TiO₂ is one of the most promising candidate materials for clean-energy generation and environmental remediation. However, the larger-than 3.1 eV bandgap of perfectly crystalline TiO₂ confines its application to the ultraviolet (UV) range. In this study, the electronic and the optical properties of undoped mixed-phase TiO₂ nanoparticles were investigated using UV and inverse photoemission, low intensity X-ray photoelectron (XP), and diffused reflectance spectroscopy methods. The facile solution-phase synthesized nanoparticles exhibited a midgap-states-induced energy gap of only ∼2.2 eV. The diffused reflectance spectrum showed sub-bandgap absorption due to the existence of a large Urbach tail at 2.2 eV. The UV photoemission spectrum evidenced the presence of midgap states. The 2.2 eV energy gap enables the nanoparticles to be photoactive in the visible energy range. The gas-phase CO₂ photoreduction test with water vapor under visible light illumination was studied in the presence of the synthesized TiO₂ nanoparticles which resulted in the production of ∼1357 ppm gr^–1_(catalyst) CO and ∼360 ppm gr^–1_(catalyst) CH₄, as compared to negligible amounts using a standard TiO₂ (P25) sample. The synthesized nanoparticles possessed a Brunauer–Emmett–Teller (BET) surface area of ∼131 m² gr^–1, corresponding to a Langmuir surface area of ∼166 m² gr^–1. The determined interplanar distances of atomic planes by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) methods were consistent. A detailed elemental analysis using XPS and inductively coupled plasma mass spectrometry (ICP-MS) demonstrated that the synthesized catalyst is indeed undoped. The catalytic activity of the undoped synthesized nanoparticles in the visible spectrum can be ascribed to the unique electronic structure due to the presence of oxygen vacancy related defects and the high surface area.

Bimetallic nanoclusters are of interest because of their utility in catalysis and sensors. The thermal characteristics of bimetallic Pt-Pd nanoclusters of different sizes and compositions were investigated through molecular dynamics simulations using quantum Sutton-Chen (QSC) many-body potentials. Monte Carlo simulations employing the bond order simulation model were used to generate minimum energy configurations, which were utilized as the starting point for molecular dynamics simulations. The calculated initial configurations of the Pt-Pd system consisted of surface segregated Pd atoms and a Pt-rich core. Melting characteristics were studied by following the changes in potential energy and heat capacity as functions of temperature. Structural changes accompanying the thermal evolution were studied by the bond order parameter method. The Pt-Pd clusters exhibited a two-stage melting: surface melting of the external Pd atoms followed by homogeneous melting of the Pt core. These transitions were found to depend on the composition and size of the nanocluster. Melting temperatures of the nanoclusters were found to be much lower than those of bulk Pt and Pd. Bulk melting temperatures of Pd and Pt simulated using periodic boundary conditions compare well with experimental values, thus providing justification for the use of QSC potentials in these simulations. Deformation parameters were calculated to characterize the structural evolution resulting from diffusion of Pd and Pt atoms. The results indicate that in Pd-Pt clusters, Pd atoms prefer to remain at the surface even after melting. In addition, Pt also tends to diffuse to the surface after melting due to reduction of its surface energy with temperature. This mixing pattern is different from those reported in some of the earlier studies on melting of bimetallics.

Earth abundant perovskite oxides exhibiting the highest CO ₂ conversion rates by the RWGS-CL process at the low temperature of 500 °C.