| The use of sunlight to decompose water into hydrogen and oxygen,and the decomposition of macromolecular organic pollutants into water and carbon dioxide is an ideal way to solve the current energy and environmental issues.Graphitic carbon nitride?g-C3N4?,a meta-free and visible-light-responsive photocatalyst,has attracted widely attention due to its potential application on photocatalytic pollutant removal,CO2 reduction as well as H2 production.However,due to low specific surface area and easy recombination of electron-holes,the photocatalytic activity of bulk g-C3N4 is poor.The noble-metal-free MoS2 has a layered structure similar to g-C3N4.It's ability to transfer carriers depends on its thickness?number of layers?.Based on this,the porous g-C3N4 prepared by the hard template method improves its specific surface area and the separation ability of photogenerated carriers.It was confirmed that the overall water splitting on mesoporous g-C3N4 was achieved under a Z-scheme system.Simultaneously,using the template method,MoS2 was synthesized by the solid-phase method with sulfur powder as the sulfur source.The growth of the Z-axis was suppressed by the confinement effect of the template to form ultrathin MoS2.Importantly,after ultrathin MoS2 was loaded on mesoporous g-C3N4 as a cocatalyst,the photocatalytic activity of g-C3N4 for Rh B degradation was further obviously promoted.The specific research is as follows:?1?Porous g-C3N4 photocatalyst was synthesized by a SiO2 hard template method with different particle size.Due to the confinement effect of SiO2,the specific surface area of porous g-C3N4 is larger than bulk gC3N4,significantly,which is increases with the decrease of the pore size?the size of SiO2?.The specific surface area of g-C3N4-15?prepared with SiO2 with a particle size of 15 nm as a template?reaches 159.7 m2?g-1,which is 11 times than bulk g-C3N4.The activity test shows that the rate of photocatalytic hydrogen production increases with the decrease of the pore size.The g-C3N4-15 sample shows the highest rate,reaching the 2.5?under full-wavelength light: ? > 320 nm?and 4.7?under visible light: ? > 420 nm?times of bulk g-C3N4,respectively.It's not only because the large specific surface area provides more active sites,but also the thin wall formed by the pore structure promotes the separation of electron holes.Because of avoiding the the weak oxidation ability of g-C3N4,the overall water splitting on mesoporous g-C3N4 was achieved under a Z-scheme system in which Bi VO4 and Fe2+/Fe3+ used asO2 evolution photocatalyst and carrier transfer mediator,respectively.When the carrier transfer medium concentration is low,the photocatalytic activity of the Z-scheme increases with the increasing the concentration of mediator.However,too high a medium concentration to enhance the photocatalytic activity,but prolonged the time to reach dynamic equilibrium?H2:O2 = 2:1?.When the concentration of the transfer mediator is 4 mmol?L-1,the mesoporous g-C3N4-15 achieved the overall water splitting under both full-wavelength(H2: 81.6 ?mol?h-1,O2: 40.4 ?mol?h-1)and visible(9.8 ?mol?h-1 and 4.4 ?mol?h-1)light irradiation with 1.8% AQY at ? = 420 nm.?2?Ultrathin MoS2 nanosheet?2 ? 9 layers?was prepared via a simple solid-state method using sulfur powder as a sulfur source and 15 nm SiO2 as a template.Benefitting by the confinement effect of SiO2 nanoparticles,few layers MoS2 nanosheet was obtained by inhibiting the growth of MoS2 along Z-axis,with a specific surface area up to 154.4 m2?g-1.Working as active site,the ultrathin MoS2 nanosheet loaded on mesoporous g-C3N4 obviously promotes photocatalytic Rh B degradation.Photoelectrochemical tests show that few layers MoS2 not only promote the rapid transfer of photogenerated electrons from mesoporous gC3N4 nanosheets to its surface,reduce the probability of carrier recombination,but decreases the migration distance of electrons in MoS2,thereby improving catalytic activity.Particularly,1.0 wt% MoS2/porous gC3N4 sample shows the highest photocatalytic activity,which 80% Rh B?10 mg?L-1?was decomposed within 15 min under visible light.Adsorption experiments show that few layers MoS2 adsorbing Rh B in large quantities,which is beneficial to the electrons transferred to its surface to quickly capture Rh B molecules and react.Capture experiments and control experiments show that ?O2-is the most important active species in photocatalytic degradation of Rh B,and CO2 is the main degradation product.After the photogenerated electrons transferred,they form ?O2-withO2,then ?O2-oxidizes Rh B adsorbed on MoS2 to H2 O and CO2.?3?Using solid phase method,ammonium molybdate as precursor and sulfur powder as sulfur source,in-situ synthesis of few layers MoS2/g-C3N4-15 composite catalyst.The number of MoS2 sheets grown by this method is small,the close contact between MoS2 and g-C3N4-15 is conducive to the migration of photogenerated electrons.The growth of MoS2 did not destroy the composition and pore structure of g-C3N4-15.MoS2 was preferentially loaded on the?002?surface of g-C3N4-15.Under visible light,the hydrogen production activity of 2.0 wt% ultrathin MoS2/g-C3N4-15 reached 246 ?mol?h-1,which was same to the mesoporous g-C3N4-15 loaded with 2.0 wt% Pt(256.7 ?mol?h-1). |
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