Dr. Valdés-Morales, Héctor

2025, Bharathkumar, S, Mohan, Sakar, Dr. Valdés-Morales, Héctor, Balakumar, S

This study reports the synthesis of erbium (Er)-doped bismuth ferrite (BiFeO3/BFO) nanoparticles at varying molar concentrations (5, 10, and 15 %) using a sol-gel method. X-ray diffraction (XRD) analysis reveals a structural transformation from rhombohedral to orthorhombic upon Er3+ doping, confirming the successful incorporation of Er3+ ions into the BFO lattice. High-resolution transmission electron microscopy (HRTEM) images show that Er-doping leads to a reduction in particle size and a modification of the surface morphology. The bandgap of the Er-doped BFO samples decreases from 2.34 to 2.15 eV with increasing Er content, attributed to the formation of new Er 4f energy levels within the band structure. The magnetic properties of the samples also improve with increasing Er concentration. Photoluminescence (PL) spectra show reduced PL intensity for the 10 % Er-doped BFO sample, indicating a decrease in recombination rates, while electrochemical impedance spectroscopy (EIS) reveals a reduction in charge transfer resistance. Among the samples, the 10 % Er-doped BFO photocatalyst exhibits the highest photocatalytic efficiency. This enhanced activity is attributed to two key factors: efficient separation and migration of photogenerated charge carriers, and a reduced recombination rate of electron-hole pairs, both driven by the rare-earth doping in BFO. Radical trapping experiments further identify hydroxyl (OH•) radicals as the primary species responsible for photocatalytic degradation. This study provides valuable insights into the tunability of BFO's bandgap energy and photocatalytic properties through Er doping.

2024, Bharathkumar, S., Mohan, Sakar, Alsaeedi, Hoda, Hwan Oh, Tae, Vignesh, Shanmugam, Sundaramoorthy, Arunmetha, Dr. Valdés-Morales, Héctor

In this study, we demonstrated the design and fabrication of iron oxide-embedded protonated graphitic carbon nitride (α-Fe2O3/p-g-C3N4) nanocomposites for photocatalytic dye degradation and heavy metal reduction applications under sunlight irradiation. The developed nanocomposites, with varying weight percentages of α-Fe2O3, were characterized for their structural (XRD, FTIR, XPS), optical (absorption and photoluminescence), morphological (FE-SEM, TEM), and electrochemical (EIS) properties to elucidate their structure-property relationships. The synthesis method ensures the uniform dispersion of α-Fe2O3 nanoparticles, with a particle size range of 50–60 nm, onto p-g-C3N4. XPS analysis suggests the formation of an electrical layer at the interface of α-Fe2O3/p-g-C3N4, facilitating the formation of a Z-scheme heterojunction. The photoluminescence and EIS spectra of the nanocomposite indicated effective separation and transfer of photo-induced charge carriers, aided by a reduced bandgap energy of ∼2.63 eV. Notably, the optimized 10 wt% α-Fe2O3/p-g-C3N4 nanocomposite exhibited superior photocatalytic activity, degrading nearly 100 % of crystal violate dye and reducing 98 % of Cr(VI) ions, compared to bare p-g-C3N4, which degraded around 43 % of the dye and reduced 39 % of Cr(VI) ions under sunlight irradiation. Scavenger studies indicated that α-Fe2O3/p-g-C3N4 nanocomposites produce adequate superoxide anions and hydroxyl radicals for dye degradation and heavy metal ion reduction. The composite also demonstrated consistent recyclability up to 5 cycles with around 100 % cyclical efficiency. The pH-dependent photoreduction and cyclic dye degradation by the 10 wt% α-Fe2O3/p-g-C3N4 photocatalyst indicated excellent stability, making it suitable for the treatment of multi-pollutant wastewater.

2020, Dr. Valdés-Morales, Héctor, 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).

2019, Drozd, Valeriya S., Zybina, Nadezhda A., Abramova, Kristina E., Parfenov, Mikhail Yu, Kumar, Umesh, Dr. Valdés-Morales, Héctor, Smirniotis, Panagiotis G., Vorontsov, Alexander V.

Anatase nanoparticles containing surface oxygen vacancies (VO) and Ti3+ are of great importance for applications in photocatalysis, batteries, catalysis, sensors among other uses. The properties of VO and their dependence on the size of nanoparticles are of great research interest and could allow obtaining advanced functional materials. In this work, a complete set of oxygen vacancies in an anatase nanoparticle of size 1.1 nm was investigated and compared to those of a twice larger nanoparticle, having the same shape and surface hydroxylation pattern. It turned out that the decrease in the size of the anatase nanoparticle strongly facilitated creation of surface oxygen vacancies and Ti3+. After their creation, oxygen vacancies undergo three transformation paths — (1) small repulsion of surrounding Ti cations with retention of the vacancy, (2) transfer of oxygen anion, leading to the movement of oxygen vacancy to a more stable position, and (3) collapse of oxygen vacancy accompanied by structure deformation towards Magneli-like phase.

2024, Dr. Valdés-Morales, Héctor, Rameshbabu, R., Siaw Paw, Johnny Koh, Kaviyarasan, Kulandaivelu, Jadoun, Sapana, Amalraj, John, Kiong, Tiong Sieh

For renewable energy, it is crucial to create effective photocatalysts with enhanced photo charge separation and transfer to produce photocatalytic hydrogen (H2) efficiently utilizing light energy. Due to their distinct qualities and features, carbonaceous materials have so far been shown to be high-performance co-catalysts to substitute some conventionally costly metal materials in photocatalytic water splitting. Here, a novel ternary nanocomposite, simple hydrothermal process ball milling assisted and wet impregnation approach, a promising ternary nanocomposite is created as an efficient solar light driven photocatalyst. Utilizing a variety of analytical techniques, 3 % Cu3P/ZnS/g-C3N4 nanocomposites as catalysts were characterized in order to check the hydrogen production and investigate their structural properties. The hydrogen production capability of the catalyst is studied by irradiating Na2SO3 + Na2S solutes using a halogen bulb (250 W). The results demonstrated that in terms of photocatalytic activity towards H2 production, 3 % Cu3P/ZnS/g-C3N4 catalyst performed better than 3 % Cu3P/ZnS, Cu3P, ZnS, and g-C3N4. A composite containing 7.5 wt% g-C3N4 demonstrated exceptional durability during photocatalytic hydrogen production, resulting in a 23,086 mol h− 1 g− 1 rate. Higher stability in electron-hole pairs created a higher absorption level of solar light could be responsible for this remarkable performance.

2021, Dr. Valdés-Morales, Héctor, Nalandhiran, Pugazhenthiran, Rajangam, R., Krishna, S., Mangalaraja, R., Ravikumar, A., Sathishkumar, P.

Low frequency (40 kHz) ultrasound-assisted technique was utilized in the synthesis of CoFe2O4, GaOOH and α-Ga2O3 nanorods. CoFe2O4 was tethered successfully at the crystal matrices of GaOOH and α-Ga2O3 nanorods to form heterojunction nanocatalysts (CoFe2O4/GaOOH; CoFe2O4/Ga2O3). The heterojunction nanocatalysts were characterized using various analytical tools to confirm the expected modifications. The band gap of GaOOH (Eg = 4.50 eV) and α-Ga2O3 (Eg = 4.46 eV) are reduced in the formed heterojunction nanocatalysts CoFe2O4/GaOOH (Eg =2.56 eV) and CoFe2O4/Ga2O3 (Eg = 2.51 eV), respectively. Moreover, the XRD and HR-TEM analyses demonstrate the formation of heterojunction nanocatalysts composed of the lattice diffusion of Co and Fe of CoFe2O4 into the matrix of α-Ga2O3 nanorods with good crystallinity. The photocatalytic efficiency was assessed during solar light-driven photocatalyic oxidation of norflurazon in single treatments and also assisted by peroxymonosulfate addition. The experimental results indicate that ~ 98% of the norflurazon (NRF) is oxidized within 40 min of solar light irradiation in the presence of CoFe2O4/α-Ga2O3 heterojunction nanophotocatalyst, having higher photocatalytic efficiency than benchmarked TiO2 nanoparticles (Degussa P25). Moreover, the results also show that the addition of peroxymonosulfate (PMS) boosts the photocatalytic oxidation and achieving 99% NRF oxidation within 10 min of solar light irradiation by the generation of SO4 •− and • OH radicals. The novel synthesized heterojunction nanophotocatalyst (CoFe2O4/α-Ga2O3) results to be highly stable after six consecutive operating cycles.

2020, Dr. Valdés-Morales, Héctor, Vorontsov, Alexander, Smirniotis, Panagiotis, Paz, Yaron

Background: Understanding the structures and properties of photocatalysts requires the developing of computational quantum models. The present study is devoted to calculating structures, bands positions and location of the HOMO/LUMO orbitals in anatase titanium dioxide (TiO2) nanoparticles comprising of exposed (001) and (100) surfaces of various sizes having different extent of hydroxylation at their edges. The (001) surface was left intact or was reconstructed by introducing an additional row of atoms every four unit cells. Two computational approaches were compared: self‐consistent charge density‐functional tight‐binding (SCC‐DFTB) and PM6. Results: The SCC‐DFTB method was found to be, for most cases, superior to the PM6 method in terms of structure, band positions and electronic orbitals. Based on the SCC‐DFTB approach it was concluded that the presence of the (1 × 4) reconstruction was essential for keeping the (001) surface flat. Otherwise the surface undergoes anisotropic shrinking and bending, which contradicts experimental data. The band gap of the de‐hydroxylated or partially hydroxylated nanoparticles was always smaller than that of nanoparticles with hydroxylated edges. No clear quantum size effects were found for these nanoparticles. Photogenerated non‐thermalized holes were found to localize around (001) facets and at their edges, while electrons tended to concentrate over the central parts of the (100) facets. Conclusion: Efficient separation of charge carriers is predicted for anatase nanoparticles having (001) and (100) external surfaces. This conclusion, and moreover, the approach of using SCC‐DFTB calculations to study faceting effects, is likely to be relevant to the developing of new, highly active, photocatalysts as well as for fundamental studies of adsorption.

2024, Dr. Valdés-Morales, Héctor, Sivakumar, Bharathkumar, Vijayarangan, R., Mohan, Sakar, Ilangovan, R., Amin, Mohammed, Vyas, Shweta, El-Bahy, Zeinhom

This study sheds light on how the properties of titanium dioxide (TiO2) are influenced when it is modified with iron (Fe), leading to the formation of Fe-doped-TiO2, Fe2O3-TiO2 composite, and single-phase FeTiO3 systems. The structural formation of the materials, oxidation state, and chemical environments of the elements are analyzed using XRD and XPS techniques. Band structures with UV–visible light driven properties and suitable redox potentials with improved recombination resistance along with an active inter- and intra-charge transfers were observed for Fe2O3-TiO2 and FeTiO3 systems. The photocatalytic efficiency was found to be superior for FeTiO3 system, degrading ~97 and 100 % of phenol, malachite green and rhodamine B dyes in 150 min, respectively along with enhanced recyclability. Interestingly, a competitive S- and Z-scheme was predicted for Fe2O3-TiO2 composite, explaining its photocatalytic mechanism. The scavenger and total organic carbon analyses revealed the radicals driving the photocatalytic reactions and the nature of degradation products, respectively.

2021, Dr. Valdés-Morales, Héctor, Otilia Diaz, N., Rodríguez, C., Durán-Álvarez, Juan, Talreja, Neetu, Quispe-Fuentes, Issis, Martínez-Avelar, Carolina, Bizarro, Monserrat, Mera, Adriana

This study describes theoretical and experimental considerations to optimize the photocatalytic degradation of caffeic acid in water using 3D-BiOBr based materials under visible light irradiation. Three BiOBr materials were synthesized through the solvothermal method using different bromide sources, namely potassium bromide (KBr) and the ionic liquid (IL) 1-butyl-3-methylimidazolium bromide. Morphological and chemical changes were observed in IL based 3D-BiOBr materials. The theoretical optimization of the experimental conditions in heterogeneous photocatalysis tests (pH and dose of catalyst) were simulated using the MODDE 12.0.1 software. A central composite design (CCD) was applied to obtain a response surface to elucidate the optimal conditions. This model predicted that the maximum photocatalytic degradation can be achieved at pH of 6.7 and a photocatalyst dose of 344 mg L−1. The optimal experimental conditions were tested using the three synthesized 3D-BiOBr materials. The results showed that the highest degradation efficiency and mineralization yield were obtained using the BiOBr microspheres synthesized with the IL at 145 °C.

2019, Vorontsov, Alexander V., Dr. Valdés-Morales, Héctor

Anatase (001)nanosheets have recently attracted great attention as very active catalysts and photocatalysts. These graphene analogs have very high surface area and unique surface properties. In the present paper, very thin two-layer anatase nanosheets are investigated computationally in the form of quantum dots of various size. Quantum size effect (QSE)was clearly observed for nanosheets with fully hydroxylated edges and size up to 14 nm and the ultimate band gap is around 3.4 eV. Dehydroxylation of nanosheets obscured QSE, decreased band gap and induced visible light absorption. Therefore, contradictory trends reported in experimental studies for anatase QSE can be ascribed to different degree of hydroxylation of the TiO 2 samples surface. All anatase nanosheet quantum dots retained their flat graphene-like shape. These findings demonstrate that dehydroxylated anatase nanosheet quantum dots are prospective visible-light active photocatalysts even if their inherent band gap is considerably larger than for bulk anatase.