A symbiotic hetero-nanocomposite that stabilizes unprecedented CaCl2-type TiO2 for enhanced solar-driven hydrogen evolution reaction

In-Situ Grafting of Single-Atomic Titanium-Nitrogen Moiety onto Carbon Nanostructures for Efficient Photovoltaic Devices

Early transition metals offer promising orthogonal reactivity to catalytic processes promoted by late transition metals. Nevertheless, exploiting variable single-atomic configurations as reactive centers is hitherto not well documented owing to their oxophilic nature. Herein we report an in-situ grafting strategy that employs nitrogenated holey carbon nitrides as a scaffold and invokes the reasonably good match of temperature-dependent pyrolysis to stabilize an atomic titanium-nitrogen (Ti₁N₂OH) moiety onto the hierarchical porous carbon support (Ti₁/NC-SAC). The Ti₁/NC-SAC as the cathode in dye-sensitized solar cells assembly exhibited superior electrocatalytic activity toward the triiodine reduction reaction, comparable to the conventional Pt cathode. DFT studies theoretically identified that the intrinsic robust triiodine reduction activity is essentially governed by the unique edge-hosted Ti sites, from both aspects, near-optimal adsorption of I intermediate and electron-donating ability. This work sheds light on the rational design of Ti-based SACs and their applications in photovoltaic fields.

Structural, Magnetic, and Electronic Properties of the Cr1-xTixO2 Solid

Cr_1-xTi_xO₂ (0 ≤ x ≤ 1) solid solution was synthesized by a high-pressure and high-temperature method, whereafter systematic experimental and computational studies were conducted on the Cr_1-xTi_xO₂ system. The crystal structure of the samples where 0 ≤ x ≤ 0.4 and x = 1 was of a rutile structure (P4₂/mnm), while samples where 0.5 ≤ x ≤ 0.9 crystallized in a CaCl₂ structure (Pnnm). The structural transformation from rutile-type to CaCl₂-type structure should be due to the combined action of positive chemical pressure and physical pressure. The saturation magnetization of the Cr_1-xTi_xO₂ samples decreased linearly with the increase of x because Ti⁴⁺ is nonmagnetic. In addition, the Curie temperature of the Cr_1-xTi_xO₂ samples also decreased noticeably with the increase of x. When nonmagnetic Ti⁴⁺ randomly replaced Cr⁴⁺ and occupied its position, the net exchange coupling in Cr_1-xTi_xO₂ would decrease. When Ti⁴⁺ occupied the majority in the system, Cr⁴⁺ ions would be separated by nonmagnetic Ti⁴⁺ ions far enough for the long-range ferromagnetic order to weaken or even disappear with the increase of x, causing the Cr_1-xTi_xO₂ system to finally approach a paramagnetic state. Density functional theory calculations were performed for the Cr_1-xTi_xO₂ system, and the predicted trends of the magnetic properties agreed well with the experimental results. These calculations also showed that Cr_1-xTi_xO₂ was still half-metallic until x reached 0.6.

Understanding the Doping Chemistry of High Oxidation States in Scheelite CaWO4 by Hydrothermal Conditions

Doping chemistry has become one of the most effective means of tuning materials' properties for diverse applications. In particular for scheelite-type CaWO₄, high-oxidation-state doping is extremely important, since one may expand the scheelite family and further create prospective candidates for novel applications and/or useful spectral signatures for nuclear forensics. However, the chemistry associated with high-valence doping in scheelite-type CaWO₄ is far from understanding. In this work, a series of scheelite-based materials (Ca_1-x-y-zEu_xK_y□_z)WO₄ (□ represents the cation vacancy of the Ca²⁺ site) were synthesized by hydrothermal conditions and solid-state methods and comparatively studied. For the bulk prepared by the solid-state method, occupation of high-oxidation-state Eu³⁺ at the Ca²⁺ sites of CaWO₄ is followed by doping of the low-oxidation-state K⁺ at a nearly equivalent molar amount. The Eu³⁺ local symmetry is thus varied from the original S₄ point group symmetry to C_2v point group symmetry. Surprisingly different from the cases in bulk, for the nanoscale counterparts prepared by hydrothermal conditions, the high-oxidation-state Eu³⁺ was incorporated in CaWO₄ at two distinct sites, and its amount is higher than that of the low-oxidation-state K⁺ even though KOH was used as a mineralizer, creating a certain amount of cation vacancies. Consequently, an apparent split emission of ⁵D₀ → ⁷F₀ was first demonstrated for (Ca_1-x-y-zEu_xK_y□_z)WO₄. The doping chemistry of high oxidation states uncovered in this work not only provides an explanation for the commonly observed spectral changes in rare-earth-ion-modified scheelite structures, but also points out an advanced direction that can guide the design and synthesis of novel functional oxides by solution chemistry routes.

Novel TiO2 Nanoparticles/Polysulfone Composite Hollow Microspheres for Photocatalytic Degradation

Nanosized titanium oxide (TiO₂) material is a promising photocatalyst for the degradation of organic pollutants, whereas the difficulty of its recycling hinders its practical application. Herein, we reported the preparation of a novel titanium oxide/polysulfone (TiNPs/PSF) composite hollow microspheres by the combination of Pickering emulsification and the solvent evaporation technique and their application for the photodegradation of methyl blue (MB). P25 TiO₂ nanoparticles dispersed on the surface of PSF microspheres. The porosity, density and photoactivity of the TiNPs/PSF composite microsphere are influenced by the TiO₂ loading amount. The composite microsphere showed good methyl blue (MB) removal ability. Compared with TiO₂ P25, and PSF, a much higher MB adsorption speed was observed for TiNPs/PSF microspheres benefited from their porous structure and the electrostatic attractions between the MB+ and the negatively charged PSF materials, and showed good degradation efficiency. For TiNPs/PSF composite microsphere with density close to 1, a 100% MB removal (10 mg L^-1) within 120 min at a catalyst loading of 2.5 g L^-1 can be obtained under both stirring and static condition, due to well dispersing of TiO₂ particles on the microsphere surface and its stable suspending in water. For the non-suspended TiNPs/PSF composite microsphere with density bigger than 1, the 100% MB removal can be only obtained under stirring condition. The removal efficiency of MB for the composite microspheres retained 96.5%, even after 20 cycles. Moreover, this composite microsphere also showed high MB removal ability at acidic condition. The high catalysis efficiency, excellent reusability and good stability make this kind of TiNPs/PSF composite microsphere a promising photocatalyst for the water organic pollution treatment.