Dyeing properties of extracts from prosopis juliflora and aloe succotrina and evaluation of remediation potentials of their waste Biomass

Abstract

In the last two decades, natural dyes have increasingly become popular over their synthetic counterparts due to their environmental friendliness and biodegradability. Whereas synthetic dyes are persistent, allergy inducing and carcinogenic, natural dyes are eco-friendly with no side effects. The main objective of this study, was to assess the potential of Aloe succotrina leaves and the heartwood of Prosopis juliflora as sources of natural dyes and the potential of their waste biomass as modified adsorbents for the removal of synthetic dyes. The specific objectives of the study were to evaluate the dyeing properties of A. succotrina and P. juliflora, to identify the compounds responsible for the dyeing properties and to determine the remediation potential of their waste biomass. Maceration was used in the extraction of P. juliflora while solvent extraction was used for extracting A. succotrina. These were used for dyeing cotton fabrics using pre-mordanting, simultaneously mordanting and post mordanting techniques. The dyed fabrics, were then tested for their suitability using wash, light and rub fastness. Gas chromatography tandem Mass spectroscopy (GC-MS) and Fourier transformed Infrared (FTIR) spectroscopy were used for evaluation of dyeing compounds. Biochar derived from the waste biomass were characterized by X-ray Diffractometer (XRD) for their crystalline properties, FTIR for their functional groups and scanning electron microscope (SEM) for surface properties. Batch adsorption experiments were conducted for the removal of synthetic dyes. The waste biomass, were transformed into biochar at pyrolysis temperatures of 300℃ and 500℃. The dye from P. juliflora, had good fastness results with the additions of mordants improving both colour and wash fastness. Dyes from A. succotrina, had good colour and light fastness with poor wash fastness. Except for the case of pre-mordanting, the use of mordants did not improve the wash fastness. The GC-MS analysis of A. succotrina revealed the presence of 27 compounds among them the dyeing compound orcinol, which could be the main source of colour. For P. juliflora, 16 compounds were identified among them catechol, a naturally occurring benzenediol resulting from the pyrolysis of catechin, a flavonoid responsible for yellow pigment in natural dyes. The XRD, FTIR and SEM results showed, a difference in physical and chemical properties with the biochar pyrolyzed at 300℃ being organic and amorphous while the biochar prepared at 500℃ being less organic and porous. For the adsorption of reactive red 120 (RR120), the q max calculated for the most effective biochar PJ300 was 20.643 mg/g against that of the commercially activated carbons of 243.5 mg/g. For methyl violet 2b (MV2b), the q max calculated for most effective biochar was 82.530 mg/g against the commercially activated carbons 504 mg/g. The experimental data fitted into Freundlich isotherm for RR120, which indicates that the process is heterogenous and Langmuir for MV2B, which indicates monolayer adsorption. In conclusion, the extracts from both plants showed potentials to be used as natural dyes. The biochar derived from the waste biomass of the two plants are recommended as alternatives to commercially activated carbon in the remediation of textile effluents.