UV Photolysis and Neem-bark-assisted Removal of Crystal Violet from Aqueous Solutions
Acho Yapi Fulgence *
Laboratory of Environmental Sciences, Nangui Abrogoua University, 02 BP 801 Abidjan 02, Ivory Coast.
Soro Donafologo Baba
Laboratory of Environmental Sciences, Nangui Abrogoua University, 02 BP 801 Abidjan 02, Ivory Coast.
Soussou Yao Idriss
Laboratory of Constitution and Reaction of Matter (LCRM); Félix Houphouët Boigny University, 22 BP 582 Abidjan 22, Ivory Coast.
Traore Karim Sory
Laboratory of Environmental Sciences, Nangui Abrogoua University, 02 BP 801 Abidjan 02, Ivory Coast.
*Author to whom correspondence should be addressed.
Abstract
Crystal Violet is a cationic triphenylmethane dye whose visible-band disappearance can result from adsorption, photochemical transformation, or other chemical reactions. This study examined direct ultraviolet (UV) irradiation under a nominal 253.7 nm low-pressure mercury lamp and a polychromatic mercury source, together with dye contact with chemically treated neem (Azadirachta indica) bark and combined bark/UV treatment. Nominal Crystal Violet concentrations of 7.35, 14.70, and 29.41 µmol/L were investigated. Residual solution colour was monitored spectrophotometrically near 590 nm. For direct irradiation at 7.35 µmol/L, apparent first-order coefficients were 0.021 and 0.012 min⁻¹ for the two lamps, respectively. Treated-bark contact produced rapid initial dye disappearance, and the apparent bark/UV constants across increasing nominal concentrations were 0.035, 0.024, and 0.016 min⁻¹. Different coupled-treatment comparisons yielded incompatible coefficient estimates, while uncertainty estimates, UV dose measurements, suitable separation controls, and transformation-product analyses were unavailable. Several stated endpoint concentrations also fell below the documented lower calibration concentration, limiting quantitative interpretation. Thus, the observations indicate apparent loss of visible Crystal Violet absorbance under the investigated conditions but do not establish mineralisation, chemical-product safety, catalytic activity, or a synergistic photochemical mechanism.
Keywords: Crystal Violet, Azadirachta indica, ultraviolet irradiation, biosorption, dye decolourization, apparent kinetics