Study On Preparation Of Modified TiO₂ Nanotubes And Photoelectrocatalytic Degradation Of Pesticide Carbaryl In Water

Photocatalysis has been considered as an extremely valuable technology in environmental governance.Its usage of solar energy as the light source to remove pollutants in water made it a research hotspot at the current stage.The technology solved the problem of energy shortage and reduced the harm brought to the environment.TiO₂ was regarded as an ideal photocatalytic material due to its low price,relatively stable properties such as chemical resistance and excellent catalytic activity.However,pure TiO₂ has certain disadvantages,including its large width in band gap and high carrier recombination rate.Most importantly,the difficulty in the separation of TiO₂ powders and the water phase under suspended state made the materials hard to be reused,which further restricted its practical application.Therefore,in order to solve the above shortcomings,this study focused on the investigation of the photocatalytic performance of TiO₂ nanotubes?TiO₂ NTs?photoelectrodes.The TiO₂ NTs were prepared by anodic oxidation method and methylene blue?MB?was chosen as the target pollutant.On this basis of TiO₂ NTs,the photocatalytic performance was optimized by adding reduced graphene oxide?RGO?and noble metal gold nanocrystals.The mechanism of photocatalytic degradation was studied by investigating the effects of modified TiO₂ NTs photoelectrode on the pesticide“silveain”in water.In this study,the response surface test was designed to prepare the neatly structured TiO₂NTs photoelectrode on Ti foil by using the anodic oxidation method.The discrepancy of the photocatalytic degradation of MB by TiO₂ NTs photoelectrode acquired under various preparation conditions was investigated.SEM,EDS,XRD,XPS,PL were used to characterize the apparentmorphology,crystal form size,composition structure of the photoelectrode.Light absorption properties of TiO₂ NTs and their photoelectrochemical properties were measured using an electrochemical workstation analysis.The results showed that the photocatalytic activity of the TiO₂ NTs photoelectrodes was the best when prepared at a 43 vol%water content,0.5 wt%ammonium fluoride concentration,oxidation temperature of 38?for 1.72 h and calcination temperature of 450?.The 35 W mercury lamp mimics sunlight,and the photocatalytic degradation efficiency of 5 mg·L^-11 MB solution reached 54%after a 120-minute exposure.TiO₂ had tubular structure with regular permutation.The diameter was 83.99 nm and the wall was 19.08 nm on average.According to free radical capture experiments,·OH and h⁺were the main active contents for photocatalytic removal of MB by TiO₂ NTs photoelectrodes.Moreover,for improving the stability and the photocatalytic performance of TiO₂ NTs photoelectrodes,electrochemical deposition was used to prepare RGO/TiO₂ NTs and Au-RGO/TiO₂ NTs.Also,response surface experiments were designed to optimize the load parameters.SEM,EDS,XRD,XPS,PL,Raman were used to characterize the photoelectrode and its electrochemical performance was then analyzed using an electrochemical workstation.The results showed that the optimal preparation condition of RGO/TiO₂ NTs is 1.1 V deposition voltage in 25?for 10 min.While the optimal preparation condition of Au-RGO/TiO₂ NTs was under the 0.2 V deposition voltage of Au for 30 s.The photocatalytic degrading efficiency of MB by RGO/TiO₂ NTs and Au-RGO/TiO₂ NTs photoelectrode under the illumination of 35 W mercury lamp for 120 min was 64%and 72%,respectively.After loading RGO and Au,part of the tube wall of TiO₂ nanotubes became thicker and the thickest part reached about 22.60 nm.However,the main structure of the nanotubes remained unchanged.After recycling for 5 times,the degradation rate was still stable above 68%.According to the free radical capture test,·OH,h⁺and·O₂^-had a certain role in the reaction process.·OH played a major role in the process of photocatalytic removal of MB,followed by h⁺.Finally,modified TiO₂ NTs photoelectrode was used to photoelectrocatalytically degrade the pesticide carbaryl in water.The results showed that under the light of a 35 W mercury lamp,the removal rate of carbaryl reached 96.5%after 480 minutes of illumination.In addition,the effects of the initial concentration and pH on the degradation of carbaryl were investigated and the degradation mechanism of carbaryl was analyzed.Carbamate functional groups has been presented during the degradation of carbaryl.The hydroxide ion?OH-?in water has replaced the carbamate groups to form 1-naphthol and methyl isocyanate,which further has reacted with H₂O to form Methylamine and CO₂.