**1. Introduction**

There is an increasing demand for new materials of natural origin to remove metal ions which include chromium from industrial liquid waste. Many researchers have evaluated and implemented the possibility of the usage of renewable-based materials to get this element. Cellulose, starch, pectin or crusted shell waste such as chitin and chitosan (Cts), which are polysaccharides as a class of natural macromolecules. They're exceedingly bioactive substances in the removal of water pollutants and are commonly derived from marine crustaceans and agricultural raw substances or by-products [1, 2].

There are thousands of different chemicals, physical and biological processes occurring between the solid adsorbent surface and the adsorbate. In the adsorption process, the active interactions occurring at the adjacent intermediate surfaces between a solid adsorbent and certain toxic metal solution and the changes in its concentration between both phases stand out. Biopolymers can be thought of as a polymer that we are used to (such as proteins, lignin, polysaccharides, chitin, chitosan, cellulose and hemicellulose) and originate from living organisms in nature. These polymers are often found in sources of carbon origin and are mostly derived from carbohydrates. Origins of some biopolymers are shown in **Figure 1**.

There have been numerous articles on chitin and Cts in recent years and it is more directed towards applications of these polymers and their modification. Some biological activities exhibited through such polymers, specially Cts and its derivatives which include biocompatibility, biodegradability, low toxicity, mucousness

#### **Figure 1.**

*Biopolymer classification: Animal, agro, and protein origins.*

and antimicrobial activity have attracted interest in medicine, pharmacy, biomedical and health-related applications [1, 3, 4]. Numerous Cts-based materials were produced such as nano and microparticles, gels, sponges, films and membranes [4]. They have created an efficient field of application for drug delivery, wound healing and tissue regeneration applications.

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*Modified Chitosan Forms for Cr (VI) Removal DOI: http://dx.doi.org/10.5772/intechopen.96737*

and agriculture (**Figure 2**).

**2.2 Chitosan production**

**2.1 Sources of chitin and chitosan**

waste has been carried out by a group scientist [3, 6].

Cts structure and application areas [8, 9].

grouped under four main steps:

2.Demineralization (removal of minerals).

1.Preparation of shells.

**2. Chitosan**

The biggest advantage of chitin and Cts is that they are a renewable resource and an environmentally friendly natural biopolymer. With these features, it has been used in many different sectors in recent years. Cts attracts more attention compared to chitin because it is commercially available and can be used in many forms. Application areas of Cts can be listed as pharmacy (controlled drug release), medical (bandage), wastewater treatment, biotechnology, cosmetics, food, textile

Chitin is usually found in nature in seaweeds, protozoa (flagellates, amoebic ciliates, etc.), selenterals, mollusks, arthropods, bacteria, fungi, insects and some plants. The richest sources of chitin are; crab, shrimp, lobster and crayfish shells. Chitin biopolymers of animal origin are mainly found in animals. Chitin is the most considerable polysaccharide on the planet. Due to its strong hydrogen bonds and high crystal property of its cohesive structure forces, chitin is an insoluble substance in normal solvents, including water and organic matter [5]. Cts is abundant in marine or terrestrial animals such as crustaceans, insects, mollusks and fungi [6] without a backbone, such as various insects and marine diatoms. Commercial production of Cts by alkaline hydrolysis by extracting chitin from shrimp shell

Cts is obtained from chitin. Rouget became aware of Cts in 1859 while conducting experimental activities on deacetylated forms of chitin [7]. Cts is obtained from waste shrimp and crab shells from the seafood industries by chemical methods in industrial processes around the world [4]. Basic structure properties of Cts are related to its molecular weight and degree of deacetylation. The crystallinity of Cts is important in classifying its particle size, moisture and ash content, which is based on its surface morphology properties. The solubility, antibacterial, polycationic character, biocompatibility and bio adhesiveness of Cts are the basis that define the

Chemical modifications of Cts have been extensively described in recent studies. Cts contains the reactive amino (-NH2) and hydroxyl (-OH) groups in its structure and can very easily be converted into new modified forms. The presence of amino groups in the Cts matrix (deacetylation degree) in macromolecular chains indicates that Cts has a polycationic property in acidic aqueous solutions. The protonation of amino groups in the polymer structure seriously affects the structure of macromolecules in solutions, and it is known that the structure behavior may be managed

Cts production is carried out by two basic methods, chemically and biologically.

Classically, the chemical method is the method in which physical and chemical methods are used together. Chemical method; the isolation of the chitin is carried out by removing other substances in the shell. The procedures for this can be

through changing the pH or ionic strength of the solution it is in.

**Figure 2.** *Field of application of Cts.*

*Modified Chitosan Forms for Cr (VI) Removal DOI: http://dx.doi.org/10.5772/intechopen.96737*

The biggest advantage of chitin and Cts is that they are a renewable resource and an environmentally friendly natural biopolymer. With these features, it has been used in many different sectors in recent years. Cts attracts more attention compared to chitin because it is commercially available and can be used in many forms. Application areas of Cts can be listed as pharmacy (controlled drug release), medical (bandage), wastewater treatment, biotechnology, cosmetics, food, textile and agriculture (**Figure 2**).
