Magnetic silica coated iron carbide/alginate beads: Synthesis and application for adsorption of Cu (II) from aqueous solutions

Fabrication of nitrogen-doped carbon dots biomass composite hydrogel for adsorption of Cu (II) in wastewater or soil and DFT simulation for adsorption mechanism

With the increase of Cu (II) content, its bioaccumulation becomes a potential pollution to the environment. It is necessary to design an economical and efficient material to remove Cu (II) without causing other environmental hazards. A novel material of alginate composite bead (ALG@NCDs) was synthesized by embedding N-doped carbon dots into pure alginate bead for the adsorption of Cu (II) from wastewater and contaminated soil. The initial concentration, the amount of adsorbent, temperature, adsorption time, and pH value were optimized for the adsorption of Cu (II). According to the Langmuir isothermal adsorption model, the maximum adsorption amount of the material to Cu (II) was 152.44 mg/g. The results of selective adsorption showed that ALG@NCDs had higher affinity to Cu (II) than to Pb (II), Co (II), Ni (II), and Zn (II). After five adsorption-desorption experiment, adsorption capacity of the ALG@NCDs was kept 89% of the initial adsorption capacity. Its Cu (II) adsorption mechanism was studied by density functional theory calculations. In addition, the material could effectively adsorb Cu (II) and release the phytonutrient Ca (II) simultaneously when applied to actual wastewater and soil. The fabricated ALG@NCDs would be a promising material for the adsorption of Cu (II) from wastewater or soil.

Continuous treatment of highly concentrated tannery wastewater using novel porous composite beads: Central composite design optimization study

This present study depicts the successful employment of fixed-bed column for total chromium removal from tannery wastewater in dynamic mode using sodium alginate-powdered marble beads (SA-Marble) as adsorbent. The SA-Marble composite beads prepared were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Brunauer, Emmett and Teller (BET) method. The adsorption process performance of this bio-sorbent was examined in batches and columns for real effluent (tannery wastewater). After 90 min, the total chromium removal efficiency could be kept above 90% in the batch experiment. The adsorption kinetics fit better with the pseudo-second-order model, indicating the chemisorption process and the adsorption capacity of about 67.74 mg g-1 at 293 K (C0 = 7100 mg L-1) was obtained. Additionally, dynamic experiments indicate that the total chromium removal efficiency could be maintained above 90% after 120 min at 293 K and 60 min at 318 and 333 K; it's an endothermic but rapid process. The effects of two adsorption variables (Temperature and time) were investigated using central composite design (CCD), which is a subset of response surface methodology (total Cr, COD, sulfate, and total phosphorus percentage removal). This work paves a new avenue for synthesizing SA-Marble composite beads and provides an adsorption efficiency of total chromium removal from tannery wastewater.

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An innovative approach to synthesize graft copolymerized acetylacetone chitosan/surface functionalized alginate/rutile for efficient Ni(II) uptake from aqueous medium

In this study, an innovative approach is followed to synthesize graft copolymerized chitosan with acetylacetone (AA-g-CS) through free-radical induced grafting. Afterwards, AA-g-CS and rutile have been intercalated uniformly into amino carbamate alginate matrix to prepare its biocomposite hydrogel beads of improved mechanical strength having different mass ratio i.e., 5.0 %, 10.0 % 15.0 % and 20.0 % w/w. Biocomposites have been thoroughly characterized through FTIR, SEM and EDX analysis. Isothermal sorption data showed good fit with Freundlich model as conferred from regression coefficient (R² ≈ 0.99). Kinetic parameters were evaluated through non-linear (NL) fitting of different kinetic models. Experimental kinetic data exhibited close agreement to quasi-second order kinetic model (R² ≈ 0.99) which reveals that chelation between heterogeneous grafted ligands and Ni(II) is occurring through complexation. Thermodynamic parameters were evaluated at different temperatures to observe the sorption mechanism. The negative values of ΔG° (-22.94, -23.56, -24.35 and - 24.94 kJ/mol), positive ΔH° (11.87 kJ/mol) and ΔS° (0.12 kJ/molK^-1) values indicated that the removal process is spontaneous and endothermic. The maximum monolayer sorption capacity (q_m) was figured as 246.41 mg/g at 298 K and pH = 6.0. Hence, 3AA-g-CS/TiO₂ could be better candidate for economic recovery of Ni(II) ions from waste effluents.

Adsorption of Copper and Arsenic from Water Using a Semi-Interpenetrating Polymer Network Based on Alginate and Chitosan

New biobased hydrogels were prepared via a semi-interpenetrating polymer network (semi-IPN) using polyacrylamide/chitosan (PAAM/chitosan) hydrogel for the adsorption of As(V) or poly acrylic acid/alginate (PAA/alginate) hydrogel for the adsorption of Cu(II). Both systems were crosslinked using N,N'-methylenebisacrylamide as the crosslinker and ammonium persulfate as the initiating agent. The hydrogels were characterized by SEM, Z-potential, and FTIR. Their performance was studied under different variables, such as the biopolymer effect, adsorbent dose, pH, contact time, and concentration of metal ions. The characterization of hydrogels revealed the morphology of the material, with and without biopolymers. In both cases, the added biopolymer provided porosity and cavities' formation, which improved the removal capacity. The Z-potential informed the surface charge of hydrogels, and the addition of biopolymers modified it, which explains the further metal removal ability. The FTIR spectra showed the functional groups of the hydrogels, confirming its chemical structure. In addition, the adsorption results showed that PAAM/chitosan can efficiently remove arsenic, reaching a capacity of 17.8 mg/g at pH 5.0, and it can also be regenerated by HNO₃ for six cycles. On the other hand, copper-ion absorption was studied on PAA/alginate, which can remove with an adsorption capacity of 63.59 mg/g at pH 4.0, and the results indicate that it can also be regenerated by HNO₃ for five cycles.

Effective biosorption of Cu(II) using hybrid biocomposite based on N-maleated chitosan/calcium alginate/titania: Equilibrium sorption, kinetic and thermodynamic studies

In this research work, a hybrid biocomposite based on N-maleated chitosan, amino-thiocarbamate functionalised calcium alginate and anhydrous Titania nanoparticles (NMC-MCA-TiO₂) was fabricated. The study involves the one pot facile synthesis of N-maleated chitosan and amino-thiocarbamate functionalised alginate under moderate conditions. Sorbent was conditioned in the form of hydrogel beads and characterized through FT-IR and SEM analysis. Newly grafted functional groups could act as potential chelating sites for enhanced Cu(II) sorption. Modified biopolymers were organo-functionalised which provided excellent support for immobilization of Titania nanoparticles (TiO₂) as inorganic filler. Kinetic data illustrated the manifestation of intrinsic chemisorption instead of simple bulk/film diffusion. Equilibrium sorption data fitted well with Freundlich adsorption model (R² ≈ 0.99) which designated the heterogeneous nature of sorbent. Maximum sorption capacity of biosorbent was found 192 mg/g at 298 K and pH = 6.0. Standard Gibbs free energy change ∆G^o (-21.53, -21.97, and - 22.42 kJ/mol), standard enthalpy change ∆H^o (5.12 kJ/mol) and standard entropy change ∆S^o (0.09 kJ/mol K^-1) values suggested that the sorption process to be spontaneous and endothermic. The sorbent 3NMC-MCA-TiO₂ could be competitive candidate for economical and rapid adsorptive removal of Cu(II) from dilute contaminated liquids.

Synthesis of hybrid biosorbent based on 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and organo-functionalized calcium alginate for adsorptive removal of Cu(II)

The present study is based on the synthesis of a novel hybrid biosorbent using 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and amino-thiocarbamate moiety functionalized sodium alginate (CDTA-CS/TSC-CA). The fabricated sorbent was employed to investigate the efficient recovery of Cu(II) from aqueous media. CDTA-CS/TSC-CA was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Analysis confirmed the successful modification of both biopolymers and subsequent loading of Cu(II) ions. CDTA-CS/TSC-CA was casted in the form of hydrogel beads having different CDTA-CS to TSC-CA mass ratios i.e., 10.0-40.0% by mass. The hydrogel beads 4CDTA-CS/TSC-CA with CDTA-CS/TSC-CA mass ratio of 40.0% was found most effective for copper sorption. Equilibrium sorption results showed that initial concentration of copper, medium pH, contact time, sorbent dosage and temperature influenced the sorption capacity (q_e). Rate of sorption data was interpreted using different kinetic models and found best fitted with pseudo second order rate expression (R² ≈ 0.99), illustrating that the rate determining step includes the electron density transfer from sorbent coordination sites to central copper ions. Crank's RIDE equation and Elovich chemisorption model (ECM) revealed the presence of two sorption phases, initially rapid sorption followed by comparatively a slow uptake. Equilibrium sorption data was well depicted by Langmuir model and maximum monolayer adsorption capacity (q_m) was computed as 276.53 mg·g^-1 at 298 K. Standard Gibbs free energy change, ∆G° (-19.99, -20.18 and -20.36 kJ/ mol), standard enthalpy change, ∆H° (-8.95 kJmol) and standard entropy change, ∆S° (0.04 kJ/mol K^-1) values suggested that the adsorption process is spontaneous and exothermic. Hence, 4CDTA-CS/TSC-CA was found efficient biosorbent for copper removal from its dilute effluents.

Enhanced Cu(II) adsorption using sodium trimetaphosphate-modified cellulose beads: equilibrium, kinetics, adsorption mechanisms, and reusability

The current study is focused on the simple synthesis of two novel biosorbent beads: BASB/STMP and CNFB/STMP, derived respectively from bleached almond shell (BAS) and cellulose nanofiber from almond shell (CNF) by means of chemical crosslinking with sodium trimetaphosphate (STMP). These biosorbents were thoroughly characterized in terms of structure (FTIR), texture (N₂ adsorption-desorption), thermal behavior (TGA/DTG), morphology (SEM), and surface properties (XPS). The adsorption kinetics of Cu(II) ions onto BASB/STMP and CNFB/STMP materials proved the chemisorption interaction between Cu(II) ions and the STMP functionalized beads. The BASB/STMP equilibrium data were successfully described by the Redlich-Peterson model and the CNFB/STMP data by the Sips model which disclosed maximum adsorption capacities of 141.44 mg g^-1 and 147.90 mg g^-1, respectively. Furthermore, the BASB/STMP bioadsorbent offers easy regeneration and better reusability with high efficiency (> 83%). This study sheds light on the preparation of low-cost adsorbents for wastewater treatment in order to improve the competitiveness and eco-friendliness of agrowaste-based processes.

Fabrication of in situ ZIF-67 grown on alginate hydrogels and its application for enhancing Cu (II) adsorption from aqueous solutions

Synthesizing high uniform metal-organic frameworks grown on natural biomass such as sodium alginate (ALG), which can efficiently remove metal ions from aqueous solution, is a challenging project. A simple and eco-friendly method of preparing ALG@ZIF-67 hydrogels by in situ synthesis of ZIF-67 onto ALG hydrogels was established. Combining the virtues of ALG with abundant hydroxyl and carboxyl groups and ZIF-67 with excellent porous structure, the obtained ALG@ZIF-67 hydrogels have excellent adsorption for Cu²⁺ (153.63 mg/g), which was much higher than that of pure ALG hydrogels (111.79 mg/g). The methodology showed that the adsorption process was in accord with the Langmuir isotherm adsorption model (R² = 0.9972) and pseudo-second-order kinetic model (R² = 0.9822). The thermodynamic experiments demonstrated that Cu (II) was absorbed by hydrogel with an endothermic and spontaneous process. The competitive adsorption experiment results of ALG@ZIF-67 hydrogel indicated that the absorption capacity of Cu (II) was higher than that of Cd (II), Ni (II), Zn (II) and Mn (II). Moreover, the ALG@ZIF-67 hydrogels still had excellent reusability after five adsorption-desorption cycles. The results indicated that the ALG@ZIF-67 hydrogels had the advantages of low cost, easy preparation, and environment friendly.

Hydroxypropyl-β-cyclodextrin-polyurethane/graphene oxide magnetic nanoconjugates as effective adsorbent for chromium and lead ions

In this work, hydroxypropyl-β-cyclodextrin-polyurethane magnetic nanoconjugates/reduced graphene oxide (HPMNPU/GO) supramolecules were prepared. The adsorbent was characterized using FTIR and SEM. The adsorbent was evaluated for its efficiency to remove Cr⁶⁺ and Pb²⁺ from aqueous solutions through batch adsorption studies following a Definitive Screening Design (DSD). Effects of solution pH, contact time, adsorbent dosage, initial metal concentration, ionic strength, GO/NC ratio and temperature on Cr ⁶⁺ and Pb ²⁺ adsorption were investigated. Optimization of the adsorption process was done using a desirability function of the Design Expert V11 software. A good agreement between experimental and predicted data proved the efficiency of this model for prediction of real optimum point. The batch experiments implied that the pseudo-second-order model (lowest sum of square error (SSE) values and correlation coefficients (R²) > 0.999) was better to describe the adsorption kinetics of Cr⁶⁺ and Pb²⁺ onto the HPMNPU/GO.

Eco-friendly floatable foam hydrogel for the adsorption of heavy metal ions and use of the generated waste for the catalytic reduction of organic dyes

Benefiting from their three-dimensional network structure and various functional groups, hydrogels have emerged as efficient adsorbents for the removal of heavy metal ions from wastewater. However, the obvious drawbacks of hydrogels such as generation of toxic secondary waste after adsorption and difficulty in their separation and collection limit their practical application in wastewater treatment. Herein, we introduced a facile strategy of combining mechanical frothing and in situ radical polymerization to prepare a floatable porous foam hydrogel, which not only efficiently removed Cu2+ from water, but also could be easily collected. After adsorption, to avoid the generation of secondary toxic waste, a sustainable strategy of turning the waste into useful materials was introduced. The waste of the Cu2+_ adsorbed hydrogel was processed using NaBH4 solution to obtain a Cu nanoparticle (Cu NP)-loaded composite hydrogel, which was further employed as a catalyst for the catalytic reduction of organic dyes. Thus, this work established a convenient and sustainable strategy for the preparation of an eco-friendly floatable foam hydrogel for the efficient removal of heavy metal ions such as Cu2+ from water and turning the generated waste into useful materials, which is a concept envisaged to be applicable to other heavy metal ion-adsorbed hydrogel systems and will efficiently avoid unwanted secondary pollution.

Efficient Separation of Heavy Metals by Magnetic Nanostructured Beads

This study reports the ability of magnetic alginate activated carbon (MAAC) beads to remove Cd(II), Hg(II), and Ni(II) from water in a mono-metal and ternary system. The adsorption capacity of the MAAC beads was highest in the mono-metal system. The removal efficiency of such metal ions falls in the range of 20–80% and it followed the order Cd(II) > Ni(II) > Hg(II). The model that best fitted in the ternary system was the Freundlich isotherm, while in the mono-system it was the Langmuir isotherm. The maximum Cd(II), Hg(II), and Ni(II) adsorption capacities calculated from the Freundlich isotherm in the mono-metal system were 7.09, 5.08, and 4.82 (mg/g) (mg/L)1/n, respectively. Lower adsorption capacity was observed in the ternary system due to the competition of metal ions for available adsorption sites. Desorption and reusability experiments demonstrated the MAAC beads could be used for at least five consecutive adsorption/desorption cycles. These findings suggest the practical use of the MAAC beads as efficient adsorbent for the removal of heavy metals from wastewater.

Response surface methodology based on central composite design for simultaneous adsorption of rare earth elements using nanoporous calcium alginate/carboxymethyl chitosan microbiocomposite powder containing Ni0.2Zn0.2Fe2.6O4 magnetic nanoparticles: Batch and column studies

In this research paper, the utilization of the magnetic calcium alginate/carboxymethyl chitosan/Ni_0.2Zn_0.2Fe_2.6O₄ (CA/CMC/Ni_0.2Zn_0.2Fe_2.6O₄) was investigated for the simultaneous aqueous adsorption of Nd (III), Tb (III), and Dy (III). The magnetic products were characterized by FE-SEM, EDX, XRD, FT-IR, TGA, and VSM techniques. The saturation magnetization value for Ni_0.2Zn_0.2Fe_2.6O₄ and CA/CMC/Ni_0.2Zn_0.2Fe_2.6O₄ was found to be 45.87 and 14.14 emu/g, respectively. Using RSM, a quadratic polynomial equation was obtained to predict the adsorption efficiency of each ion. Under the conditions of pH = 5.5, adsorbent dosage of 0.1 g, initial concentration of 30 mg/L, and contact time of 53 min predicted by RSM, the adsorption efficiencies of Nd (III), Tb (III), and Dy (III) were respectively 95.72, 96.17, and 99.44%. The isotherm and kinetic data were respectively fitted well with Freundlich and pseudo-second-order (PSO) models. The desorption of the loaded ions was effectively carried out by 0.2 M HNO₃, and the adsorbent was consecutively utilized with 2.54, 1.63, and 1.16% decrease in adsorption efficiency for Nd (III), Tb (III), and Dy (III), respectively, after the forth cycle. Additionally, the adsorption behavior of the CA/CMC/Ni_0.2Zn_0.2Fe_2.6O₄ towards Nd (III), Tb (III), and Dy (III) was studied by using a fixed-bed column technique.

High-performance two-dimensional montmorillonite supported-poly(acrylamide-co-acrylic acid) hydrogel for dye removal

High-performance two-dimensional montmorillonite supported-poly (acrylamide-co-acrylic acid) hydrogel for dye removal was investigated. Montmorillonite cooperated with acrylamide and acrylic acid via polymerization, hydrogen-bond, amidation and electrostatic interactions to form the three-dimensional reticular-structured hydrogel with the free entrance for macromolecules. Adsorption tests revealed that the efficient removal (97%) for methylene blue at high concentration (200 mg/L) could be achieved via a small dose of hydrogel (0.5 g/L) within a short time (20 min). The excellent adsorption performance was profited from the electronegative surface and fully exposed reaction sites of two-dimensional montmorillonite, which could save the treatment cost and promote the removal effect compared with the conventional adsorbents. The adsorption process of methylene blue onto hydrogel could be fitted by both the pseudo-first-order and pseudo-second-order kinetics models, and the adsorption isotherm corresponded to the Sips model. The mechanism analysis based on Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements illustrated that the reaction between carboxyl groups and methylene blue molecules as well as the cation-exchange enabled the hydrogel performing extraordinary adsorption efficiency.