Laisheng Li

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.

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.

Photochemical growth of nanoporous SnO2 at the air–water interface and its high photocatalytic activity

Nanoporous SnO2 containing two types of porous structures has been prepared at the air–water interface by a new photochemical route. This room temperature method is surfactant- and template-free, low-cost, and high-yield. Only SnSO4 and diluted H2SO4 aqueous solution were used as precursors. Under ultraviolet (UV) light irradiation, Sn2+ absorbs photons to produce metallic tin and stannic ions. The metallic tin reacts immediately with oxygen in the air to form SnO2. Meanwhile, a small amount of tin can also react with H2SO4 and is dissolved in the solution to form one type of nanoporous structure. The stannic ions are converted to insoluble H2SnO3 which dehydrates to form the other type of porous SnO2 structure during the subsequent drying process. The as-prepared porous SnO2 has higher photocatalytic activity than Degussa P25 for degrading methyl orange (MO) solution under the irradation of a xenon lamp.

Photocatalytic Ozonation of Dimethyl Phthalate over TiO2 Prepared by a Hydrothermal Method

TiO2 catalyst was prepared by two kinds of different methods. The photocatalytic activity of TiO2 prepared by the hydrothermal method is 2.5 times higher than that by sol-gel in degradation dimethyl phthalate (DMP). The combined photocatalysis with UV irradiation and ozonation (TiO2/UV/O3) process considerably improved mineralization and degradation of dibutyl phthalate compared to combined photocatalysis with UV irradiation (TiO2/UV) process, combined ozonation with UV irradiation (UV/O3) process and ozonation alone (O3) process. DMP can be quickly mineralized in TiO2/UV/O3, its mineralization process followed Langmuir-Hinshelwood model. Its rate constant k is 0.42 mg/ (L•min) and Langmuir adsorption coefficient K is 0.0417 L/mg.

Catalytic ozonation of dimethyl phthalate over cerium supported on activated carbon

Cerium supported on activated carbon (Ce/AC), which was prepared by dipping method, was employed to degrade dimethyl phthalate (DMP) in water. The mineral matter present in the activated carbon positively contributes to its activity to enhance DMP ozonation process. A higher dipping Ce(NO(3))(3) concentration and calcination process increase its microporous volume and surface area, and decreases its exterior surface area. The catalytic activity reaches optimal when 0.2% (w/w) cerium is deposited on activated carbon. Ce/AC catalyst was characterized by XRD, SEM and BET. The presence of either activated carbon or Ce/AC catalyst considerably improves their degradation and mineralization in the ozonation of DMP. During the ozonation (50mg/h ozone flow rate) of a 30 mg/L DMP (initial pH 5.0) with the presence of Ce/AC catalyst, TOC removal rate reaches 68% at 60 min oxidation time, 48% using activated carbon as catalyst, only 22% with ozonation alone. The presence of tert-butanol (a well known OH radical scavenger) strongly inhibits DMP degradation by activated carbon or Ce/AC catalytic ozonation. TOC removal rate follows the second-order kinetics model well. In the ozonation of DMP with 50mg/h ozone flow rate, its mineralization rate constant with the presence of Ce/AC catalyst is 2.5 times higher than that of activated carbon, 7.5 times higher than that of O(3) alone. Ce/AC catalyst shows the better catalytic activity and stability based on 780 min sequential reaction in the ozonation of DMP. Ce/AC was a promising catalyst for ozonizing organic pollutants in the aqueous solution.

Application of Mn/MCM-41 as an adsorbent to remove methyl blue from aqueous solution.

In this study, the application of Mn loaded MCM-41 (Mn/MCM-41) was reported as a novel adsorbent for methyl blue (MB) from aqueous solution. The mesoporous structure of Mn/MCM-41 was confirmed by XRD technique. Surface area, pore size and wall thickness were calculated from BET equation and BJH method using nitrogen sorption technique. FT-IR studies showed that Mn were loaded on the hexagonal mesoporous structures of MCM-41. It is found that the MCM-41 structure retained after loading of Mn but its surface area and pore diameter decreased due to pore blockage. Adsorption of MB from aqueous solution was investigated by Mn/MCM-41 with changing Mn content, adsorbent dosage, initial MB concentration, contact time, pH and the temperature. Under the chosen condition (25°C, 0.02 g adsorbent dosage, 6.32 pH, 50 mg L(-1) MB, 1 wt.% Mn), a high MB adsorption capacity (45.38 mg g(-1)) was achieved by Mn/MCM-41 process at 120 min, 8.6 times higher than MCM-41. The electrostatic interaction was considered to be the main mechanism for the dye adsorption. The experimental data fitted well to Freundlich and Dubinin-Radushkevich isotherms. The adsorption of MB on Mn/MCM-41 followed pseudo-second-order kinetics. Thermodynamic parameters suggested that the adsorption process is endothermic and spontaneous.

Equilibrium, kinetics and thermodynamic studies for sorption of chlorobenzenes on CTMAB modified bentonite and kaolinite.

The sorption of chlorobenzenes (CBs) by cetyltrimethylammonium bromide (CTMAB) modified bentonite and kaolinite was investigated. The sorption isotherms for CBs were nearly linear, suggesting that sorption could be described by a distribution process. The distribution coefficient (K(d)) was primarily affected by the amount of sorbed surfactant. The organic carbon normalized sorption coefficient (K(oc)), however, was particularly dependent on arrangement of the surfactant cations. The K(d) of CBs was larger for CTMAB-bentonites than that for CTMAB-kaolinites, while the case for K(oc) was opposite. Thus, the clay mineral structure and morphology had a considerable influence on the surfactant arrangement, which was responsible for the partitioning of CBs. The sorption of CBs onto both CTMAB-bentonites and CTMAB-kaolinites followed pseudo-second-order kinetics. The intra-particle diffusion model for sorption was also investigated and compared to identify sorption mechanism. The sorption of CBs both on CTMAB-bentonites and CTMAB-kaolinites was exothermic in nature and accompanied by an increase in entropy and a decrease in Gibbs energy in the temperature range of 15-35 degrees C. The results indicated that CBs strongly interacted with CTMAB modified bentonite and kaolinite.

Photochemical growth of cadmium-rich CdS nanotubes at the air–water interface and their use in photocatalysis

Cadmium-rich CdS nanotubes were directly obtained at the air–water interface by a new photochemical route. Under ultraviolet light irradiation, branch-like lamellas were first formed on the surface of the precursor solution, and then they bent into nanotubes because of the composition difference between the two sides of lamellas during photochemical reactions and sulfur–air reactions. A typical nanotube has one spherical seal and one open end. Most of the cadmium was contained in the tubes and a little was doped in the tube-walls during their formation. Such nanotubes showed higher photocatalytic activity than the corresponding pure CdS nanotubes in the photodegradation of methylene blue because of the existence metal cadmium. This route is green, template/surfactant-free, reproducible and can be extended to prepare other binary compound semiconductor nanostructures containing elements that can react either with air or another gas.

Enhanced photocatalytic ozonation of organics by g-C3N4 under visible light irradiation

Graphitic carbon nitride (g-C3N4) was employed as the active photocatalyst in the photocatalytic ozonation coupling system in the present study. g-C3N4 was prepared by directly heating thiourea in air at 550°C. XRD, FT-IR, UV-vis was used to characterize the structure and optical property. Oxalic acid and bisphenol A were selected as model substances for photocatalytic ozonation reactions to evaluate the catalytic ability of g-C3N4 (g-C3N4/Vis/O3). The results showed that the degradation ratio of oxalic acid with g-C3N4/Vis/O3 was 65.2% higher than the sum of ratio when it was individually decomposed by g-C3N4/Vis and O3. The TOC removal of biphenol A with g-C3N4/Vis/O3 was 2.17 times as great as the sum of the ratio when using g-C3N4/Vis and O3. This improvement was attributed to the enhanced synergistic effect between photocatalysis and ozonation by g-C3N4. Under visible light irradiation, the photo-generated electrons produced on g-C3N4 facilitated the electrons transfer owing to the more negative conduction band potential (-1.3V versus NHE). It meant that the photo-generated electrons could be trapped by ozone and reaction with it more easily. Subsequently, the yield of hydroxyl radicals was improved so as to enhance the organics degradation efficiency. This work indicated that metal-free g-C3N4 could be an excellent catalyst for mineralization of organic compounds in waste control.

Mechanism for enhanced degradation of clofibric acid in aqueous by catalytic ozonation over MnOx/SBA-15

Comparative experiments were conducted to investigate the catalytic ability of MnO(x)/SBA-15 for the ozonation of clofibric acid (CA) and its reaction mechanism. Compared with ozonation alone, the degradation of CA was barely enhanced, while the removal of TOC was significantly improved by catalytic ozonation (O3/MnO(x)/SBA-15). Adsorption of CA and its intermediates by MnO(x)/SBA-15 was proved unimportant in O3/MnO(x)/SBA-15 due to the insignificant adsorption of CA and little TOC variation after ceasing ozone in stopped-flow experiment. The more remarkably inhibition effect of sodium bisulfite (NaHSO3) on the removal of TOC in catalytic ozonation than in ozonation alone elucidated that MnO(x)/SBA-15 facilitated the generation of hydroxyl radicals (OH), which was further verified by electron spin-resonance spectroscopy (ESR). Highly dispersed MnO(x) on SBA-15 were believed to be the main active component in MnO(x)/SBA-15. Some intermediates were indentified and different degradation routes of CA were proposed in both ozonation alone and catalytic ozonation. The amounts of small molecular carboxylic acids (i.e., formic acid (FA), acetic acid (AA) and oxalic acid (OA)) generated in catalytic ozonation were lower than in ozonation alone, resulting from the generation of more OH.