三元LDH的改性及去除酸性橙II的光谱分析研究

吸附法由于具有效率高、成本低、无毒、简单等优点，具为最常见的废水处理方法。采用吸附法的关键是吸附剂的选择和制备。层状氢氧化物(LDH)作为一类新型吸附剂，拥有特殊的层状结构、层板元素的可调变性、层间阴离子的可交换性，近期备受关注，但其吸附能力的提升仍是亟需研究的问题。利用均苯四甲酸(PA)对三元层状氢氧化物(Ca-Mg-Al-LDH)进行插层改性，制备出新型的芳香酸阴离子改性层状氢氧化物(PA-LDH)，对其进行煅烧得到煅烧产物(PA-LDO)，并结合紫外分光光度法(UV-Vis)研究其对酸性橙II的吸附性能。通过红外光谱(FTIR)和氮气吸附-脱附实验对其进行结构表征。结果发现，PA-LDH相比LDH在1 717 cm-1处出现了一个新的峰，归属为ν(C═O)，且相对PA的C═O峰(1 668 cm-1)向高频方向移动，这可能是由于PA之间形成的缔合体被破坏，表明PA可能插层进入了LDH的间层。相比PA-LDH的红外光谱谱图，可以发现PA-LDO在3 000 cm-1附近的弱峰消失了，表明层间阴离子在煅烧过程中被破坏，但是在875和723 cm-1处与M—O和M—OH(M=Ca，Mg和Al)振动相对应的峰仍然存在，表明煅烧处理后其相似的结构依然得到了保持。通过氮气吸附-脱附实验测得PA-LDH和PA-LDO的比表面积分别为15.934 1和119.401 0 m2·g-1，说明在煅烧后，其比表面积增大，因此PA-LDO可能具有更好的吸附效果。以阴离子染料酸性橙Ⅱ为目标污染物，在pH 7.0，吸附剂用量5 mg，波长为484 nm的条件下，通过UV-Vis分析手段，分别考察了吸附时间、染料初始浓度等对PA-LDH、PA-LDO吸附性能的影响。结果表明，PA-LDH和PA-LDO对酸性橙Ⅱ的Q_max分别为561.322和1 401.639 mg·g-1，高于目前文献所报道的Q_max值。通过吸附等温实验，发现PA-LDH和PA-LDO对酸性橙II的吸附基本符合Langmuir模型，即单分子层吸附为该吸附过程的主导过程，且理论最大吸附容量分别可为588.235和1 428.571 mg·g-1，与上述实验值相接近，这说明制备的芳香酸阴离子改性层状氢氧化物对阴离子染料具有较好的吸附性能，在治理染料废水中具有一定的应用前景。

Modification of Ternary Layered Hydroxide and Removing for Orange Ⅱ With Spectroscopy

The adsorption method has become one of the most common wastewater treatment methods because of its high efficiency, low cost, non-toxicity, simple operation and so on. The key to the adsorption method is the selection and preparation of adsorbents. As a new type of adsorbent, the layered hydroxide (LDH) has attracted much attention due to its special layered structure, adjustable lamellar elements and exchangeable anions between layers. However, the improvement of LDH adsorption capacity is still an urgent problem. In this work, a novel pyromellitic acid modified layered hydroxide (PA-LDH) was prepared by intercalation modification of ternary Ca-Mg-Al-LDH with pyromellitic acid (PA), and its calcination product (PA-LDO) was obtained by calcining. UV Vis was applied to study their adsorption performance for Orange II. FTIR and BET were used to characterize the morphology and structure of the modified adsorbents. Comparing the FT-IR spectra of LDH and PA-LDH, a new peak of PA-LDH appeared at 1 717 cm-1, which may be attributed to the C═O group in PA. Moreover, the peak moved towards the high frequency, which may be due to the destruction of the polymer formed between PA, indicating that PA was successfully intercalated into the interlayer of LDH. Compared with the FT-IR spectra of PA-LDH, it could be found that the weak peak of PA-LDO near 3 000 cm-1 disappeared, implying that the interlayer anion was destroyed during the calcination process. However, the peaks corresponding to the vibration of M—O and M—OH (M=Ca, Mg and Al) at 875 and 723 cm-1 still existed, indicating that the similar structure was still maintained after calcination. The specific surface areas of PA-LDH and PA-LDO measured by nitrogen adsorption-desorption experiments were 15.934 1 and 119.401 0 m2·g-1, respectively, indicating that the specific surface area increased after calcination, so that PA-LDO may have a better adsorption effect. With anionic dye, Orange Ⅱ as the target pollutant, the effects of adsorption time, initial dye concentration and other factors on PA-LDH，PA-LDO adsorption performance were investigated by UV Vis under pH conditions 7.0, adsorbent dosage of 5 mg and wavelength of 484 nm. The Qmax of PA-LDH and PA-LDO for Orange Ⅱ were 561.322 and 1 401.639 mg·g-1, respectively, which were relatively higher than those reported in the literature. Through isothermal adsorption experiments, it was found that the adsorption of Orange Ⅱ by PA-LDH and PA-LDO basically accorded with the Langmuir model, which showed monolayer adsorption was the dominant process of the adsorption process, the theoretical maximum adsorption capacities were 588.235 and 1 428.571 mg·g-1 respectively, which were close to the experimental values mentioned above. This indicated that the layered hydroxide modified by aromatic acid anions had good adsorption performance for anionic dyes and a certain application prospect in the treatment of dye wastewater.