Mechanistic insight into the removal of aqueous Cd using an immobilized ZIF-8 and microflora cooperative composite

Hydrogel immobilized bacteria@MOFs composite towards Bisphenol A degradation and the interconnection mechanism elucidation

Bisphenol A (BPA) degradation efficiency by bacteria or by metal-organic-frameworks (MOFs) catalyzed persulfate (PMS) oxidation have been studied intensively. However, their synergistic effect on BPA degradation was less reported. In this study, we combined previously synthesized CNT-hemin/Mn-MOF with an BPA degrading bacteria SQ-2 to form a composite (SQ-2@MOFs). CNT-hemin/Mn-MOF in the composite catalyzed little PMS to promote the degradation efficiency of SQ-2 on BPA. Results indicated SQ-2@MOFs significantly accelerated BPA degradation rate than SQ-2 alone. Furthermore, SQ-2@MOFs composite was successfully immobilized in hydrogel to achieve better degradation performance. Immobilized SQ-2@MOFs could almost completely degrade 1-20 mg/L BPA within 24 h and completely degrade 5 mg/L BPA at pH 4-8. Besides, degradation byproducts also reduced by immobilized SQ-2@MOFs, which promoted the cleaner biodegradation of BPA. Metabolomics and multiple chemical characterization results revealed the interconnection mechanism between CNT-hemin/Mn-MOFs, SQ-2 and hydrogel. CNT-hemin/Mn-MOF helped SQ-2 degrade BPA into more biodegradable products, promoted electron transfer, and augmented BPA degradation ability of SQ-2 itself. SQ-2 enabled the surface electronegativity of SQ-2@MOFs more suitable for BPA contact. Meanwhile, SQ-2 avoided the loss of Fe and Mn of CNT-hemin/Mn-MOF. Hydrogel augmented the above synergistic effect. This study provided new perspective for the development of biodegradation materials through interdisciplinary integration.

Adsorptive removal of heavy metals from aqueous solutions: Progress of adsorbents development and their effectiveness

Increased levels of heavy metals (HMs) in aquatic environments poses serious health and ecological concerns. Hence, several approaches have been proposed to eliminate/reduce the levels of HMs before the discharge/reuse of HMs-contaminated waters. Adsorption is one of the most attractive processes for water decontamination; however, the efficiency of this process greatly depends on the choice of adsorbent. Therefore, the key aim of this article is to review the progress in the development and application of different classes of conventional and emerging adsorbents for the abatement of HMs from contaminated waters. Adsorbents that are based on activated carbon, natural materials, microbial, clay minerals, layered double hydroxides (LDHs), nano-zerovalent iron (nZVI), graphene, carbon nanotubes (CNTs), metal organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) are critically reviewed, with more emphasis on the last four adsorbents and their nanocomposites since they have the potential to significantly boost the HMs removal efficiency from contaminated waters. Furthermore, the optimal process conditions to achieve efficient performance are discussed. Additionally, adsorption isotherm, kinetics, thermodynamics, mechanisms, and effects of varying adsorption process parameters have been introduced. Moreover, heavy metal removal driven by other processes such as oxidation, reduction, and precipitation that might concurrently occur in parallel with adsorption have been reviewed. The application of adsorption for the treatment of real wastewater has been also reviewed. Finally, challenges, limitations and potential areas for improvements in the adsorptive removal of HMs from contaminated waters are identified and discussed. Thus, this article serves as a comprehensive reference for the recent developments in the field of adsorptive removal of heavy metals from wastewater. The proposed future research work at the end of this review could help in addressing some of the key limitations facing this technology, and create a platform for boosting the efficiency of the adsorptive removal of heavy metals.

Spectra metrology for interaction of heavy metals with extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 reveals static quenching and complexation dynamics of EPS with heavy metals

The adsorption behavior and interaction mechanisms of extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 towards chromium (Cr), lead (Pb), and cadmium (Cd) were investigated. EPS-covered (EPS-C) cells exhibited significantly higher (p < 0.0001; two-way ANOVA) removal of Cr (85.58 ± 0.39%), Pb (81.98 ± 1.02%), and Cd (73.88 ± 1%) than EPS-removed (EPS-R) cells. Interactions between EPS-heavy metals were spontaneous (ΔG<0). EPS-Cr(VI) and EPS-Pb(II) binding were exothermic (ΔH<0), while EPS-Cd(II) binding was endothermic (ΔH>0) process. EPS bonded to Pb(II) via inner-sphere complexation by displacement of surrounding water molecules, while EPS-Cr(VI) and EPS-Cd(II) binding occurred through outer-sphere complexation via electrostatic interactions. Increased zeta potential of Cr (29.75%), Pb (41.46%), and Cd (46.83%) treated EPS and unchanged crystallinity (CIXRD=0.13), inferred EPS-metal binding via both electrostatic interactions and complexation mechanism. EPS-metal interaction was predominantly promoted through hydroxyl, amide, carboxyl, and phosphate groups. Metal adsorption deviated EPS protein secondary structures. Strong static quenching mechanism between tryptophan protein-like substances in EPS and heavy metals was evidenced. EPS sequestered heavy metals via complexation with C-O, C-OH, CO/O-C-O, and NH/NH2 groups and ion exchange with -COOH group. This study unveils the fate of Cr, Pb, and Cd on EPS surface and provides insight into the interactions among EPS and metal ions for metal sequestration.

Novel ZIF-8/CNC Nanohybrid with an Interconnected Structure: Toward a Sustainable Adsorbent for Efficient Removal of Cd(II) Ions

Water pollution, especially by heavy metals, continues to pose significant challenges, emphasizing the urgency to develop sustainable processes to remove pollutants while developing sustainable materials derived from renewable sources. In the present research, a nanoscale adsorbent was prepared to remove cadmium (Cd(II)) ions from wastewater by hybridizing zeolitic imidazolate framework-8 (ZIF-8) with a cellulose nanocrystal (CNC). The prepared nanohybrid exhibited an interconnected structure in which the ZIF-8 particles were connected to each other via CNC nanoneedles. The hybridization of ZIF-8 with CNC caused a significant enhancement in the adsorption performance of the fabricated nanohybrid compared to pure ZIF-8, increasing its adsorption capacity by nearly 36%. The adsorption of ZIF/CNC followed the Langmuir isotherm model and pseudo-second-order kinetics models, remarking homogeneous adsorption onto the surface of ZIF/CNC, where chemisorption controlled the rate of adsorption. The thermodynamic study uncovered that the adsorption is spontaneous, endothermic, and entropy-governed as the randomness was increased at the solid-liquid interface. Additionally, the influence of operating variables, such as temperature, adsorbent dosage, pH, and ionic strength, was studied to mimic the adsorption capabilities of the adsorbent in real conditions. Accordingly, the optimum conditions were found to be at 45 °C and pH = 7 with a dosage of 0.4 g/L for the adsorbent. Moreover, the adsorption in a multimetal solution showed that the ZIF/CNC nanohybrid can remove various heavy metals, including Cd(II), Fe(III), Cu(II), and Pb(II) ions simultaneously. Finally, the regeneration study confirmed the great potential of the ZIF/CNC nanohybrid, which retained 94% of its initial adsorption capacity after 5 consecutive adsorption/desorption cycles.

Integrating metal-organic framework ZIF-8 with green modifier empowered bacteria with improved bioremediation

Suspended microorganisms often experience diminished efficacy in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). In this study, the potential of zeolite imidazolate framework-8 (ZIF-8) and the eco-friendly modifier citric acid (CA) was harnessed to generate a biomimetic mineralized protective shell on the surface of Bacillus subtilis ZL09-26, resulting in an enhanced capability for PAH degradation. This investigation encompassed the integrated responses of B. subtilis ZL09-26 to ZIF-8 and ZIF-8-CA at both cellular and proteomic levels. The amalgamation of ZIF-8 and CA not only stimulated the growth and bolstered the cell viability of B. subtilis ZL09-26, but also counteracted the toxic effects of phenanthrene (PHE) stress. Remarkably, the bioremediation prowess of B. subtilis ZL09-26@ZIF-8-CA surpassed that of ZL09-26@ZIF-8 and ZL09-26, achieving a PHE removal rate of 94.14 % within 6 days. After undergoing five cycles, ZL09-26@ZIF-8-CA demonstrated an enduring PHE removal rate exceeding 83.31 %. A complex interplay of various metabolic pathways orchestrated cellular responses, enhancing PHE transport and degradation. These pathways encompassed direct PHE biodegradation, central carbon metabolism, oxidative phosphorylation, purine metabolism, and aminoacyl-tRNA biosynthesis. This study not only extends the potential applications of biomineralized organisms but also offers alternative strategies for effective contaminant management.

Enhanced cadmium phytoextraction efficiency of ryegrass (Lolium perenne L.) by porous media immobilized Enterobacter sp. TY-1

Although studies on immobilized microorganisms have been conducted, their performance remains unclear for enhancing plants to remediate cadmium (Cd)-contaminated soil. In this study, a Cd-resistant strain TY-1 with good plant growth promotion traits was immobilized by biochar (BC) or oyster shell (OS) power to strengthen ryegrass to remediate Cd-contaminated soil. SEM-EDS combined with FTIR showed that TY-1 could tolerate Cd toxicity by surface precipitation, and functional groups such as hydroxyl and carbonyl groups might be involved. In the biocomposite treatments, soil pH increased, and the activity of fertility-related enzymes such as dehydrogenase increased by 109.01%-128.01%. The relative abundance of genus Saccharimonadales decreased from 7.97% to 3.35% in BS-TY and 2.61% in OS-TY, respectively. Thus, a suitable environment for ryegrass growth was created. The fresh weight, dry weight, plant height and Cd accumulation of ryegrass in TY treatment increased by 122.92%, 114.81%, 42.08% and 8.05%, respectively, compared to the control. Cd concentration in ryegrass was further increased in BC-TY and OS-TY by 24.14% and 40.23%, respectively. The improvement in soil microcosm and plant biomass forms an ongoing virtuous cycle, demonstrating that using carrier materials to improve the efficiency of microbial-assisted phytoremediation is realistic and feasible.