https://www.surfacesciencewestern.com/wp-content/uploads/2012/01/ass11_biesinger.pdf

Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn

A surface science perspective on TiO2 photocatalysis

http://max.materials.drexel.edu/wp-content/uploads/Halim_XPS_of_MXenes-2016.pdf

X-ray photoelectron spectroscopy of select multi-layered transition metal carbides (MXenes)

In lithium-sulfur batteries, many porous conductive carbon materials are proposed to confine soluble polysulfides, but the efficiency is generally low. Here, the authors use a Magneli phase of titanium oxide as the cathode host and electron conduit, which binds the lithium (poly)sulfides well, leading to excellent battery performance.

/pdf/surface-enhanced-redox-chemistry-of-polysulphides-on-a-2onatvbv7x.pdf

Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries.

Dye-sensitized solar cells (DSSCs) have emerged as an important cheap photovoltaic technology. Charge separation is initiated at the dye, bound at the interface of an inorganic semiconductor and a hole-transport material. Careful design of the dye can minimize loss mechanisms and improve light harvesting. Mass application of DSSCs is currently limited by manufacturing complexity and long-term stability associated with the liquid redox electrolyte used in the most-efficient cells. In this Minireview, dye design is discussed in the context of novel alternatives to the standard liquid electrolyte. Rapid progress is being made in improving the efficiencies of such solid and quasi-solid DSSCs which promises cheap, efficient, and robust photovoltaic systems.

Optimizing Dyes for Dye-Sensitized Solar Cells

The adsorption of nitrogen dioxide on gamma aluminium oxide (gamma-Al(2)O(3)) and alpha iron oxide (alpha-Fe(2)O(3)) particle surfaces under various conditions of relative humidity, presence of molecular oxygen and UV light has been investigated. X-Ray photoelectron spectroscopy (XPS) is used to monitor the different surface species that form under these environmental conditions. Adsorption of NO(2) on aluminum oxide particle surfaces results primarily in the formation of surface nitrate, NO(3)(-) with an oxidation state of +5, as indicated by a peak with binding energy of 407.3 eV in the N1s region. An additional minority species, sensitive to the presence of relative humidity and molecular oxygen, is also observed in the N1s region with lower binding energy of 405.9 eV. This peak is assigned to a surface species in the +4 oxidation state. When irradiated with UV light, other species form on the surface. These surface-bound photochemical products all have lower binding energy, between 400 and 402 eV, indicating reduced nitrogen species in the range of N oxidations states spanning +1 to -1. Co-adsorbed water decreases the amount of these reduced surface-bound products while the presence of molecular oxygen completely suppresses the formation of all reduced nitrogen species on aluminum oxide particle surfaces. For NO(2) on iron oxide particle surfaces, photoreduction is enhanced relative to gamma-Al(2)O(3) and surface bound photoreduced species are observed under all environmental conditions. Complementing the experimental data, N1s core electron binding energies (CEBEs) were calculated using DFT for a number of nitrogen-containing species in the gas phase and adsorbed on an Al(8)O(12) cluster. A range of CEBEs is calculated for various nitrogen species in different adsorption modes and oxidation states. These calculated values are discussed in light of the peaks observed in the XPS N1s region and the possible species that form following NO(2) adsorption and photoreaction on metal oxide particle surfaces under different conditions of relative humidity, presence of molecular oxygen and UV light.

XPS study of nitrogen dioxide adsorption on metal oxide particle surfaces under different environmental conditions

The adsorption, thermal, and UV reactions of ethanol over a TiO2(110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to −CH3 and −CH2O− groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (−CH3 and −CH2O−), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s p...

Photoreaction of ethanol on TiO2(110) single-crystal surface

The adsorption of sulfur dioxide (SO2) on titanium dioxide (TiO2) nanoparticle surfaces at 296 K under a wide range of conditions has been investigated. X-ray photoelectron spectroscopy is used to investigate the surface speciation and surface coverage of sulfur-containing products on ca. 4 nm TiO2 anatase particles that remain on the surface following adsorption of SO2. The effects of various environmental conditions of relative humidity, molecular oxygen, and broadband UV/vis irradiation as well as sample pretreatment were found to impact the speciation of adsorbed SO2 as well as the saturation coverage. In particular, in the absence of light, the majority surface species upon SO2 adsorption is found to be adsorbed sulfite. Broadband UV/vis irradiation during sulfur dioxide adsorption leads to an increase (nearly 2-fold) in the amount of adsorbed sulfur species, as compared to experiments with no light, and results in the formation of adsorbed sulfate. The formation of sulfate was quantitative in the pr...

Sulfur Dioxide Adsorption on TiO2 Nanoparticles: Influence of Particle Size, Coadsorbates, Sample Pretreatment, and Light on Surface Speciation and Surface Coverage

Mineral dust aerosol is indisputably an important component of the Earth’s atmosphere and provides a reactive surface for heterogeneous chemistry to occur These reactions can alter concentrations of key trace atmospheric gases as well as change the physicochemical properties of the dust particles The focus of this Perspective article is on several new mechanisms and reaction pathways identified in laboratory studies on components of mineral dust and on nanodust, a potentially new source of metal-containing dust from engineered nanomaterials These reactions include surface photochemical mechanisms for renoxification and sulfur dioxide oxidation and size-dependent redox chemistry of metal-containing dusts in low-pH environments including naturally occurring iron oxides and engineered metal nanoparticles These newly identified reactions have the potential to play an important role in atmospheric chemistry

Reactions on Atmospheric Dust Particles: Surface Photochemistry and Size-Dependent Nanoscale Redox Chemistry

The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO– and N–, are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed.

Pradeep M. Jayaweera

Papers

XPS study of nitrogen dioxide adsorption on metal oxide particle surfaces under different environmental conditions

Photoreaction of ethanol on TiO2(110) single-crystal surface

Sulfur Dioxide Adsorption on TiO2 Nanoparticles: Influence of Particle Size, Coadsorbates, Sample Pretreatment, and Light on Surface Speciation and Surface Coverage

Reactions on Atmospheric Dust Particles: Surface Photochemistry and Size-Dependent Nanoscale Redox Chemistry

Surface Photochemistry of Adsorbed Nitrate: The Role of Adsorbed Water in the Formation of Reduced Nitrogen Species on α-Fe2O3 Particle Surfaces