Mario J. Muñoz-Batista

Interface Effects in Sunlight-Driven Ag/g-C3N4 Composite Catalysts: Study of the Toluene Photodegradation Quantum Efficiency

Metallic silver (ranging from 1 to 10 wt %) was deposited onto a graphite-like carbon nitride photocatalyst through a microemultion method. Surface, morphological, and structural properties of the resulting materials were characterized using BET and porosity measurements, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and UV-vis and photoluminescence spectroscopy. The activity of the composite samples under sunlight-type and visible illumination was measured for toluene photodegradation and was analyzed by means of the reaction rate and the quantum efficiency parameter. To obtain the latter observable, the lamp emission properties as well as the radiation field interaction with the catalyst inside the reactor were modeled and numerically calculated. The stability of the samples under both illumination conditions was also studied. The results evidence that the composite samples containing 1-10 silver wt % outperform carbon nitride for sunlight-type and visible illumination, but the optimal use of the charge generated after light absorption is obtained for the sample with 1 wt % of silver acording to the quantum efficiency calculation. The study shows that the optimum silver-g-C3N4 contact is able to outperform TiO2 reference systems (nano-TiO2 and P25) under sunlight illumination and points out that this occurs as a direct consequence of the charge handling through the interface between catalyst components. This indicates that composite systems based on g-C3N4 can be competitive in sunlight-triggered photodegradation processes to eliminate tough polluctants such as toluene, rendering active and stable systems.

Effect of g-C3N4 loading on TiO2-based photocatalysts: UV and visible degradation of toluene

g-C3N4 was introduced into a highly active anatase TiO2-based photocatalyst using a simple yet effective impregnation method. The corresponding composite materials were obtained with a carbon nitride weight content ranging from 0.25 to 4 wt.%, and their surface, morphological and structural properties were characterized using BET and porosity measurements, X-ray diffraction, infrared, UV-vis and photoluminescence spectroscopy, and transmission electron microscopy. They were subsequently tested for toluene photoelimination under UV and sunlight-type illumination conditions. The photocatalytic performance of the materials was analysed quantitatively through calculation of the quantum yield of the reaction under all illumination conditions essayed. We observed that the addition of carbon nitride enhances the photoactivity and selectivity to CO2 of samples containing 0.5 to 1 wt.% g-C3N4. Physicochemical characterization presented evidence that the enhanced behaviour is related to the intimate contact between the two components of the photocatalyst system, which provides two new (i.e. not present in the parent system) charge carrier handling routes affecting photocatalytic properties upon UV and visible light illumination.

Ceria promotion of acetaldehyde photo-oxidation in a TiO2-based catalyst: a spectroscopic and kinetic study

A spectroscopic and kinetic study of the photo-oxidation of acetaldehyde with a CeO2–TiO2 composite catalyst is presented. Both UV and visible illumination conditions were tested. The study focuses on analysing the role of ceria in the photocatalytic behaviour by contrasting the CeO2–TiO2 behaviour with that of the appropriate TiO2 reference. To this end, we developed an intrinsic kinetic expression with explicit inclusion of the effect of photon absorption on the reaction rate as well as a reaction scheme proposed on the basis of combined Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Electron Paramagnetic Resonance (EPR) characterization. The combination of spectroscopic and kinetic tools provides quantitative evidence that the oxide–oxide contact controls the activity of the composite catalyst through the number of hole-related species able to attack the pollutant, this in turn being related to the influence of ceria defects on charge carrier fate. The abovementioned key properties controlling photoactivity are the same for UV and visible excitation, producing a highly active photocatalyst suitable for sunlight applications.

Surface CuO, Bi2O3, and CeO2 Species Supported in TiO2-Anatase: Study of Interface Effects in Toluene Photodegradation Quantum Efficiency

The enhancement of active triggered by surface deposition of Cu, Bi, and Ce containing oxidic species onto a high surface area anatase is analyzed through the calculation of the quantum efficiency for toluene photodegradation under UV and Sunlight-type illumination. To this end, series of Cu, Bi, and Ce containing oxides supported on anatase were synthesized having a growing content of the Cu, Bi, and Ce surface species and characterized with X-ray diffraction and photoelectron, UV-visible, and photoluminescence spectroscopies as well as transmission electron microscopy. Utilizing the surface concentration of Cu, Bi, and Ce species as a tool, we analyzed the influence of the system physicochemical properties affecting quantum efficiency in anatase-based materials. First, employing small surface concentrations of the Cu, Bi, and Ce species deposited onto (the unperturbed) anatase, we provided evidence that all steps of the photocatalytic event, including light absorption, charge recombination, as well as surface interaction with the pollutant and chemical output as to activity and selectivity have significance in the quantitative assessment of the enhancement of the efficiency parameter. Second, we analyzed samples rendering maximum quantum efficiency within all these series of materials. The study indicates that maximum enhancement over anatase displays a magnitude strongly dependent on the efficiency level of calculation and would thus require the use of the most accurate one, and that it occurs through a balance between optoelectronic and chemical properties of the composite materials. The (Cu, Bi, Ce) oxide-anatase interface plays a major role modulating the optoelectronic properties of the solids and thus the efficiency observable.

Phase‐Contact Engineering in Mono‐ and Bimetallic Cu‐Ni Co‐catalysts for Hydrogen Photocatalytic Materials

Understanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro-beam X-ray absorption spectroscopy study together with the computational simulation and analysis (at the X-ray cell) of the light-matter interaction occurring in powdered TiO2 -based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non-noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu-Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.