Electrosorption of Ions from Aqueous Solutions by Carbon Aerogel:  An Electrical Double-Layer Model

Abstract

An electrical double-layer model is developed to predict electrosorption of ions from aqueous solutions by carbon aerogel electrodes. The carbon aerogel electrodes are treated as electrical double-layer capacitors, and electrosorption is modeled using classical electrical double-layer theory. Because of the porous characteristics of the electrodes, the total capacity of the system is obtained by summing the contributions of the individual pores. The pore size distribution of the carbon aerogel is measured by the physical adsorption of N2 and CO2 as well as by mercury intrusion porosimetry. When a pore has a width smaller than a specific value (cutoff pore width), it does not contribute to the total capacity because of the electrical double-layer overlapping effect. This effect greatly reduces the electrosorption capacity for electrodes with significant numbers of micropores, such as carbon aerogel; thus, it is considered in the electrical doublelayer model. The model in this study focuses on the electrosorption of sodium fluoride, which exhibits minimal specific adsorption. Several equilibrium electrosorption experiments are performed under various conditions of ion solution concentration and applied voltage. When the overlapping effect is considered, modeling results agree well with experimental data obtained at voltages up to 1.2 V. Without the doublelayer overlapping correction, the model greatly overestimates the electrosorption capacity. The cutoff pore width is found to decrease with increasing ion solution concentration and applied voltage. An approximate modeling approach is also presented in this work, which is more efficient than the exact solution in terms of numerical computations.

Theory of membrane capacitive deionization including the effect of the electrode pore space

“…However, the micropores in porous activated carbon electrodes are small (less than 2 nm) and diffuse layers must be overlapping strongly. 47,48,49 Using the GCSmodel in a transport model, especially in modeling MCDI at reversed voltage during ion release, where c mA goes down strongly, leads to mathematical divergences. This led us to develop a novel approach which is presented here; namely, we describe the interior volume of the carbon particle by a "modified Donnan model".…”

Evaluation of Carbon Aerogel Manufacturing Process in Order to Desalination of Saline and Brackish Water in Laboratory Scale

“…Carbon aerogel manufacturing process involves the polymerization and pyrolysis of a mixture of formaldehyde and resorcinol [10]. In such a manner that the resorcinol and formaldehyde are dissolved to a specific ratio in a specific amount of distilled water and reacts in the presence of sodium carbonate as a catalyst.…”

“…These membrane complexes produce high volumes of saline wastewater generated throughout the course of the operation; with a high sensitivity and clogging and low flexibility of the membranes against changes in water, quality and temperature are the advantages of the membrane [10]. Problems with ion exchange resins include 1) the use of hydrochloric and sulfuric acids to regenerate resins, 2) producing a large volume of saline water, 3) and the need to dispose of the wastewater into injection wells [7,9].…”

Optimized nanoporous materials.

“…One is that the diffuse layer (in short, a decrease in capacitance due to ions thermally excited away from the interface) may affect the potential distribution inside the pore. [49] Another is that the amount of salt needed to charge the interface can be comparable to the amount of salt in the pores. [50] This amount is given by F V C vol / , where F is Faraday's constant (10 5 coul/mol).…”