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Multifunctional composites that couple high-capacity adsorbents with catalytic nanoparticles (NPs) offer a promising route toward the degradation of organophosphorus pollutants or chemical warfare ...

We determine the activity of catalytic carbon monoxide (CO) oxidation as a function of the size of gold nanoparticles (Au NP), their weight loading, and their interfacial intimacy with similarly si...

Carbon monoxide (CO) oxidation is not only an important industrial reaction but also a useful model system for investigations into reaction dynamics involving new catalyst designs. In this work, we...

Mesoporous copper–titanium dioxide (Cu/TiO2) composite aerogels with

We exploit interfacial charge transfer from titania (TiO2) to copper (Cu) to design catalytic Cu/TiO2 composite aerogels that shift the chemical state of Cu nanoparticles away from Cu2+, making them highly active for low-temperature CO oxidation. The high degree of interfacial contact between ∼2–3 nm–diameter Cu particles and the networked ∼10 nm–diameter TiO2 particles in ultraporous aerogel stabilizes a high ratio of Cu0/1+:Cu2+. The reduced nature of Cu in Cu/TiO2 aerogels is evidenced by a strong surface plasmon resonance in its diffuse reflectance UV–vis spectrum, by its X-ray photoelectron spectral features, and by infrared spectroscopic evidence of CO binding at the catalyst surface. In contrast, when larger diameter (∼50–60 nm), non–networked TiO2 particles are used to support Cu nanoparticles, the single planar nanoscale interface between Cu and the support particle stabilizes a much lower fraction of low-valent Cu. The Cu0/1+ speciation stabilized within the aerogel catalyzes low-temperature CO oxidation (

Multifunctional composites that couple high-capacity adsorbents with catalytic nanoparticles (NPs) offer a promising route toward the degradation of organophosphorus pollutants or chemical warfare agents (CWAs). We couple mesoporous TiO

Commercial anatase phase titanium dioxide was annealed under various gases (hydrogen, nitrogen, argon, and air) to induce the formation of defects. While annealing in the absence of oxygen there was a notable increase in the concentration of paramagnetic defects as measured by Electron Paramagnetic Resonance (EPR) and X-ray Photoelectron Spectroscopy (XPS). The presence of these defects increased the metal-free photocatalytic activity of the samples towards hydrogen evolution from photocatalytic methane steam reforming (MSR) under UV illumination. Catalyst activity was stable for over 42 h while illuminated owing to the regeneration of Ti3+ defects by UV photoexcitation, but rapidly decayed in the dark. The high concentration of unique Ti3+ defect sites generated during annealing catalyze hydrogen evolution, avoiding the need for precious metal cocatalysts, while anatase lacking these defects is inactive. This work shows that the implementation of defect-rich anatase TiO2 provides new catalytic pathways for hydrogen generation from photocatalytic methane steam reforming.

Elucidating structural and compositional polymorph changes of multiphase semiconductors in a quick and quantitative manner is important for their manufacturing and applications in catalysis alike. Derivative peak fitting of diffuse reflectance UV–visible spectra (DPR) is presented as an inexpensive, fast, and quantitative method to estimate both the composition of a multiphase semiconductor sample as well as the band gap energies of each component semiconductor in the mixture. Degussa P25 TiO2, a widely used catalyst support and semiconductor photocatalyst, is a mixture of anatase and rutile polymorphs. The as-received P25 samples were subjected to grinding, sieving, and calcination or a combination of these operations. Samples were analyzed via DPR, X-ray diffraction (XRD), and Raman spectroscopy to quantify the percentage of anatase and rutile polymorphs present in each sample. Compositional measurements from DPR were in good quantitative agreement with XRD and Raman analysis. The application of in situ...

Nanoparticulate (3–10 nm) TiO2 polymorphs, i.e., rutile, anatase, and srilankite (also known as TiO2-II or α-PbO2-type TiO2) phases are produced via low-pressure (e.g., 20 torr) flame synthesis at temperatures ranging from 1560K to 2650K, with burner flow velocities varying from 150 to 300 cm/s, using titanium tetra-isopropoxide (TTIP) as precursor. Interestingly, added carbon (i.e., ethylene) in the feed stream produces nanoparticles of the generally characteristic low-temperature high-pressure metastable srilankite phase. The as-synthesized nanopowder is composed of either rutile or srilankite phase, with composition dependent on particle residence time in the flow field. Under the same conditions, feed gas without carbon, e.g., hydrogen, yields anatase phase TiO2. Post heat treatment up to 773K in thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) highlights the thermal stability of the samples, while x-ray photoelectron spectroscopy (XPS) indicates the presence of carbon, with absences of Ti3+, Ti–C, and nitrogen. Microscopy reveals morphology on both the micrometer scale (scanning electron microscopy, SEM) and nanometer scale (transmission electron microscopy, TEM), while x-ray diffraction (XRD) and selected area electron diffraction (SAED) confirm polymorph variation under different synthesis conditions. CHN analysis determines that the synthesized srilankite contains a greater weight percentage of carbon than does anatase. Excess carbon doped into the lattice during low-pressure flame synthesis seems to be the key in stabilizing the high-pressure srilankite phase for such nanoparticles.

Hydrolytically biodegradable poly(ethylene glycol) (PEG) hydrogels offer a promising platform for chondrocyte encapsulation and tuning degradation for cartilage tissue engineering, but offer no bioactive cues to encapsulated cells. This study tests the hypothesis that a semi-interpenetrating network of entrapped hyaluronic acid (HA), a bioactive molecule that binds cell surface receptors on chondrocytes, and crosslinked degradable PEG improves matrix synthesis by encapsulated chondrocytes. Degradation was achieved by incorporating oligo (lactic acid) segments into the crosslinks. The effects of HA molecular weight (MW) (2.9×10(4) and 2×10(6)Da) and concentration (0.5 and 5mgg(-1)) were investigated. Bovine chondrocytes were encapsulated in semi-interpenetrating networks and cultured for 4weeks. A steady release of HA was observed over the course of the study with 90% released by 4weeks. Incorporation of HA led to significantly higher cell numbers throughout the culture period. After 8days, HA increased collagen content per cell, increased aggrecan-positive cells, while decreasing the deposition of hypertrophic collagen X, but these effects were not sustained long term. Measuring total sulfated glycosaminoglycan (sGAG) and collagen content within the constructs and released to the culture medium after 4weeks revealed that total matrix synthesis was elevated by high concentrations of HA, indicating that HA stimulated matrix production although this matrix was not retained within the hydrogels. Matrix-degrading enzymes were elevated in the low-, but not the high-MW HA. Overall, incorporating high-MW HA into degrading hydrogels increased chondrocyte number and sGAG and collagen production, warranting further investigations to improve retention of newly synthesized matrix molecules.