Study On Preparation,Performance And Adsorption Mechanism Of Wood-Based Heavy Metal Ion Adsorbent

At present,the development of novel adsorbent is a significant aspect of water remediation of heavy metal ions pollution.Wood has natural advantages as a renewable material which can be easily modified.Given the complex preparation technology,high cost and energy consumption problems of heavy metal ion adsorbent,this study based on the wood multi-dimensional hierarchical porous structure,combined delignification process and the modifiers,such as acryloyl chloride?AC?,tetraethylenepentamine?TEPA?,acrylamide?AM?,zinc 2-methylimidazole?ZIF-8?with cobalt 2-methylimidazole?ZIF-67?,to conduct top-down wood modification,and fabricated the novel wood-based heavy metal ions adsorbents by vacuum impregnation technology,grafting modification and in-situ deposition methods.The morphology structure and chemical composition of the adsorbents were characterized.The relationship between p H value,adsorption time,initial concentration,adsorption temperature and the adsorption were explored,and the adsorption mechanism were analyzed by fitting the kinetic equation and the adsorption isotherm equation.The main study conclusions are as follows:?1?AC was grafted onto the delignified wood flour,further the amino modified wood flour was prepared via the addition reaction between TEPA and carbon-carbon double bond.Suggested by the results,the Pb²⁺adsorption capacity of amino modified wood flour was 189.9 mg/g in adsorption equilibrium time 180 min.Hydroxyl and amino groups containing O and N atoms chelate with heavy metal ions,and the adsorption process was mainly single molecular layer chemisorption.?2?In the calcium chloride?CaCl₂?/hydrogen peroxide?H₂O₂?initiator system,2-hydroxyethyl methacrylate?HEMA?and AM were used as modifiers to treat delignified wood.The adsorption capacity of Cu²⁺was 46.98 mg/g,Pb²⁺was 171.39 mg/g,and Mn²⁺was 45.29 mg/g.Amino polymer filled pores,leading to the decreased porosity and specific surface area,with low adsorption speed.The adsorption process has a high fitting degree of the preso-second-order kinetic equation and Langmuir adsorption isotherm model,manifesting the adsorption process belongs to single molecular layer chemisorption in which heavy metals share electron pairs with nitrogen or oxygen atoms.?3?Modified by solution method and vacuum impregnation method,ZIF-8 and ZIF-67 were generated in situ within the delignified wood aerogel frame,and the ZIFs wood aerogel adsorbent were obtained.The Cu²⁺,Pb²⁺adsorption capacity of ZIF-8 wood aerogel was 87.35 mg/g and 316.43 mg/g,respectively.While,the Cu²⁺,Pb²⁺adsorption capacity of ZIF-67 wood aerogel was 118.50 mg/g and518.75 mg/g,respectively.With large specific surface area,numerous ZIFs particles were attached to the wood aerogel structure,thus the adsorption capacity has obvious advantages.However,it took about 8hours for the solution to permeate the aerogel to reach adsorption equilibrium.The adsorption process of the ZIFs wood aerogel adsorbent conformed to the preso-second-order kinetic equation and Langmuir adsorption isotherm model,belonging to the single-molecule layer chemisorption,which is achieved by sharing electron pairs between heavy metals and nitrogen or oxygen atoms,with the homogeneous adsorbent surface and the in weak teraction between the adsorbate on the surface.