Abstract Surface modifications of natural kaolins (Felsőpeteny, Hungary) with iron-content up to 9% (m/m) were carried out by varying acid concentration (5, 8 and 11 M HCl) and treatment time (1, 3 and 6 h) in order to evaluate the influence of treatment conditions on photochemical activity, amount of low coordinate Al defect sites, porosity, and acid/base character of the surface. Nitrogen adsorption and temperature-programmed desorption measurements showed that the acid treatment slightly reduced the pore volume and the surface area, while the average pore diameter and the number of acidic centers were increased. Solid-state 27Al NMR spectroscopy demonstrated the presence of mechanistically relevant Al defect sites. The distribution, concentration, and particle size of the iron oxide co-minerals were found to be influential to photochemical activity. Greater than 90% photochemical degradation efficiency of oxalic acid can be achieved by acid-treated samples upon 3 h exposure to 8 M HCl solution with good reproducibility.

中文翻译：

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高铁含量高岭土作为光催化剂：酸性表面改性的挑战和机理见解

摘要 通过改变酸浓度（5、8 和 11 M HCl）和处理时间（1、3 和 6 小时）对铁含量高达 9% (m/m) 的天然高岭土（Felsőpeteny，匈牙利）进行表面改性。 ) 以评估处理条件对光化学活性、低坐标 Al 缺陷位点数量、孔隙率和表面酸/碱特性的影响。氮吸附和程序升温脱附测量表明，酸处理略微减少了孔体积和表面积，而平均孔径和酸性中心的数量增加。固态 27Al NMR 光谱证明存在机械相关的 Al 缺陷位点。分布、集中、发现氧化铁共矿物的粒径和粒径对光化学活性有影响。酸处理的样品暴露于 8 M HCl 溶液 3 小时后，可以实现 90% 以上的草酸光化学降解效率，并且具有良好的重现性。