Soyer-Uzun Sezen, Yu Ping, Öner Feyza Kevser, Sen Sabyasachi
Department of Chemical Engineering, Bogazici University, Istanbul, Bebek 34342, Türkiye.
Nuclear Magnetic Resonance Facility, University of California, Davis, California 95616, United States.
J Phys Chem B. 2024 Dec 19;128(50):12638-12650. doi: 10.1021/acs.jpcb.4c06514. Epub 2024 Dec 9.
Silicate-based adsorbents offer significant advantages over traditional materials, particularly due to their superior thermal and chemical stability, enhanced regenerability, and the ability to endure more rigorous operating conditions. In this study, an amorphous Na-Ca-magnesium silicate adsorbent (SAAM) and its g-CN-modified counterpart (gCN-SAAM) were synthesized via alkali activation and a subsequent thermal process, respectively. The g-CN modification resulted in a novel hybrid adsorbent with a remarkable methylene blue (MB) adsorption capacity of 420 mg g, four times higher than the unmodified sample, setting a new benchmark. Solid-state Si (MAS and CP/MAS), H MAS, and C CP/MAS NMR spectroscopy were used to investigate the complex structures of these adsorbents and their interactions with MB. The local structure of SAAM primarily consists of Q Si units, with minor Q and Q Si species, structural water, and Mg-OH sites. Exposure to MB caused an upfield shift in the Si CP/MAS spectrum and enhanced resonances in the high-field region, indicating MB interaction with Si sites. H MAS NMR spectra revealed significant interactions between water molecules in the geopolymer-like framework of SAAM and MB. The thermal treatment of SAAM with urea to produce gCN-SAAM enhanced the polymerization of Q Si species and increased the relative fraction of Q Si sites. This treatment also reduced the intensity of some Mg-OH units, showing interaction with g-CN. After MB adsorption on gCN-SAAM, NH groups of g-CN disappeared, and shifts in the C and C sites indicated their involvement in adsorption, while Si sites remained intact. This thermal method creates a sustainable, cost-effective and efficient adsorbent for MB removal from wastewater. Multinuclear NMR spectroscopy provides detailed insights into the adsorbent's complex structure and MB interactions, potentially guiding the design of improved future adsorbents.
基于硅酸盐的吸附剂相对于传统材料具有显著优势，特别是由于其卓越的热稳定性和化学稳定性、更高的可再生性以及能够承受更严苛的操作条件。在本研究中，分别通过碱活化和随后的热过程合成了一种无定形钠钙镁硅酸盐吸附剂（SAAM）及其g-CN改性对应物（gCN-SAAM）。g-CN改性产生了一种新型杂化吸附剂，其对亚甲基蓝（MB）的吸附容量高达420 mg/g，比未改性样品高四倍，树立了新的标杆。采用固态Si（MAS和CP/MAS）、H MAS和C CP/MAS NMR光谱研究了这些吸附剂的复杂结构及其与MB的相互作用。SAAM的局部结构主要由Q Si单元组成，伴有少量Q和Q Si物种、结构水和Mg-OH位点。暴露于MB会导致Si CP/MAS光谱中的信号上移，并增强高场区域的共振，表明MB与Si位点发生了相互作用。H MAS NMR光谱揭示了SAAM类地质聚合物框架中的水分子与MB之间存在显著相互作用。用尿素对SAAM进行热处理以制备gCN-SAAM，增强了Q Si物种的聚合，并增加了Q Si位点的相对比例。该处理还降低了一些Mg-OH单元的强度，表明其与g-CN发生了相互作用。MB吸附在gCN-SAAM上后，g-CN的NH基团消失，C和C位点的位移表明它们参与了吸附过程，而Si位点保持完整。这种热方法为从废水中去除MB创造了一种可持续、经济高效的吸附剂。多核NMR光谱为吸附剂的复杂结构和MB相互作用提供了详细的见解，有可能指导未来改进型吸附剂的设计。
