Surface/interface Structure Design And Heterogeneous Catalysis Performance Of Binary Oxide Semiconductor

Heterogeneous catalysis is a catalytic reaction that occurs at a liquid-solid,gas-solid or liquid-gas interface,including photocatalysis,electrocatalysis,thermocatalysis and organic conversion,and plays a very important role in the development and utilization of clean energy and industrial production.The exploitation of heterogeneous catalysts has greatly promoted the process of various kinds of catalytic reactions.Among these catalysts,binary oxide semiconductors attract wide attentions due to their features of low toxicity,high activity and high stability as well as their simple synthesis process.Heterogeneous catalytic reactions mainly occur at the surface or interface of catalysts.Low specific surface area and weak interface interaction usually lead to low reactivity and catalytic efficiency.Many studies have shown that the exposure of special lattice plane and the construction of low dimensional or porous structures can effectively increase the reactive sites.What's more,the presence of interfaces with strong interaction can greatly improve the utilization of electrons in the catalytic reaction.Therefore,design and synthesis binary oxide semiconductor catalysts with high specific surface,special exposed lattice plane or strong interfacial interaction to obtain excellent catalytic performance are of great significance for promoting the application of heterogeneous catalysis in clean energy,industrial production or other fields.This thesis takes binary oxide semiconductors as target materials.Firstly,a low dimensional oxide semiconductor with different exposed planes,as well as a porous oxide semiconductor were designed and synthesized.Then,heterostructure nano-composite oxides with strong interface interaction were successfully constructed by solution chemistry and surface chemistry.The construction of these surface interfaces improves the catalytic performance of the materials.The main results obtained are as follows:1.Pressure-induced synthesis of CeO₂ quantum dots:High pressure solution chemical reaction was realized by introducing compression argon and digestion ripening reagents into the solvothermal reaction.Through changing the reaction pressure and time,{001}plane exposed CeO₂ cube and{111}plane exposed CeO₂truncated octahedron were synthesized.The CeO₂ nanocrystals showed an inverse growth behavior as the reaction time prolong under the pressure of 5 MPa,which is a“top-down”process.CeO₂ nanocubes with exposed plane{001}were gradually changed to truncated octahedron with exposed plane{111},and their size was reduced from 10 nm to 5 nm.This is mainly due to the low stability of plane{001},where oxygen vacancy is easier to produce in the presence of reducing digestion reagents and pressure.The stress concentrated on the oxygen vacancy could break the Ce-O bond,promoting the formation of CeO₂ truncated octahedron quantum dot with exposed plane{111}.This work may provide new direction for controllable design and synthesis low-dimensional binary oxide semiconductor with controlled crystal plane.2.Synthesis of porous SnO₂ doped with heterogeneous atoms on the surface:A series of heterogeneous atom doped porous SnO₂ were synthesized by taking Sn-containing intermetallic as precursors through an oxidation-etching process:Ni doped popcorn-like SnO₂ with a large number of 30 nm pores and two kinds of Cu doped SnO₂ nanocages with different morphologies.Due to the low solid solution limit of MO_x?M:Ni,Cu?in SnO₂,metal ions were doped on the surface of SnO₂ to form a special surface/interface structure,and a large number of pores were generated after selective removal of MO_x.Among them,Ni doped SnO₂ showed high sensitivity in formaldehyde detection at low operating temperature and short response time?23.7,50 ppm formaldehyde 170 ^oC,5s?.Cu doped SnO₂ exhibited high catalytic activity in CO oxidation and ammonium perchlorate thermal decomposition,and reduced the conversion temperature.The research could provide guidances for the synthesis of heterogeneous atom-doped porous oxides from intermetallic compounds for heterogeneous catalysis.3.Synthesis of amorphous porous NbO_x/g-C₃N₄ and strong interface coupling effect:Interfacial-enhanced amorphous porous NbO_x/g-C₃N₄ heterostructure composite were synthesized through a straightforward spontaneous coupling process.The NbO_x possesses amorphous porous structures with high specific surface area?205m²/g?and owns plenty of acidic sites?418?mol/g?as well as basic sites?184?mol/g?.These acidic and basic sites steadily electrostatically attract-NH_x and C-OH on the surface of g-C₃N₄ to form hydrogen bonds?Nb-O-H???N,Nb-O???H-O-C?,showing a strong electron interaction between NbO_x and g-C₃N₄.When tested as a catalyst for photocatalytic water splitting reaction under simulated sunlight,NbO_x/CN-0.05showed excellent photocatalysis activity(90.2?mol?g^-1?h^-1),which was significantly better than g-C₃N₄(8.9?mol?g^-1?h^-1)and NbO_x(26.3?mol?g^-1?h^-1).Under visible light,the optimal amorphous porous NbO_x/CN-0.05 heterostructure composite exhibits a hydrogen evolution rate of 53?mol?g^-1?h^-1,which is about 14 times higher than that of pristine g-C₃N₄(3.8?mol?g^-1?h^-1)and is even superior than P25(16?mol?g^-1?h^-1).The enhanced photocatalytic activity can attribute to the strong coupling effect between NbO_x and g-C₃N₄ that benefiting for the carriers separation effectively.4.Synthesis of symbiotic hetero-nanocomposite of metastable CaCl₂-type and rutile TiO₂.Symbiotic hetero-nanocomposite that contains an unprecedented CaCl₂-type titania inter-grown with rutile TiO₂ was synthesized by a solution chemistry process.By changing TiCl₄ concentration and reaction temperature,the phase diagram was drawn to obtain the formation region of this symbiotic hetero-nanocomposite.The CaCl₂ structure TiO₂ is considered to be a distorted structure of rutile with a tilt of adjacent ribbons of c-axis of rutile,which is a high-pressure metastable phase,usually produced when rutile phase TiO₂ is compressed under several GPa.Due to the symbiotic relationship,the CaCl₂ type TiO₂and rutile TiO₂ were connected through edge dislocation,which showed strong interaction and high structural stability.Therefore,a CaCl₂/rutile TiO₂ heterojunction with enhanced reduction capacity and charge separation efficiency was formed.These features endow symbiotic CaCl₂/rutile TiO₂ an excellent photocatalysis catalytic activity,which is even better than the commercial P25 without the assistance of cocatalyst.These findings may provide insight into the design and synthesis of symbiotic heterogeneous nanocomposites with strong interfacial charge separation efficiency.