Guangqing Xu

Photocatalytic properties of Bi/BiOCl heterojunctions synthesized using an in situ reduction method

Bi nanoparticles are grown on BiOCl nanosheets via an in situ chemical reduction in a KBH4 aqueous solution. Bi/BiOCl nanosheets with different contents of Bi nanoparticles can be achieved by changing the concentration of the KBH4 solution. The structure, morphology, elemental composition and optical absorption performance are characterized using an X-ray diffraction diffractometer, a scanning electron microscope, a high resolution transmission electron microscope, an X-ray photoelectron spectrometer and a UV-Vis diffuse reflection spectrometer. The photocatalytic activities of the as-prepared photocatalysts are tested using the degradation of methyl orange under both UV light and visible light irradiation. Bi nanoparticles modified on BiOCl nanosheets not only enhance the photocatalytic activity under UV light irradiation, but also achieve visible light photocatalytic activity. The mechanism of the photocatalytic processes, such as optical absorption, charge transfer and surface reactions, for the Bi/BiOCl nanosheets are discussed in detail.

NiS and MoS2 nanosheet co-modified graphitic C3N4 ternary heterostructure for high efficient visible light photodegradation of antibiotic

The development of efficient solar driven catalytic system for the degradation of antibiotics has become increasingly important in environmental protection and remediation. Non-noble-metal NiS and MoS2 nanosheet co-modified graphitic C3N4 ternary heterostructure has been synthesized via a facile combination of hydrothermal and ultrasound method, and the ternary heterostructure has been utilized for photocatalytic degradation of antibiotic agents. The antibiotics of ciprofloxacin (CIP) and tetracycline hydrochloride (TC) were photodegraded by the hybrid under the visible light. The optimal photodegradation rate of the ternary heterostructure reaches about 96% after 2h irradiation, which is 2.1 times higher than that of pure g-C3N4 for TC degradation. The photocatalytic degradation rates of the ternary heterostructure for both CIP and TC obey the pseudo-first-order kinetic model. The enhanced visible light adsorption and charge separation efficiency contribute to the photocatalytic performance of the ternary heterostructure. This work provides new insights and pathways by which efficient degradation of antibiotics can be achieved and will stimulate further studies in this important field.

A flake-tube structured BiOBr–TiO2 nanotube array heterojunction with enhanced visible light photocatalytic activity

In this study, a new flake-tube structured BiOBr–TiO2 nanotube array (TNTA) heterojunction has been successfully prepared by anodization followed by a sequential chemical bath deposition (S-CBD) method. The as-prepared samples were characterized by X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen sorption. The photocatalytic activities toward degradation of methyl orange (MO) were evaluated under simulated sunlight. The transient photocurrent response under visible-light irradiation was measured to further confirm the photocatalytic activity enhancement. The results revealed that BiOBr nanoflakes were uniformly dispersed on both inner and outer walls of TiO2 nanotubes, and the BiOBr–TNTAs-2 displayed the best photocatalytic activities, favorable stability and highest photocurrent density among all the BiOBr–TNTAs heterostructured samples. The combined effects of several factors may contribute to the remarkably enhanced photocatalytic activity for the BiOBr–TNTAs-2 sample including an open tube-mouth structure, strong visible-light absorption by BiOBr, the formation of a BiOBr–TNTAs heterojunction and a larger specific surface area.

Uniformly Dispersed and Controllable Ligand-Free Silver-Nanoparticle-Decorated TiO2 Nanotube Arrays with Enhanced Photoelectrochemical Behaviors

Homogeneously dispersed silver nanoparticles (AgNPs) were successfully decorated onto the surface of TiO2 nanotube arrays (TNTA) by means of an in situ photoreduction method. TNTA films as supports exhibit excellent properties to prevent agglomeration of AgNPs, and they also avoid using polymer ligands, which is deleterious to enhancing the properties of the fabricated NPs. The silver particle size and its content could be controlled just by changing the immersion time. Detailed SEM and TEM analyses combined with energy-dispersive X-ray spectroscopy analyses with different immersion times (5, 10, 30, 60 min) have revealed the variation tendency. The prepared Ag/TNTA composite films were also characterized by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The UV/Vis diffuse reflectance spectra displayed a redshift of the absorption peak with the growth of AgNPs. The photocurrent response and the photoelectrocatalytic degradation of methyl orange (MO) were used to evaluate the photoelectrochemical properties of the fabricated samples. The results showed that the photocurrent response and photoelectrocatalytic activity largely depended on the loaded Ag particle size and content. TNTA films with a diameter of 17.92 nm and silver content of 1.15 at% showed the highest photocurrent response and degradation rate of MO. The enhanced properties could be attributed to the synergistic effect between AgNPs and TiO2. To make good use of this effect, particle size and silver content should be well controlled to develop the electron charge and discharge process during the photoelectrical process. Neither smaller nor larger AgNPs caused decreased photoelectrical properties.

Polypyrrole (PPy) nanowire arrays entrapped with glucose oxidase biosensor for glucose detection

Well aligned PPy nanowire arrays with diameter about 20 nm have been accomplished by electrochemical polymerization within anodized aluminum oxide (AAO) template. Glucose oxidase (GOx) was galvanostatically entrapped within the PPy nanoarrays. Scanning electron microscopy (SEM) confirmed the presence of PPy nanowire arrays. The electrochemical properties and response of the PPy-GOx nanowire arrays biosensor to glucose were characterized by cyclic voltammetry and amperometry. Evident current response can be observed in the cyclic voltammogram of the PPy-GOx nanowire arrays biosensor when exposed to glucose in a phosphate buffer solution. Amperometric detection of glucose was successfully achieved and the established optimum conditions with the PPy(GOx) biosensor were 0.4 M pyrrole, 200 U/ml GOx, applied current density of 0.1 mA/cm2, polymerization time of 600 s. The biosensor achieved a detection limit of 50 μM, a linear concentration range of 0.1 mM to 8 mM, and sensitivity of 9.97 μA cm#x2212;2 mM-1.

Photoelectrochemical activity and its mechanism of mesoporous TiO2 nanotube arrays prepared with chemical etching method

Novel mesoporous TiO2 nanotube arrays were synthesized by an anodization method combined with a chemical etching method for enhancing photoelectrochemical activity. Morphologies, structures and elemental compositions of the mesoporous TiO2 nanotube arrays were characterized with scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Photoelectrochemical properties were measured with cyclic voltammetry and chronoamperometry using an electrochemical workstation equipped with a UV LED light source (365 nm). Higher photoelectrochemical activities of the mesoporous TiO2 nanotube arrays can be achieved, with the highest photocurrent being triple that of un-etched TiO2 nanotube arrays. High electrochemical active surface area, optical absorption ability and charge transfer rate play key roles in enhancing the photoelectrochemical activity of the mesoporous TiO2 nanotube arrays.

Photoelectrochemical detection performance and mechanism discussion of Bi2O3 modified TiO2 nanotube arrays

Bi2O3 were deposited on anodized TiO2 nanotube arrays by chemical bath deposition combined with calcination. The structures, elemental compositions and morphologies of the products were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and high resolution transmission electron microscopy respectively. The photoelectrochemical behaviors of TiO2 and Bi2O3/TiO2 NTAs were measured by cyclic votammetry and amperometry combined with a UV LED source. Modification of Bi2O3 on TiO2 nanotube arrays was found to decrease the photocurrent in buffer solution and increase the current response to organics addition at the same time, both of which are benefit for photoelectrochemical detection of organic compounds with high sensitivities. The mechanisms of Bi2O3 modification were further studied by analyzing the whole photoelectrochemical processes, including the optical absorption, charges transfer and surface electrochemical reactions. The photoelectrochemical COD sensor based on the optimized Bi2O3/TiO2 NTAs can achieve the detection performances with sensitivity of 1.8033 μA (mg L−1)−1 and COD range of 0–288 mg L−1.

Graphitic carbon nitride nanosheets obtained by liquid stripping as efficient photocatalysts under visible light

Herein, well-scattered g-C3N4 nanosheets were obtained using a liquid stripping method in an ammonia solution at various temperatures. The phase structures, morphologies, and elemental compositions were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, and Fourier transform infrared spectroscopy. The nanosheets with sizes of several hundred nanometers can be obtained via liquid stripping. The photocatalytic performance of the g-C3N4 nanosheets was measured by degrading RhB under visible-light illumination. The g-C3N4 (30) nanosheets can achieve the highest degradation rate of 88% in 60 min, which is 5 times that of bulk g-C3N4. The mechanisms of the enhancement were studied by discussing the whole photocatalytic process. It has been observed that high specific surface area plays a key role in enhancing the photocatalytic performance.

Synthesis of α-Bi2Mo3O12/TiO2 Nanotube Arrays for Photoelectrochemical COD Detection Application

One-dimensional anodic TiO2 nanotube arrays hold great potential as a photoelectrochemical sensor for the determination of chemical oxygen demand (COD). In this work, we report a warm synthesis of modified TiO2 nanotube arrays with enhanced photoelectrochemical determination performance. Herein, a bismuth-based semiconductor (α-Bi2Mo3O12) was introduced into TiO2 nanotube arrays by sequential chemical bath deposition (CBD) at room temperature. Field-emission scanning electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy were used to investigate the morphologies, structures, and elemental analysis of the products. The photoelectrochemical properties of TiO2 and α-Bi2Mo3O12/TiO2 NTAs were measured by amperometry and cyclic votammetry methods. The α-Bi2Mo3O12/TiO2 nanotube arrays decrease the background photocurrent and increase the current response to organics at the same time, both of which are beneficial to enhancing the photoelectrochemical detection performance. The optimized α-Bi2Mo3O12/TiO2 NTAs with enhanced photoelectrochemical detection performance can achieve a detection sensitivity of 2.05 μA·cm-2/(mg·L-1) and a COD detection range of 0.366-208.9 mg/L respectively. With the α-Bi2Mo3O12 modification, the surface electrochemical reactions of TiO2 NTAs were regulated, the mechanisms of which were also further studied.

TiO2 nanotube arrays: a study on the surface electrochemical reactions during the photoelectrochemical process

The surface electrochemical reactions of TiO2 nanotube arrays (NTAs) corresponding to different active species of TiO2 NTAs (·OH, h+, and ·O2−) play key roles during the photoelectrochemical process. Effect of the active species and surface electrochemical reactions are studied by adding capture agents of isopropyl alcohol (IPA) for ·OH, ammonium oxalate ((NH4)2C2O2) for h+, and benzoquinone (BQ) for ·O2− radicals. The changes of photocurrent with addition of capture agents confirm the existence of ·OH, h+, and ·O2− during photoelectrochemical process. IPA and (NH4)2C2O2 additions are found to enhance the photocurrent by accelerating the consumption velocity of h+ indirectly and directly and restricting the chargers recombination. BQ can decrease the photocurrent stepwise to 0 due to the indirect consumption of e− on surface of TiO2 NTAs. The consumption of h+ by forming ·OH is 38% that of the whole consumption of h+. The ratio of chargers recombination is higher than 80.8% that of the whole photogenerated chargers.