Preparation And Photocatalytic Performance Of Lignin Carbon/Semiconductor Composites

The development of photocatalytic technology plays an important role in dealing with the global environmental pollution.Photocatalysts,such as TiO₂,ZnO and etal,were widely used in the treatment of industrial wastewater.Comparing with physical adsorption and biodegradation technologies,photocatalysis has some advantages of low cost,simple operation,and short cycle.However,the electron-hole pairs are easy to combine,and have poor chemical stability,resulting in low photocatalytic activity.Therefore,carbon were used to improve the photocatalytic activity,effectively.As an important three-dimensional biomass material,lignin can be carbonized to graphene-like structure.In this study,lignin carbon/semiconductor composites with excellent optoelectronic properties were prepared via in-situ synthesis.The photocatalytic performance and mechanism were studied to provide theoretical basis and application routes for the value-added use of lignin and carbon-based photocatalyst.The main conclusions in this paper are as follows:?1?The LC/TiO₂ composites with different contents of lignin carbon?1⁷ wt%?were prepared via sol-gel method.The microstructure of the composites was microspheres.With the increase of carbonization temperature,the crystal phase of TiO₂ gradually changed from anatase to rutile,and the lignin carbon gradually decomposed.The LC/TiO₂-650 composite prepared under 650°C was a mixed crystal?A:R?8:2?and BET specific surface area was 45m²·g^-1.Lower bandgap energy?Eg=2.92 eV?resulted in excellent UV and visible absorption ability as well as electronic transmission ability.Degrading RhB under the mercury lamp,the degradation rate reached 78%in 1 h by LC/TiO₂-650 composites,which was 4.6 times of TiO₂.After three cycles the degradation rate was still kept at 76%.The mechanism study shows that the photocatalytic process of LC/TiO₂ is mainly controlled by photoelectron excitation and electron transfer.The lignin carbon coated on TiO₂has certain pores,the electrons can rapidly transfered to the interface through the lignin carbon,which effectively separated electrons and holes.?2?A series of LC/ZnO composites were prepared via in-situ compounding method under different carbonization temperatures.The lignin carbon content was 3¹1 wt%,and graphene oxide/ZnO?GO/Zn O?was prepared at 550?as comparison.The LC/ZnO composite is a graphene-like layer in which lignin carbon and ZnO are uniformly dispersed,and the ZnO inside was a typically hexagonal wurtzite.The LC/ZnO-550 composite prepared under 550?containing 5.7 wt%lignin carbon had average diameter of 300 nm and BET surface area of491 m²·g^-1 with a pore distribution of 10-100 nm.Lower bandgap energy?Eg=2.90 eV?resulted in excellent UV and visible light absorption ability as well as electronic transmission ability,which can efficient separation of photoelectron and hole.Degrading Rh B under the xenon lamp,the degradation rate reached 91%at 2 h by LC/ZnO-550 composite,the reaction rate was 6.3 times that of GO/ZnO,and it was excellent pH stability?from pH=3 to 12?.After three reuses,the degradation rate can be stabilized at 90%.For further explored its photocatalytic mechanism,LC/Zn O-550 photocatalytic is a process of adsorption and redox.On the one hand,lignin carbon provides numerous adsorption sites,which decreas solution concentration and increases the visible light transmittance.On the other hand,the lignin carbon effectively separates the photoelectron and hole,and improve photocatalytic efficiency.