Guoting Li

Degradation of Acid Orange 7 using magnetic AgBr under visible light: the roles of oxidizing species.

AgBr was creatively immobilized on a magnetic substrate (SiO(2)-coated Fe(3)O(4) nanoparticle, SFN) to achieve magnetic separation after visible light-driven photocatalytic oxidation (PCO). The resulted Ag/AgBr/SFN was characterized by TEM, vibrating sample magnetometer and other techniques. It is found that the average diameter of the Ag/AgBr/SFN particle is less than 20 nm. The typical superparamagnetic behavior of Ag/AgBr/SFN implies that the catalyst can be magnetically separated. The physicochemical features of the used Ag/AgBr/SFN after visible light irradiation were not dramatically changed by X-ray diffraction, UV-Vis diffuse reflectance spectra and Fourier transform-infrared analysis. SiO(2) interlayer was proven to slightly increase the degradation efficiency for an azo dye Acid Orange 7. UV-Vis spectra and HPLC analysis indicated that the dye was oxidized and decomposed. The photoactivity of Ag/AgBr/SFN was partly maintained after successive PCO under visible light. In order to evaluate the roles of e(-)-h(+) pairs and reactive oxygen species, the quenching effect was examined by employing Ag/AgBr/SFN and commercial TiO(2) (P-25) under visible light (lambda>400 nm) and UV-A irradiation, respectively. Active h(+) and the resulting (*)OH played the major roles for degradation. The effect of active h(+) and (*)OH were proven to be highly dependent on the concentration of photocatalysts. The effect of (*)OH was more obvious for P-25, while that of active h(+) was more predominant for Ag/AgBr/SFN.

Lead contamination and source in Shanghai in the past century using dated sediment cores from urban park lakes

Lead contamination becomes of importance to urban resident health worldwide, especially for child health and growth. Undisturbed lake sediment cores are increasingly employed as a useful tool to backdate environmental contamination history. Five intact sediment cores collected from lakes in five urban parks were dated using (210)Pb and analyzed for total Pb content and isotope ratio to reconstruct the Pb contamination history over the last century in Shanghai, China. Total Pb content in the sediment cores increased by about 2- to 3-fold since 1900s. The profile of Pb flux in each sediment core revealed a remarkable increase of Pb contamination in Shanghai over the past century, especially in the latest three decades when China was experiencing a rapid economic and industrial development. Significant correlations were found between Pb fluxes in sediment cores and Pb emission from coal combustion in Shanghai. Coal combustion emission dominated anthropogenic Pb sources during the past century contributing from 52% to 69% of total Pb in cores, estimated by a three-end member model of Pb isotope ratios. Leaded gasoline emission generally contributed <30% of total Pb, which was banned by 1997 in the Shanghai region. Our results implicate that coal combustion-based energy consumption should be replaced, or at least partially replaced, to reduce health risks of Pb contamination in Shanghai.

Effect of a magnetic field on the adsorptive removal of methylene blue onto wheat straw biochar.

Biochar pyrolyzed from wheat straw was innovatively used for the adsorptive removal of cationic dye methylene blue through exposure to a magnetic field. The adsorption capability of the biochar pyrolyzed at 200 °C exceeded that of samples pyrolyzed at higher temperatures. The surface acidic functional groups of wheat straw biochar were deduced to be more sensitive to the effects of the external magnetic field. The enhancement of the magnetic field achieved by increases in the initial dye concentration, and a decrease in the biochar dosage and solution pH, were more significant compared with those caused by other conditions. Kinetic experiments indicated that chemisorption occurred during adsorption. The qmax values for dye adsorption without, and with, an external magnetic field were found to be 46.6 and 62.5mg/g, respectively. These demonstrated that wheat straw biochar could be used for the efficient adsorption of pollutants when assisted by an external magnetic field.

Production and contribution of hydroxyl radicals between the DSA anode and water interface.

Hydroxyl radicals play the key role during electrochemical oxidation and photoelectrochemical oxidation. The production and effect of hydroxyl radicals on the interface between DSA anode and water was investigated by examining the quenching effect of iso-propanol on Orange II decolorization. We observed that with an increase in electrode potential from 4 to 12 V across electrodes at pH 7.0, the contribution percentage of hydroxyl radicals increased dramatically. More OH radicals were produced in acidic and alkaline conditions than at neutral conditions. At electrode potential of 4 V, the contribution percentage of hydroxyl radicals was obviously higher at near neutral pH conditions, while removal efficiency of Orange II achieved was the lowest concurrently. Finally, for photocatalytic oxidation, electrochemical oxidation, and photoelectrochemical oxidation using the same DSA electrode, the effect of hydroxyl radicals proved to be dominant in photocatalytic oxidation but the contribution of hydroxyl radicals was not dominant in electrochemical oxidation, which implies the necessity of UV irradiation for electrochemical oxidation during water treatment.

Mechanism of enhanced removal of quinonic intermediates during electrochemical oxidation of Orange II under ultraviolet irradiation

The effect of ultraviolet irradiation on generation of radicals and formation of intermediates was investigated in electrochemical oxidation of the azo-dye Orange II using a TiO2-modified β-PbO2 electrode. It was found that a characteristic absorbance of quinonic compounds at 255 nm, which is responsible for the rate-determining step during aromatics degradation, was formed only in electrocatalytic oxidation. The dye can be oxidized by either HO radicals or direct electron transfer. Quinonic compounds were produced concurrently. The removal of TOC by photo-assisted electrocatalytic oxidation was 1.56 times that of the sum of the other two processes, indicating a significant synergetic effect. In addition, once the ultraviolet irradiation was introduced into the process of electrocatalytic oxidation, the degradation rate of quinonic compounds was enhanced by as much as a factor of two. The more efficient generation of HO radicals resulted from the introduction of ultraviolet irradiation in electrocatalytic oxidation led to the significant synergetic effect as well as the inhibiting effect on the accumulation of quinonic compounds.

Effect of pyrolytic temperature on the adsorptive removal of p-benzoquinone, tetracycline, and polyvinyl alcohol by the biochars from sugarcane bagasse

Sugarcane bagasse was pyrolyzed under oxygen-limited conditions from 100 to 600 °C and used for the adsorptive removal of oxidation intermediate p-benzoquinone, tetracycline, and polyvinyl alcohol. The three organic pollutants have different polarities and solubilities. The carbon content increased from 57.7% of the raw bagasse to 75.3% of the biochar pyrolyzed at 600 °C, while the O content decreased from 13.2% to 6.1%. Accordingly, the biochar surface became more hydrophobic with increasing pyrolytic temperature. Interestingly, the adsorption affinity of biochars towards the three pollutants improved with an increase in the pyrolytic temperature. The adsorption of tetracycline molecules was almost unaffected by its being negatively charged with increasing solution pH. A mechanism of π-π electron-donor-acceptor interaction might contribute to the adsorption of tetracycline and p-benzoquinone, while H-bond interaction between polyvinyl alcohol and the biochar might be dominant during adsorption. The Elovich model fitted the kinetic model well, indicating that the diffusional rate-determining step was more pronounced. An isotherm study indicated that the contribution of partitioning was also dominant in the adsorption processes. Wide application of the prepared biochars is expected for the efficient adsorptive removal of organic pollutants.

Enhanced adsorptive performance of tetracycline antibiotics on lanthanum modified diatomite

A natural mineral diatomite was modified with lanthanum species using an ion exchange process to improve its adsorption performance for tetracycline removal. The prepared lanthanum-modified diatomite was characterized by scanning electron microscopy, X-ray diffractometry and Fourier transform infrared spectroscopy. The results showed that lanthanum was successfully immobilized onto diatomite, with a content of lanthanum element of about 1.5% (atomic ratio). The prepared adsorbent was evaluated for the adsorptive removal of tetracycline, and the adsorption isotherm, kinetics and mechanism were investigated. The adsorbent exhibited higher adsorption capacity than other adsorbents reported in literature, reaching 1056.9 mmol/kg. Langmuir model better fitted the experimental data than did other models. The removal of tetracycline was favorable at near neutral pH conditions. The tetracycline adsorption well followed pseudo-second-order kinetics model, and most of tetracycline was adsorbed within the initial 15 min. The increase in ionic strength reduced the tetracycline adsorptive removal, indicating that tetracycline adsorption on La-modified diatomite may be attributed to the formation of out-sphere surface complexes.

Enhanced Adsorption of Orange II Using Cationic Surfactant Modified Biochar Pyrolyzed from Cornstalk

As dissolution of raw biomass is serious when used as an adsorbent, the cheap biochar pyrolyzed from biomass might be a good matrix. Raw cornstalk biochar was intentionally modified by cetyltrimethylammonium bromide (CTAB) to prepare the composite adsorbent designed for the removal of negatively charged pollutants. After modification, the removal efficiency for anionic dye Orange II (ORII) increased from 46.9% of the virgin cornstalk biochar to 99.7% of the CTAB-modified cornstalk biochar. The uptake of ORII proved to be favorable under acidic conditions but unfavorable under alkaline conditions. By nonlinear simulation, the Elovich model was the best to describe the adsorption kinetics. For linear simulation of the kinetic data, the pseudo-second-order kinetic model fitted the experimental points better than the pseudo-first-order model. Kinetic analysis indicated that the ORII adsorption process on the CTAB-modified cornstalk biochar might be chemical adsorption accompanied by ion exchange. At 298 K, the maximal adsorption capacity of the modified biochar is 26.9 mg/g by the Langmuir model. The adsorption of ORII increased with a rise in the reaction temperature. The enthalpy and entropy of the adsorption process are calculated to be 38.45 KJ mol−1 and 185.0 J mol−1 K−1, respectively. The negative values of at 288, 298, and 308 K were −14.92, −16.50, and −18.62 KJ mol−1, respectively. The above thermodynamic analysis demonstrates that the adsorption process was endothermic and spontaneous.

Synergetic degradation of Acid Orange 7 by fly ash under ultrasonic irradiation

AbstractThe present work aimed to investigate the feasibility of fly ash, a by-product of coal combustion, for enhanced degradation of an azo dye Acid Orange 7 (AO7) under ultrasonic irradiation. X-ray diffraction and energy dispersive X-ray analysis indicated that ultrasonic irradiation did not change the crystal structure of fly ash. The decolorization efficiency of AO7 by the combined process could reach 76.7%, while ultrasonic process alone only removed 3.8% of AO7 within 60 min. A synergetic effect between fly ash and ultrasonic irradiation was firstly observed. The decolorization of AO7 fitted the first-order rate kinetics, and the K1 was 0.0246 min−1 for the combined process. Radical quenching experiment by iso-propanol (ISP) indicated that 24.8% of AO7 decolorization was contributed to hydroxyl radicals, indicating that the contribution of hydroxyl radicals was not as significant as expected. Theoretic analysis revealed that the sizes of fly ash cover the estimated resonance size of cavitation bub...

Effect of Alkali Treatment of Wheat Straw on Adsorption of Cu(II) under Acidic Condition

The convenient and feasible pretreatment method of alkali treatment is very common in the degradation process of wheat straw. However, its utilization in the pretreatment of wheat straw as alternative adsorbents for aqueous heavy metals remediation is rarely reported. The present study investigated the removal efficiency of Cu(II) ions using wheat straw with alkali pretreatment. The condition of alkali treatment on wheat straw was optimized with the adsorption capacity of Cu(II) as indicator using single-factor experiments. The influences of wheat straw dosages, pH values, contact time, and temperatures on adsorption performance for both untreated wheat straw (UWS) and alkali-treated wheat straw (AWS) were investigated. Results showed that the relatively large removal rate of Cu(II) could be obtained, and chemical behavior occurred during the adsorption process. Characteristic analysis found that the major function of alkali treatment to wheat straw was to introduce the hydroxy group, which resulted in the increase of -C-O- group. Although the adsorption capacity is not as high as the one of ligands supported adsorbents, the method is easy to operate and has a wide range of application; at the same time, it could realize both purposes of treating heavy metal pollution and solid wastes.