(196r) Polysulfide-Based Nanofiber Prepared Via Inverse Vulcanization and Electrospinning for Effective Mercury (II) Sequestration

Authors: 
Limjuco, L. A., Myongji University
Nisola, G. M., Myongji University
Parohinog, K. J., Myongji University
Valdehuesa, K. N. G., Myongji University
Chung, W. J., Myongji University
Recent progress on inverse vulcanization has opened various opportunities to develop advanced materials with useful electrochemical and optical properties which have been investigated as Li-S batteries, for IR imaging technology, and as self-healing materials. Herein, the first extensive study on the preparation of an Hg2+ adsorbent based on inverse vulcanized polysulfide (PS) is presented.

Sulfur-rich poly(sulfur-random-acrylate) (poly(S-r-Ac)) was successfully prepared via direct addition of β-carboxyethyl acrylate to molten sulfur as confirmed via FTIR and 1H and 13C NMR analyses. The viscoelastic nature (i.e. 0< phase angle (δ) <90°) and thermal properties of (poly(S-r-Ac) can be directly manipulated by adjusting molar ratio of components (i.e. S:CEA molar ratio). That is, increasing sulfur content decreased the viscosity, and Tg, and % weight remaining in simultaneous thermal analysis profiles of the PS. This trend agrees with the hypothesis that with greater amount of sulfur, sulfur rank in poly(S-r-Ac) is longer which was also confirmed by higher S-S XPS peak area of PS in S:CEA = 2:1 molar ratio. Given that S-S (226 kJ mol-1) bond energy is weaker than other intramolecular bonds present such as C-S (272 kJ mol-1), C-C (346 kJ mol-1), C-O (358 kJ mol-1), and C=O (799 kJ mol-1), it is expected that poly(S-r-Ac) with greater amount of sulfur (i.e. S:CEA=2:1) degrades at relatively lower temperature and has lower Tg than those with lesser amount of sulfur component.

Poly(S-r-Ac) is soluble to most common solvents which include dimethyl formamide (DMF), enabling it to form homogenous solution with polyacrylonitrile (PAN). Polysides blended in polyacrylonitrile (PAN) were prepared as dope solutions in DMF and were electrospun into nanofibers (NFs). The NFs with different PS loadings were characterized and were evaluated as an adsorbent for Hg2+ sequestration. Batch adsorption experiments showed that the PS (S:CEA=2:1) follows a monolayer Langmuir-type adsorption isotherm with a maximum adsorption capacity of 612 mg g-1. Kinetics study showed that the PS efficiently sequestered Hg2+ attaining adsorption equilibrium within 1.5 hrs. Lastly, prepared PS exhibited selectivity towards Hg2+ having highest concentration factor (CF=1.79 L g-1) and distribution coefficient (Kd =1.95 x 106 mL g-1) despite having the least concentration amidst other competing ions. Little affinity towards Cr2+, Zn2+, Pb2+, and Cu2+ and no affinity towards Cd2+ and Ni2+ were observed. Reusability test exhibited the ability of the prepared PS NF to be recycled using 6 M HCl as an eluent to sequester adsorbed Hg2+ in the NF.

This work demonstrates new insight for the preparation of polysulfide-based adsorbents from inverse vulcanization. It also presents new approach for easy, cheap, and effective preparation of adsorbents for Hg2+ sequestration from contaminated water or wastewater. This research was supported by NRF funded by the Ministry of Science, ICT and future Planning (2017R1A2B2002109) and the Ministry of Education (2009-0093816).