**4. Conclusion**

*Dyes and Pigments - Novel Applications and Waste Treatment*

industry hold important shares.

huge, and their applications are massive.

It comes as no surprise that the global dyes and pigments market for the year 2020 was determined to be as large as \$ 32.9 billion with an estimated growing rate of about 5% for the next few years. [9] The largest shares of the global production of dyes and pigments are the ones pertaining to textile-dyes and leather-dyes covering together nearly 75% of the global production. Furthermore, printing inks and paper dyes

All the above information indicates that the use of dyes and pigments is wellestablished in everyday life. They appear in our lives dying objects made out of various materials e.g. plastic, wood, metals, ceramics, leather, textiles etc. (see **Figure 1**) and are either applied by the manufacturers of the products or can be used by the end-user in order to protect, modify or decorate variety of objects and materials. The variety of paints depending on use and target-surface is enormous and most of the dyes and pigments are readily available to the user. This indicates a vitally tight connection between production and everyday life. Some examples of dyes and pigments used in everyday life are depicted in **Figure 1**. Their versatility is

Yet, science is constantly pushing the limits of the corresponding research field and attempts to obtain novel dyes with special functions are unceasingly being made. (Multi)functional dyes and pigments fall in a wider group of materials which can provide certain types of functionality parallel to their main operational scope. In this sense, a functional dye may for instance not only act as protective and/or decorative layer on a material (main scope), but it could act as an environment-responsive component which could in turn render a new material or device responsive and sensitive to various external stimuli (including light, pressure, heat, environment pH changes, solvent polarity etc.). In the large family of functional dyes (and pigments) fall the so-called chromic compounds/materials. These are compounds or materials which are capable of undergoing (ideally) reversible changes in a way that the user can

*Examples of dyes used in everyday life as well as in specific applications. (A) Structure of azorubine (also known as E122) a water soluble food-colorant. Photo depicts red-dyed eggs colored with azorubine. (B) Structure of "black-dye" a prominent candidate for dyes-sensitized solar cells. Photograph depicts a solar cell. (C) Structure of a viologen enolate, highly responsive in solvent polarity changes (solvatochromic dye). Photo indicates the drastic color change when moving from water (red) to solvents of lower polarity (adapted with permission by Papadakis et al. [10] (D) a pyrazoline fluorescent dye of high emission intensity. [11] (photo source: author's property). (Ε) Antonia RedTM Dextran: a novel polysaccharide with fluorescent* 

*labelling and its application in cell-imaging (source: TdB Labs) [12].*

**4**

**Figure 1.**

The variety of commercial dyes and pigments with novel properties and applications is increasing as the needs of the end-users expand. This fact is clearly reflected in the size of the corresponding market and it accounts for the extended global contemporary research endeavors towards new dyes and pigments. Based on these facts, a colorful future is envisioned.
