Facet Ratio Research Articles

Active facet determination of layered double hydroxide for oxygen evolution reaction

Correlation of edge area ratio and OER activity, cyanate inhibiting-probe and DFT calculation demonstrate that edge facet of LDHs is the real active facet in comparison with plane facet. Oxygen evolution reaction (OER) plays an indispensable role in developing renewable clean energy resources. One of the critical bottlenecks for the reaction is the development of highly efficient electrocatalyst to decrease the high overpotentials of four-electron transfer process of OER. Recently, layered double hydroxides (LDHs) have been widely investigated among the most promising electrocatalysts for OER due to their high intrinsic activity, excellent stability as well as low-cost. However, it remains unclear how the exposed facet of the LDHs affects their electrocatalytic activity. Here we elucidate the active edge facet of LDHs towards OER by combining the finely control of edge facet ratio coupled with molecular probe method and computational calculation. The LDHs with higher edge facet area ratio show superior activity with low onset potential as well as decreased Tafel slope. The active edge site is further proved by blocking the unsaturated edge sites with cyanate probe anion, of which the adsorption largely inhibits OER activity. Furthermore, based on density functional theory (DFT) calculation, two-dimensional map of theoretical overpotentials as a function of Gibbs free energy reveals that the edge (100) facet exhibits a much higher OER activity than basal plane (001) facet.

Morphology-dependent NO2 gas sensing for needle-like In2O3 chemiresistor nanosensors

One-dimensional In2O3 nanoneedles, i.e., nanoicicle and nanotower structures, have been prepared so that the interplay of surface facet and aspect ratio to gas-sensing behavior can be elucidated. The electrical resistance toward a model NO2 gas of 10 to 30 ppm concentration appears to depend critically on surface facet and aspect ratio of the nanoneedle sensors over a working temperature range from 50 to 200 °C. Sensing response (Rg/Ra) shows an interesting bell-shaped dependence with the aspect ratio. A maximum increase of the sensing response by nearly 4 times (i.e., Rg/Ra changes from 8.8 to 35.0) has been obtained when the aspect ratio was increased from 5.8 to 16.1 for the nanoicicle sensor against 10 ppm NO2 at 100 °C. This contrasts with the response increase of merely 1.5 times (i.e., Rg/Ra changes from 20.9 to 29.6) when the aspect ratio was varied from 4.3 to 10.5 for the nanotower counterpart.

Tuning the structure, morphological variations, optical and magnetic properties of SnO2/NiFe2O4 nanocomposites for promising applications

Abstract (SnO2)1-x (NiFe2O4)x (x = 0, 0.85, 0.7, 1) nanocomposites were synthesized by a three-step hydrothermal technique. The crystal structure and morphological variations of SnO2/NiFe2O4 nanocomposites were investigated provided the results of x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). The composite oxide materials having well-dispersed phases of nanocrystalline nature from together the pristine tin oxide with the tetragonal rutile phase and the spinel cubic structure of nickel ferrite. Growths of remarkable nanorods (diameter 13.79 and length 150.64) of high facet ratio are detected along with nano-octahedrons, nanoparticles and porous hallow nanocube of 30SnO2–70NFO nanocomposites. With the rise of the contents of NiFe2O4 the capability of SnO2/NiFe2O4 nanocomposites for absorption within the visible domain became significantly stronger and revealed a red-shift within the visible-light area that confirms by diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The nanocomposite SnO2/NiFe2O4 confirms a better magnetic response toward an external magnetic field that verifies by vibrating sample magnetometer (VSM). Eventually from optical and magnetic descriptions; well-supporting results in favor of photoinduced charge immigration and magnetic segregation were accomplished for nanocomposites.

Tuning electron transfer by crystal facet engineering of BiVO4 for boosting visible-light driven photocatalytic reduction of bromate

Removal of bromate (BrO3−) has gained increasing attention in drinking water treatment process. Photocatalysis technology is an effective strategy for bromate removal. During the photocatalytic reduction of bromate process, the photo-generated electrons are reductive species toward bromate reduction and photo-generated holes responsible for water oxidation. In this study, the monoclinic bismuth vanadate (BiVO4) single crystal was developed as a visible photocatalyst for the effective removal of bromate. The as-synthesized BiVO4 photocatalyst with optimized {010} and {110} facets ratio could achieve almost 100% removal efficiency of BrO3− driven by visible light with a first-order kinetic constant of 0.0368 min−1. As demonstrated by the electron scavenger experiment and density functional theory (DFT) calculations, the exposed facets of BiVO4 should account for the high photocatalytic reduction efficiency. Under visible light illumination, the photo-generated electron and holes were spatially transferred to {010} facets and {110} facets, respectively. The BiVO4 single crystal photocatalyst may serve as an attractive photocatalyst by virtue of its response to the visible light, spatially charge transfer and separation as well as high photocatalytic activity, which will make the removal of BrO3− in water much easier, more economical and more sustainable.

Nano-interface engineering in all-solid-state lithium metal batteries: Tailoring exposed crystal facets of epitaxially grown LiNi0.5Mn1.5O4 films

Understanding the solid electrolyte/cathode nano-interfacial kinetics is critical in designing advanced all-solid-state lithium metal batteries with improved performance and stability. However, the correlation between crystallographic features of cathodes and the solid nano-interface behaviour remains controversial due to the difficulty in eliminating the impact of other factors. Here, we systematically investigated the effect of exposed crystal facets of LiNi 0.5 Mn 1.5 O 4 on the solid nano-interface using the substrate orientation-dependent epitaxial growth of thin films as a model study. (100), (110), and (111)-oriented Pt/MgO substrates were used to make selective high-quality epitaxial LiNi 0.5 Mn 1.5 O 4 films with different {100}/{111}-exposed facet ratios. The atomic arrangement of the exposed facets was found to affect the electrochemical performance. Loosely packed {100} facets and densely packed {111} facets were beneficial for lithium ion diffusion and cycle stability, respectively. In particular, stable {111} facets effectively suppressed the dissolution and diffusion of transition metals at the solid nano-interface during charge-discharge, enabling a 99.6% retention after 100 cycles. In addition, this model study reveals that an amorphous cathode surface layer and a twin boundary inside the cathode are crystallographic origins that hinder the electrochemical performance of batteries. These findings suggest that crystallographic modifications of cathodes can be a key to improving the solid nano-interface. • Precise epitaxial growth creates different exposed crystal facets of LiNi 0.5 Mn 1.5 O 4. • Loosely packed {100} facets induces high capacity via fast lithium ion diffusion. • {111} facets blocks mutual diffusion across the nano-interface, enhancing stability. • Thin film model reveals crystallographic origins of the solid interface degradation.

Patellar Morphology and Osteoarthritis: A Cadaveric Analysis.

Previous studies have attempted to characterize patellar morphology and its relation to patellofemoral osteoarthritis but have utilized relatively small samples. We designed a large-scale cadaveric analysis to elucidate any potential relationship. Patellar morphology in 1,032 patellae was characterized using patellar facet concavity patterns initially developed by Wiberg and using the ratio of the lateral and medial facet lengths. Patellofemoral arthritis grading for specimens was previously completed based primarily on osteophytic burden. The average age at time of death was 56 ± 10 years. Wiberg's grading returned kappa values of 0.43 for intrarelator reliability and 0.27 for interrelator reliability. Using multiple regression analysis, Wiberg's type II was found to be correlated with patellofemoral arthritis (p = 0.003). Lateral to medial facet ratio measurements returned intraclass coefficients of 0.91 for intrarelator reliability and 0.85 for interrelator reliability. There was no association between lateral to medial facet ratio and osteoarthritis. Regression analysis between Wiberg's typing and lateral-to-medial ratio (L:M) resulted in a coefficient of determination of 0.14. To our knowledge, this is the largest study evaluating the relationship between patellar morphology and arthritis. Although there was a relationship between Wiberg's type II and patellofemoral arthritis, the Wiberg systems was not easily reproducible in our study and returned a correlation with arthritis different then anatomically expected. A more reproducible system of lateral to medial facet ratio was investigated but did not find an association with arthritic changes. Given these findings, we did not find a patella morphology grading system which is both reliable and valid in regard to association with patellofemoral arthritis.

Fabrication of a Z-Scheme {001}/{110} Facet Heterojunction in BiOCl to Promote Spatial Charge Separation.

The realization of high-efficiency carrier separation is of great meaning and challenge, which is crucial to boost the photocatalytic activity. Herein, we tackle this bottleneck by fabricating a {110}/{001} facet junction to effectively facilitate the separation of charge carriers. In this study, two different BiOCl nanoplates (BiOCl-H1 and BiOCl-H2) with coexposed {110} and {001} facets were synthesized under different pH conditions. The ratio of these facets could be adjusted by the pH value of the precursor. It was discovered that the photocatalytic performance of the obtained sample for pollutant removal is dependent on the facet ratio of these facets. Theoretical calculation results show the difference in the electronic structure and staggered alignment of these facets, thus endowing BiOCl with the possibility to fabricate a facet junction. Based on our logical analyses, the Z-scheme charge-transfer mechanism was accordingly put forward. Our work opens a new avenue for the construction of a Z-scheme facet heterojunction to enhance charge separation.

Multimodal human eye blink recognition method using feature level fusion for exigency detection

In this paper, a precise multimodal eye blink recognition method using feature level fusion (MmERMFLF) is proposed. A new feature: eye-eyebrow facet ratio (EEBFR) (formed by fusing eye facet ratio (EFR: ratio of diagonal length and width of eye) and eyebrow to nose facet ratio (EBNFR: distance between eyebrow landmarks and nose landmark)) for approximating the eye state is computed. Initially, an improved intellectual framework (Sagacious Information Recuperation Technique) that senses the emergency state using information retrieved from eye blinks, pulse rate as well as behavioral patterns(emotions) exhibited by an individual is presented. Further a novel multimodal method (MmERMFLF) for detection and counting of eye blinks is implemented. For training, one state-of-the-art database—ZJU is used. To additionally improve the performance, feature-level fusion schemes [simple concatenate and fusion codes (gaborization)] are enforced and equated. Receiver operating characteristics, error rate, sensitivity, specificity, and precision are used to demonstrate the performance of the proposed method qualitatively and quantitatively. Accuracy with proposed MmERMFLF is increased to 99.02% (using EEBGFR method with bagged ensemble classifier) in comparison to unimodal eye blink recognition system (97.60%). 99.80% genuine blinks are classified by MmERMFLF (when gaborization fusion is used) using simple tree classifier.

Effects of Matching Facet Pairs of TiO2 on Photoelectrochemical Water Splitting Behaviors

AbstractEngineering crystal facets have been proved as one of the most promising strategies for promoting photocatalytic performance of titanium dioxide (TiO2). The earlier research in this field focused on trying to obtain as high ratio of the high energy {001} facet as possible, while later found that the co‐existence of facets is more beneficial. However, controlling crystals to expose suitable facet pairs and facet ratios remains challenging. In this work, we not only comprehensively match possible low‐index facets such as {101}‐{001} and {010}‐{001} facet pairs, but also systematically tune their ratios. Moreover, these faceted particles can be directly grown onto the transparent conductive substrate, which can be directly used as a photoanode. So, their intrinsic behaviors can be precisely evaluated without interference from other exogenous factors such as binders, additives, or assembly skills. Various characterization techniques reveal that both the types of facet pairs and the ratios of facets play crucial roles on photocatalytic behaviors, due to the different electron affinity and dissociative adsorption ability of water molecules on a particular facet. Charge transport and surface chemistry have been thoroughly investigated to identify the underlying mechanism. This work sheds light on a material design strategy considering a suitable match of facet pairs for optimizing photocatalytic performance for a wide variety of applications.

Patellar facet ratio affects knee pain, stair climbing and stair descent after TKA without patellar resurfacing.

To determine whether knee pain or functional impairment after total knee arthroplasty (TKA) without patellar resurfacing are correlated with preoperative patellar morphology or postoperative patellar orientation. The hypotheses were that patellar shape, increased tilt and lateral displacement would be associated with pain and functional impairment. From a consecutive series of 152 knees that received a cemented postero-stabilized TKA, the Oxford Knee Score (OKS) and the Knee injury and Osteoarthritis Outcome Score (KOOS) were collected at a minimum follow-up of 12months. Uni- and multi-variable linear regression analyses were performed to determine associations between the collected clinical scores and patient demographics and patellar morphology, measured from pre- and post-operative frontal, lateral and skyline view radiographs. The OKS was 75 ± 23, whereas the KOOS pain, stair climbing, and descent were respectively 77 ± 24, 3.9 ± 1.1 and 3.8 ± 1.2. OKS was not associated with any radiographic outcomes, whereas KOOS pain was better for knees with larger medial patellar facets. The KOOS stair climbing and descent were also better for knees with larger medial patellar facets. The findings of this study partly confirm the hypotheses that pain and functional impairments after TKA without patellar resurfacing are associated with patellar shape. No association was revealed between postoperative patellar orientation and function nor pain. Quantitative consideration of patellar congruency could therefore prevent pain and improve function after TKA without patellar resurfacing. Retrospective study, Level III.

Enhanced Antibacterial Property of Facet-Engineered TiO2 Nanosheet in Presence and Absence of Ultraviolet Irradiation.

Titania (TiO2) has attracted much attention recently for reducing bacterial diseases by the generation of reactive oxygen species (ROS) under UV irradiation. However, demand for higher photocatalytic activity due to higher recombination of electron and hole remains. The aims of this study were to make titania with higher antibacterial property and show the mechanisms of the bactericidal effect. In this study, we hydrothermally synthesized TiO2 nanosheets (NS) with highly-oriented structures. Samples were divided into five groups, depending on the fluorine/titanium ratio in the raw material, namely NS1.0, NS1.2, NS1.5, NS1.8, and NS2.0. Facet ratio and nanosheet size increased with an increase of fluorine/titanium ratio. The photocatalytic activity of TiO2 nanosheet was assessed by the generation of ROS. Hydroxyl radicals and superoxides were generated efficiently by ultraviolet light irradiation on NS1.5 and NS1.0, respectively. Antibacterial activity against Streptococcus mutans was assessed in the presence and absence of UV irradiation; NS1.0 showed superior antibacterial properties compared to commercially available TiO2 nanoparticles, under both conditions, due to the oxidation of intracellular components and cell membrane. These results together suggested TiO2 nanosheet induced bacterial cell death by oxidation, and TiO2 facet engineering resulted in enhancement of both photocatalytic and antibacterial activities of TiO2.

A comprehensive approach for the instability of PbTe quantum dots and design of a combinatorial passivation strategy

Limited air stability circumvents the outstanding properties of the PbTe quantum dots (QDs) and hinders its utilization in the field of optoelectronics. In this respect, we present a detailed understanding on the instability of the PbTe QDs and develop a combinatorial passivation protocol based on engineering the QD surface during the growth phase and solid state ligand exchange process. The dual passivation approach yields thin films and solar cells with outstanding stabilities under ambient conditions. Prioritization of the effects of the synthetic conditions with a systematic approach discloses the crucial roles of the size, shape and stabilizing ligand/catalyst concentration on the stability. Our findings show that the stability diminishes beyond a critical size (3.6–3.9 nm) where the shape changes from octahedron to truncated octahedron. We discovered that the catalyst is a major source of the instability and optimization of its concentration leads to the smallest, extremely air stable PbTe QDs with a size less than 2 nm. We illustrate that the mid gap state formation (MGS), indispensable for any ligand exchange processes, can only be inhibited by using QDs whose capacity to withstand the severe conditions of the exchange process is improved by passivating in-situ. In-situ growth phase passivation not only control the shape by dictating the {111}/{200} facet ratio but also controls the ligand exchange rate, packing direction and MGS formation. The combinatorial passivation strategy yields air stable solar cells with a 100% increase in the efficiency and up to a fivefold increase in the short circuit current.

Fully blossomed WO3/BiVO4 structure obtained via active facet engineering of patterned FTO for highly efficient Water splitting

Materials with anisotropic properties have different electronic structures and photoelectrochemical (PEC) performance depending on the facet. Herein, we controlled the morphology of WO3 nanoflakes, and the ratio of the revealed WO3 facet using patterned F-doped SnO2 fabrication by means of direct printing. In the case of WO3 NF synthesized on patterned FTO (FB-WO3/BiVO4), the proportion of the (002) facet decreased and that of the (200) and (020) facets increased in comparison to the case when NF were synthesized on flat FTO (B-WO3/BiVO4). As the facet ratio changed, the band structure and efficiency changed. The photocurrent density of FB-WO3/BiVO4 was 1.50 mA/cm2, which was 34% higher than that of B-WO3/BiVO4 (1.12 mA/cm2) at 1.23 VRHE. Our results indicate that the efficiency of PEC water splitting can be increased by engineering the exposed facet according to the shape of the substrate, rather than varying the synthetic method.

Efficient facet regulation of BiVO4 and its photocatalytic motivation

This work investigates a series of BiVO4 with different (010) and (110) facets ratio. The crystal structure, morphology, and photophysical properties of BiVO4 samples were all characterized by XRD, FE-SEM, TEM, XPS, PL, UV–vis and BET techniques. Photocatalytic performances of BiVO4 samples with different (010) and (110) facets ratio were evaluated by the O2 evolution and decolorization of thymolblue under the simulated sunlight irradiation. It showed that a positive relationship exists between the photocatalytic activities (O2 evolution) and the (010) facet ratio. The plate-like msBiVO4 exhibited exceptional O2 evolution ability approximately 4 times greater than bipyramid msBiVO4 under the simulated sunlight. The photocatalytic performances of plate-like msBiVO4 mainly originates from the weak-binding effect of (010) facet for photo-generated carrier compared with (110)-dominant msBiVO4. The built-in of inner electric fields directed from (110) facet to (010) facet, further enhancing the transfers of photo-generated electron–hole pairs by the action of potential energy difference. The entirely exposed (110) facet of msBiVO4 in this study provides us with an opportunity to explore the key factor for its photocatalysis.

Effect of fuel and solvent on soot oxidation activity of ceria nanoparticles synthesized by solution combustion method

Effect of fuel (glycine and urea) and solvent (water, acetone and ethanol) on the soot oxidation activity of ceria nanoparticles synthesized by solution combustion method is carried out in the present study. X-ray diffraction (XRD) patterns displayed a fluorite structure and the Tauc’s plot obtained from UV-Diffusive Reflectance spectroscopy (UV-DRS) showed that the band gap value was around 2.9–3.1 eV for the synthesized ceria nanoparticles irrespective of the fuel and solvent used. Ceria nanoparticles synthesized using glycine and acetone resulted in lower crystallite size, higher facet ratios ([1 0 0]/[1 1 1] and [1 1 0]/[1 1 1]) and higher lattice strain than compared to other solvents and fuels and thus resulted in better soot oxidation activity (T50 = 416 °C). The present synthesis method has played a significant role in improving the reactive facet ratios, providing lower crystallite size and high lattice strain.

Patellofemoral Instability in Children: Correlation Between Patellofemoral Incongruence, Mechanism of Injury, and Cartilage Damage.

OBJECTIVE. The objective of our study was to assess correlation between patellofemoral incongruency and injury mechanism, recurrence, bilaterality, and cartilage damage in patients with patellofemoral instability (PFI). MATERIALS AND METHODS. Ninety-four knee MRI examinations (10 bilateral) of 84 patients with PFI (47 female and 37 male patients; mean age ± SD, 15.0 ± 2.5 years) who had patella dislocation and medial patellofemoral ligament reconstruction (MPFLR) and 66 examinations of age- and sex-matched control subjects were reviewed. The PFI group was subclassified on the basis of injury, recurrence, and bilaterality. Patellofemoral congruence was assessed in both groups with the following MRI measurements: lateral femoral trochlear inclination angle, femoral sulcus depth, medial-to-lateral facet ratio, distance between tibial tuberosity (TT) and trochlear groove (TG), and patellar tendon ratio. Patella cartilage damage was assessed in the PFI group using conventional MRI (International Cartilage Repair Society grade 0-4) and T2 relaxation time mapping at three locations. MRI measurements were compared between groups and subgroups (Wilcoxon rank sum test) and were correlated with cartilage damage (Spearman correlation). RESULTS. All MRI measurements were significantly different between the group with PFI and the group without PFI (p < 0.0001). The bilateral PFI group had significantly increased TT-TG distance (mean, 15.9 vs 13.1 mm, p < 0.05) and patellar tendon ratio (mean, 1.6 vs 1.4, p < 0.05) compared with the unilateral PFI group. The TT-TG distance positively correlated with T2 values of medial and lateral patella cartilage. There were no differences between other subgroups and no correlation between other MRI measurements and the severity of cartilage damage. CONCLUSION. In patients with PFI, the severity of patellofemoral incongruence was not associated with injury mechanism or cartilage damage. However, increased lateralization of the patellar tendon (TT-TG distance) and patella alta (patellar tendon ratio) correlated with injury to the contralateral knee requiring bilateral MPFLR.

Synergistic effect of {101} crystal facet and bulk/surface oxygen vacancy ratio on the photocatalytic hydrogen production of TiO2

Anatase titanium dioxide (TiO2) nanocrystals with different percentages (up to 95%) of exposed {101} facet and different concentration ratios of bulk single-electron-trapped oxygen vacancies (SETOVs) to surface oxygen vacancies (SOVs) were prepared by alcohol-thermal method with nanotube titanic acid as the precursor in combination with solid-state reduction by NaBH4. The as-prepared TiO2 nanocrystals were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and ultraviolet–visible light spectrometry. The effects of the percentage of crystal facets and the concentration ratio of bulk SETOVs/SOVs on the photocatalytic hydrogen production rate of TiO2 nanocrystals were investigated with positron annihilation lifetime spectroscopy as well as photocurrent test. Findings indicate that the percentage of the exposed {101} facets of the as-prepared TiO2 nanocrystals and their concentration ratios of bulk SETOVs/SOVs can be well tuned by properly adjusting the amount of NaBH4 and the reduction reaction time as well. Increasing percentage of the {101} facet of anatase TiO2 nanocrystals contributes to improving their photocatalytic hydrogen production activity, because the {101} facets of the anatase TiO2 nanocrystals possess enriched electrons and can act as the reduction sites to enhance the reduction reaction of H+ affording H2 in the sacrifice system of splitting water. Both the bulk SETOVs and SOVs contribute to the improvement of the light absorption while SOVs can facilitate the separation of photogenerated charges, thereby adding to the photocatalytic activity. However, the bulk SETOVs and excessive SOVs are also the combination centers of photogenerated charges, which means it is essential to maintain a suitable concentration ratio of the bulk SETOVs/SOVs so as to enhance the light absorption and achieve the best separation efficiency of photogenerated charges and achieve the best photocatalytic activity for hydrogen production. Particularly, when anatase TiO2 nanocrystal with a high percentage (95%) of exposed {101} facet is reduced by NaBH4 at a mass ratio of 2: 1 for 20 min, the resultant reduced H-TiO2 nanocrystal (denoted as H-TiO2-R20(2:1)) provides the highest photocatalytic hydrogen productive rate. Furthermore, the combination of 0.5% Pt/H-TiO2-R20(2:1) with 0.5% Pt/WO3 can split water to simultaneously produce H2 and O2, showing promising potential for splitting water affording hydrogen and oxygen.

Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO2 crystals

Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800 °C. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800 °C.

TiO2 Facets Shaped by Concentration-Dependent Surface Diffusion of Dopamine.

Facet engineering highlights the fundamental understanding of kinetic growth of facets with capping agents. Here, we provide a roadmap for modulating TiO2 facets using dopamine as a capping agent inspired by density functional theory calculations and molecular dynamics simulations. Our calculations revealed that the surface diffusion of dopamine and their facet-specific affinity direct the kinetic growth of TiO2{100} and {101} facets into a nonequilibrium crystal shape. Our TiO2 synthesis agreed well with the theoretical predictions, suggesting that the concentration-dependent diffusion is central in accurately tuning a desirable ratio of mixed facets. Our findings shed new light on the diffusion-limited kinetically controlled facet growth mechanism, and this fine-tuning of mixed facets on a single crystal provides a general approach to design and fabricate facets on metal oxides.

Facet effect on the photoelectrochemical performance of a WO3/BiVO4 heterojunction photoanode

Different WO3 facets have different surface energies and electronic structures, and exhibit different water oxidation abilities and photocatalytic performance as a result. Because of the material’s limited photoresponse region, loading a narrow bandgap material on WO3 is a generally known method for improving photo-harvesting. In this paper, we have synthesized WO3 films with different crystal facet ratios. After loading BiVO4 on these WO3 films, we measured the photoelectrochemical (PEC) performance to investigate the effects of WO3 facet choice on the heterojunction film electrode’s performance. We found that a high-intensity ratio of the (002) WO3 facet in X-ray diffraction (XRD) leads to a more negative onset potential and higher photocurrents in a lower potential region. The ultraviolet photoelectron spectra show a lower work function for the 002-dominant WO3 film compared to other WO3 films, which may result in a higher quasi-fermi level for the heterojunction electrode. Based on the XRD results, the high-intensity ratio of the (002) WO3 facet preferentially exposes the (020) BiVO4 facet, which may be a reason for the better charge extraction observed at low applied potential and high faradic efficiency on PEC water splitting. Together, this results in a high hole injection efficiency for 002-dominant WO3/BiVO4 films compared with WO3/BiVO4 films favoring other WO3 facet ratios.