Adsorption of Methylene Blue and Reactive Black 5 by Activated Carbon Derived from Tamarind Seeds

One of the most environmentally friendly methods to treat wastewater, especially synthetic dyes, is the production of activated carbon from agricultural waste. Tamarind seeds were transformed from negative-value waste into activated carbon in order to study the removal of synthetic dyes. The particular agro waste was soaked in ZnCl2 for chemical activation to increase its surface area and enhance its porosity. Physical activation of tamarind seeds was done by the carbonization process by burning at a temperature of 300 °C for 1 hour and cooling for 24 hours before washing with HCL to activate a pore surface for the tamarind seeds' carbon. The effects of parameters related to the adsorption of the dyes by tamarind seed activated carbon, such as contact time, initial concentration, absorbance dosage, and pH, were studied. The experimental data found that adsorption on both synthetic dyes exhibited a Langmuir isotherm in which the correlation value, R2, was 0.9227 (methylene blue) and 0.6117 (Reactive black 5). Meanwhile, the rate of adsorption for methylene blue (MB) and Reactive black 5 (RB5) by tamarind seed activated carbon was found to be well fitted in a pseudo-second-order model. More research is needed to meet the standard effluent of dyeing wastewater from the industrial sector.

Combining Experimental Data with Statistical Methods to Evaluate Hydrolyzed Reactive Dye Removal by α-Fe2O3 in a Cellulose-Based Membrane

Water contaminated with toxic dyes poses serious problems for human health and environmental ecosystems. Unfixed reactive dyes and their hydrolyzed form are soluble in water, thus, their removal is particularly challenging. Among the different methodologies, adsorption is probably the most common since it is easy to handle and has a low cost. Here, the removal by adsorption of hydrolyzed Reactive Black 5 (hydRB5) from a model wastewater through cellulose acetate/hematite membranes (CA/α-Fe2O3), designated as M1, M2 and M3, was performed. The pristine cellulose acetate membrane (CA) was designated as M0. Toward understanding the adsorption mechanism of hydRB5 on membranes, the rate of adsorption and maximum value of the adsorption capacity were evaluated using kinetic and isothermal studies, respectively. The results showed that the adsorption mechanism follows pseudo-first-order kinetics, and data are best fitted by the Langmuir isotherm method with a maximum adsorption capacity of 105.26 mg g−1 in pH~7. Furthermore, these membranes can be also regenerated by washing with NaOH and NaCl solutions, and the regeneration efficiency remains effective over five cycles. To complete the work, two statistical models were applied, an Analysis of Variance (ANOVA) and a Response Surface Methodology (RSM). The optimum value found is located in the usable region, and the experimental validation shows good agreement between the predicted optimum values and the experimental data. These composite membranes are also good candidates for the adsorption of other pollutants, even at industrial scale, due to their effective regeneration process and low production costs.

Catalytic and Physicochemical Evaluation of a TiO2/ZnO/Laccase Biocatalytic System: Application in the Decolorization of Azo and Anthraquinone Dyes

A TiO2/ZnO oxide system was proposed as a support for the immobilization of laccase from Trametes versicolor (LTV). The obtained TiO2/ZnO/LTV biocatalytic system was then applied in the decolorization/degradation of C.I. Reactive Black 5 and C.I. Acid Green 25 dyes. The efficiency of immobilization was evaluated based on catalytic properties (Bradford method, oxidation reaction of 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and physicochemical (spectroscopic, porous, electrokinetic) analysis. The immobilization process was carried out with high performance (99.4%). Immobilized laccase retained about 40% of its activity in the whole analyzed temperature range and after 10 reaction cycles. Immobilization efficiency was also indirectly confirmed by the presence of characteristic functional groups (–C–H and –C–O), nitrogen and carbon on the TiO2/ZnO/LTV biocatalytic surface, identified by spectroscopic analyses. The increase in the surface area to 126 m2/g, change of isoelectric point (2.0) and zeta potential ranges (from +12.0 to −20.0 mV) after the immobilization process were also observed. The results show that the designed biocatalytic system enables the removal of acid dyes (C.I. Reactive Black 5 and C.I. Acid Green 25) with high efficiency (99% and 70%, respectively). Mass spectroscopy analysis indicated possible degradation products formed by the cleavage of N=N and C–N bonds.