Observation of inherited plasmonic properties of TiN in titanium oxynitride (TiOxNy) for solar-drive photocatalytic applications

CsCl-flux synthesis of titanium oxynitride (Ti2.85O4N) for photocatalysis

The molten salt method is a key approach for preparing high-performance metal oxide photocatalysts, though its use in metal oxynitrides remains limited. In this work, we successfully synthesized titanium oxynitride (Ti2.85O4N) using the CsCl flux method and evaluated its photocatalytic properties. The impact of CsCl addition at different synthesis stages was systematically studied. The addition of CsCl significantly enhanced the crystallinity of the oxynitrides, reducing defects and improving the overall material quality. Specifically, Ti2.85O4N-Cl-Cl, which incorporated CsCl during both precursor synthesis and oxynitride synthesis, exhibited the highest visible-light photocatalytic activity. In photocatalytic tests, Ti2.85O4N-Cl-Cl demonstrated a remarkable degradation rate of 77% for methylene blue under visible light irradiation within 120 minutes, which is approximately 1.97 times higher than that of the Cs0.68Ti1.83O4 precursor. The reaction rate constant for Ti2.85O4N-Cl-Cl was determined to be 0.00899 min-1, indicating efficient electron-hole separation and utilization of visible light. Our findings open a new direction for high-performance oxynitride synthesis, highlighting the potential of the molten salt method in enhancing the photocatalytic properties of metal oxynitrides.

Optical and Plasmonic Properties of High-Electron-Density Epitaxial and Oxidative Controlled Titanium Nitride Thin Films

The present paper reports on the fabrication, detailed structural characterizations, and theoretical modeling of titanium nitride (TiN) and its isostructural oxide derivative, titanium oxynitride (TiNO) thin films that have excellent plasmonic properties and that also have the potential to overcome the limitation of noble metal and refractory metals. The TiNO films deposited at 700 °C in high vacuum conditions have the highest reflectance (R = ∼ 95%), largest negative dielectric constant (ε1 = -161), and maximal plasmonic figure of merit (FoM = -ε1/ε2) of 1.2, followed by the 600 °C samples deposited in a vacuum (R = ∼ 85%, ε1 = -145, FoM = 0.8) and 700 °C-5 mTorr sample (R = ∼ 82%, ε1 = -8, FoM = 0.3). To corroborate our experimental observations, we calculated the phonon dispersions and Raman active modes of TiNO by using the virtual crystal approximation. From the experimental and theoretical studies, a multilayer optical model has been proposed for the TiN/TiNO epitaxial thin films for obtaining individual complex dielectric functions from which many other optical parameters can be calculated. The advantages of oxide derivatives of TiN are the continuation of similar free electron density as in TiN and the acquisition of additional features such as oxygen-dependent semiconductivity with a tunable bandgap.

Ligand modulated charge transfers in Z-scheme configured Ni-MOF/g-C3N4 nanocomposites for photocatalytic remediation of dye-polluted water

The development of photocatalysts must be meticulous, especially when they are designed to degrade hazardous dyes that cause mutagenesis and carcinogenesis. In this meticulous approach, Ni-based metal-organic frameworks with different ligands, including terephthalic acid (NTP), 2-aminoterephthalic acid (NATP), and their composite with g-C3N4 (NTP/GCN, and NATP/GCN) have been synthesized using hydrothermal method. Structural analysis by XRD and ATR-IR revealed synergistic properties due to robust chemical interactions between the NATP-MOFs and GCN systems. A flower-like morphology was observed for both NTP and NATP, while their composites showed mixed-particulate structures mimicking the morphology of GCN. Optical analyses indicated visible-light driven properties with modulated recombination resistance in the system. Among the synthesized bare and composite systems, NATP/GCN exhibited the highest photocatalytic degradation efficiency for the cationic rhodamine B dye (~ 93% in 120 min), while it was relatively less efficient for the anionic Congo red dye, (~ 64% in 120 min). The insights gained from the fundamental characterizations including Mott-Schottky, scavenger, and electrochemical impedance analysis revealed that the amino-groups in NATP/GCN composite offered the band edge potentials suitable for the effective generation of energetic radical species with the improved carrier delocalization, recombination resistance, and charge transfer properties in the composite system through Z-scheme formation. Parametric investigations by varying the concentration of catalyst, dye, and pH along with recycle studies, demonstrated the excellent stability of the developed composites for sustainable photocatalytic applications.

In Situ Construction of Interface with Photothermal and Mutual Catalytic Effect for Efficient Solar-Driven Reversible Hydrogen Storage of MgH2

Hydrogen storage in MgH2 is an ideal solution for realizing the safe storage of hydrogen. High operating temperature, however, is required for hydrogen storage of MgH2 induced by high thermodynamic stability and kinetic barrier. Herein, flower-like microspheres uniformly constructed by N-doped TiO2 nanosheets coated with TiN nanoparticles are fabricated to integrate the light absorber and thermo-chemical catalysts at a nanometer scale for driving hydrogen storage of MgH2 using solar energy. N-doped TiO2 is in situ transformed into TiNxOy and Ti/TiH2 uniformly distributed inside of TiN matrix during cycling, in which TiN and Ti/TiHx pairs serve as light absorbers that exhibit strong localized surface plasmon resonance effect with full-spectrum light absorbance capability. On the other hand, it is theoretically and experimentally demonstrated that the intimate interface between TiH2 and MgH2 can not only thermodynamically and kinetically promote H2 desorption from MgH2 but also simultaneously weaken Ti─H bonds and hence in turn improve H2 desorption from the combination of weakened Ti─H and Ti─H bonds. The uniform integration of photothermal and catalytic effect leads to the direct action of localized heat generated from TiN on initiating the catalytic effect in realizing hydrogen storage of MgH2 with a capacity of 6.1 wt.% under 27 sun.