Zinc oxide nanoparticles encapsulated in alginate beads: a promising and recyclable adsorbent for simultaneous uptake of toxic metals

Heavy metal toxicity is a known problem and various methods are used for treatment. Adsorption has some advantages and it would be promising if environmentally friendly and cheap materials were utilized. Alginate and zinc oxide nanoparticles were selected and composite alginate beads were used for the removal of mixed metals from aqueous solutions. Batch and column experiments were conducted to determine some parameters' effects and the adsorbent's real application potential. According to the batch experiments, zinc oxide nanoparticles to alginate ratio of 0.5 g g-1, and pH levels nearby to the neutral range led to better metal removals. 0.5 ml min-1of flow rate supplied better metal removal efficiencies in columns, with the highest treatment as 86% of Pb2+. Acid treatment can be successfully applied for the regeneration of the adsorbent, at least three times only with a 4% reduction in the adsorption efficiency. Heavy metal uptake was compatible with the pseudo 2nd order model indicating chemisorption as a dominant mechanism. Also, the intraparticle diffusion model illustrated adsorption might govern more than one step. The Langmuir model had the best fit and suggested monolayer covering for Pb2+, 76.3 mg g-1. Alginate-based nanocomposite beads were useful for mixed metal removal and could be used.

Fixed-Bed Column Adsorption Studies: Comparison of Alginate-Based Adsorbents for La(III) Ions Recovery

The paper investigated the adsorption of the packed-bed column with the alginate-based adsorbents (ALG-based adsorbents) such as alginate-biochar, alginate-clinoptilolite, alginate-lignin, and alginate-cellulose for La(III) ions' removal. Fixed-bed adsorption studies with various alginate-based adsorbents were carried out and compared to the La(III) ions adsorption. The columns were filled with ALG-based adsorbent beads of approximately 1.1 ± 0.005 mm spherical shapes. The effects of the inlet concentrations on the breakthrough curves were studied in terms of the adsorption performance of the ALG-based adsorbents. The experimental data were correlated with the Adams-Bohart, Yoon-Nelson, Thomas, and Wolborska models to determine the best operational parameters. Based on the comparison of R² values, the Thomas and Yoon-Nelson models were found to be more suitable than the Adams-Bohart and Wolborska models. In the desorption study, the ALG-based adsorbents packed columns showed the maximum desorption of La(III) just after passing 100 cm³ of 1 mol/dm³ HCl. Overall, the results show that ALG-based adsorbents could be used for continuous recovery of La(III) ions from aqueous solutions and were not only cost-effective but also environmentally friendly.

Simultaneous removal of cationic and anionic dyes from simulated industrial effluents using a nature-inspired adsorbent

Alginate-grafted polyaniline (Alg-g-PANI) microparticles were synthesized through the grafting of aniline onto functionalized Alg followed by double crosslinking by glutaraldehyde and calcium chloride. The performance of the developed microparticles as adsorbent in simultaneous removal of malachite green (MG) and congo red (CR) dyes were examined by the batch method. Experimental parameters, including adsorbent amount, pH, initial dyes concentrations, and contact time were optimized. Langmuir and Freundlich adsorption models were employed to explore the equilibrium isotherm. As the Langmuir model results, the maximum adsorption capacities (Q_m) of microparticles for the MG and CR dyes were obtained as 578.3 and 409.6 mgg^-1, respectively. Adsorption kinetics for both dyes were well-fitted with the pseudo-second-order model that confirm the rate-limiting step might be the chemical adsorption. The adsorbent was regenerated via desorption process and was reusable five times without a substantial decrease in its adsorption efficacy in first three cycles. Adsorbent-dyes interactions were computationally evaluated using Gromacs package, and it was found that both MG and CR are able to interact strongly with the adsorbent. In accordance with experimental results, simulation data revealed that MG can be removed more efficiently than those of the CR. As the experimental results, we could conclude that the synthesized Alg-g-PANI microparticles can be used as a nature-inspired adsorbent for simultaneous removals of CR and MG dyes.

Coconut husk-raw clay-Fe composite: preparation, characteristics and mechanisms of Congo red adsorption

The release of unspent dyes from industries constitutes hazard and environmental challenges. For rapid and efficient removal of Congo red from aqueous solutions, a composite was prepared from coconut husk, raw clay, Fe(II) and Fe(II) compounds. Adsorption variables (initial pH of the solution, contact time, temperature and initial concentration of Congo red) were varied to understand the characteristics and mechanisms of the adsorption process. The composite was characterised using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM)–Energy dispersive X-ray (EDX) spectroscopy, nitrogen adsorption–desorption isotherm, X-ray Diffraction (XRD) spectroscopy and pH of the point zero charge (pH_pzc). The optimal values of the pH, equilibrium time and temperature for adsorption of Congo red by the composite are 2, 40 min and 50 °C, respectively. The kinetic and equilibrium data followed Avrami fractional order and Langmuir models, respectively. A 1.0 g of the composite could maximally take up 1649.3 mg of Congo red at 50 °C. The values of ΔG° are in the range of − 27.901 to − 24.492 kJ mol^–1 while the value of ΔH° is − 72.239 kJ mol^–1. Hence, the removal of the Congo red by the composite was spontaneous, feasible and exothermic. The adsorption process was biphasic and followed physisorption process. Electrostatic interaction played a significant role in the removal of Congo red by the composite. The combine data in this study have proven that the clay composite, a cheap adsorbent, can be used for remediation of water contaminated with Congo red.

A critical review on clay-based nanocomposite particles for application of wastewater treatment

Nanotechnology plays an important function in recent environmental aspects for the elimination of contaminants in the ecosystem. In recent times, nano-clay has initiated more concentration because of its distinctive physicochemical properties and characteristics. Recently, many types of research in clay-based nanocomposite were accomplished in the elimination of pollutants from water sources. Nanocomposite materials have advanced properties useful for contaminat removal such as higher surface area, thermal stability, selectivity to remove different contaminants, improved process ability, and fast decontamination. Thus, the development of clay-based composite materials is one of the upcoming directions to use effectively in water and wastewater treatment as adsorbent nanomaterials. This paper assesses the latest achievement in clay-based nanocomposite preparation, material property analysis and function for various pollutant removals. In particular, great consideration was paid to the recent progress in clay/metallic, clay-polymer, and clay-carbon composites presenting their application in the removal of different kinds of pollutants. Moreover, the mechanism of adsorption, the challenges and future perspective were also discussed to reach the optimum performance of the nanomaterials adsorbent. It is confirmed that clay-based nanocomposite materials are more cost-effective technology than conventional treatment methods.

Bimetallic p-ZnO/n-CuO nanocomposite synthesized using Aegle marmelos leaf extract exhibits excellent visible-light-driven photocatalytic removal of 4-nitroaniline and methyl orange

In the current study, the photocatalytic activity of bimetallic ZnO-CuO hetero-nanocomposite was evaluated and compared with the monometallic ZnO and CuO nanoparticles using 4-nitroaniline (4-NA) and methyl orange (MO). Bimetallic ZnO-CuO hetero-nanocomposite, ZnO, and CuO nanostructure were synthesized utilizing leaf extract of Aegle marmelos and characterized by transmission electron microscopy, X-ray diffraction, and XPS. Benefiting from the p-n heterostructures formation, bimetallic ZnO-CuO hetero-nanocomposite exhibits an excellent photocatalytic activity against 4-NA as well as MO compared to pure ZnO and CuO. In particular, bimetallic ZnO-CuO hetero-nanocomposite expressed the highest photocatalytic activity by reducing 90% of 4-NA in 20 min and by degrading 96% of MO in 10 min, whereas 65% reduction of 4-NA in 30 min and 93% degradation of MO in 45 min was exhibited by CuO and 48% reduction of 4-NA in 30 min and 98% degradation of MO in 50 min was exhibited by ZnO. Moreover, bimetallic ZnO-CuO hetero-nanocomposite maintains excellent photocatalytic activity even after five cycles indicating its stability as photocatalyst and reusability. Based on the experimental findings, bimetallic ZnO-CuO hetero-nanocomposite could be used as a photocatalyst for wastewater treatment with excellent regeneration efficiency.

Removal of Isolan Dark Blue 2SGL-01 from aqueous solutions onto calcined and uncalcined (Mg-Zn)/(Al-Fe)-(CO3)/Cl layered double hydroxides

The adsorption process of the industrialized dye Isolan Dark Blue 2SGL-01 (IDB) onto (Mg-Zn)/(Al-Fe)-(CO3)/Cl layered double hydroxides (LDHs) coded LDH21 and LDH22 and its calcined products CLDHs (CLDH21 and CLDH22), respectively, was investigated. The characterization of LDHs and CLDHs before and after loading with IDB by Fourier transform infrared, scanning electron microscope and surface area measurements showed a typical hydrotalcite structure and confirmed the loading of IDB. The adsorption parameters; initial pH, shaking time, adsorbent dose, initial concentration of IDB dye and temperature were studied. The optimum conditions for IDB adsorption were pH 4.3 and shaking time 3 h. A complete removal of IDB (> 99%) was achieved using a dosage of 2.0 g L− 1 CLDHs or LDH22, and 3.0 g L− 1 of LDH21. The adsorption processes were suggested to be best described by the pseudo-second order kinetics and Langmuir-type adsorption isotherm with monolayer capacities of 75, 91, 427 and 530 mg g− 1, onto LDH21, LDH22, CLDH21 and CLDH22, respectively. The loaded IDB was recovered from LDHs and CLDHs adsorbent using Na2CO3. CLDH22 showed best adsorption capacity of 530 mg g− 1. Its adsorption thermodynamic parameters ∆Gadsorption, ∆Hadsorption and ∆Sadsorption indicated that the adsorption processes were spontaneous and endothermic in nature. CLDH22 was successfully applied for the removal of IDB from simulated dyeing process with removal efficiency 97%.

Polyvinyl Alcohol/Calcium Carbonate Nanocomposites as Efficient and Cost-Effective Cationic Dye Adsorbents

A novel polyvinyl alcohol (PVA)/calcium carbonate-based double-layer cationic dye adsorbent was developed. Polyvinyl alcohol (50 wt %) and calcium carbonate (50 wt %) were used together with borax as a cross-linking agent. The nanocomposite was prepared using only water, without the need for any toxic solvent or hazardous chemical. The final samples were obtained by the solvent casting method. The nanocomposite adsorbent was characterized using a Fourier transform infrared (FTIR) spectroscope and a scanning electron microscope (SEM). The adsorption performance on two cationic dyes, i.e., methylene blue and safranin was studied. Dye adsorption was quantified by measuring the nanocomposite swelling, contact time, and dye concentration. Pseudo first-order and pseudo second-order kinetic models as well as intraparticle diffusion model were used to model the adsorption kinetics. Moreover, the isotherm dye adsorption was investigated by Langmuir and Freundlich models. The results revealed that the developed nanocomposite has relatively high adsorption efficiency and short adsorption time and retains its performance after several successive absorption–desorption processes. The results also showed that the pseudo-second-order model best describes the adsorption kinetics, and the Freundlich isotherm model has a better compatibility with the experimental data. Finally, an adsorption mechanism was proposed for the dye removal process. The developed PVA/CaCO₃ nanocomposite can be potentially used for efficient dye removal in wastewater treatments.

The role of kaolin and kaolin/ZnO nanoadsorbents in adsorption studies for tannery wastewater treatment

In the present study, comparative studies of kaolin and kaolin/ZnO nanocomposites for the adsorption of Cr(VI), Fe(III), COD, BOD, and chloride from tannery wastewater were investigated. ZnO nanoparticles and kaolin/ZnO nanocomposites were prepared by sol-gel followed by wet-impregnation methods. The prepared adsorbents were characterized using different analytical tools such as X-ray diffraction, Fourier transforms infrared, high-resolution transmission electron microscopy, energy dispersive spectroscopy, selective area electron diffraction and Brunauer Emmett-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). The HRSEM/EDS/XPS analysis confirmed successful immobilization of clay structural network on the lattice layers of zincite hexagonal structure of ZnO nanoparticles. BET measurement showed an increase in the surface area of kaolin/ZnO nanocomposites (31.8 m²/g) when compared to kaolin (17 m²/g). Batch adsorption studies were carried out by varying the parameters such as contact time, adsorbent dosage and temperature. The maximum removal of Cr(VI) (100%), Fe(III) (98%), COD (95%), BOD (94%) and Chloride (78%) was obtained at 15 min by kaolin/ZnO composites. While 78% Cr(VI), 91% Fe(III), 91% COD, 89% BOD and 73% Chloride were removed by kaolin under the same conditions. The kaolin/ZnO nanocomposites exhibited better adsorption performance than kaolin due to higher surface area of the former than the latter. It was found that the Jovanovic isotherm model fitted the adsorption experimental data most with the highest correlation (R² > 0.99) for both nanoadsorbents and indicate the occurrence of adsorption on monolayer and heterogeneous surfaces. The mechanism for the adsorption of metal ions in tannery wastewater onto the nano-adsorbents was examined using Weber Morris intra-particle diffusion model and Boyd plot which showed that the adsorption process was both intra-particle and film diffusion controlled. The thermodynamic parameters such as enthalpy change showed that that adsorption of metal ions and other parameters was feasible, spontaneous and endothermic. The ZnO/clay nanocomposites exhibited excellent recyclable and re-useable properties even after six repeated applications and can, therefore, be applied in wastewater treatment for removal of heavy metals and other physicochemical parameters.

Simultaneous removals of cadmium(II) ions and reactive yellow 4 dye from aqueous solution by bone meal-derived apatite: kinetics, equilibrium and thermodynamic evaluations

The simultaneous removal of Cadmium ions and reactive yellow 4 dye (RY4 dye) by bone meal-derived apatite (BMDA) were investigated in a batch process. The structural elucidation of the prepared BMDA was done using TEM, XRD, FT-IR and EDX to evaluate the structures of the adsorbent. Different experimental features such as the agitation time, BMDA dosage, temperature, initial adsorbate concentration and pH of the solution were examined on the uptake pattern of the pollutants. The mechanism of adsorption was examined with Elovich, pseudo-first-order, intraparticle diffusion and pseudo-second-order kinetic models, while Langmuir, Dubinin-Radushkevich (D-R), Freundlich and Tempkin isotherms were exploited in order to describe the behaviour of the equilibrium process. Analysis from XRD revealed peaks corresponding to single phase apatite powder, while the various forces responsible for the interactions between the BMDA surface and the pollutants were obtained to CO32−, OH− and PO43− as observed by FT-IR analysis. SEM and TEM investigations confirmed a round-like morphology which agglomerated together upon the adsorption of pollutants.

The kinetic modelling of the adsorption data were well illustrated with the pseudo-first-order model with correlation coefficient (R2) values ranging from 0.997 to 0.999. Isotherms studies revealed that best fit was achieved with Langmuir isotherm with adsorption capacities of 94.85 and 116.16 mg/g for RY4 dye and Cd(II) ions respectively. Thermodynamic study signified the uptake of the pollutants to be spontaneous, feasible and endothermic in nature. The values of entropy change (ΔS) for the sorption processes calculated are 86.57 and 60.16 J/mol/K for Cd(II) and RY4 dye, respectively.

Comparative Studies of Quaternary Ammonium Salts on the Aggregation and Dispersion Behavior of Kaolinite and Quartz

Fine particles in the presence of flotation reagents exhibit different dispersion and aggregation behaviors in a mineral suspension, and affect the flotation separation processes. In this study, the effects of three quaternary ammonium salts (i.e., dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium chloride (TTAC), and hexadecyltrimethylammonium chloride (CTAC)) on the dispersion and aggregation behaviors of kaolinite and quartz were studied. The mechanism was systematically investigated using sedimentation tests, reagent adsorption analysis, zeta potential measurements, and SEM analysis. In the absence of reagents, the kaolinite and quartz particles exhibited good aggregation behaviors at acid and neutral pHs compared with alkaline conditions. Except for CTAC, the presence of DTAC and TTAC improved the aggregation behavior of both minerals in neutral and alkaline conditions. More, the sedimentation yields of both minerals were increased significantly with increasing the concentration of DTAC and TTAC. However, the increasing concentration of CTAC resulted in an increase in the dispersion of kaolinite and quartz particles under the same conditions. At neutral and alkaline conditions, the zeta potentials and adsorbed amounts of all three salts on the mineral surfaces were increased significantly with increasing the concentrations of salts, and the adsorbed amount adopted the following sequence: CTAC > TTAC > DTAC. The zeta potential results showed that the stronger adsorption of quaternary ammonium salts on mineral surfaces at neutral and alkaline conditions was mainly because of electrostatic interactions.

Photoactive nanoarchitectures based on clays incorporating TiO2 and ZnO nanoparticles

Thought as raw materials clay minerals are often disregarded in the development of advanced materials. However, clays of natural and synthetic origin constitute excellent platforms for developing nanostructured functional materials for numerous applications. They can be easily assembled to diverse types of nanoparticles provided with magnetic, electronic, photoactive or bioactive properties, allowing to overcome drawbacks of other types of substrates in the design of functional nanoarchitectures. Within this scope, clays can be of special relevance in the production of photoactive materials as they offer an advantageous way for the stabilization and immobilization of diverse metal-oxide nanoparticles. The controlled assembly under mild conditions of titanium dioxide and zinc oxide nanoparticles with clay minerals to give diverse clay-semiconductor nanoarchitectures are summarized and critically discussed in this review article. The possibility to use clay minerals as starting components showing different morphologies, such as layered, fibrous, or tubular morphologies, to immobilize these types of nanoparticles mainly plays a role in i) the control of their size and size distribution on the solid surface, ii) the mitigation or suppression of the nanoparticle aggregation, and iii) the hierarchical design for selectivity enhancements in the catalytic transformation and for improved overall reaction efficiency. This article tries also to present new steps towards more sophisticated but efficient and highly selective functional nanoarchitectures incorporating photosensitizer elements for tuning the semiconductor-clay photoactivity.

Biowaste-Derived Hydroxyapatite for Effective Removal of Reactive Yellow 4 Dye: Equilibrium, Kinetic, and Thermodynamic Studies

This study examines the application of poultry eggshell (PES) as a source of calcium for the synthesis of hydroxyapatite (HA) via annealation. The synthesized powder (poultry eggshell hydroxyapatite (PESHA)) was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), EDAX, and transmission electron microscopy (TEM) analytical techniques. This powder was used for adsorptive removal of the Reactive Yellow 4 (RY4) dye in a batch process. Results from morphological analysis by SEM and TEM revealed that the microstructure of the apatite is made up of needle-rod-like particles with the length of 15-60 nm, breadth of 4-6 nm, and crystallite size of 86.32 nm. EDAX revealed that HA has Ca/P ratio of 1.63, indicating a nonstoichiometric apatite, whereas XRD analysis presented it as a pure monophasic hydroxyapatite powder. Fourier Transform Infrared (FTIR) spectroscopy indicated that the adsorption is due to the electrostatic interaction between the functional groups of the dye and those on the apatite surface. The maximum adsorption capacity (Q _max) of 127.9 mg g^-1 was obtained for the adsorption process, whereas the pseudo-first-order model with R ² > 0.99 best described the adsorption mechanism. Furthermore, the thermodynamic studies revealed that the adsorption process was exothermic and spontaneous in nature with ΔH and ΔS values of 120.79 kJ mol^-1 and 0.395 kJ mol^-1 K^-1, respectively. Thus, hydroxyapatite fabricated from the poultry waste of eggshell can be effectively utilized as an excellent nontoxic and cheap adsorbent for the removal of RY4 dye from aqueous medium.