Lemongrass (Cymbopogon nardus) leaves biowaste as an effective and low-cost adsorbent for methylene blue dyes removal: isotherms, kinetics, and thermodynamics studies

Preparation and characterization of biopolymer-based adsorbents and their application for methylene blue removal from wastewater

In the present study, four biopolymer-based materials consisting of native corn starch (CS), phosphate corn starch (PS), starch nanocrystals (SNCs), and phosphate corn starch nanocrystals (PSNCs) were synthesized and used for methylene blue (MB) removal as a function of various parameters, including initial MB concentration (C0, 10-500 mg L-1), adsorbent dosage (Cs, 0.02-0.15 g), contact time (t, 5-15 min), solution pH (2-11), and temperature (25-45 °C). The removal percentage of MB increased dramatically upon increasing the biopolymer dosage, temperature, and pH; while it decreased upon increasing the initial MB concentration. The adsorption behavior of biopolymer-based materials towards MB was found to be accurately described by the pseudo-second-order kinetic and Langmuir isotherm models. According to the Langmuir model, the maximum adsorption capacities of the adsorbents were ordered as follows: PSNCs (88.53 mg g-1) > SNCs (79.55 mg g-1) > PS (73.17 mg g-1) > CS (63.02 mg g-1). PSNCs was able to remove 96.8% and 76.5% of 20 mg L-1 MB in greywater and petrochemical wastewater, respectively, at an optimum pH of 9 and retained 86.42% of its usability even after five adsorption-desorption cycles. The analysis of the surface charge of the adsorbents before and after MB adsorption, combined with the FTIR spectrum of MB-saturated biopolymer-based materials, provided evidence that electrostatic interactions was the primary mechanism involved in the adsorption of MB. Meanwhile, hydrogen bonding and π-π interactions were found to have a minor contribution to the adsorption process. Based on the results, it can be inferred that PSNCs has promising potential as an adsorbent for the treatment of MB-containing wastewater, owing to its exceptional properties, which include high adsorption capacity, low cost, and applicability for multiple reuses.

Adsorption-photocatalytic degradation abilities of γ-irradiated chitosan-ZnO-AgNP composite for organic dye removal and antibacterial activity

We synthesized a γ-irradiated chitosan-ZnO-AgNPs (ICZA) composite by using a simple hydrogels method. We evaluated its adsorption/photocatalytic degradation abilities for the removal of an organic dye and its antibacterial activity. The XRD, SEM, TEM, EDS, and FTIR techniques were used to characterize the obtained samples. Based on the adsorption and degradation of methylene blue (MB) in the dark and under UV light irradiation, the adsorption and the photocatalytic activity of the as-obtained samples were evaluated. The optimum conditions for synthesizing the composite were as follows: contact time of 210 min, a dosage of 2 g/L, MB concentration of 40 mg/L, and a solution pH of 8.0. The ICZA had a high adsorption capacity, which was suitable for removing MB from the aqueous solutions; it showed a maximum adsorption capacity (qm) of 92.59 mg/g. The fit of the adsorption isotherms with the Langmuir model was satisfactory. The photocatalytic degradation ability of the composite was also better than that of other catalysts in the presence of UV light, with an apparent rate constant (kapp) of 3.08 × 10-2. The synthesized ICZA also showed good antibacterial activity against Staphylococcus aureus, with a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) of 12.5 g/mL and 50 g/mL under light-incubation and dark-incubation conditions. Finally, we discussed the hypothesized mechanism of the adsorption/photocatalytic activity and antibacterial activity of the ICZA composite in this study.

Magnetic Fe3O4 nanoparticles loaded guava leaves powder impregnated into calcium alginate hydrogel beads (Fe3O4-GLP@CAB) for efficient removal of methylene blue dye from aqueous environment: Synthesis, characterization, and its adsorption performance

In the present work, a novel Fe3O4-GLP@CAB was successfully synthesized via a co-precipitation procedure and applied for the removal of methylene blue (MB) from aqueous environment. The structural and physicochemical characteristics of the as-prepared materials were explored using a variety of characterization methods, including pHPZC, XRD, VSM, FE-SEM/EDX, BJH/BET, and FTIR. The effects of several experimental factors on the uptake of MB using Fe3O4-GLP@CAB were examined through batch experiments. The highest MB dye removal efficiency of Fe3O4-GLP@CAB was obtained to be 95.2 % at pH 10.0. Adsorption equilibrium isotherm data at different temperatures showed an excellent agreement with the Langmuir model. The adsorption uptake of MB onto Fe3O4-GLP@CAB was determined as 136.7 mg/g at 298 K. The kinetic data were well-fitted by the pseudo-first-order model, indicating that physisorption mainly controlled it. Several thermodynamic variables derived from adsorption data, like as ΔGo, ΔSo, ΔHo, and Ea, accounted for a favourable, spontaneous, exothermic, and physisorption process. Without seeing a substantial decline in adsorptive performance, the Fe3O4-GLP@CAB was employed for five regeneration cycles. Because they can be readily separated from wastewater after treatment, the synthesized Fe3O4-GLP@CAB was thus regarded as a highly recyclable and effective adsorbent for MB dye.