The interactions between TiO2 and graphene with surface inhomogeneity determined using density functional theory

Tuning the band gap of M-doped titanate nanotubes (M = Fe, Co, Ni, and Cu): an experimental and theoretical study

Herein, we report a systematic experimental and theoretical study about a wide-ranged band gap tuning of protonated titanate nanotubes H₂Ti₃O₇ (Ti-NT) by an easy ion-exchange method using a low concentration (1 wt%) of transition metal cations. To characterize and describe the effect of M doping (M = Cu²⁺, Ni²⁺, Co²⁺, and Fe³⁺) on the electronic, optical and structural properties, semiconductors were analyzed by a combination of experimental methods and density functional theory (DFT) calculations. The nanotube band gap can be modified from 1.5 to 3.3 eV, which opens the possibility to use them in several optoelectronic applications such as photocatalysts under solar light irradiation.

Sulfonated polyaniline-encapsulated graphene@graphitic carbon nitride nanocomposites for significantly enhanced photocatalytic degradation of phenol: a mechanistic study

The photocatalytic degradation of phenol through -s-PANI@g-C₃N₄ and its nanocomposites with graphene.

Origin of Charge Trapping in TiO2/Reduced Graphene Oxide Photocatalytic Composites: Insights from Theory

Composites of titanium dioxide (TiO₂) and reduced graphene oxide (RGO) have proven to be much more effective photocatalysts than TiO₂ alone. However, little attention has been paid so far to the chemical structure of TiO₂/RGO interfaces and to the role that the unavoidable residual oxygen functional groups of RGO play in the photocatalytic mechanism. In this work, we develop models of TiO₂ rutile (110)/RGO interfaces by including a variety of oxygen functional groups known to be present in RGO. Using hybrid density functional theory calculations, we demonstrate that the presence of oxygen functional groups and the formation of interfacial cross-links (Ti-O-C covalent bonds and strong hydrogen bonds between TiO₂ and RGO) have a major effect on the electronic properties of RGO and RGO-based composites. The electronic structure changes from semimetallic to semiconducting with an indirect band gap, with the lowest unoccupied band positioned below the TiO₂ conduction band and largely localized on RGO oxygen and carbon orbitals, with some contributions of RGO-bonded Ti atoms. We suggest that this RGO-based lowest unoccupied band acts as a photoelectron trap and the indirect nature of the band gap hinders electron-hole recombination. These results can explain the experimentally observed extended lifetimes of photoexcited charge carriers in TiO₂/RGO composites and the enhancement of photocatalytic efficiency of these composites.

Silicene-supported TiO2 nanostructures: a theoretical study of electronic and optical properties

Silicene boosts the photovoltaic and photocatalytic performance of TiO₂ nanostructures.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications

Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development. For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems. Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields. However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO₂ under visible-light irradiation. Many investigations have been undertaken to overcome the limitations of TiO₂ and, therefore, to enhance its photocatalytic activity under visible light. The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO₂ to the visible region. Current synthesis techniques used to elaborate several nanostructures of TiO₂ -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed. On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO₂ -based materials further.

Water on Graphene-Coated TiO2: Role of Atomic Vacancies

Beyond two-dimensional (2D) materials, interfaces between 2D materials and underlying supports or 2D-coated metal or metal oxide nanoparticles exhibit excellent properties and promising applications. The hybrid interface between graphene and anatase TiO₂ shows great importance in photocatalytic, catalytic, and nanomedical applications due to the excellent and complementary properties of the two materials. Water, as a ubiquitous and essential element in practical conditions and in the human body, plays a significant role in the applications of graphene/TiO₂ composites for both electronic devices and nanomedicine. Carbon vacancies, as common defects in chemically prepared graphene, also need to be considered for the application of graphene-based materials. Therefore, the behavior of water on top and at the interface of defective graphene on anatase TiO₂ surface was systematically investigated by dispersion-corrected hybrid density functional calculations. The presence of the substrate only slightly enhances the on-top adsorption and reduces the on-top dissociation of water on defective graphene. However, at the interface, dissociated water is largely preferred compared with undissociated water on bare TiO₂ surface, showing a prominent cover effect. Reduced TiO₂ may further induce oxygen diffusion into the bulk. Our results are helpful to understand how the presence of water in the surrounding environment affects structural and electronic properties of the graphene/TiO₂ interface and thus its application in photocatalysis, electronic devices, and nanomedicine.

Role of graphene in enhancing the mechanical properties of TiO2/graphene heterostructures

Graphene has been integrated in many heterogeneous structures in order to take advantage of its superior mechanical properties. However, the complex mechanical response of heterogeneous films incorporating graphene is not well understood. Here, we studied the mechanical behavior of atomic layer deposition (ALD) synthesized TiO₂/graphene, as a representative building block of a typical composite, to understand the mechanical behavior of heterostructures using an experiment-computational approach. The inclusion of graphene was found to significantly enhance the Young's modulus of TiO₂/graphene hetero-films for films below a critical thickness of 3 nm, beyond which the Young's modulus approaches that of pure TiO₂ film. A rule-of-mixtures was found to reasonably estimate the modulus of the TiO₂/graphene hetero-film. Experimentally, these hetero-films were observed to fail via brittle fracture. Complimentary density functional theory and finite element modeling demonstrates strong adhesion at the graphene TiO₂ interface and that graphene serves as a reinforcement, providing the hetero-film with an ability to sustain significantly high stresses at the point of failure initiation. The results and methodology described herein can contribute to the rational design of strong and reliable ultrathin hetero-films for versatile applications.

Oxygen vacancy induced fast lithium storage and efficient organics photodegradation over ultrathin TiO2 nanolayers grafted graphene sheets

In this work we have developed a unique structure of ultrathin (5nm) TiO2 nanolayers grafted graphene nanosheets (TiO2/G) and integrated oxygen vacancy (VO) into TiO2 to enhance its lithium storage and photocatalytic performances. The defective TiO2/G was synthesized by a solvothermal and subsequent thermal treatment method. When treated in a H2 atmosphere, the resulting TiO2-x/G(H2) has lower crystallinity, smaller crystal size, richer surface VO, higher surface area, larger pore volume, and lower charge transfer resistance than that reduced by NaBH4 solid, i.e., TiO2-x/G(NaBH4). More importantly, the surface VO in the TiO2-x/G(H2) could remarkably inhibit the recombination of photogenerated electron-hole pairs compared with the bulk Vo in the TiO2-x/G(NaBH4). As a result, the combination of all the factors contributed to the superiority of TiO2-x/G(H2), which demonstrated not only 70% higher specific capacity, longer cycling performance (1000 cycles) and better rate capability for lithium-ion battery, but also higher photocatalytic activity and 1.5 times faster degradation rate for organic pollutants removal than TiO2-x/G(NaBH4). The findings in this work will benefit the fundamental understanding of TiO2/G surface chemistry and advance the design and preparation of functional materials for energy storage and water treatment.

An experimental and theoretical study on the electronic and structural properties of CdSe@TiO2 nanotube arrays

The effects of the structural and electronic parameters on the water splitting over CdSe@TiO₂NT were investigated using experimental and theoretical methods.