Chia-Ming Wu

Dissolution of ZnO nanoparticles at circumneutral pH: a study of size effects in the presence and absence of citric acid.

Understanding size-dependent processes, including dissolution, of engineered nanoparticles is essential in addressing the potential environmental and health impacts of these materials as well as their long-term stability. In this study, experimental measurements of size-dependent dissolution of well-characterized zinc oxide (ZnO) nanoparticles with particle diameters in the range of 4 to 130 nm have been measured at circumneutral pH (pH 7.5) and compared. Dissolution was found to be enhanced with smaller ZnO nanoparticles compared to larger-sized particles, even though the nanoparticles were present in solution as aggregates with hydrodynamic diameters on the order of 1-3 μm in size. The presence of citric acid significantly enhanced the extent of ZnO dissolution for all sizes, and the greatest enhancement was observed for the 4 nm particles. Although these results are found to be in qualitative agreement with theoretical predictions, a linearized form of the Kelvin equation to calculate a surface free energy yielded quantities inconsistent with expected values from the literature. Reasons for this inconsistency are discussed and include potential deviations of solubility behavior from classical thermodynamics as a result of a lack of detailed knowledge of surface structure and surface properties, including the presence of different surface crystal facets, and the aggregation state.

Modulation of pore sizes of titanium dioxide photocatalysts by a facile template free hydrothermal synthesis method: implications for photocatalytic degradation of rhodamine B.

Mesoporous TiO2 photocatalysts were prepared in ethanol media by using relatively green, template free sol-gel technique. A mild hydrothermal treatment procedure was employed to tune the pore sizes of the materials. Comprehensive techniques that include powder X-ray diffraction, diffuse reflectance spectroscopy, specific surface area analysis, electron microscopy, FT-IR, TGA, and ζ-potential measurements were used to characterize the titania materials. Porosity (pore size and pore volume) of the materials were found to be key factors for the variation in the rate of photocatalytic degradation of rhodamine B; in addition to specific surface area, and surface hydroxyl groups. An increase in porosity permits effective transport of the dye molecules resulting in an increase in the rate of the degradation in materials having larger pores. A detailed electrospray ionization-mass spectrometric (ESI-MS) study was carried out for selected materials to identify photodegraded intermediates and products formed during the degradation of rhodamine B. In addition, experiments were also carried out to understand the role of reactive oxygen species (ROS). In summary, this work provides a simple way to tune pore sizes without the use of any template and an insight into the influence of pore size for the photocatalytic degradation of rhodamine B.

Visible light driven photocatalytic evolution of hydrogen from water over CdS encapsulated MCM-48 materials

CdS encapsulated cubic MCM-48 mesoporous photocatalysts were prepared by a post-impregnation method. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption isotherm, UV-visible diffuse reflectance spectroscopy (DRS), FT-IR spectrometry, X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), and photoluminescence (PL) spectroscopy were employed for the characterization of the CdS incorporated MCM-48 siliceous materials. MCM-48 was loaded with different amounts of CdS. In the current study, all the samples showed photocatalytic activity under visible light (λ > 400 nm) irradiation for production of hydrogen from splitting of water in the absence of Pt, which is usually used in photocatalytic splitting of water. The photocatalytic activity of the CdS incorporated MCM-48 mesoporous photocatalysts was found to be dependent on the CdS loading and the pore size of MCM-48 siliceous support. The highest solar hydrogen evolution rate by visible light irradiation from the splitting of water was determined to be 1.81 mmol h−1 gCdS−1 and the apparent quantum yield was estimated to be 16.6%.

Iron oxide nanoparticles induce Pseudomonas aeruginosa growth, induce biofilm formation, and inhibit antimicrobial peptide function

Given the increased use of iron-containing nanoparticles in a number of applications, it is important to understand any effects that iron-containing nanoparticles can have on the environment and human health. Since iron concentrations are extremely low in body fluids, there is potential that iron-containing nanoparticles may influence the ability of bacteria to scavenge iron for growth, affect virulence and inhibit antimicrobial peptide (AMP) function. In this study, Pseudomonas aeruginosa (PA01) and AMPs were exposed to iron oxide nanoparticles, hematite (α-Fe2O3), of different sizes ranging from 2 to 540 nm (2 ± 1, 43 ± 6, 85 ± 25 and 540 ± 90 nm) in diameter. Here we show that the greatest effect on bacterial growth, biofilm formation, and AMP function impairment is found when exposed to the smallest particles. These results are attributed in large part to enhanced dissolution observed for the smallest particles and an increase in the amount of bioavailable iron. Furthermore, AMP function can be additionally impaired by adsorption onto nanoparticle surfaces. In particular, lysozyme readily adsorbs onto the nanoparticle surface which can lead to loss of peptide activity. Thus, this current study shows that co-exposure of nanoparticles and known pathogens can impact host innate immunity. Therefore, it is important that future studies be designed to further understand these types of impacts.

Mesoporous coupled ZnO/TiO2 photocatalyst nanocomposites for hydrogen generation

The present work investigates mesoporous coupled ZnO-TiO2 based nanocomposites towards photocatalytic hydrogen generation. The effect of Zn2+ loadings was examined on the photocatalytic activities of the sol-gel derived ZnO-TiO2 nanocomposites employing a structure-directing template. ZnO-TiO2 nanocomposites were characterized by powder X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, nitrogen isotherm, Raman, and electrochemical impedance spectroscopy (EIS) methods. The photocatalytic H2 evolution of the ZnO-TiO2 suspensions was evaluated in an aqueous methanol medium under UV illumination. The Zn2+ concentrations utilized to prepare ZnO-TiO2 nanocomposites were found to have significant effect on the specific surface area, pore volume, and photocatalytic activity. The H2 evolution results obtained with ZnO-TiO2 nanocomposites were compared with H2 generation using commercial TiO2 P25 and individual ZnO nanoparticles. The photocatalytic activity of ZnO-TiO2 co...

An ionic liquid-mesoporous silica blend as a novel adsorbent for the adsorption and recovery of palladium ions, and its applications in continuous flow study and as an industrial catalyst

In this work, we report the synthesis of Aliquat-336 (ionic liquid) impregnated SBA-15 mesoporous silica, showing its effective interaction and high adsorption capacity for palladium(II) ions. The physicochemical properties of the adsorbent prior to and after adsorption of palladium(II) ions were characterized extensively using FT-IR, XRD, SEM, TEM, EDX, surface area (BET), and pore size analysis. The plausible interaction envisaged between Aliquat-336 impregnated SBA-15 and Pd(II) could be charge and ion-pair interactions. Different isotherm models were utilized to obtain the sorption parameters and the experimental data fitted adequately with the Langmuir isotherm model, with an adsorption capacity of 212.76 mg g−1. The kinetics of the adsorption process agreed well with the pseudo-second order kinetic model, and the exothermic nature of the adsorption process was revealed through thermodynamic parameters. The Aliquat-336 impregnated SBA-15 adsorbent was regenerated using thiourea. The continuous flow studies were carried out using the Thomas model and this gave an adsorption capacity of 453.89 mg g−1 and 376.38 mg g−1 at flow rates of 4 and 6 mL min−1 respectively. Furthermore, the present scheme was tested for the adsorption of palladium recovered from a spent catalyst containing 5% Pd on activated carbon.

Efficient photocatalytic hydrogen evolution system by assembling earth abundant NixOy nanoclusters in cubic MCM-48 mesoporous materials.

A cubic MCM-48 mesoporous material was employed as a support to encapsulate earth abundant NixOy species (NiO and Ni2O3). The cubic MCM-48 mesoporous support provides an excellent platform to not only effectively disperse NiO and/or Ni2O3 species but also to limit their particle sizes. The presence of Ni2O3 species at an optimal amount seems to enhance the photocatalytic activity of Ni–MCM-48 materials in comparison to a Ni–MCM-48 mesoporous material having only NiO dispersed in it. In addition, the presence of bulk NiO species also seems to be detrimental to the generation of solar hydrogen. The apparent quantum yield (AQY) of the most active material, Ni–MCM-48-2.5% was estimated to be 5.35%. This was over 250 times higher than a bulk, NiO (AQY = 0.02%) under identical experimental conditions. This study indicates that MCM-48 can be used as an effective support to disperse NixOy species.

Fe–SBA-15 catalyzed synthesis of 2-alkoxyimidazo[1,2-a]pyridines and screening of their in silico selectivity and binding affinity to biological targets

Here, we have demonstrated regioselective three-component synthesis of 2-alkoxyimidazopyridines using mesoporous Fe–SBA-15 as the catalyst and screened their in silico selectivity and binding affinity to different biological targets viz. farnesyl diphosphate synthase, phosphodiesterase III, GABAa and chemokine receptor CXCR4 using molecular docking simulations. Fe–SBA-15 has been characterized by nitrogen absorption–desorption, powder XRD, SEM, TEM studies and atomic absorption spectroscopic analysis. Fe–SBA-15 was very efficient in synthesizing imidazopyridines. The binding affinity study revealed that the 2-butoxy-3-(4-methoxyphenyl)-7-methylH-imidazo[1,2-a] pyridine (4g) moiety has exhibited even better affinity in terms of MolDock, re-rank and steric scores than the marketed anti-inflammatory drug, olprinone.

Nanocasting of Periodic Mesoporous Materials as an Effective Strategy to Prepare Mixed Phases of Titania

Mesoporous titanium dioxide materials were prepared using a nanocasting technique involving silica SBA-15 as the hard-template. At an optimal loading of titanium precursor, the hexagonal periodic array of pores in SBA-15 was retained. The phases of titanium dioxide could be easily varied by the number of impregnation cycles and the nature of titanium alkoxide employed. Low number of impregnation cycles produced mixed phases of anatase and TiO2(B). The mesoporous TiO2 materials were tested for solar hydrogen production, and the material consisting of 98% anatase and 2% TiO2(B) exhibited the highest yield of hydrogen from the photocatalytic splitting of water. The periodicity of the pores was an important factor that influenced the photocatalytic activity. This study indicates that mixed phases of titania containing ordered array of pores can be prepared by using the nanocasting strategy.

REACTIVITY AND MORPHOLOGY OF Ni, Mo, AND Ni–Mo OXIDE CLUSTERS SUPPORTED ON MCM-48 TOWARD THIOPHENE HYDRODESULPHURIZATION

In this paper, the morphology, chemical composition and reactivity of MCM-48 powders impregnated with Ni, Mo or both toward hydrodesulphurization (HDS) of thiophene were characterized. The reactivity of the catalyst was quantitatively compared with a standard industrial catalyst (from HaldorTopsoe, Denmark) and a novel WS2 nanotube-based catalysts (from R. Tenne, Israel). Morphology and chemical composition were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and EDX elemental maps. Reactivity was determined in a gas-chromatograph based mini flow reactor using thiophene as a probe molecule. The sulfided MCM-48 supported Mo catalyst showed the largest HDS activity with turnover frequencies (TOF) about half as large as for the commercial system under the test conditions used here. Presulfiding did increase activity of all MCM-48 catalysts.