Tunable Shape Microwave Synthesis of Zinc Oxide Nanospheres and Their Desulfurization Performance Compared with Nanorods and Platelet-Like Morphologies for the Removal of Hydrogen Sulfide

A tunable shape microwave synthesis of ZnO nanospheres in a cosolvent mixture is presented. The ZnO nanospheres material is investigated as a desulfurizing sorbent in a fixed bed reactor in the temperature range 200–400 °C and compared with ZnO nanorod and platelet-like morphologies. Fresh and sulfided materials were characterized by X-ray diffraction, BET specific surface area, pore volume, scanning electron microscopy, X-ray energy dispersive spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The tunable shape microwave synthesis of ZnO presents a high sulfur sorption capacity at temperatures as low as 200 °C, which accounts for three and four times the other preparations presented in this work, and reached 76% of the theoretical sulfur capacityat 300 °C

Synergetic Effects of Ultraviolet and Microwave Radiation for Enhanced Activity of TiO₂ Nanoparticles in Degrading Organic Dyes Using a Continuous-Flow Reactor

A novel continuous-flow reactor was developed to investigate the synergetic effects of ultraviolet (UV) and microwave (MW) radiation on TiO₂ nanoparticles for the enhancement of photodegradation of Direct Red-81 (DR-81) and Bromothymol Blue (BTB) dyes. The efficiency of the combined UV and MW radiation was higher than the sum of the isolated and corresponding thermal effects and directly proportional to the MW power. The % photodegradation of DR-81 after 105 min irradiation at ambient conditions was 40%, 68%, 72%, and 100% using UV/MW_100W, UV/MW_300W, UV/MW_500W, and UV/MW_700W methods, respectively. The % photodegradation of BTB under the same conditions was 58%, 78%, 82%, and 88%, respectively. High dissolved oxygen concentration increased DR-81 photodegradation, whereas ambient air conditions were optimum for BTB. The extent of photomineralization of both dyes was dependent on MW power. Degradation products showed that both dyes were successfully oxidized through different intermediate species. The properties of TiO₂ nanoparticles did not change before and after reaction; however, the positive surface charge was reduced by as much as 14 mV. Accelerated rates of dye degradation on incorporation of MW to UV were attributed to the generation of more hydroxyl and superoxide anion radicals and an increase in hydrophobicity of TiO₂

Antibody-like Biorecognition Sites for Proteins from Surface Imprinting on Nanoparticles

Natural antibodies are used widely for important applications such as biomedical analysis, cancer therapy, and directed drug delivery, but they are expensive and may have limited stability. This study describes synthesis of antibody-like binding sites by molecular imprinting on silica nanoparticles (SiNP) using a combination of four organosilane monomers with amino acid-like side chains providing hydrophobic, hydrophilic, and H-bonding interactions with target proteins. This approach provided artificial antibody (AA) nanoparticles with good selectivity and specificity to binding domains on target proteins in a relatively low-cost synthesis. The AAs were made by polymer grafting onto SiNPs for human serum albumin (HSA) and glucose oxidase (GOx). Binding affinity, selectivity, and specificity was compared to several other proteins using adsorption isotherms and surface plasmon resonance (SPR). The Langmuir–Freundlich adsorption model was used to obtain apparent binding constants (<i>K</i>_LF) from binding isotherms of HSA (6.7 × 10⁴) and GOx (4.7 × 10⁴) to their respective AAs. These values were 4–300 fold larger compared to a series of nontemplate proteins. SPR binding studies of AAs with proteins attached to a gold surface confirmed good specificity and revealed faster binding for the target proteins compared to nontarget proteins. Target proteins retained their secondary structures upon binding. Binding capacity of AA_HSA for HSA was 5.9 mg HSA/g compared to 1.4 mg/g for previously report imprinted silica beads imprinted with poly­(aminophenyl)­boronic acid. Also, 90% recovery for HSA spiked into 2% calf serum was found for AA_HSA

Titania Condensation by a Bio-Inspired Synthetic Block Copolymer

Silicatein α, an enzyme found at the center of silica spicules in marine sponges, is known to play a role in silica condensation from seawater. It has also been shown to catalyze the formation of silica from various silica precursors such as tetraethyl orthosilicate (TEOS). Inspired by the finding that the serine-26 and histidine-165 amino acids in the enzyme are required for silica formation from TEOS, we synthesized poly­(hydroxylated isoprene-<i>b</i>-2-vinylpyridine) block copolymers to mimic these amino acid residues. Here, we present the results of our investigation utilizing this biomimetic polymer to condense titania from titanium <i>iso</i>-propoxide (TiP). Our silicatein α mimic is shown to condense titania at neutral pH and room temperature and is compared to material produced by standard sol–gel methods. Heats of crystallization are observed to be 72% lower for the titania made from the mimic polymer, and indistinct X-ray diffraction peaks, even after heating well above the crystallization temperature, suggest a higher degree of titania condensation with the silicatein α mimic. Results from thermogravimetric analysis show that the mimic formed titania initially contains ∼15 wt % polymer and that the surface area increases from less than 5 to greater than 110 m²/g when heated to 400 °C. Titania made from the silicatein α mimic also shows a higher catalytic activity than does commercial Degussa P25 TiO₂ for the photodegradation of N-nitrosodimethylamine (NDMA), degrading 73% of the NDMA in two hours as compared to 62% with Degussa P25. The biomimetic system presented here offers the promise of an environmentally friendlier method of titania production and will enable applications requiring neutral pH and low temperatures, such as titania composite synthesis, surface coating, or catalyst design

Machine Learning Using Combined Structural and Chemical Descriptors for Prediction of Methane Adsorption Performance of Metal Organic Frameworks (MOFs)

Using molecular simulation for adsorbent screening is computationally expensive and thus prohibitive to materials discovery. Machine learning (ML) algorithms trained on fundamental material properties can potentially provide quick and accurate methods for screening purposes. Prior efforts have focused on structural descriptors for use with ML. In this work, the use of chemical descriptors, in addition to structural descriptors, was introduced for adsorption analysis. Evaluation of structural and chemical descriptors coupled with various ML algorithms, including decision tree, Poisson regression, support vector machine and random forest, were carried out to predict methane uptake on hypothetical metal organic frameworks. To highlight their predictive capabilities, ML models were trained on 8% of a data set consisting of 130,398 MOFs and then tested on the remaining 92% to predict methane adsorption capacities. When structural and chemical descriptors were jointly used as ML input, the random forest model with 10-fold cross validation proved to be superior to the other ML approaches, with an <i>R</i>² of 0.98 and a mean absolute percent error of about 7%. The training and prediction using the random forest algorithm for adsorption capacity estimation of all 130,398 MOFs took approximately 2 h on a single personal computer, several orders of magnitude faster than actual molecular simulations on high-performance computing clusters

Direct Sonochemical Synthesis of Manganese Octahedral Molecular Sieve (OMS-2) Nanomaterials Using Cosolvent Systems, Their Characterization, and Catalytic Applications

A rapid, direct sonochemical method has successfully been developed to synthesize cryptomelane-type manganese octahedral molecular sieve (OMS-2) materials. Very high surface area of 288 ± 1 m²/g and small particle sizes in the range of 1–7 nm were produced under nonthermal conditions. No further processing such as calcination was needed to obtain the pure cryptomelane phase. A cosolvent system was utilized to reduce the reaction time and to obtain higher surface areas. Reaction time was reduced by 50% using water/acetone mixed phase solvent systems. The cryptomelane phase was obtained with 5% acetone after 2 h of sonication at ambient temperature. Reaction time, temperature, and acetone concentration were identified as the most important parameters in the formation of the pure cryptomelane phase. OMS materials synthesized using the above-mentioned method were characterized by X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transformation infrared spectroscopy (FTIR). OMS-2 materials synthesized using sonochemical methods (K-OMS-2_SC) possess greater amounts of defects and hence show excellent catalytic performances for oxidation of benzyl alcohol as compared to OMS-2 synthesized using reflux methods (K-OMS-2_REF) and commercial MnO₂

Gas-Phase Total Oxidation of Benzene, Toluene, Ethylbenzene, and Xylenes Using Shape-Selective Manganese Oxide and Copper Manganese Oxide Catalysts

Volatile organic compounds (VOCs) continue to be the major source of direct and indirect air pollution. Here, cryptomelane-type octahedral molecular sieve (OMS-2) manganese oxide, amorphous manganese oxide (AMO), and mixed copper manganese oxide (CuO/Mn₂O₃) nanomaterials were synthesized and, together with commercial MnO₂, characterized by various techniques. These catalysts were investigated for gas-phase total oxidation of six VOCs under air atmosphere. Using OMS-2 at 250 °C, the average conversions for toluene, benzene, ethylbenzene, <i>p</i>-xylene, <i>m</i>-xylene, and <i>o</i>-xylene were 75%, 61%, 45%, 23%, 13%, and 8%, respectively, whereas using CuO/Mn₂O₃, 72%, 44%, 37%, 29%, 27%, and 26%, respectively, were obtained. Generally, the conversion of VOCs to CO₂ using the synthesized catalysts increased in the order: <i>o</i>-xylene ≈ <i>m</i>-xylene < <i>p</i>-xylene < ethylbenzene < benzene < toluene. However, using commercial MnO₂, benzene (44% conversion) was more reactive than toluene (37%), and the xylenes showed similar reactivities (13–20%). Differences in reactivity among VOCs were rationalized in terms of degree of substrate adsorption and structural effects. For example, the reactivity of xylenes was dictated by the shape-selectivity of stable OMS-2. The higher oxidative activities exhibited by OMS-2, AMO, and CuO/Mn₂O₃ as compared to commercial MnO₂ were attributed to a combination of factors including structure, morphology, hydrophobicity, and redox properties. The mobility and reactivity of active oxygen species were strongly correlated with catalytic activities. Lattice oxygen was involved in the VOC oxidation, suggesting that the reaction could proceed via the Mars–van Krevelen mechanism

Colloidal Amphiphile-Templated Growth of Highly Crystalline Mesoporous Nonsiliceous Oxides

Colloidal Amphiphile-Templated Growth of Highly Crystalline Mesoporous Nonsiliceous Oxide

Photochemical Formation and Transformation of Birnessite: Effects of Cations on Micromorphology and Crystal Structure

As important components with excellent oxidation and adsorption activity in soils and sediments, manganese oxides affect the transportation and fate of nutrients and pollutants in natural environments. In this work, birnessite was formed by photocatalytic oxidation of Mn²⁺_aq in the presence of nitrate under solar irradiation. The effects of concentrations and species of interlayer cations (Na⁺, Mg²⁺, and K⁺) on birnessite crystal structure and micromorphology were investigated. The roles of adsorbed Mn²⁺ and pH in the transformation of the photosynthetic birnessite were further studied. The results indicated that Mn²⁺_aq was oxidized to birnessite by superoxide radicals (O₂^•–) generated from the photolysis of NO₃^– under UV irradiation. The particle size and thickness of birnessite decreased with increasing cation concentration. The birnessite showed a plate-like morphology in the presence of K⁺, while exhibited a rumpled sheet-like morphology when Na⁺ or Mg²⁺ was used. The different micromorphologies of birnessites could be ascribed to the position of cations in the interlayer. The adsorbed Mn²⁺ and high pH facilitated the reduction of birnessite to low-valence manganese oxides including hausmannite, feitknechtite, and manganite. This study suggests that interlayer cations and Mn²⁺ play essential roles in the photochemical formation and transformation of birnessite in aqueous environments

Structure–Property Relationship of Bifunctional MnO₂ Nanostructures: Highly Efficient, Ultra-Stable Electrochemical Water Oxidation and Oxygen Reduction Reaction Catalysts Identified in Alkaline Media

Manganese oxides of various structures (α-, β-, and δ-MnO₂ and amorphous) were synthesized by facile methods. The electrocatalytic properties of these materials were systematically investigated for catalyzing both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline media. Extensive characterization was correlated with the activity study by investigating the crystal structures (XRD, HRTEM), morphologies (SEM), porosities (BET), surfaces (XPS, O₂-TPD/MS), and electrochemical properties (Tafel analysis, Koutechy–Levich plots, and constant-current electrolysis). These combined results show that the electrocatalytic activities are strongly dependent on the crystallographic structures, and follow an order of α-MnO₂ > AMO > β-MnO₂ > δ-MnO₂. Both OER studies and ORR studies reveal similar structure-determined activity trends in alkaline media. In the OER studies, α-MnO₂ displays an overpotential of 490 mV compared to 380 mV shown by an Ir/C catalyst in reaching 10 mA cm^–2. Meanwhile, α-MnO₂ also exhibits stability for 3 h when supplying a constant current density of 5 mA cm^–2. This was further improved by adding Ni²⁺ dopants (ca. 8 h). The superior OER activity was attributed to several factors, including abundant di-μ-oxo bridges existing in α-MnO₂ as the protonation sites, analogous to the OEC in PS-II of the natural water oxidation system; the mixed valencies (AOS = 3.7); and the lowest charge transfer resistances (91.8 Ω, η = 430 mV) as revealed from <i>in situ</i> electrochemical impedance spectroscopy (EIS). In the ORR studies, when reaching 3 mA cm^–2, α-MnO₂ shows 760 mV close to 860 mV for the best ORR catalyst (20% Pt/C). The outstanding ORR activity was due to the strongest O₂ adsorption capability of α-MnO₂ suggested by temperature-programmed desorption. As a result, this discovery of the structure-related electrocatalytic activities could provide guidance in the further development of easily prepared, scalable, and low-cost catalysts based on metal oxides and their derivatives