Enhanced Adsorption And Sensing Properties And Mechanisms Of ZnO And NiSe Nanomaterials

ZnO flower-like architectures,In doped ZnO foam structures and ultralong NiSe nanobelts were synthesized by solvothermal and solution combustion method at 550 ?.Morphologies and structures of these products were characterized by means of field emission scanning electron microscope(FESEM),scanning electron microscopy(SEM),X-ray photoelectron spectra(XPS),X-ray diffraction(XRD),transmission electron microscopy(TEM),atomic force microscopy(AFM),IR spectrum and absorption-desorption porosimetry.The adsorption performance of ZnO flower-like architectures and ultralong NiSe nanobelts for triphenylmethane dyes were studied.The effect of adsorbents morphology,adsorption time,dye concentration,pH and solution temperature for adsorption capacity were investigated,and the adsorption mechanism was discussed.The influence of hydrogenation and In-doping on the gas sensing properties of the ZnO structures was explored,and the sensing reaction mechanism was proposed.These research results would provide a base for further research on synthesises of ZnO,NiSe nanostructures,the physical and chemical properties of ZnO,NiSe nanostructures and their applications in adsorption,sensor and photocatalyst.Specific research results as follows:(1)The 3-dimensional hierarchical ZnO flower-like architectures were synthesized in a Zn(Ac)2-2H2O-Na2SeO3-KBH4-pyridine solvothermal system at 100 ? for 24 h.The flower-like architecture is assembled from ZnO nanosheets with a thickness of?1.5 nm,and the flower-like architecture specific surface area is 132 m2/g.When the ZnO flower-like architecture is used as the adsorbent for acid fuschin(AF),malachite green(MG),basic fuchsin(BF),congo red(CR)and acid red(AR)in water,the adsorption capacities for AF,MG,BF,CR and AR are 7154.9,2587.0,1377.9,85.0 and 38.0 mg/g,respectively.Evidently,the as-obtained ZnO flower-like architectures show excellent adsorption performances for triphenylmethane dyes,and the adsorption capacity of 7154.9 mg/g for AF is the highest of all adsorbents for dyes.The adsorption mechanism can be attributed to the electrostatic attraction and the formation of ion-association complex between triphenylmethane dyes and ZnO hierarchical flower-like architectures.(2)In doped ZnO foam structures with exposed {001} facets were successfully prepared by solution combustion method at 550 ?,and the influence of different In-doping concentrations on the gas sensing properties of the ZnO foam structures was explored.The ZnO foam with 5%of In-doping exhibits the highest sensitivity(about 308)to 400 ppm ethanol at 350 ?.The effect of crystallinity,crystallite size,specific surface area and surface adsorption oxygen content on gas-sensing property of ZnO samples was investigated.The excellent sensing performance to ethanol was attributed to the increase in the surface and the amount of adsorbed oxygen.(3)Hydrogenation is successfully used to enhance ZnO-based gas sensors.The hydrogenated ZnO sensors show significantly higher response to organic compound vapors than the samples without hydrogenation.The relationship between the time of hydrogenation and the oxygen content of the sample surface as well as the hydroxyl in the infrared spectrum was investigated.The resistance change of the ZnO samples before and after hydrogenation was compared.The enhanced sensing performance is attributed to the increased density of the unsaturated Zn atoms with dangling bonds on the surface resulted from the hydrogenation process.The unsaturated Zn atoms with dangling bonds are found to be active sites for the sensing reaction.The concept of the unsaturated metal atoms with dangling bonds serving as active sites can deepen understanding of the sensing reaction mechanisms and affords guidance to design more effective gas sensing materials.(4)The ultralong NiSe nanobelts were synthesized by a solvothermal reaction of Ni with Se and KBH4 in ethylenediamine at 180 ? for 12 h and subsequent annealing in Ar.The aspect ratios of nanobelts can be changed by tuning the reaction time.These NiSe nanostructures were used as adsorbents in wastewater treatment,and the adsorption capacities for MG are 329.5,366.8 and 501.5 mg/g,respectively.It was found that the adsorption performance was improved with an increase on the aspect ratios of NiSe nanostructures.The excellent adsorption performance of the as-prepared ultralong NiSe nanobelts for MG removal could be attributed to the unique honeycomb-like superstructures and high surface area.The adsorption process agreed well with the pseudo-second-order kinetics and the Langmuir isotherm equation.Thermodynamic parameters indicated the feasibility of the adsorption process.Electrostatic attraction between Malachite green and NiSe ultralong nanobelts was considered as the adsorption mechanism.