Facile synthesis of single-crystalline MnO2 nanowire arrays with high photothermal catalytic activity

A simple process has been developed to form single-crystalline β-MnO₂ nanowire arrays (NWAs) with a large surface area of 125 m² g^-1 on a glass plate working as a highly active three dimensional (3D) photothermal catalyst under the illumination of near infrared light due to the efficient light harvesting and heat confinement near the reaction field in addition to the large surface area.

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO₂ (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20-30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.

Facile Room-Temperature Synthesis of Cerium Carbonate and Cerium Oxide Nano- and Microparticles Using 1,1'-Carbonyldiimidazole and Imidazole in a Nonaqueous Solvent

Ceria nanoparticles (CeONPs) are versatile materials due to their unique catalytic properties, and cerium carbonate particles (CeCbPs) have been widely used as precursors for cerium oxide due to their ease of production. Urea is a widely used precipitant and a source of carbonate ions for the synthesis of CeONPs and CeCbPs, and the reaction temperature is important for controlling the rate of urea decomposition. However, the precise control of the temperature is often difficult, especially in large-scale reactions. Herein, we propose a homogeneous precipitation method that uses 1,1'-carbonyldiimidazole (CDI) and imidazole in acetone without heating. The decomposition rate of CDI can be controlled by the amount of water in the reaction mixture. In the synthesis of CeCbPs, unique particle morphologies of plate-, flying-saucer-, and macaron-like shapes and a wide range of sizes from 180 nm to 13 μm can be achieved by adjusting the amount of CDI, imidazole, and water in the reaction. These CeCbPs are transformed into ceria particles by calcination while maintaining their characteristic morphology. Moreover, the direct synthesis of 130 nm spherical CeONPs was possible by decreasing the amount of CDI in the reaction and the mixing time. These nanoparticles exhibited higher production efficiency and superior reactive oxygen species (ROS) scavenging properties compared to the other CeONPs obtained from calcination. These results demonstrate a novel method using CDI and imidazole in the synthesis of CeONPs and CeCbPs without the aid of a heating process, which may be useful in the large-scale synthesis and application of CeO nanomaterials.

Nanodispersed Mn3O4/γ-Al2O3 for NO2 Elimination at Room Temperature

Adsorption is an efficient method for atmospheric NO_x abatement under ambient conditions; however, traditional adsorbents suffer from limited adsorption capacity and byproduct formation. Developing a low-cost material with high capacity for atmospheric NO₂ elimination remains a challenge. Here, we synthesized a nanodispersed Mn₃O₄/γ-Al₂O₃ (Mn/Al) material that exhibits excellent ability to remove NO₂. The 10 wt % Mn/Al sample showed the highest removal capacity, with 247.6 mg_NO2/g_Mn/Al, which is superior to that of activated carbon (42.6 mg_NO2/g). There were no byproducts produced when Mn/Al was tested with ppb-level NO₂. The NO₂ abatement mechanism with Mn/Al is different from physisorption or chemisorption. NO₂ removal is mainly a catalytic process in air, during which surface hydroxyls and lattice oxygen are involved in the oxidation of NO₂ to nitrate. In contrast, a chemical reaction between Mn³⁺ and NO₂ is dominant in N₂, where Mn³⁺ is converted into Mn⁴⁺ and NO₂ is reduced to nitrite. Washing with deionized water is an effective and convenient method for the regeneration of saturated Mn/Al, and an 86% adsorption capacity was recovered after one washing. The results suggest that this low-cost Mn/Al material with easy preparation and regeneration is a promising candidate material for atmospheric NO₂ elimination.

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.

Employment of ultrasonic irradiation for production of poly(vinyl pyrrolidone)/modified alpha manganese dioxide nanocomposites: Morphology, thermal and optical characterization

This work explains the production, morphology, and features of novel nanocomposite (NC) established on poly(vinyl pyrrolidone) (PVP) as polymer background and modified alpha manganese dioxide (α-MnO₂) nanorod (NR) asan efficient filler. At first, one-dimensional α-MnO₂ nanorods (NRs) were produced by a hydrothermal technique and then they were amended with stearic acid (SA) by a solvothermal process. In following, the NCs were made by adding different volumes of α-MnO₂-SA NR (1, 3 and 5wt%) in the PVP matrix through ultrasonic irradiation as a green, low-cost, fast, and useful technique. Structural and morphological descriptions confirm crystallinity of α-MnO₂-SA NRs and showed that NRs have been separately dispersed in PVP matrix with rod-like morphology and diameter of about 40-60nm. The use of modifier and ultrasonic waves is accountable for good homogeneities of NRs. Thermogravimetric analysis revealed that thermal permanency of the obtained NCs has grown with increasing the α-MnO₂-SA content. Also, the UV-vis absorption of NCs was enhanced with the incorporation of the modified α-MnO₂ NR in PVP matrix. The substantial perfections in NCs properties are associated to compatible intermolecular relations between the surface modifying groups of the α-MnO₂-SA and PVP chain.