In-situ Grown Of G-C₃N₄/Ti₃C₂/TiO₂ Nanotube Arrays On Ti Meshes For Degradation Of Organic Pollutants Under Visible Light Irradiation

In recent years,wastewater containing large amounts of untreated industrial pollutants has been discharged into surface water or groundwater,causing serious pollution of the water environment.Rhodamine B and tetracycline hydrochloride are typical pollutants.As a green pollution treatment technology,photocatalyst has a strong oxidative degradation ability,even it can completely mineralize some kind of toxic pollutants.Titanium dioxide（TiO₂）photocatalyst has good application prospects due to its low cost and without secondary pollution.However,the band gap of TiO₂ is wide（3.2eV）and it can not use the visible light.Meanwhile,it is difficult to recover the powdered TiO₂after use in water or soil,which limits its application in the actual environment.Therefore,in this paper,3D-type TiO₂ nanotube arrays were grown in situ with titanium mesh as the matrix,which can be easily recycled because of its sheet structure.At the same time,graphitic carbon nitride（g-C₃N₄）,graphite-phase carbon nitride（g-C₃N₄）as a two-dimensional nanomaterial with a narrow band gap（2.7eV）,can effectively make up for the lack of light response of TiO₂.However,during the research of this binary material,the problem of high electron hole recombination rate still exists.A new two-dimensional material MXene with good electrical conductivity,as a co-catalyst,it can effectively promote the separation rate of photo-generated electrons and further improve the photocatalytic performance of composite materials.In this study,we successfully synthesised a ternary photocatalyst g-C₃N₄/Ti₃C₂/TiO₂ nanotube arrays in situ on Ti meshes by anodizing and chemical vapor deposition method.Different characterization and analyses methods,such as field emission scanning electron microscope（FESEM）,high-resolution transmission electron microscope（HRTEM）,X-ray powder diffraction（XRD）,UV-Vis diffuse reflectance spectroscopy（DRS）,X-ray photoelectron spectroscopy（XPS）were used to study the morphologies and optical properties of synthetic photocatalysts.These characterizations indicated that the mixture of g-C₃N₄ and Ti₃C₂ were evenly distributed on the surface of TiO₂ nanotube arrays.Photochemical analysis showed that the formation of heterostructures promoted the separation and transfer of carriers.The photocurrent density of g-C₃N₄/Ti₃C₂/TiO₂ nanotube array was 3 times of pure TiO₂ nanotube array.The optimum ratio of the g-C₃N₄/Ti₃C₂/TiO₂ nanotube arrays yielded 3 folds higher photocurrent density than TiO₂ nanotube arrays.The reaction rate constants of g-C₃N₄/Ti₃C₂/TiO₂ nanotube arrays for the degradation of rhodamine B and tetracycline hydrochloride were 0.0370 min^-1 and 0.0091 min^-1,respectively,which proved that their removal efficiency was about 3 times and 2 times higher than g-C₃N₄/TiO₂ nanotube arrays,respectively.The g-C₃N₄/Ti₃C₂/TiO₂ nanotube arrays still possessed high-efficiency treatment efficiency after 5 cycles of degradation of Rh B,showing the outstanding stability and recycling efficiency.In addition,the degradation intermediate of tetracycline hydrochloride was identified by HPLC-MS.The mechanism of the photocatalytic degradation pathway of TC-HCl was discussed.This study highlights an effective method to construct a reusable and stable ternary photocatalysts with significantly photo-degradation activities.