Controllable Synthesis Of Molybdenum-based Nanosheets And Study On Their Treatment Performance Of Dye Wastewater Treatment

Dye wastewater is one of the main threats to the environment.The chromophoric groups and organic components of dyes are difficult to degrade,which do harm to human health and the ecological environment seriously.Adsorption and photocatalysis oxidation are two effective treatments of dye wastewater.However,there are still some problems existed in these methods,i.e.low adsorption capacity,complex synthesis process,low utilization rate of light and poor stability.Therefore,a feasible and ecofriendly antisolvent recrystallization method has been established to synthesize molybdenum-based adsorbents and photocatalysts,and study their adsorption performances toward methylene blue(MB)and photocatalytic performances toward rhodamine B(RhB)in this paper.The main research works and results are as follows:A series of ammonium molybdate nanosheets(Mos),using ammonium molybdate as a precursor,were prepared by a one-step antisolvent recrystallization method at room temperature and normal pressure.The morphology and size of the nanosheets can be tuned by varying the synthetic parameters such as water-alcohol ratio,precursor concentration,organic solvents,inorganic salt.Notably,oxygen-deficient molybdate ammonium hydrates(4MoO3·2NH3·H2O,MAH)nanosheets were obtained by calcined Mos at a certain temperature.The adsorption capacity of MAH-20 nanosheets for MB(cationic dye)is up to 1151.5 mg/g.Compared with the precursor,the ammonium molybdate nanosheets are smaller in size,and more-OH and-NH3 groups are connected to the exposed surface.During calcining process,the-OH and-NH3 groups on the Mos surface fell off,resulting in oxygen vacancies on MAH nanosheets.The oxygen vacancies and negative charges on the surface of MAH nanosheets contribute to their high adsorption capacities for cationic dyes.On this basis,a series of α-MoO3 nanosheets with upright or side structure successfully synthesized by introducing CTAB in water/ethanol recrystallization system.The α-MoO3 nanosheets showed much higher photodegradation ability for Rhodamine B(RhB)under visible light irradiation than bulk c-MoO3.The degradation efficiency of the α-MoO3 nanosheets reaches 98%within 15 min,and its apparent kinetic constant(0.2351 min-1)is two orders of magnitude higher than that of cMoO3.The characterization results of the photocatalysts indicate that the main reasons for the enhanced photocatalytic activity of α-MoO3 nanosheets are that:the small size and the large surface area of the 2D nanosheets enhance the ability of the photocatalytic materials adsorbed organic compounds.Compared with bulk c-MoO3,the α-MoO3 nanosheets exhibit a wider band gap,which have a more negative potential of the photogenerated electrons,have a correspondingly greater reduction,and the photogenerated holes will have a more positive potential and a stronger oxidation,leading to a high visible-light photocatalytic activity.The introduction of oxygen vacancy defects has created an energy level between VB and CB of the α-MoO3 nanosheets,which can help to induce the separation of photogenerated charge pairs(electrons and holes).The recombination of the photogenerated electrons and holes was inhibited.And it is favorable for the photogenerated electrons diffused to the surface to combine with the O2 adsorbed on the surface to generate active species.This article investigates the preparation of molybdenum oxide nanomaterials using CTAB to control the antisolvent recrystallization process in water/ethanol system.This facile and inexpensive preparation method of molybdenum oxide nanosheets provides a reference for the development of other metal oxide nanomaterials.