Abstract
The importance of chitosan has been strongly emphasized in literature because this natural polymer could not only remove heavy metal ions in water but also have the potential for recyclability. However, reversible phase transition and its dynamics, which are highlighting areas of a recycle process, have not been studied sufficiently. Here, we present dynamic studies of the dissolution as well as the gelation of a physically crosslinked chitosan hydrogel. Specifically, a one-dimensional gel growth system and an acetate buffer solution were prepared for the precise analysis of the dominant factors affecting a phase transition. The dissolution rate was found to be regulated by three major factors of the pH level, Cu2+, and NO2–, while the gelation rate was strongly governed by the concentration of OH–. Apart from the gelation rate, the use of Cu2+ led to the rapid realization of gel characteristics. The results here provide strategies for process engineering, ultimately to determine the phase-transition rates. In addition, a microfluidic switch was successfully operated based on a better understanding of the reversible crosslinking of the chitosan hydrogel. Rapid gelation was required to close the channel, and a quick switchover was achieved by a dissolution enhancement strategy. As a result, factors that regulated the rates of gelation or dissolution were found to be useful to operate the fluidic switch.
Highlights
Chitosan is a polysaccharide obtained from the deacetylation of chitin.[1−3] Based on its unique characteristics, such as hydrophilicity, biocompatibility, and pH responsivity, a wide range of applications, such as drug delivery and sensors, have been developed.[4−9] Especially, this polymer is capable of capturing heavy metal ions through a coordination bond, so toxic metal ions in aqueous solutions can be removed by a chitosan/metal-ion complex.[10,11]
A recyclable water purification system could be achieved using a reversible crosslinking of the chitosan hydrogel
The chitosan/ Cu2+ hydrogel was obtained above pH 6.3, while the chitosan polymer was soluble in aqueous solutions at the pH level below 6.3 (Figure 1).[18]
Summary
Chitosan is a polysaccharide obtained from the deacetylation of chitin.[1−3] Based on its unique characteristics, such as hydrophilicity, biocompatibility, and pH responsivity, a wide range of applications, such as drug delivery and sensors, have been developed.[4−9] Especially, this polymer is capable of capturing heavy metal ions through a coordination bond, so toxic metal ions in aqueous solutions can be removed by a chitosan/metal-ion complex.[10,11] a recyclable water purification system could be achieved using a reversible crosslinking of the chitosan hydrogel. At the end of the study, a microfluidic switch was operated based on the reversible crosslinking of the chitosan/Cu2+ hydrogel
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