Photoreduction Of Heavy Metal Endocrne Disrupting Chemicals In Reverse Osmosis Concentrate

Reverse osmosis technology is widely used in the advanced purification process of water.The principle is to apply a pressure higher than the osmotic pressure to the solution,so that the water molecules can pass through the semi-permeable membrane,while other pollutants could be intercepted effectively,finally,the water quality can be deeply purified.However,about 25 to 35 percent reverse osmosis concentrated water would be generated from reverse osmosis technology process,which contains high salinity and a variety of new pollutants.Discharges directly without any treatment will not only be harmful to the environment and human health,but also make shortage of water resources.Endocrine disruptors is a kind of emerging pollutants with bioaccumulation in organisms.And heavy metal endocrine disruptors cannot be biodegraded,which has a great impact on human health.Therefore,how to remove heavy metal endocrine disruptors effectively from reverse osmosis concentrated water and achlieve deep purification and reuse of reverse osmosis concentrated water have become a research focus currenttly.Photocatalytic technique is simple and easy to control.It has strong redox ability and can degrade pollutants completely.It is considered as a new environmentally friendly technology with good development prospects,showing a unique advantage in reducing heavy metal endocrine disruptors.In this thesis,photocatalytic technology is employed to adsorb and reduce heavy metal endocrine disruptors in concentrated reverse osmosis water to achieve the purpose of removal.Titanium dioxide?TiO₂?is the most widely studied catalyst at present,however,the wide band gap of TiO₂ lead to a low utilization of visible light.Under the excitation of ultraviolet light,photogenerated electrons and holes are formed,which are easy to overlap,leading to reduce the photocatalytic efficiency reduced.Aiming at this problem,firstly,this theis prepared titanium dioxide?TiO₂?nanocomposites based on graphene oxide?GO?and then studied the factors affecting photocatalytic efficiency?e.g.pH,the GO content of the TiO₂/GO nanocomposites,the dosage of TiO₂/GO nanocomposites?.Nextly,GOQDs was prepared successfully.In addition,the ternary heterojunction photocatalysts WO₃/TiO₂/GOQDs was synthesized by hydro-thermal method.Besides,the factors affecting photocatalytic efficiency such as pH,the content WO₃ of WO₃/TiO₂/GOQDs and the dosage of WO₃/TiO₂/GOQDs were studied.Meanwhile,the ternary heterojunction photocatalysts Ag/TiO₂/GOQDs was synthesized by hydro-thermal method.Besides,the factors affecting photocatalytic efficiency such as pH,the content Ag of Ag/TiO₂/GOQDs and the dosage of Ag/TiO₂/GOQDs were studied.The morphology,structure and properties of the three photocatalysts were characterized by XRD,SEM,TEM,FTIR,BET and Raman.The characterization results indicate that the GO is a sheet structure with wrinkles.Besides,GOQDs have uniform particle size distribution and regular shape.Meanwhile,oxygen-containing groups on the surface of GO and GOQDs increases the dispersibility in water.The anatase TiO₂ and orthogonal crystal form of WO₃ can enhance the photocatalytic activity.Ag elemental is beneficial to capture electrons and reduce the recombination rate of photogenerated carriers.The photocatalytic experiment results of TiO₂/GO nanocomposites show that the ration of TiO₂:GO=15:8,pH=6 and the dosage of photocatalyst 150 mg can reach a high removing rate.Besides,C/C₀(Cd²⁺)=0.3368 and the removal rate was 66.32%,C/C₀(Pb²⁺)=0.1104 and the removal rate was 88.96%.The photocatalytic experiment results of WO₃/TiO₂/GOQDs ternary nanocomposites show that when the addition of WO₃0.4948g,pH=6 and the dosage of photocatalyst 150 mg can reach a high removal efficiency.Besides,C/C₀(Cd²⁺)=0.1534 and the removal rate was 84.66%,C/C₀(Pb²⁺)=0.0923 and the removal rate was 90.77%.The photocatalytic experiment results of Ag/TiO₂/GOQDs ternary nanocomposites show that when the addition of AgNO₃is 0.375g,pH=6 and the dosage of photocatalyst 150 mg can reach a high removal level.Besides,C/C₀(Cd²⁺)=0.1167 and the removal rate was 88.33%,C/C₀(Pb²⁺)=0.0978 and the removal rate was 90.22%.