Synthesis and Characterization of Magnetic Superadsorbent Fe₃O₄-PEG-Mg-Al-LDH Nanocomposites for Ultrahigh Removal of Organic Dyes

Abstract

Considering the huge demands for economical and reliable eco-remediation applications, the goal of the present work is to synthesize cost-effective and functionally efficient magnetic layered nanocomposite adsorbents for the effective adsorption of dyes followed by easy separation from wastewater. This would ensure good reusability of adsorbents without altering its adsorption capacity in a relatively short time manner. To achieve this, different molecular weights of polyethylene glycol (PEG)modified Fe 3 O 4 combined with Mg−Al-layered double hydroxides (MAN-LDH) were synthesized and characterized using powder Xray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, differential thermal analysis, energy-dispersive X-ray, and inductively coupled plasma optical emission spectroscopy. The efficacy of various adsorption parameters for the removal of methyl orange (MO) from water using Fe 3 O 4 -PEG-Mg-Al-LDH (FPL) adsorbents with different molecular weights of PEG (2FPL, 4FPL, and 6FPL) were investigated, and the results were compared. The maximum adsorption capacities of 2FPL, 4FPL, and 6FPL for MO were found to be 775.19, 826.44, and 833.33 mg/g, respectively. Detailed adsorption studies confirm that the higher adsorption capacity of 6FPL is due to the fast exchange of anions (NO 3 − ) by MO in the interlayers of MAN-LDH, larger surface area, hydrogen bonding, and electrostatic interaction between adsorbate and adsorbent. The thermodynamic data indicate that the adsorption behavior is spontaneous and endothermic in nature. The reusability of all FPL adsorbents is observed to be excellent. The MAN-LDH recoated after the 31st-cycle nanocomposites show a recovery of 100% adsorption efficiency, similar to the freshly prepared 6FPL. Such systematic studies greatly help in advancing the applications of newly functionalized nanomaterials toward ecoremediation approaches.

Removal of Anionic Dyes from Water using Polyethylene Glycol Modified Ni‐Al‐layered Double Hydroxide Nanocomposites

“…The rate constant value of k 2 increases with an increase in the initial dye concentration from 100 and 200 mg/L. These observations explain a strong interaction between PNAL and both the dyes, as observed in earlier literature …”

“…The molar proportion for Ni : Al of all the four adsorbents were close to 3. The amount of carbon present in the PNAL nanocomposite is in the order of 6PNAL > 4PNAL > 2PNAL which correlate well with the molecular weight of PEG present in the composite . The presence of nitrogen in the four adsorbents is owing to the availability of interstitial nitrate ions in/on the LDH interlayer and it comes from the precursor salts of Al.…”

“…Hence, a detailed adsorption study was performed only for 2PNAL, 4PNAL and 6PNAL adsorbents. Among these, 6PNAL has a higher percentage of adsorption due to the large adsorption sites along with more exchange capability of anions …”

“…The other divalent substituted LDH structures are almost similar to mineral hydrotalcite. At present there is more attention towards organic polymer modified LDH for effective removal of dyes from wastewater …”

Adsorption Processes in the Removal of Organic Dyes from Wastewaters: Very Recent Developments

“…Other investigations described the use of nanohybrids of Cu x O/Fe 2 O 3 /MoC as materials used in the adsorption of reactive red 195A and reactive yellow 84 (maximum capacities 435 and 278 mg/g, respectively) [16], also the use of Cr-doped ZnO in the adsorption of methyl orange (19 mg/g) and methylene blue (41 mg/g), the adsorption of methyl orange (833 mg/g) by a magnetic composite [17], and Fe 3 O 4 /PPy composites (eosin Y, methyl orange and brilliant green: 212, 149 and 264 mg/g, respectively) [18]. It was described in the literature [19], the usefulness of Ag 2 O as adsorbent of Congo red (181 mg/g), acid orange 7 (125 mg/g) and amido black 10B (83 mg/g), however this investigation, as many others, did not give any information about the desorption step.…”