Jianyun Cao

Three-dimensional graphene oxide/polypyrrole composite electrodes fabricated by one-step electrodeposition for high performance supercapacitors

Three-dimensional (3D) graphene oxide/polypyrrole (GO/PPy) composite electrodes have been fabricated via one-step electrochemical co-deposition in an aqueous solution containing pyrrole monomers, GO and LiClO4. The concentration of GO in the solution plays an important role in controlling the morphologies of the as-deposited GO/PPy composites, and a relatively low concentration of 0.1 mg mL−1 is favorable for the formation of a 3D interconnected structure. The unique 3D interconnected structure ensures fast diffusion of electrolyte ions through the electrode. As a result, the GO/PPy composite electrode with a mass loading of 0.26 mg cm−2 exhibits the highest specific capacitance of 481.1 F g−1, while the electrode with a larger mass loading of 1.02 mg cm−2 delivers the best area capacitance of 387.6 mF cm−2, at a current density of 0.2 mA cm−2. Moreover, the GO/PPy composite electrodes exhibit good rate capability with capacitance retentions over 80% when the current density load increases from 0.2 to 10 mA cm−2. Both the aqueous and solid-state supercapacitors based on GO/PPy composite electrodes show excellent capacitive properties with good cycling stability, indicating their suitability for applications in energy storage and management.

H2Ti5O11·H2O nanorod arrays formed on a Ti surface via a hybrid technique of microarc oxidation and chemical treatment

H2Ti5O11·H2O nanorod arrays deposited on a titanium (Ti) surface have been fabricated via a hybrid technique of microarc oxidation (MAO) and chemical treatment. After the MAO treatment, an amorphous phase composed porous coating containing Ca, P, Si and Na elements was formed on the Ti surface. At the beginning of the chemical treatment, the elements of Ca, P, Si and Ti dissolved from the MAO coating into the solution. With a prolonged treatment time, nanorod arrays with a long aspect ratio were formed on the coating surface instead of the porous surface. The results revealed that the formed nanorods on the Ti surface were H2Ti5O11·H2O with the growth direction of [010]. This as-prepared Ti plate with a nanorod array surface exhibits a super-hydrophilic property, an excellent apatite-inducing ability and photocatalytic properties due to the existence of OH groups in the atomic structure of H2Ti5O11·H2O. The incorporated elements of Ca, P, Si and Na, and the corrosive attack of OH groups are the two factors for the formation of H2Ti5O11·H2O. The long and thin nature of the nanorods is attributed to the anisotropy of the atomic structure of H2Ti5O11·H2O with the lowest strain energy along the [010] direction based on the solid phase transformation.

Conformal coating containing Ca, P, Si and Na with double-level porous surface structure on titanium formed by a three-step microarc oxidation

A bioactive coating containing Ca, P, Si and Na elements with a porous surface structure has been fabricated on a titanium (Ti) plate by a three-step microarc oxidation. Randomly distributed gouges (80–200 μm) have been observed from the conformal MAO coating (with micro-scale pore size of 0.6–2 μm in morphology) covered Ti surface which exhibits double-level porous structure. Meanwhile, it is noticed that Ca, P, Si and Na elements have been incorporated into the MAO coating but show different oxidation states of elements between the flat surface and gouge surface. The XPS results reveal that Ti–OH and SiO2 gel have only formed on the gouge surface because of the decreased microarc oxidizing ability in the local area. Besides, the bioactivity of the different MAO step prepared Ti plates has been examined by simulated body fluid (SBF) immersion. As expected, the three-step MAO prepared Ti with double-level porous surface structure exhibits the best apatite-inducing ability thanks to the as-introduced Ti–OH and Si–OH groups.

Biocorrosion resistance of coated magnesium alloy by microarc oxidation in electrolyte containing zirconium and calcium salts

The key to use magnesium alloys as suitable biodegradable implants is how to adjust their degradation rates. We report a strategy to prepare biocompatible ceramic coating with improved biocorrosion resistance property on AZ91D alloy by microarc oxidation (MAO) in a silicate-K2ZrF6 solution with and without Ca(H2PO4)2 additives. The microstructure and biocorrosion of coatings were characterized by XRD and SEM, as well as electrochemical and immersion tests in simulated body fluid (SBF). The results show that the coatings are mainly composed of MgO, Mg2SiO4, m-ZrO2 phases, further Ca containing compounds involve the coating by Ca(H2PO4)2 addition in the silicate-K2ZrF6 solution. The corrosion resistance of coated AZ91D alloy is significantly improved compared with the bare one. After immersing in SBF for 28 d, the Si-Zr5-Ca0 coating indicates a best corrosion resistance performance.

The effect of NaOH concentration on the steam-hydrothermally treated bioactive microarc oxidation coatings containing Ca, P, Si and Na on pure Ti surface.

The microarc oxidation (MAO) coating covered pure Ti plates are steam-hydrothermally treated in autoclaves containing NaOH solutions with different concentrations of 0, 0.001, 0.01, 0.1 and 1mol·L(-1). Due to the composition of Ti, O, Ca, P, Si and Na elements in the MAO coating, anatase and hydroxyapatite (HA) crystals are generated from the previously amorphous MAO coating after the steam-hydrothermal treatment. Meanwhile, it is noticed that the amount of HA crystals increases but showing a decline trend in aspect ratio in morphologies with the increasing of NaOH concentration. Interestingly, the steam-hydrothermally treated MAO coatings exhibit better bonding strength with Ti substrate (up to 43.8±1.1MPa) than that of the untreated one (20.1±3.1MPa). In addition, benefiting from the corrosive attack of the dissolved NaOH in water vapor on the MAO coating, Ti-OH is also formed on the steam-hydrothermally treated MAO coating surface, which can trigger apatite nucleation. Thus, the steam-hydrothermally treated MAO coatings exhibit good apatite-inducing ability.

Electron beam “ballooned” carbon sphere derived from graphene oxide by a hydrazine assisted hydrothermal method

Self-assembled carbon spheres are synthesized by a hydrazine assisted hydrothermal method using graphene oxide as precursor. The as-prepared carbon spheres show dramatic shape changes (ballooning) in response to the electron beam as an external trigger.

The water-dependent decay mechanism of biaxially-oriented corona-treated polyethylene terephthalate films

In moist environments biaxially-oriented corona-treated polyethylene terephthalate (BOPET) film undergoes a decay in surface energy with time. This decay is a significant and well-known problem and it considerably restricts the industrial application of BOPET film. In the present study the decay effect and the dynamics of corona-treated BOPET film in an aqueous environment have been studied using water contact angle and variable angle X-ray photoelectron spectroscopy (XPS) measurements. In addition the surface decay mechanism of the corona-treated BOPET film in aqueous environments was analyzed and a molecular moving model for the decay mechanism is proposed.