Abstract
Acid orange 74 (AO74) is a chromium-complex monoazo acid dye widely used in the textile industry. Due to being highly toxic and non-biodegradable, it must be removed from polluted water to protect the health of people and the environment. The aim of this study was two-fold: to evaluate the biosorption of AO74 from an aqueous solution by utilizing HCl-pretreated Lemna sp. (HPL), and to examine dye desorption from the plant material. The maximum capacity of AO74 biosorption (64.24 mg g-1) was reached after 4 h at the most adequate pH, which was 2. The biosorption capacity decreased 25% (to 48.18 mg g-1) during the second biosorption/desorption cycle and remained essentially unchanged during the third cycle. The pseudo-second-order kinetics model concurred well with the experimental results of assays involving various levels of pH in the eluent solution and distinct initial concentrations of AO74. NaOH (0.01 M) was the best eluent solution. The Toth isotherm model best described AO74 biosorption equilibrium data. FTIR analysis confirmed the crucial role of HPL proteins in AO74 biosorption. SEM-EDX and CLSM techniques verified the effective biosorption/desorption of the dye during the three cycles. Therefore, HPL has potential for the removal of AO74 dye from wastewaters.
Highlights
Azo dyes are aromatic compounds that constitute the largest and the most important group of synthetic dyes [1, 2]
Biosorption capacity decreased (64.24> 48.11> 47.04 mg g-1), the dye was completely removed from Acid orange 74 (AO74)-loaded HCl-pretreated Lemna sp. (HPL) during each cycle
Fourier-transform infrared (FTIR) spectroscopy revealed that the carboxyl and amide groups of the proteins of HPL constitute the main biosorption sites for dye removal
Summary
Azo dyes are aromatic compounds that constitute the largest and the most important group of synthetic dyes [1, 2]. Metal-complex azo acid dyes are widely used in the textile industry due to their light and wet fastness properties [3]. They have an affinity to protein fibers and polyamide but not to cellulosic fibers. Their structure includes solubilizing groups (e.g., hydroxyl, carboxyl and amino) [4] capable of forming coordination complexes with metal ions, mainly chromium, copper, cobalt, iron and nickel.
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