Adsorption mechanism of Pb2+ ions by Fe3O4, SnO2, and TiO2 nanoparticles

Template-Free Synthesis of Phosphorus/Nitrogen-Doped Mesoporous Titania Materials with Excellent Adsorption for Lysozymes

Element-doped mesoporous titanium oxide has significant advantages in substance separation and adsorption due to its larger specific surface area and stronger hydrophobicity. However, its current synthesis methods have limitations such as complicated preparation process, high production cost, or not being environmentally friendly, and the synthesis of elementally doped titanium oxide materials by simple, low-cost, and green means is the research goal of this study. In this study, phosphorus-doped mesoporous titanium oxides (TiP) materials have been synthesized through a facile template-free method in an ethanol system, which were further modified by nitrogen doping with the use of urea as the nitrogen source. Both the synthesized TiP and P-N codoped sample (N-TiP) are amorphous with mesopores. It was revealed by FTIR and XPS spectra that the formation of Ti-O-P and -O-Ti-N bonds in the synthesized samples was due to the partial substitution of phosphorus for titanium in Ti-O-Ti bonds in mesoporous titanium oxide, while nitrogen replaced some oxygen in the -O-Ti-O bonds in the form of anions. The TiP sample was estimated by the BET method to have a relatively large surface area, up to 317 m2/g. The adsorption of TiP and N-TiP materials to lysozyme protein in a buffer solution at different pH values showed that the adsorption of TiP to lysozyme protein was larger, which was 32.68 μmol/g. It shows that TiP has potential as a multifunctional adsorbent.

A hybrid mesoporous composite of SnO2 and MgO for adsorption and photocatalytic degradation of anionic dye from a real industrial effluent water

Water pollution by synthetic anionic dyes is one of the most critical ecological concerns and challenges. Therefore, there is an urgent need to find an efficient adsorbent and photocatalyst for dye removal. In the present study, we aimed to fabricate a hybrid mesoporous composite of spongy sphere-like SnO2 and three-dimensional (3D) cubic-like MgO (SnO2/MgO) as a promising adsorbent/photocatalyst to remove the anionic sunset yellow (SSY) dye from real wastewater at neutral pH conditions. The as-synthesized SnO2 and MgO composite was investigated using XRD, SEM, EDX, TEM, XPS, BET, and zeta potential. The experimental study of the SSY removal using SnO2/MgO composite was performed at different conditions, such as pH, stirring time, dose, and temperature. More than 99% of 10 mg/L SSY was effectively adsorbed from aqueous solution using 40 mg of SnO2/MgO composite at pH 7 and a stirring time of 60 min. The SSY adsorption behavior was well fitted by pseudo-second order and the Langmuir model, indicating that the SSY was chemisorbed to the composite-active sites as a monolayer. On the other hand, photocatalytic degradation process exhibited better results in terms of speed of removal and used quantity of photocatalyst, where 20 mg of SnO2/MgO composite can be used to remove > 99% of SSY dye within 30 min. Mechanism of SSY adsorption and photocatalytic degradation was discussed. In addition, elution experiments demonstrated that the SnO2/MgO composite as an SSY adsorbent could be reused for nine cycles without considerable reduction in the SSY adsorption efficiency. Therefore, this work exhibited that the mesoporous SnO2/MgO composite can be considered an effective adsorbent/photocatalyst to remove SSY dye from real industrial effluent water at neutral pH conditions.

Fabrication and application of nanosized stannic oxide for sorption of some hazardous metal ions from aqueous solutions

A batch equilibrium method was utilized to evaluate the retention of Fe(III) and Pb(II) onto stannic oxide (SnO2) nanomaterial. SnO2 was prepared by a simple precipitation method and characterized by different analytical apparatuses like FT-IR, SEM, TEM, and XRD. Scherrer’s formula and Williamson-Hall (WH) analysis were utilized to detect the crystallite size and lattice strain. The XRD and TEM data revealed that SnO2 has a nanoscale and crystalline nature. The retention study for Fe(III) and Pb(II) includes the influence of shaking time, batch factor, pH, initial concentrations, capacity, and applications. The data reveal that the maximum uptake of SnO2 was achieved at pH 2.5 and 3.7 for Fe(III) and Pb(II), respectively. SnO2 has a fast kinetic (60 min) and the reaction kinetic data obey the pseudo–second-order model. The capacity has values of 50.4 and 48.8 mg/g for Fe(III) and Pb(II), respectively. The real sample applications proved that SnO2 is an excellent sorbent for the capture of Pb(II) and Fe(III) from industrial wastewater and low-grade monazite (LGM) respectively, in addition to the capture of 59Fe radionuclide from low-level radioactive waste (LLRW).

XPS and NMR analyze the combined forms of Pb in Cladophora rupestris subcells and its detoxification

In this study, the combined forms of Pb in Cladophora rupestris (L.) (C. rupestris) were investigated via X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), different Pb concentrations (0, 0.5, and 5.0 mg/L), and C. rupestris subcells were explored. Results showed that combined forms of Pb mainly account for Pb-polysaccharides (Pb-OH of carbohydrates) in the cell wall, Pb-protein (Pb-N= and (C-N-)₂Pb) in the organelle, and Pb-organic acid (Pb-sulfates, (CO)₂-Pb and (COO)₂-Pb) in the soluble fraction. Pb-S-containing group (Pb-C-S) could formed in subcelluar when C. rupestris was subjected to high Pb stress. Meanwhile, Pb²⁺ could penetrate the C. rupestris cells via the formed chelate between GSH/MT and -OH functional groups. Results could help understand the role of subcellular fraction in the algae remediation and detoxification to heavy metal.

Photocatalytic degradation performance of gaseous formaldehyde by Ce-Eu/TiO2 hollow microspheres: from experimental evaluation to simulation

Gaseous formaldehyde present indoors is often in low-medium concentration, as compared to that contained in manufactured products, but still poses great threat to human health. Thus, this work aims to fabricate Ce-Eu/TiO₂ hollow microspheres, which showed excellent photocatalytic performance toward formaldehyde. Furthermore, photocatalytical degradation performance of Ce-Eu/TiO₂ hollow microspheres toward formaldehyde was investigated. The kinetics of degradation mechanism of gaseous formaldehyde for different concentrations and different temperatures vs time were studied, and the simulation and experimental results were also compared. It was found that formaldehyde concentration had an effect on the degradation process, which was consistent with different kinetics reactions. At low concentration, the degradation rate was decided by the adsorption rate, and no accumulation of adsorbent occurred. This process was consistent with the first-order kinetics law, which was established by L-H dynamics theory and Arrhenius equation. At medium concentration, the degradation process of formaldehyde was controlled by both adsorption and photocatalysis, which was consistent with the power law model. The 3D model of formaldehyde degradation process by Ce-Eu/TiO₂ hollow microspheres at different concentrations vs time was established, and the results showed that the simulation equations were in good agreement with the experimental results.

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.

Phosphorus regulates As uptake by rice via releasing As into soil porewater and sequestrating it on Fe plaque

Phosphorus (P) application rate can affect the As uptake by rice, but its mechanism lacks systematic studies. In this study, P fertilizers with different dosages (0, 75, 150, and 300 mg P₂O₅ kg^-1 soil) were used to investigate the effects of P on As release in soil porewater, As sequestration on Fe plaque and the change of abundance and communities of aioA and arsC genes in rhizosphere, and then explore its effect on As uptake by rice. Our results indicated that As content in brown rice under P0 and P75 treatments was 14.3-28.6% lower than that under P150 treatment. The total accumulation of As in brown rice under P0 treatment (1.51 μg plant^-1) was significantly lower than that under P150 treatment (2.17 μg plant^-1). Compared to P150 treatment, P0 treatment decreased the total As content in porewater but increased the proportion of As(V) to total As in porewater. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in rice roots and the Fe and As contents in Fe plaque were significantly higher under P0 treatment than under P150 treatment. Most of As (80.3-82.9%) sequestered by Fe plaque was in the form of arsenate (As(V)), and the associated As(V) on Fe plaque was 11.0% higher under P0 treatment than under P150 treatment. In addition, the abundance of aioA gene was 73.5% higher under P0 treatment than under P150 treatment, and the dominant aioA at genus level was Rhizobium and Rhodoferax. In general, P0 treatment led to higher root oxidation activity, which improved the formation of Fe plaque; and P0 treatment also improved the abundance of aioA gene in rhizosphere, thus increased the oxidation of As; so, P0 treatment indirectly enhanced As sequestration on Fe plaque, and that in turn reduced As accumulation in brown rice.

Rapid removal of lead(II) ions from water using iron oxide-tea waste nanocomposite - a kinetic study

Lead (Pb) ions are a major concern to the environment and human health as they are contemplated cumulative poisons. In this study, facile synthesis of magnetic iron oxide-tea waste nanocomposite is reported for adsorptive removal of lead ions from aqueous solutions and easy magnetic separation of the adsorbent afterwards. The samples were characterised by scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray diffraction, and Braunner-Emmet-Teller nitrogen adsorption study. Adsorptive removal of Pb(II) ions from aqueous solution was followed by ultraviolet-visible (UV-Vis) spectrophotometry. About 95% Pb(II) ion removal is achieved with the magnetic tea waste within 10 min. A coefficient of regression R² ≃ 0.99 and adsorption density of 18.83 mg g^-1 was found when Pb(II) ions were removed from aqueous solution using magnetic tea waste. The removal of Pb(II) ions follows the pseudo-second-order rate kinetics. External mass transfer principally regulates the rate-limiting phenomena of adsorption of Pb(II) ions on iron oxide-tea waste surface. The results strongly imply that magnetic tea waste has promising potential as an economic and excellent adsorbent for the removal of Pb(II) from water.

Phosphate-modified ferric-based material remediates lead and arsenic co-contaminated soil and enhances maize seedling growth

Soil heavy metal pollution, especially lead (Pb) and arsenic (As), is a global issue that requires urgent attention. In the present study, phosphate-modified ferric-based material (PFM) was used to remedy Pb and As co-contaminated soil. The remediation potential of PFM on Pb and As co-contaminated soil was studied by static culture experiments, and the effect on maize (Zea mays L.) seedling growth was studied using pot experiments. The results showed that the bioavailability of Pb and As in the soil and their accumulation in the seedlings were reduced when PFM was added to the soil. At 2-6 wt% PFM, the remediation rates of Pb and As reached 57%-82% and 62%-76%, respectively, and their accumulation in the seedlings decreased by 27.8%-68% and 55.6%-70%. The optimal amount of PFM was 4 wt% of the soil. There was a linear correlation between the amount of DTPA-extractable Pb or NaHCO₃-extractable As in the soil and the amount of Pb or As accumulated by the seedlings. The correlation coefficients of Pb and As reached 0.7690-0.8166 and 0.9982-0.9779. Seedling growth was also promoted. Compared with the controls, the seedling emergence rate increased by 1.4%-4%, plant height increased by 4.1%-12.4%, plant weight increased by 29.6%-37%, and the root length increased by 5%-52%. In summary, PFM offers an environmentally friendly approach with excellent potential for the remediation of Pb and As co-contaminated soil.

Removal of Pb(II) Ions from Wastewater by Using Polyethyleneimine-Functionalized Fe3O4 Magnetic Nanoparticles

A class of polyethyleneimine (PEI)-functionalized Fe3O4 magnetic nanoparticles (MNPs) has been facilely produced through a solvothermal process. The synthetic MNPs have been characterized by multiple technologies and then used for Pb(II) ion sorption from the aqueous media in different conditions. It was found the Pb(II) adsorption behaviors could be well fitted by the pseudo second-order kinetic and Langmuir isotherm models. The maximum Pb(II) adsorption capacity at 25 °C and pH 5.0 was calculated to be 60.98 mg/g. Moreover, effects of temperature, pH, and electrolyte of aqueous phase on the Pb(II) adsorption capacity of MNPs have been carefully examined. The Pb(II) adsorbing capacity was enhanced with temperature or pH rising, but reduced with the addition of various electrolytes. Additionally, the recyclability of synthetic MNPs has been also assessed. The prepared PEI-functionalized MNPs could still maintain good adsorption performance after five cycles of Pb(II) removal. These results indicated that the PEI-functionalized Fe3O4 MNPs could be readily synthesized and served as a desirable and economic adsorbent in Pb(II)-contaminated wastewater treatment.