奈米孔道之不均一電荷分布對於離子電流整流,除鹽與壓差發電之影響

Nanopore based Ion Current Rectification, Desalination and Pressure driven Energy Conversion: Effect of Non-uniform charge distribution

陳昱廷(Yue-Ting Chen)

指導教授 ： 徐治平

國立臺灣大學/工學院/化學工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101342

摘要

奈米流體裝置具有高度的應用潛力，目前已在發展中的應用有: 離子電流整流、鹽濃差發電、壓差發電、奈米孔道之海水淡化(除鹽)等應用。在本篇當中我們將展示奈米孔道之不均一電荷分布對於1.離子電流整流2.除鹽與壓差發電之影響。其中，離子電流整流會在第一章節中討論，除鹽與壓差發電會在第二章節中討論。
在第一章節中，我們考慮在一個以聚電解質改質之孔道表面的薄膜中，施以軸向的pH梯度以及電壓差，透過不同的pH梯度與電壓，可以精準地控制表面電荷的分布。存在pH梯度時，施以負偏壓時(正偏壓)時，電滲流的作用會使孔道表面的負電荷增強(變小)。因此，正負偏壓越強，整流效果(Rf=I(V-)/I(V+))越好。在本章節當中，我們將一端的pH固定在11，另一端的pH從11掃到3，發現整流比存在局部極大值。同時，本章節也有模擬不同的聚電解質厚度中對於整流效果的影響，發現聚電解質厚度同樣存在一個最佳值。
在第二章節中，我們設計四種不均一的表面電荷分布，這四種電荷分布具有相同的平均電荷。分別是Type1:出口與入口帶電相對於孔道中間較強；Type2:出口與入口相對於孔道中間帶電較弱；Type3:入口帶電較強，出口帶電較弱；Type4:出口帶電較強，入口帶電較弱。文中會探討這四種表面帶電電荷分布，在施與一個壓力差的驅動力之下，對於其發電表現與除鹽效果的影響。發電部分，則隨著濃度與壓力的變化，有不同的最適合之表面帶電分布。除鹽部分，發現Type3的表面電荷設計在不同濃度與壓力下皆有最好的除鹽效果，且可以同時提升流量。

關鍵字

奈米流體裝置 ； 奈米孔道 ； 除鹽 ； 壓差發電 ； pH梯度 ； 離子電流整流

並列摘要

Nanofluidic device is capable of many usage including ionic current rectification (ICR), pressure driven energy conservation, desalination, and salanity gradient power generation. Among these, we perform three applications: ion current rectification in chapter 1, Pressure-driven power generation and ion separation in chapter two, and the underlying mechanism is investigated.
In chapter 1, the performance of the ICR is assessed by considering a cylindrical nanopore, surface modified by a PE, subject to pH gradient and. The charged conditions of the nanopore can be tuned by modulating dual the applied pH gradient and voltage so that it can be σs can be one of the following: (1) σs is partially positive and partially negative (i.e., a bipolar nanopore). (2) σs is all negative, and uniformly distributed. (3) σs is all negative, but nonuniformly charged. (4) σs shows a local maximum or local minimum. Due to the electroosmotic flow, negative surface is enhanced (decreased) as negative (positive) potential is applied. Hence, In general, the larger the |V| the better the rectification performance. If pHU is fixed at 11 and pHL varies from 3 (i.e., applied pH gradient is strong) to 11 (free of pH gradient), Rf shows a local maximum. In addition, a optimum coating PE layer thickness is observed.
In chapter 2, we look into how the non-uniformly charged cylindrical nanopore effect the performance of pressure-driven power generation and ion separation. Four types of surface charge distribution are considered. Type1: the surface charge density near the inlet and outlet is higher (lower) for Type1(Type2)；the surface charge density near the inlet region is higher (lower) for Type3(Type4). Each of the nanopore surface is set with an averaged charge density σ ̅=-60 mC/m2. For pressure-driven power generation, how to achieve the maximum power under various bulk concentration and pressure conditions is examined. For ion separation, it is observed that high salt rejection rate and flow rate can be obtained simultaneouly through choosing the type 3 surface charge distributuon.

並列關鍵字

nanofluidic device ； nanopore ； desalination ； Pressure-driven power generation ； Ion Current Rectification ； pH-Gradient

參考文獻

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