Degradation In Crystallinity Research Articles

Enhancement of Gaseous o-Xylene Elimination by Chlorosulfonic Acid-Modified H-Zeolite Socony Mobil-5.

It is important to develop effective strategies for enhancing the removal capacity of aromatic volatile organic compounds (VOCs) by modifying conventional porous adsorbents. In this study, a novel HZSM-5 zeolite-supported sulfonic acid (ZSM-OSO3H) was prepared through ClSO3H modification in dichloromethane and employed for the elimination of gaseous o-xylene. The ClSO3H modification enables the bonding of -OSO3H groups onto the HZSM-5 support, achieving a loading of 8.25 mmol·g-1 and leading to a degradation in both crystallinity and textural structure. Within an active temperature range of 110-145 °C, ZSM-OSO3H can efficiently remove o-xylene through a novel reactive adsorption mechanism, exhibiting a removal rate exceeding 98% and reaching a maximum breakthrough adsorption capacity of 264.7 mg. The adsorbed o-xylene derivative is identified as 3,4-dimethylbenzenesulfonic acid. ZSM-OSO3H demonstrates superior adsorption performance for o-xylene along with excellent recyclability. These findings suggest that ClSO3H sulfonation offers a promising approach for modifying various types of zeolites to enhance both the elimination and resource conversion of aromatic VOCs.

High temperature stability of regrown and alloyed Ohmic contacts to AlGaN/GaN heterostructure up to 500 °C

This Letter reports the stability of regrown and alloyed Ohmic contacts to AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) for high temperature applications up to 500 °C. Transfer length method (TLM) measurements from 25 to 500 °C in air show that the regrown contacts appear to be stable up to 500 °C during short term (approximately 1 h) testing, while alloyed contacts appear to decrease in contact resistance from 300 to 500 °C though increases in the error bounds due to increase sheet resistance make it difficult to conclude definitely. Additionally, longer term testing shows both technologies remain stable at least up to 48 h at 500 °C, after which the large increase in sheet resistance makes the measurement uncertainty too large to conclude definitively. Advanced microscopy images indicate both the regrown and alloyed contact regions remain structurally intact after prolonged high temperature exposure with no visible degradation in crystallinity or metal composition.

Fungal oxidoreductases and CAZymes effectively degrade lignocellulosic component of switchgrass for bioethanol production

• Fungal oxidoreductases and CAZymes were produced in a bioreactor. • Laccase isozymes removed lignin up to 33.9 % from switchgrass. • Microscopic and spectroscopic analysis clearly indicated lignin degradation. • Laccase treatment improved 22.47 fold sugar hydrolysis over untreated biomass. • Fermentation studies showed high ethanol yield (78.32 % of theoretical yield). Ganoderma lucidum , a basidiomycetous fungus, has enormous potential in the co-production of diverse extracellular oxidoreductases and CAZymes. In the present study, G. lucidum MDU-7 produced 510 U/ml of laccases, xylanase (3.0 IU/ml) and cellulase (3.1 FPU/ml) in a lab-scale bioreactor. Laccase pretreatment of switchgrass in a laboratory-designed bioreactor resulted in better phenol degradation (64.27 %), lignin removal (33.9 %), and increase in cellulose crystallinity (12.66 %). The pretreatment efficacy was validated using various microscopic and spectroscopic techniques (SEM, FTIR, and XRD). The hydrolysis of laccase pretreated biomass using diverse cellulases from Aspergillus oryzae MDU-4, Aspergillus flavus MDU-5, Trichoderma citrinoviride MDU-1, and Trichoderma longibrachiatum MDU-6 resulted in 162.7 mg/g, 120.4 mg/g, 157.3 mg/g, and 176.25 mg/g release of sugars, respectively. The enzymatic hydrolysates containing 3.37–5.11 g/L sugars were fermented by Saccharomyces cerevisiae NCIM-3640 strain which resulted into 1.32–1.96 g/L ethanol, with high production yield (31.42–39.16 %). Our findings suggest that laccase pretreatment technology may provide a promising and environmentally benign alternative for the sustainable development of lignocellulosic biorefinery.

Assembling Native Elementary Cellulose Nanofibrils via a Reversible and Regioselective Surface Functionalization.

Selective surface modification of biobased fibers affords effective individualization and functionalization into nanomaterials, as exemplified by the TEMPO-mediated oxidation. However, such a route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the development of potential supermaterials. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving regioselective surface modification of C6-OH, which can be reverted using mild post-treatments. No polymer degradation, cross-linking, nor changes in crystallinity occur under the mild processing conditions, yielding cellulose nanofibrils bearing carboxyl moieties, which can be removed by saponification. The latter offers a significant opportunity in the reconstitution of the chemical and structural interfaces associated with the native states. Consequently, 3D structuring of native elementary cellulose nanofibrils is made possible with the same supramolecular features as the biosynthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block.

Impurity Phases and Optoelectronic Properties of CuSbSe2 Thin Films Prepared by Cosputtering Process for Absorber Layer in Solar Cells

When there is a choice of materials for an application, particular emphasis should be given to the development of those that are low-cost, nontoxic, and Earth-abundant. Chalcostibite CuSbSe2 has gained attention as a potential absorber material for thin-film solar cells, since it exhibits a high absorption coefficient. In this study, CuSbSe2 thin films were deposited by radio frequency magnetron cosputtering with CuSe2 and Sb targets. A series of CuSbxSe2 thin films were prepared with different Sb contents adjusted by sputtering power, followed by rapid thermal annealing. Impurity phases and surface morphology of Cu–Sb–Se systems were directly affected by the Sb sputtering power, with the formation of volatile components. The crystallinity of the CuSbSe2 thin films was also enhanced in the near-stoichiometric system at an Sb sputtering power of 15 W, and considerable degradation in crystallinity occurred with a slight increase over 19 W. Resistivity, carrier mobility, and carrier concentration of the near-stoichiometric thin film were 14.4 Ω-cm, 3.27 cm2/V∙s, and 1.33 × 1017 cm−3, respectively. The optical band gap and absorption coefficient under the same conditions were 1.7 eV and 1.75 × 105 cm−1, which are acceptable for highly efficient thin-film solar cells.

Crystallinity Evaluation and Dislocation Observation for an Aluminum Nitride Single-Crystal Substrate on a Wafer Scale

The crystallinity of a 35-mm-diameter AlN single-crystal substrate grown by physical vapor transport was investigated using x-ray diffraction and Raman spectral mapping. Dislocations in the same sample were observed using an etch pit method, synchrotron x-ray topography, and transmission electron microscopy. The central area of a diameter of 25 mm was featured with high crystallinity and high uniformity, whereas the rim area showed degradation in crystallinity. An improvement in the radius of curvature was confirmed along the growth direction of [ $$ 000\bar{1} $$ ]. The dislocations were revealed as etch pits, and the position-dependent etch pit density was analyzed across the whole wafer. Transmission electron microscopy showed that under the current chemical etching condition, the size of the etch pits in the [ $$ 11\bar{2}0] $$ diagonal direction was approximately linearly proportional to the magnitude of the Burgers vectors, and therefore could be used to classify dislocations.

Tuning Ni/Al Ratio to Enhance Pseudocapacitive Charge Storage Properties of Nickel–Aluminum Layered Double Hydroxide

AbstractCompared with batteries, the advantages of capacitive energy storage include high power, fast charging kinetics, and long cycling stability. Owing to their layered structure and tunable transition metal charge, layered double hydroxides (LDHs) have great potential to be applied as pseudocapacitor materials. Here, a systematic experimental study is reported on the impact of the Ni/Al ratio on the structure, morphology, ion transport kinetics, interlayer phenomena, and performance of NiAl‐LDH supercapacitor electrode materials, in which three NiAl‐LDH materials with Ni/Al ratios of 2, 3, and 4, are synthesized using a hydrothermal method. The increase of the Ni/Al ratio results in more open interlayer space resulting in faster ion diffusion kinetics. Although an increase in the Ni/Al ratio introduces more redox active sites, it leads to degradation in crystallinity and morphology, which has a significant negative impact on pseudocapacitance. Electrochemical tests suggest that at Ni/Al = 3, the NiAl‐LDH electrode exhibits optimum specific capacitance of 2128 F g−1 at 1 A g−1 with long cycle stability. This work highlights the complex interplay among compositional and structural factors on the kinetic and performance behaviors of NiAl‐LDH materials. Subtle compositional modification is an effective strategy to enhance the pseudocapacitive charge storage property of NiAl‐LDH pseduocapacitor materials.

Hydrolytic and enzymatic degradation studies of aliphatic 10-undecenoic acid-based polyesters

The hydrolytic and enzymatic degradations of aliphatic polyesters: poly (10,11-epoxyundecanoic acid) (PEAU) bearing hydroxyl groups along the main chain and poly (11-hydroxyundecanoate)diol (PHU), were studied and compared to that of commercial poly (ε-caprolactone)diol (PCL). Changes taking place after polyester degradation in sample weight, molecular weight (Mn), chemical constitution, thermal properties, crystallinity and morphology were monitored by size exclusion chromatography (SEC), 1H nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-Ray diffraction (XRD) and environmental scanning electron and atomic force microscopies (ESEM and AFM). A significant decrease of PEUA Mn in both hydrolytic and enzymatic degradation was detected versus PHU and PCL, and related to its hydrophilic character, by the presence of hydroxyl pendant groups, and the superior amorphous character. An accelerated degradation in acidic media, monitored by SEC and 1H NMR spectroscopy to study in detail all residual material of three polyesters, showed the complete degradation only in the case of PEUA and PCL.

Structural changes on hydrous and anhydrous potash alum caused by mechanical milling

ABSTRACTThe effects of ball milling on hydrous and anhydrous potash alum (potassium aluminum sulfate dodecahydrate, KAl(SO4)2 ･ 12H2O) were investigated by powder X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy. The XRD patterns for the milled hydrous samples showed that the crystal structure was unchanged even after 120 h of milling at 12 Hz, except for a lattice expansion and appearance of peaks corresponding to Al2O3 and Fe2O3. The XRD and Raman peaks of milled anhydrous potash alum were broader than those of the unmilled sample. The broadening of Bragg peaks for milled anhydrous potash alum is presumably caused by a decrease in crystallite size and degradation in crystallinity, rather than by amorphization.

Realizing luminescent downshifting in ZnO thin films by Ce doping with enhancement of photocatalytic activity

ZnO thin films doped with Ce at different concentration were deposited on glass substrates by spray pyrolysis technique. XRD analysis revealed the phase purity and polycrystalline nature of the films with hexagonal wurtzite geometry and the composition analysis confirmed the incorporation of Ce in the ZnO lattice in the case of doped films. Crystalline quality and optical transmittance diminished while electrical conductivity enhanced with Ce doping. Ce doping resulted in a red-shift of optical energy gap due to the downshift of the conduction band minimum after merging with Ce related impurity bands formed below the conduction band in the forbidden gap. In the room temperature photoluminescence spectra, UV emission intensity of the doped films decreased while the intensity of the visible emission band increased drastically implying the degradation in crystallinity as well as the incorporation of defect levels capable of luminescence downshifting. Ce doping showed improvement in photocatalytic efficiency by effectively trapping the free carriers and then transferring for dye degradation. Thus Ce doped ZnO thin films are capable of acting as luminescent downshifters as well as efficient photocatalysts.

IMPACT OF N DOPING ON THE PHYSICAL PROPERTIES OF ZnO THIN FILMS

Structural, optical and electrical properties of bare and N monodoped ZnO thin films were investigated. The samples were prepared on glass substrates by spray pyrolysis technique. N doping resulted in p type electrical conductivity as evident from the Hall measurement results. XRD analysis confirmed the structural purity of all the films and compositional analysis by energy dispersive X-ray spectroscopy verified the inclusion of N in doped films in addition to Zn and O. Doping resulted in deterioration in crystallinity. Optical transmittance got diminished with doping due to the degradation in crystallinity as well as due to the presence of deep N related defects as evident from the photoluminescence spectra. Optical energy gap red-shifted with doping percentage due to the introduction of impurity levels near the valence band edge within the forbidden gap with acceptor doping.

Radiation response of nano-crystalline cubic Zirconia: Comparison between nuclear energy loss and electronic energy loss regimes

Nano-crystalline stabilizer free cubic Zirconia films were irradiated with 400 keV Kr and 80 MeV Ag ions in order to compare the effects of nuclear collisions and electronic excitations on nano-structured materials. Grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM) measurements reveal that the radiation response of the nano-crystalline films is critically dependent on the type of irradiation i.e. energy dissipation mechanism of the impinging ions. The 400 keV Kr irradiations did not result in major structural changes except little grain growth; whereas, a significant degradation in the crystallinity of the films was observed after the 80 MeV Ag ion irradiations. The opposite behavior under the two types of irradiation is attributed to the presence of large density of grain boundaries in the nano-crystalline films. The grain boundaries act as sinks for the irradiation induced defects (created via collision cascades) in-case of the 400 keV Kr irradiations thereby leading to defect removal and hence excellent radiation tolerance. On the other hand, reduced mobility of electrons and phonons due to scattering from the grain boundaries enhances the temperature and duration of the thermal spike, created upon the 80 MeV Ag irradiations, consequently leading to the formation of the highly damaged state (significant degradation in crystallinity).

P.3.a.004 - Abnormal visual scanning during reality evaluation and its relationship to magical ideation in schizophrenia

The hydrolytic and enzymatic degradations of aliphatic polyesters: poly (10,11-epoxyundecanoic acid) (PEAU) bearing hydroxyl groups along the main chain and poly (11-hydroxyundecanoate)diol (PHU), were studied and compared to that of commercial poly (ε-caprolactone)diol (PCL). Changes taking place after polyester degradation in sample weight, molecular weight (Mn), chemical constitution, thermal properties, crystallinity and morphology were monitored by size exclusion chromatography (SEC), 1H nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-Ray diffraction (XRD) and environmental scanning electron and atomic force microscopies (ESEM and AFM). A significant decrease of PEUA Mn in both hydrolytic and enzymatic degradation was detected versus PHU and PCL, and related to its hydrophilic character, by the presence of hydroxyl pendant groups, and the superior amorphous character. An accelerated degradation in acidic media, monitored by SEC and 1H NMR spectroscopy to study in detail all residual material of three polyesters, showed the complete degradation only in the case of PEUA and PCL.

Role of temperature in the radiation stability of yttria stabilized zirconia under swift heavy ion irradiation: A study from the perspective of nuclear reactor applications

The search for materials that can withstand the harsh radiation environments of the nuclear industry has become an urgent challenge in the face of ever-increasing demands for nuclear energy. To this end, polycrystalline yttria stabilized zirconia (YSZ) pellets were irradiated with 80 MeV Ag6+ ions to investigate their radiation tolerance against fission fragments. To better simulate a nuclear reactor environment, the irradiations were carried out at the typical nuclear reactor temperature (850 °C). For comparison, irradiations were also performed at room temperature. Grazing incidence X-ray diffraction and Raman spectroscopy measurements reveal degradation in crystallinity for the room temperature irradiated samples. No bulk structural amorphization was however observed, whereas defect clusters were formed as indicated by transmission electron microscopy and supported by thermal spike simulation results. A significant reduction of the irradiation induced defects/damage, i.e., improvement in the radiation tolerance, was seen under irradiation at 850 ºC. This is attributed to the fact that the rapid thermal quenching of the localized hot molten zones (arising from spike in the lattice temperature upon irradiation) is confined to 850 ºC (i.e., attributed to the resistance inflicted on the rapid thermal quenching of the localized hot molten zones by the high temperature of the environment) thereby resulting in the reduction of the defects/damage produced. Our results present strong evidence for the applicability of YSZ as an inert matrix fuel in nuclear reactors, where competitive effects of radiation damage and dynamic thermal healing mechanisms may lead to a strong reduction in the damage production and thus sustain its physical integrity.

Comparative study for highly Al and Mg doped ZnO thin films elaborated by sol gel method for photovoltaic application

Transparent conducting oxides such as ZnO doped with Al or Mg are commonly used in solar cells, light emitting diodes, photodetectors, and ultraviolet laser diodes. In our work, we focus on a comparative study of the structural, optical, and electrical properties of ZnO films highly doped with Al (AZO) and Mg (MZO). These films are deposited on glass substrates by the sol-gel spin coating method. The doping concentrations for Al and Mg are fixed to 5%–30%. The XRD spectra indicate that all the samples are polycrystalline with hexagonal wurtzite structures, exhibiting a preferred orientation along the (002) plane. Low degradation in crystallinity was observed for MZO even at a Mg concentration of 30%. The MgO phase started to appear compared to Al-doped layers where smaller grains are formed inducing a deterioration in the films just after doping but no new phase appeared. This result is in agreement with other experimental results [J. K. Rath, Sol. Energy Mater. Sol. Cells 76, 431–487 (2003); Morris et al., J. Appl. Phys. 67, 1079–1087 (1990)]. By AFM analysis, the results indicate a significantly rough surface for MZO compared to AZO films. For equal Al and Mg dopant concentrations, we observe that the transmittance spectra of MZO thin films are wider than those of AZO, indicating a shift toward shorter wavelengths with an optical gap energy equal to 3.67 eV. The electrical measurements of AZO and MZO thin films were made using the I–V characteristic obtained by the four probe method. All the films present an ohmic behavior. The conductivity and the mobility of AZO films were found to be better than those of MZO.

Effect of shock compression on luminescence properties of CsAlSi2O6:Eu2+ for white-light-emitting diodes

Eu2+-doped CsAlSi2O6 (pollucite) phosphors were synthesized via high-temperature solid-state reaction to produce a white-light-emitting phosphor under UV irradiation. The obtained phosphors were characterized using X-ray diffraction, photoluminescence (PL), PL excitation, thermal stability, and PL decay. In contrast to previous reports, the fabricated phosphors emitted either white light or bluish white light with less thermal quenching and a higher internal-quantum efficiency (IQE) upon deep-UV excitation than upon near-UV excitation. The phosphors were subjected to shock compression at a pressure of 23 GPa to investigate the structural response of the pollucite. Although the pressure was higher than that required for a structural transition, no trace of a phase transition was observed. Although the chromaticity coordinates and thermal quenching of the shocked pollucite phosphors showed little change, a considerable degree of strain was induced and the PL intensity and IQE decreased due to a degradation in crystallinity.

An experimental investigation of temperature rise during compaction of pharmaceutical powders

During pharmaceutical powder compaction, temperature rise in the compressed powder can affect physiochemical properties of the powder, such as thermal degradation and change in crystallinity. Thus, it is of practical importance to understand the effect of process conditions and material properties on the thermal response of pharmaceutical formulations during compaction. The aim of this study was to examine the temperature rise of pharmaceutical powders during tableting, in particular, to explore how the temperature rise depends on material properties, compression speed and tablet shape. Three grades of microcrystalline cellulose (MCC) were considered: MCC Avicel pH 101, MCC Avicel pH 102 and MCC DG. These powders were compressed using a compaction simulator at various compaction speeds (10–500mm/s). Flat faced, shallow convex and normal convex tablets were produced and temperature distributions on the surface of theses tablets upon ejection were examined using an infrared thermoviewer. It was found that an increase in the compaction speed led to an increase in the average surface temperature. A higher surface temperature was induced when the powder was compressed into a tablet with larger surface curvature. This was primarily due to the increasing degree of powder deformation (i.e. the volume reduction) and the effect of interparticule/wall friction.

Effect of annealing temperature on the morphology and optical properties of ZnO tetrapods grown by a thermal evaporation technique

The effect of the thermal annealing temperature was investigated on ZnO tetrapods grown by a thermal evaporation method. The ZnO tetrapods were synthesized by thermal evaporation of Zn powder in air. The annealing was done in an oxygen gas environment at temperatures ranging from 400 to 1000°C for 1h. As the annealing temperature increased from 400°C to 800°C, the morphology of the tetrapod remained unchanged; however, the size of the tetrapods increased. With a further increase in the annealing temperature from 800°C to 1000°C, the ZnO tetrapod changed drastically to nanoneedles. As-grown and annealed samples had an identical crystal structure, which was a wurtzite structure. A strong and sharp ultraviolet emission at 380nm was observed for the 600°C –annealed sample indicating the high crystalline quality. The ultraviolet emission intensity decreased abruptly for the samples annealed at 800°C and 1000°C, which exhibits the degradation in crystallinity.

Enhanced photocatalytic activity of sol–gel derived ZnO via the co-doping process

Thin films of intrinsic, N-doped and N/Al co-doped ZnO were prepared by a sol–gel deposition process. The effect of doping on structure, optoelectronics and photocatalytic properties of ZnO were studied. It was found that the doping process reduces the commonly observed wrinkled effect. XRD pattern measurements confirmed that all the films preferentially grow in the c-axis orientation, with degradation in crystallinity in doped films. The dopant created defect can be also observed in the PL spectra and UV–vis measurements of the NZO and NAZO thin film, with reduced band gap in doped films. Photocatalytic measurements confirm that the N and N/Al dopant process enhances photocatalytic degradation of MB by narrowing the band gap.

Energy dissipation channels affecting photoluminescence from resonantly excited Er3+ ions doped in epitaxial ZnO host films

We identified prerequisite conditions to obtain intense photoluminescence at 1.54 μm from Er3+ ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er3+ ions were resonantly excited at a wavelength of 532 nm between energy levels of 4I15/2 and 2H11/2. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er3+ ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er3+ ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er3+ ions were accommodated into ZnO crystals. Optimizing the degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er2O3 crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from Er3+ ions.