Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal–organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Metal–organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

https://bioone.org/journals/harvard-papers-in-botany/volume-13/issue-2/1043-4534-13.2.299/Flora-of-China/10.3100/1043-4534-13.2.299.pdf

Flora of China

Crop productivity is affected by environmental and genetic factors. Microbes that are beneficial to plants are used to enhance the crop yield and are alternatives to chemical fertilizers and pesticides. Pseudomonas and Bacillus species are the predominant plant growth-promoting bacteria. The spore-forming ability of Bacillus is distinguished from that of Pseudomonas, and members of this genus also survive for a long time under unfavorable environmental conditions. Bacillus spp. secrete several metabolites that trigger plant growth and prevent pathogen infection. Limited studies have been conducted to understand the physiological changes that occur in crops in response to Bacillus spp. to provide protection against adverse environmental conditions. This review describes the current understanding of Bacillus-induced physiological changes in plants as an adaptation to abiotic and biotic stresses. During water scarcity, salinity and heavy metal accumulate in soil, and Bacillus spp. produce exopolysaccharides and siderophores, which prevent the movement of toxic ions and adjust the ionic balance and water transport in plant tissues while controlling the pathogenic microbial population. In addition, the synthesis of indole-3-acetic acid, gibberellic acid and 1-aminocyclopropane-1-carboxylate (ACC) deaminase by Bacillus regulates the intracellular phytohormone metabolism and increases plant stress tolerance. Cell-wall-degrading substances, such as chitosanase, protease, cellulase, glucanase, lipopeptides and hydrogen cyanide, from Bacillus spp. damage the pathogenic bacteria, fungi, nematodes, viruses and pests to control their populations in plants and agricultural lands. The normal plant metabolism is affected by unfavorable environmental stimuli, which suppress crop growth and yield. Abiotic and biotic stress factors that have detrimental effects on crops are mitigated by Bacillus-induced physiological changes, including the regulation of water transport, nutrient up-take and the activation of the antioxidant and defense systems. Bacillus association stimulates plant immunity against stresses by altering stress-responsive genes, proteins, phytohormones and related metabolites. This review describes the beneficial effect of Bacillus spp. on crop plants, which improves plant productivity under unfavorable climatic conditions, and the current understanding of the mitigation mechanism of Bacillus spp. in stress-tolerant and/or stress-resistant plants.

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Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments.

Emerging natural and tailored materials for uranium-contaminated water treatment and environmental remediation

Enrichment of uranyl from seawater is crucial for the sustainable development of nuclear energy, but current uranium extraction technology suffers from multiple drawbacks of low sorption efficiency, slow uptake kinetics, or poor extraction selectivity. Herein, we prepared the first example of amidoxime appended metal–organic framework UiO-66-AO by a postsynthetic modification method for rapid and efficient extraction of uranium from seawater. UiO-66-AO can remove 94.8% of uranyl ion from Bohai seawater within 120 min and 99% of uranyl ion from Bohai seawater containing extra 500 ppb uranium within 10 min. The uranyl sorption capacity in a real seawater sample was determined to be 2.68 mg/g. In addition, the recyclability of the UiO-66-AO framework was demonstrated for at least three adsorption/desorption cycles. The origin for the superior sorption capability was further probed by extended X-ray absorption fine structure (EXAFS) analysis on the uranium-sorbed sample, suggesting multiple amidoxime ligands ...

Ultrafast and Efficient Extraction of Uranium from Seawater Using an Amidoxime Appended Metal-Organic Framework.

The concentrations of uranium, thorium, barium, nickel, strontium and lead in the samples of the tailings and plant species collected from a uranium mill tailings repository in South China were analyzed. Then, the removal capability of a plant for a target element was assessed. It was found that Phragmites australis had the greatest removal capabilities for uranium (820 μg), thorium (103 μg) and lead (1,870 μg). Miscanthus floridulus had the greatest removal capabilities for barium (3,730 μg) and nickel (667 μg), and Parthenocissus quinquefolia had the greatest removal capability for strontium (3,920 μg). In this study, a novel coefficient, termed as phytoremediation factor (PF), was proposed, for the first time, to assess the potential of a plant to be used in phytoremediation of a target element contaminated soil. Phragmites australis has the highest PFs for uranium (16.6), thorium (8.68), barium (10.0) and lead (10.5). Miscanthus floridulus has the highest PF for Ni (25.0). Broussonetia papyrifera and Parthenocissus quinquefolia have the relatively high PFs for strontium (28.1 and 25.4, respectively). On the basis of the definition for a hyperaccumulator, only Cyperus iria and Parthenocissus quinquefolia satisfied the criteria for hyperaccumulator of uranium (36.4 μg/g) and strontium (190 μg/g), and could be the candidates for phytoremediation of uranium and strontium contaminated soils. The results show that the PF has advantage over the hyperaccumulator in reflecting the removal capabilities of a plant for a target element, and is more adequate for assessing the potential of a plant to be used in phytoremediation than conventional method.

Screening of plant species for phytoremediation of uranium, thorium, barium, nickel, strontium and lead contaminated soils from a uranium mill tailings repository in South China.

A novel amidoxime-based adsorbent of titanium-molybdopyrophosphate-g-amidoxime (TMP-g-AO) was prepared by chemical coprecipitation and subsequent chemical modifications. The successful grafting of acrylonitrile group and the subsequent conversion of acrylonitrile group to amidoxime groups were characterized by scanning electron microscopy-energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2–BET, and thermal analysis. The adsorption behavior of uranium(VI) on TMP-g-AO was investigated for low concentration uranium solution by batch experiments at a fixed pH of 8.2 ± 0.1. It is found that the adsorption rate of uranium from solution was 99.77% when the uranium concentration was 42.3 μg/L, pH = 8.2 ± 0.1, temperature = 298.15 K, and the adsorbent dosage = 0.05 g. The kinetic data follow the pseudo-second-order model, and adsorption equilibrium data fit the Langmuir model well. The thermodynamics parameters (ΔS, ΔH, and ΔG) indicate that the adsorption ...

New Amidoxime-Based Material TMP-g-AO for Uranium Adsorption under Seawater Conditions

Amidoxime modified Aspergillus niger (AMAN) was prepared by the oximation reaction. The effects of the initial pH, contact time, initial U(VI) concentration and biosorbent dose on the adsorption of U(VI) ions from radioactive wastewater in U(VI) concentrations of less than 1 mg L−1 by AMAN and the raw Aspergillus niger (RAN) were investigated. The maximum adsorption efficiency by AMAN for the 0.5 mg L−1 U(VI) solution amounted to 98.85% under the optimum adsorption conditions, while the maximum adsorption efficiency by RAN was only 77.83%. The adsorption equilibrium data were found to be best fitted to Langmuir isotherm model, and the maximum biosorption capacity of AMAN for U(VI) was estimated to be 621 mg g−1 at 298 K. The biosorption kinetics followed the pseudo-second order model and intraparticle diffusion equation. The Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) showed that the adsorption process of U(VI) was spontaneous, feasible and endothermic. The SEM-EDS study indicated that much more U(VI) ions were adsorbed by AMAN than by RAN. FT-IR study showed that the –NH2 and N–OH groups of amidoxime were the dominant ones for binding UO22+ ions. Moreover, AMAN was found to have excellent selective adsorption capability of U(VI) due to amidoxime groups. The UO22+ ions adsorbed by AMAN could be desorbed using 0.1 M HCl, and the desorption efficiency reaching 87.28% at the 8th cycle of adsorption and desorption.

Adsorption and recovery of U(VI) from low concentration uranium solution by amidoxime modified Aspergillus niger

Vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China

Experiments on the removal and recovery of U(VI) from aqueous solution by tea waste were conducted. The adsorbent was characterized by scanning electron microscope and energy dispersive spectrometer before and after the adsorption treatment. The removal of U(VI) amounts to 86.80 % at optimum pH 6. The adsorption process reaches its equilibrium in 12 h at 308 K, and the kinetic characteristic can be described by the pseudo-second-order kinetic equation. The amount of adsorption increases from 22.92 to 142.21 mg g−1 with the decrease of tea waste dosage from 100 to 10 mg for solution with an initial uranium concentration of 50 mg L−1. Desorption for the four strippants is higher than 80 %. The equilibrium data are more agreeable with Freundlich isotherm than Langmuir isotherm.

Wang Yongdong

Papers

Screening of plant species for phytoremediation of uranium, thorium, barium, nickel, strontium and lead contaminated soils from a uranium mill tailings repository in South China.

New Amidoxime-Based Material TMP-g-AO for Uranium Adsorption under Seawater Conditions

Adsorption and recovery of U(VI) from low concentration uranium solution by amidoxime modified Aspergillus niger

Vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China

Removal and recovery of uranium from aqueous solution by tea waste