Ag<Subscript>2</Subscript>S/Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> co-sensitized TiO<Subscript>2</Subscript> nanorod arrays prepared on conductive glass as a photoanode for solar cells

TiO₂ nanorod arrays (TiO₂ NRAs) were synthesized through a hydrothermal method. Ag₂S and Bi₂S₃ were then grown on the surface of TiO₂ NRAs with successive ionic layer adsorption and reaction method. The pristine rutile TiO₂ NRAs, Ag₂S/TiO₂, Bi₂S₃/TiO₂, and Bi₂S₃/Ag₂S/TiO₂ electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible absorption spectroscopy, and electrochemical analysis. According to photoelectrochemical (PEC) measurement, an enhanced short circuit current density was obtained for the co-sensitized TiO₂ NRAs under simulated sunlight illumination, which was 10.7 times higher than that of the TiO₂ NRAs. Appropriate potential positions of conduction band and valence band of Bi₂S₃ that match well those of rutile TiO₂ NARs and Ag₂S lead to the improved PEC performance. In addition, the PEC property of the co-sensitized TiO₂ NRAs under visible light irradiation was also investigated and showed a dramatically enhanced photocurrent response.     

TiO<Subscript>2</Subscript> nanotube arrays: hydrothermal fabrication and photocatalytic activities

Titanium dioxide nanotube arrays (TiO₂ NTAs) with rutile phase have been fabricated successfully via a two-step hydrothermal method. TiO₂ nanorod arrays (TiO₂ NRAs) are first hydrothermally grown on FTO substrate. Then the TiO₂ NTAs can be obtained by controlling the HCl concentration of the hydrothermal etching process. The TiO₂ NTAs have been characterized by X-ray diffractometer, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscope. Evolution of TiO₂ nanoarrays are accompanied by enhanced of the surface area and optical properties. Compared with TiO₂ NRAs, the prepared TiO₂ NTAs is more efficient in the photodegradation of methyl orange. These results reveal that the hydrothermal chemical etching provide a flexible and straightforward route for design and preparation of TiO₂ NTAs, promising for new opportunities in photocatalysts and other fields.     

Construction of hierarchical TiO<Subscript>2</Subscript> nanorod array/graphene/ZnO nanocomposites for high-performance photocatalysis

The photocatalytic performance of heterostructure photocatalysts is limited in practical use due to the charge accumulation at the interface and its low efficiency in utilizing solar energy during photocatalytic process. In this work, a ternary hierarchical TiO₂ nanorod arrays/graphene/ZnO nanocomposite is prepared by using graphene sheets as bridge between TiO₂ nanorod arrays (NRAs) and ZnO nanoparticles (NPs) via a facile combination of spin-coating and chemical vapor deposition techniques. The experimental study reveals that the graphene sheets provide a barrier-free access to transport photo-excited electrons from rutile TiO₂ NRAs and ZnO NPs. In addition, there generates an interface scattering effect of visible light as the graphene sheets provide appreciable nucleation sites for ZnO NPs. This synergistic effect in the ternary nanocomposite gives rise to a largely enhanced photocurrent density and visible light-driven photocatalytic activity, which is 2.6 times higher than that of regular TiO₂ NRAs/ZnO NPs heterostructure. It is expected that this hierarchical nanocomposite will be a promising candidate for applications in environmental remediation and energy fields.     

Preparation of Sb<Subscript>2</Subscript>S<Subscript>3</Subscript> film on functional organic self-assembled monolayers by chemical bath deposition

In this work, self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) were applied to induce the nucleation and growth of the antimony sulfide (Sb₂S₃) films on the functional ITO glass substrate at low temperature. The structure, morphology, and optical properties of the Sb₂S₃ films were investigated by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and UV–vis spectroscopy. After thermal treatment at 200 °C for 1 h in air, the orthorhombic Sb₂S₃ was formed as a predominant phase in the deposited thin films. When the deposited films were thermally treated at 400 °C for 1 h in air, the orthorhombic Sb₂S₃ was decomposed and a cubic Sb₂O₃ was formed. The optical band energies of the as-deposited and thermally treated Sb₂S₃ films at 200 °C for 1 h in air and nitrogen were found to be 2.05 eV, 1.77, and 1.76 eV, respectively. As chemical templates, the OTS-functionalized SAMs played an important role in controlling the nucleation and growth of Sb₂S₃ films at low temperature. The results obtained from different preparation parameters applied in the present work will allow controlling the growth of the Sb₂S₃ films with uniform surface.     

In<Subscript>2</Subscript>S<Subscript>3</Subscript> nanoparticles dispersed on g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets: role of heterojunctions in photoinduced charge transfer and photoelectrochemical and photocatalytic performance

Fast recombination of photogenerated charge carriers is a major problem in the photoelectrochemical and photocatalytic processes. In this work, we report significantly improved PEC performance of a nanocomposite consists of In₂S₃ nanoparticles dispersed on g-C₃N₄ nanosheets synthesized by a simple and facile wet chemical route. The results of high-resolution TEM study show that the obtained In₂S₃ nanoparticles of size 10–20 nm exist in cubic phase and are uniformly dispersed on the surface of g-C₃N₄ nanosheets. The In₂S₃/g-C₃N₄ nanocomposite with 25 weight percentage of In₂S₃ exhibits 8.5 times higher photocurrent density than the single-phase g-C₃N₄ under visible light illumination. The enhanced photocurrent density exhibited by the In₂S₃/g-C₃N₄ nanocomposite is attributed to the efficient separation of photogenerated charge carriers. The charge transfer mechanism in In₂S₃/g-C₃N₄ heterojunction was studied by a series of experiments, such as electrochemical impedance spectroscopy, photoelectrochemical measurement and photoluminescence emission spectroscopy. The intimate interface promotes the charge transfer and inhibits the recombination rate of photogenerated electron–hole pairs, which significantly improves the photoelectrochemical performance. A detailed charge transfer mechanism is discussed based on the Mott–Schottky plot study. This heterojunction material is found to be an efficient photocatalyst for the degradation of both cationic rhodamine B dye and anionic methyl orange dye as the lifetime of photogenerated charge carriers is higher in the composite than in single-phase In₂S₃ and g-C₃N₄. A strong correlation between the photoelectrochemical and the photocatalytic performances is observed in this composite.     

Electrochemically induced Ti<Superscript>3+</Superscript> self-doping of TiO<Subscript>2</Subscript> nanotube arrays for improved photoelectrochemical water splitting

We report a facile electrochemical reduction method to synthesize Ti³⁺-self-doped TiO₂ nanotube arrays (TNTs), where the effects of reduction duration and potential on the photoelectrochemical performance were systematically investigated. The X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra confirmed the presence of Ti³⁺ in the TNTs. Under the optimum reduction condition, the Ti³⁺-self-doped TNTs exhibited remarkably enhanced photocurrent density and photoconversion efficiency, which were nearly 3.1 and 1.75 times that of pristine TNTs, respectively. The enhancement of PEC performance is due to the improved electrical conductivity, accelerated charge transfer rate at the TNTs/electrolyte interface, as well as the improved visible light response, which is elucidated by electrochemical impedance spectra, Mott–Schottky, and UV–Vis diffuse reflection spectra.     

Graphene as an intermediary for enhancing the electron transfer rate: A free-standing Ni<Subscript>3</Subscript>S<Subscript>2</Subscript>@graphene@Co<Subscript>9</Subscript>S<Subscript>8</Subscript> electrocatalytic electrode for oxygen evolution reaction

A highly active and stable oxygen evolution reaction (OER) electrocatalyst is critical for hydrogen production from water splitting. Herein, three-dimensional Ni₃S₂@graphene@Co₉₂S₈ (Ni₃S₂@G@Co₉S₈), a sandwich-structured OER electrocatalyst, was grown in situ on nickel foam; it afforded an enhanced catalytic performance when highly conductive graphene is introduced as an intermediary for enhancing the electron transfer rate and stability. Serving as a free-standing electrocatalytic electrode, Ni₃S₂@G@Co₉S₈ presents excellent electrocatalytic activities for OER: A low onset overpotential (2 mA·cm^?2 at 174 mV), large anode current density (10 mA·cm^?2 at an overpotential of 210 mV), low Tafel slope (66 mV·dec^?1), and predominant durability of over 96 h (releasing a current density of ～14 mA·cm^?2 with a low and constant overpotential of 215 mV) in a 1 M KOH solution. This work provides a promising, cost-efficient electrocatalyst and sheds new light on improving the electrochemical performance of composites through enhancing the electron transfer rate and stability by introducing graphene as an intermediary.

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Formation and structural phase transitions of mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> xerogels under hydrothermal conditions

We have studied the effect of the hydrothermal synthesis temperature on Al₂O₃ structure formation and examined the role of the phase composition of the precursor gel and surfactant in the formation of the pore structure of Al₂O₃. A technique has been proposed for the synthesis of TiO₂/Al₂O₃ binary xerogels, and the effect of TiO₂ content on the pore structure parameters and adsorption properties of TiO₂/Al₂O₃ has been investigated.     

Photocatalytic reduction of CO<Subscript>2</Subscript> with H<Subscript>2</Subscript>O over modified TiO<Subscript>2</Subscript> nanofibers: Understanding the reduction pathway

Nanosized metal (Pt or Pd)-decorated TiO₂ nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO₂ NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO₂ under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO₂ NFs were found to exhibit enhanced performance compared to Pt-decorated TiO₂ NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO₂ NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg^?1·h^?1 methanol. The CO₂ photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.

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Network-like CuInS<Subscript>2</Subscript> photocathode and modified with noble metal co-catalyst for photoelectrochemical water splitting

It is of great significance to explore new preparation methods and control the morphology and proportion of metal ions for the photoelectrochemical (PEC) water splitting of ternary sulfide photoelectrode. In this paper, the network-like CuInS₂ film photocathodes were firstly prepared by hydrothermal growth method. The effects of different [Cu²⁺]/[In³⁺] molar ratios and concentrations of growth solution on CuInS₂ films were investigated in detail. The mechanism of the synthetic reaction was studied. The best PEC photocurrent density of the CuInS₂ film photoelectrode is ??0.81 mA/cm² at ??0.6 V versus RHE when the [Cu²⁺]/[In³⁺] molar ratio is 0.4, the growth solution concentration is 8 mmol/L CuCl₂·2H₂O, 20 mmol/L InCl₃·4H₂O and 60 mmol/L C₂H₅NS. For the purpose of further improving photoelectrochemical properties of CuInS₂ thin films, the Pt co-catalyst was loaded. The synthesized CuInS₂–Pt thin film yielded a photocurrent density for ??1.92 mA/cm² at ??0.6 V versus RHE due to the fast photogenerated electrons capture ability of Pt co-catalyst. The method of constructing photoelectrode film and the co-catalyst mechanism contributes to a sensational way for PEC water splitting of sulfide.     

Oxalic acid assisted hydrothermal synthesis and optical absorption property of WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites

The WO₃/TiO₂ nanocomposites were successfully prepared via a facile oxalic acid assisted hydrothermal process. The oxalic acid played a vital role on the preparation of WO₃/TiO₂ nanocomposites. Notably, it has been observed that the nanocomposites exhibited the wider absorption edge, and the higher photocatalytic activity, compared with pure TiO₂. In addition, the photocatalytic mechanism was proposed, and it elaborated that WO₃/TiO₂ nanocomposite promoted the separation of the photoproduction carriers, and improved photocatalytic activity. The WO₃/TiO₂ nanocomposite may have a potential application as a UV–visible photocatalyst.     

Facile fabrication of hierarchical BiVO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> heterostructures for enhanced photocatalytic activities under visible-light irradiation

BiVO₄/TiO₂ nanocomposites were fabricated by a facile wet-chemical process, followed by the synthesis of TiO₂ hierarchical spheres via hydrothermal method. The BiVO₄/TiO₂ nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results showed that prepared TiO₂ presented hierarchical spherical morphology self-assembled by nanoparticles and an anatase–brookite mixed crystal phase. The introduction of monoclinic BiVO₄ components retained the hierarchical structures and expanded the light response to around 510 nm. Type II BiVO₄/TiO₂ heterostructured nanocomposites exhibited improved photocatalytic degradation towards methylene blue under visible-light irradiation, especially for the composite photocatalysts with atomic Ti/Bi?=?10, which showed double degradation rate than that of pure BiVO₄. The enhanced photocatalytic mechanism of the heterostructured BiVO₄/TiO₂ nanocomposites was discussed as well.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Photoreduction synthesis of silver on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites and their catalytic activity for the degradation of methyl orange

This paper demonstrates the preparation of pure TiO₂, 40% of Bi₂O₃ in TiO₂ and Ag loaded Bi₂O₃/TiO₂ nanocomposites by the hydrothermal method followed by the photoreduction process. The crystal structure, morphology and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy respectively. The dispersion of Ag nanoparticles on the surface of Bi₂O₃/TiO₂ nanocomposites are found to bring the conduction band near to the valence band, resulting in the narrow band gap compared to pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The XRD analysis demonstrated that silver nanoparticles were dispersed finely on the surface of Bi₂O₃/TiO₂ nanocomposites. All the characterization results revealed that the Ag/Bi₂O₃/TiO₂ nanocomposites were smaller crystallite size, stronger absorbance in the visible region and greater surface area than pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The photoluminescence intensity decreases with an increase in the UV-illumination time of Ag loaded Bi₂O₃/TiO₂ revealing a decrease in the recombination rate of electron–hole pairs. In order to test them as a photocatalyst, methyl orange was used as a standard. The photocatalytic degradation of methyl orange shows that the ABT5 sample exhibits the maximum degradation efficiency of 99% within 180 min of irradiation.     

Preparation of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/CF composites for enhanced microwave absorbing performance

To meet the demand of electromagnetic absorption, cheap and easily available microwave absorbents are urgently required. As an important functional material, carbon fibers (CFs) have been widely reported, however, too high conductivity easily leads to the impedance mismatch, which is not favorable to the microwave absorbing performance (MAP). To address this challenge, in this study, novel TiO₂/Fe₃O₄/CF composites with tunable magnetic were synthesized by hydrothermal method and characterized by SEM, XRD, XPS and VSM. As absorbents, the minimum reflection loss (R_L) value is ??41.52 dB at a thickness of 2.1 mm, and the corresponding bandwidth with effective attenuation (R_L?<???10 dB) is up to 5.65 GHz (4.54–10.19 GHz). More importantly, the plausible mechanisms for the enhanced MAP are explored.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Ho<Subscript>2</Subscript>S<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> phase diagram

The Ho₂S₃-Ga₂S₃ system has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its phase diagram has been constructed. The system contains three ternary compounds: Ho₃GaS₆, HoGaS₃, and Ho₆Ga_10/3S₁₄. Their melting behavior has been studied for the first time. The compound Ho₆Ga_10/3S₁₄ melts congruently at 1435 K; Ho₃GaS₆ and HoGaS₃ melt incongruently at 1370 and 1250 K, respectively. The Ho₂S₃-Ga₂S₃ system is a pseudobinary join of the ternary system Ho-Ga-S. At room temperature, the β-Ga₂S₃-based solid solution extends to 1.5 mol % Ho₂S₃; the Ho₂S₃ solubility in γ-Ga₂S₃ is 10 mol %. The compounds HoGaS₃ and Ho₃GaS₆ crystallize in orthorhombic symmetry (Ho₃GaS₆: a = 10.40 Å, b = 13.20 Å, c = 6.44 Å, Z = 4; HoGaS₃: a = 6.8 Å, b = 9.92 Å, a = 3.08 Å, Z = 4). Ho₆Ga_10/3S₁₄ has a hexagonal structure (a = 9.62 Å, c = 6.04 Å).     

Preparation of sub-micron size anatase TiO<Subscript>2</Subscript> particles for use as light-scattering centers in dye-sensitized solar cell

The sub-micron size anatase TiO₂ particles with size about 0.2-0.3 μm were synthesized with basic peptizing agent and hydrothermal method and added into TiO₂ film as light scattering center. The addition of the sub-micron size anatase TiO₂ particles enhanced light scattering and dye adsorption abilities of the TiO₂ film. When the weight proportion of the sub-micron size/nano-size TiO₂ particles in the TiO₂ film attained to 1.25/10, the highest energy conversion efficiency about 7.41% was obtained, which was 23% enhancement comparing with the TiO₂ film containing pure nano-size TiO₂ particles. It presented an efficient way for improving the photovoltaic performance of dye-sensitized solar cell.     

Ab initio study of magnetism at the TiO<Subscript>2</Subscript>/LaAlO<Subscript>3</Subscript> interface

In this article, we study the possible relation between the electronic and magnetic structures of the TiO₂/LaAlO₃ interface and the unexpected magnetism found in undoped TiO₂ films grown on LaAlO₃. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO₃ has a layered structure along the (001) direction with alternating LaO and AlO₂ planes, with nominal charges of +1 and −1, respectively. As a consequence of that, an oxygen-deficient TiO₂ film with anatase structure will grow preferently on the AlO₂ surface layer. We have therefore performed ab initio calculations for superlattices with TiO₂/AlO₂ interfaces with interfacial oxygen vacancies. Our main results are that vacancies lead to a change in the valence state of neighbor Ti atoms but not necessarily to a magnetic solution and that the appearance of magnetism depends also on structural details, such as second neighbor positions. These results are obtained using both the local spin density approximation (LSDA) and LSDA + U approximations.     

MoS<Subscript>2</Subscript>/CoS<Subscript>2</Subscript> composites composed of CoS<Subscript>2</Subscript> octahedrons and MoS<Subscript>2</Subscript> nano-flowers for supercapacitor electrode materials

In pursuing excellent supercapacitor electrodes, we designed a series of MoS₂/CoS₂ composites consisting of flower-liked MoS₂ and octahedron-shaped CoS₂ through a facile one-step hydrothermal method and investigated the electrochemical performance of the samples with various hydrothermal time. Due to the coupling of two metal species and a big amount of well-developed CoS₂ and MoS₂, the results indicated that the MoS₂/CoS₂ composites electrodes exhibited the best electrochemical performance with a large specific capacitance of 490 F/g at 2 mV/s or 400 F/g at 10 A/g among all samples as the hydrothermal time reached 48 h (MCS₄₈). Furthermore, the retention of MCS₄₈ is 93.1% after 10000 cycles at 10 A/g, which manifests the excellent cycling stability. The outstanding electrochemical performance of MCS₄₈ indicates that it could be a very promising and novel energy storage material for supercapacitors in the future.