Sonication-polished anodic TiO<Subscript>2</Subscript> nanotube array-based photoanode for efficient solar energy conversion

In this work, the capping layer atop anodic TiO₂ nanotube arrays (NTAs), which hinders filling of other guest materials and transport of charge carriers, is discerned to be TiO₂ nanotapes. Then, it is completely removed by a novel sonication-polishing (SP) treatment, after which Sb₂S₃ is subsequently introduced to fill the nanotubes by chemical bath deposition. The morphological, structural, and optical properties of the SP-treated TiO₂ NTAs and TiO₂ NTAs/Sb₂S₃ heterogeneous structures are characterized systematically. The results indicate that SP treatment opens the tops of nanotubes with diameters of ～120 nm, which endure a phase conversion from amorphous to anatase after calcination at 450 °C; besides, stibnite Sb₂S₃ with a band gap of ～1.75 eV inside the TiO₂ networks is formed upon heat treatment at 330 °C in Ar, which enhances the absorption in visible light range. The photoelectrochemical (PEC) and photovoltaic properties for the SP-treated TiO₂ NTAs are investigated. Results shows that the photoresponse of TiO₂ NTAs is improved by the SP treatment, and the photocurrent for the TiO₂ NTAs/Sb₂S₃ electrode is substantially enhanced as compared to the bare TiO₂ one. A high efficiency of 6.28 % is achieved in a TiO₂ NTAs/Sb₂S₃ PEC cell. In addition, charge recombination in the photoanode of dye-sensitized solar cells (DSSCs) is observed to be greatly retarded by using the SP-treated TiO₂ NTAs as compared to TiO₂ nanoparticles (NPs). Thus, the SP anodic TiO₂ NTAs are promising in applications in various PEC areas such as photocatalysis and sensitized solar cells.     

Supercapacitive performance of homogeneous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> nanotube arrays enhanced by carbon layer and oxygen vacancies

Self-supported and binder-free electrodes based on homogeneous Co₃O₄/TiO₂ nanotube arrays enhanced by carbon layer and oxygen vacancies (Co₃O₄/co-modified TiO₂ nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co₃O₄ nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co₃O₄ nanoparticles, a maximum specific capacitance of 662.7 F g^?1 can be achieved, which is much higher than that of Co₃O₄ decorated on pristine TNAs (Co₃O₄/TNAs; 166.2 F g^?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g^?1, revealing the excellent long-term electrochemical cycling stability of Co₃O₄/m-TNAs. Thus, this kind of heterostructured Co₃O₄/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.     

Sr,Zn co-doped TiO<Subscript>2</Subscript> xerogel film made of uniform spheres for high-performance dye-sensitized solar cells

This study comes up with the facile preparation of Sr,Zn co-doped TiO₂ xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs). The film contains 2.5-μm-diameter spheres assembled from 60 nm nanoparticles. X-ray photoelectron spectroscopy (XPS) shows that Sr²⁺ and Zn²⁺ ions to be well incorporated into the TiO₂ crystal lattice without forming specific strontium and zinc compositions. The crystallite size, phase composition, and band structure of the spheres depend on the dopants concentration. Isolated energy levels near valence band as a result of the foreign ions introduction improve the photocatalytic activity of the prepared TiO₂ spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 0.4 at.% Zn showed the highest power conversion efficiency of 7.87 % and short circuit current density of 18.75 mA cm^?2 thanks to lower charge transfer resistance (2.16 Ω cm²), lower electron transit time (1.19 ms), and higher electron diffusion coefficient (18.1 × 10⁴ cm² S^?1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of the simultaneous introduction of alkaline earth ions and transition ions into TiO₂ xerogel films will open up a new insight into the fabrication of high performance DSCs.     

Synthesis and thermal decomposition of neodymium(III) peroxotitanate to Nd<Subscript>2</Subscript>TiO<Subscript>5</Subscript>

Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd₂TiO₅. The last one possesses numerous valuable electrophysical properties. TiCl₄, Nd(NO₃)₃·6H₂O and H₂O₂ in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH₃. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O composition. The absorption band observed in IRS at 831 cm^?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm^?1—terminal groups Ti–OH and at 1491 and 1384 cm^?1—the bridging OH^?-groups Ti–O(H)–Ti. Nd₂TiO₅ was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O to Nd₂TiO₅ was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd₄[Ti₂O₄(OH)₁₂] is obtained. From 208 to 390 °C, the terminal OH^?-groups are separated and Nd₄[Ti₂O₇(OH)₆] is formed. In the range of 390–824 °C, the bridging OH^?-groups are completely decomposed to Nd₂TiO₅. The optimal conditions for obtaining nanocrystalline Nd₂TiO₅ are 900 °C for 6 h and 20–80 nm.     

Hydrothermal synthesis of brookite TiO<Subscript>2</Subscript> nanoparticles for dye-sensitized solar cell

We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO₂) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO₂ thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO₂ sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I₂ + 0.1 M KCl) electrolyte at 40 mW cm^?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.

Open image in new window

Graphical abstract ?

     

Study of quasi-solid electrolyte in dye-sensitized solar cells using surfactant as pore-forming materials in TiO<Subscript>2</Subscript> photoelectrodes

A novel polymer gel electrolyte was used to improve the performance and long-term stability in dye-sensitized solar cells (DSSCs). The polymer gel electrolyte (PGE) was prepared by mixing 5 wt% poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and 2 % TiO₂ nanoparticles. The conductivity of PGE with P25 reached 9.98 × 10^?3 S/cm, which increased by 34.9 % compared with 7.40 × 10^?3 S/cm of PGE without P25, and the diffusion coefficient was also increased by 19.0 %. Different photoelectrodes were obtained by using three kinds of surfactants (cetylamine, octadecylamine, and P123) as pore-forming materials, and their morphologies were contrasted through scanning electron microscopy (SEM). The results showed that gel electrolyte can increase the short-circuit current density (J _sc) from 11.01 to 12.99 mA/cm² in DSSCs. Moreover, unlike the liquid electrolyte, the gel electrolyte is more conducive to the TiO₂ photoelectrodes with larger pores. In conclusion, the efficiency of DSSC with gel electrolyte and P123 as pore-forming material was 6.73 %, which was 12 % higher than the liquid electrolyte in the same test condition. In addition, the sealed gel electrolyte DSSCs showed better stability than did liquid electrolyte DSSCs during nearly 600 h.     

Interlaced polyaniline/carbon nanotube nanocomposite co-electrodeposited on TiO<Subscript>2</Subscript> nanotubes/Ti for high-performance supercapacitors

A series of PANI-CNTs/TiO₂ nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO₂ nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO₂ nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO₂ nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO₂ nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO₂ nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm^?2 with 90% retention after 1000 cycles) compared to the PANI/TiO₂ nanotubes/Ti (70 mF cm^?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm^?2, indicating its great potential for supercapacitor applications.

Open image in new window

Graphical abstract Interlaced polyaniline/carbon nanotube nanocomposite electrodeposited on TiO₂ nanotubes/Ti

     

Glucose biosensors based on Ag nanoparticles modified TiO2 nanotube arrays

A GOx/Ag/TiO₂ glucose biosensor was achieved by photoreducing Ag nanoparticles on TiO₂ nanotube arrays (NTAs) following with adsorption of GOx. The morphology, structure, and element component of Ag/TiO₂ NTAs were characterized by scanning electron microscope, transmission electron microscope, and X-ray diffraction. Ag nanoparticles were uniformly deposited on surface of TiO₂ NTAs with average size of 15 nm and the size and distribution changed with the immersing time of TiO₂ NTAs in AgNO₃ aqueous solution. Electrochemical properties of Ag/TiO₂ NTAs were characterized by cyclic voltammetry and amperometric detection of H₂O₂, revealing that TiO₂ NTAs with immersing time of 30 min achieve the best electrochemical activity. The GOx/Ag/TiO₂ NTAs biosensor with optimum conditions achieves a sensitivity of 0.39μA mM^?1 cm^?2 with liner range from 0.1 to 4 mM.     

Photoelectrochemical starch-O<Subscript>2</Subscript> biofuel cell consisting of chlorophyll derivative-sensitized TiO<Subscript>2</Subscript> anode and enzyme-based cathode

A new photoelectrochemical starch-O₂ biofuel cell has been developed, consisting of chlorin-e₆ (Chl-e₆) adsorbed on a TiO₂ layer onto an optical transparent conductive glass electrode as a photoanode, bilirubin oxidase (BOD)-modified electrode as a cathode, and a solution containing starch, glucoamylase, glucose dehydrogenase and NAD⁺ as fuel. The short-circuit photocurrent and the open-circuit photovoltage of this cell are 9.0 μA cm^?2 and 530 mV, respectively. The maximum power, FF and \(\eta\) values are estimated to be 1.7 μW cm^?2, 0.36 and 0.0017 %, respectively. Thus, this new type of the photochemical starch-O₂ biofuel cell has been developed by using the visible light photosensitization of Chl-e₆ on a TiO₂ film photoanode.     

Photodegradation of 2-nitrophenol catalyzed by CoO, CoS and CoO/CoS nanoparticles

The nanoparticles of CoO, CoS and CoO/CoS composite are synthesized using precipitation method. The X-ray diffraction, UV–Vis absorption spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and FT-IR spectroscopy are used to characterize the prepared nanoparticles. The EDX analysis shows the formation of CoO_0.67S_0.33 composite. The XRD pattern indicates the hexagonal structure for nanocomposite. The formation of Co–O and Co–S bonds is confirmed by FT-IR spectra. The band-gap energies of 2.97, 3.06 and 2.91 eV are obtained from UV–Vis spectra of CoO, CoS and CoO/CoS nanoparticles, respectively. The results of photodegradation of 2-nitrophenol show that the photoreactivity order of nanocatalysts is CoO/CoS > CoO > CoS. The pseudo first-order kinetic rate constants of 6.4 × 10^?3, 4.3 × 10^?3 and 12.2 × 10^?3 min^?1 are obtained for CoO, CoS and CoO/CoS nanoparticles, respectively, at photodegradation reaction conditions of pH 10, 30 mg/L of 2-NP and 1.3 g/L of the catalyst. The proposed nanocomposite shows an acceptable reusability and stability against photocorrosion in four-cycle photodegradation experiments.     

A P/N type compounded Cu<Subscript>2</Subscript>O/TiO<Subscript>2</Subscript> photo-catalytic membrane for organic pollutant degradation

A heterojunction thin film consisting of n-type titanium dioxide (TiO₂) and p-type cuprous oxide (Cu₂O) was fabricated on an FTO conducting glass. The TiO₂ films were grown on the FTO glass by sol–gel and spray pyrolysis methods, and Cu₂O was deposited on it via the hydrothermal method. The morphology, crystalline structure, and optical absorption characteristics were studied by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible diffuse reflectance spectrum, respectively. The results show that the surface of the Cu₂O/TiO₂ film was composed of net and large grains, which contributed to a large specific surface area. The crystal phase of the TiO₂ in the Cu₂O/TiO₂ film remained anatase. The crystal phase of the Cu₂O could not be detected as it is found in traces. The Cu₂O/TiO₂ film had a stronger optical absorption ability than the pure TiO₂ film. To investigate catalytic activity, a photocatalytic degradation experiment of the Cu₂O/TiO₂ film was performed in a homemade thin-layer micro-reactor. The photocatalytic degradation of methylene blue increased with increasing amounts of deposited Cu₂O until a maximum limit was reached. The photocatalytic activity might have declined with an increase in Cu₂O content. The metallic oxide has the potential to screen other photocatalysts from the UV source.     

A selective and sensitive sensor based on highly dispersed cobalt porphyrin-Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-graphene oxide nanocomposites for the detection of methyl parathion

A new type of graphene-Co₃O₄ functionalized porphyrin was synthesized and used for selective and sensitive detection of methyl parathion (MP). Co₃O₄ nanoparticles were firstly modified onto graphene oxide sheets and the porphyrin/Co₃O₄/graphene nanocomposites were then synthesized by self-assembly decoration of anion porphyrin on Co₃O₄-modified graphene sheets by π–π stacking. By dexterously controlling the electrochemical reduction variables and optimizing the electrode preparation parameters, with the satisfactory conductivity, strong adsorption toward MP, the developed novel sensor fabricated with the as-synthesized nano-assembly for determination of MP shows some satisfactory properties such as a wide linear concentration range (from 4.0?×?10^?7 M to 2.0?×?10^?5 M), low detection limit (1.1?×?10^?8 M), favorable repeatability, long-time storage stability, and satisfactory anti-interference ability. It also had high precision for the real sample analysis, which indicated the good perspective for field application.     

Optical,electrical, and electrochemical behavior of p-type nanostructured SnO<Subscript>2</Subscript>:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO₂ thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO₂ thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO₂ sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO₂ thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni²⁺ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm² (V s)^?1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO₂ thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2?×?10^?15 to 6.5?×?10^?15 cm² s^?1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.     

Synthesis and charge-discharge performance of Li<Subscript>5</Subscript>SiN<Subscript>3</Subscript> as a cathode material of lithium secondary batteries

Li₅SiN₃ crystals are synthesized by direct reaction between Li₃N and Si₃N₄ with the molar ratio Li₃N/Si₃N₄ of 10:1. Reaction is performed at 1073 K for 1 h under a nitrogen atmosphere of 700 Torr. The lattice constant determined by the X-ray powder diffraction method is 4.718 Å. Four broad Raman peaks are observed at 196, 286, 580, and 750 cm^?1. By analogy with LiMgN, the broad peak at 580 cm^?1 with a half width of 140 cm^?1 is attributed to homogenously random distribution of Li and Si atoms. The band gap of Li₅SiN₃ is found to be a direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. Comparison with the conventional cathode materials for lithium ion batteries, this gap value is close to d-d transition energy of Mn in LiMn₂O₄ (1.63 eV or 2.00 eV) and that of Co in LiCoO₂ (2.1 eV), suggesting that Li₅SiN₃ is a possible cathode material. The 5 × 5 mm²-sized lithium secondary battery of Li₅SiN₃ cathode/propylene carbonate + LiClO₄ electrolyte/Li anode structure shows a discharge capacity of 2.4 μAh cm^?2 for a discharge current of 1.0 μA.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Preparation and methane adsorption of two-dimensional carbide Ti<Subscript>2</Subscript>C

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti₂C, a member of MXenes), formed by exfoliating Ti₂AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti₂C with O termination has a specific surface area (SSA) of 671 m² g^?1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti₂C with mesopores shown methane capacity of 11.58 cm³ (STP: 0 °C, 1 bar) g^?1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m² g^?1. For Ti₂C sample intercalated with NH₃·H₂O, the adsorbed amount was increased to 16.81 cm³ (STP) g^?1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti₂C was increased to 52.76 cm³ (STP) g^?1. For fully exfoliated Ti₂C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v^?1. Ti₂C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.     

Assessment of operating parameters for photocatalytic degradation of a textile dye by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/clinoptilolite nanocatalyst using Taguchi experimental design

In the current study, a nanophotocatalyst doped with of TiO₂ and Fe₂O₃ nanoparticles supported on Iranian clinoptilolite was synthesized and characterized by XRD, XRF, SEM, and EDX analyses. The results suggested the successful loading of TiO₂ and Fe₂O₃ nanoparticles onto the surface of clinoptilolite. The SEM images confirmed the average size of nanoparticles deposited on zeolite, which was about 20–40 nm. Furthermore, application of the synthesized photocatalyst in photocatalytic degradation of Acid Black 172 dye was studied using the Taguchi method and the chosen parameters were as follows: pH (2–7), dye concentration (50–200 mg/l), irradiation time (30–120 min), and catalyst dosage (0.5–1.5 g/l). The results indicate that dye concentration, pH, and irradiation time are respectively the most effective factors in these experiments while with the minimum dosage of the catalyst (0.5 g/l), up to 90 % removal efficiency could be achieved. The optimum value for each parameter was pH = 2, dye concentration = 50 mg/l, catalyst dosage = 1 g/l and irradiation time = 60 min, and the dye removal efficiency reached up to 100 % at these optimal conditions. Furthermore, after five-times recycling and reusing the catalyst, the efficiency of the photocatalytic degradation was reduced from 91.5 to 65.9 %, which is still an acceptable value.     

Synthesis,Characterization and Photocatalytic Application of TiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> Nanocomposite Obtained Under Non-thermal Plasma Condition at Atmospheric Pressure

A plasma-assisted synthesis of TiO₂/SnO₂ nanocomposite is described. In this approach, a precursor containing a mixture of [TiCl₃ and SnCl₂] exposed to electric discharge was oxidized by plasma-generated reactive species (HO^·/H₂O = 2.85 eV/SHE). SnO₂ microstructures with a diameter of 10–40 µm were coated by thin layers TiO₂ nanorods with mean diameter of 6–8 nm. The obtained TiO₂/SnO₂ nanocomposite was characterized by transmission and scanning electron microscopy, X-ray diffraction and Fourier transform infrared. TiO₂/SnO₂ nanocomposite was found to be a promising new material for the photocatalytic discoloration of aqueous Remazol Brilliant Blue-R dye under daylight and UVA light sources, due to the combined effects of large specific surface area and heterojunction which efficiently separates the electron–hole pairs delaying the charge recombination. The leaching test indicated that the nanocomposite is stable easily reusable.     

Nanofibers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C@MWCNTs as the cathode material for lithium-ion batteries

Vanadium pentoxide (V₂O₅) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V₂O₅ nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V₂O₅ nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g^?1 (between 2.0 and 4.0 V vs. Li/Li⁺), good cycling stability (223 mAh g^?1 after 50 cycles), and good rate performance (~?150 mAh g^?1 at 2 A g^?1). This can attribute to the carbon wrapped on the V₂O₅ nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V₂O₅ coated by carbon layer and composited with MWCNT NFs (V₂O₅/C@MWCNT NFs) to ensure the material is more stable.     

Ni<Subscript>0.37</Subscript>Co<Subscript>0.63</Subscript>S<Subscript>2</Subscript>-reduced graphene oxide nanocomposites for highly efficient electrocatalytic oxygen evolution and photocatalytic pollutant degradation

A series of Ni_0.37Co_0.63S₂-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo₂S₄ to Ni_0.37Co_0.63S₂ and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm^?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec^?1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.

Open image in new window

Graphical abstract A series of Ni_0.37Co_0.63S₂-reduced graphene oxide nanocomposites with different graphene contents has been successfully prepared and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The NCS@rGO-2 catalyst-modified stainless steel wire mesh (SSWM) electrode delivers a stable current density of 10 mA cm^?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec^?1. At the same time, the NCS@rGO-2 catalyst is also first investigated as an efficient photocatalyst for degradation of MB.