Chemical Modification Of Graphite Phase Carbon Nitride Nanosheets And Its Photocatalytic Disinfection Application

Solar energy can be widely used for water disinfection and purification.Purification of pathogens in water by reactive oxygen species generated from photocatalytic reactions has been considered a promising approach.This dissertation reported on an efficient metal-free thin film prepared by a sort of solar water disinfection material.Firstly,the edge carboxyl and carbonyl functionalized graphite-phase carbon nitride nanosheets were prepared by an improved Hummer's method,and the functionalized edges were further exposed through self-assembly to improve the disinfection performance.For the first time,we have conducted in-depth researches on the mechanism of accelerating the generation of hydrogen peroxide by exposing carboxyl and carbonyl groups at the edge of the g-C3N4 nanosheets.The disinfection efficiency was tested under simulated visible light.In addition,we also prepared a prototype fixed-bed reactor and polymer bags with surface-modified edge-functionalized graphite-phase carbonitride nanosheets for scaled water disinfection.The main research includes:(1)An improved Hummer's method for the preparation of ultra-thin graphite-phase carbon nitride nanosheets was developed,and functionalization of C=O,-COOH and-OH can be manipulated by controlling the oxidation time with concentrated sulfuric acid and KMnO4,and a reduction process was also developed by ultilizing hydrazine hydrate.When the oxidation treatment time reaches 30 minutes,the ultra-thin graphite-phase carbon nitride nanosheets are successfully prepared from top to bottom,and their edges are functionalized with carboxyl and carbonyl groups.With the increase of oxidation time,hydroxyls are further functionalized on the surface of these nanosheets.The amount of hydroxyl groups reaches the limit when the treatment time reaches 60 minutes.Functionalization of carboxyl,carbonyl,and hydroxy groups can gradually shift the bottom position of the g-C3N4 conduction band from 1.1 eV to 1.4 eV,and as the degree of oxygen functionalization increases,the degree of uptake of the bottom of the conduction band increases.By testing the lifetime of photogenerated electron-hole pairs of a series of oxygen-functionalized nanosheets,the mechanism of the increase of carrier lifetime due to valence electrons on hydroxyl oxygen atoms is proposed.This mechanism can be used to develop new water oxidation reactions.These calulation results provides powerful theoretical guidance for the as-proposed mechanism.(2)Nano-film(F-g-C3N4-30)photocatalysts was prepared by the ultilization of edge carboxyl,carbonyl functionalized ultra-thin graphitic carbon nitride nanosheets(g-C3N4-30)as raw materials for solar water disinfection of photocatalysts.99.9999%disinfection efficiency(Ultilizing 5 cm2 nanoflim catalyst)can be achieved in 60 minutes under visble light illumination.The amount of ROS produced in the light of g-C3N4-30 and the sacrificial reagent quenching experiments for various ROS have shown that the production of oxygen-reduction-related ROS is significantly high,and such reactive oxygen species play the most important role in the disinfection process.In addition,the mechanism of the increase in band-bending amplitude at the edge of the nanosheets can be attributed to the ultra-thin two-dimensional morphologies of g-C3N4-30 and the functionalization of carbonyl and carboxyl groups at the edge was proposed.This mechanism can explain rolls of carboxyl,carbonyl in the decrease of recombination rate of photogenerated electron hole pair in functionalized ultrathin graphite phase nitrided carbon nanosheets.Through first-principle simulations,it was confirmed that the cumulative effect of C=O and-COOH on the edge of g-C3N4-30 and the presence of electron depletion layers near edges provide a powerful theoretical evidence mechanism for the above-mentioned proposed new mechanism.(3)Ultra-thin graphitic carbon nitride nanosheets functionalized with an edge carbonyl group and a carboxyl oxygen were used as a raw material to develop a self-assembled preparation method for exposing their edges more efficiently on a nano film.A disinfection efficiency of 99.9999%was achieved by ultizing this film(5 Cm2)in 30 minutes,which is higher than disinfection efficiencies of most of the powder photocatalyst disinfection systems currently reported.The elemental state and valence band position of the film were studied.It is found that the surface energy band of this film could be shifted up by about 0.15 eV due to the high exposure of the functionalization of-COOH and-C=O.This further confirms that the more effective exposure of the g-C3N4-30's edge can further increase the production of ROS,thus improving the disinfection performance of the system.Furthermore,F-g-C3N4-30-EP modified fixed-bed disinfection reactors and sealed bags were developed for futher disinfection applications.The volume of water that can be purified after one-time disinfection of one sealed bag(Ultilizing 600 cm2 nanoflim catalyst)is approximately 10 L.It can provide at least four adults with the germ-free drinking water needed for one day.The fixed bed reactor as a model of a fully automatic water disinfection device can provide new guidance for designing a new water disinfection process.