Synthesis And Photocatalytic Hydrogen Production Of Dehydroabietic Acid Derived Carbon Dots/Titanium Dioxide

In this paper,two types of dehydroabietic acid derived carbon dots with photoluminescence properties were synthesized using dehydrogenated rosin as a carbon source by hydrothermal carbonization.Then,using titanium dioxide（P25,TiO₂）and dehydroabietic acid derived carbon dots as raw materials,three dehydroabietic acid derived carbon dots/TiO₂ composites were synthesized by hydrothermal method,and their catalytic performance for hydrogen production under Xenon lamp simulated sunlight（AM1.5,100 m W/cm²）irradiation was studied.The main research contents are as follows:（1）Using dehydroabietic acid as a carbon source and water as a solvent,dehydroabietic acid-based carbon dots（D-CDs）were prepared by the one-step hydrothermal carbonization method,and then compounded with TiO₂ to prepare D-CDs/TiO₂ composites.（1）The microscopic morphology,elemental composition,and functional group structure of D-CDs were analyzed using TEM,XPS,FTIR,and ¹H NMR.The results showed that D-CDs were mainly composed of graphitized carbon core and surface groups.D-CDs are uniformly dispersed spherical nanoparticles with an average particle size of about 4 nm.The optical performance analysis of D-CDs solution shows that its fluorescence emission wavelength is excitation dependent and concentration dependent,and its fluorescence emission intensity has good temperature response,temperature cycling,and stability against photobleaching;The solid-state fluorescence emission of D-CDs also has excitation wavelength dependence.The fluorescence lifetimes of D-CDs in solution and solid state were 3.73 ns and 3.06 ns,respectively;The quantum yield of photoluminescence（PLQY）was 12.6%and 4.14%,respectively.（2）The SEM,TEM,XRD,FTIR,and XPS were used to analyze the morphology,crystal form,structure,and elemental composition of pure TiO₂ and four D-CDs/TiO₂ composites（named TD7,TD9,TD11,and TD13,respectively）.The results showed that D-CDs and TiO₂ were successfully synthesized;Research on photocatalytic hydrogen production showed that with the increase of the loading amount of D-CDs,the hydrogen production amount of D-CDs/TiO₂ first increased and then decreased,and the maximum hydrogen production amount of TD11 was 3.83 times that of pure TiO₂;TD11 exhibits good hydrogen production stability and good photocatalytic stability.The optical absorption,photo-electrochemistry,and photoluminescence properties of D-CDs/TiO₂were analyzed using UV-vis diffuse reflection spectroscopy,fluorescence spectroscopy,photocurrent,electrical impedance,linear scanning,and fluorescence spectroscopy.The results showed that the loaded D-CDs increased the absorption redshift range and photocurrent intensity of TiO₂,decreased the impedance radius and initial potential,and decreased the fluorescence intensity and fluorescence lifetime of TiO₂,thereby improving the photocatalytic hydrogen production performance of TiO₂.（2）Using dehydroabietic acid as a carbon source and ethylenediamine as a nitrogen source,dehydroabietic acid-based nitrogen-doped carbon dots（D-NCDs）were prepared by a one-step hydrothermal carbonization method.Then,D-NCDs/TiO₂ composites were prepared by combining them with TiO₂.（1）The structure of D-NCDs were analyzed and showed that D-NCDs were mainly composed of graphitized carbon nuclei and surface groups;Its average particle size of D-NCDs is about 2.85 nm;The optical performance analysis of D-NCDs solution shows that its fluorescence emission wavelength is excitation dependent and concentration dependent,and its fluorescence emission intensity has good temperature response,temperature cycling,stability against photobleaching,and aggregation induced emission（AIE）characteristics;The solid-state fluorescence emission of D-NCDs also has excitation wavelength dependence and photobleaching resistance stability;The fluorescence lifetimes of D-NCDs in solution and solid state were 7.36 ns and 7.11 ns,respectively;The PLQY was 33.85%and 6.86%,respectively.（2）The structure of pure TiO₂ and four D-NCDs/TiO₂ composites（named TN5,TN7,TN9,and TN11,respectively）were analyzed and showed that D-NCDs and TiO₂ were successfully synthesized;The analysis of photocatalytic hydrogen production performance of D-NCDs/TiO₂ shows that with the increase of D-NCDs loading,the hydrogen production capacity first continuously increases and then decreases,with TN9 having the largest hydrogen production capacity,6.45 times that of pure TiO₂;And TN9 exhibited good hydrogen production stability and good photocatalytic stability.The optical absorption,photoelectrochemistry,and photoluminescence properties of D-NCDs/TiO₂ were analyzed and showed that the loaded D-NCDs promoted the absorption redshift range and photocurrent intensity of TiO₂,reduced the impedance radius and initial potential,and reduced the fluorescence intensity and fluorescence lifetime of TiO₂,thereby improving the photocatalytic hydrogen production performance of TiO₂.（3）Using TiO₂and N-doped carbon dots（E-NCDs）that synthesized from ethanolamine passivated dehydroabietic acid as raw materials,four types of E-NCDs/TiO₂ composites（named TE5,TE7,TE9,TE12）were prepared by a one-step hydrothermal synthesis.SEM,TEM,XRD,FTIR,and XPS were used to analyze the morphology,crystal form,structure,and elemental binding mode of TiO₂ and E-NCDs/TiO₂.The results showed that E-NCDs and TiO₂ were successfully synthesized through Ti-O-C bonds,and the loading of E-NCDs had no effect on the morphology of TiO₂;The analysis of the photocatalytic hydrogen production performance of E-NCDs/TiO₂ shows that with the increase of the loading amount of E-NCDs,the hydrogen production amount of E-NCDs/TiO₂ first increases and then decreases,and the maximum hydrogen production amount of TE9 is 6.41 times that of pure TiO₂,and TE9 exhibits good hydrogen production stability and good photocatalytic stability.The optical absorption,photo-electrochemistry,and photoluminescence properties of E-NCDs/TiO₂ were analyzed and showed that the loaded E-NCDs promoted the absorption redshift range and photocurrent intensity of TiO₂,reduced the impedance radius and initial potential,and reduced the fluorescence intensity and fluorescence lifetime of TiO₂,thereby improving the photocatalytic hydrogen production performance of TiO₂.Combining the photocatalytic hydrogen production performance,structural characterization,and photoelectrochemical properties of E-NCDs/TiO₂,and using Zeta potential analysis and finite difference time domain（FDTD）simulation,it is confirmed that the photocatalytic hydrogen production mechanism of E-NCDs/TiO₂ is that E-NCDs act as electron storage cells,and photons promote the transfer of photogenerated electrons from the conduction band of TiO₂ to E-NCDs under illumination,which delays the recombination of photoelectron hole pairs and improves the separation efficiency of photogenerated carriers,And make more photogenerated electrons participate in the photocatalytic hydrogen production reaction,thereby improving the photocatalytic reduction activity.