Molecular dynamics study of ion rejection process based on Janus nanochannel

doi:10.11949/0438-1157.20241417

Abstract

Abstract:

Seawater desalination is the process of producing fresh water by desalination of seawater, which is a new technology to realize the increase of water resource utilization. In this paper, we propose a Janus nanochannel model, which consists of hydrophilic and hydrophobic segments with high and low temperatures at the ends of the channel. Based on molecular dynamics simulations, it is found that the desalination process can be greatly enhanced by using the Janus nanochannel. The evaporation of liquid water and ion rejection was realized in the hydrophilic section of the channel, and the thermo-osmosis transport of water molecules under the action of temperature gradient was realized in the hydrophobic section. The results show that Janus nanochannels provide an 87.5% increase in water production rate compared to conventional hydrophobic channels, and maintain more than 95% ion removal compared to conventional hydrophobic channels. The water production rate in the channel during the desalination process is positively correlated with the temperature difference, the channel width, the system temperature, and the difference in the hydrophilicity of the walls at the two ends, while there exists an optimal value for the percentage of hydrophilicity of the walls. The Janus nanochannel model proposed in the present paper can provide theoretical guidance for the future membrane desalination process.

Key words: desalination, Janus nanochannel, membrane, nanomaterials, molecular simulation

摘要：

海水淡化即利用海水脱盐来生产淡水的过程，是实现水资源利用开源增量的一种新技术。通过分子动力学模拟的方法，构建了由亲疏水材料复合而成的Janus纳米通道，在通道两端分别布置高低温热源，液态水在通道亲水段实现蒸发脱盐，水分子在疏水段的温度梯度作用下实现热渗透输运，从而实现海水淡化过程。结果表明，相较于传统疏水通道，Janus纳米通道的产水速率有87.5%的提升，并能保持95%以上的离子去除率，且在脱盐过程中通道内的产水速率与温差、通道宽度、系统温度及两端壁面亲疏水差异呈正相关关系，而亲疏水壁面的占比则存在一个最佳值。所提出的关于Janus纳米通道脱盐过程的分子动力学模拟可以为未来基于低品位余热利用的膜法海水淡化过程提供理论指导。

关键词: 脱盐, Janus纳米通道, 膜, 纳米材料, 分子模拟

CLC Number:

TQ 028.8

Zirui LI, Kai QI, Jun WANG, Guodong XIA. Molecular dynamics study of ion rejection process based on Janus nanochannel[J]. CIESC Journal, 2025, 76(7): 3531-3538.

李姿睿, 齐凯, 王军, 夏国栋. 基于Janus纳米通道的脱盐过程分子动力学模拟研究[J]. 化工学报, 2025, 76(7): 3531-3538.

Figures/Tables 16

Fig.1 The calculation model of Janus nanochannel in ion rejectionn process

Table 1 Parameters of L-J potential

离子/原子	σ/nm	ε/eV	q/e
Na⁺	0.333	0.0153	1.0
K⁺	0.349	0.0137	1.0
Cl^－	0.442	0.0051	-1.0
H	0	0	0.4238
O	0.354	0.009	-0.8476
Ag	0.264	0.345	—

Table 2 Parameters of coupling strength parameter for varying types of Janus nanochannels

类型	k_H	k_L
Ⅰ	0.5	0.5
Ⅱ	0.6	0.4
Ⅲ	0.7	0.3
Ⅳ	0.8	0.2
Ⅴ	0.9	0.1

Fig.2 The contact angle with different surface wettability

Fig.3 Variation of contact angle with k

Fig.4 The schematic diagram of the liquid level in the nanochannel

Fig.5 Effect of coupling strength parameter k on the volumetric flux of water vapor

Fig.6 Water production rate of different types of Janus nanochannels

Fig.7 Water yield of Janus nanochannel and hydrophobic nanochannel

Fig.8 Ion removal rate under different nanochannels

Fig.9 Comparison of water production rate and ion removal rate with literature

Fig.10 Effect of temperature difference on water production rate of Janus nanochannel

Fig.11 Effect of channel width on water production rate of Janus nanochannel

Fig.12 Effect of system temperature on water production rate of Janus nanochannel

Fig.13 Effect of proportion of hydrophilic wall length on water production rate of Janus nanochannel

Fig.14 Schematic diagram of the force of the wall surface on water molecules

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