The design and development of an environmentally benign porous adsorbent for effective simultaneous adsorption of organic dyes and heavy metals from water are important but remain a big challenge. Herein, we have designed a layered double hydroxide/metal–organic framework-based hierarchical nanocomposite (LDH/MOF HNC) by a facile, room-temperature in situ approach. This paper for the first time reports a hierarchical trimodal micro-meso-macroporous LDH/MOF composite with a high surface area (surface area 1282 m² g⁻¹ and pore volume 0.93 cm³ g⁻¹), synthesised by uniformly growing MOF nanocrystals on the surface of LDH nanosheet ultrathin films. An attempt is made to quantitatively demonstrate the adsorption data via suitable nonlinear kinetic and isotherm equations for single, simultaneous, and consecutive adsorption of the orange II reactive dye and Cr(VI). Experiments were performed at various values of pH (6.0–11.0), adsorbent dosages (1.0–8.0 mg), adsorbate concentrations (5–500 mg L⁻¹), and temperatures (293–323 K). The Langmuir model revealed a satisfactory fit to the equilibrium data of the LDH/MOF HNC (correlation coefficients R² > 0.98) with a calculated maximum adsorption capacity of 1173 and 733 mg g⁻¹ for orange II and Cr(VI), respectively, in a simultaneous adsorption system. The results of the study demonstrated that LDH/MOF HNCs could potentially be applied as a promising nanoadsorbent for the simultaneous removal and extraction of toxic dyes and metals from water.

To date, many nanoadsorbents have been developed and used to eliminate heavy metal contamination, however, one of the challenges ahead is the preparation of adsorbents from processes in which toxic organic solvents are used in the least possible amount. Herein, we have developed a new carboxylic acid-functionalized layered double hydroxide/metal–organic framework nanocomposite (LDH/MOF NC) using a simple, effective, and green in situ method. UiO-66-(Zr)-(COOH)₂ MOF nanocrystals were grown uniformly over the whole surface of COOH-functionalized Ni₅₀Co₅₀-LDH ultrathin nanosheets in a green water system under a normal solvothermal condition at 100 °C. The synthesized LDH/MOF NC was used as a potential adsorbent for removal of toxic Cd(II) and Pb(II) from water and the influence of important factors on the adsorption process was monitored. Various non-linear isotherm and kinetic models were used to find plausible mechanisms involved in the adsorption, and it was found that the Langmuir and pseudo-first-order models show the best agreement with isotherm and kinetic data, respectively. The calculated maximum adsorption capacities of Cd(II) and Pb(II) by the LDH/MOF NC were found to be 415.3 and 301.4 mg g⁻¹, respectively, based on the Langmuir model (pH = 5.0, adsorbent dose = 0.02 g, solution volume = 20 mL, contact time = 120 min, temperature = 25 ℃, shaking speed 200 rpm).

In this paper, we report an environmentally-friendly and low cost synthetic approach for large-scale fabrication of 2-dimentional porous Ni/Co-NO3-based layered double hydroxide (Ni/Co-NO3-LDH) nanosheet through ultrasonic-assisted process. The synthesis procedure used ethylene glycol/water system as an eco-friendly solvent system. The synthesized LDH was characterized by FE-SEM, TEM, XRD, and FT-IR techniques. FE-SEM and TEM images showed porous structure surface morphology of the synthesized LDH. Also, For Ni/Co-NO3-LDH, a hexagonal ultrathin layered was obtained owing to ultrasonic irradiation and applied processing conditions. The prepared LDH was used as sorbent in dispersive micro solid-phase extraction procedure. Two phenolic acids including p-hydroxybenzoic acid and p-coumaric acid were selected as model compounds. Some experimental factors affecting the extraction efficiency of the analytes were investigated and optimized. Finally, the sorbent was used for the extraction of model compound from fruit juice samples followed by high performance liquid chromatography. Linear dynamic range of 0.5-500µgL-1 with a low detection limit (0.1µgL-1) was obtained by the method. The relative standard deviations were 2.5 and 4.3% for p-hydroxybenzoic acid and p-coumaric acid, respectively. All recoveries were between 82 and 92%.

Amino-modified MCM-41/poly(vinyl alcohol) nanocomposite (M-MCM-41/PVOH NC) was developed for the adsorption of Cd(II) from aqueous media. M-MCM-41/PVOH NC was prepared through ultrasonic-assisted and simple blending procedure with economical and environmentally friendly polymer. The as-prepared adsorbent was characterized by FT-IR, TEM, FE-SEM and TGA. The contact time, solution pH and initial concentration of Cd(II) were found to affect the adsorption of Cd(II) from aqueous media. Kinetic studies were carried out and pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, and intra-particle diffusion (IPD) reaction kinetic models were examined. The kinetic results revealed that the adsorption of Cd(II) onto M-MCM-41/PVOH NC followed PSO kinetic model and is a chemical adsorption. The equilibrium adsorption data were evaluated by different isotherms viz. Langmuir, Freundlich, and Dubinin Radushkevich (D-R) equations. The equilibrium data fitted better with the Langmuir isotherm and the maximum adsorption capacity of M-MCM-41/PVOH NC at 298K was calculated to be 46.73mgg-1 for Cd(II) on a typical saturated monomolecular layer with a fixed number of localized adsorption sites.