Selective Chemical Dissolution Research Articles

Analysing the potential of the selective dissolution of elastane from mixed fiber textile waste

Textile products are composed of various blends of synthetic or natural polymers. Elastane increases the functionality during use phase, but impedes high quality recycling. This study investigates the selective chemical dissolution of elastane from blended textile. Hansen solubility parameters and COSMO-RS were applied for solvent screening. The most recommended biobased solvents were experimentally validated with polyester, polyamide, cotton, wool and elastane for which solubility limits were determined and hence, their selectivity towards elastane dissolution. A TGA-corrected gravimetric method was developed as quantification tool and showed that tetrahydrofurfuryl alcohol and ɣ-valerolactone have comparable elastane dissolution capabilities to classical solvents (5 mg elastane/g solvent). Polyester/elastane and polyamide/elastane blends were subjected to this process as case studies. The LCA study showed that this selective solvent-based dissolution process saves 60% CO2-eq./kg textile waste compared to incineration. This interdisciplinary work can set the benchmark for further developing and upscaling physical/dissolution recycling processes for blended textiles.

The role of chromium content in aqueous passivation of a non-equiatomic Ni38Fe20CrxMn21-0.5xCo21-0.5x multi-principal element alloy (x = 22, 14, 10, 6 at%) in acidic chloride solution

The effect of the Cr content on the corrosion behavior in a series of single-phase non-equiatomic Ni38Fe20CrxMn21-0.5xCo21-0.5x (6 < x < 22 at%) multi-principal element alloys (MPEAs) was investigated in acidified NaCl solutions. Comparisons were made with binary solid solution Co-Cr, Ni-Cr, and Fe-Cr alloys over a similar range of Cr contents. The corrosion behavior was evaluated using in-situ AC and DC electrochemical methods and ex-situ surface sensitive characterization techniques. Passivity and various levels of local corrosion resistance were obtained in the MPEA with 10 at% Cr or above. The binary Ni-Cr alloys with 12–30 at% Cr behaved similarly. The MPEA with 6 at% Cr and binary alloys with 5, 6, or 10 at% Cr were marginally passive or active and underwent localized corrosion during both linear sweep voltammetry and potentiostatic hold experiments. Passive films formed during potentiostatic hold experiments were characterized with X-ray photoelectron spectroscopy and atom probe tomography. Cr cation enrichment in the passive films was observed for all alloys and similar enrichment factors were obtained as a function of Cr content regardless of whether MPEA or binary alloy except for the Fe-Cr alloy. Moreover, passive current density was correlated with the Cr cation fraction in the passive film. The degree of Cr enrichment was attributed to a combination of thermodynamic and kinetic factors, such as selective chemical dissolution of alloying elements as well as limitation due to solute depletion at the metal oxide interface in alloys with a bulk Cr content ≤ 10 at%.

Combined fabrication of terahertz hollow-core metal rectangular waveguide cavity using electrochemical deposition and selective chemical dissolution

The terahertz hollow-core metal rectangular waveguide cavity is a typical terahertz rectangular cavity structure that has several advantages and is widely used. However, the fabrication of the terahertz hollow-core metal rectangular waveguide cavity with high working frequency has not made recent breakthroughs, especially when the working frequency is 1-THz and above. In this paper, a combined process of electrochemical deposition and selective chemical dissolution is proposed first to manufacture the terahertz hollow-core metal rectangular waveguide cavity with high working frequency. Taking the fabrication of a 1.7-THz hollow-core metal rectangular waveguide as an example, the manufacturing methods and experiments of each step are described systematically. A terahertz hollow-core metal rectangular waveguide cavity with an end face size of 81.9 × 162.7 µm2, the edge radius less than 10 µm, the internal bottom surface roughness less than 0.08 µm, and the internal side surface roughness less than 0.3 µm is obtained. These experimental results are matched with the processing requirements of a 1.7-THz hollow-core metal rectangular waveguide. This flexible and controllable combined process makes it possible to manufacture more types of terahertz hollow-core metal rectangular cavity structures with high working frequency.

Preparation and Characterization of Highly Porous Polyacrylonitrile Electrospun Nanofibers Using Lignin as Soft Template via Selective Chemical Dissolution Technique.

In this study, polyacrylonitrile (PAN) was mixed with a renewable polymer, lignin, to produce electrospun nanofibers by using an electrospinning technique. Lignin was utilized as a soft template that was removed from the nanofibers by using a selective dissolution technique to create porous PAN nanofibers. These nanofibers were characterized with Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), thermogravimetry analysis (TGA), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) to study their properties and morphology. The results showed that lignin can be homogeneously mixed into the PAN solution and successfully electrospun into nanofibers. FESEM results showed a strong relationship between the PAN: lignin ratio and the diameter of the electrospun fibers. Lignin was successfully removed from electrospun nanofibers by a selective chemical dissolution technique, which resulted in roughness and porousness on the surface of the nanofibers. Based on the BET result, the specific surface area of the PAN/lignin nanofibers was more than doubled following the removal of lignin compared to PAN nanofibers. The highest specific surface area of nanofibers after selective chemical dissolution was found at an 8:2 ratio of PAN/lignin, which was 32.42 m2g−1 with an average pore diameter of 5.02 nm. The diameter of electrospun nanofibers was also slightly reduced after selective chemical dissolution. Porous PAN nanofibers can be seen as the precursors to the production of highly porous carbon nanofibers.

Quantitative estimations of iron oxide minerals in the Late Pleistocene paleosol of the Yangtze River Delta: Implications for the chemical weathering, sedimentary environment, and burial conditions

Iron oxide minerals are widely present in soil and known to be closely associated with soil-forming environments. In this study, a detailed quantitative analysis of the iron oxide minerals in the Late Pleistocene hard clay of the Yangtze River Delta (YRD) was conducted using new integrated methods of magnetism, selective chemical-dissolution, and diffuse reflectance spectroscopy. A variety of established chemical weathering indexes and optically stimulated luminescence (OSL) chronology were also applied in the investigations of the hard clay in the study area. These methods allowed for detailed examinations of the chemical weathering, sedimentary environmental conditions, and the post-depositional processes of the hard clay deposits in the YRD. This study’s A-CN-K diagram revealed that the hard clay had entered an intermediate weathering stage. In addition, various chemical weathering indexes demonstrated that the hard clay had undergone three stages of chemical weathering from bottom to top as follows: 1) A relatively high stage of chemical weathering; 2) A low chemical weathering stage with a slightly increasing trend; and 3) A relatively high chemical weathering stage with a weakly decreasing trend. It was found that when χ, χfd, Fed/Fet, Gt, and Hm/Gt were not reliable indicators of chemical weathering for the hard clay, Fed could be a useful proxy. In the current study, based on the OSL ages and several paleoclimatic proxies, it was suggested that the climate conditions in the YRD had transitioned from a relatively weak to a strong East Asian summer monsoon phase during the periods between the marine oxygen isotope stages (MIS) 4 and MIS 3. Furthermore, the low values of χ and χfd in the hard clay indicated an intense dissolution of fine-grained strong magnetic minerals. Meanwhile, the relatively high Feo/Fed ratios in the superficial horizon displayed the predominance of poorly crystalline forms of iron oxides. In summary, the analysis results implied that the hard clay had undergone post-burial processes of ferrolysis, as well as dissolved organic matter translocation from the overlying Holocene sediment. The aforementioned post-burial processes for the hard clay had occurred under reduction–oxidation cycles, which were mainly driven by the rise of the groundwater levels with the Holocene transgression.

Helical Nanostructure Formation By Nanoconfinement of Spatiotemporal Patterns in Electrochemical Reactions

Spatiotemporal pattern formation in anodization and electrodeposition is of interest since the patterns can be encoded as structures. Such materials having unique periodic structures can show a variety of properties, and thus the strategy of materials production based on dynamic self-organization has become one of the hot topics. Among the production of materials based on spatiotemporal pattern formation, we have recently focused on spatial symmetry breaking which leads to the formation of chiral materials such as nanohelices. In the present paper, we will show two examples of helical nanostructure formation based on spatiotemporal pattern formation in electrochemical reactions. As the first example, we discuss the helical nanopore formation in a silicon wafer by platinum(Pt)-assisted chemical etching (PacEtch). When a silicon wafer modified with metallic nanoparticles is immersed in an etchant containing HF and H2O2, the local corrosion of silicon is highly enhanced at the interface between metal and silicon. This local corrosion results in the formation of track-pores, the diameter of which is determined by the size of the metallic nanoparticles. The track-pores are generally cylindrical, but they show helical shapes especially when using Pt nanoparticles for local corrosion. Since the etching of silicon is local corrosion, the oxidation reaction must be balanced with the reduction reaction which is the reduction of H2O2. We measured the corrosion potential during PacEtch and found that it is located in the potential region where a negative differential resistance is observed in the reduction of H2O2 on a Pt electrode. We have also confirmed that the reduction of H2O2 spontaneously oscillates when we apply the same potential as the corrosion potential using both a Pt disk electrode and the etchant. These results suggest that the periodic shapes of helical nanopores formed by PacEtch originate from the periodic reduction of H2O2 on the Pt nanoparticles.As another example, we show the co-electrodeposition of palladium (Pd) and copper (Cu). When the co-electrodeposition of Pd-Cu was conducted in an aqueous solution containing PdCl2 and CuCl2, a 2-dimensional target micropattern was spontaneously formed. The spatial pattern formation resulted in the spontaneous formation of a multilayer of Pd-rich and Cu-rich layers. The characteristic size of the target micropattern is ~2 µm. As the next step, we utilized a porous alumina membrane with 200 nm in diameter, whose one of the top surfaces were covered with a gold thin film to be utilized as the working electrode. When Pd-Cu was deposited within the nanopores of the membrane, Pd-Cu rods were obtained. Interestingly, the Pd-rich region grew helically in the rod, which was clearly observed by selective chemical dissolution of the Cu-rich region. This result suggests that spontaneous helical pattern formation is achieved by confining the 2-dimensional spatiotemporal pattern within cylindrical nanopores which is much smaller than the characteristic 2-dimensional pattern. These two examples strongly suggest that the nanoconfinement of spatiotemporal pattern formation leads to spatial symmetry breaking and results in spontaneous helical pattern formation. We believe that the production of helical materials by nanoconfinement of spatiotemporal patterns is a new class of materials science in chirality.

Porous pyramidal silicon structures for improved light sensing performance

In this study, a highly sensitive and high-gain metal-semiconductor-metal photodetector was successfully fabricated based on textured silicon substrates. Texturing of silicon substrate is an efficient technique to control its surface reflectivity by increasing the specific surface area. A combination of porous and pyramidal structures of silicon was introduced to dramatically enhance the light-capturing ability and minimize the reflection coefficient of the silicon substrates. To fabricate pyramidal structures, selective chemical dissolution of silicon was carried out. To form porous structures on pyramidal silicon, electrochemical etching process with different etching time was followed. The morphology and structure of samples were characterized using field-emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The optical properties were investigated using Raman, photoluminescence (PL) and reflectance spectroscopy. Results indicated that the optical reflectivity can be minimized when an optimal etching time is applied which can be due to the enhancement in the exposed area and ability of light capturing. The enhanced porosity of the optimized substrate was illustrated by its elevated PL intensity. For studying the effect of porous layer on the optoelectrical properties of pyramidal structures, metal-semiconductor-metal (MSM) photodetectors were fabricated by deposition of Schottky contacts of Au on different samples. The device with the optimal porous layer exhibited enhanced sensitivity to the incident illumination due to the huge surface area and reduction in the reflection coefficient. Moreover, the ultrafast sensing behavior of this device reflects its improved optoelectrical performance in light detection.

Hydration/modification of fly ash in a fluidized bed

This study aimed to introduce fluidized bed reactor-vapor deposition (FBR-VD) into the modification of fly ash(FA) using the activators of HCl (HC), H2SO4 (HS), NaOH (NH), Na2SO4 (NS), and NaCl (NC) to reveal the modification mechanism and hydration process of FA. The simple and effective modification device is innovatively combined with building materials to promote the utilization of FA, and the chemical reagents of HC and HS are firstly used in constructive materials to modify FA. The fluidity, compressive strength and the risk of Cl− presence were analyzed. The hydration process was conducted by the hydration heat, chemical shrinkage, selective chemical dissolution method, scanning electron microscopy (SEM) and thermogravimetric-differential scanning calorimetry (TG-DSC). The modification mechanism was investigated by X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FTIR). The results demonstrate that HC can significantly improve the fluidity of the FA-cement paste and modifiers can increase the intensity at different ages except for NS. The Cl− in the modifiers does not affect the safety of concrete. The modifiers of NC, HC, NH, and HS can enhance the early hydration rate and the degree of hydration of FA to increase the compressive strength of the FA-cement paste. Modifiers can promote the cleavage of the Si–O bond and the Al–O bond of the network structure in FA, effectively activating the pozzolanic activity of FA.

Improved photovoltaic performance of graphene-based solar cells on textured silicon substrate

Abstract Graphene has attracted much interest as an active layer in heterojunction solar cells due to its outstanding properties such as flexibility, transparency, mechanical strength and elevated carrier mobility. In this research, a new technique was presented in order to enhance the efficiency of graphene–based heterojunction solar cells by employing a textured silicon (Si) substrate. Here, two sets of devices were fabricated based on flat and pyramidal structure of Si and the photovoltaic properties of graphene/Si heterojunction solar cells were compared. Selective chemical dissolution of Si wafers was carried out in order to produce pyramidal skeleton. Reduced graphene oxide (rGO) was then transferred on pyramidal Si through electrophoretic deposition (EPD) technique. The evidence of graphene layers on Si substrates was studied using Raman spectroscopy, X–ray diffractometry (XRD) and atomic force microscopy (AFM) analysis. The morphology of samples indicated an enhancement in rGO/Si interface area when the pyramidal structure is applied. Moreover, the enhanced surface area of this sample which is due to elevated roughness of pyramidal structure and wrinkles of graphene layers promotes its antireflective behavior which was proven using reflectance spectroscopy. The average reflectance of the graphene layer on the textured Si was ∼14% in the wavelength range of 400–800 nm which is lower than that of rGO on flat Si. The improved optical properties of graphene on pyramidal silicon can broaden its potential applications in optoelectrical devices such as high-efficiency solar cells. In order to study the photovoltaic properties of rGO/Si samples, a passive layer was formed on Si substrate and a square frame of Ag was coated on it which was acted as a top contact. The current–voltage characteristics showed that the efficiency of rGO/Si heterojunction solar cells was improved when textured silicon was applied.

Integral fabrication of terahertz hollow-core metal rectangular waveguides with a combined process using wire electrochemical micromachining, electrochemical deposition, and selective chemical dissolution

The application requirements of terahertz hollow-core metal rectangular waveguides with a high-working frequency have become increasingly urgent with the rapid development of terahertz technology. Integral fabrication of terahertz hollow-core metal rectangular waveguides can improve considerably the transmission performance of terahertz signals. However, with current manufacturing techniques, the high-precision integral fabrication of high-working-frequency terahertz hollow-core metal rectangular waveguides is difficult owing to their characteristically small end face size and the need for strict dimensional accuracy and high internal surface quality. In this paper, an innovative combined process of wire electrochemical micromachining, electrochemical deposition, and selective chemical dissolution is proposed firstly to overcome this puzzle. Taking the fabrication of an integral 1-THz hollow-core metal rectangular waveguide as an example, the manufacturing methods involved in each step are described particularly, together with the corresponding experimental investigations. With the end face size of 127 μm × 254 μm, edge radius less than 5 μm, and internal surface roughness less than 0.08 μm, the experimental results satisfy the design requirements for a 1-THz hollow-core metal rectangular waveguide. This study demonstrates that the proposed combined process is flexible, controllable, and suitable for the high-precision integral fabrication of high-working-frequency terahertz hollow-core metal rectangular waveguides.

Fabrication and formation mechanisms of ultra-thick porous anodic oxides film with controllable morphology on type-304 stainless steel

In this work, pore initialization and further growth of metal-oxides-film (MOsF) with nanoporous structure on stainless steel (SS) substrate by electrochemical anodization have been investigated for controlling morphology of the porous MOsF. The competition between electric field assisted dissolution of the oxidized metals and anodization of SS substrate are analyzed by current-time response combined with the thickness variation of the barrier layer. The current density-time (i-t) curves show a drastic increase-a drastic drop-a gradual increase-stable shape while the barrier layer thickness presents a drastic increase-a gradual decrease-stable trend. Furthermore, the morphology (pore size, pore shape and film thickness) of the porous MOsF on SS substrate is strongly dependent on voltage drop across the barrier layer, anodizing duration and chemical constituents of the SS substrate. An electric field-assisted selective chemical dissolution model has been proposed to explain the formation of porous MOsF with cross-connected nanotube-shaped pores. An anodic etching model and an equivalent circuit of anodization system are built to theoretically analyze the formation mechanisms of pore shrinking (pore size varies from 53 ± 7 nm at the top to 34 ± 4 nm at the bottom) across the porous MOsF. Based on the achieved results, we are able to design an anodization scheme by step-potential tailoring to fabricate thick, porous MOsF with uniform nanostructures. By applying the step-potential tailoring anodization to keep a quasi-stable electric field across the barrier layer, ultra-thick (>17 μm), uniform, porous nanostructured MOsF on the SS substrates have been reported.

Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand

The Bangladesh lowlands are traversed by the largest sediment flux on the planet. Detritus generated mostly in Himalayan highlands and conveyed through the Ganga–Brahmaputra rivers and Meghna estuary reaches the Bay of Bengal, where it forms a composite deltaic system. This study integrates the vast existing database on Ganga–Brahmaputra sediments of all grain sizes from clay to sand with new petrographic, mineralogical, and geochemical data on estuarine and shallow-marine sands. A large spectrum of compositional signatures was used to: (i) assess the relative supply of the Ganga and Brahmaputra rivers to estuarine and shelfal sediments; (ii) define the compositional variability of estuarine sediments and the impact exerted by hydraulic sorting and climate-related chemical weathering on provenance signals; (iii) define the compositional variability of shelf sediments and the potential hydrodynamic segregation of fast-settling heavy minerals in coastal environments and of slow-settling platy micas on low-energy outer-shelf floors; (iv) consider the potential additional mud supply from the western subaerial part of the delta formerly built by the Ganga River; and (v) draw a preliminary mineralogical comparison between fluvio-deltaic sediments and turbidites of the Bengal–Nicobar deep-sea fan, thus tracing sediment dispersal across the huge sedimentary system extending from Tibet to the equatorial Indian Ocean. All investigated mineralogical and geochemical parameters, as well as Sr and Nd isotope ratios and clay–mineral assemblages, showed a clear prevalence in sediment supply from the Brahmaputra (60–70%) over the Ganga (30–40%). Heavy-mineral suites and Sr and Nd isotope fingerprints of Bengal shelf sediments are nearly identical to those of the Brahmaputra River and Meghna estuary, also because the Brahmaputra carries almost twice as many Ca-plagioclase grains and heavy minerals including epidote than the Ganga, and these minerals control the large majority of the Sr and Nd budgets. The experience gained in modern settings can be directly extrapolated only to the recent past, because sediments older than the late Pleistocene and buried more than a few hundred meters begin to lose less durable ferromagnesian minerals by selective chemical dissolution, which makes quantitative estimates progressively less robust in more deeply buried older strata.

Providing significantly enhanced photocatalytic H2 generation using porous PtPdAg alloy nanoparticles on spaced TiO2 nanotubes

In the present work we introduce a simple approach to produce porous PtPdAg alloy nanoparticles on TiO2 nanotubes by a simple combined sputtering-dewetting-dealloying process. In a first step, three individual metals (Pt, Pd and Ag) were sequentially sputter-deposited on spaced TiO2 nanotubes, followed by a thermal dewetting treatment in Ar to convert these metal layers into ternary PtPdAg alloyed particles. Dealloying was carried out by a selective chemical dissolution of Ag in piranha solution that finally generated porous alloyed nanoparticles located on the TiO2 nanotube walls. The porous PtPdAg-decorated TiO2 nanotubes show enhanced photocatalytic H2 generation in comparison with porous Pt (67% increase) or any monometallic decoration (>120% increase). The photocatalytic enhancement is not only due to the increased number of active sites (larger surface area) of the porous particles but also due to the synergistic effects of the different alloying elements.

Comprehensive Study of Au Nano-Mesh as a Catalyst in the Fabrication of Silicon Nanowires Arrays by Metal-Assisted Chemical Etching

Silicon nanowires (SiNWs) arrays have become one of low-dimensional structural nanomaterials for the preparation of high-performance optoelectronic devices with the advantages of highly efficient light trapping effect, carrier multiplication, and adjustable optical bandgap. The controlled growth of SiNWs determines their electrical and optical properties. The morphology of silicon nanowires fabricated by conventional metal-assisted chemical etching (MACE) involving the Ag-based etching process cannot be precisely controlled. Ultra-thin anodic aluminum oxide (AAO) is one of the new-pattern nanostructure assembly systems for the synthesis of nanomaterials. The synthesized nanostructure arrays can be tuned to exhibit different optical and electrical properties in a certain wavelength range by adjusting the AAO membrane parameters. In this paper, we demonstrate an ultra-thin Au nano-meshes array from a single hexagonal AAO membrane as a replication master instead of conventional Ag particles as etching catalyst. The extended ordered silicon nanowires arrays are fabricated by the selective chemical dissolution of nanoscale noble metal meshes that exhibit excellent anti-reflection performance in broadband wavelengths and a wide incidence angle.

Ru nanoparticles on TiO2 with various anatase-to-rutile ratios tuned by selective chemical dissolution: Effect of support polymorph composition on selective benzene hydrogenation

Using P25 TiO2 as the precursor, phase-pure anatase and rutile TiO2 as well as TiO2 with tunable anatase-to-rutile molar ratios (nA/nR) were prepared via a facile “selective chemical dissolution” approach. The Ru/TiO2 catalysts were then synthesized and comprehensively characterized by spectroscopic techniques and transmission electron microscopy. It is confirmed that these catalysts possessed similar physicochemical parameters and hydrophilicity, but different Ru sizes (2.3–4.5 nm). Ru nanoparticles (NPs) supported on TiO2 with nA/nR of 2.66 (Ru/TiO2-1.5%HF) exhibited moderate size of 3.4 nm and electron-deficient state, which was originated from the unique Ru-on-anatase/rutile junction structure. In selective benzene hydrogenation, the turnover frequencies of benzene of the mixed phase TiO2-supported Ru catalysts were similar irrespective of the nA/nR ratios and ranged between phase-pure anatase and rutile TiO2-supported Ru catalysts, which can be ascribed to the size effect of Ru. For the cyclohexene selectivity, Ru NPs supported on TiO2 with nA/nR of 0.88–2.66 exhibited higher S0 (92–95%) than Ru NPs on TiO2 with other nA/nR ratios, in which the Ru/TiO2-1.5%HF catalyst displayed a maximum of 95%. We demonstrated that in addition to the proper Ru size, the electron-deficiency of Ru on the Ru/TiO2-1.5%HF catalyst contributed greatly to the highest selectivity since it can promote the desorption of cyclohexene to avoid suffering over-hydrogenation.

The Himalayan Foreland Basin from collision onset to the present: a sedimentary–petrology perspective

Abstract This chapter summarizes the available stratigraphic, petrographical and mineralogical evidence from sediments and sedimentary rocks on the evolution of the Himalayan belt and its associated foreland basin. The use of compositional signatures of modern sediments to unravel provenance changes and palaeodrainage evolution through time is hampered by a poor match with detrital modes of ancient strata markedly affected by selective chemical dissolution of unstable minerals during diagenesis. Only semi-quantitative diagnoses can thus be attempted. Volcanic detritus derived from Transhimalayan arcs since India–Asia collision onset at c. 60 Ma was deposited onto the Indian lower plate throughout the Protohimalayan stage, with the exception of the Tansen region of Nepal that is characterized by quartz-arenites yielding orogen-derived zircon grains. During the Eohimalayan stage, begun in the late Eocene when most sedimentation ceased in the Tethys Himalayan domain, low-rank metasedimentary detritus was overwhelming in the central foreland basin, where a widespread unconformity developed spanning locally as much as 20 myr. Volcanic detritus from Transhimalayan arcs remained significant in northern Pakistan. Arrival of higher-rank metamorphic detritus since the earliest Miocene, and the successive occurrence of garnet, staurolite, kyanite and finally sillimanite, characterized the Neohimalayan stage, when repeated compositional changes in the foreland-basin succession document the stepwise propagation of crustal deformation across the Indian Plate margin and widening of the thrust belt with exhumation of progressively more external tectonic units. The correspondence in time between the activity of major thrusts and petrofacies changes indicates a promising approach to accurately reconstruct the geological evolution of the coupled orogen–basin system. Conversely, a poor conceptual framework and the general reliance on ad hoc mechanisms to explain phenomena unpredicted by simplified models represent major factors limiting the robustness of palaeotectonic interpretations. Improved knowledge requires taking into full account the dynamic role played by still poorly understood subduction processes – rather than exclusively the effect of passive loading – as well as the role played by the presence of inherited structures on the downgoing Indian Plate, which control both lateral variability of orogenic deformation and the location of depocentres in the foreland basin.

Chemically dependent mechanical properties of natural andesite rock fractures

Different engineering rock works are affected by chemical–mechanical coupling phenomena in rock mass. Friction, strength of fracture walls, shape of asperities, and roughness control hydraulic and mechanical behaviors of fractures, which are all affected by chemical solutions. In addition, the efficiency of some operations such as leaching depend on the fracture conductivity in a confined condition. To evaluate the effects of leaching agents on the mechanical and geometrical properties of andesite rock fractures, a set of laboratory-scale experiments were conducted on three types of andesite in a sulfate medium with different pH values. Although the cohesion and shear strength reduced by decreasing the pH value, the roughness and shear stiffness of fractures did not follow a unique trend. Scanning electron microscope images indicated that the reason is mainly due to the selective chemical dissolution of the more reactive minerals in acidic solution. It is shown that fracture conductivity is a strong function of confining stress, asperities resistance, and aperture in such a way that confining pressure decreases the conductivity appreciably and the reduction rate depends on the mineralogy of fracture surfaces.

Nanoporous metallic structures by de-alloying bulk glass forming Zr-based alloys

Nanoporous structures have been produced by selective chemical dissolution of two multicomponent bulk glass-forming alloys with a supposed proper content of the more noble metals - Zr65Ni30Pd5 and Zr55Ni30Al10Pd5. The Al-containing alloy reveals open three-dimensional pores, while the selective dissolution of the Al-free ternary alloy results in larger surface pores and a number of disconnected ligaments. The average width of the ligaments, composed of 3–5 nm nanocrystals, is about 50 nm and the mean pore size for the de-alloyed quaternary alloy is 90 nm. The effect of Al on the ligament morphology and pore size is analyzed.

Association with pedogenic iron and aluminum: effects on soil organic carbon storage and stability in four temperate forest soils

Soil organic carbon (SOC) can be stabilized via association with iron (Fe) and aluminum (Al) minerals. Fe and Al can be strong predictors of SOC storage and turnover in soils with relatively high extractable metals content and moderately acidic to circumneutral pH. Here we test whether pedogenic Fe and Al influence SOC content and turnover in soils with low Fe and Al content and acidic pH. In soils from four sites spanning three soil orders, we quantified the amount of Fe and Al in operationally-defined poorly crystalline and organically-complexed phases using selective chemical dissolution applied to the soil fraction containing mineral-associated carbon. We evaluated the correlations of Fe and Al concentrations, mean annual precipitation (MAP), mean annual temperature (MAT), and pH with SOC content and 14C-based turnover times. We found that poorly crystalline Fe and Al content predicted SOC turnover times (p < 0.0001) consistent with findings of previous studies, while organically-complexed Fe and Al content was a better predictor of SOC concentration (p < 0.0001). Greater site-level MAP (p < 0.0001) and colder site-level MAT (p < 0.0001) were correlated with longer SOC turnover times but were not correlated with SOC content. Our results suggest that poorly crystalline Fe and Al effectively slow the turnover of SOC in these acidic soils, even when their combined content in the soil is less than 2% by mass. However, in the strongly acidic Spodosol, organo-metal complexes tended to be less stable resulting in a more actively cycling mineral-associated SOC pool.

Electrochemically Formed TiO2 Nanotube Arrays Site Selectively Decorated with Porous Au Particles By a Controlled Dewetting-Dealloying Approach - a Platform for Efficient Photocatalytic H2 Evolution

In the last decades TiO2 has received large attention due to its ability to “photocatalytically” split H2O into H2 and O2. Under “open-circuit” conditions, noble metal-modified (mainly Pt, Au or Pd) TiO2 is needed for H2 photo-generation.1 Not only the presence but also the size, amount and distribution of the noble metal particles affect the photocatalytic efficiency of TiO2.2,3 In this contribution we show that a most effective way to control the size and distribution of co-catalytic nanoparticles deposited on ordered TiO2 nanotube arrays is a controlled sputter-dewetting process.4 For this, we first grow electrochemically highly-ordered arrays of short aspect-ratio TiO2 nanotube in a o-H3PO4/HF electrolyte.5 The tubes growth is based on a simple anodization of a Ti metal substrate in self-ordering electrochemical conditions, and the morphology of the formed tubular oxide structures can be simply adjusted by the experimental conditions. These arrays of TiO2 nanotubes are coated with sputtered Au and Ag films, and a following controlled thermal treatment is carried out that leads at the same time to Au-Ag alloying and thermal dewetting of the conformal metallic film, that is, the sputtered metals are converted into an array of orderly distributed alloyed Au-Ag nanoparticles. By adjusting the sputtering conditions, we are able to selectively deposit the Au-Ag nanoparticles at the rim and/or within the cavity of the TiO2 nanotubes. Subsequently, we perform a dealloying process, consisting in the selective chemical dissolution of Ag in a HNO3 solution, this leaving behind nanoporous Au particles on/into the tubes. Compared to tubes decorated by conventional approaches, remarkably enhanced photocatalytic H2 production is obtained upon porousification of the embedded Au nanoparticles. These porous Au/TiO2 nanotube structures show a remarkable photocatalytic enhancement particularly when the Au porous particles are selectively formed at the rims of the tubes (“crown” position). [1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 2014, 114, 9385–9454. [2] N. T. Nguyen, J. Yoo, M. Altomare, P. Schmuki, Chem. Commun. 2014, 50, 9653–9656. [3] N. T. Nguyen, M. Altomare, J. E. Yoo, N. Taccardi, P. Schmuki, Adv. Energy Mater. 2015, doi: 10.1002/aenm.201501926. [4] N. T. Nguyen, M. Altomare, J. Yoo, P. Schmuki, Adv. Mater. 2015, 27, 3208–3215. [5] J. E. Yoo, K. Lee, M. Altomare, E. Selli, P. Schmuki, Angew. Chem. Int. Ed. 2013, 52, 7514–7517. Figure 1