Junmin Nan

One-pot solvothermal synthesis of three-dimensional (3D) BiOI/BiOCl composites with enhanced visible-light photocatalytic activities for the degradation of bisphenol-A

Three-dimensional (3D) BiOI/BiOCl composite microspheres with enhanced visible-light photodegradation activity of bisphenol-A (BPA) are synthesized by a simple, one-pot, template-free, solvothermal method using BiI(3) and BiCl(3) as precursors. These 3D hierarchical microspheres with heterojunction structures are composed of 2D nanosheets and have composition-dependent absorption properties in the ultraviolet and visible light regions. The photocatalytic oxidation of BPA over BiOI/BiOCl composites followed pseudo first-order kinetics according to the Langmuir-Hinshelwood model. The highest photodegradation efficiency of BPA, i.e., nearly 100%, was observed with the BiOI/BiOCl composite (containing 90% BiOI) using a catalyst dosage of 1 g L(-1) in the BPA solution (C(0)=20 mg L(-1), pH=7.0) under visible light irradiation for 60 min. Under these conditions, the reaction rate constant was more than 4 and 20 times greater than that of pure BiOI and the commercially available Degussa P25, respectively. The superior photocatalytic activity of this composite catalyst is attributed to the suitable band gap energies and the low recombination rate of the photogenerated electron-hole pairs due to the presence of BiOI/BiOCl heterostructures. Only one intermediate at m/z 151 was observed in the photodegradation process of BPA by liquid chromatography combined with mass spectrometry (LC-MS) analysis, and a simple and hole-predominated photodegradation pathway of BPA was subsequently proposed. Furthermore, this photocatalyst exhibited a high mineralization ratio, high stability and easy separation for recycling use, suggesting that it is a promising photocatalyst for the removal of BPA pollutants.

Efficient adsorption and visible-light photocatalytic degradation of tetracycline hydrochloride using mesoporous BiOI microspheres.

A novel microsphere-like BiOI hierarchical material was successfully synthesized by a one-step solution method at room temperature using polyvinylpyrrolidone (PVP) as structure directing reagent, its morphology, structure, surface area, photoabsorption were characterized, and the removal of tetracycline hydrochloride (TC) was evaluated under dark adsorption and visible light irradiation. It was shown that the BiOI microspheres formed in the precursor solution with PVP exhibit a mesoporous surface layer, 28.1m(2)g(-1) surface area, 1.91 eV band gap energy (E(g) value), and twofold removal ability to tetracycline hydrochloride (TC), i.e. adsorptive separation and visible light photocatalytic degradation. The adsorption process of TC on BiOI microspheres can be described by pseudo-second-order kinetics model and both Freundlich and Langmuir equations well described the adsorption isotherm but the former is better. More importantly, the BiOI microspheres exhibit an excellent photocatalytic degradation and mineralization capability to TC under visible light irradiation, which comes from its electronic band structure, high surface area and high surface-to-volume ratio. In addition, the BiOI microspheres are stable during the reaction and can be used repeatedly, showing promising prospect for the treatment of TCs in future industrial application.

Oxygen-rich bismuth oxyhalides: generalized one-pot synthesis, band structures and visible-light photocatalytic properties

A series of bismuth oxyhalides with controllable composition and band structure have been successfully synthesized by a facile and general one-pot hydrothermal route using Bi2O3 as the starting material; their band structures and visible-light-induced photocatalytic performances are investigated.

Hydrothermal-hydrolysis synthesis and photocatalytic properties of nano-TiO2 with an adjustable crystalline structure.

Tri-phase (anatase, rutile, and brookite), bi-phase (anatase and rutile), and mono-phase (rutile) TiO(2) nanomaterials with different morphologies were successively synthesized using a hydrothermal-hydrolysis method and adjusting the Ti(4+)/Ti(3+) molar ratio in a precursor solution. The properties of the fabricated nanomaterials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photocatalytic reaction, and other techniques. It has been shown that TiO(2) nanorods can be obtained by increasing the Ti(4+)/Ti(3+) molar ratio in a precursor solution from 1:0 to 0.3:0.7. TiO(2) nanoparticles are formed if the Ti(3+) fraction in the solution is further increased. The selective synthesis of TiO(2) nanomaterials is explained by a decrease in the reaction rate and by changes in acidity with increasing Ti(3+) content. The tri-phase nanorods and bi-phase nanoparticles synthesized with Ti(4+)/Ti(3+) molar ratios from 1:0 to 0.8:0.2 and 0.2:0.8 to 0:1, respectively, have a higher degradation ability with respect to methylene blue aqueous solutions under UV irradiation at ambient temperature compared to purely rutile TiO(2) nanorods synthesized with Ti(4+)/Ti(3+) molar ratios from 0.7:0.3 to 0.3:0.7. The high photocatalytic activity of the multi-phase TiO(2) samples is primarily attributed to their larger band gap and suppressed recombination of photo-generated electron-hole pairs.

Electrochemical chiral recognition of tryptophan using a glassy carbon electrode modified with β-cyclodextrin and graphene

AbstractWe report on a method for electrochemical enantioselective recognition of tryptophan (Trp) enantiomers. It is based on competitive host-guest interaction between a deoxy-(2-aminoethylamino)-β-cyclodextrin (CD) bound to graphene nanosheets and the Cu(II) complexes of the Trp enantiomers via a ligand exchange mechanism. Chiral recognition was investigated via cyclic voltammetry and electrochemical impedance spectroscopy. The results reveal that the CD bound to graphene displays a stronger interaction with the Cu(II) complex of L-Trp than to that of D-Trp. The method was applied to the determination of the ratio of Trp enantiomers in mixtures. FigureThe CD-GNs are dipped in D-Trp or L-Trp solution containing Cu(II), the complexes of metal ion with L-Trp caused more remarkable difference in the [Fe(CN)6]3−/4− than the complexes of metal ion with D-Trp.

Adsorptive separation and photocatalytic degradation of methylene blue dye on titanate nanotube powders prepared by hydrothermal process using metal Ti particles as a precursor.

Titanate nanotube powders (TNTPs) with the twofold removal ability, i.e. adsorptive separation and photocatalytic degradation, are synthesized under hydrothermal conditions using metal Ti particles as a precursor in the concentrated alkaline solution, and their morphology, structure, adsorptive and photocatalytic properties are investigated. Under hydrothermal conditions, the titanate nanotubes (TNTs) with pore diameter of 3-4nm are produced on the surface of metal Ti particles, and stacked together to form three-dimensional (3D) network with porous structure. The TNTPs synthesized in the autoclave at 130°C for 24h exhibits a maximum adsorption capability of about 197mg g(-1) in the neutral methylene blue (MB) solution (40mg L(-1)) within 90min, the adsorption process can be described by pseudo second-order kinetics model. Especially, in comparison with the adsorptive and the photocatalytic processes are performed in turn, about 50min can be saved through synchronously utilizing the double removal ability of TNTPs when the removal ratio of MB approaches 95% in MB solution (40mg L(-1)) at a solid-liquid (S/L) ratio of 1:8 under ultraviolet (UV) light irradiation. These 3D TNTPs with the twofold removal properties and easier separation ability for recycling use show promising prospect for the treatment of dye pollutants from wastewaters in future industrial application.

One-pot synthesis of micro/nano structured β-Bi2O3 with tunable morphology for highly efficient photocatalytic degradation of methylparaben under visible-light irradiation

β-Bi2O3 micro/nanostructures with tunable morphologies were synthesized via a one-pot solvothermal–calcining route, and their photocatalytic activity toward degrading methylparaben (MeP, a widely used preservative with estrogenic activity) was evaluated under visible-light (λ ≥ 420 nm) irradiation. The formation process of β-Bi2O3 catalysts can be described as reduction of Bi3+ through a solvothermal reaction, followed by oxidization of metal Bi via calcination in air. During this process, the organic reductants (single or a mixture of ethylene glycol, D-fructose, and ascorbic acid) play important roles in determining the final morphologies and structures of the materials. Photocatalytic tests reveal that MeP can be effectively degraded and mineralized by using synthetic β-Bi2O3 catalysts, and the reaction rate constant of an optimum sample is more than 25 and 160 times faster than a commercial Bi2O3 and synthetic N-TiO2, respectively. The superior photocatalytic activity of the optimum product is ascribed to its pure beta phase with a narrower band gap, good absorption of visible light, more efficient separation of electrons and holes, relatively higher BET specific surface area, and three-dimensional architectures, which favor more surface active sites and easier mass and photoinduced charge transportations. In addition, the main reactive oxygen species and possible degradation intermediates were detected, and the results suggest that photogenerated holes and superoxide radicals are the predominant species in the photochemical oxidation process.

Electrocatalytic oxidation and simultaneous determination of catechol and hydroquinone at a novel carbon nano-fragment modified glassy carbon electrode

In this paper, the electrochemical oxidation and differential pulse voltammetry (DPV) determination of catechol (CC) and hydroquinone (HQ) are studied at a novel carbon nano-fragment (CNF) modified glassy carbon electrode (CNF/GCE). The CNF modifier is prepared using the graphite cycled in lithium-ion batteries as the raw material through a ball mill process. The redox reactions of CC and HQ at the CNF/GCE are a two proton and electron process and controlled by the diffusion step. Compared to the GCE, the as-prepared CNF/GCE shows enhanced electrocatalytic activity and a peak potential difference of about 104 mV towards the oxidation of CC and HQ in a 0.1 mol L−1 acetate buffer solution (ABS, pH = 5.9), which makes it suitable for simultaneous determination of CC and HQ by DPV. Under the optimized conditions, the oxidation peak current of CC is linear over a range from 2.0 × 10−6 mol L−1 to 2.0 × 10−4 mol L−1 in the presence of 5.0 × 10−5 mol L−1 HQ with a detection limit of 1.0 × 10−7 mol L−1 (S/N = 3). Correspondingly, the oxidation peak current of HQ is linear over a range from 6.0 × 10−6 mol L−1 to 2.0 × 10−4 mol L−1 in the presence of 5.0 × 10−5 mol L−1 CC with a detection limit of 2.5 × 10−7 mol L−1 (S/N = 3). In addition, this CNF/GCE exhibits high selectivity, reproducibility and stability, showing its promising application prospect.

A glassy carbon electrode modified with electrochemically reduced graphene for simultaneous determination of guanine and adenine

In this paper, the direct electrochemical oxidation and differential pulse voltammetry (DPV) determination of guanine and adenine are studied by using an electrochemically reduced graphene oxide (er-GO) modified glassy carbon electrode (er-GO/GCE). Compared to the GCE and the GO/GCE, the as-prepared er-GO/GCE shows excellent electrocatalytic activity towards guanine and adenine, with an increase of oxidation current along with a negative shift of oxidation potential. Using the as-prepared er-GO/GCE, the simultaneous determination of guanine and adenine is successfully carried out, and the detection limits (based on S/N of 3) for guanine and adenine are 1.5 × 10−7 mol L−1 and 2.0 × 10−7 mol L−1, respectively. In addition, this er-GO/GCE exhibits a high selectivity, reproducibility and stability, and also can be used for the detection of guanine and adenine in the thermally denatured calf thymus DNA and urine, showing its promising application in the analysis of real samples.

Flower-like Bi4O5I2/Bi5O7I nanocomposite: facile hydrothermal synthesis and efficient photocatalytic degradation of propylparaben under visible-light irradiation

Nonstoichiometric bismuth oxyiodide materials have exhibited high potential for applications in visible-light photocatalytic environmental cleaning and solar energy conversion. Herein, novel Bi4O5I2/Bi5O7I nanocomposites, BiOI nanosheets, Bi4O5I2 nanoflowers, and Bi5O7I microfibers are synthesized by controlling the alkalinity of reaction solutions in a facile one-pot hydrothermal route. The as-prepared Bi4O5I2/Bi5O7I nanocomposite exhibits excellent visible-light photocatalytic performance for the degradation of propylparaben (PPB, a potential environmental contaminant structure that contains a benzene ring, hydroxyl, and carboxyl), which is approximately 32, 33, and 4 times higher than that of pure BiOI, Bi5O7I, and Bi4O5I2, respectively. The enhanced photocatalytic activity of the Bi4O5I2/Bi5O7I composite can be attributed to enhancement of charge separation by the formation of Bi4O5I2/Bi5O7I interfaces, more positive valence band edge potential at +2.18 V, good absorption from UV to visible light, three-dimensional flower-like morphology composed of number nanoflakes, and large specific surface area with mesoporous features. The band structures of Bi4O5I2 and Bi5O7I, the electrochemical oxidation behaviors of PPB, and the roles of the primary photogenerated oxidative species are analyzed, then a reasonable photocatalytic mechanism is proposed based on the experimental results. In addition, the as-synthesized Bi4O5I2/Bi5O7I heterojunction remains stable throughout photocatalytic process and can be used repeatedly, indicating its potential for practical applications.