功能化MOFs纳米晶强化陶瓷膜资源化处理重金属废水的机理研究

Heavy metal pollution poses a serious threat to human health and life safety. In order to realize resource recovery of heavy metal ions such as Cd(II), Pb(II), Cu(II), and Ni(II), this project first presents functionalized metal-organic frameworks (MOFs) for enhanced ceramic membrane in the treatment of wastewater containing heavy metals. Firstly, ultrasound method is applied for rapid preparation of controllable amine-functionalized MOFs nanocrystals, and then by post-synthetic modifications, a novel adsorbent for heavy metal ions remediation will be obtained with high capacity. Towards the viewpoints of thermodynamics and kinetics, mechanisms for the adsorption/desorption of heavy metal ions on the MOFs surface are examined to realize the adsorption-desorption process controllable. Secondly, the functionalized MOFs nanocrystals as adsorbent are coupled with ceramic membrane ultrafiltration technology. Various influences of operating pressure, temperature, cross-flow velocity, mode of operation, the pH values and other factors are investigated on MOFs adsorption-desorption process, to clarify the interaction between MOFs and heavy metal ions as well as the membrane surface at the molecular level, and then the enhancement mechanism of MOFs is determined. Thirdly, the membrane fouling mechanism caused by functional MOFs nanocrystals are determined. Darcy's law, models of pore blocking and cake filtration, etc. are used for the theory calculations. The surface properties of the fouled membrane are studied, so as to determine an appropriate cleaning method, thus supporting the membrane fouling mechanism vise versa. Through a long-term study to address the repeatability and reliability of the cleaning method, the practical application of MOFs nanocrystals will be promoted in the field of heavy metal wastewater treatment.

重金属污染严重危害人类健康和生命安全。本课题首次提出用功能化金属-有机骨架(MOFs)强化陶瓷膜处理重金属废水，以实现镉、铅、铜、镍等重金属离子的资源化回收。首先，利用超声法快速可控制备氨基功能化MOFs纳米晶，通过合成后期修饰获得高性能新型重金属离子吸附剂。从热力学和动力学角度，研究MOFs对重金属离子的吸脱附机制，实现吸脱附过程可调控。其次，将功能化MOFs纳米晶吸附剂耦合陶瓷膜超滤技术。考察操作压力、温度、错流速度、操作模式、pH值等对MOFs吸附和解吸附过程的影响，从分子水平上阐明MOFs与重金属离子及膜面间的相互作用，确定MOFs的强化机制。再次，确定功能化MOFs纳米晶的膜污染机理。利用达西定律、孔堵塞模型、滤饼模型等进行理论计算。研究污染膜面性质，确定适宜的清洗方法，佐证膜污染机理。通过长期实验，考察清洗方法的重复性和可靠性，促进MOFs纳米晶在重金属废水处理领域的实际应用。

重金属污染严重危害人类健康和生命安全。本课题首次提出用功能化金属-有机骨架(MOFs)强化陶瓷膜处理重金属废水，以实现重金属离子的资源化回收。首先，利用微波法快速(3 min)可控制备氨基功能化MOFs纳米晶，确定合适的晶体成长条件，使制备方法和过程环境友好化，无二次污染，产品稳定性好，能耐酸碱。合成后期利用三聚氰胺改性MOFs，密度泛函理论计算结果显示两者之间存在电荷转移和轨道转换。实验证实三聚氰胺通过化学反应成功掺入到MOFs中。改性MOFs对Pb (II)的吸附量比未改性MOFs的吸附量增大1.7倍，应用前景良好。其次，从热力学和动力学角度研究功能化MOFs纳米晶的吸脱附特性，进行不同种类、不同浓度重金属离子的MOFs纳米晶吸附实验，考察平衡时间、温度、pH、重金属量浓度等因素对MOFs纳米晶吸附去除重金属离子性能的影响。30°C、pH值为6、吸附120 min，MOFs对浓度为10 mg/L的Pb(II)去除率为99.95%。当浓度为40 mg/L，Cd(II)的吸附量为177.35 mg/g。吸附数据符合准二级动力学模型(R^2>0.99)。因△G°为负，吸附过程自发。Cd(II)吸附为吸热和熵驱动过程，Pb(II)与这一趋势一致(T<40°C)，但T≥40°C反之。调控pH能够较好地实现脱附。再次，将氨基功能化MOFs纳米晶吸附剂耦合陶瓷膜超滤技术，资源化去除废水中Pb(II)。氨基功能化MOFs呈类球形，粒径约100 nm，晶型为UiO-66-NH2。研究了跨膜压力(TMP)、错流速度(CFV)、温度(T)和pH对耦合过程的影响。结果表明，平均孔径为50nm的陶瓷膜可完全截留MOFs(100%)。TMP=0.15 MPa，CFV=4.0 m/s，T=35°C，对Pb(II)的去除率最高(61.4%)，相应通量下降最低、滤饼污染程度最低，平衡吸附量高达1795.3 mg/g。在35°C，△G°为负，吸附过程自发。△H°和△S°值为正，吸附是吸热和熵驱动过程。准二级动力学模型可很好地描述吸附过程(R^2=0.9997)，氨基和Pb(II)发生配位反应。控制pH4.5可有效实现Pb(II)的脱附。用柠檬酸铵+硝酸溶液(0.5%(w/w))清洗，膜通量恢复率近100%。氨基功能化MOFs纳米晶耦合陶瓷膜超滤技术用于重金属废水处理及资源回收具有很大的潜力。