Search Results (22)

In this study, original titanium dioxide (TiO₂) and cerium (Ce)-doped TiO₂ nanorod array photoanodes are prepared by hydrothermal method combined with high-temperature annealing, and their morphology, photoelectrochemical properties, and photocatalytic hydrogen production ability are systematically evaluated. X-ray diffraction (XRD) analysis shows that as the Ce content increases, the diffraction peak of the rutile phase (110) shifts towards lower angles, indicating the successful doping of different contents of Ce into the TiO₂ lattice. Photoelectric performance test results show that Ce doping significantly improves the photocurrent density of TiO₂, especially for the 0.54wt% Ce-doped TiO₂ (denoted as CR5). The photocurrent density of CR5 reaches 1.98 mA/cm² at a bias voltage of 1.23 V (relative to RHE), which is 2.6 times that of undoped TiO₂ (denoted as R). Photoelectrochemical hydrolysis test results show that the hydrogen yield performance under full-spectrum testing conditions of Ce-doped TiO₂ photoanodes is better than that of original TiO₂ as well, which are 37.03 and 12.64 µmol·cm⁻²·h⁻¹ for CR5 and R, respectively. These results indicate that Ce doping can effectively promote charge separation and improve hydrogen production efficiency by reducing resistance, accelerating charge transfer, and introducing new electronic energy levels. Our findings provide a new strategy for designing efficient photocatalysts with enhanced photoelectrochemical (PEC) water-splitting performance. Full article

The efficient adsorption and removal of As(III), which is highly toxic, remains difficult. TiO₂ shows promise in this field, though the process needs improvement. Herein, how doping regulates As(OH)₃ adsorption over TiO₂ surfaces is comprehensively investigated by means of the DFT + D3 approach. Doping creates the bidentate mononuclear (Ce doping at the Ti_5c site), tridentate (N, S doping at the O_2c site), and other new adsorption structures. The extent of structural perturbation correlates with the atomic radius when doping the Ti site (Ce >> Fe, Mn, V >> B), while it correlates with the likelihood of forming more bonds when doping the O site (N > S > F). Doping the O_2c, O_3c rather than the Ti_5c site is more effective in enhancing As(OH)₃ adsorption and also causes more structural perturbation and diversity. Similar to the scenario of pristine surfaces, the bidentate binuclear complexes with two Ti-O_As bonds are often the most preferred, except for B doping at the Ti_5c site, S doping at the O_2c site, and B doping at the O_3c site of rutile (110) and Ce, B doping at the Ti_5c site, N, S doping at the O_2c site, and N, S, B doping at the O_3c site of anatase (101). Doping significantly regulates the As(OH)₃ adsorption efficacy, and the adsorption energies reach −4.17, −4.13, and −4.67 eV for Mn doping at the Ti_5c site and N doping at the O_2c and O_3c sites of rutile (110) and −1.99, −2.29, and −2.24 eV for Ce doping at the Ti_5c site and N doping at the O_2c and O_3c sites of anatase (101), respectively. As(OH)₃ adsorption and removal are crystal-dependent and become apparently more efficient for rutile vs. anatase, whether doped at the Ti_5c, O_2c, or O_3c site. The auto-oxidation of As(III) occurs when the As centers interact directly with the TiO₂ surface, and this occurs more frequently for rutile rather than anatase. The multidentate adsorption of As(OH)₃ causes electron back-donation and As(V) re-reduction to As(IV). The regulatory effects of doping during As(III) adsorption and the critical roles played by crystal control are further unraveled at the molecular level. Significant insights are provided for As(III) pollution management via the adsorption and rational design of efficient scavengers. Full article

Addressing the pressing needs for alternatives to fossil fuel-based energy sources, this research explores the intricate interplay between Rhodium (Rh₃) clusters and titanium dioxide (TiO₂) to improve photocatalytic water splitting for the generation of eco-friendly hydrogen. This research applies the density functional theory (DFT) coupled with the Hartree–Fock theory to meticulously examine the structural and electronic structures of Rh₃ clusters on TiO₂ (110) interfaces. Considering the photocatalytic capabilities of TiO₂ and its inherent limitations in harnessing visible light, the potential for metals such as Rh₃ clusters to act as co-catalysts is assessed. The results show that triangular Rh₃ clusters demonstrate remarkable stability and efficacy in charge transfer when integrated into rutile TiO₂ (110), undergoing oxidation in optimal adsorption conditions and altering the electronic structures of TiO₂. The subsequent analysis of TiO₂ surfaces exhibiting defects indicates that Rh₃ clusters elevate the energy necessary for the formation of an oxygen vacancy, thereby enhancing the stability of the metal oxide. Additionally, the combination of Rh₃-cluster adsorption and oxygen-vacancy formation generates polaronic and localized states, crucial for enhancing the photocatalytic activity of metal oxide in the visible light range. Through the DFT analysis, this study elucidates the importance of Rh₃ clusters as co-catalysts in TiO₂-based photocatalytic frameworks, paving the way for empirical testing and the fabrication of effective photocatalysts for hydrogen production. The elucidated impact on oxygen vacancy formation and electronic structures highlights the complex interplay between Rh₃ clusters and TiO₂ surfaces, providing insightful guidance for subsequent studies aimed at achieving clean and sustainable energy solutions. Full article

In response to the vital requirement for renewable energy alternatives, this research delves into the complex interactions between ruthenium (Ru₃) clusters and rutile titanium dioxide (TiO₂) (110) interfaces, with the aim of enhancing photocatalytic water splitting processes to produce environmentally friendly hydrogen. As the world shifts away from traditional fossil fuels, this study utilizes the density functional theory (DFT) and the HSE06 hybrid functional to thoroughly assess the geometric and electronic properties of Ru₃ clusters on rutile TiO₂ (110) surfaces. Given TiO₂’s renown role as a photocatalyst and its limitations in visible light absorption, this research investigates the potential of metals like Ru to serve as additional catalysts. The results indicate that the triangular Ru₃ cluster exhibits exceptional stability and charge transfer effectiveness when loaded on rutile TiO₂ (110). Under ideal adsorption scenarios, the cluster undergoes oxidation, leading to subsequent changes in the electronic configuration of TiO₂. Further exploration into TiO₂ surfaces with defects shows that Ru₃ clusters influence the creation of oxygen vacancies, resulting in a greater stabilization of TiO₂ and an increase in the energy required for creating oxygen vacancies. Moreover, the attachment of the Ru₃ cluster and the creation of oxygen vacancies lead to the emergence of polaronic and hybrid states centered on specific titanium atoms. These states are vital for enhancing the photocatalytic performance of the material within the visible light spectrum. This DFT study provides essential insights into the role of Ru₃ clusters as potential supplementary catalysts in TiO₂-based photocatalytic systems, setting the stage for practical experiments and the development of highly efficient photocatalysts for sustainable hydrogen generation. The observed effects on electronic structures and oxygen vacancy generation underscore the intricate relationship between Ru₃ clusters and TiO₂ interfaces, offering a valuable direction for future research in the pursuit of clean and sustainable energy solutions. Full article

Addressing the urgent need for sustainable energy sources, this study investigates the intricate relationship between rhodium (Rh₅) nanoclusters and TiO₂ rutile (110) surfaces, aiming to advance photocatalytic water splitting for green hydrogen production. Motivated by the imperative to transition from conventional fossil fuels, this study employs density functional theory (DFT) with DFT-D3 and HSE06 hybrid functionals to analyse the geometrical stabilities and electronic structures of Rh₅ nanoclusters on TiO₂ rutile (110). TiO₂, a prominent photocatalyst, faces challenges such as limited visible light absorption, leading researchers to explore noble metals like Rh as cocatalysts. Our results show that bipyramidal Rh₅ nanoclusters exhibit enhanced stability and charge transfer when adsorbed on TiO₂ rutile (110) compared to trapezoidal configurations. The most stable adsorption induces the oxidation of the nanocluster, altering the electronic structure of TiO₂. Extending the analysis to defective TiO₂ surfaces, this study explores the impact of Rh₅ nanoclusters on oxygen vacancy formation, revealing the stabilisation of TiO₂ and increased oxygen vacancy formation energy. This theoretical exploration contributes insights into the potential of Rh₅ nanoclusters as efficient cocatalysts for TiO₂-based photocatalytic systems, laying the foundation for experimental validations and the rational design of highly efficient photocatalysts for sustainable hydrogen production. The observed effects on electronic structures and oxygen vacancy formation emphasize the complex interactions between Rh₅ nanoclusters and the TiO₂ surface, guiding future research in the quest for clean energy alternatives. Full article

The relationship between structure and reactivity plays a dominant role in water dissociation on the various TiO₂ crystallines. To observe the adsorption and dissociation behavior of H₂O, the reaction force field (ReaxFF) is used to investigate the dynamic behavior of H₂O on rutile (110) and anatase (101) surfaces in an aqueous environment. Simulation results show that there is a direct proton transfer between the adsorbed H₂O (H₂O_ad) and the bridging oxygen (O_br) on the rutile (110) surface. Compared with that on the rutile (110) surface, an indirect proton transfer occurs on the anatase (101) surface along the H-bond network from the second layer of water. This different mechanism of water dissociation is determined by the distance between the 5-fold coordinated Ti (Ti_5c) and O_br of the rutile and anatase TiO₂ surfaces, resulting in the direct or indirect proton transfer. Additionally, the hydrogen bond (H-bond) network plays a crucial role in the adsorption and dissociation of H₂O on the TiO₂ surface. To describe interfacial water structures between TiO₂ and bulk water, the double-layer model is proposed. The first layer is the dissociated H₂O on the rutile (110) and anatase (101) surfaces. The second layer forms an ordered water structure adsorbed to the surface O_br or terminal OH group through strong hydrogen bonding (H-bonding). Affected by the H-bond network, the H₂O dissociation on the rutile (110) surface is inhibited but that on the anatase (101) surface is promoted. Full article

Griffinite (IMA 2021-110), ideally Al₂TiO₅, is a new mineral from inclusions in corundum xenocrysts from the Mount Carmel area, Israel. It occurs as subhedral crystals, ~1–4 μm in size, together with Zr-rich rutile within a corundum grain. In this study, a mean of eight electron probe microanalyses gave TiO₂ 44.41 (24), Al₂O₃ 55.13 (18), FeO 0.47 (5), and MgO 0.37 (2), totaling 100.38 wt%, which corresponded, on the basis of a total of five oxygen atoms, to (Al_1.97Mg_0.02Fe_0.01)Ti_1.01O_5. Electron back-scatter diffraction studies revealed that griffinite is orthorhombic and in the space group Cmcm, with a = 3.58 (2) Å, b = 9.44 (1) Å, c = 9.65 (1) Å, and V = 326 (2) Å3 with Z = 4. The six strongest calculated powder diffraction lines [d in Å (I/I₀) (hkl)] are 3.347 (100) (110); 2.658 (90) (023); 4.720 (77) (020); 1.903 (57) (043); 1.790 (55) (200); and 1.688 (44) (134). In the crystal structure, Al³⁺ and Ti⁴⁺ are disordered into two distinct distorted octahedra, which form edge-sharing double chains. Griffinite is a high-temperature oxide mineral, formed in melt pockets in corundum-aggregate xenoliths derived from the upper mantle beneath Mount Carmel, Israel. The new mineral is named after William L. Griffin, a geologist at Macquarie University, Australia. Full article

CO₂ is the most abundant greenhouse gas, and for this reason, it is the main target for finding solutions to climatic change. A strategy of environmental remediation is the transformation of CO₂ to an aggregated value product to generate a carbon-neutral cycle. CO₂ reduction is a great challenge because of the large C=O dissociation energy, ~179 kcal/mol. Heterogeneous photocatalysis is a strategy to address this issue, where the adsorption process is the fundamental step. The focus of this work is the role of adsorption in CO₂ reduction by means of modeling the CO₂ adsorption in rutile metallic oxides (TiO₂, GeO₂, SnO_2, IrO₂ and PbO₂) using Density Functional Theory (DFT) and periodic DFT methods. The comparison of adsorption on different metal oxides forming the same type of crystal structure allowed us to observe the influence of the metal in the adsorption process. In the same way, we performed a comparison of the adsorption capability between two different surface planes, (001) and (110). Two CO₂ configurations were observed, linear and folded: the folded conformations were observed in TiO₂, GeO₂ and SnO₂, while the linear conformations were present in IrO₂ and PbO₂. The largest adsorption efficiency was displayed by the (001) surface planes. The CO₂ linear and folded configurations were related to the interaction of the oxygen on the metallic surface with the adsorbate carbon, and the linear conformations were associated with the physisorption and folded configurations with chemisorption. TiO₂ was the material with the best performance for CO₂ interactions during the adsorption. Full article

Green synthesis of metal nanoparticles in nanosized form has acquired great interest in the area of nanomedicine as an environmentally friendly and cost-effective alternative compared to other chemical and physical methods. This study deals with the eco-friendly green synthesis of titanium dioxide nanoparticles (TiO₂ NPs) utilizing Juniperus phoenicea leaf extract and their characterization. The biosynthesis of TiO₂ NPs was completed in 3 h and confirmed by UV-Vis spectroscopy, a strong band at 205.4 nm distinctly revealed the formation of NPs. Transmissions electron microscopy (TEM) analysis showed the synthesized TiO₂ NPs are spherical in shape, with a diameter in a range of 10–30 nm. The XRD major peak at 27.1° congruent with the (110) lattice plane of tetragonal rutile TiO₂ phase. Dynamic light scattering (DLS) analysis revealed synthesized TiO₂ NPs average particle size (hydrodynamic diameter) of (74.8 ± 0.649) nm. Fourier transmission infrared (FTIR) revealed the bioactive components present in the leaf extract, which act as reducing and capping agents. The antimicrobial efficacy of synthesized TiO₂NPs against, Staphylococcus aureus, and Bacillus subtilis (Gram-positive), Escherichia coli and Klebsiella pneumoniae (Gram-negative), Yeast strain (Saccharomyces cerevisiae) and fungi (Aspergillus niger, and Penicillium digitatum) assayed by a disc diffusion method. TiO₂NPs inhibited all tested strains by mean inhibition zone (MIZ), which ranged from the lowest 15.7 ± 0.45 mm against K. pneumoniae to the highest 30.3 ± 0.25 against Aspergillus niger. The lowest minimum inhibitory concentration (MIC) and bactericidal (MBC) values were 20 μL/mL and 40 μL/mL of TiO₂NPs were observed against Asp. niger. Moreover, it showed significant inhibitory activity against human ovarian adenocarcinoma cells with IC₅₀ = 50.13 ± 1.65 µg/mL. The findings concluded that biosynthesized TiO₂ NPs using Juniperus phoenicea leaf extract can be used in medicine as curative agents according to their in vitro antibacterial, antifungal, and cytotoxic activities. Full article

In this work, brookite TiO₂ nanocrystals with co-exposed {001} and {120} facets (pH0.5-T500-TiO₂ and pH11.5-T500-TiO₂), rutile TiO₂ nanorod with exposed {110} facets and anatase TiO₂ nanocrystals with exposed {101} facets (pH3.5-T500-TiO₂) and {101}/{010} facets (pH5.5-T500-TiO₂, pH7.5-T500-TiO₂ and pH9.5-T500-TiO₂) were successfully synthesized through a one-pot solvothermal method by using titanium (V) iso-propoxide (TTIP) colloidal solution as the precursor. The crystal structure, morphology, specific surface area, surface chemical states and photoelectric properties of the pHx-T500-TiO₂ (x = 0.5, 1.5, 3.5, 5.5, 7.5, 9.5, 11.5) were characterized by powder X-ray diffraction (XRD), field scanning transmission electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), nitrogen adsorption instrument, X-ray photoelectron spectroscopy (XPS), UV-Visible diffuse reflectance spectra and electrochemical impedance spectroscopy (EIS). The photocatalytic activity performance of the pHx-T500-TiO₂ samples was also investigated. The results showed that as-prepared pH3.5-T500-TiO₂ nanocrystal with exposed {101} facets exhibited the highest photocatalytic activity (95.75%) in the process of photocatalytic degradation of methyl orange (MO), which was 1.1, 1.2, 1.2, 1.3, 1.4, 1.6, 10.7, 15.1 and 27.8 fold higher than that of pH5.5-T500-TiO₂ (89.47%), P25-TiO₂ (81.16%), pH9.5-T500-TiO₂ (79.41%), pH7.5-T500-TiO₂ (73.53%), pH0.5-T500-TiO₂ (69.10%), CM-TiO₂ (61.09%), pH11.5-T500-TiO₂ (8.99%), pH1.5-T500-TiO₂ (6.33%) and the Blank (3.44%) sample, respectively. The highest photocatalytic activity of pH3.5-T500-TiO₂ could be attributed to the synergistic effects of its anatase phase structure, the smallest particle size, the largest specific surface area and exposed {101} facets. Full article

Earth abundant transition metal oxides are low-cost promising catalysts for the oxygen evolution reaction (OER). Many transition metal oxides have shown higher OER activity than the noble metal oxides (RuO₂ and IrO₂). Many experimental and theoretical studies have been performed to understand the mechanism of OER. In this review article we have considered four earth abundant transition metal oxides, namely, titanium oxide (TiO₂), manganese oxide/hydroxide (MnO_x/MnOOH), cobalt oxide/hydroxide (CoO_x/CoOOH), and nickel oxide/hydroxide (NiO_x/NiOOH). The OER mechanism on three polymorphs of TiO₂: TiO₂ rutile (110), anatase (101), and brookite (210) are summarized. It is discussed that the surface peroxo O* intermediates formation required a smaller activation barrier compared to the dangling O* intermediates. Manganese-based oxide material CaMn₄O₅ is the active site of photosystem II where OER takes place in nature. The commonly known polymorphs of MnO₂; α-(tetragonal), β-(tetragonal), and δ-(triclinic) are discussed for their OER activity. The electrochemical activity of electrochemically synthesized induced layer δ-MnO₂ (EI-δ-MnO₂) materials is discussed in comparison to precious metal oxides (Ir/RuO_x). Hydrothermally synthesized α-MnO₂ shows higher activity than δ-MnO₂. The OER activity of different bulk oxide phases: (a) Mn₃O₄(001), (b) Mn₂O₃(110), and (c) MnO₂(110) are comparatively discussed. Different crystalline phases of CoOOH and NiOOH are discussed considering different surfaces for the catalytic activity. In some cases, the effects of doping with other metals (e.g., doping of Fe to NiOOH) are discussed. Full article

Uniform-size rutile TiO₂ microrods were synthesized by simple molten-salt method with sodium chloride as reacting medium and different kinds of sodium phosphate salts as growth control additives to control the one-dimensional (1-D) crystal growth of particles. The effect of rutile and anatase ratios as a precursor was monitored for rod growth formation. Apart from uniform rod growth study, optical properties of rutile microrods were observed by UV−visible and photoluminescence (PL) spectroscopy. TiO₂ materials with anatase and rutile phase show PL emission due to self-trapped exciton. It has been observed that synthesized rutile TiO₂ rods show various PL emission peaks in the range of 400 to 900 nm for 355 nm excitation wavelengths. All PL emission appeared due to the oxygen vacancy present inside rutile TiO₂ rods. The observed PL near the IR range (785 and 825 nm) was due to the formation of a self-trapped hole near to the surface of (110) which is the preferred orientation plane of synthesized rutile TiO₂ microrods. Full article

The adsorption of 4-mercaptobenzoic acid (4-MBA) on anatase (101) and rutile (110) TiO₂ surfaces has been studied using synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy techniques. Photoelectron spectroscopy results suggest that the 4-MBA molecule bonds to both TiO₂ surfaces through the carboxyl group, following deprotonation in a bidentate geometry. Carbon K-edge NEXAFS spectra show that the phenyl ring of the 4-MBA molecule is oriented at 70° ± 5° from the surface on both the rutile (110) and anatase (101) surfaces, although there are subtle differences in the electronic structure of the molecule following adsorption between the two surfaces. Full article

In this paper, real-time time-dependent density-functional theory (RT-TDDFT) calculations are performed to analyze the optical property and charge transitions of a single noble metal atom deposited on rutile TiO${}_2$ (110) surface. The model structures are built reflecting the equilibrium positions of deposited adatoms atop the TiO${}_2$ surface. The absorption spectra are calculated for all model structures under study. To provide deeper insight into photo-absorption processes, the transition contribution maps are computed for the states of deposited adatoms involved in transitions. Assuming the photon energy is enough to overcome the band gap of TiO${}_2$ (∼3 eV), the photogenerated electrons of TiO${}_2$ seem to be partly accumulated around deposited Au atoms. In contrast, this is rarely observed for deposited Ag and Cu atoms. Based on our calculations, we have identified the transition state mechanism that is important for the design strategy of future photocatalytic materials. Full article

The distribution of individual water molecules’ self-diffusivities in adsorbed layers at TiO₂ surfaces anatase (101) and rutile (110) have been determined at 300 K for inner and outer adsorbed layers, via classical molecular-dynamics methods. The layered-water structure has been identified and classified in layers making use of local order parameters, which proved to be an equally valid method of “self-ordering” molecules in layers. Significant distinctness was observed between anatase and rutile in disturbing these molecular distributions, more specifically in the adsorbed outer layer. Anatase (101) presented significantly higher values of self-diffusivity, presumably due to its “corrugated” structure that allows more hydrogen bonding interaction with adsorbed molecules beyond the first hydration layer. On the contrary, rutile (110) has adsorbed water molecules more securely “trapped” in the region between Ob atoms, resulting in less mobile adsorbed layers. Full article