Chemical Synthesis And Photocatalytic,Gas Sensitive Performance Of ZnO/Ag-based Nanscale Photocatalysts Regulated By Mn

Since modern times,the development of science and technology has not only promoted the prosperity of industry and economy,but also brought increasingly serious environmental pollution.Effluent,flue gas and energy crisis have posed an enormous challenge to the survival of people.The development of a remediation technology with efficiency,inexpensive and environmentally friendly has become a research emphasis.In recent years,photocatalytic technology using nanostructured semiconductors has shown great potential,which can directly utilize solar energy to mineralize pollutants into CO₂ and H₂O.Semiconductor ZnO photocatalysts was widely studied due to its nontoxic,low cost,excellent photochemical properties and high stability.However,as a wide band gap（3.37 e V）semiconductor with large exciton binding energy（60 Me V）,the restricted light-harvesting ability and short photogenerated carrier life time of ZnO limit its large-scale practical applications.In this paper,a series of ZnO-Ag nanocomposite photocatalysts containing Mn were prepared by a modified polymer network gel method,the inherent defects and photocatalytic propertied of ZnO were significantly improved.X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,UV-vis absorption spectroscopy（UV-vis）,photoluminescence spectroscopy（PL）,surface photovoltage（SPV）and surface photocurrent（SPC）were used to characterize the morphology,optical and structure properties of the prepared samples,and the effects of surface defects,impurity level,heterostructure and the transfer of valence state on the photocatalytic activity of ZnO are discussed in detail.The main contents including:1.Mn-doped ZnO（Mn:ZnO）and Ag-decorated Mn-doping ZnO（Mn:ZnO/Ag）nanocomposite photocatalytic systems were prepared by a facile polymer network-gel method,respectively.The photocatalytic activities of Mn:ZnO and Ag/ZnO were further enhanced by adjusting the synergistic effect between Mn ions and Ag granules,and achieving effective visible light absorption and photo-induced electron-hole separation in the ZnO photocatalyst.The photocatalytic results showed that the optical properties and photodegradation activity of both Mn:ZnO and Ag/ZnO were significantly improved by（1 mol%）Mn doping and Ag（3 mol%）decoration.Under simulated sunlight irradiation,the degradation efficiency of organic pollutants were about 3 times and 2 times that of pure ZnO and Ag/ZnO,respectively.XRD and SEM results showed that the particle size of ZnO increases significantly,the particles were more evenly dispersed uniform,and the deterioration of crystalline quality caused by Mn doping was also improved.The XPS spectra revealed that+2 and+3 valence states of Mn coexisted in ZnO,the introduction of Ag could transform part of Mn³⁺to Mn²⁺,producing more Mn²⁺states which favorable to the photocatalytic activity reaction,and more oxygen vacancy defects on the ZnO surface.UV-Vis,PL,SPV and SPC optical analysis indicated that the deep level transition related to Mn³⁺state was an important factor for the reducing of the photocatalytic performance of Mn-doped ZnO.In addition to the further enhancement of visible light absorption,the synergistic effects of Mn ion and Ag also resulted in effective photogenerated carrier separation in ZnO,which ultimately facilitated the enhancement of photocatalytic activity.2.A series of（Mn₂O₃,Ag）co-decorated ZnO synergistically coupled heterostructural photocatalysts were prepared by a modified two-step polymer network gel method,Methylene blue（MB）can be completely degraded by ZnO（AZM3）decorated with 3 mol%Mn₂O₃ for～20 min and～80 min under simulated sunlight and visible light,in which the degradation efficiency were about 3 times and4.8 times than that of Ag/ZnO,respectively.Meanwhile,this heterostructured photocatalyst also showed excellent gas sensitive activity towards NO₂ gas detection,which is obviously enhanced compared with Ag/ZnO under UV and visible light.The results of UV-Vis,SPV and PL showed that the synthesized（Ag,Mn₂O₃）co-decorated ZnO catalyst had high visible light-harvesting ability and prolonged photogenerated carrier life,its carrier separation efficiency was about 9 times higher than that of the Ag decorated Mn-doping ZnO.The results of photocatalytic decomposition experiments,with the addition of different scavengers confirmed that the effective charge separation across heterogeneous interface through the Mn₂O₃-ZnO heterostructure can drive the photogenerated holes（h⁺）with high oxidability migrate to the surface of the catalyst,and enhance the photocatalytic activity of ZnO.This strategy provides a new pathway to further improve the ability of visible light collection and realize efficient carrier separation by consciously designing and constructing multi-heterostructure photocatalyst with different functions.