Synthesis And Properties Of Heterogeneous Nanophotocatalysts Based On ZnO-g-C₃N₄

The use of dyes in the paper,plastic,textile and other industries has led to an increase in the amount of dye wastewater discharged into aquatic systems,resulting in environmental pollution.The traditional wastewater treatment methods used to remove dye pollutants have some limitations,such as low decontamination efficiency,secondary pollution and secondary toxic metabolites.In recent years,semiconductors photocatalytic systems driven by solar driven have been rapidly developed and are considered as a positive way to solve current environmental and energy problems.Zinc oxide（ZnO）is a traditional one component material which has attracted much attention because of its high photosensitivity,low cost and harmless to human body.However,ZnO has some defects,such as only responding to UV light and easily recombining photogenerated electron-hole pairs,which astrict its use in the photochemical catalysis domain.In this paper,ZnO/g-C₃N₄ nanocomposite with ultrathin core-shell heterostructure and ZnO ternary nanocomposite photocatalyst co-modified with Ag and g-C₃N₄ were prepared by polymer network gel method.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,ultraviolet-visible absorption spectroscopy（UV-vis）,photoluminescence spectrum（PL）,specific surface area measurement（BET）,surface photovoltage（SPV）and surface photocurrent tests（SPC）were used to characterize the prepared samples,The changes of microstructure,morphology,photoelectric characteristics and photocatalytic performance of the photocatalyst before and after the introduction of g-C₃N₄ were compared.The main contents of this paper are as follows:1.Core-shell structure ZnO/g-C₃N₄ nano-photocatalysts with ultrathin amorphous g-C₃N₄ layer were synthesized via facile polymer network gel method applying zinc oxide and dicyandiamide as the raw materials.When the molar ratio of zinc oxide to dicyandiamide was 1:1,the sample（D/Z-1）had the best photocatalytic activity.Under simulated light irradiation,the pseudo-first-order kinetic constants of D/Z-1 for photocatalytic degradation of methylene blue,methyl orange and rhodamine B solution（4 mg/L）were about 3.3 times,4.6 times and 9.3 times that of ZnO,respectively.XRD and SEM results showed that the crystallinity of the prepared core-shell heterostructure composite nanophotocatalyst was almost unaffected,but the specific surface area increased.XPS measurement revealed that the adsorption capacity of the composite sample to hydroxyl was enhanced.UV-vis absorption spectrum indicated that the tight binding between the core-shell enhanced the absorption of the composite sample in the visible light region,so more photogenerated electron-hole pairs could be generated under the same illumination conditions.PL,SPV and SPC spectra showed that under appropriate g-C₃N₄ loading,the separation efficiency of photoexcited carriers was significantly improved.These factors promoted the enhancement of photocatalytic activity.2.Ag and g-C₃N₄ co-modified ZnO ternary nanocomposite photocatalysts were prepared by polymer network gel method.The characterization results showed that ternary composites had increased specific surface area,significantly enhanced visible light absorption,and markedly inhibited light excited electron hole pair recombination rate compared with other single component photocatalysts or binary composite photocatalysts.Under simulated light irradiation,the removal efficiency of ternary composite photocatalysts for high concentrations of methylene blue,methyl orange and rhodamine B（8 mg/L）were about 4.3 times,13.9 and 23.1 times higher than those of pure ZnO,respectively,about 2.0 times,2.2 times and 3.1 times of Ag/ZnO.The performance improvement was attributed to the synergistic effect between the formation of various heterostructures and the local surface plasmon resonance effect of Ag nanoparticles.It provides a reference for designing carbon-based materials/noble metal/metal oxide nanocomposite photocatalyst materials with high photocatalytic activity.