Hydrothermal Preparation And Photocatalytic Properties Of Silver Antimonate-based Semiconductor Materials

Printing and dyeing,paper making,medicine and other industries,while improving people’s lives,have also brought about a serious problems of waste water pollution.The industrial waste water is rich in organic substances,which do great harm to the human body and other organisms,and it is difficult to be degraded by microorganisms in the natural environment.So,these organic-rich industrial waste water needs to be effectively treated before discharge.Semiconductor photocatalyst,which can degrade refractory organic compounds directly into carbon dioxide and water without loss,has been praised as“the most ideal environmental purification technology in the world”.Silver antimonate semiconductor is one of the most useful catalysts because the photocatalyst can be excited by visible light or indoor light sources to generate electrons and holes,and can make the best use of light resources.However,the efficiency of photocatalysis of single-phase silver antimonate is low due to its quite low oxidation and reduction potential and easily recombination of photogenerated electrons and holes.Therefore,it is an important research direction to reduce the recombination rate of photogenerated electrons and holes and to improve the photocatalytic efficiency of silver antimonate-based photocatalysts.So far,the preparation methods of silver antimonite-based photocatalyst mostly adopt the two-step technology in which the silver antimonate particles firstly have prepared and then the composite was loaded or compounded on the silver antimonate particles.In general,the less steps in the preparation process means that the less equipment,plant and staff investment is required to start production and that the higher economic benefits may be obtained.Therefore,it is very important to optimize the technological process and explore the one-step preparation of silver antimonate-based photocatalyst.In this thesis,we focus on improving the efficiency of photogenerated electro-hole separation and simplifying the preparation process of the silver antimonate-based photocatalyst.A one-step hydrothermal synthesis method has been developed.Ag-loaded Ag/Ag_1.69Sb_2.27O_6.25binary nanocomposites,graphene-enhanced graphene@Ag/Ag Sb₂O_5.18ternary composite,silver-reinforced Ag₂S/Ag/Ag Sb₂O_5.18ternarystructurecompositeand Ag₃PO₄/Ag/Ag Sb₂O_5.18Z-type ternary heterojunction semiconductor were synthesized,respectively.The photocatalytic activity and mechanism of silver antimonate-based composite semiconductors have been studied using both Rhodamine B（Rh B）and tetracycline hydrochloride（OTC-HCl）.The specific contents of this study are as follows:（1）Preparation,characterization and photocatalytic activity of Ag/Ag_1.69Sb_2.27O_6.25Ag-supported semiconductor materials.An Ag/Ag_1.69Sb_2.27O_6.25sesame-ball-type nanocomposite has been prepared via a one-step hydrothermal method.The morphology,particle size and structure of the nanocomposites have been controlled synthesized.The reaction mechanism of Ag⁺reduced to silver in hydrothermal system has been revealed.The photocatalytic activity of Ag_1.69Sb_2.27O_6.25and its sintered product have been studied.Compared with Ag/Ag_1.69Sb_2.27O_6.25,Ag/Ag_1.69Sb_2.27O_6.25-900（calcined at 900℃）had stronger photocatalytic activity in which under the irradiation of 300 W xenon lamp for 120 min,42.5%Rh B and 66.8%OTC-HCl could be degraded,respectively.The surface-plasmon-enhanced Ag-loaded Ag_1.69Sb_2.27O_6.25model are proposed and reasonably account for high efficiency electron-hole transfer mechanism of Ag/Ag_1.69Sb_2.27O_6.25.（2）Preparation,characterization and photocatalytic activity of graphene@Ag/Ag Sb₂O_5.18graphene-enhanced semiconductor materials.A ternary graphene@Ag/Ag Sb₂O_5.18composite photocatalyst has been prepared via a one-step hydrothermal method.The formation mechanism of graphene@Ag/Ag Sb₂O_5.18in hydrothermal system has been revealed in which Ag-loaded Ag Sb₂O_5.18particles are coated with graphene sheets to inform graphene@Ag/Ag Sb₂O_5.18.Based on the Ellingham diagram,the action laws of Ag and graphene in the calcination process have been also revealed,respectively.Studies on photocatalytic properties show that the Ag/Ag Sb₂O_5.18composite with graphene exhibits excellent photocatalytic performance and the photocatalytic performance can be further enhanced by calcination.About 80%Rh B or 85%OTC-HCl could be decomposed by graphene@Ag/Ag Sb₂O_5.18-500 under xenon lamp irradiation for 120 min.The graphene-enhanced Ag-loaded graphene@Ag/Ag Sb₂O_5.18model has been proposed and reasonably accounts for high efficiency electron-hole transfer mechanism of graphene@Ag/Ag Sb₂O_5.18.（3）Preparation,characterization and photocatalytic activity of Ag₂S/Ag/Ag Sb₂O_5.18silver-enhanced semiconductor material.An Ag₂S/Ag/Ag Sb₂O_5.18composite photocatalyst has been prepared via a one-step hydrothermal method.Ag₂S/Ag/Ag Sb₂O_5.18powder has been sintered at 250℃.It was demonstrated theoretically that Ag-enhanced Ag₂S/Ag/Ag Sb₂O_5.18-250 could be obtained by sintering at 250℃.The resultsofphotocatalyticexperimentsshowedthat Ag₂S/Ag/Ag Sb₂O_5.18-250 had excellent photocatalytic degradation performance.Under the irradiation of xenon lamp for 120 min,85%Rh B or 78%OTC-HCl has been decomposed,respectively.The plasma-Z heterojunction of Ag₂S/Ag/Ag Sb₂O_5.18model has been proposed and reasonably account for high efficiency electron-hole transfer mechanism of Ag₂S/Ag/Ag Sb₂O_5.18.（4）Preparation,characterization and photocatalytic activity of Ag₃PO₄/Ag/Ag Sb₂O_5.18Z-type heterojunction semiconductor material.Monodisperse spherical Ag₃PO₄/Ag/Ag Sb₂O_5.18composite has been prepared by a one-step hydrothermal synthesis technique.The Ag₃PO₄/Ag/Ag Sb₂O_5.18composites with different morphology and particle size have been controlled synthesized by adding surfactant.The Ag₃PO₄/Ag/Ag Sb₂O_5.18composites have been sintered and the as-sintered at different temperatures have been obtained.The photocatalytic activities of Ag₃PO₄/Ag/Ag Sb₂O_5.18have studied and the results showed that the photocatalytic activity of Ag₃PO₄/Ag/Ag Sb₂O_5.18composites was better than those of their monomers and the photocatalytic activity can be improved by sintering.Under the irradiation of xenon lamp for 90 min,Ag₃PO₄/Ag/Ag Sb₂O_5.18-250 could decompose 90%Rh B or 98%OTC-HCl,respectively.The Ag₃PO₄/Ag/Ag Sb₂O_5.18Z-type heterojunction semiconductor model was proposed and reasonably account for high efficiency electron-hole transfer mechanism of Ag₃PO₄/Ag/Ag Sb₂O_5.18.In this paper,the design,synthesis,characterization and properties of above four kinds of silver antimonate-based semiconductor photocatalysts have been studied.The photocatalytic degradation of both Rh B（rich in printing and dyeing wastewater）and OTC-HCl（rich in pharmaceutical wastewater）has been studied.The research results are expected to be applied to the treatment of waste water from packaging and printing,textile printing,bio-pharmaceutical industry and so on.