A method for dye extraction using an aqueous two-phase system: Effect of co-occurrence of contaminants in textile industry wastewater

Recovery of value-added products from wastewater using Aqueous Two-Phase Systems - A review

Aqueous two-phase system (ATPS) is long seen as a technique that promotes higher purity and yield in a single step. It is witnessing increased acceptance as a preferred choice for combined goals of concentration, separation and purification of a target product, be it industrially valuable or environmentally contaminating. Purification of biomolecules like enzymes, proteins, nucleic acids, viruses, etc. has been the forte of ATPS. Currently, the technique is used for concentrating the toxic fractions from diverse industrial let offs, from food, dairy, beverage, pharmaceuticals, agriculture, dyeing, tannery and metal-processing industries. Apart from being simple, efficient, rapid, flexible, economical, and biocompatible, the selectivity, purity and yield are on par and sometimes higher than the traditional downstream steps. From an industrial angle too, problems related to scale-up of ATPS are being actively addressed. Many novel approaches are being added by way of varying ATPS components to increase the yield and purity. Another case in point is the inclusion of optimization techniques for zeroing in on the precise setting of the operating parameters. With increasing impetus to the approach, we attempt to draw attention from academia and industries, alike, that are developing novel tweaks to the currently existing practices in ATPS. This review aims to assess and evaluate the different types of ATPS that have been used for the recovery of valuables and contaminants from industrial waste discharges.

One-step procedure for peroxidase concentration, dye separation, and color removal by aqueous two-phase system

The aim of our study is to develop a one-step procedure to remove and degrade dyes from wastewater using a low-cost and efficient system based on aqueous two-phase system (ATPS), a well-known technique used to concentrate and recover enzymes. We investigated the catalytic proprieties of rice bran peroxidase (RBP) and found that this homemade enzyme can remain bound to its substrate for up to 5 days in controlled environments, without denaturing and while maintaining stable oxidation reduction potential (ORP) and pH. This biomolecule showed affinity for the ATPS technique prepared with polyethylene glycol and salt, which improved the relative activity up to 170%. The red dye separation in ATPS top phase was achieved in 3 min, in the RBP presence, with 100% of efficiency, and color removal of 87% was obtained in 24 h of enzymatic reaction. The process has promise to be scaled up to 10-fold and to reuse the reagents from the bottom phase of the ATPS.

Geopolymer/Zeolite composite materials with adsorptive and photocatalytic properties for dye removal

This study investigated the adsorption capacities and photocatalytic activities of geopolymer-zeolite composite materials by incorporating different amounts of zeolite and TiO2 in a geopolymer matrix for dye removal. Geopolymers with SiO2/Al2O3 molar ratio of 2.5 were synthesized from metakaolin. The geopolymers containing zeolite and TiO2-doped zeolite exhibited similar behavior in terms of mineral compositions, microstructures and chemical frameworks. The compressive strength of geopolymer-zeolite composite materials decreased with increasing amount of zeolite and TiO2-doped zeolite (0-40 wt%) because of the increase in the porosity of composite materials. The maximum methylene blue adsorption capacity and photocatalytic efficiency of the powdered geopolymer composites with 40 wt% TiO2-doped zeolite was 99.1% and was higher than that of the composites with 40 wt% zeolite without TiO2-doping (92.5%). In addition, the geopolymer composites with TiO2-doped zeolite exhibited excellent stability after repeated usage as photocatalysts. The adsorption capacity and photocatalytic activity of pelletized geopolymer composites decreased because of the reduction in their specific surface area.

Application of aqueous two-phase system for selective extraction and clean-up of emerging contaminants from aqueous matrices

This review approaches how aqueous two-phase systems (ATPS), in their various compositions (e.g., polymer + salt, copolymer + salt, ionic liquid + salt, acetonitrile + salt), can be efficiently used for extraction, preconcentration, and clean-up of analytes in aqueous samples to determine the compounds classified as emerging contaminants (ECs). In the literature, there are some studies using ATPS applied to ECs, like pesticides, pharmaceuticals, illicit drugs, personal care products, alkaloids, and hormones, even when in trace concentrations. The ATPS is an alternative to the conventional liquid-liquid extraction technique. However, it is predominantly composed of water and do not generally use organic solvents and, therefore, is based on the principles of green chemistry. An ATPS approach has a unique advantage because it can extract neutral, anionic, cationic, polar, and nonpolar compounds, even when present simultaneously in the same sample. This review covers how this simple and low environmental impact technique has been employed for the analysis of different classes of emerging contaminants.

A thiourea cross-linked three-dimensional graphene aerogel as a broad-spectrum adsorbent for dye and heavy metal ion removal

A honeycomb-like three-dimensional graphene-based aerogel applied to remove pollutants was assembled via a mild, easy-to-operate hydrothermal synthesis method.

Photocatalytic activity of graphene oxide-TiO2 thin films sensitized by natural dyes extracted from Bactris guineensis

This study synthesized and characterized composites of graphene oxide and TiO2 (GO-TiO2). GO-TiO2 thin films were deposited using the doctor blade technique. Subsequently, the thin films were sensitized with a natural dye extracted from a Colombian source (Bactris guineensis). Thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements were used for physico-chemical characterization. All the samples were polycrystalline in nature, and the diffraction signals corresponded to the TiO2 anatase crystalline phase. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) verified the synthesis of composite thin films, and the SEM analysis confirmed the TiO2 films morphological modification after the process of GO incorporation and sensitization. XPS results suggested a possibility of appearance of titanium (III) through the formation of oxygen vacancies (Ov). Furthermore, the optical results indicated that the presence of the natural sensitizer and GO improved the optical properties of TiO2 in the visible range. Finally, the photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution, and pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. These results indicated that the presence of GO has an important synergistic effect in conjunction with the natural sensitizer, reaching a photocatalytic yield of 33%.

Selective separation of Cu, Ni and Ag from printed circuit board waste using an environmentally safe technique

Printed circuit boards (PCBs) make up a large part of e-waste and include high concentrations of high-value metals. Therefore, the recovery of these metals is interesting from both the environmental and economic points of view. Here, the extraction/separation of copper, nickel and silver from PCB leachate was studied using an aqueous two-phase system (ATPS) formed by triblock copolymers with an electrolyte and water, which is in compliance with the principles of green chemistry. The best conditions for the selective extraction consisted of 1-(2-pyridylazo)-2-naphthol (3.5 mmol kg^-1) at pH = 6.0 in 6 sequential steps for the Cu(II), dimethylglyoxime (5.00 mmol kg^-1) at pH = 9.0 for the Ni(II) and thiocyanate (5.20 mmol kg^-1) at pH = 9.0 for the Ag(I). These conditions were applied sequentially for extraction of Cu, Ni and Ag from the PCB leachate, obtaining high separation factor (S) values between the analyte and the metallic concomitants (S_Cu,Ni = 1,460, S_Cu,Fe = 15,500, S_Cu,Ag = 15,900, S_Ni,Fe = 32,700, S_Ni,Ag = 34,700 and S_Ag,Fe = 4800). The maximum extraction percentages (%E) for Cu, Ni and Ag were 99.9%, 99.9% and 99.8%, respectively. After the extraction, a single step stripping process was performed, resulting in more than 82% of the ion available in a clean lower phase. For the first time, an ATPS has been used for sequential extraction of several metal analytes from a real sample.

Waste Plant Material as a Potential Adsorbent of a Selected Azo Dye

This paper discusses the adsorption of Direct Orange 26 azo dye on sunflower husk - an agricultural waste product. During the study, sorption kinetics and equilibrium as well as sorption capacity of the husk were investigated. The adsorption kinetics was analyzed using pseudo-first and pseudo-second order equations, which indicated a chemical sorption mechanism. The sorption equilibrium was approximated with the two-parameter Freundlich and Langmuir equations and the three-parameter Redlich-Peterson equation. The main experiments were carried out in a laboratory adsorption column under different process conditions. Experimental data were interpreted with the Thomas model, based on the volumetric flow rate, initial composition of the feed solution and mass of the adsorbent. The results of modeling the adsorption equilibrium, adsorption kinetics and adsorption dynamics were evaluated statistically.