(377q) Room-Temperature Synthesis of Carboxylated-Mxene Nanosheets for Mercury Scavenging

Toxic metals in drinking water affect millions of people worldwide. They are ubiquitous in the environment and pose a harmful effect on human health, especially for children. For example, mercury ions are converted to methylmercury (CH₃Hg) in the aqueous phase, which is one of the most toxic forms of mercury¹. The U.S. Environmental Protection Agency has regulated the level of mercury in wastewater effluents². Water treatment can be used to remove mercury from wastewater effluents. There are a few methods that have successfully been used for this purpose, but their energy and chemical costs are high. Adsorption has been regarded as one of the easy, effective, and economical techniques for the removal of heavy metals from contaminated streams^3-5.

Recently, Ti₃C₂T_x MXene has been explored as an efficient sorbent for heavy metals^6-8. Its abundant active sites, negative zeta potential, high conductivity, excellent dispersity in water, and a large surface area have made it an ideal sorbent for environment remediation^7-19. However, pristine MXenes usually tends to oxidize in aqueous media, which makes them unstable. One of the surface functional groups of the MXene is the hydroxyl group, which allows for MXene surface modification and thus for changing the MXene properties.

In this work, to overcome the Ti₃C₂T_x MXene oxidization in aqueous media and improve its potential for water treatment, we modified the MXene with a chloroacetic acid solution at room temperature and prepared carboxylated-MXene (MXene–COOH). The MXene–COOH was characterized by means of SEM, EDX, TEM, FTIR, XRD, and zeta potential measurements. Not only has MXene–COOH high stability and dispersity in aqueous media but also negative zeta potential, attracting positively charged pollutants. We conducted a batch-adsorption process to understand the influence of different parameters on the adsorption of Hg²⁺onto the MXene and MXene–COOH nanosheets. The removal efficiency of Hg²⁺ for the MXene and MXene–COOH were found to be 72 and 99.4% at pH 5.5 over 60 min, respectively. In addition, we calculated the thermodynamic parameters such as ΔG°, ΔH°, and ΔS°.

Keywords: Adsorption, Mercury Ions, MXenes, Carboxylated-MXene, Wastewater Treatment.

References

1. Hu, X.; Mu, L.; Lu, K.; Kang, J.; Zhou, Q., Green Synthesis of Low-Toxicity Graphene-Fulvic Acid with an Open Band Gap Enhances Demethylation of Methylmercury. ACS Applied Materials & Interfaces 2014, 6 (12), 9220-9227.
2. Bolger, P. T.; Szlag, D. C., An electrochemical system for removing and recovering elemental mercury from a gas stream. Environmental science & technology 2002, 36 (20), 4430-4435.
3. Efome, J. E.; Rana, D.; Matsuura, T.; Lan, C. Q., Insight studies on metal-organic framework nanofibrous membrane adsorption and activation for heavy metal ions removal from aqueous solution. ACS applied materials & interfaces 2018, 10 (22), 18619-18629.
4. Zhang, Q.; Dan, S.; Du, K., Fabrication and Characterization of Magnetic Hydroxyapatite Entrapped Agarose Composite Beads with High Adsorption Capacity for Heavy Metal Removal. Industrial & Engineering Chemistry Research 2017, 56 (30), 8705-8712.
5. Cao, C.-Y.; Qu, J.; Yan, W.-S.; Zhu, J.-F.; Wu, Z.-Y.; Song, W.-G., Low-Cost Synthesis of Flowerlike α-Fe2O3 Nanostructures for Heavy Metal Ion Removal: Adsorption Property and Mechanism. Langmuir 2012, 28 (9), 4573-4579.
6. Naguib, M.; Gogotsi, Y., Synthesis of two-dimensional materials by selective extraction. Accounts of chemical research 2014, 48 (1), 128-135.
7. Shahzad, A.; Rasool, K.; Miran, W.; Nawaz, M.; Jang, J.; Mahmoud, K. A.; Lee, D. S., Two-Dimensional Ti3C2T x MXene Nanosheets for Efficient Copper Removal from Water. ACS Sustainable Chemistry & Engineering 2017, 5 (12), 11481-11488.
8. Peng, Q.; Guo, J.; Zhang, Q.; Xiang, J.; Liu, B.; Zhou, A.; Liu, R.; Tian, Y., Unique lead adsorption behavior of activated hydroxyl group in two-dimensional titanium carbide. Journal of the American Chemical Society 2014, 136 (11), 4113-4116.
9. Guo, J.; Peng, Q.; Fu, H.; Zou, G.; Zhang, Q., Heavy-metal adsorption behavior of two-dimensional alkalization-intercalated MXene by first-principles calculations. The Journal of Physical Chemistry C 2015, 119 (36), 20923-20930.
10. Mi, X.; Huang, G.; Xie, W.; Wang, W.; Liu, Y.; Gao, J., Preparation of graphene oxide aerogel and its adsorption for Cu2+ ions. Carbon 2012, 50 (13), 4856-4864.
11. Chandra, V.; Park, J.; Chun, Y.; Lee, J. W.; Hwang, I.-C.; Kim, K. S., Water-dispersible magnetite-reduced graphene oxide composites for arsenic removal. ACS nano 2010, 4 (7), 3979-3986.
12. Tiwari, J. N.; Mahesh, K.; Le, N. H.; Kemp, K. C.; Timilsina, R.; Tiwari, R. N.; Kim, K. S., Reduced graphene oxide-based hydrogels for the efficient capture of dye pollutants from aqueous solutions. Carbon 2013, 56, 173-182.
13. Ying, Y.; Liu, Y.; Wang, X.; Mao, Y.; Cao, W.; Hu, P.; Peng, X., Two-dimensional titanium carbide for efficiently reductive removal of highly toxic chromium (VI) from water. ACS applied materials & interfaces 2015, 7 (3), 1795-1803.
14. Naguib, M.; Mochalin, V. N.; Barsoum, M. W.; Gogotsi, Y., 25th anniversary article: MXenes: a new family of two‐dimensional materials. Advanced Materials 2014, 26 (7), 992-1005.
15. Anasori, B.; Xie, Y.; Beidaghi, M.; Lu, J.; Hosler, B. C.; Hultman, L.; Kent, P. R.; Gogotsi, Y.; Barsoum, M. W., Two-dimensional, ordered, double transition metals carbides (MXenes). Acs Nano 2015, 9 (10), 9507-9516.
16. Mashtalir, O.; Naguib, M.; Mochalin, V. N.; Dall'Agnese, Y.; Heon, M.; Barsoum, M. W.; Gogotsi, Y., Intercalation and delamination of layered carbides and carbonitrides. Nature communications 2013, 4, 1716.
17. Mashtalir, O.; Lukatskaya, M. R.; Zhao, M. Q.; Barsoum, M. W.; Gogotsi, Y., Amine‐assisted delamination of Nb2C MXene for Li‐Ion energy storage devices. Advanced Materials 2015, 27 (23), 3501-3506.
18. Rasool, K.; Mahmoud, K. A.; Johnson, D. J.; Helal, M.; Berdiyorov, G. R.; Gogotsi, Y., Efficient Antibacterial Membrane based on Two-Dimensional Ti 3 C 2 T x (MXene) Nanosheets. Scientific reports 2017, 7 (1), 1598.
19. Li, G.; Tan, L.; Zhang, Y.; Wu, B.; Li, L., Highly Efficiently Delaminated Single-Layered MXene Nanosheets with Large Lateral Size. Langmuir 2017, 33 (36), 9000-9006.