# Preparation of Freeze-Dried Porous Chitosan Microspheres for the Removal of Hexavalent Chromium  
[PERSON]  
1 Laboratory of Blonic Engineering (Ministry of Education), College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China; [EMAIL_ADDRESS] (W.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (J.T.) 1  
[PERSON]  
1 Laboratory of Blonic Engineering (Ministry of Education), College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China; [EMAIL_ADDRESS] (W.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (J.T.) 1  
[PERSON]  
1 Laboratory of Blonic Engineering (Ministry of Education), College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China; [EMAIL_ADDRESS] (W.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (J.T.) 1  
[PERSON]  
2 School of Engineering, Huzhou University, Huzhou 313000, China; [EMAIL_ADDRESS] 2  
[PERSON]  
1 Laboratory of Blonic Engineering (Ministry of Education), College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China; [EMAIL_ADDRESS] (W.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (J.T.) 1  
[PERSON]  
1 Laboratory of Blonic Engineering (Ministry of Education), College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China; [EMAIL_ADDRESS] (W.S. ); [EMAIL_ADDRESS] (J.X. ); [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (J.T.) 1  
Footnote 1: email: {L.G.,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,  
water should not exceed 0.05 mol/L according to United States Environmental Protection Agency [3]. In the last decade, many removal methods for Cr(VI) compounds have been applied, such as coagulation/flocculation [4], membrane treats [5], oxidation/reduction [6], ion exchange [7], adsorption [8; 9], and so on. However, the majority of these methods may produce secondary pollution, non-degradable sludge compounds, and require a great deal of capital [10]. Adsorption is simple, highly effective, cost-effective, and reusable compared to other methods. Adsorbents are the key in the treatment of heavy metal ion wastewater by adsorption. In particular, porous adsorption materials with a number of grafted functional groups and that are exposed on the surface or mesopore channel can allow more active groups to interact with pollutants and thus improve adsorption capacity [9; 10]. Therefore, adsorbents with more functional groups and a larger specific surface area are a research direction for the development of the adsorption materials. Most of the existing inorganic adsorbents have some disadvantages, such as a high cost, complex preparation processes, small size, poor adsorption capacity, and poor recovery [11]. Due to the advantages of having easily available raw materials, being renewable and non-toxic, having a low cost, their biodegradability, as well as having diverse active groups and easy modification, natural polymer materials and their derivatives have been prepared using green and environmentally friendly adsorption materials for the heavy metal ion treatment of wastewater [11; 12]. Chitosan is a natural-based polysaccharide with good compatibility, bio-functionality, and degradability, obtained by chitin deacetylation, and is widely used in many fields, such as medicine, food, chemical industry, cosmetics, metal extraction and recycling, water treatment, and tissue engineering [4; 13]. It has abundant active functional groups, amine groups (-NH\({}_{2}\)), and hydroxyl groups (-OH), which have good affinity with several metal ions [14]. Various forms of chitosan adsorbents have been used for Cr(VI) adsorption. Chitosan gel beads and flakes have been used for Cr(VI) adsorption and exhibited a distinguishable difference in terms of adsorption capacity [15; 16], such as 34.4 mg/g of chitosan wet beads and 156.2 mg/g of solid chitosan flakes, respectively [16].