Investigation of the removal kinetics, thermodynamics and adsorption mechanism of anionic textile dye, Remazol Red RB, with powder pumice, a sustainable adsorbent from waste water

Excessive growth and abnormal use of dyes and water in the textile industry cause serious environmental problems, especially with excessive pollution of water bodies. Adsorption is an attractive, feasible, low-cost, highly efficient and sustainable technique in terms of green chemistry for the removal of pollutants from water. This study aims to investigate the removal kinetics, thermodynamics and adsorption mechanism of Remazol Red RB, which was chosen as a representative anionic reactive dye, from synthetic wastewater using powdered pumice, taking into account various experimental parameters such as initial dye concentration, adsorption time, temperature and pH. Moreover, to support the proposed adsorption mechanism, before and after adsorption of the samples, the Fourier transform infrared spectrophotometer (FTIR) spectra, X-ray powder diffraction (XRD) diffractograms and High resolution transmission electron microscopy (HRTEM) images were also taken and used. The results show that powder pumice can be an efficient adsorbent for anionic dye removal with a relatively high adsorption capacity of 38.90 mg/g, and it is very effective in 30-60 min in mild conditions. The experimental data showed a high agreement with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm equation. In addition, thermodynamically, the process exhibited exothermic nature and standard isosteric enthalpy and entropy changes of -4.93 kJ/mol and 16.11 J/mol. K were calculated. It was determined that the adsorption mechanism was predominantly based on T-shaped pi-pi interactions and had physical characteristics.

Adsorption of Anionic Dyes from Wastewater onto Magnetic Nanocomposite Powders Synthesized by Combustion Method

In the present study, new magnetic nanocomposites were successfully prepared by combustion method, characterized by X-ray diffraction, Fourier transform infrared spectroscopy, magnetic measurements, N2 adsorption–desorption thermal analysis, and scanning electron microscopy, and tested as adsorbents for the removal of anionic dyes (Acid Yellow 42 and Acid Red 213) from aqueous solutions. The influence of process variables solution pH, adsorbent dose, initial dye concentration and temperature on the adsorption was evaluated. The best kinetic model that fitted with experimental data was a pseudo-second order model, and the equilibrium data were correlated by Langmuir isotherm model for the investigated dyes. Maximum removal efficiencies of 98.54% and 97.58% was obtained for Acid Yellow 42 and Acid Red 213, respectively, indicating the superior adsorption capacity of the new synthesized magnetic nanocomposites. The thermodynamic parameters indicated the spontaneous and endothermic nature of the adsorption process.

Pentaclethra macrophylla stem bark extract anchored on functionalized MWCNT-spent molecular sieve nanocomposite for the biosorption of hexavalent chromium

nsufficient innovative research on the sequestration of Cr(VI) from the aquatic ecosystem has made Cr(VI) a recalcitrant water contaminant that often affects water sources. In this work, a novel plant anchor-nanocomposite was fabricated from the spent molecular sieve, multi-walled carbon nanotubes, and the extract from the stem bark of Pentaclethra macrophylla. It was envisaged that due to the phytochemical constituent of the modifier, this nanocomposite could also act as potent adsorbents for the treatment of Cr(VI) polluted water. To the best of our knowledge, the application of Pentaclethra macrophylla stem bark extract as a modifier for the green fabrication of nanocomposite has not been reported. The resulting composites showed good uptake capacity for Cr(VI) as well as efficient reusability.

Aspects regarding colour fastness and adsorption studies of a new azo-stilbene dye for acrylic resins

The aim of this study was the colour fastness investigation of the new synthetized direct symmetrical azo-stilbene dye, using two of the film field domain reference tests, namely the wet-scrub and the UV tests. The dye was incorporated in a water-based resin, and then was applied on a PCV foil. The film colour parameters were determined before and after 200 wet-scrub cycles. Further, the dye was mixed with an acrylo-polyurethanic resin and then was applied on an aluminium plate, which was exposed to UV radiation for 414 h. The film colour parameters were recorded periodically. The maxima of the reflectance spectra depend on the UV time exposure. The quality of the film was analysed by the degree of gloss. A second focus was the elimination of the dye's traces from wastewaters (these may be resulted from the industries which apply surface coating methods), using the active carbon powder. The main operational adsorption process parameters influence were investigated. Equilibrium, kinetic and thermodynamic studies were performed. The adsorption process was confirmed by the CIEL*a*b* colour space analysis. All colour studies were investigated using UV-Vis spectroscopy.

Sequencing batch biosorption of micropollutants from aqueous effluents by rapeseed waste: Experimental assessment and statistical modelling

Rapeseed (RS) waste was used for sequential biosorption from aqueous solutions of two target micropollutants: lead ions and Reactive blue 19 (Rb19) dye, through an integrated approach, combining experimental assessment and statistical modeling. In both cases of sequential biosorption, a pseudo-second order kinetic model fitted the biosorption data well. Intraparticle diffusion proved to be the rate-limiting step in the sequential retention of both micropollutants. A selective desorption of metal ions and anionic dye at pH 2.5 and 10.5, respectively was observed. The quadratic models generated by response surface methodology (RSM) adequately described the sequential biosorption process and the desorption process, respectively. XPS and FTIR analysis indicated the mechanisms involved in the retention of target pollutants.

Kinetics, Isotherm, and Thermodynamic Study for Ultrafast Adsorption of Azo Dye by an Efficient Sorbent: Ternary Mg/(Al + Fe) Layered Double Hydroxides

The extremely high adsorption efficiency of malachite green (MG) was examined through a series of batch experiments by using Fe³⁺-doped Mg/Al layered double hydroxides (LDHs). The incorporation of iron into Mg/Al LDH with varying Al + Fe molar ratio of 4 + 1, 3 + 2, 2 + 3, and 1 + 4 increased the adsorption capacity with respect to time. The spectral analysis and N₂ sorption studies showed that there was retention of surface morphology in all of the iron-modified LDH samples. The experimental evidences showed that the adsorbent Mg/(Al + Fe) with a molar ratio of 10:2 + 3 had a significant removal, i.e., 99.94% for MG with the initial concentration of 1000 mg L^-1 at pH ∼ 9 and at room temperature in 5 min. With further increase in iron loading (at ratio 10:1 + 4), there was a decrease in the removal of MG due to the agglomeration of Fe₂O₃ on the surface. The adsorption process was best fitted to the Freundlich isotherm followed by the pseudo-second-order model. The standard thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were obtained over the temperature range of 20-50 °C. It was observed that the adsorption of MG onto Mg/(Al + Fe) LDH was spontaneous, exothermic, and enthalpy driven in the physisorption mode. A worthy desorption efficiency was achieved by using ethanol and water, which was more than 90% in the three cycles. Maintaining almost the same removal efficiency of MG even after three cycles indicated Mg/(Al + Fe) LDH as a promising material for wastewater treatment. This work was anticipated to open up new possibilities in dealing with anionic dye pollutants.

Removal of Colored Organic Pollutants from Wastewaters by Magnetite/Carbon Nanocomposites: Single and Binary Systems

This work develops a methodology for selective removal of industrial dyes from wastewaters using adsorption technology based on magnetic adsorbents. The magnetic nanoparticles embedded within a matrix of activated carbon were tested as adsorbents for removal of industrial dyes from aqueous solutions. The effects of four independent variables, solution pH, initial concentration of pollutant, adsorbent dose, contact time, and their interactions on the adsorption capacity of the nanocomposite were investigated in order to optimize the process. The removal efficiency of pollutants depends on solution pH and increases with increasing the carbon content, with initial concentration of the pollutants, the temperature, and the dose of magnetite/carbon nanocomposites. Pseudo-second-order kinetic model was fitted to the kinetic data, and adsorption isotherm analysis and thermodynamics were used to elucidate the adsorption mechanism. The maximum adsorption capacities were 223.82 mg g−1 for Nylosan Blue, 114.68 mg g−1 for Chromazurol S, and 286.91 mg g−1 for Basic Red 2. The regeneration and reuse of the sorbent were evaluated in seven adsorption/desorption cycles. The optimum conditions obtained for individual adsorption were selected as starting conditions for simultaneous adsorption of dyes. In binary systems, in normal conditions, selectivity decreases in the order: Red Basic 2 > Nylosan Blue > Chromazurol S.

Nitrogen-functionalised carbon nanotubes as a novel adsorbent for the removal of Cu(ii) from aqueous solution

Nitrogen-functionalized multiwalled carbon nanotubes synthesized were effective and efficient for the removal of Cu²⁺ from aqueous solutions.

Effectiveness of carbon nanotube–cobalt ferrite nanocomposites for the adsorption of rhodamine B from aqueous solutions

Magnetic cobalt ferrite–carbon nanotube nanocomposites are effective and reusable adsorbents for remediation of wastewaters contaminated with dyes.

Hydrothermal and activated synthesis of adsorbent montmorillonite supported porous carbon nanospheres for removal of methylene blue from waste water

Novel adsorbent, montmorillonite supported porous carbon nanospheres (MMT-PCN) were conveniently synthesized by a hydrothermal carbonization and chemical activation treatment with ZnCl₂.

Adsorption removal of Congo red over flower-like porous microspheres derived from Ni/Al layered double hydroxide

Flower-like porous microspheres of Ni/Al mixed oxide, consisting of a hollow core and mesoporous shell, can achieve a superior adsorption and regeneration capacity toward Congo red.

Ultra small gold nanoparticles–graphitic carbon nitride composite: an efficient catalyst for ultrafast reduction of 4-nitrophenol and removal of organic dyes from water

Synthesis of ultra-small gold particles on g-C₃N₄ sheets was reported. This Au–C₃N₄ composite exhibited superior catalytic activity toward reduction of 4-nitrophenol and adsorption, photocatalytic degradation of dyes.