-C3N4 and Bi2O2CO3,respectively.Moreover,it also has good photocorrosion resistance.The photocatalytic activity was still good after five times of reuse.(3)Aiming at the common problem that the catalytic conversion of refractory pollutants in water is strongly dependent on precious metals,the semi-metal bismuth(Bi),which is cheap and widely sourced,was selected as the substitute of precious metals.Using ethylene glycol as the medium and its reductive property,the Bi-g-C3N4 binary heterojunction photocatalyst was prepared by a simple solvo-thermal method.Study found that,based on the in situ reduction and the growth of Bi nanoparticles loaded to g-C3N4 surface,can not only form a schottky junction,at the same time also can produce the surface from the SPR effect,such as promoting the composite material of charge carrier separation.In addition,low temperature solvent heat treatment can change the conduction band position of g-C3N4,making it more negative than the reduction potential,so it can change the enrichment position of photogenerated electrons,enhance the reduction ability,and promote it to show more superior photocatalytic performance.The results of surface analysis and calculation show that the semi-metal Bi has the plasma behavior of noble metal.The catalyst integrates the surface plasmon resonance excitation with the Schottky junction,which not only expands the visible light absorption region of g-C3N4,but also further promotes the charge transfer.The photocatalytic evaluation experiment of X-3B,which is difficult to degrade in water,also strongly proves this point.Under the experimental conditions,the photocatalytic efficiency can reach 97.95%in 90 min,which is 4.95 times that of monomer g-C3N4.In addition,the cycle test proves that the material still has good photocatalytic activity after 5 experiments. |
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