Methyl violet 2B

Methyl violet 2B (IUPAC name: N-(4-(bis(4-(dimethylamino)phenyl)methylene)cyclohexa-2,5-dien-1-ylidene)methanaminium chloride) is a green powder which is soluble in water and ethanol but not in xylene. It appears yellow in solution of low pH (~0.15) and changes to violet with pH increasing toward 3.2.^[1]

Methyl violet 10B

Methyl violet 10B has six methyl groups. It is known in medicine as Gentian violet (or crystal violet or pyoctanin(e)^[2]) and is the active ingredient in a Gram stain, used to classify bacteria. It is used as a pH indicator, with a range between 0 and 1.6. The protonated form (found in acidic conditions) is yellow, turning blue-violet above pH levels of 1.6.^[3]

Methyl violet 10B inhibits the growth of many Gram positive bacteria, except streptococci.^{[citation needed]} When used in conjunction with nalidixic acid (which destroys gram-negative bacteria), it can be used to isolate the streptococci bacteria for the diagnosis of an infection.^{[citation needed]}

Chemical bleaching

Chemical bleaching is achieved by oxidation or reduction. Oxidation can destroy the dye completely, e.g. through the use of sodium hypochlorite (NaClO, common bleach) or hydrogen peroxide.^[4][5] Reduction of methyl violet occurs in microorganisms but can be attained chemically using sodium dithionite.

Biodegradation

Biodegradation has been well investigated because of its relevance to sewage plants with specialized microorganisms. Two microorganisms that have been studied in depth are the white rot fungus and the bacterium Nocardia Corallina.^[6][7]

Photodegradation

Light alone does not rapidly degrade methyl violet,^[8] but the process is accelerated upon the addition of large band-gap semiconductors, TiO₂ or ZnO.^[9][10]

Other methods

Many other methods have been developed to treat the contamination of dyes in a solution, including electrochemical degradation,^[11] ion exchange,^[12] laser degradation, and absorption onto various solids such as activated charcoal.