Chemical Synthesis And Photocatalytic Performance Of ZnO-based Heterostructured Nanoscale Photocatalysts

Since the industrial revolution,the impact of waste gas,sewage and energy crisis increasingly affects the living environment of human beings,principally because economic development depends on natural resources all the time.Photocatalytic techniques have made significant ongoing contributions to the breakthrough of environmental treatment and energy generation on earth.Successful wide bandgap metal oxide semiconductors?MOSs?such as Zn O,Ti O₂,Sn O₂,Zr O₂,etc.,which are considered as alternatives to conventional semiconductors in optoelectronics,have profound scientific value in the fields of energy harvesting,water treatment,antibiosis,and optoelectronic devices.Among them,Zn O has been widely concerned due to its relatively superior physical and chemical properties and low cost performance.However,a single wide band gap semiconductor cannot avoid limited light-harvesting capabilities,and its photocatalytic performance is limited by the short lifetime of photo-excited carriers.In this thesis,Ag/Zn Cu O and Cu_xO/Zn O nano-photocatalysts with high visible light absorption capacity were prepared by different accesses.The samples were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,ultraviolet-visible absorption spectrum?UV-vis?,photoluminescence spectroscopy?PL?,time-resolved photoluminescence spectroscopy?TS-PL?,surface photovoltage?SPV?and surface photocurrent?SPC?measurements,and the effects of impurity levels and surface photo-excited carriers on the photocatalytic performance of heterogeneous structures were discussed.The main contents are as follows:1.Cu-incorporated Ag/Zn O photocatalysts were prepared by a two-step polymer network gel method.By balancing synergies and antagonisms that arise from incorporating Cu and Ag within a single Zn O-based catalytic platform,the photocatalytic activity of Ag/Zn O based on three-dimensional modified polymer network structures can be further significantly enhanced.XRD and SEM results depict that the grain size of Zn O nanoparticles decreases after the incorporation of Cu,but the dispersion of the particles is improved.XPS measurement reveals that Cu coexists as Cu²⁺and Cu⁺in the sample.The photocatalytic results show that the performance of Ag/Zn O heterostructure?Z0?is significantly improved by only 0.2mol%Cu incorporation?Z0.2?and the first-order degradation kinetics constants?K?are 2 and 1.5 times higher than that of Ag/Zn O under simulated sunlight and UV light.The synergies between Cu ions and metallic Ag are mainly the significantly enhanced visible light absorption capacity and the prolonged photo-excited charge lifetime.However,with the excessive introduction of Cu precursors,the surface Cu²⁺is found to inhibit the interfacial charge transfer between Ag and Zn O NPs under UV and visible light irradiation,but the transformation from Cu²⁺to Cu⁺is also presumed to be a driving factor for the boost of photocatalytic reactions.2.Cu_xO-loaded Zn O?Cu_xO/Zn O?heterostructured photocatalysts with significantly improved visible light absorption capacity and photo-generated carrier lifetime were prepared using a facile sol-gel process.Under the action of effective migration of strong oxidizing holes?h⁺?towards the catalyst surface,Cu_xO/Zn O exhibits excellent photocatalytic activity and stability in photo-oxidation degradation of various organic dyes under simulated sunlight irradiation.Particularly,the degradation rate of methylene blue?MB?exceeds 93%in only 10 minutes with 3mol%Cu_xO-decorated Zn O?3%CXZ?under simulated solar light,and the first-order kinetic degradation constant?K?was 0.2982,much higher than that of Ag/Zn O,indicating the potential of copper oxides to be a substitute for noble metal as a co-catalyst.The dominant surface photo-generated carrier types were re-designed by preparing photocatalysts with polymer network gel method.The SPV and photocatalytic results show a significant improvement in the surface photo-reduction capacity.Under visible light illumination,the yield of photocatalytic hydrogen production is 132.30 umol·g^-h^-over sample 10 mol%Cu_xO-loaded Zn O?10%CXZ?r??,which is 1.6 times higher than that over 3%CXZ?80.51 umol·g^-h^-?prepared by sol-gel method.The yields of reducing CO₂ to CO and CH₄ over sample10%CXZ?r?under simulated solar irradiation are 1.8 times than that over 3%CXZ.Moreover,the surface photoreduction ability of the materials can be used for efficient photocatalytic degradation by introducing H₂O₂.This strategy may provide templates for targeted development of photocatalysts for specific fields.