Doped 1D Nanostructures of Transition-metal Oxides: First-principles Evaluation of Photocatalytic Suitability

Nanosized tubular clay minerals as inorganic nanoreactors for energy and environmental applications: A review to fill current knowledge gaps

Modern society pays further and further attention to environmental protection and the promotion of sustainable energy solutions. Heterogeneous photocatalysis is widely recognized as one of the most economically viable and ecologically sound technologies to combat environmental pollution and the global energy crisis. One challenge is finding a suitable photocatalytic material for an efficient process. Inorganic nanotubes have garnered attention as potential candidates due to their optoelectronic properties, which differ from their bulk equivalents. Among them, clay nanotubes (halloysite, imogolite, and chrysotile) are attracting renewed interest for photocatalysis applications thanks to their low production costs, their unique physical and chemical properties, and the possibility to functionalize or dope their structure to enhance charge-carriers separation into their structure. In this review, we provide new insights into the potential of these inorganic nanotubes in photocatalysis. We first discuss the structural and morphological features of clay nanotubes. Applications of photocatalysts based on clay nanotubes across a range of photocatalytic reactions, including the decomposition of organic pollutants, elimination of NOx, production of hydrogen, and disinfection of bacteria, are discussed. Finally, we highlight the obstacles and outline potential avenues for advancing the current photocatalytic system based on clay nanotubes. Our aim is that this review can offer researchers new opportunities to advance further research in the field of clay nanotubes-based photocatalysis with other vital applications in the future.

Density functional theory for doped TiO2: current research strategies and advancements

Since the inception of the density functional theory (DFT) by Hohenberg and Kohn in 1964, it rapidly became an indispensable theoretical tool across various disciplines, such as chemistry, biology, and materials science, among others. This theory has ushered in a new era of computational research, paving the way for substantial advancements in fundamental understanding. Today, DFT is routinely employed for a diverse range of applications, such as probing new material properties and providing a profound understanding of the mechanisms underlying physical, chemical, and biological processes. Even after decades of active utilization, the improvement of DFT principles has never been slowed down, meaning that more accurate theoretical results are continuously generated with time. This work highlights the latest achievements acquired by DFT in the specific research field, namely the theoretical investigations of doped TiO2systems, which have not been comprehensively reviewed and summarized yet. Successful progress in this niche is currently hard to imagine without the support by DFT. It can accurately reveal new TiO2properties after introducing the desired dopant and help to find the optimal system design for a specific application prior to proceeding to more time-consuming and expensive experimental research. Hence, by evaluating a selection of the most recent research studies, we aim to highlight the pertinent aspects of DFT as they relate to the study of doped TiO2systems. We also aim to shed light on the strengths and weaknesses of DFT and present the primary strategies employed thus far to predict the properties of various doped TiO2systems reliably.

Influence of Doping-Ion-Type on the Characteristics of Al2O3-Based Nanocomposites and Their Capabilities of Removing Indigo Carmine from Water

Globally, the continuous contamination of natural water resources is a severe issue, and looking for a solution for such a massive problem should be the researcher’s concern. Herein, Al2O3, Al2O3-CuO, Al2O3-NiO, and Al2O3-CoO were prepared via a simple and fast route, utilizing glucose as a capping material. All synthesis conditions were uniform to make the fabricated nanomaterials’ characteristics exclusively influenced by only the ion type. The SEM analysis showed that the particles of the synthesized Al2O3, Al2O3-CuO, Al2O3-NiO, and Al2O3-CoO were all less than 25 nm. The Al2O3-NiO showed the smallest particle size (11 to 14 nm) and the best BET surface area of 125.6 m2 g−1. All sorbents were tested for removing organic pollutants, as exemplified by indigo carmine (IGC) dye. The Al2O3-NiO possessed the highest adsorption capacity among the other sorbents for which it had been selected for further investigations. The IGC sorption reached equilibrium within 2.0 h, and the kinetic study revealed that the IGC removal by Al2O3-NiO nanocomposite fitted the FOM and the LFM. The sorbent showed an experimental adsorption capacity (qt) of 456.3 mg g−1 from a 200 mg L−1 IGC solution and followed the Langmuir model. The thermodynamic findings indicated an endothermic, spontaneous, and physisorption nature. The seawater and groundwater samples contaminated with 5.0 mg L−1 IGC concentrations were fully remediated using the Al2O3-NiO nanocomposite. The reuse study showed 93.3% average efficiency during four successive cycles. Consequently, prepared Al2O3-NiO nanocomposite is recommended for the treatment of contaminated water.

Structural and electronic properties of double-walled G-C3N4 nanotubes: a density functional theory study

In the present work, we investigated the geometric, electronic, and photocatalytic properties of g-C₃N₄single-walled nanotube (SWCNNTs) and g-C₃N₄double-walled nanotubes (DWCNNTs). The negative strain energy indicates that the SWCNNTs have a stable structure, while the most stable combination in the DWCNNT is (6, 0)@(12, 0). The energy band gaps of (n, 0) SWCNNTs increase while that of (n,n) SWCNNTs decrease as the diameter increase. Moreover, the calculated nanotubes have the ability of photocatalytic water splitting, and the valance band maximum of nanotubes are much lower than that of the monolayer, indicating that the nanotubes have better oxidation capacity than the monolayer. On the other hand, our calculations show that DWCNNTs have type II band alignment with a band gap width significantly smaller than that of SWCNNTs. Interestingly, DWCNNT exhibited a smaller effective mass of electrons than SWCNNTs, which is beneficial to electron migration. Therefore, the construction of nanotube is an effective way to improve the photocatalytic performance of g-C₃N₄monolayer materials.

Influence of Au, Ag, and Cu Adatoms on Optical Properties of TiO2 (110) Surface: Predictions from RT-TDDFT Calculations

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 TiO2 (110) surface. The model structures are built reflecting the equilibrium positions of deposited adatoms atop the TiO2 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 TiO2 (∼3 eV), the photogenerated electrons of TiO2 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.

Extraction–Pyrolytic Method for TiO2 Polymorphs Production

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO2) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) for the production of nanocrystalline TiO2 powders. A titanium-containing precursor (extract) was prepared by liquid–liquid extraction using valeric acid C4H9COOH without diluent as an extractant. Simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC), as well as the Fourier-transform infrared (FTIR) spectroscopy were used to determine the temperature conditions to fabricate TiO2 powders free of organic impurities. The produced materials were also characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The results showed the possibility of the fabrication of storage-stable liquid titanium (IV)-containing precursor, which provided nanocrystalline TiO2 powders. It was established that the EPM permits the production of both monophase (anatase polymorph or rutile polymorph) and biphase (mixed anatase–rutile polymorphs), impurity-free nanocrystalline TiO2 powders. For comparison, TiO2 powders were also produced by the precipitation method. The results presented in this study could serve as a solid basis for further developing the EPM for the cheap and simple production of nanocrystalline TiO2-based materials in the form of doped nanocrystalline powders, thin films, and composite materials.

Effect of Ag loading position on the photocatalytic performance of TiO2 nanocolumn arrays

Plasmonic metal/semiconductor composites have attracted great attention for efficient solar energy harvesting in photovoltaic and photocatalytic applications owing to their extremely high visible-light absorption and tuned effective band gap. In this work, Ag-loaded TiO₂ nanocolumn (Ag-TNC) arrays were fabricated based on anodic aluminum oxide (AAO) template by combining atomic layer deposition (ALD) and vacuum evaporation. The effects of the Ag loading position and deposition thickness, and the morphology, structure and composition of Ag-deposited TNC arrays on its optical and photocatalytic properties were studied. The Ag-filled TiO₂ (AFT) nanocolumn arrays exhibited higher removal efficiency of methylene blue (MB) compared with Ag-coated TiO₂ (ACT) nanocolumn arrays and pure TiO₂ nanocolumns arrays. Both experimental and theoretical simulation results demonstrated that the enhanced photocatalytic performance of AFT nanocolumn arrays was attributed to the surface plasmon resonance (SPR) of Ag and the absorption of light by TiO₂. These results represent a promising step forward to the development of high-performance photocatalysts for energy conversion and storage.

First-Principles Evaluation of the Morphology of WS2 Nanotubes for Application as Visible-Light-Driven Water-Splitting Photocatalysts

One-dimensional tungsten disulfide (WS₂) single-walled nanotubes (NTs) with either achiral, i.e., armchair (n, n) and zigzag-type (n, 0), or chiral (2n, n) configuration with diameters d _NT > 1.9 nm have been found to be suitable for photocatalytic applications, since their band gaps correspond to the frequency range of visible light between red and violet (1.5 eV < Δε_gap < 2.6 eV). We have simulated the electronic structure of nanotubes with diameters up to 12.0 nm. The calculated top of the valence band and the bottom of the conduction band (ε_VB and ε_CB, respectively) have been properly aligned relatively to the oxidation (ε_O2/H2O) and reduction (ε_H2/H2O) potentials of water. Very narrow nanotubes (0.5 < d _NT < 1.9 nm) are unsuitable for water splitting because the condition ε_VB < ε_O2/H2O < ε_H2/H2O < ε_CB does not hold. For nanotubes with d _NT > 1.9 nm, the condition ε_VB < ε_O2/H2O < ε_H2/H2O < ε_CB is fulfilled. The values of ε_VB and ε_CB have been found to depend only on the diameter and not on the chirality index of the nanotube. The reported structural and electronic properties have been obtained from either hybrid density functional theory and Hartree-Fock linear combination of atomic orbitals calculations (using the HSE06 functional) or the linear augmented cylindrical waves density functional theory method. In addition to single-walled NTs, we have investigated a number of achiral double-walled (m, m)@(n, n) and (m, 0)@(n, 0) as well as triple-walled (l, l)@(m, m)@(n, n) and (l, 0)@(m, 0)@(n, 0) nanotubes. All multiwalled nanotubes show a common dependence of their band gap on the diameter of the inner nanotube, independent of chirality index and number of walls. This behavior of WS₂ NTs allows the exploitation of the entire range of the visible spectrum by suitably tuning the band gap.