Immobilization of methylene blue onto bentonite and its application in the extraction of mercury (II)

Adsorption of Malachite Green Dye onto Mesoporous Natural Inorganic Clays: Their Equilibrium Isotherm and Kinetics Studies

Contamination of water with organic dyes is a major environmental concern as it causes serious life-threatening environmental problems. The present research was designed to evaluate the potential of three different natural inorganic clays (NICs) i.e., Pakistani bentonite clay (PB), bentonite purchased from Alfa Aesar (BT), and Turkish red mud (RM) for malachite green (MG) dye removal from an aqueous solution. Various analytical techniques, namely X-ray fluorescence spectrometry (XRF), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller surface area measurement (BET), and thermogravimetric analysis (TGA), were used to investigate the physicochemical properties of the NICs samples. The effect of adsorption operational parameters such as contact time, aqueous phase pH, dye concentration, and amount of NICs on the adsorption behavior of MG onto NICs samples were investigated under the batch adsorption system. The equilibrium and kinetic inspection reflected the best description of MG adsorption behavior by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. The results indicated that the adsorption was favorable at higher pH. The maximum adsorption capacities calculated by Langmuir isotherm for PB, BT, and RM were found to be 243.90 mg/g, 188.68 mg/g, and 172.41 mg/g, respectively. It can be concluded that natural inorganic clays with a higher surface area can be used as an effective adsorbent material to remove the MG dye from an aqueous solution.

Efficient removal of Hg2+ from aqueous solution by a novel composite of nano humboldtine decorated almandine (NHDA): Ion exchange, reducing-oxidation and adsorption

Efficient removal of Hg²⁺ from aqueous solution is key for environmental protection and human health. Herein, a novel composite of nano humboldtine decorated almandine was synthesized from almandine for the removal of Hg²⁺. Results showed that the Hg²⁺ removal process followed pseudo-second-order kinetic model and Langmuir equation, and the maximum adsorption capacity was 575.17 mg/g. Furthermore, Hg²⁺ removal by the composite was pH-dependent and low pH value facilitated the removal of Hg²⁺. SEM and HADDF-STEM results suggested a new rod morphology was generated and the adsorbed mercury was mainly enriched into this structure after reaction with Hg²⁺ solution. The removal mechanisms of Hg²⁺ by the composite was pH dependent, and included ion exchange, surface complexation, reduction and oxidation. Our results demonstrated that the composite was an ideal material for Hg²⁺ removal and the transformation ways of mercury related species could be a significant but currently underestimated pathway in natural and engineered systems.

Cetyltrimethylammonium bromide intercalated and branched polyhydroxystyrene functionalized montmorillonite clay to sequester cationic dyes

Herein, Cetyltrimethyl ammonium bromide (CTAB) intercalated and branched polyhydroxystyrene (BPS) functionalized montmorillonite (MMT) nano-composite (BPS-CTAB-MMT) was developed, characterized, and its potential as an adsorbent was tested in sequestering cationic dyes viz. rhodamine B (RB), crystal violet (CV), and methylene blue (MB) from aqueous environment. N₂ adsorption/desorption isotherm showed mesoporous BPS-CTAB-MMT surface with a BET surface area of 273.8 m²/g. The appearance of sharp spikes at 2855 and 2925 cm^-1 (associated with symmetric and asymmetric tensions of C - H bonds) in infra-red spectrum of BPS-CTAB-MMT indicates successful intercalation of MMT with CTAB and functionalization with BPS. The observed crystallite size of BPS-CTAB-MMT was 66 nm. Comparatively greater weight loss for BPS-CTAB-MMT (11%) than MMT (9%) was observed during thermogravimetric analysis. The adsorption of dyes on BPS-CTAB-MMT was pH dependent with maximum uptake was observed in the pH range: 5-6. For initial dyes concentration (C_o) range: 50-150 mg/L, the observed equilibration time for CV was 300 min, whereas for RB and MB the equilibration time varied between 300 and 360 min. Modeling investigations revealed the applicability of Sips isotherm and pseudo-second-order (PSO) kinetic models to dyes adsorption data. Sips maximum adsorption capacity (q_s) values for RB, CV, and MB at 55 °C were 476.5, 438.7, and 432.7 mg/g, respectively. The adsorption of dyes on BPS-CTAB-MMT was thermodynamically favorable. Desorption studies showed 42.1% RB and 41.9% CV recovery with 0.1 M NaOH and CH₃COCH₃, respectively, while only traces of MB were recovered with tested eluents.

RETRACTED: Adsorption of Crystal violet on raw and acid-treated montmorillonite, K10, in aqueous suspension

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. After further consultation with the experts conducting research in the area of XRD and FTIR spectrum, it has been concluded that the appropriate action for this case is the full retraction of the article from the Journal of Environmental Management. The rationale for this decision is what the journal has concluded to be the fabrication of data associated with Figure 2a in the manuscript which shows three distinct areas in the noise patters with unusual similarities to be considered as coincidental. The data presented in Figure 2a jeopardizes the quality of the manuscript and the conclusions drawn based on the data presented in Figure 2.

Study of organically-modified montmorillonite clay for the removal of copper(II)

2-Oxyhydrazino-N-(2-methylen-yl-hydroxyphenyl)pyridinium (OMHP) ion was immobilized onto Na-montmorillonite clay (MMT). The modified clay (OMHP-MMT) was used for the removal of Cu(II). Experiments were carried out as a function of solution pH, stirring time, effect of some common ions and eluent type, concentration and volume. MMT, OMHP-MMT, and OMHP-MMT-loaded Cu(II) were characterized by X-ray diffractometry, electronic and infrared spectra, and elemental and thermogravimetric analyses. OMHP is suggested to be intercalated into MMT parallel to the aluminosilicate layers, with a capacity of 56.4 mEq/100g. OMHP-MMT shows good stability in 0.1-1 mol L(-1) hydrochloric or nitric acids, ammonia hydroxide, concentrated Na(+), K(+), NH(4)(+), Cl(-) or SO(4)(2-). It shows good removal efficiency and selectivity towards Cu(II) at pH 3.0-8.0 and stirring time 10 min with an removal capacity of 119 mEq/100g. Most common ions do not interfere with the removal process except Fe(3+). Extracted Cu(II) could be quantitatively recovered by 10 mL 1% thiourea in 0.1 mol L(-1) HCl with 100-fold preconcentration factor. OMHP-MMT was successfully applied to recover Cu(II) from different samples.