Fabrication Of Mg₃Si₄o₁₀?OH?₂/MgFe₂O₄ In Situ Grown On Diatomite And Their Adsorption Properties

Chromium is regarded as one of the most toxic heavy mental contaminants,which can invade the human body through the digestive tract,respiratory or the skin and cause serious health issues.They may lead to chromosomal aberrations and tumorigenesis due to their long-time remaining in human body.Therefore,considerable attention has been paid to removal these toxic heavy metal ions from water and soil.Chromium in an aqueous environment exists as anion(CrO₄^2-,Cr₂O₇^2-),and their safety threshold is extremely low?0.01ppm?.Thus,it is difficult to meet the standard of chromium emissions after treatment of industrial wastewater.Adsorption is recognized as one of the most effective pathways in Cr-containing wastewater treatment and easy for application in scale.However,the adsorption efficiency is usually limited by the property of the adsorbents.Hence,it is critical to develop new types of absorbents with porous structure,high specific surface area and rich surface functional groups.Porous materials are created synthetically,and the high cost limits their wide application in industry.Hence,an effective and low-cost adsorbent needs to be developed.Another challenge for treating Cr-containing wastewater is toxicity migration,which means toxicity can transfer in the biological chain with water and soil.It is important for toxicity degradation after removal of Cr ions.The surface modification of raw diatomite with highly active nanostructured materials possesses the merits of both nanoscale metal oxides and micron-scale porous substrate.It not only keeps the oxidation and reduction property of objects?e.g.,Fe,Mn,Al/Mg?,but also endows the raw diatomite with high surface,high density unsaturated dangling bond and kinds of numerous surface functional groups,which can solve the problems of low adsorption capacity and toxicity degradation of raw diatomite.Nanostructured magnesium oxide as well as magnesium silicate was synthesized via a hydrothermal method by using MgCl₂·6H₂O,NH₃·H₂O and CTAB.Mechanism of transformation from MgO to Mg₃Si₄O₁₀?OH?₂ as well as crystal growth and morphology control was investigated in detail.When ferrous oxalate added the above solution system,MgFe₂O₄/diatomite with photocatalytic property could be obtained.XRD,SEM,TEM,BET,XPS and ZPC Tests were applied for the charaction of the samples.MgO/diatomite and Mg₃Si₄O₁₀?OH?₂/diatomite obtained after hydrothermal treatment at 180 ^oC for 0.5h and 9 possess a high specific surface area of103 and 149 m²/g,respectively.What is more,the specific surface area of MgFe₂O₄/diatomite reaches up to 335 m²/g.All of the above materials mentioned in situ grown on diatomite were polycrystalline,possessed a sheet-like morphology with uniform pores concentrated in 0-20nm.Removal mechanism of Cr??? and adsorption property of samples prepared were investigated in the text.Under darkness,the maximal adsorption capacity of MgO/diatomite,Mg₃Si₄O₁₀?OH?₂/diatomite and MgFe₂O₄/diatomite was 461,535 and543 mg/g,respectively.The highest Cr???removal efficiency?99-100%?was achieved at pH=3-4 or 8-9 over the Mg3Si4O10?OH?2/diatomite and MgFe2O4/diatomite samples.The MgFe2O4/diatomite can reduce Cr???into Cr?III?for its photoresponse ability in both UV–light and visible light.The calculated maximal Cr???adsorption capacity on equilibrium under UV-light and visible light was 556and 570 mg/g,respectively.XPS and FT-IR techniques were used to character samples after adsorption,and both MgFe2O4/diatomite and Mg₃Si₄O₁₀?OH?₂/diatomite possess large amounts of hydroxyl groups and active adsorption sites on their surfaces.Both samples were negatively charged at pH=2-12,suggesting electrostatic interactions did not exert a significant effect on the adsorption of Cr???.The Cr???ions were mainly chemically adsorbed on the samples.