Controlled Fabrication Of Low-dimensional MXene Based Nanohybrids With Efficient Photocatalytic Performance

Organic dye wastewater from industrial production has been the major threat of environment due to its intrinsic property like toxic,corrosive,carcinogenic,non-degradable and chemically stable etc.As a new eco-friendly and economical energy technology,photocatalysis can completely oxidize and decompose organic pollutants into non-toxic small molecules under the excitation of light.The design and construction of photocatalysts with broad spectral response,efficient catalytic ability,low cost and good stability are the primary requirements of photocatalytic technology development.In favor of the unique two-dimensional structure,high electrical conductivity and good hydrophilicity,MXenes is considered as an ideal co-catalysts to construct high photon utilization and activity photocatalytic system by combined with semiconductor materials.In this paper,low-dimensional MXene nanosheets were prepared by a simple wet chemical etching method,and then coupled with visible light respond WO₃semiconductor for two different photocatalytic systems construction.In addition,the internal photocatalytic mechanism is further illuminated by serious characterization and analysis.The details of the study are as follows.（1）The Ti₃C₂ MXene nanosheets were obtained by etching off the Al layer from bulk Ti₃Al C₂ MAX ceramic through HF or Na F/HCl agent treatment.And the effects of these two etching acids for the morphological structure and crystallinity were further analyzed.Besides,the reaction time of etching progress was also adjusted for the high quality Ti₃C₂ nanosheets preparation.As the SEM image displayed,the Ti₃C₂-Na F multilayer nanosheets was obtained after Na F/HCl etching and were spontaneously agglomerated together.Otherwise,the Ti₃C₂-HF nanosheets showed a loosen accordion-like structure with a nanoscale lamellar spacing,and the thickness of the nanosheets is about 20 nm.Compared with Ti₃C₂-Na F samples,the Ti₃C₂-HF nanosheets hold more smoother surface,which is favorable for constructing the heterojunctions.After acid treatment at room temperature for 48 h,the Al layer of Ti₃Al C₂ was completely removed which can be clearly confirmed by XRD diffraction peaks.Furthermore,FTIR spectra proved the existence of-OH groups on Ti₃C₂-HF nanosheets surface,indicating the good hydrophilic ability of Ti₃C₂-HF.In addition,the Ti₃C₂-HF nanosheets have good light absorption ability in the wavelength range of 200～800 nm and no obvious light absorption edge due to the metal-like properties.Therefore,the obtained Ti₃C₂-HF nanosheets can be used as an excellent co-catalyst to improve the material photoreactivity and catalytic activity（2）A novel sandwich-like Ti₃C₂/WO₃ nano-heterojunction were constructed by in situ growing of ultrathin WO₃ nanosheets on few-layer Ti₃C₂ MXene nanosheets surface through one-step hydrothermal method.The photodegradation rate of Ti₃C₂/WO₃ nanocomposite photocatalyst was improved nearly 9 times compared with that of single WO₃.The optimized Ti₃C₂/WO₃ achieves the greatest reaction rate of(16.08×10^-3 min^-1)toward tetracycline hydrochloride degradation.The improved the photocatalytic properties was ascribe to the high conductivity of Ti₃C₂,the ultrathin two-dimensional structure of WO₃ and Ti₃C₂,the tight interfacial contact and the formation of Schottky junctions by greatly promoted the photogenerated carrier separation rate and charge transfer ability.Besides,the main active species involved in the photodegradation reaction and proposed three possible degradation pathways was also identified.（3）For fully utilized of photocatalysis and membrane separation technology,Ti₃C₂/WO₃/PVDF photocatalytic membrane system was constructed through the ultrasonic self-assembly method and vacuum filtration method.The obtained photocatalytic membrane held high Rh B degradation activity,anti-fouling and recycling ability.SEM image presented that the Ti₃C₂/WO₃ nanoparticles were successfully loaded on the PVDF membrane backbone by vacuum filtration.And there is strong interaction between Ti₃C₂/WO₃ and PVDF membrane.After Ti₃C₂/WO₃ immobilization,the hydrophilicity of Ti₃C₂/WO₃/PVDF photocatalytic membrane was significantly enhanced than pristine PVDF membrane.The improved hydrophilicity is facilitated the water permeation and the organic pollutants adsorption.Meanwhile,a higher photocatalytic performance of the Ti₃C₂/WO₃/PVDF membrane was observed than Ti₃C₂/WO₃ in favor of the multi-hollow skeleton structure of PVDF membrane.Under visible light irradiation,the degradation rate constant of Rh B could up to 6.1×10^-3 min^-1.More importantly,due to the support of PVDF,the Ti₃C₂/WO₃/PVDF membrane exhibited high performance retention rate of 94%after 5 cycles.The photocatalyst modification also effectively improved the anti-fouling performance of PVDF membranes,and 5 wt%Ti₃C₂/WO₃/PVDF membranes maintained a high flux recovery rate of 92%after the anti-fouling test,with a water flux up to 480 L m² h^-1.The improved anti-fouling performance was mainly attributed to the high electrical conductivity of Ti₃C₂ and the formation of the built-in electric field at Ti₃C₂/WO₃ interface,which promote the separation rate and charge transfer rate of photogenerated carriers then increase the photocatalytic degradation rate toward adsorbed dye.