Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed

Polypyrrole Coating via Lemieux-von Rudloff Oxidation on Magnetite Nanoparticles for Highly Efficient Removal of Chromium(VI) from Wastewater

An alternative way for the coating of polypyrrole (PPy) polymer on hydrophobic magnetite (Fe3O4) nanoparticles is reported here to capture toxic chromium ions, Cr (VI), present in water. Iron oxide magnetic nanoparticles (Fe3O4) were synthesized by the conventional coprecipitation technique using FeCl3·6H2O and FeSO4·7H2O iron precursors and subsequently modified with oleic acid (OA). Then OA-Fe3O4 hydrophobic nanoparticles were oxidized using the Lemieux-von Rudloff reaction to transfer OA into hydrophilic azelaic acid (AA) (HOOC(CH2)7COOH-modified magnetic nanoparticles (AA-Fe3O4). Finally, a PPy polymer coating was formed by a seeded polymerization of pyrrole, using AA-Fe3O4 as seeds. The average size of PPy/Fe3O4 nanocomposites is 12.33 nm and is almost spherical in shape. The surface composition is confirmed by FTIR and thermogravimetry analyses. An X-ray diffraction study confirmed the formation of highly crystalline Fe3O4 nanoparticles, and the crystallinity was retained after the surface modification. The adsorption study suggested that the Cr(VI) ion adsorption is highly pH-dependent and the maximum amount of adsorption is obtained at pH 2.0. The adsorption results revealed that the Langmuir model provided the best fit for the isotherm, with a maximum adsorption capacity reaching approximately 173.22 mg g-1 at 323 K. Spontaneous and endothermic adsorption processes were confirmed by evaluating the thermodynamic parameters obtained in this investigation. The kinetics study showed that the interaction between Cr(VI) ions and magnetic nanocomposites was directed by a pseudo-second-order rate process indicating chemisorption. The prepared PPy/Fe3O4 nanocomposites would be promising adsorbents to purify water by eliminating Cr(VI) metal ions from wastewater.

Removal of Chromium Species by Adsorption: Fundamental Principles, Newly Developed Adsorbents and Future Perspectives

Emerging chromium (Cr) species have attracted increasing concern. A majority of Cr species, especially hexavalent chromium (Cr(VI)), could lead to lethal effects on human beings, animals, and aquatic lives even at low concentrations. One of the conventional water-treatment methodologies, adsorption, could remove these toxic Cr species efficiently. Additionally, adsorption possesses many advantages, such as being cost-saving, easy to implement, highly efficient and facile to design. Previous research has shown that the application of different adsorbents, such as carbon nanotubes (carbon nanotubes (CNTs) and graphene oxide (GO) and its derivatives), activated carbons (ACs), biochars (BCs), metal-based composites, polymers and others, is being used for Cr species removal from contaminated water and wastewater. The research progress and application of adsorption for Cr removal in recent years are reviewed, the mechanisms of adsorption are also discussed and the development trend of Cr treatment by adsorption is proposed.

Comparative transcriptome analysis reveals the differential response to cadmium stress of two Pleurotus fungi: Pleurotus cornucopiae and Pleurotus ostreatus

Pleurotus has great potential for heavy metal mycoremediation. Using comparative transcriptome analysis, the response of Pleurotus ostreatus and Pleurotus cornucopiae under Cd contamination was evaluated. P. ostreatus and P. cornucopia accumulated 0.34 and 0.46 mg/g Cd in mycelium, respectively. Cd removal elevated with its concentration elevation, which reached 56.47% and 54.60% for P. ostreatus and P. cornucopia with Cd at 20 mg/L. Low-level Cd (≤ 1 mg/L) had no significant influence on either fungus, while varied response was observed under high-level Cd. 705 differentially expressed genes (DEGs) were identified in P. cornucopia at Cd1 and Cd20, whereas 12,551 DEGs in P. ostreatus. Differentially regulated functional categories and pathways were also identified. ATP-binding cassette transporters were involved in Cd transport in P. cornucopia, whereas the endocytosis and phagosome pathways were more enhanced in P. ostreatus. 26 enzymes including peroxisomal enzymes catalase and superoxide dismutase were upregulated in P. ostreatus, whereas only cytosolic catalase was overexpressed in P. cornucopia, suggesting their different Cd detoxification pathways. Also, the mitogen-activated protein kinase signaling pathway involved in Cd resistance in both species instead of glutathione metabolism, although more active in P. ostreatus. These findings provided new insight into the molecular mechanism of mycoremediation and accumulator screening.

Mechanisms into the removal and translocation of cadmium by Oudemansiella radicata in soil

This study investigated the removal and translocation mechanism of cadmium (Cd) by Oudemansiella radicata (O. radicata) in mushroom-soil rhizosphere and the fruiting body of mushroom. For this, the biomass, physiochemical parameters, and Cd distribution of O. radicata were examined in the soil spiked with 0, 10, 20, and 30 mg kg^-1 Cd. The soil microecology and the Cd fractionation in the soil rhizosphere were also measured. Results showed that, O. radicata possesses high capability to tolerate Cd, although its surface phenotypic structure was influenced by high concentrations of Cd. The observed concentrations of Cd in O. radicata were in the following order: root (the part of stipe in soil) > pileus > stipe. The presence of Cd led to an increase in the production of antioxidant enzymes and glutathione (GSH). These results suggested that antioxidant enzymes and GSH assisted detoxification and accumulation of Cd within the mushroom. Meanwhile, in the soil rhizosphere, the concentrations of oxalic, citric, and malic acids were enhanced with the treatment of Cd, indicating that the production of these acids was closely related to the presence of Cd in soils. Additionally, the proportion of acid-soluble Cd was increased and the soil microecology (microbial counts, urease, and acid phosphatase activities) also enhanced with the inoculation of O. radicata. Overall, this study demonstrated that O. radicata is a promising candidate for the remediation of Cd-contaminated soil.

Fe3O4 nanoparticle-coated mushroom source biomaterial for Cr(VI) polluted liquid treatment and mechanism research

Agrocybe cylindracea substrate-Fe3O4 (ACS-Fe3O4), a Fe3O4 nanoparticle-coated biomaterial derived from agriculture waste from mushroom cultivation, was developed to remove hexavalent chromium (Cr(VI)) from liquid. After modification, material surface became uneven with polyporous and crinkly structure which improved Cr-accommodation ability in a sound manner. Optimized by the Taguchi method, Cr(VI) removal percentage was up to 73.88 at 240 min, 40°C, pH 3, Cr(VI) concentration 200 mg l-1, dosage 12 g l-1, rpm 200. The efficient Cr(VI) removal was due to the combined effect of adsorption and redox. In addition, verification test using tannery wastewater, with removal percentage of Cr(VI) and total Cr reaching 98.35 and 95.6, provided further evidence for the efficiency and feasibility of ACS-Fe3O4. The effect of storage time of the material on Cr(VI) removal was small, which enhanced its value in practical application. Results indicated that metal removal was mainly influenced by solution concentration, adsorbent dosage and treatment time. The experimental data obtained were successfully fitted with the Langmuir isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that ACS-Fe3O4 as novel material derived from waste, with long-term stability, could be applied for heavy metal removal from wastewater and waste cycling.

Depletion of Cr(VI) from aqueous solution by heat dried biomass of a newly isolated fungus Arthrinium malaysianum: A mechanistic approach

For the first time, the heat dried biomass of a newly isolated fungus Arthrinium malaysianum was studied for the toxic Cr(VI) adsorption, involving more than one mechanism like physisorption, chemisorption, oxidation-reduction and chelation. The process was best explained by the pseudo-second order kinetic model and Redlich-Peterson isotherm with maximum predicted biosorption capacity (Q_m) of 100.69 mg g⁻¹. Film-diffusion was the rate-controlling step and the adsorption was spontaneous, endothermic and entropy-driven. The mode of interactions between Cr(VI) ions and fungal biomass were investigated by several methods [Fourier Transform-Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD) and Energy-Dispersive X-ray spectroscopy (EDX)]. X-ray Photoelectron Spectroscopy (XPS) studies confirmed significant reduction of Cr(VI) into non-toxic Cr(III) species. Further, a modified methodology of Atomic Force Microscopy was successfully attempted to visualize the mycelial ultra-structure change after chromium adsorption. The influence of pH, biomass dose and contact time on Cr(VI) depletion were evaluated by Response Surface Model (RSM). FESEM-EDX analysis also exhibited arsenic (As) and lead (Pb) peaks on fungus surface upon treating with synthetic solutions of NaAsO₂ and Pb(NO₃)₂ respectively. Additionally, the biomass could also remove chromium from industrial effluents, suggesting the fungal biomass as a promising adsorbent for toxic metals removal.

Mycoremediation potential of Pleurotus species for heavy metals: a review

Mycoremediation is one of the biotechniques that recruits fungi to remove toxic pollutants from environment in an efficient and economical manner. Mushrooms, macro-fungi, are among the nature's most important mycoremediators. Pleurotus species (also called oyster mushrooms) are considered to be the most popular and widely cultivated varieties worldwide and this might be attributed to their low production cost and higher yields. Apart from their nutritive and therapeutic properties, Pleurotus species have high biosorption potential due to their extensive biomass, i.e. mycelial production. The genus has been reported to accumulate high levels of heavy metals. The current state-of-the art review mainly summarises previous investigations carried out by researchers on different roles and mechanisms played by Pleurotus species on heavy metals mycoremediation.