Cloaking by coating: How effectively does a thin, stiff coating hide a soft substrate?

From human tissue to fruits, many soft materials are coated by a thin layer of a stiffer material. While the primary role of such a coating is often to protect the softer material, the thin, stiff coating also has an important effect on the mechanical behaviour of the composite material, making it appear significantly stiffer than the underlying material. We study this cloaking effect of a coating for the particular case of indentation tests, which measure the `firmness' of the composite solid: we use a combination of theory and experiment to characterize the firmness quantitatively. We find that the indenter size plays a key role in determining the effectiveness of cloaking: small indenters feel a mixture of the material properties of the coating and of the substrate, while large indenters sense largely the unadulterated substrate

Synthesis of noble metal-decorated NH2-MIL-125 titanium MOF for the photocatalytic degradation of acetaminophen under solar irradiation

This work reports the solvothermal synthesis of a titanium-based metal organic framework (NH2-MIL-125(Ti)) and the further deposition of palladium, platinum and silver nanoparticles on its framework, with the aim to obtain visible light-driven photocatalysts. The structure of the NH2-MIL-125 was not affected by the incorporation of the metal nanoparticles, while the textural properties changed depending on the metal used. All M/NH2-MIL-125 (M = Pd, Pt, Ag) synthesized materials showed enhanced light absorption in the visible region due to the effect of the metal nanoparticles, which were mainly in reduced state as confirmed by XPS analyses. The metal nanoparticles were between 1.8 and 3.8 nm in size depending of the metal. They were responsible for the reduction in the recombination process, as suggested by photoluminescence measurements. The photocatalytic performance of M/NH2-MIL-125 was tested for the degradation of acetaminophen (ACE) under simulated solar irradiation. Pt/NH2-MIL-125 achieved the highest conversion rate (rate constant of 0.0165 min−1), with complete conversion of the contaminant in less than three hours. Scavengers studies confirmed that O.-2[rad]− radicals play a main role in the degradation process, followed by .OH radicals. The catalytic stability of Pt/NH2-MIL-125 was confirmed upon three successive reaction cycles. Different water matrices were tested to understand the effect of common inorganic ions, being the presence of bicarbonates the most detrimental to the performance of the photocatalytic processThis research was funded by the State Research Agency (PID2019-106186RB-I00/AEI/10.13039/501100011033). V. Muelas-Ramos thanks to MCIU for BES-2017-082613 gran

Equilibrium, kinetics and breakthrough curves of acetaminophen adsorption onto activated carbons from microwave-assisted FeCl3-activation of lignin

Activated carbons have been prepared by chemical activation of lignin with FeCl3 using microwave (MW) heating. The use of MW significantly reduced the activation time compared to conventional heating. Microwave power, impregnation ratio (R: mass ratio of FeCl3 to lignin precursor) and MW holding time have been studied as variables affecting the development of porous texture. The optimum conditions were found at 800 W, R = 5 and 30 min MW heating time. Under those conditions an essentially microporous activated carbon was obtained, with BET surface area higher than 1150 m2·g−1 and acidic surface, whose pH at the point of zero charge was 4.2. This activated carbon was tested for the adsorption of acetaminophen, as model emerging contaminant, from aqueous phase. The adsorption isotherms, obtained at 20, 40 and 60 °C, fitted well to Redlich–Peterson model. The maximum acetaminophen adsorption reached about 300 mg·g−1 at 60 °C. Values of 35.5 kJ·mol−1 and 238.3 J·mol−1·K−1 were obtained for the enthalpy and entropy of adsorption, respectively. Those positive values are indicative of an endothermic process and increased randomness at the solid/solution interface upon adsorption. The adsorption kinetics was better described by pseudo-second order driving force model. Breakthrough curves were also obtained at different adsorption temperatures, flow rates and acetaminophen inlet concentrations. They fitted well to a logistic-type equation representative of the Bohart-Adams, Thomas and Yoon-Nelson models. Adsorbent regeneration with hot water (80 °C) revealed easy and complete desorption thus providing a promising view of the potential application of this activated carbonThe authors acknowledge the financial support from the State Research Agency (PID2019-106186RB-I00/AEI/10.13039/501100011033, Spain). M. Penas-Garzón thanks Spanish MECD for FPU16/00576 gran

Chloroform conversion into ethane and propane by catalytic hydrodechlorination with Pd supported on activated carbons from lignin

Conversion of chloroform (TCM) by gas-phase catalytic hydrodechlorination (HDC) has been addressed to maximize the selectivity to ethane and propane. Several own-made Pd (1 wt%) catalysts have been tested. The catalysts were prepared by incipient wetness impregnation of five different activated carbons. These carbons were obtained by chemical activation of lignin with different activating agents, namely, H3PO4, ZnCl2, FeCl3, NaOH and KOH. The catalysts were fully characterized by N2 adsorption–desorption at −196 °C, CO2 adsorption at 0 °C, TPR, NH3-TPD, XRD, XPS and TEM. The activating agents provided important differences in the characteristics of activated carbon supports, and hence in the resulting catalysts, in terms of their porous texture, surface acidity, Pd oxidation state and Pd particle size distribution. NaOH and KOH activation led to carbons with the highest surface areas (2158 and 2991 m2 g−1 , respectively) and low Pd0 / Pdn+ ratios, while ZnCl2- and H3PO4-activated carbons yielded the highest surface acidity and mean Pd particle sizes. The analysis of the TOF values revealed that the HDC of TCM on these catalysts is a structure-sensitive reaction, increasing TOF values with Pd particle size. The best results, in terms of selectivity to ethane and propane, were obtained with the catalysts supported on KOH- and NaOH-activated carbons. The former allowed 80% selectivity to the target compounds at almost complete dechlorination (>99%) at 300 °C. The KOH-based catalyst showed fairly good stability at a reaction temperature of 200 °CThe authors gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) through the project CTM 2014-5300

UiO-66-based metal organic frameworks for the photodegradation of acetaminophen under simulated solar irradiation

This work reports the solvothermal synthesis of UiO-66-based MOFs with three different ligands and its application to the breakdown of aqueous acetaminophen under simulated sunlight. This pharmaceutical is a representative contaminant of emerging concern that enters water bodies mainly through wastewater treatment plant discharges. The synthesis approach of the MOFs was fitted using a zirconium alkoxide as metal cluster precursor and 2-aminoterephthalic and 2,5-dihydroxyterephthalic acids as ligands to prepare UiO-66-NH2 and UiO-66-(OH)2 MOFs, respectively. These new MOFs have enhanced visible light harvesting and narrower band gap than the UiO-66. Among all, UiO-66-NH2 yielded the highest removal of acetaminophen under simulated solar irradiation in batch test. The activity and stability of UiO-66-NH2 were demonstrated for the first time in a continuous flow test, where stable performance was observed upon 30 h on stream. The degradation pathway of acetaminophen was elucidated based on coupling, ring-opening, and oxidation reactions. DFT calculation confirmed that the indirect semiconductor behavior of UiO-66-NH2 upon light excitation occurred through ligand-ligand charge transfer. Overall, promising UiO-66-based MOFs photocatalysts were obtained for effective degradation of acetaminophen with the assistance of solar lightThis research was funded by the National State Research Agency of Spain (project number: PID2019-106186RB-I00/AEI/10.13039/501100011033). Yilan Wang acknowledges the support from the China Scholarship Council (CSC No. 201908610198). We also thank to Prof. Shi Ye for his help with density functional theory calculatio

Degradation of diclofenac in water under LED irradiation using combined g-C3N4/NH2-MIL-125 photocatalysts

This study reports the photocatalytic degradation of diclofenac by hybrid materials prepared by combination of graphitic carbon nitride (g-C3N4) and titanium-metal organic framework (NH2-MIL-125), in different mass proportions (MOF:C3N4 of 25:75, 50:50 and 75:25). The hybrid materials were fully characterized, and their properties compared to those of the individual components, whose presence was confirmed by XRD. The porous structure was the result of the highly microporous character of the MOF and the non-porous one of g-C3N4. The band gap values were very close to that of MOF component. Photoluminescence measurements suggested an increase on the recombination rate associated to the presence of g-C3N4. Photodegradation tests of diclofenac (10 mg·L-1) were performed under UV LED irradiation at 384 nm. The hybrid materials showed higher photocatalytic activity than the individual components, suggesting the occurrence of some synergistic effect. The photocatalyst with a MOF:g-C3N4 ratio of 50:50 yielded the highest conversion rate, allowing complete disappearance of diclofenac in 2 h. Experiments with scavengers showed that superoxide radicals and holes played a major role in the photocatalytic process photodegradation, being that of hydroxyl radicals less significant. From the identification of by-products species, a degradation pathway was proposed for the degradation of diclofenac under the experimental operating conditionsThis work was financially supported by Associate Laboratory LSRELCM - UID/EQU/50020/2020 - funded by national funds through FCT/ MCTES (PIDDAC) and by project POCI-01-0145-FEDER-030674, financed by the ERDF through COMPETE2020 and POCI – and by national funds through FCT (Portugal). This research was also funded by Spanish Ministry of Economy and Competitiveness (project CTQ2016-78576-R, FEDER funds) and the State Research Agency (PID2019- 106186RB-I00/AEI/10.13039/501100011033) (Spain). V. MuelasRamos thanks to MCIU for BES-2017-082613 grant. Authors thank the TEM images from the Centro Nacional de Microscopía Electronica ´ (Spain). Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigacion-SAI ´ for EDX mapping images, Universidad de Zaragoza (Spain) and the Research Support Service of XPS data from University of Málaga (Spain

Phase-Field Approach for Faceted Solidification

We extend the phase-field approach to model the solidification of faceted materials. Our approach consists of using an approximate gamma-plot with rounded cusps that can approach arbitrarily closely the true gamma-plot with sharp cusps that correspond to faceted orientations. The phase-field equations are solved in the thin-interface limit with local equilibrium at the solid-liquid interface [A. Karma and W.-J. Rappel, Phys. Rev. E53, R3017 (1996)]. The convergence of our approach is first demonstrated for equilibrium shapes. The growth of faceted needle crystals in an undercooled melt is then studied as a function of undercooling and the cusp amplitude delta for a gamma-plot of the form 1+delta(|sin(theta)|+|cos(theta)|). The phase-field results are consistent with the scaling law "Lambda inversely proportional to the square root of V" observed experimentally, where Lambda is the facet length and V is the growth rate. In addition, the variation of V and Lambda with delta is found to be reasonably well predicted by an approximate sharp-interface analytical theory that includes capillary effects and assumes circular and parabolic forms for the front and trailing rough parts of the needle crystal, respectively.Comment: 1O pages, 2 tables, 17 figure

Continuum field description of crack propagation

We develop continuum field model for crack propagation in brittle amorphous solids. The model is represented by equations for elastic displacements combined with the order parameter equation which accounts for the dynamics of defects. This model captures all important phenomenology of crack propagation: crack initiation, propagation, dynamic fracture instability, sound emission, crack branching and fragmentation.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Additional information can be obtained from http://gershwin.msd.anl.gov/theor

Crack path instabilities in DCDC experiments in the low speed regime

We studied the low speed fracture regime (0.1mm/s - 1nm/s) in different glassy materials (soda-lime glass, glass-ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on DCDC (double cleavage drilled compression) specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force (AFM) microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. (Phys. Rev. Letters (1996) 76} p1497).Comment: 16 pages, 10 figures, submitted to Journal of Non-Crystalline Solid

(E)-N′-(2-Hydroxy­benzyl­idene)-2-(4-isobutyl­phen­yl)propanohydrazide

The title hydrazide compound, C20H24N2O2, exists in a trans configuration with respect to the acyclic C=N bond and an intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. The mean plane through the formohydrazide unit is essentially planar [maximum deviation = 0.025 (2) Å], and forms dihedral angles of 24.45 (16) and 87.14 (16)° with the two benzene rings. In the crystal structure, inter­molecular N—H⋯O and C—H⋯O hydrogen bonds link neighbouring mol­ecules into extended chains along the c axis, which incorporate R 2 2(16) ring motifs. An inter­molecular C—H⋯π inter­action is also observed