Study On The Preparation And Properties Of A New Type Of Photoinduced Desorption Material With Citric Acid/Carbon Quantum Dots Modified Bismuth Carbonate

Among bismuth metal oxides,Bi₂O₂CO₃ has become a new star because of its special "sandwich"structure and excellent photocatalytic activity.Bi₂O₂CO₃ apossess a typical "sillen" structure,in which[Bi₂O₂]²⁺ and CO₃^2-layers overlap with excellent crystal growth anisotropy.Therefore,controlling the reaction conditions,such as temperature,pH,hydrothermal time can produce different morphologies of Bi₂O₂CO₃,it provides a new method to optimize its performance and could effect of its adsorption performance at first.Adsorption is an important interfacial phenomenon,and has been widely used in separation,purification and catalysis areas.Therefore,various adsorbents are emerging.The regeneration of adsorbents is the key to solve secondary pollution and make adsorbents reusable.Using light is a novel and environmental friendly technology,by which not only regenerates adsorbents,but also realizes the full use of green energy.In this study,a new photoinduced desorption material,CA/CDs/Bi₂O₂CO₃,was prepared via a simple hydrothermal method using citric acid?CA?as modification reagent.That is the adsorption of organic pollutants under the dark conditions and then desorption under the light conditions.As-prepared materials were characteriazed using X ray diffraction?XRD?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?and Fourier transform infrared spectroscopy?FTIR?,X ray photoelectron spectroscopy?XPS?,fluorescence spectroscopy?PL?,specific surface area?BET?and Zeta potential.The influences of synthesis conditions on the morphorlogies and properties of the materials were studied,as well as influcing factors on adsorption and desorption processes,Furthermore,the mechanism of adsorption and desorption were also investigated.The main contents and conclusions are as follows:?1?The influences of hydrothermal time and the pH value of the hydrothermal liquid on the morphology and adsorption properties of the materials were studied.The results showed that the as-prepared CA/CDs/Bi₂O₂CO₃ exhibited sheet structure and excellent adsorption and desorption performance with hydrothermal time 8 h and the hydrothermal mother liquid pH?8.The specific surface area increased from 2.6056 m2/g to 21.2908 m2/g after citric modification,and the surface charge of Bi₂O₂CO₃ was getting more negative,thus the adsorption rate for cationic dyes methylene blue was improved.?2?The influcing effects on adsorption and desorption performance of CA/CDs/Bi₂O₂CO₃,inculding CA/CDs dosage,concentration of the materials,pH value of the dyesolution,heavy metal ions and the light sources were studied.The results showed that the CA/CDs/Bi₂O₂CO₃ exhibited higher adsorption rate and desorption rate for methylene blue dye under following conditions:the mass ratio of CA/CDs to Bi₂O₂CO₃ was 300%,the pH value of dye solution was about 8,and material concentration was 0.6g/L,the adsorption rates and desorption rates were decreased when Cu²⁺,Fe³⁺,Mg²⁺,Zn²⁺ existed in the dye solution;the desorption rate was also related to the energy of the light source.?3?The adsorption and desorption mechanism of CA/CDs/Bi₂O₂CO₃ was proposed as follows:Citric acid is easily decomposed during hydrothermal process and-COO-connected to the crystal surface of Bi₂O₂CO₃.As a result,the surface of Bi₂O₂CO₃ is with negative charge and methylene blue is adsorbed onto the surface by electrostatic force in dark.While under light irradiation with high energy?365 nm and 420 nm?,-COO^- bond is broken and the dye molecule is desorbed.