Removal of sulfide from aqueous solutions using novel alginate–iron oxide magnetic hydrogel composites

Co/Ni/Cu-NH2BDC MOF@natural Egyptian zeolite ore nanocomposite for calcium ion removal in water softening applications

Water softening is a treatment process required to remove calcium (Ca(II)) and magnesium (Mg(II)) cations from water streams. Nanocomposites can provide solutions for such multiple challenges and have high performance and low application costs. In this work, a multimetallic cobalt, nickel, and copper 2-aminoterephthalic acid metal-organic framework ((Co/Ni/Cu-NH2BDC) MOF) was synthesized by a simple solvothermal technique. This MOF was supported on an Egyptian natural zeolite ore and was used for the adsorption of Ca(II) ions for water-softening applications. The adsorbent was characterized using Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), N2 adsorption-desorption isotherms, and zeta potential measurements. The adsorption isotherm data for the prepared adsorbent toward Ca(II) were best fit using the Redlich-Peterson model and showed a maximum adsorption capacity of 88.1 mg/g. The adsorption kinetics revealed an equilibrium time of 10 min, which was best fit using the Avrami model. The intermolecular interactions of Ca(II) ions with zeolite and MOF were investigated by Monte Carlo simulations, molecular dynamics simulations, and FTIR and XRD analyses. The adsorption sites in the zeolite structure were oxygen atoms, while those in the MOF structure were amine nitrogen atoms. The Ca(II) ions are coordinated with the solvent molecules in both structures. Finally, the in vitro cytotoxicity of this nanocomposite was assessed, revealing viability levels of 74.57 ± 2.1% and 21 ± 2.79% for Vero and African green monkey kidney and human liver (HepG2) cells, respectively. Cytotoxicity assays help assess the environmental impact of these materials, ensuring that they do not harm aquatic organisms or disrupt ecosystems. Thus, this study demonstrated the valorization of MOF/zeolite as a valuable and industry-ready adsorbent that can appropriate Ca(II) contaminants from aqueous streams.

Biochar-layered double hydroxide composites for the adsorption of tetracycline from water: synthesis, process modeling, and mechanism

Antibiotic-contaminated water is a crucial issue worldwide. Thus, in this study, the MgFeCa-layered double hydroxides were supported in date palm-derived biochar (B) using co-precipitation, hydrothermal, and co-pyrolysis methods. It closes gaps in composite design for pharmaceutical pollutant removal, advances eco-friendly adsorbents, and advances targeted water cleanup by investigating synthesis methodologies and gaining new insights into adsorption. The prepared B-MgFeCa composites were investigated for tetracycline (TC) adsorption from an aqueous solution. The B-MgFeCa composites synthesized through co-precipitation and hydrothermal methods exhibited better crystallinity, functional groups, and well-developed LDH structure within the biochar matrix. However, the co-pyrolysis method resulted in the LDH structure breakage, leading to the low crystalline composite material. The maximum adsorption of TC onto all B-MgFeCa was obtained at an acidic pH range (4-5). The B-MgFeCa composites produced via hydrothermal and co-pyrolysis methods showed higher and faster TC adsorption than the co-precipitation method. The kinetic results can be better described by Langmuir kinetic and mixed order models at low and high TC concentrations, indicating that the rate-limiting step is mainly associated with active binding sites adsorption. The Sip and Freundlich models showed better fitting with the equilibrium data. The TC removal by B-MgFeCa composites prepared via hydrothermal, the highest estimated uptake which is around 639.76 mg.g-1 according to the Sips model at ambient conditions, and co-pyrolysis was mainly dominated by physical and chemical interactions. The composite obtained via the co-precipitation method adsorbed TC through chemical bonding between surface functional groups with anionic species of TC molecule. The B-MgFeCa composite showed excellent reusability performance for up to five cycles with only a 30% decrease in TC removal efficiency. The results demonstrated that B-MgFeCa composites could be used as promising adsorbent materials for effective wastewater treatment.

Valorization of date palm leaves for adsorptive remediation of 2,4-dichlorophenoxyacetic acid herbicide polluted agricultural runoff

Alarming rates of water contamination by toxic herbicides have prompted the need and attention for easy, efficient, and affordable treatment options with a touch of circular economy aspects. This study valorized date palm leaf (DPL) wastes into a valuable adsorbent for remediating agricultural wastewater polluted with 2,4-Dichlorophenoxyacetic acid (2,4-DPA) herbicide. The DPL precursor was modified with H₂SO₄ treatment and both biomass samples were characterized by various analytical techniques. Acid treatment modified the morphology, thermal, and textural properties of the final product (TDPL) while maintaining the structure and surface chemistry intact. Simulated wastewaters containing 2,4-DPA were subsequently treated using TDPL as an adsorbent. Optimum adsorption conditions of pH 2, dosage 0.95 g/L, shaking speed 200 rpm, time 120 min, and temperature 30 °C showed a good herbicide removal efficiency in the range of 55.1-72.6% for different initial feed concentrations (50-250 mg/L). Experimental kinetic data were better represented by the pseudo-second-order model, while the Freundlich isotherm was reliable in describing the equilibrium behavior of the adsorption system. Further, the thermodynamic analysis revealed that the adsorption occurred spontaneously, favorably, and exothermically. Plausible sorption mechanism involved electrostatic interactions, weak van der Waals forces, hydrogen bonds, and π-π interactions between the participating phases. Conspicuously, TDPL application to real-world situations of treating actual herbicide-polluted agricultural runoff resulted in a 69.4% remediation efficiency. Thus, the study demonstrated the valorization of date palm leaves into a valuable and industry-ready adsorbent that can sequester toxic 2,4-DPA herbicide contaminant from aqueous streams.

Decorated reduced graphene oxide transfer sulfides into sulfur and sulfone in wastewater

Sulfides cannot be completely removed using oxidation due to the production of sulfate. In this work, a reduced graphene oxide (RGO)/Fe3O4 hybrid material was synthesized via a simple in situ chemical method for sulfide removal. The adsorption capacity of RGO/Fe3O4 was evaluated by sulfide removal from aqueous solution, and different experimental parameters including contact time, solution pH, adsorbent dosage, ion strength and temperature were investigated. The equilibrium data were in accordance with the Langmuir linear isotherm with a maximum uptake capacity of 173 mg g-1. The adsorption of sulfide by the RGO/Fe3O4 hybrid material can be attributed to the synergistic effect of both chemical and physical adsorption according to kinetic, adsorption isotherm and thermodynamic studies. The RGO/Fe3O4 material with oxygenated functional groups could convert sulfides to stable elemental sulfur and sulfone organics. The external magnetic field could easily separate the magnetic RGO/Fe3O4 adsorbent from the liquid. This research provides a novel strategy for the green and low-cost treatment of sulfide-containing wastewater by the RGO/Fe3O4 hybrid material.

Nickel-Catalyzed mesoporous biochar for enhanced adsorptive oxidation of aqueous Sulfide: An investigation of influencing factors and mechanisms

Biochar (BC) is a low-cost and electroactive adsorbent for removing sulfide in aqueous media, which toxifies aquatic organisms and corrodes water treatment facilities. However, it lacks a pore structure for sulfide ion (S^2-) mass transfer to active sites. Herein, it is shown that nickel-modified biochar (BC-Ni) adsorbed S^2- 2.72-fold faster than BC alone and attained a 1244 ± 252 mg-sulfide/g maximum adsorption capacity due to markedly increased mesopores, while BC attained 583 ± 250 mg-sulfide/g. Factors influencing S^2-sorption and theoretical sorption kinetics and isotherms models were evaluated. Structural and surface compositions of BC and BC-Ni were examined using state-of-the-art characterizations. The results suggest that S^2- was adsorbed via pore diffusion, pore filling, and cation bridging and oxidized to elemental sulfur and sulfate with quinone and hydrogen peroxide generated from dehydrogenation of hydroquinone on the BC-Ni by metallic nickel in the carbon matrix. This study would spur biomass valorization and desulfurization.

Nano-activated carbon derived from date palm coir waste for efficient sequestration of noxious 2,4-dichlorophenoxyacetic acid herbicide

Alarming water contamination rates by toxic herbicides have drawn attention to treat these pollutants using efficient, easy, and economic techniques. In this work, date-palm coir (DPC) waste-based nano-activated carbon (DPC-AC) was successfully prepared and examined for adsorptive removal of toxic 2,4-dichlorophenoxyacetic acid (2,4-DPA) herbicide from synthetic wastewater. The DPC-AC was synthesized via a single-step carbonization-KOH activation approach. The nanosorbent displayed a flaky morphology with graphitic structure and oxygen-rich surface functionalities. The nanocarbon with a mean particle size of 163 nm possessed a high specific surface area of 947 m²/g with an average pore size of 2.28 nm. High 2,4-DPA removal efficiency of 98.6% was obtained for the optimal adsorption conditions of pH 2, dosage 0.15 g, rotational speed 100 rpm, time 90 min, and initial 2,4-DPA concentration of 100 mg/L. Langmuir isotherm best described the equilibrium behavior with a theoretical maximum of 50.25 mg/g adsorption capacity for the system. Pseudo-second order model was more appropriate in quantifying the kinetics for all initial feed concentrations. Thermodynamically, the adsorption process was spontaneous, endothermic, and involved low activation energy. A plausible mechanism for the adsorption-desorption of 2,4-DPA onto DPC-AC is also discussed. Cost analysis and regenerability studies proved the economic value ($3/kg) and reusable nature of DPC-AC without any significant loss in its performance. Overall, this study highlights the advantages of DPC waste valorization into efficient nanoadsorbent and the sequestration of noxious 2,4-DPA herbicide from its aqueous streams using this nanosorbent.

Sulfide remediation from wastewater using hydrothermally synthesized δ-MnO2/porous graphitic carbon as adsorbent

A facile hydrothermal assisted in-situ precipitation technique was employed for synthesizing highly efficient porous graphitic carbon/manganese dioxide (PGC/MnO₂) nanocomposite adsorbent using calcium alginate as carbon precursor. Morphological and structural characterization using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction techniques confirmed the interconnected nanoporous architecture and birnessite (δ) MnO₂ polymorph evenly distributed on the PGC structure. The synergistic effect of PGC and MnO₂ was exploited for enhanced sulfide removal from wastewater via adsorptive oxidation. The effect of different experimental parameters, including solution pH, initial sulfide concentration, adsorbent dosage, and contact time on removal efficiency was investigated. The equilibrium and kinetic data for sulfide adsorption by PGC/MnO₂ nanocomposite fitted well with Langmuir isotherm and pseudo-second-order kinetic model, respectively. The maximum uptake capacity of sulfide by the nanocomposite was determined as 500 mg/g with complete sulfide removal. Further, it was estimated that a typical field application using the synthesized nanocomposite adsorbent would require 0.5-1 g/L per 200 mg/L of sulfide contaminated wastewater. Based on the experimental results, a schematic of the adsorptive oxidation mechanism of PGC/MnO₂ nanocomposite is proposed.

Augmented biohydrogen production from rice mill wastewater through nano-metal oxides assisted dark fermentation

This study highlights biohydrogen production enrichment through NiO and CoO nanoparticles (NPs) inclusion to dark fermentation of rice mill wastewater using Clostridium beijerinckii DSM 791. NiO (~26 nm) and CoO (~50 nm) NPs were intrinsically prepared via facile hydrothermal method with polyhedral morphology and high purity. Dosage dependency studies revealed the maximum biohydrogen production characteristics for 1.5 mg/L concentration of both NPs. Biohydrogen yield was improved by 2.09 and 1.9 folds higher for optimum dosage of NiO and CoO respectively, compared to control run without NPs. Co-metabolites analysis confirmed the biohydrogen production through acetate and butyrate pathways. Maximum COD reduction efficiencies of 77.6% and 69.5% were observed for NiO and CoO inclusions respectively, which were higher than control run (57.5%). Gompertz kinetic model fitted well with experimental data of NPs assisted fermentation. Thus, NiO and CoO inclusions to wastewater fermentation seems to be a promising technique for augmented biohydrogen production.

Adsorptive oxidation of sulfides catalysed by δ-MnO2 decorated porous graphitic carbon composite

Removal of dissolved sulfide contaminants from aqueous model solution using bio-derived porous graphitic carbon (PGC) impregnated with δ-MnO₂ was investigated. The composite adsorbent was synthesized using the chemical wet deposition method wherein MnO₂ was deposited on carbon walls through an in-situ reaction between permanganate and ethanol. Formation of transition metal oxide of manganese in the form of birnessite nanoparticles on interconnected PGC cell structure was confirmed by transmission electron microscopy, scanning electron microscopy, elemental analysis, and X-Ray diffraction characterization studies. The composite nanomaterial was tested for sulfide removal from aqueous solution at various conditions, including the pH, adsorbent dosage, initial solution concentration, and contact time. Adsorption results demonstrated an excellent adsorption capacity of ca. 90% within 20 min of contact time at 298 K. Equilibrium data collected from batch adsorption experiments fitted well with the Langmuir isotherm model (K_L = 190 L/mg; R² = 0.99). The maximum adsorption capacity of the composite was estimated as 526.3 mg S^2-/g at highly alkaline conditions compared to ca. 340 mg/g for a δ-MnO₂ adsorbent. Adsorptive oxidation of sulfides on composite MnO₂-PGC adsorbent was found to be controlled by the chemisorption process in accordance with the pseudo-second-order reaction model. Characterization of spent adsorbents revealed that sulfide was removed through adsorptive oxidation resulting in the formation of agglomerated particles of metal sulfate complexes and elemental sulfur. Analysis of reaction mechanism revealed that both MnO₂ and PGC played a role in the adsorptive oxidation of sulfides to CaSO₄ and elemental sulfur.

Biosorption performance of date palm empty fruit bunch wastes for toxic hexavalent chromium removal

Biosorption ability of date palm empty fruit bunch (DPEFB) was examined for the removal of toxic hexavalent chromium (Cr⁶⁺) ions from synthetic wastewater. The pretreated DPEFB biosorbent was studied for its morphology and surface chemistry through Scanning electron microscopy, Energy dispersive elemental analysis and Fourier transform infrared spectroscopy. Effect of biosorption parameters such as pH, biosorbent dosage, contact time, temperature, initial feed concentration and agitation speed on the Cr⁶⁺ ions removal efficiency by DPEFB was critically evaluated. The isoelectric point for the DPEFB sorbent was observed at pH 2, above which it was dehydronated to capture the positively charged Cr⁶⁺ ions. Batch biosorption studies showed that an optimal chromium removal efficiency of 58.02% was recorded by the DPEFB biosorbent for pH 2, dosage 0.3 g, 100 rpm agitation speed, 120 min contact time, 50 mg/L initial feed concentration and 30 °C operational temperature. Thermodynamic analysis showed that the binding of Cr⁶⁺ ions on DPEFB surface was exothermic, stable and favorable at room temperature. Equilibrium behavior of chromium binding on DPEFB was more aligned to Temkin isotherm (R² = 0.9852) highlighting the indirect interactions between Cr⁶⁺ ions and the biosorbent. Kinetic modeling revealed that the biosorption of Cr⁶⁺ ions by DPEFB obeyed pseudo-second order model than the pseudo-first order and intra-particle diffusion models. Reusability studies of the DPEFB sorbent showed that NaNO₃ was an effective regenerant and the biosorbent can be efficiently reused up to three successive biosorption-desorption cycles for chromium removal. In summary, the results clearly showed that the DPEFB biowaste seems to be an efficient, economic and eco-friendly biosorbent for sustainable removal of toxic hexavalent chromium ions from domestic and industrial wastewater streams.

Continuous Phenol Removal Using a Liquid–Solid Circulating Fluidized Bed

A liquid-solid circulating fluidized bed (LSCFB) helps to overcome the shortcomings of conventional fluidized beds by using a particle separation and return system as an integral part of the overall reactor configuration. Batch adsorption experiments were carried out for the removal of phenol from a synthetically prepared solution using fresh activated-carbon-coated glass beads. The morphological features and surface chemistry of the adsorbent were analyzed via SEM and FTIR techniques. The adsorbent dosage, contact time and temperature were varied along with solution pH to assess their effects on the adsorbent performance for phenol removal. Isotherm modeling showed that the phenol removal using the activated-carbon glass beads followed the Langmuir model. Effectively, it was observed at an adsorbent loading of 2.5 g/150 mL of feed volume and a contact time of 3 h produced an 80% efficiency in the batch study. Furthermore, on scaling it up to the column, the desired 98% phenol-removal efficiency was obtained with an adsorbent dosage of 250 g and contact time of 25 min. Adsorbent regeneration using 5% (v/v) ethanol showed a 64% desorption of phenol from the sorbent within 20 min in the LSCFB.