Structure and Properties of Water on the Anatase TiO₂(101) Surface: From Single-Molecule Adsorption to Interface Formation

The interaction of water with titanium dioxide surfaces has a vital role in many energy- and environment-related applications, such as dye-sensitized solar cell, photocatalytic or photoelectrochemical hydrogen production, and environmental purification. Structure and properties of water on the anatase TiO₂(101) surface have been studied by using a combination of density functional theory and force field molecular dynamics. Owing to the amphotericity of this surface and the competition between water–water and water–substrate interactions, the structure and properties of water on the anatase TiO₂(101) surface exhibited some peculiar and complicated features. The overall evolutionary process of interface formation has been obtained by investigating the coverage-dependent adsorption configuration and energy of water. The competition between water–water and water–substrate interaction results in the existence of a stable bilayer of water (Θ ≥ 2 ML) and an ice-like structure of water at higher coverage (Θ ≥ 3 ML). Both static and dynamic calculation results have showed that a highly ordered structure occurs in the first few water molecule layers, and this order decreases as one moves toward the bulk region. The electric fields across the interface and in the electric double layer were estimated to be about 10 and 2 eV, respectively. This study may provide new insight into the static and dynamic properties of the water–TiO₂ interface and elucidate the reactions that occur on the TiO₂ surface

Back Electron Transfer at TiO₂ Nanotube Photoanodes in the Presence of a H₂O₂ Hole Scavenger

Adding charge scavengers, which usually are more unstable than water, is an effective method to quantify the quantum efficiency loss of photoelectrode during the charge separation, transfer, and injection processes of the water splitting reaction. Here, we detected, on TiO₂ nanotube photoanodes after using hydrogen peroxide (H₂O₂) as a hole scavenger, a nearly 40% saturated photocurrent decrease in alkaline electrolyte and a negligible saturated photocurrent difference in acid electrolyte. We found that the photoelectrons were trapped in the surface states of TiO₂ with nearly the same storage capacity of electrons in a wide range of pH values from 1.0 to 13.6. However, kinetics of a back reaction, H₂O₂ reduction by the photoelectrons trapped in surface states, is about 10 times higher for that in alkaline electrolyte than in acid electrolyte. As a result, the pH-dependent kinetic difference in H₂O₂ reduction induced the negative effects on the saturated photocurrent. Our results offer a new insight into understanding the effects of back electron transfer on electrochemical behaviors of surface states and charge scavengers

Theoretical Insight into Charge-Recombination Center in Ta₃N₅ Photocatalyst: Interstitial Hydrogen

Ideal Ta₃N₅ is a promising candidate photocatalyst for solar water splitting. In a common synthetic route, both oxygen and hydrogen impurities are inevitably formed during the nitridation of TaO_<i>x</i> precursor by ammonia. The introduced hydrogen impurities would bond with oxygen in the form of hydroxyl groups, resulting in additional bands bracketing band edges. This configuration adds Ta₃N₅ electron–hole recombination centers, leading to a high onset potential. Hydrogen impurities would also introduce hydrogen bonds which aggravate charge recombination by additional charge transport paths from anions to hydroxyl recombination centers. In addition, hydride ions of hydroxyl groups may be activated into protons at high bias and may relay hole transport in Ta₃N₅, endowing the material with high saturated photocurrent. In summary, hydrogen impurities would aggravate the onset potential of Ta₃N₅ in the way of high electron–hole recombination. More broadly, hydrogen impurities may be common in (oxy)­nitrides and other covalent materials; they may add to the photocatalysts’ high onset potential via electron localizations and might introduce high charge recombination for covalent semiconductors

Oxygen-Impurity-Induced Direct–Indirect Band Gap in Perovskite SrTaO₂N

Oxynitride semiconductors are considered to be promising candidates for solar water splitting. In this work, we show that oxygen-rich SrTaO₂N has a band gap with direct–indirect character through twin valence-band maximums (VBMs), resulting in good photoelectronic responses. Compared with the direct band gap of ideal SrTaO₂N, the additional indirect VBM of the oxygen-rich solid solution was found to be due to strontium–oxygen hybridization, using orbital projections based on hybrid/GW density functional theory (DFT). This twin-VBM character was validated by strontium K-edge absorption through extended X-ray absorption fine structure (EXAFS) analysis. The twin-VBM character of the band structure can enhance the photoelectronic response and hole transport. Our findings provide a viable strategy for enhancing the solar water splitting performance of oxynitrides

Study on the Ambient Temperature as an Important but Easily Neglected Factor in the Process of Preparing Photovoltaic All-Inorganic CsPbIBr₂ Perovskite Film by the Elegant Solvent-Controlled Growth Strategy

All-inorganic CsPbIBr2 perovskite has received extensive attention in the field of solar cells due to its good wet and thermal stability as well as a moderate band gap. In the preparation of CsPbIBr2 film by one-step spin-coating method, the amount of dimethyl sulfoxide solvent remaining in the precursor film has a great influence on the process of film growth. Therefore, it is necessary to ensure that an appropriate amount of solvent exists in the precursor film before annealing. Herein, we adopted the solvent-controlled growth (SCG) strategy, that is, standing by the precursor films in the nitrogen glovebox for a period of time before annealing, to make sure that excess solvent can be evaporated from the precursor film. In this work, we found that the ambient temperature is an important but easily neglected factor in the process of preparing CsPbIBr2 film by the SCG strategy. When the ambient temperature is 20 °C, SCG treatment is required to obtain a flat and dense CsPbIBr2 film. However, SCG treatment is not essential at 30 °C. The ambient temperature has an impact on the evaporation rate of the solvent in the precursor film, and thus affects the effect of the SCG strategy. This work highlights that, when preparing CsPbIBr2 film by a one-step spin-coating method, in order to obtain a high-quality CsPbIBr2 film, the influence of ambient temperature on solvent-controlled growth strategy should be considered

Formation of Hierarchical Structure Composed of (Co/Ni)Mn-LDH Nanosheets on MWCNT Backbones for Efficient Electrocatalytic Water Oxidation

Active, stable, and cost-effective electrocatalysts are attractive alternatives to the noble metal oxides that have been used in water splitting. The direct nucleation and growth of electrochemically active LDH materials on chemically modified MWCNTs exhibit considerable electrocatalytic activity toward oxygen evolution from water oxidation. CoMn-based and NiMn-based hybrids were synthesized using a facile chemical bath deposition method and the as-synthesized materials exhibited three-dimensional hierarchical configurations with tunable Co/Mn and Ni/Mn ratio. Benefiting from enhanced electrical conductivity with MWCNT backbones and LDH lamellar structure, the Co₅Mn-LDH/MWCNT and Ni₅Mn-LDH/MWCNT could generated a current density of 10 mA cm^–2 at overpotentials of ∼300 and ∼350 mV, respectively, in 1 M KOH. In addition, the materials also exhibited outstanding long-term electrocatalytic stability

Modified Solvothermal Strategy for Straightforward Synthesis of Cubic NaNbO₃ Nanowires with Enhanced Photocatalytic H₂ Evolution

To further improve the photocatalytic H₂ evolution activity, NaNbO₃ photocatalyts simultaneously possessing cubic crystal structure and 1D morphology have been successfully synthesized via a modified solvothermal strategy. During the process of synthesis employing ethylene glycol as solvent, a temperature fluctuation during the autoclaving period is proposed to regulate the grain growth without any other additives or calcinations. It is demonstrated that the structure-directing effect of the solvent is enhanced in the condition of the temperature fluctuation, contributing to the formation of 1D nanostructure. Otherwise, the irregular NaNbO₃ nanoparticles with severe aggregation resulted. Photocatalytic H₂ evolution activities of samples under ultraviolet light irradiation with 0.5 wt % of Pt cocatalyst indicate that NaNbO₃ nanowires expectedly exhibit an enhanced activity of 699 μmol h^–1 g^–1, approaching twice that of NaNbO₃ nanoparticles. The higher photocatalytic activity of NaNbO₃ nanowires is attributed to their large specific surface area, high chemical purity, and powerful reduction ability, which have been confirmed by the further characterizations and analysis based on crystal structure, valence state, elemental composition, and energy band structure. The modified solvothermal strategy provides an alternative pathway to regulate the crystal growth, which can effectively integrate the unique morphology with desired crystalline structure toward increasing photocatalytic activity

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe₂O₃ Core–Shell Nanowire Array as Photoanode

Hematite (α-Fe₂O₃) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe₂O₃ limits the performance of α-Fe₂O₃ photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe₂O₃ nanocrystal shell (ITO@α-Fe₂O₃) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe₂O₃ nanocrystal film using chemical bath deposition (CBD) method. The <i>J</i>–<i>V</i> curves and IPCE of ITO@α-Fe₂O₃ core–shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe₂O₃ on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe₂O₃ nanocrystals in the core–shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe₂O₃ and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe₂O₃ core–shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40 000 s

Additional file 1: Figure S1. of PKM2 regulates neural invasion of and predicts poor prognosis for human hilar cholangiocarcinoma

PKM2 expression in HC tissues. A, Western blotting revealed the expression pattern of KK1, PFKB, and PKM2 in HC (T) and matched adjacent noncancerous normal tissue (N) (A). B, Graphical representation of the different expressions of KK1, PFKB, and PKM2 between N and T from (A) using Image J. C, Western blotting showed higher expressions of PKM2 in tumor (“T”) than normal (“N”) in another three cases of HC. Figure S2. PFKB expression and HC patient survival. Kaplan-Meier survival curves for patients with HC according to expression of PFKB. DFS (A) and OS (B) did not differ significantly between HC patients with low or high PFKB expression. Cum, cumulative. Figure S3. Subgroup survival analysis of PKM2 expression in HC patients according to TNM category. A, patients with stage I or II HC and high PKM2 expression had a shorter median time to recurrence than did those with stage I or II HC but without PKM2 overexpression. B, patients with stage III or IV HC and high PKM2 expression had a significantly shorter median time to recurrence than did patients with stage III or IV HC but with low PKM2 expression. C, the median OS duration was significantly worse in patients with stage I or II HC and PKM2 expression than in those with stage I or II HC but with low PKM2 expression. D, the median OS duration was significantly worse in patients with stage III or IV HC and PKM2 expression than in those with stage III or IV HC but with low PKM2 expression. Cum, cumulative. Figure S4. Representative MS/MS spectrum showing the peptide of PKM2 protein. A, the intensity of repots ions of precursor peptides indicating protein expression levels. N, normal bile duct tissue. B, MS/MS spectra demonstrating identified sequences of the peptide LAPITSDPTEATAVGAVEASFK leading to identification of PKM2. Figure S5. Localization of PKM2 expression in HC cells. A and B, cytoplasmic staining for PKM2 in well/moderately differentiated cancer cells. C and D, cytoplasmic and nuclear staining (arrow) for PKM2 in poorly differentiated cancer cells. Figure S6. Xenograft models of HC. A and B, tumor cells were treated with either control shRNA or PKM2 shRNA and orthotopically implanted into nude mice as described in Materials and Methods. Tumor cells with high PKM2 expression had a higher frequency of lymph node metastasis and liver lesions than did cells with low PKM2 expression (red arrows). C, tumors with downregulated PKM2 expression had lower SDC2 expression than did those with high PKM2 expression. Figure S7. Kaplan-Meier survival curves for patients with HC according to SDC2 expression. A, patients with high SDC2-expressing tumors had a shorter median DFS duration than did patients with low SDC2-expressing tumors. B, the median OS duration in patients with high SDC2 expression did not differ significantly from that in patients with low SDC2 expression. Cum, cumulative. Figure S8. Effect of metformin treatment on tumor cell growth. A, Metformin inhibited the ability of cell proliferation of RBE cells in vitro as determined by using the CCK8 assay. B, Representative photos of HC protein staining positivity and expression pattern of IHC staining were presented. (PPTX 6948 kb

Additional file 2: Table S1. of PKM2 regulates neural invasion of and predicts poor prognosis for human hilar cholangiocarcinoma

Association between expression of PKM2, PFKB, and HK1 and clinical variables in HC patients. Table S2. Multivariate analysis of variables associated with TTP and OS in HC patients. Table S3. Multivariate analysis of variables associated with OS in HC patients. Table S4. Correlation of SDC2 expression and clinicopathological factors in HC patients. Table S5. Correlation between PKM2 protein overexpression and SDC2 protein overexpression in HC patients. (DOCX 40 kb