Titanate Nanosheets Research Articles

Oxygen Evolution Reaction on Ni‐based Two‐dimensional (2D) Titanate Nanosheets: Investigation on Effect of Fe Co‐doping and Fe Incorporation from Electrolyte on the Activity

AbstractIn this paper, Ni‐based titanate nanosheets are used as a model system to reveal how incorporation of Fe affects their catalytic ability for the oxygen evolution reaction (OER). The Fe incorporation effects are studied without structural and morphological changes due to the rigid framework of TiO2 based nanosheets. Transition metal doped titanate nanosheets are prepared by cation‐assisted exfoliation of protonated layered potassium titanate. Fe incorporation within the lattice of Ni doped titanate nanosheets by co‐doping stabilizes nickel ions in lower oxidation state by charge transfer effect, caused increased OER activity at Ni sites by the electronic interaction. In contrast, incorporation of Fe from the electrolyte, highly‐active Fe sites at edges or corners of Ni doped titanate nanosheets are formed by electrochemical cycling in Fe‐containing electrolyte rather than electronic effects on Ni. Through this work, Fe incorporation effects are experimentally revealed without crystal structural or morphological changes, and a method to produce a highly active and stable OER catalyst is provided.

Au-nanorod-anchored {0 0 1} facets of Bi4Ti3O12 nanosheets for enhanced visible-light-driven photocatalysis

Generally, plasmonic photocatalyst suffers from limited visible-light responsive and inefficient charge transfer through the noble metal/semiconductor interface, leading to unsatisfactory photocatalytic activity. To solve this problem, herein we design and prepare a high efficiency photocatalyst i.e. gold nanorods/bismuth titanate nanosheets (BTO-Au NRs), in which Au NRs selectively anchored on the active {001} facets of BTO. Upon a mild hydrothermal process, excessive organic ligands around Au NRs is removed, and as a result a clear interface forms between {001} facets of BTO NSs and Au NRs, which is beneficial to interfacial charge transfer between BTO NSs and Au NRs. The as-prepared BTO-Au NRs can harvest sunlight from visible to near-infrared light by tuning their length-to-diameter aspect ratios. The optimizing BTO-Au NRs (aspect ratios of Au NRs is 3.8) exhibits a high photocatalytic activity for the degradation of the pollutants such as α-naphthol (α-NP) and rhodamine B (RhB) under visible irradiation, with 5 and 22-fold photocatalytic efficiency with respect to BTO under the same condition, respectively. The remarkably boosted activity is demonstrated to be due to the synergetic effects of enlarged the optical adsorption range, exposed active {001} facets of BTO, as well as plasmon-induced hot electron from Au NRs transferred to the matched conduction band of {001} faceted BTO. This study offers insights into plasmonic hot electron-enabled and active facet-exposed photocatalysis, which will be valuable for the design of novel and high-efficiency plasmonic metal/semiconductor hybrid photocatalysts.

Toward an Effective Control of the H2 to CO Ratio of Syngas through CO2 Electroreduction over Immobilized Gold Nanoparticles on Layered Titanate Nanosheets

In recent years, the electroreduction of CO2 to valuable products has emerged as a rational answer to rising CO2 emissions and a strategic approach to incorporate renewable electricity from intermittent sources (e.g., wind and solar) into the global energy supply. The reduction of CO2 to CO has been highlighted in the widely explored industrial conversion of syngas (CO and H2) to fuels. Herein, we report a promising electrocatalyst incorporating well-dispersed gold nanoparticles (Au NPs) on ultrathin titanate nanosheets (TiNS). By tuning the contents of Au (in the ranges of 0 to 93 wt % Au) in the hybrid Au/TiNS architecture, CO product selectivity was effectively controlled (in the range of CO Faradaic efficiency from 3 to over 80%) with the sole additional formation of H2, which is of pronounced industrial interest. Most importantly, a control of both component amounts was suggested to result in a variation of corresponding electronic properties based on the interaction between Au NP and TiNS substrate, dictating the stabilization of formed reaction intermediates and resulting product selectivity. In addition, our Au/TiNS achieved optimally high CO and H2 production current densities, with 73 wt % Au at the low cathodic potential region (−0.6 to −0.9 VRHE). The suggested synergetic effect between both catalytic components underlines the promising character of this hybrid system and is expected to significantly add to the strategic production of syngas for subsequent applications.

Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe3O4@TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe3O4@TNS nanosheets had high specific areas (114.9 m2 g−1 for core-shell Fe3O4@TNS and 130.1 m2 g−1 for yolk-shell Fe3O4@TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe3O4@TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities (Qmax) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g−1 for core-shell Fe3O4@TNS and 82.85, 173.01 and 283.29 mg g−1 for yolk-shell Fe3O4@TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (ΔH0, ΔS0 and ΔG0) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na+ and UO22+. The yolk-shell Fe3O4@TNS had more extraordinary sorption efficiency than core-shell Fe3O4@TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe3O4@TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications.

Ternary PVDF-based terpolymer nanocomposites with enhanced energy density and high power density

The development of advanced dielectric materials with high electric energy densities is of crucial importance in modern electronics and electric power systems. Herein, a kind of ternary poly(vinylidene fluoride)-based ferroelectric terpolymer nanocomposites are prepared using a facile solution cast method. The ternary nanocomposite that is composed of barium strontium titanate (BST) and boron nitride nanosheets (BNNS) can achieve increased dielectric constant and breakdown strength simultaneously. At the optimized filler contents, the ternary nanocomposite discharges an energy density of 24.4 J/cm3, which is 295% that of pristine terpolymer. Moreover, microsecond discharge speed of 2.81 μs along with a power density that is over 13 times that of the current commercial available biaxially oriented polypropylene (BOPP) have been achieved under an electric field of 200 MV/m. The incorporation of uniformly dispersed multicomponents into polymer matrix paves a way to significantly improve energy storage capability for dielectric polymer nanocomposites film capacitors.

Single-crystal TiO2 nanorods assembly for efficient and stable cocatalyst-free photocatalytic hydrogen evolution

TiO2 with abundant surface oxygen vacancies is notoriously difficult to stabilize upon photochemical oxidation, which in turn limits its photocatalytic application. To address this limitation, the gray fries cake-like TiO2 assembly composed of single-crystal TiO2 nanorods by in-situ carbon adherence was fabricated via hydrogenation of protonic titanate nanosheets (PTN) under normal pressure. During the hydrogenation process, the residual butyl alcohol adsorbed on PTN from tetrabutyl titanate hydrolysis can be in-situ converted into carbon in company with the formation of oxygen vacancies (O-vacancies) on TiO2. The carbon layer and O-vacancies are able to induce the growth of single-crystal TiO2 nanorods and their assembly to form the fries cake-like structure. Moreover, the carbon layer can not only offer a favorable reduction environment to generate rich O-vacancies on TiO2, but also efficiently improve these O-vacancies and TiO2 nanorods’ stability during catalytic reaction. O-vacancies/carbon layer can serve as electron trap active sites which can capture and transfer electrons to improve the separation of electron-hole pairs. As a consequence, in the absence of any co-catalysts, a high efficiency of hydrogen evolution was achieved for the TiO2 assembly with 69.7 μmol h−1 (quantum efficiency ∼2.3% at 420 nm) under solar light irradiation. After laying six months, our TiO2 assembly still exhibited high photocatalytic performance, which is superior to previous TiO2-based photocatalyst. The results indicate that the photocatalytic activity of TiO2 assembly can be enhanced by stabilizing the surface rich oxygen vacancies with carbon coating.

Few-layered titanate nanosheets with large lateral size and surface functionalization: potential for the controlled exfoliation of inorganic-organic layered composites.

Herein, few-layered titanate nanosheets with a large lateral size and surface functionalization were synthesized via the exfoliation of precursor layered composites in an organic medium. The combination of layered compounds, intercalated guests, and dispersion media has the potential for the synthesis of nanosheets with controlled lateral sizes, thicknesses, and surface chemistry through exfoliation.

PEGylated titanate nanosheets: hydrophilic monolayers with a superior capacity for the selective isolation of immunoglobulin G

A novel organic-inorganic hybrid was prepared by anchoring (3-aminopropyl)triethoxysilane (APTES) on the surface of monolayer titanate nanosheets and subsequent modification with hydrophilic polyethylene glycol (PEG). The PEGylated hydrophilic monolayer titanate nanosheets were abbreviated as PEG-APTES-TiNSs, and they exhibit a lateral dimension of dozens of nanometers and a thickness of ca. 1.9 nm. PEGylation of the titanate nanosheets significantly improved their selectivity toward the adsorption of glycoproteins through strong hydrophilic interaction, providing an adsorption capacity of 2540.9 mg g-1 for immunoglobulin G (IgG). The retained IgG is readily collected at a recovery rate of 83.4% with 0.5% (m/v) ammonium hydroxide (NH4OH) as the stripping reagent. PEG-APTES-TiNSs are applied for the selective adsorption of IgG from human serum, which is further confirmed by SDS-PAGE assay.

Titanate Fibroin Nanocomposites: A Novel Approach for the Removal of Heavy-Metal Ions from water.

In this study, we report the fabrication of nanocomposites made of titanate nanosheets immobilized in a solid matrix of regenerated silk fibroin as novel heavy-metal-ion removal systems. The capacity of these nanocomposite films to remove lead, mercury, and copper cations from water was investigated, and as shown by the elemental quantitative analysis performed, their removal capacity is 73 mmol/g for all of the ions tested. We demonstrate that the nanocomposites can efficiently retain the adsorbed ions, with no release of titanate nanosheets occurring even after several exposure cycles to ionic solutions, eliminating the risk of release of potentially hazardous nanosubstances to the environment. We also prove that the introduction of sodium ions in the nanocomposite formulation makes the materials highly selective toward the lead ions. The developed biopolymer nanocomposites can be potentially used for the efficient removal of heavy-metal-ion pollutants from water and, thanks to their physical and optical characteristics, offer the possibility to be used in sensor applications.

A Pd/Monolayer Titanate Nanosheet with Surface Synergetic Effects for Precise Synthesis of Cyclohexanones

A catalyst composed of monolayer nonstoichiometric titanate nanosheets (denoted as TN) and Pd clusters is constructed for precise synthesis of cyclohexanone from phenol hydrogenation with high conversion (>99%) and selectivity (>99%) in aqueous media under light irradiation. Experimental and DFT calculation results reveal that the surface exposed acid and basic sites on TN could interact with phenol molecules in a nonplanar fashion via a hexahydroxy hydrogen-bonding ring to form a surface coordination species. This greatly facilitates the adsorption and activation of phenol molecules and suppresses the further hydrogenation of cyclohexanone. Moreover, the surface Pd clusters serve as the active sites for the adsorption and dissociation of hydrogen molecules to provide active H atoms. The synergistic effect of the surface coordination species, TN and Pd clusters remarkably facilitate the high yield of cyclohexanone in photocatalysis. Finally, the possible thermo/photocatalytic mechanisms on Pd/TN are propo...

Highly selective oxidation of furfuryl alcohol over monolayer titanate nanosheet under visible light irradiation

Monolayer H1.4Ti1.65O4·H2O nanosheet (denoted as NST) has been prepared as a photocatalyst for the oxidation of furfuryl alcohol (denoted as FA) to furaldehyde under visible light irradiation. The photocatalytic activity of NST is over 10 times higher than that of its layered counterpart. This enhanced activity may be attributed to the high percentage of exposed Lewis acid sites in NST. The in-situ FTIR result suggests that FA are efficiently chemosorbed on the exposed Lewis acid sites forming the surface coordination species via CO groups, resulting in the activation of FA. The surface coordination species would respond to visible light absorption. Furthermore, The XAFS result shows that the signals for TiO and Ti–Ti in NST are weaker dramatically and the signals positions are shifted by 0.03Å in the higher R direction as compared with those in layered counterpart, suggesting the more exposed Ti and O defects in NST. The oxygen molecules absorbed on these surface defects are activated forming O2− by photo-electrons under visible light irradiation. Finally, a possible mechanism has been proposed at a molecular level.

Synthesis and fluorescence properties of lanthanide-supported titanate nanosheets

Metal oxide nanosheets are increasingly applied as catalysts, hard coatings, and other transparent thin film materials. Here, we developed a novel and appropriate photodeposition method for liquid-phase-synthesized titanate nanosheets (TNS). Lanthanide (Ln) oxide was suspended in the TNS dispersion, and the mixture was irradiated with UV light. Ln bearing on TNS (Ln/TNS) was easily achieved by this method. Eu/TNS, Sm/TNS, and Dy/TNS exhibited photoluminescence properties. In particular, Eu/TNS emitted strong red fluorescence under UV irradiation. Furthermore, the Ln/TNS retained the layered structure and diamond-like shape of TNS.

Titanate nanosheets cause caspase-dependent apoptosis of human immune cells with giant vacuole formation through endosomal defect in monocytes

Titanate nanosheets cause caspase-dependent apoptosis of human immune cells with giant vacuole formation through endosomal defect in monocytes

Synergistic effect of Fe2O3 and CeO2 co-modified titanate nanosheet heterojunction on enhanced photocatalytic degradation

CeO2 and Fe2O3 co-modified titanate nanosheet (Fe2O3/CeO2@TNS) was prepared by one-pot hydrothermal method; the photocatalyst exhibited large surface area with CeO2 and Fe2O3 particles well dispersed on the surface. The results of XRD, BET, and Raman proved that the CeO2 and Fe2O3 introduced in the TNS influenced its structure evolution from 3D to 2D. The modification resulted in a shift of the absorption edge toward a longer wavelength and the band gap reduced to 2.87 eV. The three-component systems performed excellent photocatalytic activity and cycle stability on phenol and methyl blue (MB) solution under sunlight; nearly total phenol and MB were degraded in dozens of minutes. And the reaction rate constant (K) of Fe2O3/CeO2@TNS on phenol degradation was 1.77, 3.25, 4.88, and 13-fold of Fe2O3@TNS, CeO2@TNS, bare TNS, and P25, respectively. The enhanced photocatalytic activity could be ascribed to the efficient separation of photogenerated pairs through the formation of tandem n-n-n heterojunction among the three-component systems. This work will be useful for the design of other tandem n-n-n heterojunction photocatalytic systems for application in energy conversion and environmental remediation.

Photocatalytic Oxidative Decomposition of Methylene Blue by Rh-Doped Titanate Nanosheets ([Ti4−xRhxO9]2−)

Abstract We investigated the adsorption and photocatalytic decomposition of methylene blue (MB) by colloidal suspensions of Rh-doped titanate nanosheets ([Ti4−xRhxO9]2−; Ti4NS:Rhx) prepared by exfoliating H2Ti4−xRhxO9 in aqueous tetramethylammonium hydroxide, revealing that doped nanosheets showed a slightly enhanced adsorption capacity compared to their non-doped counterparts. This behavior was ascribed to the elevated ionic charge of doped Ti4NS and the thus increased volume charge density. Accordingly, Ti4NS:Rhx exhibited a higher MB adsorption capacity than previously reported [Ti3−xRhxO7]2−. Moreover, we found that Ti4NS:Rhx catalyzed the photodegradation of MB under UV light irradiation, additionally showing that the activity of this catalyst can be improved by Rh doping, probably due to the large contribution of Rh3+/Rh4+ shuttling to effective MB degradation.

Fluorescence Properties of the Lanthanide Supported onto Titanate Nanosheets

Fluorescence Properties of the Lanthanide Supported onto Titanate Nanosheets

Surfactant-assisted formation of silver titanates as active catalysts for methanol electro-oxidation

Silver nanoparticles successfully incorporated in titanate nanosheets and synthesized hydrothermally via employing cetyltrimethylammonium bromide (CTAB) and triblock copolymer (pluronic F127) assisted templates were thoroughly characterized using transmission electron microscopy-selected area electron diffraction (TEM-SAED), X-ray diffraction, diffuse reflectance UV/visible absorption spectroscopy, N2 sorptiometry, FTIR and Raman spectroscopy. The dispersed Ag nanoparticles of uniform size (2–3nm) were found to contact intimately with titanateF127 nanosheets to show superior crystallinity, wider layer distances and higher surface area and pore volume (SBET=51.1m2g−1,Vp=0.081cm3g−1) than Ag/titanateCTAB (7.2m2g−1, 0.02cm3g−1). This constructed Ag/titanateF127 exhibits markedly improved electrocatalytic (1.4-fold) and photoelectrocatalytic (4.0-fold) activities and stabilities towards methanol oxidation than that of Ag/titanateCTAB; as determined using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The enhanced activity of Ag/titanateF127 was also attributed to electron transfer across the interface potential of the composite Ag-titanateF127 as well as the delay of charge recombination that has been substantiated not only via exposed Ag but also through the non-decomposed carbon template. This enhanced electron transfer and electronic conductivity was established by impedance spectroscopy, and exhibits the maximum obtained photocurrent density (2.0mAcm−2) under visible light illumination (λ>420nm, 88W). The results revealed that the template F127 had a significant effect not only on enhancing the titanate crystallinity and exhibiting a surface plasmon resonance band; unlike Ag/titanateCTAB, but also in acquiring a high pore volume value and widened layers, which all work towards improving the Ag-titanateF127 durability for methanol oxidation.

Copper-Decorated Titanate Nanosheets: Novel Homogeneous Monolayers with a Superior Capacity for Selective Isolation of Hemoglobin.

Novel unilamellar and homogeneous titanate nanosheets were prepared by anchoring (3-aminopropyl)triethoxysilane (APTES) and chelating copper ions, also know by the short form Cu-APTES-TiNSs. The nanosheets were uniform two-dimensional lamellas/monolayers with a thickness of 1.9 nm, and they were further characterized by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, and N2 adsorption-desorption. The copper-decorated titanate nanosheets possess a copper content of 4.28 ± 0.14% and exhibit a favorable selectivity to the adsorption of hemoglobin, with a considerable capacity of 5314.2 mg g-1. The adsorbed hemoglobin is easily collected with a recovery rate of 91.3% by using 0.5% w/v sodium dodecyl sulfate as an eluent. Circular dichroism spectra confirmed that virtually no conformational alteration is observed for hemoglobin. Cu-APTES-TiNSs are further applied for the selective adsorption of hemoglobin from the human whole blood.

Incorporation of titanate nanosheets to enhance mechanical properties of water-soluble polyamic acid

Pyromeliticdianhydride (PMDA) and 4’,4’-oxydianiline (ODA) were used as monomers of polyimide. To synthesise a water soluble polyimide precursor (polyamic acid salt), triethylamine (TEA) was added to polyamic acid with a TEA/COOH mole ratio of 1:1. Titanate nanosheets were synthesised by solid-state reaction, ion-exchanged with acid, and exfoliated by TEA. Exfoliated titanate nanosheets were mixed with water soluble polyamic acid salt as reinforcing filler. Drop casting was deployed to synthesise polyamic acid/titanate nanosheet nanocomposite films. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to study the morphology and dispersion of nanosheets in the colloidal dispersion and the solid film composite. Modulus and hardness of nanocomposites was provided by nanoindentation. Hardness increased by 90% with addition of 2% TiNS while modulus increased by 103% compared to pure polymer. This behaviour agrees well with Halpin-Tsai theoretical predictions up to 2 wt% filler loading; agglomeration occurs at higher concentrations.

Titanate nanotubes and nanosheets as a mechanical reinforcement of water-soluble polyamic acid: Experimental and theoretical studies

Abstract Titanate nanosheets (TiNS), titanate nanotubes (TiNT), and scrolled titanate nanosheets (STiNS) were used to synthesise polymer nanocomposites by solution processing. The hardness was found to increase by 90% on addition of 2% TiNS while the modulus ( Er ) increased by 103% compared to the pure polymer. Small angle X-ray scattering (SAXS) measurements of composite films were used to study alignment of nanostructures within the polymer. The obtained data on mechanical properties of composites have been tested against theoretical values and it was established that both nanostructures alignment as well as their mechanical properties affect the hardness and modulus of the polymer composites. At a low content of TiNS, the reinforcement behaviour matched well with Halpin-Tsai theory which assumes the filler has unidirectional orientation. After addition of 2 wt% TiNT, the hardness and modulus of the polyamic acid salt composites increased by 91% and 165%, respectively, and were higher than theoretical predictions, indicating that both TiNT and STiNS, prepared by hydrothermal synthesis, may have higher mechanical properties than bulk TiO 2 . At a high filler loading (>2 wt%), the mechanical properties of composites do not fit established theories due to agglomeration of titanate nanostructures.