title: Structure and properties of Co-doped cryptomelane and its enhanced removal of Pb²⁺ and Cr³⁺ from wastewater.
abstract: Cryptomelane is a reactive Mn oxide and has been used in removal of heavy metal from wastewaters. Co-doped cryptomelane was synthesized by refluxing at ambient pressure and characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure spectroscopy, and its performances for removal of Pb(2+) and Cr(3+) from aqueous solutions were investigated. Co doping has a negligible effect on the structure and morphology of cryptomelane but increases the specific surface area and Mn average oxidation state. Mn and Co K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that Co barely affects the atomic coordination environments of Mn, and distances of edge- and corner-sharing Co-Me (MeCo, Mn) pairs are shorter than those of the corresponding Mn-Me pairs, implying the replacement of framework Mn(III) by Co(III). These Co-doped cryptomelanes can quickly oxidize Cr(3+) to be HCrO4(-) and remove 45%-66% of the total Cr in the reaction systems by adsorption and fixation, and they have enhanced Pb(2+) adsorption capacities. Thus these materials are promising adsorbents for heavy metal remediation. The results demonstrate the design and modification of environmental friendly Mn oxide materials and can help us understand the interaction mechanisms of transition metals with Mn oxides.
authors.affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China. Electronic address: lihui@udel.edu.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Fan
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Mengqiang
authors.initials: M
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Xionghan
authors.initials: X
authors.lastname: Feng
authors.affiliation: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China. Electronic address: yinhui666@mail.hzau.edu.cn.
authors.forename: Hui
authors.initials: H
authors.lastname: Yin
mesh_terms: D000327:Adsorption; D002857:Chromium / Q000737:chemistry*; D003035:Cobalt / Q000032:analysis; D007854:Lead / Q000737:chemistry*; D017895:Manganese Compounds / Q000032:analysis*; D010084:Oxidation-Reduction; D010087:Oxides / Q000032:analysis*; D056951:Photoelectron Spectroscopy; D011188:Potassium / Q000032:analysis; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D002857:Chromium; D003035:Cobalt; D007854:Lead; D017895:Manganese Compounds; D010087:Oxides; D011188:Potassium; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Co doping; Cr(3+) oxidation; Cryptomelane; EXAFS; Pb(2+) adsorption