Search

Considerable efforts have been made to develop hematite as a promising material for photoelectrochemical (PEC) water splitting. However, the fast recombination of carriers in the bulk and on the surface greatly constrains the solar-to-chemical fuel conversion efficiency. Herein, a precise method was utilized to alleviate the recombination by constructing p-n junction of CaFe2O4/α-Fe2O3 and further modifying with Co3O4. The structural information and chemical composition of the ternary compound were systematically characterized. The photocurrent density at 1.23 V vs RHE (reversible hydrogen electrode) of the photoanode increased by five times compared to the bare α-Fe2O3, and the onset potential also shifted negatively to 0.6 V vs RHE. The formation of p-n junction and surface Co3O4 modification were proven to enhance the charge separation in the bulk and on the surface, respectively. Also the Co3O4 played a bifunctional role of passivating the surface states and accelerating the water oxidation kinetics.

The rational design and construction of heterojunctions as the photoanodes are considered as the effective strategy to enhanced photoelectrochemical (PEC) water splitting performance. Herein, Bi2S3@Sn: α-Fe2O3 nanowires heterostructures were successfully constructed by the two-step hydrothermal method. The rational design of Bi2S3@Sn: α-Fe2O3 yielded photocurrent density up to 4.18 mA/cm2(1.23 VRHE), which was 5.5 times higher than the pristine α-Fe2O3. The superior PEC performance can be attributed to the efficient charge separation efficiency by the type II heterojunction, which was evidenced by the photoluminescence spectroscopy. The impedance spectra revealed the two semiconductors coexisted in the heterojunction, and it also showed the charge transfer resistance decreased significantly, which can be attributed to the enhanced charge separation efficiency within the heterojunction. This work is expected to provide the rational strategy to design and prepare efficient heterostructures to modulate the charge separation efficiency.

Mesoporous aligned hematite nanoflakes (MA-α-Fe2O3) were in situ electrochemically synthesized on the fluorine-doped tin oxide coated glass (FTO) substrate and studied for electrocatalytic reduction and sensing H2O2. Morphology and crystallinity of films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The vertical aligned MA-α-Fe2O3 mesostructured films showed (1 1 0) preferential growth, offering both the fast electron transfer path and diffusion of reactants and products. Thus the sensing performance of MA-α-Fe2O3 displayed an unprecedented sensitivity of 422.5 μA/(mM cm2), a wide linear range up to 3.145 mM and an excellent detection limit of 22 μM. Furthermore, the sensor also exhibited good anti-interference, reproducibility, stability, feasibility for real sample detection. These results indicated that MA-α-Fe2O3 could be a promising electrochemical material as nonenzymatic H2O2 sensor.

The objective of this study is to examine the potential of using polyelectrolyte complex (PEC) nanoparticles to enhance the adsorption of anionic surfactants on negatively charged surface of quartz sand grains. The hypothesis is that a cationic PEC layer formed on the negatively charged quartz surface can enhance the adsorption of anionic surfactants on quartz sand grains. Both static adsorption tests and a quartz crystal microbalance with dissipation monitoring (QCM-D) were used to test the hypothesis. We measured the rate and extent of adsorption of an anionic sulfate surfactant onto bare quartz sand grains versus sand grains pre-treated with PECs. Total organic carbon (TOC) and total nitrogen (TN) analyses were used to quantitatively measure the adsorption of surfactant and PECs. Real-time adsorption monitoring was performed on silica model surfaces by QCM-D. Consistent with our hypothesis, the results showed that the level of adsorption of the anionic sulfate surfactant on PEC treated quartz sand grains (21.5 mg/g of sand) was indeed significantly higher than that on bare untreated sand grains (negligible adsorption). Our results also confirmed a proposed four-stage adsorption mechanism for the enhanced adsorption of anionic surfactants on negatively charged quartz sand grains treated with PEC nanoparticles.

The limited conductivity in hematite has been currently considered as a critical bottleneck in improving the efficiency of solar-driven water oxidation. Here we shed light on the improvement of carrier conductivity by combing orientation control and transition metal doping. To rule out the influence of surface facets of hematite when adjusting the film orientation, the hematite photoanode films were fabricated by assembling the spherical particles with single crystalline nature. The doped hematite particles were aligned with (001) plane normal to the substrate by a magnetic field (MF) during the drop-casting process. A considerable improvement in photocurrent density was resulted from the orientation control, which is due to the increased carrier density from Sn doping and efficient charge transportation in the (001) plane observed through electrochemical impedance spectra.

Photoelectrochemical cathodic protection (PECP) provides a sustainable and attractive approach for protecting metals. However, the wide bandgap of the photoanodes leads to low utilization of solar energy that inhibits further development of PECP. Herein, the narrow bandgap of α-Fe2O3 is found with PECP capacity, and a significant increase in the open circuit potential and photocurrent density is observed after Sn doping. Under illumination, the OCP of 304 stainless steel (304SS) coupled with α-Fe2O3/0.5 mM Sn shifts to −640 mVAg/AgCl, which is 460 mV more negative than the corrosion potential of 304SS, and 100 mV negative than the OCP of α-Fe2O3. The photocurrent density improves to 37 μA/cm2, which is 3.7 times higher than the α-Fe2O3. Further electrochemical impedance investigations reveal that the enhanced PECP performance can be attributed to the increased carrier density, the negative shift of the flat band potential, and the suppressed photocarrier recombination. We believe that our study on α-Fe2O3 and doping strategy provide an insight to improve PECP effectively.

Hematite (α-Fe2O3) is one of the most promising candidates for a photoanode for photoelectrochemical water splitting. However, it has low efficiency because of poor conductivity in the bulk and sluggish oxygen evolution (OER) kinetics on the surface. In this study, a Co-doped α-Fe2O3 photoanode was prepared by the hydrothermal method. It had increased charge separation efficiency and accelerated surface reaction kinetics simultaneously. At the optimal Co content, the photocurrent density of the Co-doped α-Fe2O3 increased by 23 times to 0.54 mA/cm2 at 1.23 VRHE in 1 M NaOH electrolyte; this increase was attributed to the improvement in carrier density and charge transfer behavior. Moreover, the cathodic shift of onset potential for Co-doped α-Fe2O3 reached 290 mV owing to the accelerated OER kinetics. This work reveals the key roles of Co doping and provides a suitable photoanode for solar hydrogen technology.

For the mission-oriented systems, it is not feasible to do any preventive maintenance when the mission is executing. However, the replacement time obtained by traditional replacement policies might be planned during the mission duration. The planned number of missions derived by traditional methods may overestimate the actual value. It would fail to complete the missions or increase the risk of system failure during the mission durations. And the major accident and unimaginable economic losses might occur. Therefore, an appropriate preventive maintenance policy with mission durations should be proposed to guarantee the required reliability and maintainability of the systems. To maintain the large and complex systems, we firstly extend the periodic replacement with minimal repair for systems which are designed to perform multiple missions. Then, two maintenance triggering approaches, i.e., the replacement first and replacement last are discussed, respectively. The optimum replacement time and number of missions are presented analytically and numerically. Finally, the comparison of above replacement policies in maintaining the reconnaissance system of unmanned aerial vehicle is given based on assumed data. The suggested models in this paper can provide better guidance The suggested models in this paper can provide better guidance for maintaining the systems which should implement the periodic replacement policies with minimal repair.

Optical thermometry based on luminescent materials has garnered much attention due to its many advantages. But higher sensitivity is still expected in physiological temperature range which is of special significance in medicine and biology. For this purpose, quadrivalent manganese doped lutetium aluminum garnet, Lu 3 Al 5 O 12 : Mn 4+ , or simply LuAG: Mn 4+ , has been successfully synthesized by sol-gel method and its temperature dependent luminescence has been investigated in the present work. Compared to the common red emission phosphors Y 3 Al 5 O 12 : Mn 4+ (YAG:Mn 4+ ) with same structure, LuAG:Mn 4+ has a stronger crystal field strength and a higher thermal-quenching activation energy ( ΔE ) of 5732 cm −1 . Rapid thermal quenching of the Mn 4+ luminescence occurred above room temperature around 90 °C for our LuAG:Mn 4+ sample. Temperature dependent decay curves of Mn 4+ emission from LuAG:Mn 4+ revealed that an extraordinary high sensitivity can be achieved from luminescence lifetime measurements covering physiological temperature range with a sensitivity of 3.75% K −1 at 38 °C.

When the missions arrive, it is not feasible to shut down engineering systems for preventive maintenance policies. Otherwise, it would cause major economic losses and even unimaginable accident. Hence, it is interesting and significative to provide appropriate preventive maintenance policies with mission durations to improve the system reliability and maintainability. For the electronic systems consisting of a block or group of units whose ages are not easy observed and only failures are known, we firstly extend the block replacement policy with random arrival time of mission durations. As a required reliability is needed at the mission time and no replacement can be done during the mission durations preventively. From the points of cost and maintainability, two maintenance triggering approaches, i.e., replacement first and replacement last, are discussed in analytical ways, respectively. Furthermore, three replacement policies are compared theoretically and numerically with optimum mission durations and planned replacement time. In addition, a case illustration in maintaining the electronic systems of active phased array radar (APAR) is given when the arrival time of mission durations follows an exponential distribution and the failure time of electronic systems has a gamma distribution.

The structural properties and the 4f→5d transitions of Ce 3+ in strontium silicates (Sr 3 SiO 5 and Sr 2 SiO 4 ) were investigated using the density functional theory (DFT) with the supercell models and the wavefunction-based CASSCF/CASPT2 embedded cluster methods. The calculated 4f→5d transition energies are associated with two types of Ce 3+ sites and show good consistency with the experimental spectra available. Moreover, the crystal-field parameters and the anisotropic g -tensors as well as the signs of the product of the principal g -values ( g x g y g z ) for Ce 3+ sites were obtained based on the calculated energies and wavefunctions.

A series of Yb 3+ /Er 3+ codoped transparent oxyfluoride glass ceramics with various amounts of Yb 3+ have been successfully fabricated and characterized. Under 980 nm laser prompting, the samples produce intense red, green and blue up-conversion emissions, and the emission intensities increase with Yb 3+ concentration and heat treatment temperature. Before losing good transparency in the visible region, optimum emission intensities are obtained for the sample with 25 mol% of Yb 3+ at a heat treatment temperature of 680 °C. A possible up-conversion mechanism is proposed from the dependence of emission intensities on pumping power. The fluorescence intensity ratio between the two thermally coupled levels 2 H 11/2 versus 4 S 3/2 was measured with the laser output power of 57 mW to avoid the possible laser induced heating effect. The fluorescence intensity ratio values in the temperature range from 295 K to 723 K can be well fitted with the equation: A exp (−∆ E / k B T ), where A = 6.79 and ∆ E =876 cm −1 . The relative temperature sensitivity at 300 K was evaluated to be 1.4% K −1 . All the results suggest that the Yb 3+ /Er 3+ codoped CaF 2 glass ceramics is an efficient up-conversion material with potential in optical fiber temperature sensing.

A series of (NaMgPO4)0.98−x/3: Eu 0 . 02 3 + , Na x + phosphors were prepared by the solid-state method. XRD results confirm that the phosphors contain mixture phases of crystals. The doped effect of Na+ ions on fluorescent properties of the phosphors is discussed. The results indicate that the doping effect of Na+ ions on PL intensity (615 nm) and R (the intensity ratio of 5D0→7F2 to 5D0→7F1) is just the opposite. The former is a positive effect, while the latter is a negative effect. Meanwhile, R of all samples is larger than 1. But, the difference among the R of all samples is too small to affect the chromaticity coordinates of the samples. These measurements showed that the sample of (NaMgPO4)0.97: Eu 0 . 02 3 + , Na 0 . 03 + with the optimized molar concentration of Na+ ions (3%), could be a potential red-emitting phosphor for UV-based white LED.

Uniform hierarchical BiOI nanoflowers composed of nanoplates with rough surfaces have been synthesized by a mild and rapid room-temperature solution synthesis approach. The effects of reaction parameters on the formation of 3D flower-like nanostructure were discussed. The morphology variations of the nanostructures were achieved by simply varying the reaction parameters in the system. The photocatalytic properties of the obtained samples for photodegradation of RhB dye under visible light irradiation were investigated, indicating that the flowerlike BiOI hierarchical nanostructure exhibits much higher photocatalytic activity than the sphere-like BiOI nanostructures owing to the larger surface areas, higher light absorption, and better photo-induced charge separation.

A novel multi-metal co-doped phosphor La 0.9 Ce 0.05 Li 0.05 Mn 0.05 PO 4 was obtained by calcining its precursor La 0.9 Ce 0.05 Li 0.05 Mn 0.05 PO 4 ⋅0.92H 2 O at 750 °C in the air. The hydrate precursor was synthesized via solid-state reaction at 60 °C. The reason why the spin-forbidden ( 4 T 1 ( 4 G) → 6 A 1 ( 6 S)) transition of Mn 2+ is released in this product is because of the introduction of Li + ions. The most probable mechanism was estimated with three methods. The results show that the Iso-temperature method is a local optimal one while both Masterplots and Nonlinear model-fitting methods are global optimization methods. The value of pre-exponential factor A was obtained the reaction mechanism.

A series of single-phase Eu 3+ , Tb 3+ , Bi 3+ co-doped LaPO 4 phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb 3+ and Bi 3+ could enhance emission of Eu 3+ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb 3+ and Bi 3+ is about 2.0% and 2.0%, respectively. The co-doping Tb 3+ and Bi 3+ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu 3+ , indicating that the energy transfer occurs from Tb 3+ and Bi 3+ to Eu 3+ ions. From further investigation it can be found that co-doping Tb 3+ and Bi 3+ ions can also induce excitation energy reassignment between 5 D 0 – 7 F 1 and 5 D 0 – 7 F 2 in these phosphors, and result in more energy assignment to 5 D 0 – 7 F 2 emission in LaPO 4 :Eu 3+ , Tb 3+ , Bi 3+ . Our research results displayed that La 0.94 PO 4 :Eu 3+ 0.02 , Tb 3+ 0.02 , Bi 3+ 0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.

A series of Eu3+ doped (AMgPO4)1.00−x:Eu3+x (A=Li+, Na+, K+) phosphors were prepared by the solid-state method. XRD results confirm that the samples contain mixture phases of crystals. Cation effect of Li+, Na+, K+ on the PL properties of (AMgPO4)1.00−x:Eu3+x phosphors is discussed. The results indicated that among the three cations, Na+ not only provides the most intensity of Eu3+ emission, but also produces electric-dipole dominated transition (5D0→7F2) and results to obtain the most red color. The optimized molar concentrations of Eu3+ for the three kinds of samples are 6, 8, 10%, which (NaMgPO4)0.92:Eu3+0.08 is a potential candidate as the red-emitting phosphor for UV-based white LED.

Aluminum borate nanowires were synthesized in a molten salt method at 1100 °C in the air by using ammonium aluminum carbonate hydroxide (AACH) and H 3 BO 3 as starting materials. The as-synthesized samples were examined by XRD and SEM. The results showed that Al 18 B 4 O 33 nanowires with an orthorhombic structure were formed at 1100 °C. A self-catalytic mechanism was proposed for the growth mechanism of the nanowires on the basis of the experimental phenomena.

The hollow nanostructured hematite photoanodes were prepared by using template-assisted electrodeposition and heat-treatment process. The morphologies of the films were regulated through the synthesis parameters such as potential sweep rate, annealing temperature and Sn concentration in electrolyte, and confirmed by scanning electron microscopy and transmission electron microscopy. Sn-doping of hematite was achieved by using electrolyte containing tin salt. The photocurrent of Sn-doped hematite film reaches 0.25 mA/cm 2 in 1 M NaOH at 1.23 V vs. RHE by optimizing the synthesis parameters. It is noted that both Sn doping and hollow nanostructure can affect and improve the PEC performance of hematite film.

Cu 2 ZnSnS 4 photovoltaic semiconductor films (CZTS) were deposited by RF magnetron sputtering using a home-made Cu 2 S–ZnS–SnS 2 –S mixed powder target. The phase information of the CZTS films was studied via X-ray diffraction and Raman scattering techniques. The films prepared at substrate temperatures between 150 °C and 200 °C exhibited strong preferential orientation of grains along . Higher substrate temperature (over 200 °C) induced a flower-like structure of CZTS films without preferred orientation and the light absorption coefficients were largely enhanced. The energy band gaps of CZTS films deposited at different substrate temperatures were approximate 1.7 eV.