DFT insights into competing mechanisms of guaiacol hydrodeoxygenation on a platinum cluster

In a scenario of declining fossil resources and increasing demand for renewable and sustainable alternatives, biomass is the only source able to offer an easy and gradual transition in the use of current energy technologies based on the exploitation of carbon derivatives. Its conversion to liquid fuels has oriented our study towards the computational mechanistic analysis of the guaiacol catalytic hydrodeoxygenation, which is currently considered one of the most challenging routes for upgrading biomass-derived bio-oils. For this purpose, a subnanometric Pt10 platinum cluster was chosen as the catalyst model, with Pt as a computational reference element for catalytic hydrogenation, and guaiacol as a model compound of bio-oils. DFT calculations revealed that the energy barriers related to the cleavage of C(sp2)-O bonds in the direct deoxygenation mechanism are significantly lower (by an average of 60 kJ mol−1) than those in the deoxygenation-through-hydrogenation mechanism in which C(sp3)-O bond breaking from a saturated ring occurs. Even if the ring hydrogenation is easier in the oxygenated compound, the analysis reveals that the direct deoxygenation mechanism is favoured at all temperatures. Furthermore, the results obtained highlight that, from a thermodynamic perspective, the removal of oxygen groups preferentially occurs by the elimination of the -OCH3 fragment as methanol and then of the -OH fragment as a water molecule

Multimodal confined water dynamics in reverse osmosis polyamide membranes

While polyamide (PA) membranes are widespread in water purification and desalination by reverse osmosis, a molecular-level understanding of the dynamics of both confined water and polymer matrix remains elusive. Despite the dense hierarchical structure of PA membranes formed by interfacial polymerization, previous studies suggest that water diffusion remains largely unchanged with respect to bulk water. Here, we employ neutron spectroscopy to investigate PA membranes under precise hydration conditions, and a series of isotopic contrasts, to elucidate water transport and polymer relaxation, spanning ps-ns timescales, and Å-nm lengthscales. We experimentally resolve, for the first time, the multimodal diffusive nature of water in PA membranes: in addition to (slowed down) translational jump-diffusion, we observe a long-range and a localized mode, whose geometry and timescales we quantify. The PA matrix is also found to exhibit rotational relaxations commensurate with the nanoscale confinement observed in water diffusion. This comprehensive ‘diffusion map’ can anchor molecular and nanoscale simulations, and enable the predictive design of PA membranes with tuneable performance

DFT Study of Pt Particle Growth inside β-Zeolite Cages

The preferred location and the corresponding energetics of zeolite-embedded single metal atoms and small metal particles are hot topics within active site optimization and catalyst tuning, even as part of bifunctional materials design. In this context, periodic density functional theory was used to provide insights on the interactions of a platinum atom with the microporous cages of a purely silicious β-zeolite (BEA) framework. Cluster growth was subsequently addressed, up to Pt3@BEA systems, following a one-by-one platinum atom addition; platinum migration between cages was taken into account as well. An unbiased approach was employed, which allowed a wide panorama of structures being considered in addition to a thorough analysis in terms of energetics, cluster geometries, and cavity distortions. Calculations revealed that the optimal interaction geometry for a single platinum atom is realized where two strong Pt-O bonds in almost linear arrangement can form, regardless of the cavity involved. This can cause distortions or even breaking of the zeolite structure, a factor which however is not decisive in determining the energetics of systems with two and three platinum atoms. Platinum migration is associated with energy barriers ranging from 100 to 200 kJ mol-1, depending on the cages. Up to the dimensions considered here, preference for clustering is observed, being the embedded Pt3 systems in almost all cases energetically favored with respect to isolated atoms within the BEA framework

DFT study on zeolites’ intrinsic Brønsted acidity: The case of BEA

Since Brønsted acidity is a crucial aspect for the applications of zeolitic materials in heterogeneous catalysis, great effort was devolved to characterize the number, strength and location of the potentially active acidic sites. Quantum chemical calculations can turn out essential in estimating the intrinsic acidity by computing deprotonation energy (DPE) values, although each method comes with its own difficulties. In this context, three approaches within density functional theory were employed to study the intrinsic acidity of 30 topologically distinct Brønsted sites in the β-zeolite framework. Advantages and disadvantages of the three methods were outlined and the acidity order between the sites was assessed, being the DPE range 59 kJ mol−1 wide, with the proposed best approach. By dividing the range into three portions, the sites were classified as having high, medium and low acidity. Hydrogen bonds formation was found to be a contributing factor in determining a low Brønsted acidity

Evaluating Pharmacy Student Attitudes Toward the Medium of Comics for Providing Information on Adult Immunizations

Objectives: This study aimed at designing and assessing educational materials for adult immunizations through the medium of comics. The study design evaluated the effects of two vaccine information flyers (a CDC flyer vs a flyer designed in Comic medium) on participants’ attitude towards the flyers. Methods: A between-group, randomized trial was used to compare the effectiveness of two vaccine information flyers on participants’ attitude towards the flyers. Upon approval from the human subjects review committee, student participants (age ≥18 years) were randomly assigned either the CDC or comic flyer. They were then asked to respond to survey items developed to measure the flyers’ effect on participants’ attitude towards the flyer. Items were measured using a 7-point semantic differential scale. Cronbach’s alpha was computed for reliability testing of the study instrument. Independent-samples t-test was used to compare means of the two groups with respect to their attitudes toward the flyer. Results: A total of 170 third-year pharmacy students participated in the study (N = 91 for Comic flyer & N = 79 for CDC flyer). There was a significant difference in attitudes toward the flyer between students who read comic flyers (mean = 6.14; SD = 0.62) and those who read CDC flyers (mean = 4.93; SD = 1.20). Additional comments provided by students further confirmed the quantitative findings of the study. Student responses to the use of comics as a medium of providing information on adult immunization were constructive and encouraging. Conclusion: The study findings showed that the flyer with comics was evaluated more attractive than the CDC flyer. The positive findings of our study could provide a new direction for developing educational materials about adult immunizations. Future research on comics, as a medium of communication, could explore its use as a tool for providing healthcare information to consumers.   Type: Original Researc

Saturated phase densities of (CO2 + H2O) at temperatures from (293 to 450) K and pressures up to 64 MPa

An apparatus consisting of an equilibrium cell connected to two vibrating tube densimeters and two syringe pumps was used to measure the saturated phase densities of (CO2 + H2O) at temperatures from (293 to 450) K and pressures up to 64 MPa, with estimated average standard uncertainties of 1.5 kg · m−3 for the CO2-rich phase and 1.0 kg · m−3 for the aqueous phase. The densimeters were housed in the same thermostat as the equilibrium cell and were calibrated in situ using pure water, CO2 and helium. Following mixing, samples of each saturated phase were displaced sequentially at constant pressure from the equilibrium cell into the vibrating tube densimeters connected to the top (CO2-rich phase) and bottom (aqueous phase) of the cell. The aqueous phase densities are predicted to within 3 kg · m−3 using empirical models for the phase compositions and partial molar volumes of each component. However, a recently developed multi-parameter equation of state (EOS) for this binary mixture, Gernert and Span [32], was found to under predict the measured aqueous phase density by up to 13 kg · m−3. The density of the CO2-rich phase was always within about 8 kg · m−3 of the density for pure CO2 at the same pressure and temperature; the differences were most positive near the critical density, and became negative at temperatures above about 373 K and pressures below about 10 MPa. For this phase, the multi-parameter EOS of Gernert and Span describes the measured densities to within 5 kg · m−3, whereas the computationally-efficient cubic EOS model of Spycher and Pruess (2010), commonly used in simulations of subsurface CO2 sequestration, deviates from the experimental data by a maximum of about 8 kg · m−3

Sub-100 nm wrinkling of polydimethylsiloxane by double frontal oxidation

We demonstrate nanoscale wrinkling on polydimethylsiloxane (PDMS) at sub-100 nm length scales via a (double) frontal surface oxidation coupled with a mechanical compression. The kinetics of the glassy skin propagation is resolved by neutron and X-ray reflectivity, and atomic force microscopy, combined with mechanical wrinkling experiments to evaluate the resulting pattern formation. In conventional PDMS surface oxidation, the smallest wrinkling patterns attainable have an intrinsic lower wavelength limit due to the coupling of skin formation and front propagation at fixed strain ε_{prestrain}, whose maximum is, in turn, set by material failure. However, combining two different oxidative processes, ultra-violet ozonolysis followed by air plasma exposure, we break this limit by fabricating trilayer laminates with excellent interfacial properties and a sequence of moduli and layer thicknesses able to trivially reduce the surface topography to sub-100 nm dimensions. This method provides a powerful, yet simple, non-lithographic approach to extend surface patterning from visible to the deep UV range