| Modern industrial technology is developing rapidly,which improves the quality of our daily life and leads to a sharp increase in energy consumption and aggravated environmental pollution problems in the meantime.The birth of photocatalytic technology provides new ideas for solving the above problems,and the key of this technology is to design efficient,environmentally friendly and low-cost photocatalysts.Zn O is an n-type semiconductor with the advantages of high redox activity,good stability,and non-toxicity,etc.,thus it is widely used as photocatalyst.However,the wind band energy of Zn O?about 3.2 e V?makes it only respond to ultraviolet light,meanwhile,the photo-generated electrons and hole pairs are easy to recombine,which limit the conversion and utilization of sunlight.Therefore,it is necessary to search a suitable method to optimize and improve the properties of Zn O.In this paper,we chose Zn O as the matrix,investigated the effects of Cu WO4 and carbon materials on the morphology,structure,optical properties and photocatalytic performance of Zn O.The specific research contents are as follows:?1?The binary Cu WO4/Zn O composite photocatalysts were synthesized by hydrothermal method.The effects of Cu WO4 mass ratios on the morphology and crystal structure of Zn O were investigated by X-ray diffraction?XRD?,scanning electron microscope?SEM?,Raman spectroscopy,etc.According to the results of the experiments,the as-prepared Cu WO4/Zn O exhibited good crystal form,high purity,significantly enhanced absorbance to visible light and reduced fluorescence intensity.The degradation of methylene blue?MB?solution was conducted under the irradiation of simulated sunlight.After the irradiation of 120 min,the degradation rates of Cu WO4/Zn O composites were all higher than that of single Cu WO4 and Zn O.Among them,3%Cu WO4/Zn O showed the best photocatalytic performance towards MB,the degradation rate of which was 98.9%.The rate constant of 3%Cu WO4/Zn O was 0.03656min-1,which was?11.3 and?3.5 times than that of Cu WO4 and Zn O,respectively.After five cycles of photodegradation tests,the degradation rate of 3%Cu WO4/Zn O was still as high as98.1%,indicating the high stability and recyclability of the Cu WO4/Zn O composite.Then,the trapping experiments were designed to determine the active groups reacted in photodegradation,and the order of their contributions to the process was:h+and·OH>·O2->e-.Last,a possible photocatalytic mechanism was discussed.The electron transfer path between Cu WO4 and Zn O restrained the recombination of photo-generated electron-hole pair,thereby improving photocatalytic performance.?2?The ternary carbon/Cu WO4/Zn O composite photocatalysts were prepared by hydrothermal method.And the effects of carbon types and mass fractions on the physical properties and photocatalytic performance of Zn O were explored.Carbon nanotubes?CNT?and nanographene sheets?G?were selected as the dopants,the mass fractions of which were 1%,5%,10%,and 15%.According to the experimental results,the samples possessed high crystallinity.D and G peaks appeared in the Raman spectrum.The Raman spectrum,combined with the infrared spectrum,confirmed that the ternary C/Cu WO4/Zn O composite photocatalysts were fabricated successfully.From the ultraviolet-visible diffuse reflection spectra,the visible light absorption capacity of C/Cu WO4/Zn O was significantly higher than that of Zn O and Cu WO4/Zn O.The obtained composite samples were used for photocatalytic degradation of MB,the degradation efficiencies of which were higher than that of Zn O.Among CNT/Cu WO4-Zn O,15%CNT/Cu WO4-Zn O showed the best photocatalytic property with the degradation efficiency of 97.1%,and its reaction rate constant k was 2.8 times bigger than that of Zn O.Moreover,among G/Cu WO4-Zn O,1%G/Cu WO4-Zn O had the highest degradation rate of 87.1%towards MB,and its pseudo first-order kinetic reaction rate constant was 0.017 min-1,which was 1.7 times higher than that of Zn O.In addition,the stability of C/Cu WO4/Zn O was explored,and the ideal mechanism of photocatalytic degradation of MB by C/Cu WO4/Zn O was finally discussed.The high light absorption performance of carbon materials promoted its absorption of sufficient light energy,then generated more photoelectrons.Simultaneously,the photoelectrons transferred to Cu WO4 and Zn O,charge migration also occurred between Cu WO4 and Zn O,which hindered the photoinduced electrons-holes recombination and improved the photocatalytic performance. |
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