The (gas Phase) Hydrothermal Preparation Of Functionalized Carbon-based Composites And Their Cr(?) Adsorption Properties

In recent years,water pollution accompanied by rapid industrial development is becoming a tricky problem.Especially heavy metals cannot be broken down by microorganisms,and their long-term accumulation in the environment has caused great harm to our living environment and life and health,of which Cr(?)is considered the one of most toxic pollutants.Hydrothermal carbon has good application prospects in the treatment of heavy metal wastewater because of its environmental protection,simple and efficient preparation process and stable physical and chemical properties.However,the negatively charged surface properties limit its application in anionic pollutants adsorption such as Cr(?).In this paper,a simple one-step(gas phase)hydrothermal method was used to functionally and compositely modify hydrothermal carbon,which greatly improved the adsorption performance of hydrothermal carbon for Cr(?).The main research contents are as follows:(1)A modified one-step steam-hydrothermal carbonization method was used to prepare amino,carboxyl,and thiol-modified hydrothermal carbon materials(labeled HT-N,HT-AA,and HT-SCY,respectively).With the help of SEM,FT-IR,XPS,Raman,Elemental analysis,N2 adsorption-desorption,XRD and other technical means to comparatively study the changes in the above samples in terms of micro-morphology,texture properties,surface functional groups and quantity.The results of adsorption experiments at room temperature showed that the adsorption amount of the sample is related to the surface functional groups of the material.The maximum adsorption capacities are as follows: HT-N(171.23 mg/g)> HT-AA(94.25 mg/g)> HT-SCY(15.41 mg/g).The adsorption performance of HT-N on Cr(?)increased with the increase of ethylenediamine concentration.The adsorption data of Cr(?)on functionalized carbon materials at room temperature fitted the Langmuir model and the pseudo-second-order kinetic model.In addition,the coexistence anion experiments showed that several anions do not significantly interfere with the adsorption of Cr(?)on HT-N.The disturbance capability of the coexisting anions on the adsorption of Cr(?)on HT-AA were as follows: SO42-> C2O42-> CO32-> HPO42-> Cl-.The functionalized groups(-COOH,-NH2)played an important role in the adsorption of Cr(?).The main adsorption mechanism involved electrostatic interaction and complexation between the functionalized groups and Cr(?),and then then the adsorbed Cr(?)was partly reduced to Cr(III)with the help of electron donors.(2)The Al OOH-coated carbon sphere(CS)composite adsorbent(CS@Al OOH)were prepared by a one-step hydrothermal method.SEM tests showed that Al OOH flakes form a star fruit-like structure and densely arranged outward on carbon spheres,providing a large number of surface active sites for Cr(?).CS@Al OOH exhibited an adsorption capacitie nearly 10 times higher than that of pure CS.Under the adsorption conditions of p H=2,the concentration of Cr(?)is 20 mg/g,and the concentration of the adsorbent is 0.4 g/L,the adsorption capacity is 49.23 mg/g,the removal rate is 98.46%.Its kinetic data fitted the pseudo-second-order kinetic model indicating it's chemisorption.(3)Based on the synthesized CS@Al OOH as the matrix,a nickel-aluminum hydrotalcite was grown in situ by a hydrothermal method,and further calcined in an N2 atmosphere to prepare a layered double oxides/carbon sphere composite adsorbent(LDO@CS).SEM tests showed that the hydrotalcite flakes were arranged on the carbon spheres to form a petal-like structure on the carbon spheres,which provided abundant surface adsorption sites and abundant pores,which was beneficial to the rapid adsorption of Cr(?).LDO@CS retains a loose and porous petal-like structure,and has better adsorption performance than a single material.Under the adsorption conditions of p H=2,the concentration of Cr(?)is 20 mg/g,and the concentration of the adsorbent is 0.4 g/L,the adsorption capacity can reach 50 mg/g,and the removal rate is close to 100%.Its kinetic data fitted the pseudo-second-order kinetic model indicating it's chemisorption.This method is suitable for the preparation of different types of composite materials MAl-LDH@CS(M=Mg,Co,etc.).