Chitosan-based magnetic bioadsorbent beads from eucalyptus sawdust waste for the Direct Violet-51 dye remediation: Eco-friendly strategy and statistical optimization

Novel chitosan-magnetite-silica ternary capsules for highly efficient sequestration of reactive dyes from aqueous media

The main goal of this study was to synthesize novel Chitosan Magnetite Silica (CMS) adsorbent capsules and apply them for effective sequestration of anionic dyes Remazol brilliant blue 19 (RB-19) and Remazol golden yellow G -17 (RY-17) dye. The CMS capsules were synthesized and applied for batch study and evaluated using statistical modelling. Various analytical techniques, such as Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetry-Differential Thermal Analysis (TG-DTA), Brunauer-Emmett-Teller (BET) surface area analysis, UV-Vis Spectrophotometry, and Vibrating Sample Magnetometry (VSM), were employed to validate the formation of the CMS. Rough surface as shown by SEM analysis, presence of various functional groups as shown by FT-IR spectrum and presence Fe atoms in EDX spectrum are indication of formation of complete composite. The surface area of CMS recorded by BJH method was 39.05 m2 g-1 with pore capacity 0.259 cm3 g-1. According to IUPAC classification, class IV isotherm was observed for nitrogen adsorption-desorption curves. The specific magnetization of CMS was 4.28 emu g-1 indicating fare degree of magnetism making it easily separable using external magnet. Batch trails as well as screening experiments were conducted for the sequestration of RB and RY dyes. Dose 50 mg, interface time 60 min and solution pH of 3.0 depicted maximum removal efficacy of more than 95 % in both dyes even at high initial concentration of 200 mg L-1. The adsorption capacities for RB-19 dye and RY-17 dye were found to be 455.86 and 344.06 mg g-1 respectively in accordance with pseudo second order kinetics (R2 = 0.997 and 0.962 respectively) and Langmuir adsorption isotherm (R2 = 0.972 and 0.992 respectively) models. Six adsorption-desorption cycles were conducted for regeneration potential of CMS showcasing repeated usability after regeneration in alkaline medium. E-factor value of 0.04 depicted CMS capsules was sustainable in and eco-friendly with low waste generation.

A comparison of freeze- and air-dried chitosan salicylaldehyde/calcium oxide biocomposites for optimized removal of acid red 88 dye

Chitosan salicylaldehyde/calcium oxide nanoparticle (CS-SL/CaO) was synthesized by hydrothermal process and isolated via different drying processes, namely, air-drying (AD) and freeze-drying (FD). The physicochemical properties of freeze-dried CS-SL/CaO nanoparticle (CS-SL/CaO-FD) and air-dried CS-SL/CaO nanoparticle (CS-SL/CaO-AD) were compared. In particular, the adsorption properties reveal that the specific surface area of CS-SL/CaO-FD increased by ca. 6 times (BET SA = 7.28 m2/g) greater than CS-SL/CaO-FD (BET SA = 1.26 m2/g). Also, the adsorptive removal of acid red 88 dye (AR88) from aqueous media was optimized by employing the Box-Behnken design (BBD). The optimal adsorption conditions obtained from desirability functions test for the removal of AR88 dye employed a dosage of 0.09 g/100 mL of adsorbent dosage at a solution pH of 5.6 and 25 °C. The best AR88 dye removal was found for the adsorbents CS-SL/CaO-AD (38.2 %) and CS-SL/CaO-FD (86.1 %), which concur with differences in the adsorbent surface areas. Moreover, the adsorption kinetics and isotherm profiles for CS-SL/CaO-FD were described by the pseudo second order (PSO) and Temkin models, where the maximum adsorption capacity of AR88 by CS-SL/CaO-FD 175.4 was mg/g. These findings reveal the potential application of the CS-SL/CaO-FD towards removal of toxic cationic dye (AR88) from an aqueous environment.

Interfacial Adsorption Interactions of Dyes and Chitosan/Activated Carbon@Curcumin Derivatives in Single-Component and Binary Solutions

The remediation of wastewaters contaminated with dyes (discharged mainly from industry) is very important for preserving environmental quality and human health. In this study, a new composite chitosan (CS)-based adsorbent combined with activated carbon (AC) and curcumin (Cur) (abbreviated hereafter as CS/AC@Cur) in three different ratios (12.5%, 25%, and 50%) was synthesized for the removal of anionic [reactive black 5 (RB5)] and cationic [methylene blue (MB)] dyes in single-component or binary systems. The synthesized materials were completely characterized through Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller analysis, and X-ray diffraction. Specifically, a decrease in the surface area of CS/AC@ was observed with the addition of curcumin, from 163 to 18 m2/g, for all CS/AC@Cur derivatives. In terms of the adsorption results, the optimal derivative for the removal of both RB5 and MB was found to be CS/AC@Cur50%, providing 93% removal at pH 2.0 ± 0.1 for RB5 and 54% removal at the optimum pH of 9.0 ± 0.1 due to electrostatic attractions. The Elovich and pseudo-second-order kinetic model, with a correlation coefficient R2 of >0.98, better tailored the results, indicating that adsorption was controlled by chemisorption. In addition, the Sips (Langmuir-Freundlich) isotherm model fitted better to the results, with calculated capacities of 338 and 307 mg/g for RB5 and MB, respectively. The thermodynamic analysis showed a spontaneous and endothermic procedure, with chemisorption as the main mechanism. Reuse experiments showed that the removal efficiency was retained at high levels, while stability studies revealed that the adsorbent retains its structural integrity, even at extreme pH values. Finally, the adsorption of RB5 and MB in a mixed solution was investigated, providing a competitive effect between the anionic and cationic dyes.

A strategy for the efficient removal of acidic and basic dyes in wastewater by organophilic magadiite@alginate beads: Box-Behnken Design optimization

In this study, four adsorbents were developed: layered silicate magadiite material (mag), Hexadecyltrimethylammonium intercalated magadiite (HDTMA@mag), a cross-linked composite of sodium alginate and magadiite (ALG@mag) and a cross-linked composite of sodium alginate and HDTMA@magadiite (ALG@HDTMA@mag). The adsorbents were evaluated for their effectiveness in removing of Methylene Blue (MB) and Eriochrome Black T (EBT) dyes. The prepared adsorbents were characterized using SEM, XRD, FTIR, and zeta potential measurements. Kinetic modeling results indicated that both film diffusion and intraparticle diffusion are useful as rate-determining processes in adsorption for all adsorbents. For both dyes, the Langmuir isotherm model provided a good correlation with the adsorption equilibrium data. ANOVA analysis for the best adsorbent (ALG@HDTMA@mag beads) revealed that MB removal was significantly influenced by the positive individual effects of contact time and ALG@HDTMA@mag dose. However, the individual effect of MB concentration exhibited an antagonistic effect throughout the adsorption process. The optimal parameters for achieving an adsorption capacity of 118.54 mg/g were a dye concentration of 60 ppm, a contact period of 1800 min, and an ALG@HDTMA@mag dose of 50 mg.

Cellulose-citric acid-chitosan@metal sulfide nanocomposites: Methyl orange dye removal and antibacterial activity

In this study, to develop efficient adsorbents in removing water pollution, new cellulose-citric acid-chitosan@metal sulfide nanocomposites (CL-CA-CS@NiS and CL-CA-CS@CuS) were synthesized by one-pot reaction at mild conditions and characterized using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), Energy Dispersive X-ray (EDX) and Brunauer-Emmett-Teller (BET) isotherm. The results of characterization techniques confirm that the desired compounds have been successfully synthesized. The as-prepared composites were applied for the removal of methyl orange (MO) dye from aqueous solutions using a batch technique, and the effect of key factors such as initial pH, shaking time, MO concentration, temperature and adsorbent dose were investigated and discussed. Adsorption results exhibited positive impact of temperature, shaking time and adsorbent dose on the MO removal percent. The MO removal percent has been increased over a wide range of pH from 2 (27.6 %) to 6 (98.8 %). Also, almost being constant over a wide range of MO concentration (10-70 mg/L). The results demonstrated that the maximum removal percentage of MO dye (98.9 % and 93.4 % using CL-CA-CS@NiS and CL-CA-CS@CuS, respectively) was achieved under the conditions of pH 6, shaking time of 120 min, adsorbent dose of 0.02 g, MO concentration of 70 mg/L and temperature of 35 °C. The pseudo-second-order (PSO) and Langmuir models demonstrated the best fit to the kinetic and equilibrium data. Also, the thermodynamic results showed that the MO removal process is endothermic and spontaneous in nature. The MO adsorption can be happened by different electrostatic attraction, n-π and π-π stacking and also hydrogen bonding interaction. In addition, antibacterial activity of CL-CA-CS@NiS and CL-CA-CS@CuS nanocomposites exhibited a superior efficiency against S. aureus.

Insights into adsorption performance and mechanism of chitosan-bentonite biocomposites for removal of imazethapyr and imazamox

In the present study, chitosan-bentonite biocomposites were synthesised by ultrasonication, characterized using spectral techniques and assessed for their effectiveness in removing imazethapyr and imazamox from aqueous solution. The response surface methodology based box behnken design was utilized to generate optimum conditions viz. pH (1 to 9), adsorbent dose (0.01 to 1.0 g), contact time (0.5 to 48 h) and temperature (15 to 55 °C) for adsorption of herbicides on biocomposites. Based on model predictions, 60.4 to 91.5 % of imazethapyr and 31.7 to 46.4 % of imazamox was efficiently removed under optimal conditions. Adsorption data exhibited a strong fit to pseudo-second-order kinetic (R2 > 0.987) and Freundlich isotherm (R2 > 0.979). The adsorption capacity ranged from 3.88 to 112 μg1-ng-1mLn and order of adsorption was: low molecular weight chitosan-bentonite> medium molecular weight chitosan-bentonite> high molecular weight chitosan-bentonite> bentonite. Thermodynamic experiments suggested a spontaneous, exothermic process, reducing the system randomness during adsorption. Desorption experiments revealed successful desorption ranging from 91.5 to 97.0 % using 0.1 M NaOH. The adsorption mechanism was dominated by synergistic electrostatic interactions and hydrogen bonding. These results collectively indicated the potential environmental remediation application of chitosan-bentonite biocomposites to adsorb imazethapyr and imazamox from wastewaters.