The hydrogen bond network reconstruction at the titanium/water interface was monitored by Raman spectroscopy. In addition, the adsorption properties and the surface electron properties of hydrogen bond cluster (HBC) configurations were analyzed using adsorption energy, work function, Mulliken charge population, and density of states (DOS) by the first-principles method based on density functional theory (DFT). Our results show that the hydrogen bond network of the aqueous solution is reconstructed under the interaction with the anatase TiO2(101) surface with the transformation of the chain and free hydrogen bonds to complex hydrogen bonds. The adsorption energy of a single water molecule and HBC on the anatase TiO2(101) surface are the lowest with the 1-DD-h (−0.851 eV) and 3-D-h-DDA (−1.048 eV) configurations, respectively. Over the long term, artificially regulating the structure of the HBC might be an effective and general way to slow down the metal anodic reaction without surface modification. Furthermore, the surface charge concentrates on the bridging oxygen atom, which will be the active site of the interface reaction. It is helpful to clarify the anodic corrosion reaction mechanism of the titanium spontaneous oxide film/water interface.

Poor selectivity is a common problem faced by gas sensors. In particular, the contribution of each gas cannot be reasonably distributed when a binary mixture gas is co-adsorbed. In this paper, taking CO2 and N2 as an example, density functional theory is used to reveal the mechanism of selective adsorption of a transition metal (Fe, Co, Ni, and Cu)-decorated InN monolayer. The results show that Ni decoration can improve the conductivity of the InN monolayer while at the same time demonstrating an unexpected affinity for binding N2 instead of CO2. Compared with the pristine InN monolayer, the adsorption energies of N2 and CO2 on the Ni-decorated InN are dramatically increased from −0.1 to −1.93 eV and from −0.2 to −0.66 eV, respectively. Interestingly, for the first time, the density of states demonstrates that the Ni-decorated InN monolayer achieves a single electrical response to N2, eliminating the interference of CO2. Furthermore, the d-band center theory explains the advantage of Ni decorated in gas adsorption over Fe, Co, and Cu atoms. We also highlight the necessity of thermodynamic calculations in evaluating practical applications. Our theoretical results provide new insights and opportunities for exploring N2-sensitive materials with high selectivity.

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Ion adsorption and hydrogen bond (HB) network reconstruction in electric double layer (EDL) have a profound impact on the interface properties. The microstructure in the bulk phase of 1.00–21.30 wt.% Na2SO3 aqueous solutions are investigated by X-ray scattering, confocal Raman spectroscopy, and classical molecular dynamics. The electronic properties of SO3 2‑ adsorption and the geometric structure of the HB network in the EDL at the titanium TiO2(101) surface are studied by density functional theory (DFT) and classical molecular dynamics. The SO3 2– strongly weakens the fully hydrogen-bonded water (FHW) and transforms it into partial hydrogen-bonded water (PHW). The HB transformation index (HBTI = PHW/FHW) shows a linear relationship with the mass fraction of Na2SO3. The TiOb-parallel adsorption configuration of SO3 2‑ enhances the ionicity of the Ob–Ti6 bond, resulting in the formation of oxygen vacancies at the titanium passive film surface. Besides, SO3 2‑ and Na+ are enriched and thermodynamic supersaturated in the inner Helmholtz layer (IHL), and the ions are diluted in the outer Helmholtz layer (OHL). The diffusion coefficient of SO3 2‑ and water molecules in EDL decreases seriously, which is easy to causes salt scaling on the surface of titanium passive film. This work provides evidence for the destruction of titanium passive film by SO3 2‑.

The apparent cathodic current on the Ti surface in acidic solution is composed of three reactions: the reductions of the oxide film, H+, and O2. However, classical electrochemical tests usually provide coupled multi-reaction currents. Furthermore, dissolved oxygen makes in situ measurements significant due to the thermodynamic instability of Ti. In this study, the effects of pre-reduction and dissolved oxygen on hydrogen evolution reaction (HER) kinetics on the Ti surface were investigated by electrochemical and composition characterizations. The HER current was quantitatively separated from the apparent cathodic current from Ti, including the reductions of the oxide film, H+, and O2 by scanning electrochemical microscopy. The HER transfer coefficient and standard rate constant for Ti spontaneously passivated in air (P-Ti) are both 0.48/4.9 × 10–12 cm/s in aerated and O2-saturated solutions, while those for Ti activated by electro-reduction (EA-Ti) are 0.25/3.6 × 10–7 cm/s and 0.25/3.1 × 10–7 cm/s, respectively. The variable HER behavior is caused by the changes in the film electronic structure and composition except for the competition reduction between O2 and H+ as indicated by Mott–Schottky and surface-enhanced Raman spectroscopy. The deviation from 0.5 in the transfer coefficient implies that the Tafel slope and HER mechanism should be analyzed with caution.

In order to exploit Co–Cu synergistic effect to develop catalyst with high activity, CoCuAl-layered double oxides was synthesized from CoCuAl-layered double hydroxides. The prepared CoCuAl-LDOs possessed high purity, uniform morphology, and a large special surface area (103.8 m2/g). CoCuAl-LDOs is an efficient catalyst for activating peroxymonosulfate (PMS) to degrade organic pollutants. Acid orange 7 (AO7, 20 mg/L) can be completely degraded within 30 min using 0.1 g/L CoCuAl-LDOs and 0.1 g/L PMS. The CoCuAl-LDOs/PMS system also exhibited good performance over a wide pH range. SO4 •– was identified as the main reactive species responsible for pollutant degradation. More importantly, the structure–property relationship was investigated by H2-TPR and XPS. It was found that the high performance of CoCuAl-LDOs is attributed to the Co–Cu synergistic effect which can accelerate the redox cycle of Co2+/Co3+. This study sheds light on the Co–Cu synergistic effect for developing catalyst with high performance toward activating PMS in environmental remediation.