Controllable synthesis of coral-like hierarchical porous magnesium hydroxide with various surface area and pore volume for lead and cadmium ion adsorption

Magnetic composite microspheres with a controlled mesoporous shell for highly efficient DNA extraction and fragment screening

Rapid extraction and screening of high-purity DNA fragments is an indispensable technology in advanced molecular biology. In this article, mesoporous magnetic composite microspheres (MSP@mTiO2) with tunable pore sizes were successfully fabricated for high-purity DNA extraction and fragment screening. Owing to the strong complexation ability of Ti ions with DNA phosphate groups and the high specific surface area of mesoporous microspheres, the MSP@mTiO2 microspheres possess excellent adsorption performance, where the saturated loading capacity of MSP@mTiO2 with a specific surface area of 122 m2 g-1 is as high as 575 μg mg-1 for a salmon sperm specimen. ITC experiments demonstrated that DNA adsorption on MSP@mTiO2 microspheres is mainly driven by entropy, which gives us more potential ways to regulate the balance of adsorption and desorption. Meanwhile, the mesoporous MSP@mTiO2 microspheres exhibit a much higher extraction efficiency compared with non-porous MSP@TiO2 for whole genome DNA from Arabidopsis thaliana plants. Interestingly, DNA fragments with different lengths could be screened by simply regulating the pore size of MSP@mTiO2 or the concentration of Na3PO4 in the eluent. A small pore size and low phosphate concentration are advantageous for the extraction of short-stranded DNA fragments, and DNA fragments (≤1000 bp) can be efficiently extracted when the mesopore size of MSP@mTiO2 is lower than 7.6 nm. The extraction results from the mesoporous composite microspheres provide new promising insights into the purification and screening of DNA from complex biological samples.

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.

Contrasting effects of MgAl- and MgFe-based layered double hydroxides on phosphorus mobilization and microbial communities in sediment

The effects of two types of layered double hydroxides (LDH) in-situ treatment on sediment phosphorus (P) mobilization and microbial community's structure were studied comparatively. The results presented that magnesium/aluminum-based (MA) and magnesium/iron (MF)-based LDH displayed great phosphate uptake ability in aqueous solution in a broad pH range of 3-8. The maximum phosphate sorption capacity of MA was 64.89 mg/g, around four times greater than that of MF (14.32 mg/g). Most of phosphate bound by MA and MF is hard to re-liberate under reduction and ordinary pH (5-9) conditions. In the in-situ remediation, the MA and MF capping/amendment both prevented P migration from the sediment to the overlying water (OL-water) under long-term anaerobic conditions, and MA had a better interception efficiency compared to MF in the same application mode. MA amendment significantly reduced mobile P (Mob-P) content in sediment and could remain its stable Mob-P inactivation capacity over a wide pH range. On the contrary, MF amendment increased Mob-P content in sediment and exhibited a variable ability to inactivate Mob-P under elevated pH conditions. MF can decrease Mob-P content at pH of 7 and 11 but increase Mob-P content at pH of 8-10. Under resuspension conditions, MA and MF capping groups still maintained low P levels in OL-water, while MA capping simultaneously showed a certain degree of resistance to sediment resuspension, but it had a weaker stabilizing effect for sediment than MF. Microbial community analysis manifested neither MA nor MF addition observably altered the sediment microbial diversity, but impacted the functional microorganisms' abundance and reshaped the microbial community's structure, intervening the sediment-P stabilization. Viewed from environmental friendliness, control efficiency, stability of P fixation capacity, and application convenience, MA capping wrapped by fabric is more suitable for addressing internal P loading in eutrophic lakes and holds great potential application.

Ultrasensitive determination of selenium in water and food samples by ICP-MS: UiO-66-NH2 for preconcentration and direct slurry hydride generation

BACKGROUND

Selenium is an indispensable microelement for humans and food is the main source of selenium intake. As one of the best techniques for the determination of selenium, inductive coupling plasma-mass spectrometry (ICP-MS) features some unique advantages, such as wide linear range and high sensitivity. Nevertheless, it still remains a challenge to achieve the accurate and high sensitivity determination of ultra-trace selenium in food samples by ICP-MS owning to the high first ionization energy of selenium and interferences from sample matrices as well as isobaric interferences.

RESULTS

In this work, UiO-66-NH2 (metal organic framework, MOF) was fast synthesized by microwave method and employed for the preconcentration of ultra-trace selenium with an adsorption efficiency of nearly 100%. The selenium-adsorbed MOF was collected by filtration, and then simply converted to slurry for in situ hydride generation (HG) for sensitive detection of selenium by ICP-MS. Various factors affecting the adsorption of selenium by the MOF (including pH, adsorption time, and amount of MOF) together with main parameters of hydride generation (including concentrations of HCl and NaBH4) were carefully evaluated. Experimental results show that effective matrix separation can greatly reduce interference, with an excellent detection limit of 1 ng/L. The practicability and accuracy of this method were successfully confirmed by the determination of trace selenium in several food samples.

SIGNIFICANCE

UiO-66-NH2 (MOF) was used as an effective adsorbent for the preconcentration of selenium prior to direct slurry sampling HG-ICP-MS determination. Direct slurry sampling avoided additional elution procedures and was conducive to eliminating matrix and isobaric interferences. High sensitivity and anti-interference determination were achieved for determination of ultra-trace Se in complex food samples.

Facile fabrication of Fe3O4@Mg(OH)2 magnetic composites and their application in Cu(ii) ion removal

In this study, we fabricated magnetic Fe3O4@Mg(OH)2 composites through the seed deposition technique to achieve Cu(ii) ion removal from aqueous solutions. As indicated by the characterization results, three-dimensional flower-like spheres composed of external Mg(OH)2 were formed, with nano-Fe3O4 particles uniformly embedded in the "flower petals" of the spheres. The efficacy of Fe3O4@Mg(OH)2-3 in Cu(ii) ion removal was examined through batch experiments. The impact of solution pH on removal efficiency was examined, and the pseudo-second-order model and the Langmuir model provided good fits to the adsorption kinetics and isotherm data, respectively. Remarkably, Fe3O4@Mg(OH)2-3 exhibited a significant removal capacity of 1051.65 mg g-1 for Cu(ii) ions. Additionally, the composite displayed a notable saturation magnetization value of 17.3 emu g-1, facilitating isolation from sample solutions through external magnetic fields after Cu(ii) ion absorption. At the solid-liquid interface, a mechanism involving ion exchange between Mg(ii) and Cu(ii) cations was realized as the mode of Cu(ii) ion removal. The composites' effective adsorption properties and rapid magnetic separation highlighted their suitability for use in treating copper-contaminated water.

Preparation of basic magnesium carbonate nanosheets modified pumice and its adsorption of heavy metals

Heavy metal pollution in wastewater poses a grave danger to the environment and the human body. Pumice is a mineral with abundant reserves and low prices, and its prospect of heavy metal adsorbent is very broad. In this work, we modified pumice with basic magnesium carbonate nanosheets by a convenient hydrothermal synthesis. The adsorption capacity of heavy metals is greatly improved. The effects of different pH and adsorption dosages are investigated. All the optimum pH values for Cu2+, Pb2+, and Cd2+ are 5. The adsorption of three kinds of ions conforms to the quasi-second-order adsorption kinetics model. The theoretical adsorption capacities of Cu2+, Pb2+, and Cd2+, which are calculated by the Langmuir model, are 235.29 mg/L, 595.24 mg/L, and 370.34 mg/L, respectively. The adsorption of Cu2+ and Cd2+ fit the Langmuir model better. The Freundlich model is fitted well with the adsorption of Pb2+. In the experiment simulating real wastewater, the adsorption capacity of heavy metals is not affected. It also shows good reusability in three regeneration cycles. And Mg5(CO3)4(OH)2·4H2O@pumice adsorption column showed the good removal efficiency of three heavy metals at different concentrations and different spatial velocities in the column experiment. Thus, it is believed that the Mg5(CO3)4(OH)2·4H2O@pumice is a promising adsorbent for the efficient removal of heavy metals.

Coal gangue-based magnetic porous material for simultaneous remediation of arsenic and cadmium in contaminated soils: Performance and mechanisms

Remediation of arsenic (As) and cadmium (Cd) co-contaminated soil is a challenge in environmental remediation. In this study, coal gangue-based magnetic porous material (MPCG) was designed for simultaneous immobilization of As and Cd in contaminated soil. After the incubation experiment, the effects of CG and MPCG on the availability and fractions of As and Cd and the related microbial functional genes were analyzed to explore the potential remediation mechanisms of MPCG for As and Cd in contaminated soil. The results showed that the stabilization effect of MPCG on As and Cd was significantly higher than that of coal gangue. It reduced the available As and Cd by 17.94-29.81% and 14.22-30.41%, respectively, and transformed unstable As/Cd to stable. The remediation mechanisms of MPCG on As included adsorption, oxidation, complexation and precipitation/co-precipitation. Meanwhile, the remediation mechanisms of MPCG for Cd included adsorption, ion exchange, complexation and precipitation. In addition, MPCG increases the abundance of sulfate-reducing bacteria (dsrA) by 43.39-381.28%, which can promote sulfate reduction. The sulfide can precipitate with As and Cd to reduce the availability of As and Cd in soil. Thus, MPCG is a promising amendment for achieving the remediation of As and Cd co-contaminated soil.

Preparation of Biochar Composite Microspheres and Their Ability for Removal with Oil Agents in Dyed Wastewater

Oil agents produced from the degreasing treatment of synthetic fibers are typical pollutants in wastewater from printing and dyeing, which may cause large-scale environmental pollution without proper treatment. Purifying oily dye wastewater (DTY) at a low cost is a key problem at present. In this study, biochar microspheres with oil removal ability were prepared and derived from waste bamboo chips using the hydrothermal method. The structure of the biochar microsphere was regulated by activation and modification processes. Biochar microspheres were characterized, and their adsorption behaviors for oily dye wastewater were explored. The results show that the adsorption efficiency of biochar microspheres for oily dye wastewater (DTY) was improved significantly after secondary pyrolysis and the lauric acid grafting reaction. The maximum COD removal quantity of biochar microspheres for DTY was 889 mg/g with a removal rate of 86.06% in 30 min. In addition, the kinetics showed that chemisorption was the main adsorption manner. Considering the low cost of raw materials, the application of biochar microspheres could decrease the cost of oily wastewater treatment and avoid environmental pollution.

Electrocatalytic hydrodechlorination system with antiscaling and anti-chlorine poisoning features for salt-laden wastewater treatment

The high salinity and coexistence of scaling ions (Ca²⁺, Mg²⁺, HCO₃^-) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl^- poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L ^- 1) with Ca²⁺ (80.0 mg L ^- 1), Mg²⁺ (30.0 mg L ^- 1) and HCO₃^- (180.0 mg L ^- 1), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl^- poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl^- at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pd^δ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.

Rapid and enhanced adsorptive mitigation of groundwater fluoride by Mg(OH)2 nanoflakes

Fluoride is one of the most abundant anions in groundwater, posing a significant threat to the safe drinking water supply worldwide. Fluoride contamination in drinking water at levels greater than 1.5 mg L^-1 causes a variety of serious health problems. To address this problem, the current study deals with the synthesis of Mg(OH)₂ nanoflakes by a facile and simple hydrothermal method in the absence of any added template. The sizes of these nanoflakes are in the range of 90 to 200 nm. These nanoflakes are pure and crystalline, possessing hexagonal phase structures. The surface areas of Mg(OH)₂ nanoflakes are varying from 75.8 to 108.1 m² g^-1. These Mg(OH)₂ nanoflakes exhibit excellent adsorption performance for fluoride over a pH range of 2.0 to 9.0 with a maximum Langmuir adsorption capacity of 3129 mg g^-1 at pH 7.0 at 313 K which is the highest for such kind of adsorbent reported so far. The adsorption process is spontaneous and endothermic which primarily follows pseudo-second-order kinetics. The adsorbent is effective in the presence of co-existing anions and is reusable up to the fifth cycle with a minimal loss of adsorption performance. The nanoflakes can effectively remove highly concentrated groundwater fluoride to a permissible limit within a short time which increases the versatility of using these nanoflakes for practical applications.

Improvement mechanism of water resistance and volume stability of magnesium oxychloride cement: A comparison study on the influences of various gypsum

The development of magnesium oxychloride cement can effectively utilize the waste of potash industry and reduce its harm to the environment. Although magnesium oxychloride cement paste (MOCP) has excellent performance in dry environment, its performance is greatly deteriorated in water or humid environment, which severely limits its practical application. In order to improve the water resistance of MOCP, MOCP was modified by various gypsum in this study, and the intrinsic mechanism was explored. Results showed that replacing MgO with gypsum delayed the setting time of MOCP and effectively improved its volume stability. Although the incorporation of gypsum reduced the 14-d air-cured compressive strength of MOCP, waste gypsum was able to significantly improve the water resistance of MOCP compared to natural gypsum. When 80% flue gas desulfurization gypsum and phosphogypsum (weight of magnesium oxide) were incorporated into MOCP, the 14-d air-cured compressive strength of MOCP was only decreased by 14.49% and 15.94% compared with the control group, but its 28-d water immersion strength retention coefficient (SRC) could still reach 61.02% and 46.55%, respectively. However, for the control group and MOCP with 80% natural gypsum, the 28-d SRC were only 28.99% and 8.41%. The incorporation of high-volume waste gypsum to MOCP not only reduced the relative content of MgO, but also improved the stability of the 5-phase in water, which was beneficial to improve the water resistance of MOCP. In addition, high-volume waste gypsum-modified MOCP had lower cost and carbon emissions, and exhibited superior water resistance and sustainability compared to existing MOCP compositions.