Dr. Valdes-Morales, Hector

2020, Dr. Valdes-Morales, Hector, Pugazhenthiran, Nalandhiran, Mangalaraja, R., Vijaya, S., Suresh, S., Kandasamy, M., Sathishkumar, P., Gracia-Pinilla, M., Murugesan, S., Anandan, S.

A facile, fluorine-free and non-toxic one-pot solvothermal technique was adopted to synthesis TiO2 nanoflowers with anatase phase having 98% highly exposed {001} facets (TiO2 {001} NFs). The morphology, grain size and crystallinity of pure TiO2 {001} NFs and reduced graphene oxide (RGO) sheets modified TiO2 {001} NFs (RGOTiO2 {001} NFs) were inspected by diffuse reflectance spectroscopy (DRS), X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM images showed the development of anatase TiO2 {001} NFs with high crystallinity and uniform shape. The influence of RGO on the performance of the TiO2 {001} NFs as a photoanode material in dye-sensitized solar cell (DSSC) was examined. High energy conversion efficiency (ɳ) was observed for the DSSC based on a photoanode made of RGO-TiO2 {001} NFs when compared to DSSCs based on photoanodes fabricated using pure TiO2 {001} NFs and commercial Degussa P25 TiO2, which exhibited η of 6.78, 4.59 and 2.71%, respectively. The improved performance of the DSSC based on a photoanode composed of RGOTiO2 {001} NFs was due to its good crystallinity, high dye intake and enhanced light-harvesting properties. Moreover, the presence of RGO greatly hindered the recombination of photogenerated electrons and increased their lifespan. This work discloses a novel efficient photoanode design for improving performance of the DSSCs.

2022, Dr. Valdes-Morales, Hector, Pugazhenthiran, Nalandhiran, Mangalaraja, Ramalinga, Sathishkumar, Panneerselvam, Murugesan, Sepperumal

In this work, crystal facets, bandgap, size and shape of reduced graphene oxide (rGO) modified anatase {001} black TiO2 nanosheets (rGO-B-TiO2 NSTs) were tailored for the photocatalytic oxidation of ethylene under high humidity content. XRD, Raman and HR-TEM analyses confirm that rGO-B-TiO2 NSTs have a 94 % of exposed {001} facets with high number of oxygen vacancies. In addition, rGO-B-TiO2 NSTs exhibit increased values of surface area and porosity compared to its pristine form. A 48 and 34 μmol g− 1 of ethylene are adsorbed at the surface of rGO-B-TiO2 NSTs in the absence and in the presence of humidity, respectively. In addition, operando DRIFTS analyses provide the insight of surface interactions between ethylene molecules and adsorption sites of rGO-B-TiO2 NSTs. The photocatalytic removal efficiencies of the synthesized materials under both UV and visible light irradiation proceed as follows: rGO-B-TiO2 NSTs > B-TiO2 NSTs > TiO2 NSTs > commercial TiO2 NPs. Further, ethylene is very quickly photocatalytic oxidized when rGO-B-TiO2 NSTs is applied under UV light irradiation, having a 72 and 92 % ethylene removal in the absence and in the presence of humidity, respectively. Moreover, a 48 and 58 % of ethylene removal takes place in the absence and presence of humidity under visible light irradiation, respectively. Results indicate that rGO-B-TiO2 NSTs boost the photocatalytic activity through their virtue of visible-light absorption properties (Bandgap = 2.61 eV) and the rapid electron-hole separation at the rGO {001} black TiO2 NSTs interfaces. Such findings are confirmed through UV-visible diffused reflectance, photoelectrochemical and photoluminescence analyses. Nanosheets made of rGO modified {001} black TiO2 could be used as an effective photocatalyst for the removal of ethylene from large volume fruit storage areas by exploiting a simple light source in the presence of high content of humidity.

2020, Dr. Valdes-Morales, Hector, Olowoyo, Joshua, Saini, Upasana, Kumar, Manoj, Singh, Hitendra, Omorogie, Martins, Babalola, Jonathan, Vorontsov, Alexander, Kumar, Umesh, Smirniotis, Panagiotis

The development of visible-light active photocatalysts is highly desirable for CO2 reduction to hydrocarbons and alcohols using sunlight. Here, we report the metal-organic frameworks (MOF) of amino-benzene dicarboxylate with titanium oxocluster center (NH2-MIL-125(Ti)) and modified with reduced graphene oxide (RGO), RGO-NH2-MIL-125(Ti), ideal for the visible-light-driven photocatalytic reduction of CO2 to hydrocarbons and methanol. The catalyst provides high quantum efficiency and selectivity for methanol. The cluster model and self-consistent charge density functional tight binding methods were used to investigate the photogenerated charge separation for NH2-MIL-125(Ti). The quantum modelling suggests that holes were accumulated in the central ring Ti8O8(OH)4, where strongly adsorbed electron donor, triethanolamine, undergoes photooxidation while electrons were located in the organic ligand of MOF including the NH2 group. The binding affinity of NH2 reaction sites to CO2 possibly work to improve the photocatalytic reduction of CO2 to methanol. The RGO also play an important role for charge separation and better photocatalytic reduction with RGO-NH2-MIL-125(Ti).