Surface/interface Structure Design and Heterogeneous Catalysis Performance of Binary Oxide Semiconductor

Author:Zhang Yue Lan

Supervisor:li guang she


Degree Year:2019





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 MOx(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 MOx.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 NbOx/g-C3N4 and strong interface coupling effect:Interfacial-enhanced amorphous porous NbOx/g-C3N4 heterostructure composite were synthesized through a straightforward spontaneous coupling process.The NbOx 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-NHx 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 NbOx and g-C3N4.When tested as a catalyst for photocatalytic water splitting reaction under simulated sunlight,NbOx/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 NbOx(26.3?mol?g-1?h-1).Under visible light,the optimal amorphous porous NbOx/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 NbOx 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.