Designing sub-nanometer pores for efficient boron removal

X Zhang and MJ Wei and Y Wang, DESALINATION, 533, 115755 (2022).

DOI: 10.1016/j.desal.2022.115755

Efficient boron removal is one of the key challenges for reverse osmosis membranes. Understanding the transport behavior of boric acid (B(OH)3) at the molecular level is of great importance to design pores with high perm selectivity. Herein, via non-equilibrium molecular dynamics simulations, the B(OH)3 rejection is found to be closely related to the hydrophilicity, shape, and size of sub-nanometer pores. Among these structure parameters, the role of the pore shape is dominant as the slit pore has & LE;20% B(OH)3 rejections regardless of the pore hydrophilicity and slit width. It is due to the nature of the B(OH)3 molecule being plate-like, even when it is hydrated. Such a unique structure makes the B(OH)3 rejection depend on the major diameter of the non-circular pores. On the other hand, the circular pore, which has the same diameter in all directions, is the most suitable to reject B(OH)3 molecules while providing high water permeance. With a circular pore shape, hydrophilic pores favor the B(OH)3 rejection because the preferentially adsorbed water molecules inside pores can impede the passage of B(OH)3. These findings are expected to guide the rational design and screening of the nanoporous materials for efficient boron removal.

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