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Adsorption, a popular technique for removing azo dyes from aqueous streams, is influenced by several factors such as pH, initial dye concentration, temperature and adsorbent dosage. Any strategy that seeks to identify optimal conditions involving these factors, should take into account both kinetic and equilibrium aspects since they influence rate and extent of removal by adsorption. Hence rigorous kinetics and accurate equilibrium models are required. In this work, the experimental investigations pertaining to adsorption of acid orange 10 dye (AO10) on activated carbon were carried out using Central Composite Design (CCD) strategy. The significant factors that affected adsorption were identified to be solution temperature, solution pH, adsorbent dosage and initial solution concentration. Thermodynamic analysis showed the endothermic nature of the dye adsorption process. The kinetics of adsorption has been rigorously modeled using the Homogeneous Surface Diffusion Model (HSDM) after incorporating the non-linear Freundlich adsorption isotherm. Optimization was performed for kinetic parameters (color removal time and surface diffusion coefficient) as well as the equilibrium affected response viz. percentage removal. Finally, the optimum conditions predicted were experimentally validated., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The present study investigated the degradation of an aqueous Allura Red AC (AR–AC) solution by activating hydrogen peroxide with bicarbonate using cobalt ion (Co2+) as the catalyst. Four independent variables (H2O2, NaHCO3, Co2+, and dye concentrations) were analyzed in the composite central design (CCD). AR–AC degradation was optimized using the response surface methodology (RSM). Under optimal degradation conditions (41.86 mg/L AR–AC, 5.58 mM H2O2, 2.00 mM NaHCO3, and 9.00 µM Co2+), decolorization > 99.86%, mineralization (CO2 to conversion) of 12.99%, and total nitrogen removal of 51.97% were achieved. The predicted values for the three response variables were consistent with the experimental values, with determination coefficients (R2) greater than 0.9053. Because cobalt ions (Co2+) are a source of water pollution, after oxidation, these were adsorbed on sodium bentonite (Na–Bent), obtaining a final concentration of <0.01 mg/L. Bicarbonate-activated hydrogen peroxide is a potential technology for dye wastewater treatment that operates at an alkaline pH and at ambient temperature. [ABSTRACT FROM AUTHOR]

Graphene zirconium oxide nanocomposite (Gr@ZrO2‐NC) has been functionalized with cetyltrimethylammonium bromide (CTAB or CT) or butanediyl‐1,4, bis (N, N‐hexadecyl ammonium) dibromide (cationic gemini surfactant (CGS)). Structural, morphological, optical and thermal properties of synthesized adsorbents (Gr@ZrO2‐NC, CT‐Gr@ZrO2‐NC and CGS‐Gr@ZrO2‐NC) are investigated using XRD, FTIR, electron microscopy and TGA. CGS‐Gr@ZrO2‐NC showed faster removal efficacy (90 % within the first 25 min) for anionic azo dyes (methyl orange, MO and Congo red, CR) compared to other adsorbents. This effect may be due to the creation of stronger hydrophobic region at the surface of adsorbent with CGS. Effects of concentration, contact time and pH were also seen. The adsorption efficacy remained better even in the simultaneous presence of MO and CR. Adsorption data with time showed that the pseudo‐second‐order kinetic model has been obeyed. Adsorbents were regenerated successfully with ethylene glycol (∼83 %). [ABSTRACT FROM AUTHOR]

Waste water from the textile industry is one of the major sources of contamination causing serious health problems. In textile waste water, dyes are the main pollutant. In this research work textile waste water was treated with various organic acid-activated clays to remove the dyes. Pink Azo dye was selected as a component to remove from waste water. Adsorbent selected was bentonite clay and was activated by acids such as phosphoric, acetic, oxalic, and citric acids. Adsorbent characteristics have been analyzed through infrared spectroscopy (FTIR) and Scanning Electron Microscope (SEM) while the removal of dye at various temperatures has been analyzed through Ultraviolet (UV) analysis. It was observed that the bentonite clay-treated with phosphoric acid had relatively maximum capacity to remove the dye while the clay treated with oxalic acid got minimum capacity to remove the dye from same waste water.

This paper investigates the photoinduced change of refractive index in dye (methyl red, MR)-doped blue phase (DDBP) cells by illumination of a pump beam. Through excitation of light irradiation with proper photon energy, MR can transform from trans-state to cis-state and successively diffuse and anisotropically adsorb on the inner glass substrate of the DDBP cell along the direction perpendicular to the polarisation of the pump beam. The adsorbed MR molecules can effectively rotate the orientation of the liquid crystal (LC) molecules and thereby modulate the effective refractive index of the DDBP cell. The SEM images of the adsorbed regions of the illuminated DDBP samples were also taken for discussing the relation between the pump intensity and the photoinduced birefringence. [ABSTRACT FROM AUTHOR]

In this research, the amine functionalized magnetic silica‐based nanocomposite as a solid‐phase extraction adsorbent coupled with high‐performance liquid chromatography was applied for the preconcentration and determination of Sudan dyes in environmental waters and a food sample. The synthesized core‐shell Fe3O4@silica nanoparticles were functionalized with amino groups and characterized by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy techniques. The experimental parameters optimized and under the best conditions, the sorbent was successfully used to extract the target analytes. The result showed that a good linearity with a r‐value of greater 0.990, and the limits of detection were from 0.082 to 0.12 µg L−1. The relative recoveries obtained by analysing the spiked water samples were in the range of 90–102% and the relative standard deviations were between 0.590 and 7.94%. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study adsorption kinetics of titanium oxide–silicon dioxide based aerogels. [•] Materials are shown effective sorbents of azo-dye. [•] Surface area plays key role in adsorption, but does not explain kinetics entirely. [•] Presence of cobalt or manganese ions enhances adsorption. [Copyright &y& Elsevier]

A sequential adsorption/photocatalytic regeneration process to remove tartrazine, an azo-dye in aqueous solution, has been investigated. The aim of this work was to compare the effectiveness of an adsorbent/photocatalyst composite – TiO2deposited onto activated carbon (AC) – and a simple mixture of powders of TiO2and AC in same proportion. The composite was an innovative material as the photocatalyst, TiO2, was deposited on the porous surface of a microporous-AC using metal-organic chemical vapour deposition in fluidized bed. The sequential process was composed of two-batch step cycles: every cycle alternated a step of adsorption and a step of photocatalytic oxidation under ultra-violet (365 nm), at 25°C and atmospheric pressure. Both steps, adsorption and photocatalytic oxidation, have been investigated during four cycles. For both materials, the cumulated amounts adsorbed during four cycles corresponded to nearly twice the maximum adsorption capacitiesqmaxproving the photocatalytic oxidation to regenerate the adsorbent. Concerning photocatalytic oxidation, the degree of mineralization was higher with the TiO2/AC composite: for each cycle, the value of the total organic carbon removal was 25% higher than that obtained with the mixture powder. These better photocatalytic performances involved better regeneration than higher adsorbed amounts for cycles 2, 3 and 4. Better performances with this promising material – TiO2deposited onto AC – compared with TiO2powder could be explained by the vicinity of photocatalytic and AC adsorption sites. [ABSTRACT FROM PUBLISHER]

Abstract: The removal of Remazol Red 3BS (C.I. 239) dye by HMS ordered mesoporous silica, aminopropyl-modified HMS (HMS-NH2) and β-cyclodextrin-modified HMS (HMS-CD) materials was studied in the present work. The modified materials were functionalized in situ by adding the organic modifiers (3-aminopropyltriethoxysilane and a silylated derivative of MCT-β-CD) in the synthesis mixture and using dodecylamine as the mesopore structure directing agent. The successful incorporation of aminopropyl groups in HMS-NH2 and of cyclodextrin moieties in HMS-CD was verified by means of FT-IR spectroscopy, elemental analysis and N2 porosimetry. The HMS-CD material exhibited significantly higher adsorption capacity compared to that of the HMS-NH2 material, while the parent HMS mesoporous silica showed negligible adsorption capability. The maximum adsorption capacities obtained (at the optimum pH 2) on the basis of the Langmuir analysis were 0.28mmol/g for HMS-CD and 0.14mmol/g for HMS-NH2. It was shown that the HMS-CD sorbent can be effectively regenerated by the surfactant-enhanced regeneration method using SDS and that can be reused without significant loss of its adsorption capabilities. [Copyright &y& Elsevier]