Preparation Of Silver Loaded Titania/graphene Nanocomposites And Their Degradation Performance For Organic Pollutants

At present,as one of the most serious sources of water pollution,printing and dyeing wastewater with large emissions,high concentration,complex composition and dark color poses a great threat to humans and the ecological environment.TiO₂ photocatalytic technology is recognized as the most potential environmentally friendly technology by degrading or even mineralizing dye molecules through a series of redox reactions under illumination.By preparing nano-scale TiO₂ particles with different aspect ratios,TiO₂crystals with different crystal phases and different morphologies,and composites with graphene and silver-loaded TiO₂,explore an effective way to increase the photocatalytic activity and enhance the visible light response of TiO₂.The main contents of the paper are as follows:?1?Using tetrabutyl titanate as precursor,oleic acid and oleylamine as anionic and cationic surfactants,anatase TiO₂ nanoparticles with tuned size and aspect ratio were obtained by solvothermal method.Finely adjusting the average size and aspect ratio of these nanoparticles by varying the oleic acid/oleylamine molar ratio while maintaining a constant total molar content,and increasing the molar concentration of total capping agent in the solvent at a constant molar ratio?oleic acid/oleylamine=1:1?.The change in molar ratio or molar concentration enables the growth rate along different crystal faces of the TiO₂ nanoparticles to be controlled,and thus the aspect ratio of these nanoparticles.In addition,Photocatalytic degradation efficiency of methyl blue of a sample prepared with molar ratio of 6:24 for oleic acid to oleylamine is 11%more than other samples due to its low diffuse reflectance in the visible region.?2?Using tetrabutyl titanate as precursor,ethanol as solvent,oleylamine as surfactant,acetic acid as surface-active solvent,a novel one-dimensional single crystal anatase TiO₂nanorods with adjustable aspect ratio and band gap were synthesized by one-step alcohol thermal method.By changing the molar ratio of oleylamine/tetrabutyl titanate while maintaining a constant oleylamine/acetic acid molar ratio?acetic acid/oleylamine molar ratio=1:1?,The average size,aspect ratio and band gap of the nanorods can be easily adjusted.With the increase of the molar ratio of oleylamine/tetrabutyl titanate,the average size and aspect ratio of TiO₂ nanorods increase,the specific surface area increases,the band gap becomes wider,and the redox capacity increases,the performance of photocatalytic degradation of rhodamine B is significantly improved.When the oleylamine/tetrabutyl titanate molar ratio is 20/1,TiO₂ photocatalyst has a better photocatalytic effect on the degradation of Rhodamine B than P-25.?3?Using titanium tetrachloride as a precursor,ethanol as a solvent,and lithium acetate as a surfactant,TiO₂ photocatalyst was synthesized by a facile one-step alcoholysis method.Pure anatase TiO₂ nanoparticles with a particle size of about 10 nm and uniform distribution were prepared by controlling the temperature and the addition of lithium ions.Pure anatase phase TiO₂ nanoparticles with a particle size of about 10 nm and uniform distribution were obtained by controlling the temperature and the addition of lithium ions.Irregular masses with a particle size of 100-200 nm and spheres composed of a long nanorod having a diameter of less than 10 nm and having a radius in the range of 300-350nm were obtained by adding acetic acid and regulating the concentrations of acetic acid and ethanol solvents.Introducing graphene oxide on the high concentration of acetic acid and ethanol solvents obtained round bars with diameter of 5-15 nm and aspect ratio of about 5,and diamonds with short axis length of 5-15nm and ratio of long axis to short axis of about 2.5.Most of the obtained nanoparticles are affected by the quantum size effect,and the band gap is widened?3.23³.24 eV?,which makes the conduction band potential more negative,the valence band potential more positive,the redox capacity more enhanced,and the optical absorption blue-shifted.The addition of acetic acid directly leads to a transformation of the anatase phase to the rutile phase and a decrease in the band gap width?about 0.1 eV lower?.The introduction of graphene oxide greatly reduces the band gap width of TiO₂?0.5 eV less than the 3.20 eV of the typical anatase phase?,enhances its photocatalytic activity in the visible range,and Improve the adsorption performance of the dye.Under ultraviolet light irradiation,the degradation effect of Rhodamine B of the sample prepared at 150?and without adding lithium ions is significantly better than P-25.Within the first 3.5 hours of visible light exposure,The degradation efficiency of Rhodamine B of sample compounded with graphenehas been higher than P-25.?4?Based on the TiO₂ sample prepared at 150?without adding lithium ions as described in?3?,using glucose as a carbon source,sodium chloride and potassium chloride as a salt treatment agent,and silver nitrate as a silver source,silver-loaded TiO₂/graphene composites were prepared by calcination at 800?for 6 h in a tube furnace.The amount of silver loading was adjusted to 0,5%,and 3%.The obtained samples were mainly composed of stone-like particles with a size of about 1?m,but nanowires appeared when the silver loading amount was 3%.The three samples were mixed with anatase and rutile.The ratios of anatase phase and rutile phase corresponding to samples with silver loading amount of 0,5%and 3%were 6.4/93.6,2.4/97.6 and 13.4/86.6,the band gaps are 2.76,2.84,2.77 eV respectively.The compounding with graphene greatly enhances the adsorption of the dye on the sample.Under ultraviolet light,in the degradation of rhodamine B experiment,the adsorption efficiency of the three samples composited with graphene is 38 to 50 times that of P-25,and the photocatalytic degradation rate constant k of the sample with 3%silver loading amount reached nearly three times of P-25.In the visible light photocatalytic degradation of rhodamine B,the adsorption efficiency of the three samples was 20 times higher than P-25,and the degradation efficiency reached nearly 2 times of P-25 after 4 hours of visible light irradiation.