| Energy shortage and environmental pollution have become two important factors restricting the sustainable development of society.The vigorous development and utilization of high-efficiency and renewable clean energy has attracted extensive attention by various governments.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.The development the high efficient,stable and cheap photocatalysts is the crucial issue of photocatalytic technology.The practical application of the traditional photocatalytic materials with wide band gap,especially TiO2,is subject to severe restrictions,due to their limited ultraviolet light utilization and low quantum yield contributing to the easy recombination of photogenerated electrons/holes.Graphitic carbon nitride（g-C3N4）has be considered as a promising photocatalytic material because of its wide range of raw materials,simple preparation process,suitable band structure and good chemical stability.However,the low specific surface area,high recombination rates of photogenerated carriers and relative low visible-light response of pristine bulk g-C3N4 greatly hinder its development and practical application.This dissertation is devoted to develop the high photocatalytic activity of g-C3N4 based photocatalysts,which mean to focus the strategies of spectrum response,photogenerated carrier separation rate and nanostructured engineering.（1）Photocatalytic hydrogen evolution has broad prospects as a clean solution for the energy crisis.However,the rational design of catalyst complex,the H2 evolution efficiency,and the yield are great challenge.Herein,3D hierarchical g-C3N4 architectures assembled by ultrathin carbon rich nanosheets（3D CCNS）were prepared via an extremely facile hexamethylenetetramine（HMTA）activation approach at bulk scale,indicating the validation of scale-up production process.The 2D ultrathin carbon rich nanosheets were several hundred nanometers in width but only 5-6 nanometers in thickness,and gave rise to a unique 3D interconnected network.The unique composition and structure of the nanosheets endow them with remarkably light absorption spectrum with the tunable bandgap,high electrical conductivity,fast charge separation and large surface areas with abundant reaction active sites,and thus significantly improved H2 production performance.As high as 7.8% quantum efficiency can be achieved by irritating 3D CCNS at 420 nm with a H2 evolution rate >2.7×104 μmol/g/h,which is 31.3 times higher than the pristine g-C3N4.Our work introduces an extremely facile route for mass production of doping modified 3D g-C3N4-based photocatalyst with excellent H2 evolution performances.（2）The CdS@g-C3N4 heterojunction photocatalyst has attracted tremendous attention in photocatalytic hydrogen evolution,but how to further enhance its photoactivity is still a huge challenge.Herein,we develop a facile strategy to form a double-modified Cd S@g-C3N4 heterojunction through the simultaneous phosphorus（P）doping and defects creation in one-step process.Various characterization results confirmed the intimate heterojunction,P doped via P-N bond formation and abundant defects on the double-modified Cd S@g-C3N4.The optimized photocatalyst showed a remarkable H2 evolution rate of 383.59 μmol/h,which was 52.05,4.11,and 1.52 times higher than those of pristine g-C3N4,Cd S,and unmodified Cd S@g-C3N4 respectively.The superior H2 evolution performance can be attributed to the following factors:（1）P doping induced a mid-gap state,resulting in the improved ability to harvest visible light and prolong the lifetime of photogenerated electrons;（2）defects could narrow bandgap and trap electrons,accelerating the transfer of these electrons to H+;（3）core-shell nanostructures and intimate interfacial contact promote the separation and transfer of interface charges owing to customized charge transport pathways.This work highlights a feasible strategy for developing superior photocatalysts by heteroatom doping and defect engineering.（3）The construction of heterogeneous catalysts with high efficiency is important for the degradation of organic pollutants.Catalysts with small cluster dispersions are thus highly desirable to maximize the amount of active-sites and enhance the atom efficiency.Here,a simple and scalable method was designed to fabricate amorphous sub-nanometer Cu doped Fe OOH clusters/ultrathin g-C3N4 nanosheet（Cu-Fe OOH/CNNS）hybrids as heterogeneous photo-Fenton catalysts.The fabricated hybrids possess unique hierarchical nanostructure,comprising abundant uniformly dispersed ultrafine Cu-Fe OOH clusters tightly anchored on the CNNS surface.The optimal loading content of Cu-Fe OOH clusters decolorized 98.7% Methylene Blue（MB）within 40 min in a wide p H value range of 4.8-10.1,which is more than 8.1 times faster than pristine CNNS.Moreover,influential factors,including initial MB concentration,H2O2 concentration,initial p H and multiform organic contaminants,such as azo dye,nitrophenol and antibiotic,were investigated and analyzed in details.The degradation efficiency remained the same even after 10 th cycles,suggesting the robustness and stability of the fabricated hybrids.The excellent degradation efficiency is attributed to the cluster active sites and the synergistic activation of Fe/Cu/CNNS promoting the generation of ?OH for MB degradation.A practical application of water remediation at 15 L scale was also performed with expected MB degradation efficiency under the coexisting dyes.The fabricated hybrid is expected for practical industrialization applications and this design and fabrication strategy provided a generic route for further design of high activities catalysts for PFR.（4）The development of effective approaches for the preparation of 0D quantum dots（QDs）/2D nanosheets（NSs）heterostructure,which have been proven to be favorable for heterogeneous catalysis,is highly desirable but remains a great challenge.Herein,0D metal oxide nanocrystals-2D ultrathin g-C3N4 nanosheets heterostructure（Co3O4/CNNS）are synthesized via a facile chemical reaction,followed by annealing in air.Ultrafine Co3O4 QDs（2.2-3.2 nm）are uniformly and tightly attached on the surface of g-C3N4 nanosheets.Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline（TC）via peroxymonosulfate（PMS）activation.The optimal catalyst,namely,Co3O4/CNNS-1100,exhibited excellent performance and 98.7% TC can be degraded under visible light irradiation.Moreover,TC degradation is almost completely insusceptible to several real water samples.Meanwhile,other dye pollutants can also be efficiently degraded by the Co3O4/CNNS-1100/PMS/vis system.The quenching tests display that that the h+,?OH,O2?- and SO4?- are responsible for TC removal.The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic-and chemical-processes in the PMS activation.This work brings in new insight in developing multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification. |
