| Since the industrial revolution,the excessive exploitation and abusing of various fossil energies have caused the increasingly energy and environments issues of human society.The vigorous development and utilization of the high-efficiency and renewable clean energy have received extensive attention by various governments.At present,the photocatalytic water splitting and photodegradation technologies based on the solar light as driven force have been widely considered as the most most prospective way for solving the energy and environment concerns.Among the various semiconductors,graphitic carbon nitride?g-C3N4?is regarding as a promising visible-light-driven photocatalyst and has received greatly attention in the field of photocatalysis.More importantly,g-C3N4 possesses some unqiue characteristics in photocatalytic applications,such as proper bandgap energy,excellent stability and low-cost synthesizing condition.Nevertheless,g-C3N4 prepared from the thermal condensation process generally has relatively small surface area causing by the?-?conjugated electronic system,leading to the serious restricting its charge separation efficiency and visible-light utilization.Therefore,it is urgent to explore the efficient strategies for high-efficiency improvement the photoactivities of g-C3N4-based photocatalysts.In this paper,the high-photoactivity g-C3N4 nanosheets as well as several g-C3N4-based heterojunctions photocatalysts were fabricated via the simple but controllabe methods.The microstructure and phys-chemical properties of the as-prepared g-C3N4-based photocatalysts were tested by multiple techniques.Moreover,the photocatalytic performance were carefully investigated by hydrogen evolution from water and photodegradation pollutants from wastewater.In addition,the photocatalytic mechanism and photostability were also studied.The main study contents in this thesis are listed below:1.Fabrication of two-dimensional g-C3N4 nanosheets and investigation on their visible-light photocatalytic activity towards the hydrogen evolution from water splitting?1?Ultrathin two-dimensional?2D?g-C3N4 nanosheets were directly prepared by thermal polymerization of the hydrothermally pretreated melamine as precursor.The as-synthesized nanosheets with an average thickness of around 3 nm could be obtained by tuning the hydrothermal pretreatment temperature at 200 ?.The as-obtained g-C3N4 nanosheets possessed high specific surface area,large band gap,and fast charge carries separation capability with respect to the bulk g-C3N4.Moreover,the resultant g-C3N4 nanosheets not only exhibited the outstanting visible-light-driven photocatalytic H2 generation activity from water splitting?6-folds higher than bulk g-C3N4?,but also displayed the good photostability.?2?2D g-C3N4 nanosheets with different thicknesses were directly prepared by thermal polymerization of the HCl-induced hydrothermally pretreated melamine as precursor.Moreover,the g-C3N4 nanosheets over nanometer scale thickness could be precisely controlled through facile adjusting the HCl concentration.The thinner g-C3N4 nanosheets possessed a high specific surface area,a large band gap and fast charge separation ability with respect to the bulk g-C3N4.In addition,the thinner g-C3N4 nanosheets not only depicted the superior visible-light-induced photocatalytic H2 production activity from water splitting?9-folds higher than bulk g-C3N4?,but also displayed the good photostability.2.Constructing of M2O5/g-C3N4?M=V,Nb,Ta?heterojunctions photocatalysts and study on their photodegradation/photosplitting water performance?1?V2O5/g-C3N4 heterojunctions photocatalysts were firstly fabricated via a simple in-situ growth strategy.The photocatalytic performance of the as-obtained photocatalysts were carefully investigated through the photodegradation of dye?rhodamine B,RhB?and antibiotic?tetracycline,TC?pollutants under visible-light illumination.Photocatalysis results showed that the as-synthesized V2O5/g-C3N4heterojunctions photocatalysts could significantly enhance the visible-light photocatalytic activity towards the organic pollutants degradation.Moreover,the1.0wt%V2O5 modified sample heterojunction exhibited the optimum photocatalytic efficiency.The as-fabricated V2O5/g-C3N4 heterojunctions photocatalysts can greatly enlarge the BET surface area and improve the charge carries separation with respect to the pure g-C3N4.Importantly,the improving photocatalytic mechanism was found to be an all-solid-state Z-scheme charge transferring route.?2?Nb2O5/g-C3N4 heterojunctions photocatalysts were firstly synthesized via a facile one-step heating strategy.The photocatalytic activity of as-obtained photocatalysts were carefully evaluated by photodegradation of tetracycline hydrochloride under visible-light irradiation.Photocatalysis results showed that the as-synthesized Nb2O5/g-C3N4 heterojunctions photocatalysts could significantly enhance the visible-light photocatalytic activity towards the antibiotic degradation.Moreover,the 3.0wt%Nb2O5 modified heterojunction sample exhibited the optimum photocatalytic efficiency.The as-fabricated Nb2O5/g-C3N4 heterojunctions photocatalysts can greatly enlarge the BET surface areas and improve the charge carries separation with respect to the pure g-C3N4.In addition,the improving photocatalytic mechanism was detailed investigated,and it was found that the superoxide radical and hole are the major active species in the photodegradation reaction.?3?Ta2O5/g-C3N4 heterojunctions photocatalysts were firstly synthesized via a facile one-step heating strategy.The photocatalytic activity of as-prepared samples were carefully investigated through photosplitting water for hydrogen evolution under visible-light irradiation.Photocatalysis results showed that the as-synthesized Ta2O5/g-C3N4 heterojunctions photocatalysts could greatly enhance the visible-light photocatalytic activity.Moreover,the 7.5wt%Ta2O5 modified heterojunction sample not noly exhibited the optimum photocatalytic performance?4.2-folds higher than pure g-C3N4?,but also displayed the good photostability. |
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