Interfacial Charge Transfer Transitions in Colloidal TiO₂ Nanoparticles Functionalized with Salicylic acid and 5-Aminosalicylic acid: A Comparative Photoelectron Spectroscopy and DFT Study

Abstract

Interfacial charge transfer (ICT) complexes between wide-band-gap metal oxides and small colorless organic molecules have promising use in a variety of applications. The possibility to control optical properties and alignment of energy levels by a proper combination of inorganic and organic parts of ICT complexes is the main advantage of such materials. We used vacuum-ultraviolet electron imaging photoelectron spectroscopy (VUV PES) to determine the ionization potentials of isolated TiO 2 nanoparticles surface-modified with salicylic acid (SA) and 5-aminosalicylic acid (5-ASA). The VUV PES measurements indicated a shift of the photoemission onset from 7.2 eV, observed for pristine TiO 2 nanoparticles, to 6.5 and 5.9 eV for the surfacemodified ones, with SA and 5-ASA, respectively. These results are consistent with the red shift of the absorption onset observed upon surface modification of TiO 2 colloids. To obtain a detailed description of the optical properties of surface-modified TiO 2 with SA and 5-ASA, density functional theory (DFT) calculations were performed with periodic boundary conditions (PBCs) and with a finite-size TiO 2 cluster. The PBC model provides a qualitatively good description of electronic states of oxide surfaces functionalized with small organic molecules, while an excellent agreement between experimentally determined and calculated band gap values using a finite-size model was found.

Conformer-Dependent VUV Photodynamics and Chiral Asymmetries in Pure Enantiomers of Gas Phase Proline

“…These aerosols were produced by nebulization of a 1 g/L solution of Pro in He (2 bars) within an atomizer (TSI, model 3062) followed by a drying stage composed of two silica gel columns before being introduced into a new aerodynamic lens (ADL) that transmits and focuses sub-micron nanoparticles (30-300 nm with 100 % efficiency) into the ionization region. [75][76][77] As compared to the previously-used ADL for Ala, the present one offers a much higher nanoparticle throughput, mechanical stability and reproducibility, and operational duty cycle. After traversing two 2-mm skimmers, the aerosols impinged onto a hot tip made of porous tungsten and heated up via a heating cartridge so that the tip temperature was set to 415 K and 493 K, the two temperatures used for the two sets of data obtained with the TD method, in conditions referred to as TD415 and TD493.…”

Velocity map imaging VUV angle-resolved photoelectron spectroscopy of isolated silver sulfide nanoparticles

“…However, since in this nanosystem <Da, more photoelectrons should be emitted from the particles on the directly irradiated side, leading to a forward/backward asymmetry in the photoelectron angular distribution [9]. Typical backgroundcorrected electron image (Figure 2a) shows a clear asymmetry in the direction of the photon beam propagation, thus confirming that the synchrotron radiation was probing the aerosol particles [9,4,10]. The photoemission spectrum and the dependence of the asymmetry parameter  on the electron binding energy are presented in Figure 2b.…”

“…So far, several nanosystems were investigated by VUV velocity map imaging photoemission spectroscopy (VUV VMI-PES). These include NaCl particles [9], gold nanoparticles [4], methylammonium lead bromide perovskite nanocrystals [5], charge transfer complexes based on colloidal TiO2 nanoparticles [10], and chiral nanosystems produced from serine aqueous solutions [11]. In this study, we report on the electron energy and angular distributions of the photoelectrons emitted from isolated silver sulfide nanoparticles (Ag2S NP).…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Other related molecules with enediol functional moiety have been proposed, such as 2,3-dihydroxynaphthalene (or 2,3-naphthalenediol, DHN) [110][111][112][113] and ascorbic acid [114]. Salicylic acid [102,113,115,116], as well as the correlated 1-hydroxy-2-naphthoic acid [117] and 5-aminosalicylic acid [116], have shown good sensitization potential, with results comparable to catechol. Interestingly, also glucose, a safe, cheap, and available biomass-derived compound, is able to sensitize TiO 2 [103] or TiO 2 /reduced graphene oxide [118] by surface adsorption, allowing visible light activity in Cr(VI) reduction and O 2 reduction to H 2 O 2 .…”