Core-Shell MnO2-SiO2 Nanorods for Catalyzing the Removal of Dyes from Water

Facile synthesis of Fe3O4/CuO a core-shell heterostructure for the enhancement of photocatalytic activity under visible light irradiation

A magnetically separable Fe₃O₄/CuO core-shell heterostructure photocatalyst was synthesized by hydrothermal method. The obtained photocatalyst was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible diffuse reflectance (UV-DRS). The obtained photocatalyst was used for the degradation of azo dye Direct Red 89 (DR89), under visible light irradiation provided by fluorescent lamp of 100 W in the presence of 7 mL of H₂O₂ (30%); the results of the photocatalytic activity for Fe₃O₄/CuO photocatalyst showed that in the presence of 0.75 g dispersed in 250 mL of 40 mg/L of DR89 dye at pH 6 the dye was completely removed after 240 min. Moreover, the photocatalytic activity of the prepared Fe₃O₄/CuO was enhanced 11 and 9 times compared with the pure Fe₃O₄ or CuO. The effect of initial dye concentrations on the photocatalytic activity was studied in the range of 20-60 mg/L, and the results showed that the catalyst has a good photocatalytic activity of 89% even at high concentration (60 mg/L). Furthermore, the catalyst maintained its activity after 5 cycles, and its paramagnetic property facilitates its recovery. The excellent photodegradation activity of Fe₃O₄/CuO was attributed to the low band gap of the catalyst equal to 1.54 eV and the enhancement of light absorption in visible range of 330-780 nm, but also to a better charge carriers separation, due to the presence of Fe₃O₄ that reduces electron/hole recombination.

Surface modification of polypropylene membrane for the removal of iodine using polydopamine chemistry

The development of stable and effective iodine removal systems would be highly desirable in addressing environmental issues relevant to water contamination. In the present research, a novel iodine adsorbent was synthesized by self-polymerization of dopamine (PDA) onto inert polypropylene (PP) membrane. This PP/PDA membrane was thoroughly characterized and its susrface propeties was analyzed by various analytical techniques indcluding field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), contact angle, and surface free energy measurement. The PP/PDA membranes were subsequently used for batchwise removal of iodine at different temperatures (25-70 °C), pH (2-7), and surface areas (1-10 cm²) to understand the underlying adsorption phenomena and to estimate the membrane capacity for iodine uptake. The increase in temperature and pH both led to higher adsorption of iodine. The present approach showed a removal efficiency of over 75% for iodine using 10 cm² PP/PDA membrane (18.87 m² g^-1) within 2 h at moderate temperatures (∼50 °C) and pH > 4, about 15 fold compared to the PP control membrane. The adsorption kinetics and isotherms were well fitted to the pseudo-second-order kinetic and Langmuir isotherm models (R² > 0.99). This adsorbent can be recycled and reused at least six times with stable iodine adsorption. These findings were attributed to the homogenous monolayer adsorption of the iodide on the surface due to the presence of catechol and amine groups in the PP/PDA membrane. This study proposes an efficient adsorbent for iodine removal.

Recent developments in MnO2-based photocatalysts for organic dye removal: a review

The textile industry consumes a large volume of organic dyes and water. These organic dyes, which remained in the effluents, are usually persistent and difficult to degrade by conventional wastewater treatment techniques. If the wastewater is not treated properly and is discharged into water system, it will cause environmental pollution and risk to living organisms. To mitigate these impacts, the photo-driven catalysis process using semiconductor materials emerges as a promising approach. The semiconductor photocatalysts are able to remove the organic effluent through their mineralization and decolorization abilities. Besides the commonly used titanium dioxide (TiO₂), manganese dioxide (MnO₂) is a potential photocatalyst for wastewater treatment. MnO₂ has a narrow bandgap energy of 1~2 eV. Thus, it possesses high possibility to be driven by visible light and infrared light for dye degradation. This paper reviews the MnO₂-based photocatalysts in various aspects, including its fundamental and photocatalytic mechanisms, recent progress in the synthesis of MnO₂ nanostructures in particle forms and on supporting systems, and regeneration of photocatalysts for repeated use. In addition, the effect of various factors that could affect the photocatalytic performance of MnO₂ nanostructures are discussed, followed by the future prospects of the development of this semiconductor photocatalysts towards commercialization.

Mutual effects of U(VI) and Eu(III) immobilization on interpenetrating 3-dimensional MnO2/graphene oxide composites

Radioactive contamination poses grievous latent threat to biology together with ecological balance. It is of great significance to eliminate radionuclides from nuclear waste solution. Herein, interpenetrating 3-dimensional (3D) MnO₂/GO composites (MGs) were rationally constructed by integrating α-crystal manganese dioxide (MnO₂) nanowire with graphene oxide (GO) via a simple ultra-sonication process. Preliminary experiments showed that the MG composite with mass ratio of 1:2 (M₁G₂) was the optimal material with superior adsorption capacities for U(VI) (271.7 mg/g) and Eu(III) (83.5 mg/g) at pH ~5.0 (298 K), as compared with commercial GO and individual MnO₂. Furthermore, M₁G₂ had high selectivity for U(VI) and Eu(III), which could remove >80% of target ions in the presence of NO₃^-, Cl^-, CO₃^2-, HCO₃^-, Mg²⁺, K⁺ or Na⁺ ions. It exhibited excellent stability under a wide range of pH 3-10 and great resistance to high ionic strength. More importantly, kinetic studies exhibited that M₁G₂ could efficiently capture target ions within ultra-short kinetic equilibrium time (<1 min). The interaction mechanism was clearly visualized by analyzing characterization data, showing that oxy-gen-containing functional groups took a major part for the binding of target ions. The excellent characteristics including the simple, fast and large-scale synthesis and the efficient performance endowed M₁G₂ with potential to remedy radioactive pollution in actual wastewater.

Synthesis of Hollow Flower-Like Fe3O4/MnO2/Mn3O4 Magnetically Separable Microspheres with Valence Heterostructure for Dye Degradation

In this manuscript, hollow flower-like ferric oxide/manganese dioxide/trimanganese tetraoxide (Fe3O4/MnO2/Mn3O4) magnetically separable microspheres were prepared by combining a simple hydrothermal method and reduction method. As the MnO2 nanoflower working as precursor was partially reduced, Mn3O4 nanoparticles were in situ grown from the MnO2 nanosheet. The composite microspheres were characterized in detail by employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), vibration sample magnetometer (VSM) and UV–visible spectrophotometer (UV–vis). Under visible light conditions, the test for degrading rhodamine B (RhB) was used to verify the photocatalytic activity of the photocatalyst. The results showed that the efficiency of the Fe3O4/MnO2/Mn3O4 photocatalyst in visible light for 130 min is 94.5%. The catalytic activity of photocatalyst far exceeded that of the Fe3O4/MnO2 component, and after four cycles, the catalytic performance of the catalyst remained at 78.4%. The superior properties of the photocatalyst came from improved surface area, enhanced light absorption, and efficient charge separation of the MnO2/Mn3O4 heterostructure. This study constructed a green and efficient valence heterostructure composite that created a promising photocatalyst for degrading organic contaminants in aqueous environments.

Fabrication of core-shell α-MnO2@polydopamine nanocomposites for the efficient and ultra-fast removal of U(vi) from aqueous solution

The development of functional nanoparticles with ultra-fast and high adsorption capacities is an important strategy for wastewater treatment. Here, α-MnO2@polydopamine nanocomposites (α-MnO2@PDAs) were synthesized by coating α-MnO2 nanowires with polydopamine and were used to remove U(vi) from solutions. The α-MnO2@PDAs possessed a large surface area (22.8 m2 g-1), excellent dispersibility, and abundant surface functional groups. The adsorption of U(vi) was clearly influenced by pH rather than ionic strength, which suggested inner-sphere surface complexation. The adsorption could reach equilibrium within 5 min, and the kinetics was well fitted by the pseudo-second-order model. The maximum adsorption capacity determined from the Langmuir model at 298 K and different pH values was in the order of pH 5.0 (383.14 mg g-1) > 8.0 (213.22 mg g-1) > 3.0 (158.73 mg g-1), which indicated that the α-MnO2@PDAs could still remove U(vi) efficiently at a pH of 8, which is close to the pH of natural water. Spectroscopic analyses suggested that favourable adsorption occurred on active binding sites, e.g., phenolic O-H and amide functional groups. The higher removal efficiency of the α-MnO2@PDAs for U(vi) was due to electrostatic attraction and surface complexation. Moreover, the practical applicability of the α-MnO2@PDAs in the treatment of real wastewater was confirmed by their high adsorption capacity for U(vi) from natural or synthetic water.

Simple construction of core–shell MnO2@TiO2 with highly enhanced U(vi) adsorption performance and evaluated adsorption mechanism

Simple construction of core–shell MnO₂@TiO₂ with highly enhanced U(vi) adsorption performance and evaluation of its adsorption mechanism.

Microhydrangeas with a high ratio of low valence MnOx are capable of extremely fast degradation of organics

Low valence manganese oxides are essential to directly produce abundant ˙OH radicals for extremely fast catalytic degradation of dye pollutants.