High-Sensitivity Photoelectrochemical Ultraviolet Photodetector with Stable pH-Universal Adaptability Based on Whole Single-Crystal Integrated Self-Supporting 4H-SiC Nanoarrays.

Emerging photoelectrochemical (PEC) photodetectors (PDs) have notable advantages over conventional PDs and have attracted extensive attention. However, harsh liquid environments, such as those with high corrosivity and attenuation, substantially restrict their widespread application. Moreover, most PEC PDs are constructed by assembling numerous nanostructures on current collector substrates, which inevitably contain abundant interfaces and defects, thus greatly weakening the properties of PDs. To address these challenges, a high-performance pH-universal PEC ultraviolet (UV) PD based on a whole single-crystal integrated self-supporting 4H-SiC nanopore array photoelectrode is constructed, which is fabricated using a two-step anodic oxidation approach. The PD exhibits excellent photodetection behavior, with high responsivity (218.77 mA W-1), detectivity (6.64 × 1013 Jones), external quantum efficiency (72.47%), and rapid rise/decay times (17/48 ms) under 375 nm light illumination with a low intensity of 0.15 mW cm-2 and a bias voltage of 0.6 V, which is fall in the state-of-the-art of the wide-bandgap semiconductor-based PDs reported thus far. Furthermore, the SiC PEC PD exhibits excellent photoresponse and long-term operational stability in pH-universal liquid environments. The improved photodetection performance of the SiC PEC PD is primarily attributed to the synergistic effect of the nanopore array structure, integrated self-supporting configuration, and single-crystal structure of the whole photoelectrode.

Interfacial behavior of polar and nonpolar frozen/unfrozen liquids interacting with hydrophilic and hydrophobic nanosilicas alone and in blends.

HYPOTHESIS: Various nanosilica characteristics depend on hydrophobization strongly affecting interfacial phenomena. Is it possible to prepare hydrophilic samples with hydrophobic silica (AM1) alone and in blends with hydrophilic one (A-300)? It can be done with addition of a small amount of water to the powders which then are mechanically treated. EXPERIMENTS: Nanosilicas were characterized using adsorption, desorption, microscopic, spectroscopic, and quantum chemistry methods. 1H NMR spectroscopy and cryoporometry were applied to AM1 and AM1/A-300 blends wetted and mechanically treated. Wetted blends were studied with additions of n-decane and chloroform-d. FINDINGS: The powders wetted at h = 0.3-3.0 g of water per gram of dry solids have increased bulk density. Samples are in gel-like state at h = 4-5 g/g. Water interaction energy with nanoparticles nonmonotonically depends on h (maximal at h = 3 g/g). Upon mechanical treatment of wetted blends (h < 1.5 g/g), separated AM1 structures are absent. At greater h values, blend reorganization occurs to form AM1 aggregates covered by A-300 shells. Organics can displace water from mesovoids toward narrower pores inaccessible for larger molecules or into larger voids to reduce the contact area between immiscible liquids. Freezing point depression caused by confined space and dissolution effects is affected by the blend organization.

Interfacial behavior of n-decane bound to weakly hydrated silica gel and nanosilica over a broad temperature range.

The interfacial and temperature behavior of n-decane bound to weakly hydrated nanosilica A-400 (initial, heated, or compacted) or silica gel Si-60 was studied using low-temperature (1)H NMR spectroscopy applied to static samples that allowed us to observe signals only of mobile decane and unfrozen water molecules. For deeper insight into the phenomena studied, interactions of n-decane, 1-decanol, and water with a set of nanosilicas and silica gels were analyzed using DSC and thermoporometry. Both NMR and DSC results demonstrated that during heating of frozen samples at a heating rate of 5 K/min a portion of decane or decanol remained frozen at temperature higher than the freezing point of bulk liquid (Tf). For decane and decanol adsorbed onto silica gels Si-40, Si-60, and Si-100, the number, position, and intensity of freezing and melting peaks observed in the DSC thermograms over the 170-300 K range during cooling and heating of samples depended on the pore size distribution of silicas as well as on the amounts and type of adsorbates. The position of the main freezing peak of decane for all samples was close to Tf because the alkane amount was greater than the pore volume; i.e., a fraction of decane was bulk liquid. According to (1)H NMR data, a portion of decane, which was in a quasi-crystalline solid state characterized by fast molecular exchange (i.e., short transverse relaxation time) and not observed in the spectra, was greater than a portion of decane frozen at temperatures close to Tf during cooling that appears in the DSC endotherms of heated samples.

Textural characteristics of model and natural bone tissues and interfacial behavior of bound water.

Water, as a probe liquid bound in model systems (highly disperse hydroxyapatite - protein composites as a model of the main components of bones) and rat bone tissues healthy and affected by osteoporosis occurred due to experimental Alzheimer's disease (EAD), has been investigated using low-temperature (1)H NMR spectroscopy, NMR cryoporometry, TG/DTG/DTA, DSC, and TG and DSC thermoporometry. The textural characteristics of these intact systems cannot be studied using the standard adsorption methods, but the cryoporometry and thermoporometry methods give these characteristics. The (1)H NMR spectra of water bound in model and natural bone tissues include signals, which can be assigned to strongly associated (typical) water (SAW, chemical shift of proton resonance δ(H)=5-6 ppm) and weakly associated (atypical) water (WAW) at δ(H)=1-2 ppm. Contributions of SAW and WAW give information on textural organization of both model and natural bones. The influence of such co-adsorbates as HCl, CDCl(3), CD(3)CN, C(6)D(6), and (CD(3))(2)SO on the interfacial behavior and clustering of bound water depends on their polarity, amounts of components, and textural and structural features of the materials analyzed with the (1)H NMR spectroscopy and cryoporometry methods. According to the NMR cryoporometry data, the EAD causes an increase in nanoporosity of the bone tissues. The total porosity and the specific surface area of biostructures (accessible for water molecules and estimated using NMR cryoporometry and TG thermoporometry methods with a model of cylindrical pores) are larger for the EAD sample. Weakly polar chloroform-d has a significant influence on the organization of water in the bone tissue, and this effect is greater for the EAD sample as more porous material.

Behaviour of water bound in bone marrow cells affected by organic solvents of different polarity.

The behaviour of intracellular water affected by organic solvents of different polarity in partially dehydrated marrow cells obtained from tubular bones of broiler chickens was studied using (1)H NMR spectroscopy at 210-290K. The (1)H NMR spectra of intracellular water include two signals which can be assigned to strongly (SAW, chemical shift of the proton resonance delta(H)=4-5ppm) and weakly (WAW, delta(H)=1.2-1.7ppm) associated waters which can be also divided into weakly (WBW, frozen at 250-0.8kJ/mol) and strongly (SBW, unfrozen at T<250K, DeltaG<-0.8kJ/mol) bound intracellular waters. Solvents of different polarity such as dimethylsulfoxide-d(6) (Me(2)SO-d(6)), acetonitrile-d(3), and chloroform-d differently affect structure, Gibbs free energy, and molecular mobility of intracellular water. A maximal fraction of SBW in WAW and a minimal fraction of SBW in SAW are observed on absorption of acetonitrile (0.8g/g) by cells. The opposite results are on addition of Me(2)SO (0.8g/g) which strongly changes organisation of intracellular water and enhances the freezing point depression of SBW.