*Article* **Facile and Scalable Synthesis and Self-Assembly of Chitosan Tartaric Sodium**

**Sixuan Wei, Rujie Peng, Shilong Bian, Wei Han, Biao Xiao \* and Xianghong Peng \***

Key Laboratory of Optoelectronic Chemical Materials and Devices (Ministry of Education), School of Optoelectronic Materials & Technology, Jianghan University, Wuhan 430056, China; WSX15927474220@163.com (S.W.); 18007161071@163.com (R.P.); bianshilong5200@163.com (S.B.); e781206379@gmail.com (W.H.)

**\*** Correspondence: biaoxiao@jhun.edu.cn (B.X.); pxh@jhun.edu.cn (X.P.)

**Abstract:** Chitosan-based nanostructures have been widely applied in biomineralization and biosensors owing to its polycationic properties. The creation of chitosan nanostructures with controllable morphology is highly desirable, but has met with limited success yet. Here, we report that nanostructured chitosan tartaric sodium (CS-TA-Na) is simply synthesized in large amounts from chitosan tartaric ester (CS-TA) hydrolyzed by NaOH solution, while the CS-TA is obtained by dehydrationcaused crystallization. The structures and self-assembly properties of CS-TA-Na are carefully characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy ( 1H-NMR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), transmission electron microscopy (TEM), a scanning electron microscope (SEM) and a polarizing optical microscope (POM). As a result, the acquired nanostructured CS-TA-Na, which is dispersed in an aqueous solution 20–50 nm in length and 10–15 nm in width, shows both the features of carboxyl and amino functional groups. Moreover, morphology regulation of the CS-TA-Na nanostructures can be easily achieved by adjusting the solvent evaporation temperature. When the evaporation temperature is increased from 4 ◦C to 60 ◦C, CS-TA-Na nanorods and nanosheets are obtained on the substrates, respectively. As far as we know, this is the first report on using a simple solvent evaporation method to prepare CS-TA-Na nanocrystals with controllable morphologies.

**Keywords:** chitosan; tartaric acid; nanocrystal; self-assembly; evaporation; dehydration of crystallization
