| Hydrogen energy is one of the main clean energy sources due to its advantages such as non-polluting,high-energy and storable when it is used as a fuel.Among of various means for production of hydrogen,photocatalytic water splitting is a way to realize the conversion of solar energy into hydrogen energy,and has broad application prospects.The researchers have developed a number of semiconductor photocatalysts for water splitting since the development of photocatalytic technology.Although the current semiconductor photocatalyst has made significant progresses,it still faces many problems such as instability,toxicity,high cost,wide bandgap,low quantum efficiency.Graphitic carbon nitride?g-C3N4?,a graphite-like and metal-free semiconductor,has attracted considerable interest in photocatalytic hydrogen evolution under visible light,due to its excellent chemical and thermal stability,integrate with other semiconductors easily and low cost.Unfortunately,the photocatalytic activity of pristine g-C3N4 for hydrogen evolution is still need to be improved owing to small specific surface area,limited utilization of visible light and fast recombination rate of photo-induced carrier.At present,the strategies for enhancing the photocatalytic activity of g-C3N4 can be divided into three major categories including nanocarbon loading,hetero-junction construction,and dimensionality tuning.Among them,nanocarbon material loading can form a Schottky junction of carbon with g-C3N4 to promote charge transfer.Hetero-junction construction could induce the band bending and form internal electrical field,which can significantly boost the spatial charge separation.For dimensionality tuning,it can shorten the path of electrons to surface for redox reaction and increase the separation rate of electrons and holes.In this paper,we gained bulk g-C3N4 by calcining melamine,and then it was protonated by HNO3 to make its surface charge change from negative to positive.Then,protonated g-C3N4 would be self-assembled with negatively charged graphene oxide under electrostatic force to form binary composite?protonated g-C3N4/rGO?.On this basis,the B-doped g-C3N4 dots?BCNDs?were loaded onto the surface of protonated g-C3N4/rGO to form ternary non-metal heterojunctions?protonated g-C3N4/rGO/BCNDs?,and it would further boost the photocatalytic activity.In addition,we substituted the protonated g-C3N4 in g-C3N4/rGO/BCNDs with CNNS with a large specific surface area,which can shorten the migration path of electrons involved in photoreaction.The primary experimental details and conclusions are as follows:?1?To solve the problem of low charge mobility of bulk g-C3N4,we obtained protonated g-C3N4/rGO binary composite under electrostatic action and hydrothermal action.The mobility of the charge is increased between the two materials by forming a Schottky junction.The morphology and composition of composites were characterized by TEM,Zeta potential,XRD,FT-IR,BET,XPS and so on.The photocatalytic activity online analysis system was applied to research the photocatalysis activity of the materials under visible light.The results show that the photocatalytic activity of protonated g-C3N4/rGO increased to 307.7?mol·g-1·h-1,which is 4.5 and 25.2 times that of bulk g-C3N4(69.7?mol·g-1·h-1)and protonated g-C3N4(12.2?mol·g-1·h-1),respectively.Among them,rGO as an electron transport bridge promotes the charge transfer in protonated g-C3N4/rGO,and effectively enhances its photocatalytic hydrogen evolution activity.?2?To settle the issue of low charge mobility of bulk g-C3N4,BCNDs were loaded onto the surface of protonated g-C3N4/rGO,which promotes charge transfer and further enhances photocatalytic activity.The characterization of protonated g-C3N4/rGO/BCNDs by TEM,XRD,FT-IR,BET,XPS and so on were carried out,and the photocatalytic hydrogen evolution mechanism was analyzed.The consequence suggest that the photocatalytic activity are increased to 741.4?mol·g-1·h-1,which is 2.4 and 2.3 times that of protonated g-C3N4/0.2 wt%rGO(307.7?mol·g-1·h-1)and protonated g-C3N4/?7 mL?BCNDs(320.0?mol·g-1·h-1),respectively.In the ternary heterojunction,the advantages of graphene and BCNDs can be combined to trigger synergistic effects and improve photocatalytic activity commonly.?3?To work out the trouble of the small specific surface area of bulk g-C3N4,we gained g-C3N4 nanosheets?CNNS?with the larger area by thermal oxidation stripping.And then,it is combined with the BCNDs and rGO to get CNNS/rGO/BCNDs ternary composites and further enhance the photocatalytic hydrogen evolution activity.Moreover,CNNS/rGO/BCNDs composites were characterized by TEM,XRD,FT-IR,BET,XPS and so on.The ultimateness imply that the photocatalytic activity is increased to 2036.1?mol·g-1·h-1,which is 11.5,7.5,1.7 times that of CNNS(176.9?mol·g-1·h-1),CNNS/0.2 wt%rGO(270.1?mol·g-1·h-1)and CNNS/?12 mL?BCNDs(1145.5?mol·g-1·h-1),respectively.The specific surface area of CNNS(166.3 m2·g-1)was 8.2 times higher than that of bulk g-C3N4(20.4m2·g-1).The specific surface area of g-C3N4 muscles,which could significantly shorten the charge migration path,suppres charge recombination,and further enhance photocatalytic activity. |
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