Preparation and Photocatalytic Performance Reasearch of Structure-adjustable g-C3N4 by Co-pyrolysis Method

Author:Liu Cheng Yin

Supervisor:zhang yi he huang hong wei


Degree Year:2019





Graphitic carbon nitride(g-C3N4)has received great attention as an environmentally friendly photocatalyst,which possess many charming characteristics,such as unique electronic structure,chemical and thermal stability,facile synthesis and metal free.Nonetheless,pristine g-C3N4,as a photocatalytic material,is restricted by low specific surface area and deficient separation of charge carriers.To remedy these drawbacks,we employ in situ co-pyrolysis route to fabricate tedious morphology and doping of g-C3N4.It can significantly promote separation and transfer of charge carriers.Besides,this synthetic route is also applicable to preparation of heterojunctions with other semiconductors forming close interface relationship,which can greatly promote the separation and transfer of photogenerated charge carriers accounting for the huge enhancement in photocatalytic oxidation and reduction activity.The specific research content is as follows:(1)A horn-like hollow mesoporous ultrathin g-C3N4 tube materials had been synthesized via high temperature co-pyrolysis method utilizing melamine and substantial ammonium bromide(NH4Br).The advantage merits of hollow/mesoporous/ultrathin can profoundly enhance photocatalytic performance for H2 evolution with a high apparent quantum efficiency of 14.3%at 420 nm.In the complex thermal polymerization process,we found that the formation and decomposition of horn-like Br-containing intermediate was the key to form this particular structure.Selective photo-deposition results reflected the phenomenon of charge enrichment at the horn tips and the efficient spatial anisotropic charge separation.(2)The porous g-C3N4 was synthesized by high temperature co-pyrolysis strategy using melamine and NH4HCO3.The visible-light photocatalytic properties for rhodamine B degradation and NO removal were greatly improved.(3)The O substituted g-C3N4 was achieved by introduction of substantial ammonium acetate in the thermal polymerization process of melamine.The replacement of O atoms for lattice N atoms by forming C-O=C bonds for the first time generated an acceptor level realizing the wide-range-photoresponsivity and tunable band structure.The O-g-C3N4 sample showed the most enhanced hydrogen production activity under visible light irradiation.Besides,the similar O substituted g-C3N4 samples can also be obtained by pyrolysis of ammonium acetate with other nitrogen-rich precursors(such as urea and thiourea),demonstrating that it was a general approach for O substitution.(4)The porous Cl intercalated g-C3N4 photocatalysts were fabricated via high temperature co-pyrolysis strategy of melamine and ammonium chloride.The advanced photocatalyst simultaneously achieved microstructure modification and doping with chemical element.Cl intercalated g-C3N4 can significantly promote charge transport by establishing interlayer pathways.Also,narrowed band gap,more negative conduction-band level and porous structure endowed Cl-g-C3N4 with superior abilities on photocatalytic H2 evolution,CO2 reduction,removal of azo model dye rhodamine B and gaseous NO.(5)The n-n type g-C3N4/Bi5O7I heterojunctions were prepared via high temperature co-pyrolysis strategy by using melamine and BiOI.This synthetic method enabled intimate interfacial interaction between g-C3N4 and Bi5O7I with chemical bonding,which is beneficial to improve the rhodamine B and phenol photodegradation performance.