Enhanced adsorption of Cr(VI), Ni(II) ions from aqueous solution using modified Eichhornia crassipes and Lemna minor

Cellulose Nanocrystals and Lignin Nanoparticles Extraction from Lemna minor L.: Acid Hydrolysis of Bleached and Ionic Liquid-Treated Biomass

Using biomass to develop and obtain environmentally friendly and industrially applicable biomaterials is increasingly attracting global interest. Herein, cellulose nanocrystals (CNCs) and lignin nanoparticles (LNPs) were extracted from Lemna minor L., a freshwater free-floating aquatic species commonly called duckweed. To obtain CNCs and LNPs, two different procedures and biomass treatment processes based on bleaching or on the use of an ionic liquid composed of triethylammonium and sulfuric acid ([TEA][HSO4]), followed by acid hydrolysis, were carried out. Then, the effects of these treatments in terms of the thermal, morphological, and chemical properties of the CNCs and LNPs were assessed. The resulting nanostructured materials were characterized by using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the two methodologies applied resulted in both CNCs and LNPs. However, the bleaching-based treatment produced CNCs with a rod-like shape, length of 100-300 nm and width in the range of 10-30 nm, and higher purity than those obtained with ILs that were spherical in shape. In contrast, regarding lignin, IL made it possible to obtain spherical nanoparticles, as in the case of the other treatment, but they were characterized by higher purity and thermal stability. In conclusion, this research highlights the possibility of obtaining nanostructured biopolymers from an invasive aquatic species that is largely available in nature and how it is possible, by modifying experimental procedures, to obtain nanomaterials with different morphological, purity, and thermal resistance characteristics.

Effective removal of Cr (VI) ions using low-cost biomass leaves (Sambucus nigra L.) in aqueous solution

The tannery industries have become an important part of societal growth; however, these processes have produced huge volumes of effluents containing heavy metals, particularly Cr(VI) oxyanions. The study is crucial and cost-effective for reducing the chromium (VI) from industrial wastewater. In order to meet the sustainable development goal (SDG) objective 6.3, the capacity of Sambucus nigra L. to adsorb heavy metal is established with the purpose of eradicating hazardous chemical contamination and reducing pollution. In this study, discontinuous tests were carried out to determine the efficiency of Cr(VI) sorption on leaves of Sambucus nigra L. Adsorption factors such as pH, temperature, adsorbent dosage, and contact time were evaluated. At a dosage of 3 g/L and pH 2, an efficiency of 98.22% was achieved under favorable conditions. The equilibrium and kinetic models that best fitted the experimental data are non-linear Freundlich and; pseudo-second order, and intra-particle diffusion, respectively. The thermodynamic parameters of the adsorption process, including Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0), were measured at 291, 303, 323, and 343 K, indicating that the phenomena was spontaneous and endothermic. The chemical analyses and surface morphology of the adsorbent were analyzed using SEM (scanning electron microscopy), EDS (energy dispersive spectroscopy), FTIR (Fourier transform infra-red), XRD (X-ray diffraction), and ICP-OES (inductively coupled plasma optical-emission spectroscopy) techniques. The results showed that Sambucus nigra L. has a significant removal efficiency of Cr(VI) in the contaminated solutions, establishing adsorbent as a low cost, readily available, and environmentally friendly and ensuring its potential for industrial usage.

Biorefining of rapeseed meal: A new and sustainable strategy for improving Cr(VI) biosorption on residual wastes from agricultural byproducts after phenolic extraction

Phenolic recovery from agricultural byproducts has been highlighted due to their health-promoting bioactivities. However, uncontrolled discard of residues after extraction process would induce environmental pollution and bioresource waste. In this study, biorefining of phenolic-rich rapeseed meal (RSM) and its defatted sample (dRSM) was attempted by holistic utilization of phenolic extract and residue separately. Phenolic removal could significantly improve residues' Cr(VI) adsorption capacities by about 21%, which presented extended physical surface and more released functional groups. Moreover, simulating raw material by remixing 3% separated phenolic extracts or main component sinapic acid therein with corresponding residues further improved about 12% adsorption efficiencies. These indicated that the different present forms of phenolics had opposite effects on Cr(VI) removal. While natural conjugational form inhibited hosts' biosorption, free form had enhanced functions for either extract or residue. Four optimal adsorption parameters (pH, adsorbent dosage, contact time and initial Cr(VI) concentration), three kinetic (pseudo-first order, pseudo-second order and intra-particle diffusion) models and two isotherms (Langmuir and Freundlich) were used to reveal the adsorption process. The maximum Cr(VI) adsorption capacity on residues could reach about 100 mg/g, which was superior to that of most biosorbents derived from agricultural byproducts, even some biochar. Together with the residues' advantages with everlasting capacity after 3 adsorption-desorption cycles and excellent abilities for adsorbing multiple co-existed metal ions (Cr(VI), Cd(II), Cu(II), Pb(II), Ni(II) and Zn(II)), phenolic recovery was first proved to be a new and sustainable strategy for modifying biosorbents from agricultural byproducts with zero waste.

Duckweed Potential for the Phytoremediation of Linear Alkylbenzene Sulfonate (LAS): Identification of Some Intermediate Biodegradation Products and Evaluation of Antioxidant System

Duckweed (Lemna minor L.) has a high potential for wastewater treatment. Here, its capability for bioremoval of linear alkylbenzene sulfonate (LAS) as one of the primary contaminants of water resources was evaluated. The effect of some operational parameters on surfactant removal efficiency was determined. Also, the impact of LAS on several physiological responses of Lemna was investigated. LAS remediation efficiency of L. minor was elevated with increasing LAS concentration, duckweed weight, and temperature. Furthermore, the optimal pH for removal was 7-8.5. The benzenesulfonate ring and five homologs of sulfophenyl carboxylate were identified as intermediates in the LAS degradation pathway. A decrease in relative growth rate and pigment contents was observed by increasing LAS concentration. In contrast, an increase in hydrogen peroxide content and electrolyte leakage indicated oxidative stress by LAS. Induction of enzymatic/non-enzymatic antioxidants was observed during the surfactant remediation process, indicating their role in overcoming free radicals generated under surfactant stress.

Lemna minor, a hyperaccumulator shows elevated levels of Cd accumulation and genomic template stability in binary application of Cd and Ni: a physiological and genetic approach

In this study, to determine whether having potential to be used as hyperaccumulator for Cd and Ni, numerous experiments were designed for conducting assessments for physiological and genotoxic changes along with defining possible alterations on mineral nutrient status of Lemna minor L. by applying Cd-Ni binary treatments (0, 100, 200 and 400 µM). Our study revealed that there were increases in the concentrations of B, Cr, Fe, K, Mg, and Mn whereas decreases were noticed in the concentrations of Na and Zn and the levels of Ca were inversely proportional to Cd-Ni applications showing tendency to increase at the low concentration and to decrease at the high concentration. Randomly Amplified Polymorphic DNA (RAPD) and Inter Simple Sequence Repeat (ISSR) analyses revealed that rather than band losses and new band formations, mostly intensity changes in the band profiles, and low polymorphism and high genomic template stability (GTS) were observed. Although, to date, L. minor was defined as an efficient hyperaccumulator/potential accumulator or competent phytoremedial agent by researchers. Our research revealed that L. minor showing high accumulation capability for Cd and having low polymorphism rate and high genomic template stability is a versatile hyperaccumulator, especially for Cd; therefore, highly recommended by us for decontamination of water polluted with Cd. NOVELTY STATEMENTMany studies have been focused on the effects of individual metal ions. However, heavy metal contaminants usually exist as their mixtures in natural aquatic environments. Especially, Cd and Ni coexist in industrial wastes.In this study, the accumulation properties of Lemna minor for both Cd and Ni were investigated and the effects of Cd and Ni on the bioaccumulation of B, Ca, Cu, Fe, Mg, K, Mn, Na, Pb and Zn in L. minor were also determined. This study furthermore aimed to assess the genotoxic effects of Cd and Ni found in being extended concentrations on DNA using the Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) method.

Removal of organic dyes from wastewater using Eichhornia crassipes: a potential phytoremediation option

Wastewater from textile industries is a potential source of organic dyes in natural water bodies. Environmental concerns of chemical methods for removal of dyes from wastewater are no more a viable solution, and there is growing concern to develop alternative approaches such as green chemistry and phytoremediation. This study reports the removal of organic dyes from wastewater using Eichhornia crassipes (Mart.) Solms (water hyacinth), as an easily available and fast-growing plant species. Growth of water hyacinth among individual cationic (rose bengal (RB), methylene blue (MB), crystal violet (CV), auramine O (AO), rhodamine B (RhB) and anionic (xylenol orange (XO), phenol red (PR), cresol red (CR), methyl orange (MO)) dye solutions and degradation of dyes were monitored. Results indicated that water hyacinth has good absorption and degradation potential for both types of dyes (cationic or anionic) and effectively removes dyes from solution. Water hyacinth can be used as a suitable and effective phytoremediate for removal of organic dyes from the wastewater.Graphical abstract.

Comparative adsorption capabilities of rubbish tissue paper-derived carbon-doped MgO and CaCO3 for EBT and U(VI), studied by batch, spectroscopy and DFT calculations

Water pollution due to organic dyes and radionuclides is a challenging issue to the modern world. Cheap and efficient adsorbents are needed for their removal from wastewaters. Carbon-doped magnesium oxide (C-MgO) and calcium carbonate (C-CaCO₃) were synthesized by the in situ hydrothermal treatment of Mg(OH)₂ and Ca(OH)₂ with carbon, and applied for the removal of eriochrome black T (EBT) at pH = 2.0 and uranium (U(VI)) at pH = 6.0. The Langmuir monolayer adsorption capacities of C-MgO (3.62 × 10^-4 mol/g for EBT and 8.10 × 10^-4 mol/g for U(VI)) were higher than those of C-CaCO₃ (2.53 × 10^-4 mol/g for EBT and 5.92 × 10^-4 mol/g for U(VI)). The high adsorption capacity of C-MgO was also evidenced with DFT calculations which showed that the sorption energies (ΔE) of C-MgO for EBT (20.62 kcal/mol) and U(VI) (63.41 kcal/mol) were higher than those of C-CaCO₃ for EBT (10.21 kcal/mol) and U(VI) (34.29 kcal/mol). In all cases, the electrostatic interactions were involved in the adsorption process. The sorption kinetic data followed pseudo-second-order kinetics. The results demonstrate that both C-MgO and C-CaCO₃ are reusable and can be effectively applied for the elimination of EBT and U(VI) from wastewater.