MgO coated magnetic Fe3O4@SiO2 nanoparticles with fast and efficient phosphorus removal performance and excellent pH stability

A review: metal and metal oxide nanoparticles for environmental applications

Environmental pollution has become a major issue since chemical species from different sources (e.g., textile industries, paper industries, dye industries, etc.) have been introduced into our living environment. If these chemical species are not properly treated, they will be highly toxic and hazardous to living organisms. Thus, it is important to remove the chemical species before discharge into the environment. Varieties of techniques, such as degradation, adsorption, photocatalysis, etc., have been employed to remove the chemical species. In recent years, metal and metal oxide nanoparticles, which exhibit high degradation and adsorption performance, have been widely used in environmental treatment. Here we provide a detailed overview of the environmental applications of metal and metal oxide nanoparticles, particularly in water treatment. The metal and metal oxide nanoparticles possess immense potential in environmental applications, however, challenges such as agglomeration, toxicity concerns, and cost-effectiveness are acknowledged. Through a comprehensive analysis of existing literature, this review systematically integrates critical research data. And it presents relevant research findings, aiming to explore environmentally sustainable nanomaterials with superior contaminant removal efficiency and broad applicability.

Recovery of Co(ii), Ni(ii) and Zn(ii) using magnetic nanoparticles (MNPs) at circumneutral pH

Growing demand for metals, particularly those with irreplaceable utility within renewable energy technology dictates an urgent demand for the development of new innovative approaches for their extraction from primary and secondary sources. In this study, magnetic nanoparticles (MNP) were investigated for their ability to remove cobalt (Co2+), nickel (Ni2+), and zinc (Zn2+) ions from neutral pH aqueous solutions under anoxic conditions. A MNP suspension (1 g L-1 or 5 g L-1) was exposed to varying concentrations of Co(ii), Ni(ii), and Zn(ii) (10-1000 mg L-1) in both single and mixed systems for 48 hours at pH 7.0 ± 0.1. Results show that MNPs can remove these ions to low concentrations (K d values: Zn: 0.07 L g-1; Co: 0.02 L g-1; and Ni: 0.01 L g-1 in single metal systems). Transmission Electron Microscopy (TEM) analysis confirmed relatively homogenous surface coverage of MNPs by each metal, while X-ray Absorption Spectroscopy (XAS) measurements determined sorption via the formation of coordinate bonds between the sorbed metals and surface oxygen atoms (Fe-O). Overall, our results show that MNPs can serve as an effective and reusable sorbent for Zn, Ni and Co ions from circumneutral pH waters.

Application of Box-Behnken design to optimize the phosphorus removal from industrial wastewaters using magnetic nanoparticles

Phosphorus is essential for all living organisms and limits aquatic plant growth. Pulp mill effluents, particularly from Eucalyptus bleached kraft pulp mills, contain phosphorus concentrations that vary with operational conditions. This variability poses challenges for effective treatment and phosphorus removal. However, uncontrolled release of phosphorus-rich wastewaters causes eutrophication. This study focuses on optimizing phosphorus removal from such effluents using cobalt ferrite nanoparticles, with an emphasis on process optimization to address this variability. Minimizing phosphorus concentrations is crucial in wastewater engineering and surface water management. By employing design of experiments and response surface methodology, we aim to fine-tune the phosphorous removal process and pinpoint the key factors with the most significant impact. Optimal conditions for achieving over 90% removal from an effluent with 5 mg P/L were identified as a sorbent dose greater than 1.3 g/L and a pH range between 5 and 7, all within a contact time of only 15 min. For a contact time of 1 and 24 h, the conditions adjust to a sorbent dose greater than 0.97 and 0.83 g/L, respectively, with the pH range remaining the same. Our results highlight the effectiveness of cobalt ferrite nanoparticles as sorbents in the removal of phosphorus for water treatment purposes. This approach presents a sustainable and proficient strategy for phosphorus recovery from pulp mill effluents, thereby lessening environmental repercussions and offering a valuable resource for future use. This contributes to the maintenance of water quality and ecosystem preservation.

Efficient and regenerative phosphate removal from wastewater using stable magnetite/magnesium iron oxide nanocomposites

Using magnetite-based nanocomposite adsorbents to remove and recycle phosphate from wastewater is crucial for controlling eutrophication and ensuring the sustainable use of phosphorus resources. However, the weak structural stability between magnetite and adsorptive nanoparticles often reduces phosphate removal efficiency in real-world applications. This instability primarily results from the loss of adsorptive nanoparticles from the magnetite surfaces, particularly when metal oxide nanoparticles are used for phosphate removal and recycling. In this study, we present a top-down approach that involves lattice locking magnesium iron oxide nanoparticles to the magnetite core, preventing magnesium loss from the magnetite surfaces. These nanocomposites exhibit exceptional performance in both phosphate recycling and removal, with a maximum adsorption capacity of 101.8 mg P·g-1. Excellent adsorption performance is also observed even in the presence of competing anions at phosphate-to-competing ion molar ratios of 1:5, 1:25, and 1:100, as well as dissolved organic matter, across a broad pH range of 4-10. The adsorbent also demonstrated minimal magnesium release during regeneration and in acidic conditions. Microscopic and spectroscopic analyses reveal that surface precipitation is the primary mechanism of phosphate removal in the magnesium-containing shells. The findings of this study address the current limitations of magnetite nanocomposites in phosphate removal, paving the way for the development of highly stable and sustainable nanocomposites for various chemical removal and recycling applications in wastewater treatment.

Enhanced adsorption of phosphate by rice straw-based biochar prepared via metal impregnation and bio-template technology

Phosphate removal from water through green, highly efficient technologies has received much attention. Biochar is an effective adsorbent for phosphate removal. However, adsorption capacity of phosphate on pristine rice straw-based biochar was not optimistic due to low anion exchange capacity. In this study, Fe-modified, Mg-modified and MgFe-modified rice straw-based biochar (Fe-BC, Mg-BC and MgFe-BC) were prepared by combining metal impregnation and biological template methods to improve the adsorption capacity of phosphate. The surface characteristics of biochar and the adsorption behavior of phosphate on biochar were investigated. The modified biochar had the specific surface area of 17.910-39.336 m2/g, and their surfaces were rich in a large number of functional groups and metal oxides. Phosphate release was observed on pristine rice straw-based biochar without metal impregnation. The maximum adsorption capacities of phosphate on MgFe-BC, Mg-BC and Fe-BC at 298 K were 6.93, 5.75 and 0.23 mg/g, respectively. Adsorption was a spontaneous endothermic process, while chemical adsorption dominated and electrostatic attraction and pores filling existed simultaneously. Based on the site energy distribution theory study, the standard deviation of MgFe-BC decreased from 6.96 to 4.64 kJ/mol with temperature increasing, which proved that the higher the temperature would cause the lower heterogeneity. Moreover, the effects of pH, humic acid, co-existing ions and ionic strength on phosphate adsorption of MgFe-BC were also discussed. MgFe-BC with fine pores and efficient adsorption sites is an ideal adsorbent for phosphate removal from water.

New design to enhance phosphonate selective removal from water by MOF confined in hyper-cross-linked resin

Although polymeric anion exchange resins can remove phosphonates, they lack selectivity for target phosphonates and are susceptible to interference by anions and other substances. Here, we developed a novel strategy via confining MIL-101(Fe)-NH2 inside commercial resins IRA-900 for high-efficient and precise phosphonate removal, accompanying with the improvement of the stability and recovery of MIL-101(Fe)-NH2. The obtained nanocomposite MIL-101(Fe)-NH2@IRA-900 (MFNI) exhibited significantly enhanced phosphonate removal in the presence of competing anions (Cl-, SO42-, NO3- and CO32-) and natural organic matter (humic acid) at high concentrations (2-4 times of phosphonate concentration). Moreover, MFNI displayed the highest phosphonate adsorption capacity (12.9 mg P/g) and the fastest adsorption kinetics (120 min) than hydrated ferric oxides modified IRA-900 (HFOI) (6.7 mg P/g, 180 min), MIL-101(Fe)-NH2 (7.6 mg P/g, 240 min) and IRA-900 (5.6 mg P/g, 360 min). Such higher adsorption affinity and anti-interference ability came from the synergistic effect of the host IRA-900 (hydrogen-bond interaction and electrostatic attraction) and the embedded MIL-101(Fe)-NH2 (ligand exchange). The depleted MFNI could be regenerated with a binary NaOH-NaCl solution and reused without significant loss of capacity. Column adsorption runs by using MFNI indicated the fresh MFNI could achieve 100 % removal of PPOA in 10.5 h continuously feeding, which offered the possibility of achieving potential large-scale applications. In general, a new MOF-confined design approach was practiced to achieve selective elimination of phosphates and to improve the stability and recovery of MOF.