引用本文:王 锐,方 敦,牛鹏举,许海娟,魏世勇.Mn2+掺杂对晶质氧化铁结构与红外光谱特征的影响[J].土壤学报,2020,57(4):898-907. DOI:10.11766/trxb201901110021
WANG Rui,FANG Dun,NIU Pengju,XU Haijuan,WEI Shiyong.Influence of Mn-doping on Structure and FT-IR Properties of Crystalline Iron Oxides[J].Acta Pedologica Sinica,2020,57(4):898-907. DOI:10.11766/trxb201901110021
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Mn2+掺杂对晶质氧化铁结构与红外光谱特征的影响
王 锐1,2, 方 敦3, 牛鹏举4, 许海娟1,2, 魏世勇1,2
1. 湖北民族大学化学与环境工程学院,湖北恩施 445000;2. 生物资源保护与利用湖北省重点实验室(湖北民族大学),湖北恩施 445000;3.华中农业大学资源与环境学院;4.安阳工学院文法学院
摘要:
制备针铁矿和赤铁矿的混合晶质氧化铁(CIO)和不同摩尔比例(R)的Mn2+掺杂晶质氧化铁(CIO-Mnx(x=0.1、0.2、0.3和0.5))样品。根据样品的X-射线衍射(XRD)和透射电镜(TEM)结果分析Mn2+掺杂对晶质氧化铁结构与形貌的影响;对样品的傅里叶红外图谱(FT-IR)的高波数(3 000~3 700 cm-1)和低波数(450~750 cm-1)两个区间做分峰拟合,分析Mn2+掺杂晶质氧化铁的羟基官能团和晶体结构化学键的变化特征。结果显示,R为0.1~0.3的Mn2+掺杂抑制了针铁矿和赤铁矿等晶质氧化铁的形成;R为0.5的Mn2+掺杂导致样品中形成了掺锰磁铁矿,且存在少量的针铁矿而没有明显的赤铁矿。CIO样品中存在自由羟基、吸附水羟基、表面缔合羟基和结构羟基共四类羟基。在R为0.1~0.3范围内,随着R的增大,样品中自由羟基和吸附水羟基的相对含量降低,而表面缔合羟基和结构羟基的相对含量增大。此外,Mn2+掺杂导致样品中自由羟基和结构羟基的吸收带波数降低,而吸附水羟基和表面缔合羟基的吸收带波数随R的增大而增大。CIO样品中Fe-O振动在455 cm-1和619 cm-1附近红外吸收带的强度和峰形与样品中针铁矿颗粒的形貌有关,478 cm-1和560 cm-1附近的红外吸收与样品中赤铁矿的结晶度密切相关。分析表明,CIO-Mnx样品中的赤铁矿结构中阳离子空位与Mn2+耦合产生了567~589 cm-1附近的吸收,其强度随着R的增大而增强。CIO-Mn0.5样品中形成了Mn2+替代Fe2+的掺锰磁铁矿,导致样品在593 cm-1处出现了Mn-O晶格振动吸收带。
关键词:  晶质氧化铁  锰掺杂  红外  羟基  晶体结构
基金项目:国家自然科学基金项目(41561053)
Influence of Mn-doping on Structure and FT-IR Properties of Crystalline Iron Oxides
WANG Rui1,2, FANG Dun3, NIU Pengju4, XU Haijuan1,2, WEI Shiyong1,2
1. Department of Chemistry and Environmental Engineering, Hubei Minzu University, Enshi, Hubei 445000, China;2. Hubei Key Laboratory of Biologic Resources Protection and Utilization (Hubei Minzu University), Enshi, Hubei 445000, China;3.College of Resources and Environment, Huazhong Agricultural University;4.School of Literature and Law, Anyang Institute of Technology
Abstract:
【Objective】 Manganese (Mn) doping may affect iron oxide in structure and property, and then influence its performance in adsorption, catalysis and so on, especially its utilization in soils and environment. However, it is still little known about the detailed influence of Mn2+ doping in microstructure owing to complex hydrogen bonding and similar chemical bonding of the iron oxide crystallines. 【Method】 In this study, samples of crystalline iron oxides (CIO) and samples of Mn2+ doped CIO different in molar ratio (R) (CIO-Mnx, x=0.1, 0.2, 0.3 and 0.5, separately) were prepared out of goethite and hematite. Influences of Mn2+ doping on iron oxide in crystal structure and morphology were analyzed with the aid of XRD and TEM. Peak fitting was performed of the two wave number ranges, high (3 000-3 700 cm-1) and low (450-750 cm-1) of the FT-IR graphs of the samples, and changes in hydroxyl functional group and crystalline chemical bonding of Mn2+-doped CIO were analyzed. 【Results】 Results show that Mn2+-doping just inhibited the formation of CIO, such as goethite and hematite, when R was less than 0.3, but promoted the formation of Mn-doped magnetite, some goethite and no visible hematite, when R was 0.5. In the CIO samples existed four types of hydroxyls, that is free hydroxyls, adsorbed hydrohydroxyls, surface associated hydroxyls and structural hydroxyls. With R rising from 0.1 to 0.3, relative content of the first two types decreased, while the latters increased. Adsorption peaks of the free hydroxyls and structural hydroxyls red shifted with Mn2+ doped, but those of adsored hydrohydroxyls decreased and those of surface associated hydroxyls behaved on the contrary when R increased from 0.1 to 0.3. When R was 0.5, structural hydroxyls almost disappeared, relative content of the surface associate hydroxyls varied between that of CIO and that of CIO-Mnx, and wavenumber of the adsorption band of surface associated hydroxyls was close to that of the CIO sample. Intensity and shape of the adsorption peaks of crystal structure Fe-O around 455 cm-1 and 619 cm-1 were related to the morphology of goethite, and those of the adsorption peaks around 478 cm-1 and 560 cm-1 were to the crystallinity of hematite. Intensity and wavenumber of the adsorption peak of hematite at 560 cm-1 decreased when R increased from 0.1 to 0.3, and adsorption peaks at 478 cm-1 disappeared with Mn2+ doped. When the R was 0.5, adsorption peaks almost disappeared at 543 cm-1, widened and intensified at 474 cm-1 and 593 cm-1, and remained the same as that of CIO at 619 cm-1. According to analysis, the vacant sites for cations in the structure of hematite in CIO-Mnx samples might get coupled with Mn2+ to form adsorption peaks around 567~589 cm-1, of which intensity increased with rising R. In CIO-Mn0.5 samples, Mn-doped magnetite formed with Mn2+ replacing Fe2+, thus forming a lattice vibrated Mn-O adsorption band around 593 cm-1. 【Conclusion】 According to the results of the study for CIO and CIO-Mnx, a spot of Mn2+ inhibited the crystallization of CIO, which increased the varieties of hydroxy on the surface of CIO-Mnx and changed the composition of hydroxyl in the samples. That the Mn2+ replaced the Fe3+adsorbed at vacancies in CIO caused a strong absorption around 567~589 cm-1 in IR spectra. But the mass of Mn2+doping could change the CIO from goethite and hematite to Mn-doped magnetite, which appeared the different FT-IR characterizations of hydroxyl and crystalline structure.
Key words:  Crystalline iron oxides  Mn2+-doping  FT-IR  Hydroxyl  Crystal structure