Preparation And Performance Of Porous Photocatalytic Fiber Based On Graphitic Carbon Nitride

With the rapid development of science and technology,environmental pollution and energy shortage have become increasingly serious.While seeking breakthroughs and innovations,mankind has gradually turned their attention to the treatment of pollutants and the transformation of green chemistry.As we all know,photocatalytic technology,as an environment-friendly new technology,has the advantages of simple operation,low energy consumption,no secondary pollution and high efficiency,which is an ideal choiceto solve environmental and energy problems.Among them,photocatalyst,as the core of photocatalytic reaction,can effectively convert light energy into chemical energy,and then realize the degradation of pollutants,hydrogen production from water decomposition,CO₂ reduction and organic synthesis.Compared with other photocatalysts,graphitc carbon nitride（g-C₃N₄）,as a polymer semiconductor with nano-sheet layered stacked structure,has been used in environmental restoration,organic synthesis and other fields because of its high chemical and thermal stability,unique band structure.Since the powder photocatalyst is easy to agglomerate and difficult to recover in practical application,it is necessary to develop suitable carriers.The synthetic fiber is an ideal carrier with the advantages of high specific surface area,easiness in operation and excellent chemical stability,which provides the attachment points for the catalyst.However,most preparation methods of photocatalytic fibers are inefficient and complex,which can easily make the catalyst partially or completely wrapped,resulting in the degradation of photocatalytic performance and limiting large-scale production.Furthermore,photocatalytic fiber is abandoned in the natural environment,which is difficult to be biodegraded,resulting in secondary pollution.Therefore,we choose to introduce pore structure into the fiber to effectively increase the specific surface area,improve the attachment point of powder catalyst in the fiber,and provide more reaction space.Moreover,polylactic acid（PLA）is an ideal green material,which can effectively reduce secondary pollution because of good biocompatibility,degradability and mechanical properties.Herein,graphitic carbon nitride/polylactic acid fiber composite（T-g-C₃N₄/PLA）was constructed by centrifugal-electrostatic spinning and alkali treatment.The results of scanning electron microscope（SEM）,transmission electron microscope（TEM）and Fourier infrared spectroscopy（FTIR）showed that g-C₃N₄ was uniformly dispersed in porous PLA fiber.It also indicateed that alkali treatment was beneficial to expand the pore size to form macroporous（>100 nm）.The experiment of specific surface area（BET）displayed that the doping of g-C₃N₄was beneficial to increase the specific surface area and increase the pore size.The above results indicated that T-g-C₃N₄/PLA with highly hierarchical macro/mesoporous structure on the surface and core.The porous structure of fiber could provide abundant space to immobilize g-C₃N₄nanosheets,avoiding the wrapping of g-C₃N₄ inside the fiber and creating more active sites for photocatalytic reaction.The photocatalytic degradation experiments using carbamazepine（CBZ）as the simulated substrate showed that T-g-C₃N₄/PLA exhibited high photocatalytic activity,good reusability,and maintained good photocatalytic performance in complex environment.Furthermore,capture agent experiments and electron paramagnetic resonance（EPR）displayed that superoxide radical（·O₂^-）,singlet oxygen（¹O₂）and hole（h⁺）were the main active species of CBZ photocatalytic degradation.Meanwhile,the possible degradation process of CBZ was speculated by ultra performance liquid chromatography-mass spectrometry（UPLC-MS）.Intermediates were formed by some chemical bonds of CBZ destroyed,which were further mineralized into CO₂ and H₂O.Finally,the results of advanced polymer chromatography（APC）were proved that T-g-C₃N₄/PLA could be biodegraded in natural without secondary pollution.In order to further study the photocatalytic performance of porous photocatalytic fiber in Suzuki coupling.Firstly,g-C₃N₄ and Pd Cl₂ was used to prepare Pd@CN by microwave-assisted deposition.Then porous T-Pd@CN/PLA was obtained by centrifugal-electrospinning and alkali treatment.SEM,TEM,EDX,XPS,FTIR and XRD displayed that the structure and properties of Pd@CN was similar to g-C₃N₄.In addition,Pd@CN was uniformly dispersed in porous PLA fiber.T-Pd@CN/PLA still maintained a highly porous structure on the surface and core.In T-Pd@CN/PLA photocatalytic Suzuki coupling,the effects of light,porous structure and alkali treatment,alkali,Pd content,ratio of water to ethanol,reaction substrate,reaction time and other factors on the reaction system were studied.When K₂CO₃ as basic substance,4 m L H₂O:Et OH（1:1）as the reaction solvent and T-Pd@CN/PLA as the catalyst,the conversion rate of bromobenzene and phenylboronic acid under 40 min illumination was over 99%.Finally,by carrying out the coupling reaction of different substrates under optimized reaction conditions,T-Pd@CN/PLA fiber displayed excellent photocatalytic performance,regardless of the position of the substituent in the substrate,and regardless of whether the substituent was an electron donating group or an electron withdrawing group.T-Pd@CN/PLA fiber could be used in various organic synthesises effectively.These porous photocatalytic fiber composites had great potential in wastewater treatment and Suzuki coupling.The preparation method of this paper provided a feasible idea for the loading of powder catalyst.