| | Group of dyes | Characteristics | Application | References |
| | Direct dyes | (i) Dyeing process with one action, without the assistance of an affixing agent;
simplest and cheapest dyes
(ii) Water soluble anionic dyes;
substantive to form aqueous media in the electrolytes
(iii) High affinity for cellulose fibers
(iv) Apply to the dye materials to improve wash fastness properties (chelation with salts of metals and treatment with a cationic dye-complexing resin or formaldehyde)
(v) Some contain sulphonate functionality to improve solubility (negative charge of dyes and fibers repel each other)
(vi) Its flat length enable and shape to lie along-side cellulose fiber and maximum (vii) Van-der-Waals, hydrogen bonds, and dipole
(ix) Dyeing method: exhaust/beck/continuous | Cotton, cellulosic, regenerated cellulose, paper, leather, nylon, and blends
| [6, 7] |
| | Vat dyes | (i) Water insoluble dyes
(ii) Apply as soluble leuco salt after reduction in an alkaline solution with sodium hydrogen sulfide
(iii) The leuco form is reoxidized to the insoluble keto form to redevelop the crystal structure
(iv) More chemically complex
(v) Dyeing methods: exhaust, package, continuous | Cotton, linen and rayon, soap | [8, 9] |
| | Organic pigments | (i) Negatively charged compounds
(ii) Made from ground up colored rocks, minerals, animals, and plants
(iii) No chemical information
(iv) Classification based on the dye’s source and color
(v) Application requires a mordant | Cotton, paper, cellulosic, blended fabrics | [10, 11] |
| | Reactive dyes | (i) React directly with the fiber molecules to form chemical bonds
(ii) Conceivable to achieve very high wash fastness properties
(iii) Require facile dyeing methods
(iv) Simple chemical structure
(v) The largest dye class
(vi) Adsorption spectra with a narrow adsorption band
(vii) Dyeing is bright
(viii) Dyeing methods: exhaust, beck cold pad batch, and continuous | Cellulosic fabric and fibers | [12, 13] |
| | Dispersed dyes | (i) Water insoluble nonionic
(ii) Require additional factors (dye carrier, pressure, and heat) to penetrate synthetic dyes
(iii) Dispersed in aqueous media wherever the dye is dissolved into fibers
(iv) Especially on polyester and to a lesser extent on cellulose acetate, nylon, acrylic fibers, and cellulose
(v) Niche market in dye diffusion thermal transfer process for electronic photography and thermal transfer printing
(vi) Dyeing method: high temperature exhaust, continuous
| Synthetic/hydrophobic fibers from aqueous dispersion | [14, 15] |
| | Acid dyes | (i) Water soluble anionic dyes
(ii) Typical pollutants: color, organic acid, unfixed dyes
(iii) Dyeing methods: exhaust, beck, and continuous | Silk, wool, synthetic fibers, leather, nylon, modified acrylics, paper, ink-jet printing, food, cosmetics | [16, 17] |
| | Azoic dyes | (i) Contain one azo group (mono azo), two azo group (disazo), three azo (trisazo), four azo group (tetrakisazo), or more (polyazo) groups
(ii) Attach to two classes of which at least one but usually both are aromatic
(iii) Exist in the transform 1 in (iv) which the bond angle is 120° and the nitrogen atoms are sp2 hybridized
(v) Consist of electron accepting substituents and electron donating substituents
(vi) Named as carbocyclic azo dyes if include only aromatic groups (naphthalene and benzene)
(vii) Named as heterocyclic azo dyes if include heterocyclic group | Printing inks, pigments | [18, 19] |
| | Basic dyes | (i) Water soluble cationic dyes
(ii) Can be applied directly to cellulosic with no mordants (or metal-like copper and chromium)
(iii) Yield colored cations in solutions
(iv) Apply as brightness of shade is more important than fastness to washing and light
(v) Some basic dyes show biological activity and are used in medicine as antiseptics
(vi) Salt-forming counter ion
(vii) Colorless anion of a low molecular mass, organic, or inorganic acid
(viii) Can be turned to water soluble dye bases by addition of alkali
(ix) The positive charge is localized on an ammonium group
(x) Dyeing methods: exhaust, beck, and continuous | Silk, wool, cotton, polyacrylonitrile, modified nylons, modified polyester, tannin-mordanted cotton | [20, 21] |
| | Oxidation dyes | (i) Primarily aromatic compounds that belong to three major chemical families (Diamines, Aminophenols (amino naphthols) and Phenols or naphthols)
(ii) Colorless and are typically a low molecular weight product
(iii) Categories-oxidation base as a primary, intermediate and coupler as a secondary, intermediate | Hair | [22, 23] |
| | Developed dyes | Any group of direct azo dyes which after applying to the fiber can be diazotized further and coupled on the fiber to form shades faster to washing | Cellulosic fibers, fabric | [24, 25] |
| | Mordant dyes | A substance utilized to set dyes on fabrics or tissue sections by forming a coordination complex with the dye that attaches to the tissue or fabric | Cellulosic fibers, fabric, silk, wool | [26–28] |
| | Optical/ fluorescent brightener | (i) Absorb light in the violet region and ultraviolet (mostly 340–370 nm) of the electromagnetic spectrum, and reemit light in the blue region (usually 420–470 nm)
(ii) Utilized to increase the appearance of color of paper and fabric, causing a “whitening” effect, making materials look less yellow by increasing the overall amount of blue light reflected | Synthetic fibers, leather, cotton, sport goods | [29–31] |
| | Solvent dyes | (i) Water insoluble
(ii) Free of polar solubilizing groups such as carboxylic acid, sulfonic acid, or quaternary ammonium | Wood staining, solvent inks, waxes, coloring oils, plastic, gasoline oil | [32, 33] |
| | Anthraquinone | (i) The oldest dyes (4000 years)
(ii) No natural counterpart
(iii) Low cost effectiveness | Wrapping of mummies | [34] |
| | Indigoid | (i) Expensive
(ii) Made of tyrian purple
(iii) Give progressively paler blue shades
(iv) Oxidation process of indigoid gives phenylacetic acid | Textile, wool, linen, cotton
Use exclusively for dyeing denim jeans, jackets | [35] |
| | Sulfur dyes | (i) Made by heating aromatic or heterocyclic compounds with species that release sulfur or sulfur
(ii) Classified by sulfur bake, polysulfide melt dyes, and polysulfide bake
(iii) Not well-defined chemical compounds
(iv) Mostly contain various thiophenolic and heterocyclic sulfurs
(v) On oxidation, the monomeric molecules cross-linked into large molecules form disulfide bridge
(vi) Dyeing methods: continuous | Cotton, other cellulosic | [36] |
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