Yaocheng Deng

Enhanced photocatalytic degradation of norfloxacin in aqueous Bi2WO6 dispersions containing nonionic surfactant under visible light irradiation.

Photocatalytic degradation is an alternative method to remove pharmaceutical compounds in water, however it is hard to achieve efficient rate because of the poor solubility of pharmaceutical compounds in water. This study investigated the photodegradation of norfloxacin in a nonionic surfactant Triton-X100 (TX100)/Bi2WO6 dispersion under visible light irradiation (400-750nm). It was found that the degradation of poorly soluble NOF can be strongly enhanced with the addition of TX100. TX100 was adsorbed strongly on Bi2WO6 surface and accelerated NOF photodegradation at the critical micelle concentration (CMC=0.25mM). Higher TX100 concentration (>0.25mM) lowered the degradation rate. In the presence of TX100, the degradation rate reached the maximum value when the pH value was 8.06. FTIR analyses demonstrated that the adsorbed NOF on the catalyst was completely degraded after 2h irradiation. According to the intermediates identified by HPLC/MS/MS, three possible degradation pathways were proposed to include addition of hydroxyl radical to quinolone ring, elimination of piperazynilic ring in fluoroquinolone molecules, and replacement of F atoms on the aromatic ring by hydroxyl radicals.

Rapid adsorption of 2,4-dichlorophenoxyacetic acid by iron oxide nanoparticles-doped carboxylic ordered mesoporous carbon.

The ordered mesoporous carbon composite functionalized with carboxylate groups and iron oxide nanoparticles (Fe/OMC) was successfully prepared and used to adsorb 2,4-dichlorophenoxyacetic acid (2,4-D) from wastewater. The resultant adsorbent possessed high degree of order, large specific surface area and pore volume, and good magnetic properties. The increase in initial pollutant concentration and contact time would make the adsorption capacity increase, but the pH and temperature are inversely proportional to 2,4-D uptake. The equilibrium of adsorption was reached within 120 min, and the equilibrated adsorption capacity increased from 99.38 to 310.78 mg/g with the increase of initial concentration of 2,4-D from 100 to 500 mg/L. Notablely, the adsorption capacity reached 97% of the maximum within the first 5 min. The kinetics and isotherm study showed that the pseudo-second-order kinetic and Langmuir isotherm models could well fit the adsorption data. These results indicate that Fe/OMC has a good potential for the rapid adsorption of 2,4-D and prevention of its further diffusion.

Catalytic reduction–adsorption for removal of p-nitrophenol and its conversion p-aminophenol from water by gold nanoparticles supported on oxidized mesoporous carbon

A highly efficient method for removal of p-nitrophenol and its conversion p-aminophenol from water was proposed using a novel catalyst-adsorbent composite of gold nanoparticles supported on functionalized mesoporous carbon (Au@CMK-3-O). The immobilized gold nanoparticles presented excellent catalytic ability to converse p-nitrophenol into p-aminophenol with the help of sodium borohydride, and the oxidized mesoporous carbon (CMK-3-O) serving as both carrier and adsorbent also exhibited high efficiency to remove p-aminophenol. The morphology and structure of the composite were characterized via SEM, TEM, FTIR and XPS analysis. Moreover, the mechanism of reaction process and the parameters of kinetics and thermodynamics were investigated. The activation energy was figured as 86.8 kJ mol(-1) for the adsorption and reduction of p-nitrophenol to p-aminophenol. The thermodynamic analysis based on the rate constants evaluated by pseudo-first-order model reveals that the adsorption-reduction process is an endothermic procedure with the rise of randomness. The anti-oxidation and regeneration study indicates that Au@CMK-3-O can be reused for 6 times with more than 90% conversion efficiency and keep high activity after exposing in air for 1 month, which possesses great prospects in application of nitroaromatic pollutant removal.

Label free detection of lead using impedimetric sensor based on ordered mesoporous carbon-gold nanoparticles and DNAzyme catalytic beacons.

A novel label-free impedimetric sensing system based on DNAzyme and ordered mesoporous carbon-gold nanoparticle (OMC-GNPs) for the determination of Pb(2+) concentration was developed in the present study. Firstly, gold nanoparticles deposited on the modified electrode surface were employed as a platform for the immobilization of thiolated probe DNA, and then hybridized with DNAzyme catalytic beacons. Subsequently, in the presence of Pb(2+), the DNAzyme could be activated to cleave the substrate strand into two DNA fragments, which causes differences in the electrical properties of the film. Randles equivalent circuit was employed to evaluate the electrochemical impedance spectroscopy (EIS) result. The charge transfer resistance (R(CT)) value for the [Fe(CN)6](3-/4-) redox indicator was remarkably decline after hybridization with Pb(2+). The difference in RCT values before and after hybridization with Pb(2+) showed a linear relation with the concentration of the Pb(2+) in a range of 5×10(-10)-5×10(-5) M, with a detection limit of 2×10(-10) M (S/N=3). Furthermore, with the application of Pb(2+) dependent 8-17DNAzyme, the proposed sensing system exhibited high selectivity without using any labeled probes. This biosensor demonstrated a promising potential for Pb(2+) detection in real sample.

Phosphorus-doped ordered mesoporous carbons embedded with Pd/Fe bimetal nanoparticles for the dechlorination of 2,4-dichlorophenol

Palladium/iron (Pd/Fe) bimetallic nanoparticles were embedded within phosphorus-doped ordered mesoporous carbons (Pd/NZVI@P) with high dechlorination activity for 2,4-dichlorophenol (2,4-DCP). The Pd/Fe bimetal nanoparticles of about 15 nm diameter embedded in phosphorus-doped ordered mesoporous carbons (P-OMCs) were homogeneously distributed. The high dechlorination activity was mainly attributed to the homogeneous distribution of Pd/Fe bimetal nanoparticles, which were characterized by transmission electron microscopy (TEM) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) with image mapping. Dechlorination kinetics indicated that the dechlorination rates of 2,4-DCP increased with the increasing of Pd content. The use of P-OMCs as supporting materials to embed enough Pd/Fe bimetal nanoparticles kept the nanoparticles highly active and stable. Besides, solution pH had a significant effect on the dechlorination of 2,4-DCP and the passivation of the Pd/NZVI@P samples. The effects of the number and position of chlorine atoms for different chlorophenols (CPs) on the dechlorination activity were also revealed; the result indicated that the dechlorination of CPs by catalytic reduction preferentially begins from the para-position of the ring, and more chlorine atoms of CPs are favorable for the occurrence of the dechlorination reaction. This study demonstrated that P-OMC is a promising supporting material for the preparation of some effective composite metals for the catalytic dechlorination of CPs.

Treatment of arsenic in acid wastewater and river sediment by Fe@Fe2O3 nanobunches: The effect of environmental conditions and reaction mechanism

High concentration of arsenic in acid wastewater and polluted river sediment caused by metallurgical industry has presented a great environmental challenge for decades. Nanoscale zero valent iron (nZVI) can detoxify arsenic-bearing wastewater and groundwater, but the low adsorption capacity and rapid passivation restrict its large-scale application. This study proposed a highly efficient arsenic treatment nanotechnology, using the core-shell Fe@Fe2O3 nanobunches (NBZI) for removal of arsenic in acid wastewater with cyclic stability and transformation of arsenic speciation in sediment. The adsorption capacity of As(III) by NBZI was 60 times as high as that of nanoscale zero valent iron (nZVI) at neutral pH. Characterization of the prepared materials after reaction revealed that the contents of As(III) and As(V) were 65% and 35% under aerobic conditions, respectively, which is the evidence of oxidation included in the reaction process apart from adsorption and co-precipitation. The presence of oxygen was proved to improve the adsorption ability of the prepared NBZI towards As(III) with the removal efficiency increasing from 68% to 92%. In order to further enhance the performance of NBZI-2 in the absence of oxygen, a new Fenton-Like system of NBZI/H2O2 to remove arsenic under the anoxic condition was also proposed. Furthermore, the removal efficiency of arsenic in acid wastewater remained to be 78% after 9 times of cycling. Meanwhile, most of the mobile fraction of arsenic in river sediment was transformed into residues after NBZI treatment for 20 days. The reaction mechanism between NBZI and arsenic was discussed in detail at last, indicating great potential of NBZI for the treatment of arsenic in wastewater and sediment.

pH-dependent degradation of p-nitrophenol by sulfidated nanoscale zerovalent iron under aerobic or anoxic conditions.

Sulfidated nanoscale zerovalent iron (S-NZVI) is attracting considerable attention due to its easy production and high reactivity to pollutants. We studied the reactivity of optimized S-NZVI (Fe/S molar ratio 6.9), comparing with pristine nanoscale zerovalent iron (NZVI), at various pH solutions (6.77-9.11) towards p-nitrophenol (PNP) under aerobic and anoxic conditions. Studies showed that the optimized extent of sulfidation could utterly enhance PNP degradation compared to NZVI. Batch experiments indicated that in anoxic S-NZVI systems the degradation rate constant increased with increasing pH up to 7.60, and then declined. However, in aerobic S-NZVI, and in anoxic or aerobic NZVI systems, it decreased as pH increased. It was manifested that anoxic S-NZVI systems preferred to weaker alkaline solutions, whereas aerobic S-NZVI systems performed better in acidic solutions. The highest TOC removal efficiency of PNP (17.59%) was achieved in the aerobic S-NZVI system at pH 6.77, revealing that oxygen improved the degradation of PNP by excessive amounts of hydroxyl radicals in slightly acidic conditions, and the TOC removal efficiency was supposed to be further improved in moderate acidic solutions. Acetic acid, a nontoxic ring opening by-product, confirms that the S-NZVI system could be a promising process for industrial wastewater containing sulfide ions.

New insights into the activity of a biochar supported nanoscale zerovalent iron composite and nanoscale zero valent iron under anaerobic or aerobic conditions

In this work, to gain insight into the mechanism of p-nitrophenol (PNP) removal using the reactivity of a biochar supported nanoscale zerovalent iron composite (nZVI/biochar) and nanoscale zero valent iron (nZVI) under anaerobic or aerobic conditions, batch experiments and models were conducted. The PNP removal rate in the more acidic solutions was higher, while it was significantly suppressed at higher pH, especially at pH 9.0. The peak value of the apparent rate constants suggests that the reactivity of nZVI/biochar could be much stronger than that of nZVI under the same aeration conditions. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using nZVI/biochar or nZVI. The reaction constants obtained through a Langmuir–Hinshelwood mechanism under different aeration conditions followed the trend nZVI/biochar (N2) > nZVI/biochar (air) > nZVI (N2) > nZVI (air), indicating that nZVI/biochar under anaerobic conditions exhibits enhanced activity for the degradation of PNP. The nZVI/biochar under anaerobic conditions has the lowest Arrhenius activation energy of PNP degradation–adsorption, suggesting that the surface interaction of eliminating PNP has a low energy barrier. In addition, TOC removal under anaerobic conditions was negligible compared with that under the aerobic system and the total number of iron ions leaching at solution pH 3.0 in the nZVI/biochar or nZVI system under air aeration conditions was much higher than that under nitrogen aeration conditions. The profiles of the intermediates formed during the PNP degradation indicated that in the anaerobic environment, reduction was the predominant step in the removal process, while the degradation of PNP could be regarded as a combination of oxidation and reduction in an aerobic environment.

Plasmonic resonance excited dual Z-scheme BiVO4/Ag/Cu2O nanocomposite: synthesis and mechanism for enhanced photocatalytic performance in recalcitrant antibiotic degradation

The utilization of solar energy based on semiconductor photocatalysts for pollutant removal and environmental remediation has become a research hot spot and attracted great attention. In this study, a novel ternary BiVO4/Ag/Cu2O nanocomposite has been successfully synthesized via simple wet impregnation of Cu2O particles coupled with a subsequent photo-reduction pathway for the deposition of metallic Ag on the surface of BiVO4. The resulting BiVO4/Ag/Cu2O photocatalyst was used for the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). Results showed that the coating contents of the Cu2O and Ag particles presented a great effect on the eventual photocatalytic activity of the photocatalysts, and the optimum coating contents of Cu2O and Ag were obtained with their mass ratios of 3% and 2%, respectively. Under optimum conditions, nearly 91.22% TC removal efficiency was obtained based on ternary BiVO4/Ag/Cu2O nanocomposites, higher than that of pure BiVO4 (42.9%) and binary BiVO4/Cu2O (65.17%) and BiVO4/Ag (72.63%) nanocomposites. Meanwhile, the enhanced total organic carbon (TOC) removal efficiency also indicated the excellent photocatalytic degradation ability of the BiVO4/Ag/Cu2O nanocomposites. As for their practical application, the effects of initial TC concentration, various supporting electrolytes and different irradiation conditions were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs) was used to show the by-products of TC molecule degradation. Cycling experiments indicated the high stability of the as-prepared photocatalysts. Furthermore, the results obtained from radical trapping experiments and ESR measurements suggested that the photocatalytic degradation of TC in the BiVO4/Ag/Cu2O based photocatalytic system was the joint action of the photogenerated holes (h+), superoxide radical (˙O2−) and hydroxyl radical (˙OH). The enhanced photocatalytic activity of BiVO4/Ag/Cu2O was attributed to the synergistic effect of Cu2O, Ag and BiVO4, especially the surface plasmon resonance effect and the established local electric field brought about by metallic Ag. Additionally, to deeply understand the reaction mechanism, a dual Z-scheme charge transfer pathway has been proposed.

Facile fabrication of mediator-free Z-scheme photocatalyst of phosphorous-doped ultrathin graphitic carbon nitride nanosheets and bismuth vanadate composites with enhanced tetracycline degradation under visible light

To realize the sustainable employment of solar energy in contaminant degradation and environmental recovery, design and development of an efficient photocatalyst is urgently needed. Herein, a novel direct Z-scheme composite photocatalysts consist of phosphorous-doped ultrathin g-C3N4 nanosheets (PCNS) and bismuth vanadate (BiVO4) are developed via a one-pot impregnated precipitation method. The as-prepared hybrid nanocomposite was utilized for the degradation tetracycline (TC) under visible light irradiation. Among the composites with various PCNS/BiVO4 ratios, the prepared PCNS/BVO-400 photocatalyst presents the best performance, showing a TC (10mg/L) removal efficiency of 96.95% within 60min, more than double that of pristine BiVO4 (41.45%) and higher than that of pure PCNS (71.78%) under the same conditions. The effects of initial TC concentration, catalyst dosage, pH value and different water sources have been studied in detail. The improved photocatalytic performance of the as-prepared PCNS/BiVO4 nanocomposites could be attributed to the promoted separation efficiency of the photogenerated electrons and the enhanced charge carrier lifetime (1.65ns) owing to the synergistic effect between the PCNS and BiVO4. The degradation intermediates and decomposition pathway of TC were also analyzed and proposed. Additionally, radical trapping experiments and ESR measurement indicated that the photogenerated holes (h+), superoxide radical (O2-) and hydroxyl radical (OH) all participated in the TC removal procedure in the reaction system. The high performance of PCNS/BVO-400 in real wastewater indicated the potential of the prepared composite in practical application. This work provides an efficient and promising approach for the formation of high performance Z-scheme photocatalyst and study the possibility for real wastewater treatment.