Facile fabrication of gelatin/bentonite composite beads for tunable removal of anionic and cationic dyes

Synthesis of magnetic bentonite-gelatin hydrogel beads and their applications in Cu2+ capturing

Heavy metal ions that exist in groundwater and farmland jeopardize the ecological environment and are very difficult to remove because of the complicated actual environment. Raw bentonite-gelatin beads (RB-GT) and magnetic bentonite-gelatin beads (MB-GT) synthesized in this work would be an appropriate tool to solve this problem. Those beads are synthesized by a facile hybrid injection method. Their adsorption behaviors on Cu(II) ions were systematically investigated using the batch adsorption method. The beads were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption isotherm and adsorption kinetic study showed that the Cu2+ adsorption by MB-GT beads fitted the Langmuir model and the pseudo-second model. The adsorption maximum capacities reached 192.5 mg/g and 236.5 mg/g with Cu concentration of 1000 mg/L for RB-GT and MB-GT beads, respectively. The competitive adsorption with other heavy metal ions (Ni(II), Pd(II) and Cd(II)) were compared. The adsorption of Cu(II) mechanisms is also further discussed.

Facile fabrication of a broad-spectrum starch/poly(α-l-lysine) hydrogel adsorbent with thermal/pH-sensitive IPN structure through simultaneous dual-click strategy

A thermal/pH-sensitive interpenetrating network (IPN) hydrogel was prepared facilely from starch and poly(α-l-lysine) through amino-anhydride and azide-alkyne double-click reactions in one pot. The synthesized polymers and hydrogels were systematically characterized using different analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rheometer. The preparation conditions of the IPN hydrogel were optimized via one-factor experiments. Experimental results indicated the IPN hydrogel possessed pH and temperature sensitivity. Effect of different parameters (pH, contact time, adsorbent dosage, initial concentration, ionic strength, and temperature) on adsorption behavior were investigated in monocomponent system with cationic methylene blue (MB) and anionic Eosin Y (EY) as model pollutants. The results indicated that the adsorption process of the IPN hydrogel for MB and EY followed pseudo-second-order kinetics. The adsorption data for MB and EY fitted well with the Langmuir isotherm model, indicating monolayer chemisorption. The good adsorption performance was due to various active functional groups (-COOH, -OH, -NH₂, etc.) in the IPN hydrogel. The strategy described here opens up a new way for preparing IPN hydrogel. The as-prepared hydrogel exhibits potential application and bright prospects as an adsorbent in wastewater treatment.

Hectorite-CTAB-alginate composite beads for water treatment: kinetic, isothermal and thermodynamic studies

Encapsulation of hectorite-modified CTAB with Ca-alginate formed reusable adsorbent beads for wastewater treatment. The thermogravimetric analysis (TGA) investigation indicated excellent thermal stability results for BHec-40 compared to Hec-40. Although the mesoporous surface area of BHec-40 decreased to 79.74 m2 g-1 compared to 224.21 m2 g-1 for Hec-40, the hectorite-CTAB-alginate beads showed high adsorption capacity and stability for methyl orange (MO) adsorption with more than 60% removal after five adsorption-desorption cycles. The influence of pH (3-11), temperature (30, 40, and 50 °C), initial concentration (50-400 mg L-1), and contact time were studied to obtain the kinetics and thermodynamics of adsorption. The outcomes revealed a maximum monolayer adsorption capacity of 117.71 mg g-1 for BHec-40. The kinetics of adsorption demonstrated the suitability of using the pseudo-first-order kinetic model, while the equilibrium adsorption data follows the Langmuir isotherm. Thermodynamic analysis indicates physisorption of MO onto BHec-40. BHec-40 improves the reusability as an adsorbent for the removal of anionic dyes from aqueous media.

Adsorptive removal of crystal violet from wastewater using sodium alginate-gelatin-montmorillonite ternary composite microbeads

In this study, the performance of the montmorillonite-filled sodium alginate/gelatin (SA-GEL-MMT) ternary biocomposite microbeads on the adsorptive removal of crystal violet (CV) dye was investigated. Firstly, the composites containing different weight ratios of MMT such as 10 %, 15 %, and 20 % were prepared. The composite beads were cross-linked using a calcium chloride (3%wt/v) solution. To determine the optimum sorption conditions the studies were performed at different parameters namely temperature, pH, contact time, sorbent dose, and dye concentration. From the sorption studies, the maximum capacity of the microbeads was found as 1000.0 mg/g whereas the maximum removal of the dye was 92.1 % at pH = 7 and a temperature of 25 °C. Additionally, the kinetic studies showed that the sorption of the dye followed the pseudo-second-order kinetics. Moreover, the adsorptive removal of the dye occurs spontaneously. This study suggests that the use of SA-GEL-MMT can be highly effective and reusable for the treatment of wastewater.

Efficient Congo Red Removal Using Porous Cellulose/Gelatin/Sepiolite Gel Beads: Assembly, Characterization, and Adsorption Mechanism

Porous sustainable cellulose/gelatin/sepiolite gel beads were fabricated via an efficient 'hydrophilic assembly-floating droplet' two-step method to remove Congo red (CR) from wastewater. The beads comprised microcrystalline cellulose and gelatin, forming a dual network framework, and sepiolite, which acted as a functional component to reinforce the network. The as-prepared gel beads were characterized using FTIR, SEM, XRD, and TGA, with the results indicating a highly porous structure that was also thermally stable. A batch adsorption experiment for CR was performed and evaluated as a function of pH, sepiolite addition, contact time, temperature, and initial concentration. The kinetics and isotherm data obtained were in agreement with the pseudo-second-order kinetic model and the Langmuir isotherm, with a maximum monolayer capacity of 279.3 mg·g^-1 for CR at 303 K. Moreover, thermodynamic analysis demonstrated the spontaneous and endothermic nature of the dye uptake. Importantly, even when subjected to five regeneration cycles, the gel beads retained 87% of their original adsorption value, suggesting their suitability as an efficient and reusable material for dye wastewater treatments.

Facile synthesis of Zr4+ incorporated chitosan/gelatin composite for the sequestration of Chromium(VI) and fluoride from water

The development of industrialization and agricultural activities have carried various negative impacts to living organisms in recent decades and also, the frequent problem of inorganic pollution have been environmental anxiety to the community. Among these, Cr⁶⁺ and F^- are priority poisonous pollutants from many industries. In this work, we present a low-cost synthesis procedure to obtain biocompatible zirconium incorporated chitosan-gelatin composite (CS-Zr-GEL) were fabricated and explored for the adsorptive removal of toxic Cr⁶⁺ and F^- from water. The adsorption mechanism of toxic Cr⁶⁺ and F^- was done by batch mode as a function of contact time, solution pH and co-existing ions. The obtained materials were extensively studied by several physico-chemical techniques to access their properties by X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analysis. Additionally, the fabricated adsorbent is highly dependent on solution pH. The kinetic and isotherm data were fitted using pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity for CS-Zr-GEL is 138.89 and 12.13 mg/g at 323K for Cr⁶⁺ and F^- respectively. These findings demonstrate that the CS-Zr-GEL adsorbent represents a promising candidate that would have a practical influence on water/wastewater treatments.

Electrospinning of multifunctional cellulose acetate membrane and its adsorption properties for ionic dyes

Electrospinning of cellulose acetate with appropriated solvent system is the most straightforward method for fabricating micro- and nanofibers. To simultaneously and effectively remove both cationic and anionic dyes, a novel cost-effective multifunctional cellulose acetate (CA) fibers membrane was prepared by electrospinning followed by deacetylation, carboxymethylation and polydopamine (PDA) coating. The adsorption properties of PDA@DCA-COOH membrane were evaluated with methylene blue (MB) and Congo red (CR) as the ionic representatives for their removal. The results indicated that carboxyl, hydroxyl and amine multifunctional groups had been successfully grafted on the surface of the nanofibers with the maximum adsorption capacities of 69.89 and 67.31 mg g-1 for MB and CR, respectively, in the individual systems. The effect of co-existed dyes, inorganic salts and surfactants on the uptake of MB and CR in the simulated real complex system was strongly depended on the initial pH and ionic strength of the solution. The excellent adsorption capacities of the composite membrane were due to strong electrostatic attraction through the abundant functional groups on PDA@DCA-COOH surface. Based on its excellent recycling performance and adsorption property, PDA@DCA-COOH has a promising potential as an effective adsorbent in water treatment.

A multifunctional gelatine-quaternary ammonium copolymer: An efficient material for reducing dye emission in leather tanning process by superior anionic dye adsorption

Leather wastewater is one of the most polluting industrial emissions. The efficiency of wastewater remediation is limited by its complex composition. Herein, a novel strategy for designing modified gelatine with higher degree of quaternization (MG-2) is presented. The higher degree of quaternization allows sufficient adsorption of dyes in the tanning process. It is an in situ, environmentally friendly, and innovative strategy to limit dye emissions and can circumvent the subsequent waste management. Dyes such as Direct Purple N and Acid Black 24 could be adsorbed completely within 5 min by the MG-2 film formed from MG-2 solution. In addition, a remarkable efficiency in removing Acid Red 73, Golden Orange G, and Acid Orange II (>96.1% removal rates) was achieved within 30 min. The adsorption equilibrium data suggested that the adsorption capacity was positively correlated to the concentration of MG-2. When Acid Orange II and MG-2 were used in the industrial re-tanning process, the residual dye concentration in wastewater was only 23.1 mg L^-1, indicating that MG-2 is a promising re-tanning agent for adsorbing dyes in the leather tanning process.