Characteristics of Chitosan Nanoparticles for Water and Wastewater Treatment: Chitosan for Water Treatment

Chitosan Properties And Preparation

Chitin, as shown in Figure 1, is the acetylated precursor to chitosan. The removal of these acetyl functional groups allows for higher solubility due to the increase in positive charge. Due to its deacetylation, chitosan is considered a pseudo-natural biopolymer which is predominantly characterized by its degree of deacetylation (DD) and molecular weight (MW). Considering that these two properties are directly proportional, the degree of solubility can be seen as inversely proportionate to the MW and directly proportionate to the DD. The degree of deacetylation is a molar percentage which differentiates chitin from chitosan at precisely 50% mol. This 50% DD allows for solubility in acidic aqueous solutions.

Figure 1.

Chitin, chitosan, cellulose (Alvarenga, 2011)

Acetylated Chitosan, or Chitin, is known to exist in two allomorphs, α and β. The more abundant α Chitin is found within traditional yeast, fungi, shrimp, crab, krill, lobster, and crawfish. The less abundant β Chitin is found within the protein in squid pens and is not an industrial source. Beyond knowledge of the biopolymer’s source, differentiation can be determined through Nuclear Magnetic Resonance (NMR) spectroscopy and infrared in conjunction with X-ray diffraction (Younes & Rinaudo, 2015). Moreover, whereas α Chitin contains two antiparallel molecules per unit cell, β Chitin contains merely one. β Chitin is more reactive; however, both α and β allomorphs remain insoluble.

Chitosan’s solubility can also be affected by the distribution of acetyl compounds as well as ionic concentration. Chitosan’s cationic property enables it to strongly adsorb negatively charged toxins. This positive charge can be modified by pH, while chitosan acts with inverse efficacy to its pH for coagulation and flocculation. This capability of changing solubility and cationic charge through pH causes both desirable and undesirable aspects considering that the extent of coagulation and flocculation can also be manipulated to repel particles and prevent agglomeration.