The physicochemical properties of chitosan obtained from the shells of swimming crab (Portunus trituberculatus) and prepared via subcritical water pretreatment were examined. At the deacetylation temperature of 90 °C, the yield, ash content, and molecular weight of chitosan in the shells prepared via subcritical water pretreatment were 12.2%, 0.6%, and 1187.2 kDa, respectively. These values were lower than those of shells prepared via sodium hydroxide pretreatment. At the deacetylation temperature of 120 °C, a similar trend was observed in chitosan molecular weight, but differences in chitosan yield and ash content were not remarkable. At the same deacetylation temperature, the structures of chitosan prepared via sodium hydroxide and subcritical water pretreatments were not substantially different. However, the compactness and thermal stability of chitosan prepared via sodium hydroxide pretreatment was lower than those of chitosan prepared via subcritical water pretreatment. Compared with the chitosan prepared by sodium hydroxide pretreatment, the chitosan prepared by subcritical water pretreatment was easier to use in preparing oligosaccharides, including (GlcN)2, via enzymatic hydrolysis with chitosanase. Results suggested that subcritical water pretreatment can be potentially used for the pretreatment of crustacean shells. The residues obtained via this method can be utilized to prepare chitosan.

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The nano-ZnO and nano-TiO 2 were added into chitosan (CS) anion layer to prepare polyvinyl alcohol (PVA) -sodium alginate (SA)/ TiO 2 -ZnO-CS (here, PVA:polyvinyl alcohol; SA:sodium alginate) bipolar membrane (BPM), which was characterized using scanning electron microscopy, atomic force microscopy (AFM), thermogravimetric analysis (TG), electric universal testing machine, contact angle measurer, and so on. Experimental results showed that nano-TiO 2 -ZnO exhibited better photocatalytic property for water splitting at the interlayer of BPM than nano-TiO 2 or nano-ZnO. The membrane impedance and voltage drop (IR drop) of the BPM were obviously decreased under the irradiation of high-pressure mercury lamps. At a current density of 60 mA/cm 2 , the cell voltage of PVA-SA/TiO 2 -ZnO-CS BPM-equipped cell decreased by 1.0 V. And the cell voltages of PVA-SA/TiO 2 -CS BPMequipped cell and PVA-SA/ZnO-CS BPM-equipped cell were only reduced by 0.7 and 0.6 V, respectively. Furthermore, the hydrophilicity, thermal stability, and mechanical properties of the modified BPM were increased.