Efficient Removal of Congo Red, Methylene Blue and Pb(II) by Hydrochar–MgAlLDH Nanocomposite: Synthesis, Performance and Mechanism

Abstract

Organic dyes and heavy metals often coexist in industrial effluents, and their simultaneous removal is a grand challenge. Herein, a hydrochar and MgAl layered double hydroxide (HC–MgAlLDH) nanocomposite was prepared via a facile one-step hydrothermal route, and applied to remove anionic Congo red (CR), cationic Methylene blue (MB) and Pb(II) from aqueous solutions. The nanocomposite was formed by interweaving amorphous HC and crystalline MgAlLDH nanoplates and possessed more functional groups, lower zeta potential and larger specific surface area than uncomposited MgAlLDH. Batch removal experiments showed that the components HC and LDH dominated the CR and MB removals, respectively, whereas Pb(II) removal was conjointly controlled by the two components. The maximum Langmuir removal capacities of the nanocomposite to sole CR, MB, or Pb(II) were 348.78, 256.54 or 33.55 mg/g. In binary and ternary systems, the removal capacities of CR and MB only slightly decreased, while the capacity of Pb(II) increased by 41.13–88.61%. The increase was related to the coordination of Pb(II) with the sulfur-containing groups in dyes and the precipitation of PbSO4. Therefore, the simultaneous removal of CR, MB and Pb(II) was involved in a synergistic effect, including electrostatic adsorption, π–π interaction, coordination and precipitation. The present work shows that the HC–MgAlLDH nanocomposite has great potential for wastewater integrative treatment.

Uncalcined Zn/Al Carbonate LDH and Its Calcined Counterpart for Treating the Wastewater Containing Anionic Congo Red Dye

“…The maximum dye removal of 78.38% was observed for uncalcined LDH at pH 6 and further increase in pH decreases the percentage removal due to breaking of LDH structure. Simultaneously, calcined LDH demonstrated complete dye removal, reaching 100%, within a broad pH range spanning from 3 to 7 [55,56]. The increase in the percentage of adsorption can be attributed to the positive charge that develops on the adsorbent surface at an acidic pH.…”

Recent Progress on the Adsorption of Heavy Metal Ions Pb(II) and Cu(II) from Wastewater

“…Symptoms of Pb(II) poisoning occur when the concentration of Pb(II) is too high in the internal organs, soft tissues and blood. The poisoning mechanism of Pb(II) in the human body is to inhibit the enzyme containing sulfhydryl in cells, which harms the biochemical and physiological functions of human body, which could cause problems in early childhood neurodevelopment [ 29 , 30 ], behavioral disorders [ 31 ], a drop in IQ, etc. [ 32 ].…”

Methylene Blue Dye Adsorption on Iron Oxide-Hydrochar Composite Synthesized via a Facile Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels’ Waste

“…Their samples had a surface area in the range of 42-53 m 2 /g and had a removal percentage for MB dye in the range of 60-80% [36]. Y. Haung et al prepared MgAl-hydrochar nanocomposites using the hydrothermal method and found that they had a maximal adsorption capacity of Langmuir (q L ) for MB dye of 257 mg/g [56]. T. Tran et al used coffee husk to prepare hydrochar with a surface area of 34 m 2 /g, which was used in the adsorption of MB dye with a maximum methylene blue adsorption capacity of 104 mg/g [57].…”

“…Hydrothermal carbonization R% = 60-80 [36] Hydrochar-MgAl double hydroxide Hydrothermal route q L = 157 mg/g [56] Activated hydrochar Hydrothermal carbonization q L = 357 mg/g [50] Hydrochar Hydrothermal carbonization q L = 5.12 mg/g [58] Magnetic biochar Microwave pyrolysis q L = 144.9 mg/g [59] Activated Hydrochar Hydrothermal carbonization q L = 200.01 mg/g [60] q L is maximum Langmuir removal capacities, R% is the removal efficiency.…”