| The adsorption performances for organic dyes of the adsorbents used widely are not satisfying.To solve the problem,mechanochemical method was used to prepare molybdenum trioxide,which method has the advantages of low cost,simple operation,mild conditions and being industrialized easily.The relationship between structure and adsorption performance of the adsorbent was explored by wet grinding and changing the crystal structure,so that adsorbents with high performance could be found.In this work,micro-nano orthorhombic Mo O3 was synthesized by mechanochemical process,and the effect of wet grinding time on its phase,morphology,specific surface area,Zeta potential and adsorption properties was systematically studied.What's more,hexagonal Mo O3 nanorods and bicrystalline Mo O3(containing?-Mo O3 and h-Mo O3)were prepared by similar synthesis process.The Mo O3 formation mechanism was explained by XRD results of the samples during the ball milling process and simultaneous thermal analysis of the precursor.Finally,the adsorption performance on Rhodamine B(Rh B)of bicrystalline Mo O3 was investigated,including the effects of reaction time,initial concentration,p H and temperature.In addition,the kinetics and thermodynamics analysis of adsorption process was performed.The results of this work suggest:based on the mechanochemical reaction of ammonium molybdate tetrahydrate((NH4)6Mo7O24·4H2O)and oxalic acid dihydrate(C2H2O4·2H2O)and subsequent calcination,the preparation of?-Mo O3,h-Mo O3 and bicrystalline Mo O3 can be successfully controlled,respectively.h-Mo O3 was prepared under the condition of(NH4)6Mo7O24·4H2O and(C2H2O4·2H2O)in molar ratio of1:6;when the molar ratio was 1:4,excessive(NH4)6Mo7O24·4H2O formed?-Mo O3,so the final product contained two crystal structures;while?-Mo O3 was obtained by phase transformation of h-Mo O3 formed by ball milling.The equilibrium adsorption capacity of?-Mo O3 wet-milled for 2 h adsorbing Rh B was 473.02 mg/g,which was better than?-Mo O3 without wet-milling treatment(303.49 mg/g).Surprisingly,bicrystalline Mo O3 used for Rh B removal has superior properties,its equilibrium adsorption capacity can be reached 740.71 mg/g,which is very close to the maximum adsorption capacity(751.88 mg/g).The adsorption process is in good agreement with Langmuir model.The outstanding properties can maintain in a large range of p H value(4?8).The equilibrium adsorption capacity at 313K was much higher than those at303K and 323K.This adsorption is an endothermic,entropy increasing and spontaneous reaction and belongs to chemical adsorption attributed to the interaction between the negative charges on the surface of bicrystalline Mo O3 and the cations in Rh B.In short,this work firstly proposes a new,cheap and scalable method based on mechanochemical reaction to synthesize micro-nano Mo O3,and the crystal structure of Mo O3 can be controlled.Furthermore,bicrystalline Mo O3 used for Rh B removal has an excellent adsorption performance and is promising to be applied in the treatment of organic dye wastewater. |
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