| In recent years,due to its environmental friendliness and low cost,semiconductor photocatalysis has received extensive attention.Among the photocatalytic materials,due to the good stability and efficient photocatalytic activity,rutile phase Ti O2,2H phase SnS2and g-C3N4 have wide applications in organic matter decomposition and H2O2 synthesis,respectively.Limited by the wide bandgap,the materials show poor photocatalytic activity under visible light.Due to the unique localized surface plasmon resonance（LSPR）property,Au nanoparticles（Au NPs）show good response to visible light with wavelengths between 500 to 650 nm and can effectively improve the catalytic performance of photocatalysts under visible light.To analyze the modification effect,Au NPs were introduced into Ti O2,SnS2 and g-C3N4.Furthermore,the enhancement behavior and the corresponding microscopic mechanisms of Au NPs in the visible light photocatalysis process were studied.To improve the visible and near-infrared light photocatalytic activity of Ti O2,the Schottky heterostructures of rutile phase Ti O2 nanosheets and Au NRs with different aspect ratios were obtained.By adjusting the aspect ratios,the longitudinal LSPR modes of Au NRs can be tuned,which can extend the response range to near-infrared region.Under visible and near-infrared light,with the increase of aspect ratio of Au NRs,the decomposition efficiency of Rh B can be gradually improved,which can reach more than2 times of Ti O2.The visible light photocatalytic behavior of Ti O2 nanosheets in experiment is originated from the surface photosensitization of Ti O2 by Rh B molecules,which is consistent with the theoretical analysis.Similarly,according to the calculated results,under visible light,the non-equilibrium carriers relaxed from the individual excitations in Au NRs induced by LSPR can be transferred to Ti O2 through the Dexter mechanism.With the increase of aspect ratios,the absorption coefficients of the longitudinal dipole mode of Au NRs are gradually increased,and the absorption peak positions are gradually red-shifted,which effectively improved the near-field intensity distribution of the system and is beneficial to the nonequilibrium electron transfer process from Au NRs to Ti O2 nanosheets.The 2H phase SnS2 tends to exhibit the truncated dodecahedral flake-like structure,and the interactions of these surfaces with Au NPs tends to show different characteristics.Therefore,the geometrical and electronic structure characteristics of the adsorbed Au clusters with the（001）and（101）surfaces of SnS2 were calculated.Compared with the adsorption energy of-3.77 e V on the（001）surface,the formation energy of（101）surface and Au cluster is ca.-5.29 e V,indicating a more stable structure.Under vacuum level,the calculated valence and conduction band edge of the（101）surface of SnS2 are-6.15 e V and-3.86 e V respectively,while the Fermi level of Au cluster is about-5.07 e V.This facilitated the transfer behavior of photo induced non-equilibrium carriers through the Dexter mechanism.In experiments,among the obtained composite structures,the Au NPs are mainly adsorbed on（101）and the equivalent surfaces of SnS2 nanoflakes,no adsorption behavior can be observed in the（001）surface.Under visible light,due to the introduction of Au NPs,the photo-dark current ratio of SnS2 can be increased from 2.0 to4.0,and the degradation rate of MO solution is increased 6 times,indicating that due to the relaxation process of LSPR,the photogenerated carriers of Au NPs can be injected into the（101）and the equivalent surfaces of SnS2,thereby improving the photocatalytic activity.To analyze the effect of morphology difference on visible light photocatalytic activity of SnS2-Au NPs Schottky structures,the differences of optical properties of the core-shell and Janus structures of Au NPs and SnS2 nanoparticle composite systems（SnS2-Au NPs）under visible light were compared.Different with the wide bandgap semiconductors,the absorption cross-section value of the Janus structure of SnS2-Au NPs is twice of the core-shell structure under visible light,and the near field intensity at the interface is up to about 6 times of the core-shell structure and sole SnS2 nanoparticles.In experiments,compared with the core-shell structure,the Janus structure shows higher visible light absorption coefficient and lower recombination rate of photogenerated carriers.In addition,the visible light degradation rate to MO solution of the Janus structure is about 4 times of SnS2 and core-shell structure.This is mainly attributed to the effective localized field enhancement for SnS2 materials and the transport behavior of hot electrons induced by the LSPR properties of Au NPs in the Janus structure.As a typical organic visible light photocatalytic material,the surface structure and optical properties of g-C3N4 can be adjusted through the surface protonation treatment（p-C3N4）,thereby affecting the photocatalytic activity.To improve the visible light response and the H2O2 generation activity,Au NPs were introduced to p-C3N4.Under the introducing of Au NPs,the absorption cut-off wavelength of the material system can be extended from 450 nm to 650 nm,and the absorption coefficient to visible light can also be increased to about 0.8-1.2.In experiments,compared with sole g-C3N4 and p-C3N4,the introduction of Au NPs can significantly enhance the H2O2 generation activity of the photocatalysts under visible light.This property originates from the localized field enhancement and non-equilibrium carrier injection induced by Au NPs.In addition,due to the size reduction after protonation treatment and the addition of protons to the imine group at the material edges,the p-C3N4 shows higher H2O2 generation activity than g-C3N4.As the theoretical analysis demonstrates,compared with sole g-C3N4,the desorption energy of H2O2 molecules on the surface of p-C3N4 is reduced from 1.12 e V to 0.97 e V,which effectively promoted the desorption behavior of H2O2 molecules on the surface of the material and thereby improved the photocatalytic reaction. |
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