Sewage Sludge ZnCl2-Activated Carbon Intercalated MgFe-LDH Nanocomposites: Insight of the Sorption Mechanism of Improved Removal of Phenol from Water

High surface area activated carbon from a pineapple (ananas comosus) crown via microwave-ZnCl2 activation for crystal violet and methylene blue dye removal: adsorption optimization and mechanism

In this investigation, microwave irradiation assisted by ZnCl2 was used to transform pineapple crown (PN) waste into mesoporous activated carbon (PNAC). Complementary techniques were employed to examine the physicochemical characteristics of PNAC, including BET, FTIR, SEM-EDX, XRD, and pH at the point-of-zero-charge (pHpzc). PNAC is mesoporous adsorbent with a surface area of 1070 m2/g. The statistical optimization for the adsorption process of two model cationic dyes (methylene blue: MB and, crystal violet: CV) was conducted using the response surface methodology-Box-Behnken design (RSM-BBD). The parameters include solution pH (4-10), contact time (2-12) min, and PNAC dosage (0.02-0.1 g/100 mL). The Freundlich and Langmuir models adequately described the dye adsorption isotherm results for the MB and CV systems, whereas the pseudo-second order kinetic model accounted for the time dependent adsorption results. The maximum adsorption capacity (qmax) for PNAC with the two tested dyes are listed: 263.9 mg/g for CV and 274.8 mg/g for MB. The unique adsorption mechanism of MB and CV dyes by PNAC implicates multiple contributions to the adsorption process such as pore filling, electrostatic forces, H-bonding, and π-π interactions. This study illustrates the possibility of transforming PN into activated carbon (PNAC) with the potential to remove two cationic dyes from aqueous media.

Layered Double Hydroxides as Rising-Star Adsorbents for Water Purification: A Brief Discussion

Within the frame of this article, briefly but comprehensively, we present the existing knowledge, perspectives, and challenges for the utilization of Layered Double Hydroxides (LDHs) as adsorbents against a plethora of pollutants in aquatic matrixes. The use of LDHs as adsorbents was established by considering their significant physicochemical features, including their textural, structural, morphological, and chemical composition, as well as their method of synthesis, followed by their advantages and disadvantages as remediation media. The utilization of LDHs towards the adsorptive removal of dyes, metals, oxyanions, and emerging pollutants is critically reviewed, while all the reported kinds of interactions that gather the removal are collectively presented. Finally, future perspectives on the topic are discussed. It is expected that this discussion will encourage researchers in the area to seek new ideas for the design, development, and applications of novel LDHs-based nanomaterials as selective adsorbents, and hence to further explore the potential of their utilization also for analytic approaches to detect and monitor various pollutants.

Process Optimization and Modeling of Phenol Adsorption onto Sludge-Based Activated Carbon Intercalated MgAlFe Ternary Layered Double Hydroxide Composite

A sewage sludge-based activated carbon (SBAC) intercalated MgAlFe ternary layered double hydroxide (SBAC-MgAlFe-LDH) composite was synthesized via the coprecipitation method. The adsorptive performance of the composite for phenol uptake from the aqueous phase was evaluated via the response surface methodology (RSM) modeling technique. The SBAC-MgAlFe-LDH phenol uptake capacity data were well-fitted to reduced RSM cubic model (R² = 0.995, R²-adjusted = 0.993, R²-predicted = 0.959 and p-values < 0.05). The optimum phenol adsorption onto the SBAC-MgAlFe-LDH was achieved at 35 °C, 125 mg/L phenol, and pH 6. Under the optimal phenol uptake conditions, pseudo-first-order and Avrami fractional-order models provided a better representation of the phenol uptake kinetic data, while the equilibrium data models’ fitting follows the order; Liu > Langmuir > Redlich–Peterson > Freundlich > Temkin. The phenol uptake mechanism was endothermic in nature and predominantly via a physisorption process (ΔG° = −5.33 to −5.77 kJ/mol) with the involvement of π–π interactions between the phenol molecules and the functionalities on the SBAC-LDH surface. The maximum uptake capacity (216.76 mg/g) of SBAC-MgAlFe-LDH was much higher than many other SBAC-based adsorbents. The improved uptake capacity of SBAC-LDH was attributed to the effective synergetic influence of SBAC-MgAlFe-LDH, which yielded abundant functionalized surface groups that favored higher aqueous phase uptake of phenol molecules. This study showcases the potential of SBAC-MgAlFe-LDH as an effective adsorbent material for remediation of phenolic wastewater

Sustainable wastewater treatment by biochar/layered double hydroxide composites: Progress, challenges, and outlook

Biochar/layered double hydroxide (LDH) composites have gained considerable attention in recent times as low-cost sustainable materials for applications in water treatment. This paper critically evaluates the latest development in applications of biochar/LDH composites in water treatment with an emphasis on adsorption and catalytic degradation of various pollutants. The adsorption of various noxious contaminants, i.e., heavy metals, dyes, anions, and pharmaceuticals onto biochar/LDH composites are described in detail by elaborating the adsorption mechanism and regeneration ability. The synergistic effect of LDH with biochar exhibited significant improvement in specific surface area, surface functional groups, structure heterogeneity, stability, and adsorption characteristics of the resulting biochar/LDH composites. The major hurdles and challenges associated with the synthesis and applications of biochar/LDH composites in water remediation are emphasized. Finally, a roadmap is suggested for future research to assure the effective applications of biochar/LDH composites in water purification.

Magnetic Mg-Fe/LDH Intercalated Activated Carbon Composites for Nitrate and Phosphate Removal from Wastewater: Insight into Behavior and Mechanisms

This experimental work focused on the synthesis, characterization, and testing of a unique, magnetically separable, and eco-friendly adsorbent composite material for the advanced treatment and efficient removal of nitrate and phosphate pollutants from wastewater. The MgAl-augmented double-layered hydroxide (Mg-Fe/LDH) intercalated with sludge-based activated carbon (SBAC-MgFe) composites were characterized by FT-IR, XRD, BET, VSM, SEM, and TEM techniques, revealing homogeneous and efficient dispersion of MgFe/LDH within the activated carbon (AC) matrix, a highly mesoporous structure, and superparamagnetic characteristics. The initial solution pH, adsorbent dose, contact time, and temperature parameters were optimized in order to reach the best removal performance for both pollutants. The maximum adsorption capacities of phosphate and nitrate were found to be 110 and 54.5 mg/g, respectively. The competition between phosphate and coexisting ions (Cl⁻, CO₃²⁻, and SO₄²⁻) was studied and found to be remarkably lower in comparison with the nitrate adsorption. The adsorption mechanisms were elucidated by kinetic, isotherm, thermodynamic modeling, and post-adsorption characterizations of the composite. Modeling and mechanistic studies demonstrated that physisorption processes such as electrostatic attraction and ion exchange mainly governed the nitrate and phosphate adsorption. The composite indicated an outstanding regeneration performance even after five sequences of adsorption/desorption cycles. The fabricated composite with magnetically separable characteristics can be used as a promising adsorbent for the removal of phosphate and nitrate pollutants from wastewater.