Investigation on the efficiency and mechanism of Cd(II) and Pb(II) removal from aqueous solutions using MgO nanoparticles

Novel nanocomposite and biochar insights to boost rice growth and alleviation of Cd toxicity

Cadmium (Cd) is an unessential and pervasive contaminant in agricultural soil, eventually affecting the food and instigating health issues. The implication of nanocomposites in agriculture attained significant attention to drive food security. Nanocomposites possess exceptional characteristics to stun the challenges of chemical fertilizers that can enhance plant yield and better nutrient bioavailability. Similarly, biochar has the ability to immobilize Cd in soil by reducing mobility and bioavailability. Rice husk biochar is produced at high temperature pyrolysis under anoxic conditions and a stable carbon-rich material is formed. To strive against this issue, rice plants were subjected to Cd (15, 20 mg kg- 1) stress and treated with alone/combined Ca + Mg (25 mg L- 1) nanocomposite and rice husk biochar. In our study, growth and yield traits showed the nurturing influence of Ca + Mg nanocomposite and biochar to improve rice defence mechanism by reducing Cd stress. Growth parameters root length 28%, shoot length 34%, root fresh weight 19%, shoot fresh weight 16%, root dry weight 9%, shoot dry weight 8%, number of tillers 32%, number of grains 20%, and spike length 17% were improved with combined application of Ca + Mg and biochar, with Cd (20 mg kg- 1), rivalled to alone biochar. Combined Ca + Mg and biochar application increased the SPAD 23%, total chlorophyll 26%, a 19%, b 18%, and carotenoids 15%, with Cd (20 mg kg- 1), rivalled to alone biochar. MDA 15%, H2O2 13%, and EL 10% were significantly regulated in shoots with combined Ca + Mg and biochar application with Cd (20 mg kg- 1) compared to alone biochar. POD 22%, SOD 17%, APX 18%, and CAT 9% were increased in shoots with combined Ca + Mg and biochar application with Cd (20 mg kg- 1) compared to alone biochar. Cd uptake in roots 13%, shoots 14%, and grains 21% were minimized under Cd (20 mg kg- 1) with combined Ca + Mg and B. pumilus application, compared to alone biochar. Subsequently, combined Ca + Mg and biochar application is a sustainable solution to boost crop production under Cd stress.

Enhanced cadmium removal by a magnetic potassium ferrocyanide framework: Performance and mechanism study

Polluted environments often contain large amounts of toxic metals, such as cadmium, which pose a major threat to ecosystems and public health. Contamination by cadmium and its compounds is often observed in areas surrounding zinc mining sites and electroplating factories, and the control of cadmium pollution is essential for environmental safety and health. In this study, a highly efficient and straightforward separation strategy for K4Fe(CN)6@Fe3O4 nanocomposites is successfully developed to capture the Cd ions in the water environment. Batch adsorption experiments revealed that K4Fe(CN)6@Fe3O4 exhibited a high cadmium removal rate (greater than 98 %) at a pH level of 6.0 and solid-liquid ratio of 1.0 g/L at room temperature (298 K). Kinetic analysis revealed that the adsorption process followed a pseudo-second-order model and cadmium was rapidly removed in the first 10 min, with chemisorption dominating the capture of Cd2+ by K4Fe(CN)6@Fe3O4. Adsorption isotherms revealed a heterogeneous adsorption behavior, with a maximum adsorption capacity of 40.78 mg/g. The intrinsic adsorption of Cd2+ by K4Fe(CN)6@Fe3O4 occurring primarily through electrostatic interaction and ion exchange. In addition, K4Fe(CN)6@Fe3O4 exhibited an excellent regeneration capacity. Therefore, integrating Fe3O4 into the metal cyanide not only provided the composite material with excellent chemical stability and selective adsorption sites for Cd2+, but also facilitated subsequent sorbent collection and recovery. Overall, this study presents a simple and feasible approach for integrating Fe3O4 into potassium ferrocyanide frameworks for efficient cadmium removal from contaminated water.

Impacting the Surface Chemistry of NiAu by Immobilizing on MgO/N-Rich Nanoporous Carbon Heterostructures for Boosting Catalytic Activities

Tuning the physical and chemical interaction between metal-metal' (M-M') and metal-support is an ideal way to realize enhanced catalytic activity of metal nanoparticles (NPs). As a proof of concept, herein we report the fabrication of nickel-gold (Ni-Au) alloy nanoparticles attached to N-doped nanoporous carbon (NPC) intervened with MgO (Ni73Au27@MgO-NPC), achieved through the impregnation of metal precursors into Schiff-base network polymer (SNP) framework along with Mg(OH)2 and pyrolysis at 800 °C in N2 atmosphere. With high stability and heterogeneity, the nickel rich Ni73Au27@MgO-NPC exhibited higher catalytic activities with turnover frequencies of 29,272 h-1 (hydrogenation of p-nitrophenol), 93,843 h-1 (degradation of methyl orange), and 2,218 h-1 (epoxidation of stilbene), compared to commercial 10 wt % Pd/C. Enhanced catalytic activity is correlated to the synchronized electron density enhancement in Au, by Ni and MgO/N-rich nanoporous carbon heterostructures, as evident from detailed X-ray photoelectron spectroscopic studies.

Efficient fluoride removal using nano MgO: mechanisms and performance evaluation

In this study, highly efficient fluoride removal of nano MgO was successfully synthesized using a simple hydrothermal precipitation method. Hexadecyl trimethyl ammonium bromide (CTMAB) was utilized as a surfactant. Its long-chain structure tightly wrapped around the precursor crystal of basic magnesium chloride, inhibiting the growth of precursor crystals, reducing their size, and improving crystal dispersion. This process enhanced the adsorption capacity of nano MgO for fluoride. The adsorption performance of nano MgO on fluoride was investigated. The results indicate that pseudo-second-order kinetics and the Langmuir isotherm model can describe the adsorption behavior for fluoride, with a maximum adsorption capacity of 122.47 mg/g. Methods such as XRD, SEM, XPS, and FTIR were employed to study the adsorption mechanisms of the adsorbent. Additionally, factors potentially affecting adsorption performance in practical applications, such as pH and competing ions, were examined. This study enhances our profound understanding of the defluorination effectiveness and mechanisms of nano MgO.

Effects of magnesium hydroxide morphology on Pb(ii) removal from aqueous solutions

In this study, magnesium hydroxide (MH) particles with distinct morphologies were obtained through direct precipitation and subsequent hydrothermal treatment with various magnesium salts. The synthesized products were systematically characterized and utilized for the removal of Pb(ii) ions from aqueous solutions. The adsorption process of Pb(ii) by two different MH structures, namely flower globular magnesium hydroxide (FGMH) and hexagonal plate magnesium hydroxide (HPMH), adhered to the Langmuir isotherm and pseudo-second-order model. FGMH exhibited higher Pb(ii) removal capacity (2612 mg g-1) than HPMH (1431 mg g-1), attributable to the unique three-dimensional layered structures of FGMH that provide a larger surface area and abundant active sites. Additionally, metallic Pb was obtained by recycling the adsorbed Pb(ii) through acid dissolution-electrolysis. Furthermore, Pb(ii) removal mechanisms were investigated by analyzing adsorption kinetics and isotherms, and the adsorbed products were characterized. Based on the findings, the removal process occurs in two key stages. First, Pb(ii) ions bind with OH- ions on the surface upon diffusing to the MH surface, resulting in Pb(OH)2 deposits in situ. Concurrently, Mg(ii) ions diffuse into the solution, substituting Pb(ii) ions in the MH lattice. Second, the resultant Pb(OH)2, which is unstable, reacts with CO2 dissolved in water to yield Pb3(CO3)2(OH)2. Therefore, owing to its outstanding Pb(ii) adsorption performance and simple preparation method, FGMH is a promising solution for Pb(ii) pollution.

Mechanochemical synthesis of cysteine-gum acacia intermolecular complex for multiple metal(loid) sequestration from herbal extracts

The ubiquitous heavy metal(loid)s (HMs) contamination has triggered great concern about food safety, while sequestration and separation of trace HMs from herbal extracts still calls for appropriate sorbent materials. In this work, gum acacia was modified by cysteine to form a cysteine-acacia intermolecular complex (Cys-GA complex) via facile mechanochemical synthesis, aiming at capturing multiple HMs simultaneously. Preliminary screening confirms the superiority of Cys-CA complex for both cationic and anionic HMs, and determines an optimum Cys/GA mass ratio of 9:1 to achieve high removal capacities for Pb(II) (938 mg g-1), Cd(II) (834 mg g-1), As(V) (496 mg g-1), and Cr(VI) (647 mg g-1) in simulated aqueous solution. The analysis on HMs-exhausted Cys-GA complex indicates that Pb(II), As(V), and Cr(VI) tend to be removed through chelation, electrostatic attraction, and reduction, while Cd(II) can only be chelated or adsorbed by electrostatic interaction. The batch experiments on commercial herbal (e.g. Panax ginseng, Glycine max, Sophora flavescens, Gardenia jasminoides, Cyclocarya paliurus, and Bamboo leaf) extracts indicate that Cys-GA complex can reduce HMs concentration to attain acceptable level that comply with International Organization for Standardization, with negligible negative effect on its active ingredients. This work provides a practical and convenient strategy to purify HMs-contaminated foods without introducing secondary pollution.

Hierarchical 3D Flower-like Metal Oxides Micro/Nanostructures: Fabrication, Surface Modification, Their Crucial Role in Environmental Decontamination, Mechanistic Insights, and Future Perspectives

Hierarchical micro/nanostructures are constructed by micro-scaled objects with nanoarchitectures belonging to an interesting class of crystalline materials that has significant applications in diverse fields. Featured with a large surface-to-volume ratio, facile mass transportation, high stability against aggregation, structurally enhanced adsorption, and catalytical performances, three dimenisional (3D) hierarchical metal oxides have been considered as versatile functional materials for waste-water treatment. Due to the ineffectiveness of traditional water purification protocols for reclamation of water, lately, the use of hierarchical metal oxides has emerged as an appealing platform for the remediation of water pollution owing to their fascinating and tailorable physiochemical properties. The present review highlights various approaches to the tunable synthesis of hierarchical structures along with their surface modification strategies to enhance their efficiencies for the removal of different noxious substances. Besides, their applications for the eradication of organic and inorganic contaminants have been discussed comprehensively with their plausible mechanistic pathways. Finally, overlooked aspects in this field as well as the major roadblocks to the implementation of these metal oxide architectures for large-scale treatment of wastewater are provided here. Moreover, the potential ways to tackle these issues are also presented which may be useful for the transformation of current water treatment technologies.

Macroporous honeycomb-like magnesium oxide fabricated as long-life and outstanding Pb(II) adsorbents combined with mechanism insight

The macroporous honeycomb-like MgO (MHM) had been successfully prepared by hard template method using polystyrene (PS) spheres with different particle sizes of about 400, 600, and 800 nm, respectively. The adsorption performance (3700, 3470, and 3087 mg/g) and specific surface areas (64.0, 51.4, and 34.4 m2/g) of MHM materials were inversely proportional to their pore diameters. Among the prepared MHM materials, MHM-400 exhibited the most excellent adsorption performance of 3700 mg/g towards Pb(II) at 25 °C. In this study, the macropore size in MHM played a major role in the adsorption process; Dubinin-Radushkevich (D-R) model further indicated that Pb(II) removal by MHM-400 was dominated by chemical adsorption. The thermodynamic analysis (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0) revealed that the Pb(II) adsorption was spontaneous and endothermic. After storing for 360 days, the Pb(II) removal efficiency of MHM-400 was still higher than 98.2%, exhibiting ultra-long life for Pb(II) capture. MHM-400 also exhibited high anti-interference ability towards typically coexisting ions (Na+ and K+). According to the density functional theory (DFT) calculation, the Pb could be adsorbed on the top site of the oxygen atom at the surface of the cubic MgO (200) plane; the adsorption energy (Ead) was 0.159 eV. The XRD and FTIR analyses revealed the further formation of Pb3(CO3)2(OH)2 and PbO after Pb(II) adsorption. Furthermore, MHM-400 could effectively remove both Cd(II) and Pb(II) ions from wastewater within 20 min, and the adsorption efficiency achieved > 99%, suggesting that MHM-400 was a potential material for effective Pb(II) removal.

Removal of Cd2+ from wastewater to form a three-dimensional fiber network using Si-Mg doped industrial lignin-based carbon materials

In this study, SiMg doped industrial lignin-based carbon materials (SLCs) were prepared by water bath silicification and MgCl₂ activation to remove Cd²⁺ from aqueous solutions. What's more, the doping of SiMg jointly promoted the excellent physicochemical properties of the material, e.g., high specific surface area, good pore volume, and numerous oxygen-containing groups. The Cd²⁺ batch adsorption experiments proved that SLCs have good Cd²⁺ removal capacity within pH 3-7, and the adsorption model demonstrated the adsorption process as a physicochemically complex process. The maximum adsorption of Cd²⁺ in the SLC was 665.35 mg/g, and the contributing factors to the removal of Cd²⁺ were as follows: ion exchange (59.36 %) > Cd²⁺ precipitation (24.93 %) > oxygen-containing functional group complexation (14.79 %) > Cd²⁺-π interactions (0.92 %). In addition, the complexation of SiO, MgO, and Cd precipitates allowed the formation of a three-dimensional fiber mesh structure. The application of SLCs has the potential to eliminate Cd²⁺ pollution in water bodies, and its preparation is simple and environmentally friendly. Finally, this study provides a theoretical basis for an in-depth understanding of the mechanism of heavy metal adsorption by inorganic nonmetals in combination with metal oxides.

Effects and mechanism on cadmium adsorption removal by CaCl2-modified biochar from selenium-rich straw

As every-one knows, cadmium contamination poses a significant and permanent threat to people and aquatic life. Therefore, research on how to remove cadmium from wastewater is essential to protect the natural environment. In this study, agricultural and forestry waste straw sprayed with selenium-enriched foliar fertilizer was prepared as biochar, which was altered by calcium chloride (CaCl₂) to remove Cd²⁺ from water. The outcomes demonstrated that biochar generated by pyrolysis at 700 °C (BC700) had the best adsorption effect. Secondly, pseudo-second-order kinetics and Langmuir adsorption models were used to predict the Cd²⁺ adsorption. Finally, electrostatic adsorption, ion exchange, and complexation of oxygen functional groups (OFGs) were demonstratedto be the main adsorption mechanisms. These conclusions indicate that selenium-rich straw biochar is a novel adsorbent for agroforestry waste recovery. Meanwhile, this work will offer a promising strategy for the overall utilization of rice straw.

Bioinorganic Nanoparticles for the Remediation of Environmental Pollution: Critical Appraisal and Potential Avenues

Nowadays, environmental pollution has become a critical issue for both developed and developing countries. Because of excessive industrialization, burning of fossil fuels, mining and exploration, extensive agricultural activities, and plastics, the environment is being contaminated rapidly through soil, air, and water. There are a variety of approaches for treating environmental toxins, but each has its own set of restrictions. As a result, various therapies are accessible, and approaches that are effective, long-lasting, less harmful, and have a superior outcome are extensively demanded. Modern research advances focus more on polymer-based nanoparticles, which are frequently used in drug design, drug delivery systems, environmental remediation, power storage, transformations, and other fields. Bioinorganic nanomaterials could be a better candidate to control contaminants in the environment. In this article, we focused on their synthesis, characterization, photocatalytic process, and contributions to environmental remediation against numerous ecological hazards. In this review article, we also tried to explore their recent advancements and futuristic contributions to control and prevent various pollutants in the environment.

Effective immobilization of geogenic As and Pb in excavated marine sedimentary material by magnesia under wet-dry cycle, freeze-thaw cycle, and anaerobic exposure scenarios

Massive amounts of marine sedimentary materials with geogenic heavy metal(loids) are excavated by the subsurface construction projects and then exposed to weathering conditions, which pose potential threats to the environment. In the present study, 2 % magnesia (MgO) was applied to immobilize geogenic arsenic (As) and lead (Pb) in excavated marine sedimentary material. To better evaluate the immobilization efficiency under different environmental scenarios, the untreated and amended solids were subjected to wet-dry cycles, freeze-thaw cycles, and anaerobic incubation until 49 days. The leaching behaviors of As and Pb were investigated and their size fractionations in the leachates were compared. The results indicate that most Pb exists in particulate and agglomerated colloidal fractions (0.1-5 μm) in the leaching suspensions, while most As is found in dissolved forms (<0.1 μm). It is therefore necessary to consider the element type and exposure scenarios during environmental risk evaluation, particularly using the batch test as a routine compliance testing procedure. In the control test without MgO addition, the wet-dry cycle resulted in the "self-induced" immobilization of As and Pb. The pH decreases to the neutral range and the formation of amorphous Fe-(oxyhydr)oxides following pyrite oxidation largely explained the decreased As and Pb leaching. In comparison, the freeze-thaw cycle and anaerobic incubation tended to enhance As and Pb leaching. Overall, MgO addition significantly reduced the leachability of As and Pb and displayed sustained immobilization performance under all studied scenarios. These findings could be largely attributed to solid particle aggregation induced by MgO addition, including the adsorption of As and Pb onto newly formed Fe-(oxyhydr)oxides and/or MgSi precipitates. This study offers a simple and effective strategy for the sustainable management of excavated marine sedimentary materials contaminated by geogenic As and Pb.

Effective and stable adsorptive removal of Cadmium(II) and Lead(II) using selenium nanoparticles modified by microbial SmtA metallothionein

Metallothionein SmtA-modified selenium nanoparticles (SmtA-SeNPs), efficient adsorbents for Cd(II) and Pb(II), were synthesized in the present work. The ligand, microbial SmtA protein, was synthesized using an engineered strain Escherichia coli, posing the benefits of simplicity, safety, and high production. SmtA-SeNPs were spheres with diameters between 68.1 and 122.4 nm, containing amino, hydroxyl, and sulfhydryl functional groups with negatively charged (pH > 5). SmtA-SeNPs displayed better adsorption performance than dissociative SmtA and SeNPs. The adsorption of Cd(II) and Pb(II) mainly depends on the electrostatic attractions and the metal chelation of abundant functional groups. The maximum adsorption capacity was 506.3 mg/g for Cd(II) and 346.7 mg/g for Pb(II), which were higher than the values of most nanoparticles. In addition, SmtA-SeNPs were immobilized with a membrane filter to produce a SmtA-SeNPs filter, and the percentage removal of Cd(II) and Pb(II) increased from 26.75% to 98.13% for Cd(II) and from 9.95% to 99.20% compared with the blank filter. Moreover, the SmtA-SeNPs filter was regenerated using subacid deionized water, and the filter exhibited a stable removal ratio of Cd(II) and Pb(II) in ten continuous cycles of Cd(II)- or Pb(II)-containing wastewater treatment. The residual amounts of Cd and Pb met national standard levels of wastewater discharge.

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

A regenerable MgO-coated magnetic Fe₃O₄@SiO₂ (FSM) composite effectively avoided the agglomeration of nano-MgO, which was resoundingly used for efficient and rapid phosphorus removal from aqueous solutions. Based on an initial screening of synthesized FSM with different Mg/citric acid molar ratios in terms of phosphorus adsorption capacity, an FSM composite with a Mg-citric acid molar ratio of 1:1 (FSM-1:1) was determined as the optimal choice. Scanning electron microscope (SEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) showed that the prepared Fe₃O₄ was triumphantly loaded and the nano-MgO nanoparticles were evenly distributed on the surface of magnetic mesoporous silica. N₂ adsorption-desorption experiments manifested that FSM-1:1 had a large specific surface area of 124.3 m²/g and the pore size distribution calculated based on the BJH model was centered at 9.36 nm. Furthermore, FSM-1:1 not only exhibited fast adsorption kinetics (60 min) but also had a high maximum theoretical adsorption capacity of 223.6 mg P/g, which was superior to all the other Mg-based adsorbents. Remarkably, due to the coating of MgO, FSM-1:1 exhibited ultra-high stability in the pH range of 3-11, a wider range than many other Mg-modified sorbents. Our adsorbents also showed excellent selectivity for phosphate anions even in the presence of various coexisting anions (e. g. NO₃^-, Cl^- and SO₄^2-) with varying ionic strengths (0.01 and 0.1 M), good recyclability, the removal rate of phosphate still reached 89.0% after three cycles. Electrostatic attraction, Lewis acid-base interaction and the ligand exchange between Mg-OH and phosphate anions were responsible for the phosphate adsorption mechanisms.

Insight into the role and mechanism of polysaccharide in polymorphous magnesium oxide nanoparticle synthesis for arsenate removal

The low cost and non-toxic of magnesium oxides make it a potential eco-friendly material for arsenic removal. Polysaccharide is a kind of green modifier to obtain nanoscale MgO particles with a higher adsorption affinity. In this study, the impact of chain structures of polysaccharides on the morphology features and arsenate removal efficiency of MgO-NPs were investigated. Pullulan and starch facilitated the synthesis of flower-like MgO-NPs, and pectin facilitated the synthesis of plate-like ones. Although the two kinds of flower-like MgO-NPs undergone similar time to reach equilibrium, the one obtained from the starch-synthesis route showed a higher arsenate adsorption capacity (98 mg g^-1), due to that their bushy and smaller petals on the surface provide more active sites for arsenic adsorption. The pectin-synthesis route also produced MgO-NPs with higher arsenate adsorption capacity (101 mg g^-1), ascribed to stacking of nano-plates on their surfaces facilitated to form defect surfaces. However, due to their lower BET area, the plate-like MgO-NPs took twice times to reach equilibrium for arsenic adsorption compared with the others. In the stage for the hydrolysis of MgO, hydroxyl groups on the polymer chain provide active sites to physically trap or bond with MgO particles and then to produce hydrolyzed precursors. The poly chain containing inter- and intra-hydroxyl groups directed MgO molecular growing into hydroxide crystals with 3D frameworks during their nucleation and growth. However, pectin only provides inter-hydroxyl groups and directs to form hydroxides with 2D frameworks. Furthermore, the rapid-nucleation vs. slow-growth model in the stage of pyrolysis of hydroxide crystals successfully interprets the thinner petals and complex chemical phases of the final nanoparticles obtained from the pullulan-synthesis route. This work may provide direction and perspectives for the rational design of well-performing MgO materials for arsenate removal.

MgO-loaded nitrogen and phosphorus self-doped biochar: High-efficient adsorption of aquatic Cu2+, Cd2+, and Pb2+ and its remediation efficiency on heavy metal contaminated soil

In this study, the MgO-loaded fish scale biochar (MgO-FB) was synthesized by impregnation of MgCl₂ using fish scales as precursor, and the modified biochar was applied for the adsorption of aquatic Cu²⁺, Cd²⁺, and Pb²⁺, and the immobilization of heavy metals in soils. The maximum adsorption capacities of MgO-FB for Cu²⁺, Cd²⁺, and Pb²⁺ were 505.8, 327.2, and 661.2 mg/g, respectively. In addition, MgO-FB can keep the excellent adsorption capacity under various environmental disturbances including pH, humic acid, and high ionic strength. Multiple characterizations and comparative experiments have demonstrated that the hydroxyapatite components and the MgO micro-nanoparticles on MgO-FB enhanced the adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ through ion-exchange and precipitation process. The metal-π electron coordination and complexation with oxygen-, nitrogen-, and phosphorus-containing groups were also responsible for the removal of heavy metal ions. Besides, MgO-FB also performed excellently for the immobilization of Cu, Cd, and Pb in soils, and the contents of available Cu, Cd, and Pb were reduced by 84.2%, 74.2%, and 53.7% respectively with the addition of MgO-FB. In general, these results show that waste fish scales co-pyrolysis with MgCl₂ impregnation can be considered as a promising and efficient material for the remediation of heavy metal contaminated waters and soils.

Full factorial design and dynamic modelling of silent and ultrasound-assisted lead and cadmium removal by porous biosorbent

Present work aimed to analyse single and competitive lead and cadmium batch adsorption, using experimental studies and mathematical modelling. The experiments were conducted in silent and ultrasound-assisted systems, in aqueous environment, using grinded hazelnut shells as porous biosorbent. The influence of process factors (pH, adsorbent concentration, adsorbent particle size, and initial species concentration in liquid phase) on species removal efficiency was evaluated when process equilibrium was attained. The statistical study, following a 2⁴ factorial experimental design, allowed the development of a model to predict variables influence. Based on the obtained results a deeper analysis of the separation efficiency, depending on process factors, was conducted. The dynamic study was performed based on experimentally obtained removal rates, modelled considering species diffusion, with reversible kinetics of sorption inside solid particles. Hence, the dynamics of removal efficiency was determined for several representative experiments. The equilibrium isotherms data, best fitted by an appropriate Langmuir model, were used in the dynamic model to reduce the number of model parameters which normally require experimental identification.

Highly Selective Removal of Cationic Dyes from Wastewater by MgO Nanorods

The organic synthetic dyes employed in industries are carcinogenic and harmful. Dyes must be removed from wastewater to limit or eliminate their presence before dumping into the natural environment. The current study aims to investigate the use of MgO nanoparticles to eliminate basic fuchsine (BF), as a model cationic dye pollutant, from wastewater. The MgO nanorods were synthesized through a coprecipitation method. The obtained nanocomposite was characterized using various techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET), and FTIR spectroscopy. It was found that the variation of dye concentration and pH influenced the removal of BF by MgO. The adsorption capacity of 493.90 mg/g is achieved under optimum operating conditions (pH = 11, contact time = 236 min, and initial BF concentration = 200 ppm). Pseudo-second-order adsorption kinetics and Freundlich isotherm models best fitted BF sorption onto MgO nanorods. The BF sorption mechanism is associated with the electrostatic attractions and hydrogen bond between the O-H group of MgO and the NH2 groups of BF, as indicated by the pH, isotherms, and FTIR studies. The reusability study indicates that MgO was effectively used to eliminate BF in at least four continuous cycles. The investigation of MgO with different dyes suggests the high adsorption selectivity of BF, crystal violet (CV), and malachite green (MG) dyes compared with methyl orange (MO) dye. Overall, MgO nanorods can act as a potential and promising adsorbent for the efficient and rapid removal of cationic dyes (CV, MG, and BF) from wastewater.

Recent advances in nanoremediation: Carving sustainable solution to clean-up polluted agriculture soils

Agriculture is one of the foremost significant human activities, which symbolizes the key source for food, fuel and fibers. This activity results in a lot of ecological harms particularly with the excessive usage of chemical fertilizers and pesticides. Different agricultural practices have remained industrialized to advance food production, due to the growth in the world population and to meet the food demand through the routine use of more effective fertilizers and pesticides. Soil is intensely embellished by environmental contamination and it can be stated as "universal incline." Soil pollution usually occurs from sewage wastes, accidental discharges or as byproducts of chemical residues of unrestrained production of numerous materials. Soil pollution with hazardous materials alters the physical, chemical, and biological properties, causing undesirable changes in soil fertility and ecosystem. Engineered nanomaterials offer various solutions for remediation of contaminated soils. Engineered nanomaterial-enable technologies are able to prevent the uncontrolled release of harmful materials into the environment along with capabilities to combat soil and groundwater borne pollutants. Currently, nanobiotechnology signifies a hopeful attitude to advance agronomic production and remediate polluted soils. Studies have outlined the way of nanomaterial applications to restore the eminence of the environment and assist the detection of polluted sites, along with potential remedies. This review focuses on the latest developments in agricultural nanobiotechnology and the tools developed to combat soil or land and or terrestrial pollution, as well as the benefits of using these tools to increase soil fertility and reduce potential toxicity.

KHCO3 activated biochar supporting MgO for Pb(II) and Cd(II) adsorption from water: Experimental study and DFT calculation analysis

A new strategy that simultaneous use of KHCO₃ activated biochar and nano-MgO incorporation for Pb²⁺ and Cd²⁺ removal from water was raised. After activating by KHCO₃, the BC showed a higher surface area and could carry more MgO nanoparticles the BC owned. The synthesized MgO-K-BC had a large adsorption capacity for Pb²⁺ (1625.5 mg/g) and Cd²⁺ (480.8 mg/g). Multiple characterization and comparative test have been performed to demonstrate that ion-exchange, precipitation, and complexation are the main mechanisms for Pb²⁺ and Cd²⁺ removal by MgO-K-BC. In order to further explore the adsorption mechanism in-depth, the density functional theory (DFT) calculation combined with experimental results were performed. The O-top of MgO was the most stable adsorption site for Pb²⁺/Cd²⁺ adsorption compared with other adsorption sites (Mg-top, bridge, and hollow). In addition, the results of charge density maps and projected density of state (PDOS) showed that the overlap of electron cloud and orbits between MgO and Pb²⁺ were denser than Cd²⁺, indicating that MgO-K-BC had a stronger affinity for Pb²⁺ than Cd²⁺, so that, MgO-K-BC had a higher adsorption capacity for Pb²⁺ than Cd²⁺. This work provides a deep understand of the mechanism for heavy metals adsorption by metal oxide and a practical and theoretical guidance for adsorbent preparation with high adsorption ability for heavy metal.

Green and eco-friendly synthesis of TiO2 nanoparticles and their application for removal of cadmium from wastewater: reaction kinetics study

The heavy metal cadmium (Cd) is known to be a widespread environmental contaminant and a potential toxin that may adversely affect human health across the globe. Green nanotechnology has recently received a lot of attention for developing eco-friendly, low-cost renewable and sustainable materials for the efficient removal of persistent contaminants from wastewater, including heavy metals (HMs). The current study compared the ability of titanium dioxide nanoparticles (TiO2 NPs) synthesized from Trianthema portulacastrum (A) and Chenopodium quinoa (B) extracts to remove Cd from wastewater. The washed biomass of both the plants was dried under shade for a few days and was ground into the fine particles in a blender. The powdered biomass of T. portulacastrum and C. quinoa was soaked separately in distilled water (@ 10 g/100 ml) for 36 h. The stock solution of titanium (0.3 M) was prepared from concentrated titanium tetraisopropoxide (TTIP) and was mixed with the plant extracts at 1:2 ratio of extract to TTIP solution with continuous stirring at room temperature. A light brown scum like TiO2-NPs were obtained at the bottom of china dish and calcined at 450 °C for 4 h. Finally, after natural cooling, the TiO2-NPs were collected and used for the sorption of Cd through wastewater. Sorption attributes of both TiO2 NPs (A, B) were investigated over contact time, dosage of adsorbent, pH, and initial concentration of Cd. Maximum sorption was obtained (46 mgg−1) by TiO2 NPs (A), followed by 44 mg Cd g−1 with TiO2 NPs (B) at pH 4.2, an optimum adsorbent dosage 0.7 g L−1, Cd initial level 30 mg L−1, with contact time of 2 h. Pseudo-second-order kinetic model was suited for adsorption experimental data using both nanoparticles. These results validated the potential use of TiO2 NPs to remove liquified cadmium at high concentrations from the industrial wastewater.

Recent Progress on Nanomaterial-Based Membranes for Water Treatment

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, the nanomaterials pave a new pathway for ultra-fast and extremely selective water purification membranes. Membrane enhancements after the inclusion of many nanomaterials, including nanoparticles (NPs), two-dimensional (2-D) layer materials, nanofibers, nanosheets, and other nanocomposite structural materials, are discussed in this review. Furthermore, the applications of these membranes with nanomaterials in water treatment applications, that are vast in number, are highlighted. The goal is to demonstrate the significance of nanomaterials in the membrane industry for water treatment applications. It was found that nanomaterials and nanotechnology offer great potential for the advancement of sustainable water and wastewater treatment.

A State-of-the-Art Review on Innovative Geopolymer Composites Designed for Water and Wastewater Treatment

There is nothing more fundamental than clean potable water for living beings next to air. On the other hand, wastewater management is cropping up as a challenging task day-by-day due to lots of new additions of novel pollutants as well as the development of infrastructures and regulations that could not maintain its pace with the burgeoning escalation of populace and urbanizations. Therefore, momentous approaches must be sought-after to reclaim fresh water from wastewaters in order to address this great societal challenge. One of the routes is to clean wastewater through treatment processes using diverse adsorbents. However, most of them are unsustainable and quite costly e.g. activated carbon adsorbents, etc. Quite recently, innovative, sustainable, durable, affordable, user and eco-benevolent Geopolymer composites have been brought into play to serve the purpose as a pretty novel subject matter since they can be manufactured by a simple process of Geopolymerization at low temperature, lower energy with mitigated carbon footprints and marvellously, exhibit outstanding properties of physical and chemical stability, ion-exchange, dielectric characteristics, etc., with a porous structure and of course lucrative too because of the incorporation of wastes with them, which is in harmony with the goal to transit from linear to circular economy, i.e., "one's waste is the treasure for another". For these reasons, nowadays, this ground-breaking inorganic class of amorphous alumina-silicate materials are drawing the attention of the world researchers for designing them as adsorbents for water and wastewater treatment where the chemical nature and structure of the materials have a great impact on their adsorption competence. The aim of the current most recent state-of-the-art and scientometric review is to comprehend and assess thoroughly the advancements in geo-synthesis, properties and applications of geopolymer composites designed for the elimination of hazardous contaminants viz., heavy metal ions, dyes, etc. The adsorption mechanisms and effects of various environmental conditions on adsorption efficiency are also taken into account for review of the importance of Geopolymers as most recent adsorbents to get rid of the death-defying and toxic pollutants from wastewater with a view to obtaining reclaimed potable and sparkling water for reuse offering to trim down the massive crisis of scarcity of water promoting sustainable water and wastewater treatment for greener environments. The appraisal is made on the performance estimation of Geopolymers for water and wastewater treatment along with the three-dimensional printed components are characterized for mechanical, physical and chemical attributes, permeability and Ammonium (NH4+) ion removal competence of Geopolymer composites as alternative adsorbents for sequestration of an assortment of contaminants during wastewater treatment.

Quantitative analysis on the mechanism of Cd2+ removal by MgCl2-modified biochar in aqueous solutions

In this study, a pristine biochar (BC) and MgCl₂-modified biochar (MBC) were prepared using Pennisetum sp. straw for removing Cd²⁺ from aqueous solutions. Scanning electron microscope (SEM) imaging combined with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), as well as the surface area and porosity analyses were used to reveal the physico-chemical characteristics of the pristine and modified adsorbents. Results suggested that MgCl₂ impregnation during the synthesis had enhanced the specific surface area and pore volume of the biochar. Batch adsorption experiments indicated that the Cd²⁺ adsorption data of MBC fitted the Langmuir isothermal and pseudo-second order kinetic models, indicating a chemical adsorption was undergoing in the system. The maximum adsorption capacity of Cd²⁺ on MBC was 763.12 mg/g, which was 11.15 times higher than that of the pristine BC. The Cd²⁺ removal by MBC was mainly attributed to the mechanisms in an order: Cd(OH)₂ precipitation (73.43%) > ion exchange (22.67%) > Cd²⁺-π interaction (3.88%), with negligible contributions from functional group complexation, electrostatic attraction and physical adsorption. The MBC could thus be used as a promising adsorbent for Cd²⁺ removal from aqueous solutions.

Efficient performance of magnesium oxide loaded biochar for the significant removal of Pb2+ and Cd2+ from aqueous solution

Lead (Pb) and cadmium (Cd) are considered as a typical heavy metals in aqueous solution, which may pose adverse health effects on human beings. For the removal of these two pollutants, magnesium oxide (MgO) was successfully immobilized onto eucalyptus biochar (BC) matrix via simple and cost-effective pyrolysis process of MgCl₂-pretreated eucalyptus biomass under high temperature (500 °C). Synthesized MgO nanoparticles-biochar composites (MBC) exhibited superior removal performance for target pollutants, and achieve 99.9% removal efficiency for Pb(II) and Cd(II) at optimum conditions (0.02 g, pH in range of 4-7, and reaction time 120, 240 min). Furthermore, the maximum theoretical adsorbing amount of MBC was 829.11 mg/g for Pb(II) and 515.17 mg/g for Cd(II). Pseudo-second-order model and Langmuir models were well-determined for isotherm and adsorption kinetics. FTIR, XRD, and XPS analysis revealed that precipitation and ion exchange was of great importance for the removal of contaminants. Besides, cation-π interaction and complexation from the carbon-containing functional groups should not be neglected. Considering the advantage of low-cost, facile preparation, and brilliant adsorption capacity, it is anticipated that MBC has a promising prospect for the broad application in Pb(II)/Cd(II)-containing wastewater treatment.

Superadsorbent Fe3O4-coated carbon black nanocomposite for separation of light rare earth elements from aqueous solution: GMDH-based Neural Network and sensitivity analysis

A series of nanocomposites adsorbents with different magnetite/carbon black ratios were synthesized by using the co-precipitation method and used for separation of LREEs (Ce, La, and Nd) from aqueous solution. The adsorption efficiency of nanocomposites is strongly dependent on both pH and the loading carbon on nanocomposite. The maximum adsorption capacity (370 mg/g) was reported by nanocomposite with 20% Fe3O4 and 80% carbon in pH 7 for LREE initial concentration of 250 ppm. Results revealed that the LREEs adsorption behavior of the optimal adsorbent fits well with Langmuir isotherm and pseudo-first-order kinetic model. Moreover, the average values of thermodynamic parameters suggest the endothermic and irreversible chemisorption mechanism. An empirical correlation was obtained by using GMDH (Group Method of Data Handling)-based Neural Network to predict the adsorption kinetics of LREEs as a function of ion's electronegativity, molecular weight, and initial concentration. The results showed that the correlation can predict the experimental data mostly lower than 12.5% and it can predict the results of other researches with similar conditions with up to 25% from the experimental values. Finally, the results of sensitivity analysis revealed that the adsorption of LREEs is more sensitive to ions electronegativity and molecular weight at equilibrium conditions.

Understanding the fundamentals of microbial remediation with emphasize on metabolomics

The post-genomic tool metabolomics is a great advancement in science and technology which acquires novel strategies and pathways to analyze various biological compounds. Metabolomics aids in retrieving the qualitative and quantitative data from the various biological system. The current review is focused on the application of metabolomics in bioremediation and helps to focus on the xenobiotic compounds which are discharged into the environment and have long term impact. The microbial based biodegradation can be effectively used along with the combination of metabolomic approach for a better understanding of the breakdown of certain recalcitrant. Additionally, this review also discusses the candidate gene approach which helps to comprehend the functional analysis of microbial genes in response to different contaminants. Therefore, this review intends to discuss the metabolomics in bioremediation by studying the complete set of metabolites involved during the process of degradation and their interaction with the environment.

Efficient degradation of tetracycline in wide pH range using MgNCN/MgO nanocomposites as novel H2O2 activator

Currently existing Fenton-like catalysts were limited in wastewater treatment owing to their potential transition-metal poisoning, narrow applicable pH range and high dependence on external energy excitation. In this work, the MgNCN/MgO nanocomposites were firstly synthesized by a facile one-pot calcination of melamine and basic magnesium carbonate, and used as novel H₂O₂ activator for antibiotic removal. It was found that the MgNCN/MgO composite calcined at 550°C with the mass ratio of melamine to basic magnesium carbonate at 2:1, exhibited an excellent catalytic ability to tetracycline (TC) degradation in a wide pH range of 4-10 without any external energy input. More than 90% of TC (100 mL, 50 mg/L) could be degraded within 30 min by 10 mg of the nanocomposite in the presence of 0.2 mL of 30 wt% H₂O₂. Based on the experimental results, it was concluded that the Mg-N coordination between MgNCN and MgO in MgNCN/MgO nanocomposites activated H₂O₂ to produce primary singlet oxygen (¹O₂) and minor hydroxyl radicals (·OH), responding for TC degradation. In addition, the degradation pathways of TC were deduced by determining the generated intermediates during the degradation process. This work provided a novel idea for designing transition-metal-free catalysts for nonradical activation of H₂O₂ in the absence of external energy excitation.

Magnetic Fe3O4/attapulgite hybrids for Cd(II) adsorption: Performance, mechanism and recovery

Herein, a Fe₃O₄ decorated attapulgite adsorbent (FA) is fabricated for the removal of Cd(II) from wastewater, and subsequently a feasible strategy for converting the saturated waste adsorbent to CdS/FA photocatalyst is reported. Owing to the in situ growth of Fe₃O₄ on the attapulgite (ATP), the FA adsorbents exhibit enlarged surface area and increased adsorption sites. More importantly, the strong interaction between Fe₃O₄ and ATP leads to changes of coordination environment around the O‒Fe‒O bond with the ATP. Based on the results of density functional theory calculations, the electrons are more readily transferred from Fe to O, and the hanging O atoms with more electronegativity act as the efficient adsorption sites for Cd(II), efficiently improving the adsorption performance of the Fe₃O₄ phases. Furthermore, the waste FA adsorbent could be conveniently separated from the treated water by magnets and converted to CdS/FA photocatalyst, which exhibits satisfying degradation efficiency for tetracycline with low concentration. This work provides a potential strategy to optimize the ATP-based materials for heavy ions adsorption and reutilize the waste adsorbents.

Template synthesis of ordered mesoporous MgO with superior adsorption for Pb(II) and Cd(II)

Ordered mesoporous MgO was synthesized via template method by using magnesium nitrate as a precursor and amphiphilic triblock copolymer Pluronic F127 as a template. The products were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and the Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface areas. The effects of aging time, relative humidity, and magnesium nitrate content on the morphology and textural properties of the products were studied. When the aging time was 36 h and the relative humidity was 40%, the ordered mesoporous MgO with uniform pore sizes (3.2 nm), high specific surface areas (517.2 m²/g), and high pore volumes (0.42 cm³/g) were obtained. Furthermore, the adsorption properties of ordered mesoporous MgO as adsorbent for removal of Pb(II) and Cd(II) ions were studied. The adsorption kinetics and isotherm data agreed well with pseudo-second-order model and Langmuir model, indicating that the adsorption of heavy metal ions on the ordered mesoporous MgO was mainly chemical and homogeneous adsorption. The maximum adsorption capacities for Pb(II) and Cd(II) ions were up to 3073.5 mg/g and 1485.1 mg/g, respectively.

Rhizopus oryzae-Mediated Green Synthesis of Magnesium Oxide Nanoparticles (MgO-NPs): A Promising Tool for Antimicrobial, Mosquitocidal Action, and Tanning Effluent Treatment

The metabolites of the fungal strain Rhizopus oryaze were used as a biocatalyst for the green-synthesis of magnesium oxide nanoparticles (MgO-NPs). The production methodology was optimized to attain the maximum productivity as follows: 4 mM of precursor, at pH 8, incubation temperature of 35 °C, and reaction time of 36 h between metabolites and precursor. The as-formed MgO-NPs were characterized by UV-Vis spectroscopy, TEM, SEM-EDX, XRD, DLS, FT-IR, and XPS analyses. These analytical techniques proved to gain crystalline, homogenous, and well-dispersed spherical MgO-NPs with an average size of 20.38 ± 9.9 nm. The potentiality of MgO-NPs was dose- and time-dependent. The biogenic MgO-NPs was found to be a promising antimicrobial agent against the pathogens including Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans with inhibition zones of 10.6 ± 0.4, 11.5 ± 0.5, 13.7 ± 0.5, 14.3 ± 0.7, and 14.7 ± 0.6 mm, respectively, at 200 μg mL-1. Moreover, MgO-NPs manifested larvicidal and adult repellence activity against Culex pipiens at very low concentrations. The highest decolorization percentages of tanning effluents were 95.6 ± 1.6% at 100 µg/ 100 mL after 180 min. At this condition, the physicochemical parameters of tannery effluents, including TSS, TDS, BOD, COD, and conductivity were reduced with percentages of 97.9%, 98.2%, 87.8%, 95.9%, and 97.3%, respectively. Moreover, the chromium ion was adsorbed with percentages of 98.2% at optimum experimental conditions.

Experimental and DFT studies on the characteristics of PbO/PbCl2 adsorption by Si/Al- based sorbents in the simulated flue gas

Mineral oxides are effective in-furnace sorbents used to control lead (Pb) emissions in flue gas at high temperatures. In this paper, the PbO/PbCl₂ adsorption characteristics of sorbents were investigated via experimental and density functional theory (DFT) methods. The results show that Si/Al-based compounds can chemically adsorb Pb, and the adsorption is related to the Si-O and Al-O bonds in the sorbents. Exposed Si and O atoms on SiO₂ surfaces and exposed Al and O atoms on Al₂O₃ surfaces are the active sites for Pb adsorption, and PbO is easier to remove than PbCl₂. Pb adsorption is promoted in a mixture of SiO₂ and Al₂O₃. Doping Si atoms into Al₂O₃(100) promotes PbO adsorption, and doped three-coordinate Si atoms have a more obvious promotion effect than doped two-coordinate Si atoms. Doping Al atoms into SiO₂(001) has no obvious effect on PbO adsorption. The effect of temperature on Pb adsorption was studied by thermodynamic analysis. The Gibbs free energy difference for PbO adsorption on SiO₂(001) increases from -373.04-32.42 kJ/mol as the temperature increases from 300 to 1800 K. High-temperature calcination changes the bond length and bond angle of the system, affecting the stabilities of atomic configurations and decreasing the Pb adsorption capacity.

Simultaneous adsorption of Cd2+ and photocatalytic degradation of tris-(2-chloroisopropyl) phosphate (TCPP) by mesoporous TiO2

In this work, the prepared mesoporous TiO₂ was employed to eliminate the environmental risk induced by the combined pollution (tris-(2-chloroisopropyl) phosphate (TCPP) and Cd²⁺). The prepared material was characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (UV-DRS), Raman imaging spectrometer (Raman), N₂ adsorption/desorption isotherm and X-ray photoelectron spectroscopy (XPS). In the combined pollution system, the prepared TiO₂ simultaneously exhibited a higher adsorption and photocatalytic activity for Cd²⁺ and TCPP at neutral condition, respectively. The adsorption of Cd²⁺ and photo-degradation of TCPP by mesoporous TiO₂ followed pseudo-second-order and pseudo-first-order kinetics model, respectively. The removal efficiency of TCPP was improved from 67% to 100% when the concentration of co-existed Cd²⁺ increased from 0.5 mg L^-1 to 2 mg L^-1, due to the fact that the adsorbed Cd²⁺ on the surface of TiO₂ scavenged electron and thus inhibited the photo-generated electron-hole pairs recombination. In addition, six degradation intermediates were determined by high resolution mass spectrum (HRMS) and potential transformation pathways of TCPP under the co-existence of Cd²⁺ were proposed. The results suggested that rapid and high-efficient simultaneous removal of Cd²⁺ and TCPP was feasible, which laid the basis for the remediation of other combined pollution in the future.

Selective Capacitive Removal of Pb2+ from Wastewater over Redox-Active Electrodes

Water pollution has become an environmental hazard. Diverse metal cations exist in wastewater; lead is the most common heavy metal pollutant among them. Selective removal of highly toxic and ultradiluted lead ions from wastewater is a major challenge for water purification. Here, selective capacitive removal (SCR) of lead ions from wastewater over redox-active molybdenum dioxide/carbon (MoO₂/C) electrodes was developed by an environment-friendly asymmetric capacitive deionization (CDI) method. The MoO₂/C spheres act as cathodes of an asymmetric CDI device and effectively reduce the concentration of Pb²⁺ from 50 ppm to <0.21 ppb. Moreover, the SCR efficiency of lead ions over redox-active MoO₂/C electrodes is >99% in mixtures of 100 ppm Pb(NO₃)₂ and 100 ppm NaCl solutions. In addition, the electrodes exhibit high regeneration performance in mixtures of NaCl and Pb(NO₃)₂ and high SCR efficiency for lead ions from mixtures of heavy metal ions. The tetrahedral structure of the [MoO₄] lattice is shown to be more favorable for the intercalation of lead ions. In situ Raman spectroscopy further shows that the transition of the crystal interface between [MoO₆] and [MoO₄] cluster lattice could be electrochemically controlled during SCR. Therefore, this study provides a new direction for the SCR of lead ions from wastewater.

Pb2+ and Cd2+ recovery from water using residual tea waste and SiO2@TW nanocomposites

This work reports the fabrication of SiO₂@TW nanocomposites and their application for Pb²⁺ and Cd²⁺ ions sequestration from simulated water. Residual tea waste has also been used for metal ions sequestration to compare the potential of SiO₂@TW nanocomposites. The SEM, TEM, BET, FTIR and EDX techniques were employed for the characterization of SiO₂@TW nanocomposites and residual tea waste. Particle sizes of SiO₂@TW nanocomposites was in the range of 6.8-12 nm. The experiments were carried out in batch mode to explore the effect of various operating parameters on the sequestration of Pb²⁺ and Cd²⁺ ions from water. The experimental data was subjected to various thermodynamic, kinetic and isothermic models. According to Langmuir model, the maximum adsorption efficiency of the SiO₂@TW nanocomposites was 153 mg/g for Pb²⁺ and 222 mg/g for Cd²⁺ but maximum adsorption efficiency of residual tea waste for Pb²⁺ was 125 mg/g and for Cd²⁺ was 142.9 mg/g. This study suggested that due to the presence of active sites SiO₂@TW nanocomposites has greater potential for metal sequestration than residual tea waste.

Using MgO nanoparticles as a potential platform to precisely load and steadily release Ag ions for enhanced osteogenesis and bacterial killing

Bio-functional fillers including bio-ceramic, degradable metallic and composite particles are commonly introduced into bone tissue engineering (BTE) scaffolds to endow the materials with specific biological functions for enhanced bone defect therapy. In this work, MgO nanoparticles (NPs) were employed as a potential platform for precise loading and sustained release of Ag⁺. The results showed that MgO NPs possessed strong adsorption capacity (almost 100%) towards Ag⁺ in AgNO₃ solutions with different concentrations (0.1, 1 and 10 mM). After the adsorption of Ag⁺ in AgNO₃ solutions, cube-shaped MgO NPs transformed to lamella-structured nano-composites (NCs) composed of Mg(OH)₂ and Ag₂O, which were referred as MgO-xAg (x = 0.1, 1 or 10) NCs depending on the employed concentration of AgNO₃ solution. After being suspended in distilled water, as-prepared positively charged NCs underwent a fast degradation process during the initial 4 days. From day 4 and 14, steady release behaviors of Mg²⁺ and/or Ag⁺ from the NCs were noticed. With the lowest loading amount of Ag⁺, MgO-0.1Ag NCs did not exhibit significant modulatory effect on SaOS-2 cell response. On the contrary, MgO-10Ag NCs loaded with the highest amount of Ag⁺ showed significant cyto-toxicity towards SaOS-2 cells. With appropriate amount of Ag⁺ loading, MgO-1Ag NCs showed significantly stimulatory effects on SaOS-2 cell proliferation and differentiation. This is evidenced by the enhanced cell viability, alkaline phosphatase (ALP) activity and collagen (COL) production as well as the gene expressions of ALP, COL and osteoprotegerin (OPG) in MgO-1Ag group. Moreover, MgO-1Ag exhibited strong bactericidal capacity against both Escherichia coli and Staphylococcus aureus. Together, the results indicate that MgO could be employed as a potential platform for precise loading and sustained release of Ag⁺. MgO-1Ag NCs are promising to be used as bio-functional fillers in BTE scaffolds for simultaneously promoted osteogenesis and bacterial killing.

Removal of Sb(III) from wastewater by magnesium oxide and the related mechanisms

Pollution and remediation of antimony in aquatic ecosystems have been paid increasing attention. In the present work, environmentally friendly nano-MgO was used for the first time to remove Sb(III) from the water system. The batch experiments indicated that the nano-MgO calcined at 400 °C (named 400-MgO) exhibited superior adsorption capacity for Sb(III). The adsorption isotherm was fitted well with the Freundlich model, and especially when the initial concentration is 15 mg‧L^-1, the adsorption capacity is as high as 140.1 mg‧g^-1. Researches through X-ray diffraction (XRD), Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) showed that the main removal mechanisms lie in the generation of Mg active sites, which is capable of coordinating Sb(III), during the hydration process of MgO, providing a nucleation center for the progressive production of MgSb₂O₄. As a whole, precipitation is the predominant mechanism for MgO to remove Sb(III). Over time, a part of MgO is hydrated to Mg(OH)₂, and consequent chemisorption also helps to remove Sb(III). Our work has demonstrated that nano-MgO is a promising adsorbent for Sb(III) removal from contaminated water and provided new insights into the interaction mechanism between MgO and Sb(III).