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As one of the most toxic heavy metal ions, lead pollution has become an urgent problem. Here, a cubic crystal nanoparticle (Prussian blue analogue, PBA), referred to as potassium manganese ferrocyanide (KMFC) was synthesized and used as a highly-effective sorbent for removing Pb(II) from aqueous solution. KMFC is a mesoporous material that has excellent ion exchange properties, which was confirmed by a series of characterizations. This paper investigated the adsorptive attributes of KMFC for lead ions in aqueous solution. The influences of temperature, contact time and pH on adsorption were studied in batch experiments. The KMFC possessed a robust adsorption capacity for resident lead ions in aqueous solution, which attained 1075.27 mg g−1 at room temperature (25 °C), based on the Langmuir model, which was far higher than any previously reported values. The adsorption process was well fitted to a pseudo-second-order kinetic model, as well as Langmuir and Temkin isotherm models, and was endothermic and spontaneous on the basis of thermodynamic analysis. The adsorption of Pb(II) on the surface of KMFC started with electrostatic attraction, due to the electronegativity of KMFC. Further, ion exchange was the dominant mechanism in this adsorption process, which was confirmed by FTIR, XPS, and other supplementary experiments. The good chemisorption (K+ exchange) properties of KMFC suggested that it likely has excellent prospects in applications for heavy metal ions adsorption. This study not only provided a new perspective for the design and development of heavy metal sorbents but provided a deep insight into the mechanism of adsorption of heavy metal ions by PBA.

The adsorption behavior and mechanism of Cr(VI) on different acid-modified UiO-66s (Form-UiO-66 and Ac-UiO-66) were systematically investigated for the first time through a series of characterizations, and theoretical calculations of batch experiments. The characterization results demonstrate that acid-modified UiO-66 exhibited a larger specific surface area than did unmodified UiO-66. In addition, since the regulator (formic acid) of Form-UiO-66 was the stronger competition, the specific surface area of Form-UiO-66 (1138 m2 g−1) was larger than that of Ac-UiO-66 (915 m2 g−1). Under optimal experimental conditions, the maximum adsorption capacity of Cr(VI) was 243.9 mg g−1 on Form-UiO-66, and 151.52 mg g−1 on Ac-UiO-66, which was far higher than on the reported unmodified UiO-66 (36.4 mg g−1). The results of pH testing, zeta potential, and X-ray photoelectron spectroscopy analysis indicate that Cr(VI) ions were fixed to adsorbent surfaces via electrostatic adsorption. Acid-modified UiO-66 increased the surface active site via the increase in its specific surface area to enhance adsorption capacity of Cr(VI). These results indicated that both the surface charge and specific surface area of the adsorbent primarily determined the Cr(VI) adsorption capacity. Acid modified UiO-66 exhibited enhanced adsorption capacity, stability, and regeneration, compared to traditional adsorbents, and these results provide new insights into adsorption by MOFs.

Lead pollution has become a global concern due to its ubiquity and persistence. This study describes two Fe Mn oxide substrate adsorbents, namely, Fe Mn binary oxides (FMBO) and mesoporous Fe Mn binary oxide (MFMBO) covered with tannic acid film (FMBO@TA-Fe3+ and MFMBO@TA-Fe3+), for the treatment of Pb2+ in water. The characterization results showed that TA was successfully coated onto the surfaces of FMBO and MFMBO. The maximum capacities of Pb2+ on FMBO@TA-Fe3+ and MFMBO@TA-Fe3+ were 322.08 and 357.14 mg g−1, respectively, which were twice those of FMBO and MFMBO. The adsorption of Pb2+ on the adsorbents was a spontaneous, endothermic process with increasing disorder through thermodynamics studies. An overall mechanism was proposed for Pb2+ adsorption, the improved adsorption performance of FMBO@TA-Fe3+ and MFMBO@TA-Fe3+ is ascribed to the mesoporous characteristics and the introduction of hydroxyl groups. Further investigation indicated the adsorption of Pb2+ could be attributed to electrostatic interactions on FMBO@TA-Fe3+ and MFMBO@TA-Fe3+, and cation exchange existed through the formation of these internal surface complexes. The Pb2+-loaded adsorbents could be effectively desorbed in a dilute hydrochloric acid solution, promoting recycling and reuse of the regenerated adsorbents. These results warrant the promising application of FMBO@TA-Fe3+ and MFMBO@TA-Fe3+ for the removal of Pb2+, and this work first proposed TA film-modified FMBO and MFMBO to improve its adsorption capacity in the application of environmental remediation.

In this study, a novel and highly efficient ternary photocatalytic ZnFe2O4/TiO2/CDs nanocomposite was successfully synthesized by a hydrothermal method. The properties and structures of the samples were characterized by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier transform infrared spectrometry (FT-IR), and photoluminescence spectrum (PL). The UV–vis diffuse reflectance spectrum was used to demonstrate that carbon quantum dots could increase the absorption of visible light wavelengths. When compared with TiO2/3.00 wt%CDs and ZnFe2O4/TiO2 nanocomposites, the ternary photocatalysts exhibited the enhanced photocatalytic activity under solar-spectrum irradiation. A low CDs content of 3.00 wt% in the ternary photocatalysts possessed excellent performance in the decomposition of Rhodamine B (RhB). Act as donator and receiver, CDs can efficiently improve the ability of electron transfer and separate the electron-hole pairs. OH and O2 − were confirmed to be involved in the photocatalytic degradation of RhB base on the Electron spin resonance (ESR) tests, and the photocatalytic mechanism of the ZnFe2O4/TiO2/3.00 wt%CDs was proposed. After four sequential operational cycles, the ZnFe2O4/TiO2/CDs maintained its photocatalytic efficiency, indicating its high photocatalytic stability. Therefore, our results provide a high efficient photocatalytic nanocomposite that synthetized by a facile method, and have implications in the removal of environmental persistent pollutants under ternary photocatalysts mediated solar degradation

Multi-cycle and long-term ablation behavior of Cf/ZrB2-SiC composite was evaluated by plasma ablation flame at 2500 °C. The composites can be protected by the oxide layer with uniform distribution of ZrO2 particles in SiO2 melt. However, the structural stability of the oxide layer could be destroyed due to the phase transition of ZrO2 and violent evaporation of SiO2, resulting from the aggregation and growth of ZrO2 during multi-cycle and long-term ablation. It is of great significance to optimize the composition and microstructure of the oxide layer to retard the aggregation, growth and phase transition of ZrO2.

In situ immobilization constitutes a promising technology for the mitigation of contaminants, through the reduction of metal bioavailability and mobility. This study investigated the adsorption isotherms and kinetic characteristics of humin extracted from peat soils. We also studied the influences of the pH, ionic strengths, and soluble organic matter concentrations of soil solutions on the adsorptive properties of humin, and compared its ability to detoxify potentially toxic metals in both actual and simulated soil solutions. The study results indicated that humin contains a massive population of oxygen-containing functional groups. Its adsorption capacity for Pb(II) was greater than that for Cu(II), which exceeded that for Cd(II). The adsorption of humin for Pb(II) conformed to the Freundlich model, while the adsorption of humin for Cd(II) and Cu(II) followed the Langmuir model. The adsorption kinetics of humin with respect to potentially toxic metals aligned well with second-order kinetics equa...