Ji-Dong Gu

Modifying Fe3O4 nanoparticles with humic acid for removal of Rhodamine B in water

Humic acid (HA) modifying Fe(3)O(4) nanoparticles (Fe(3)O(4)/HA) was developed for removal of Rhodamine B from water. Fe(3)O(4)/HA was prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TEM images revealed the Fe(3)O(4)/HA (with ≈ 10 nm Fe(3)O(4) cores) were aggregated as aqueous suspensions. With a saturation magnetization of 61.2 emu/g, the Fe(3)O(4)/HA could be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the Rhodamine B to Fe(3)O(4)/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities of 161.8 mg/g. The Fe(3)O(4)/HA was able to remove over 98.5% of Rhodamin B in water at optimized pH.

Effects of allylthiourea, salinity, and pH on ammonia/ammonium-oxidizing prokaryotes in mangrove sediment incubated in laboratory microcosms

Anaerobic ammonium-oxidizing (anammox) bacteria, aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB) are three groups of ammonia/ammonium-oxidizing prokaryotes (AOPs) involved in the biochemical nitrogen cycling. In this study, the effects of allylthiourea (ATU), pH, and salinity on these three groups from mangrove sediment were investigated through microcosm incubation in laboratory. ATU treatments (50, 100, and 500xa0mgxa0L−1) obviously affected the community structure of anammox bacteria and AOB, but only slightly for AOA. ATU began to inhibit anammox bacteria growth slightly from dayxa010, but had an obvious inhibition on AOA growth from the starting of the study. At 100xa0mgxa0L−1 of ATU or higher, AOB growth was inhibited, but only lasted for 5xa0days. The pH treatments showed that acidic condition (pHxa05) had a slight effect on the community structure of anammox bacteria and AOA, but an obvious effect on AOB. Acidic condition promoted the growth of all groups of AOPs in different extent, but alkaline condition (pHxa09) had a weak effect on AOB community structure and a strong effect on both anammox bacteria and AOA. Alkaline condition obviously inhibited anammox bacteria growth, slightly promoted AOA, and slightly promoted AOB in the first 20xa0days, but inhibited afterward. Salinity treatment showed that higher salinity (20 and 40u2009‰) resulted in higher anammox bacteria diversity, and both AOA and AOB might have species specificity to salinity. High salinity promoted the growth of both anammox bacteria and AOB, inhibited AOA between 5 and 10xa0days, but promoted afterward. The results help to understand the role of these microbial groups in biogeochemical nitrogen cycling and their responses to the changing environments.

Synthesis of nanoscale zero-valent iron immobilized in alginate microcapsules for removal of Pb(II) from aqueous solution

Alginate microcapsules immobilized nanoscale zero-valent iron (M-NZVI), with diameters from several hundreds nanometers to several micrometers, were synthesized using ferric and calcium ions as the cross-linking cations, and then tested for removal of Pb(II) from aqueous solution. The size of NZVI particles was only a few nanometers according to transmission electron microscopy (TEM) observation. The synthesized alginate microcapsules were stable in air for as long as they were dried and contained 9.97% of iron by weight. When 0.5 g L−1 of M-NZVI were introduced into an aqueous solution containing 300.0 mg L−1 of Pb(II), 88% of Pb(II), 581.7 mg g−1 of Pb(II) uptake amount were removed from the system in 15 min. The kinetics of the removal reactions, including an initial adsorption phase and a subsequent reduction, is complicated. In addition, the synthesized M-NZVI showed a higher removal capability of Pb compared to NZVI and Ca-alginate particles. This newly synthesized material could be regenerated and reused at least 4 times when the initial concentrations of Pb(II) were ≤200.0 mg L−1. The higher reaction rates and greater removal capacity suggest that M-NZVI may be a potential material for in situ remediation of metal contaminated water and sediments.

Iron improving bio-char derived from microalgae on removal of tetracycline from aqueous system

Novel magnetic carbonaceous bio-char was hydrothermal prepared from microalgae under different loadings of iron and its structures and surface chemistry were characterized with Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherm (BET). The morphology of bio-char changed from sheet to particle as iron loading increased and its surface area also increased. When 3.0xa0g of dried microalgae and 6.0xa0mmol iron salt ((NH4)2SO4·FeSO4·6H2O) were mixed and treated, the obtained bio-char possessing the highest amount of oxygen-containing functional groups resulted in the best adsorption performance on tetracycline (TC). This adsorption process was fitted to Langmuir adsorption isotherm and the maximum adsorption capacity was 95.86xa0mg/g, which is higher than other bio-char reported. The iron loading contributed to the higher adsorption capacity of bio-char, which may be due to three factors, the high surface area, more hydrogen bonding, and bridging effects of the structural Fe for TC. Our data suggest that bio-char may have more important role in stabilization of pollutants in the environment.

La-EDTA coated Fe3O4 nanomaterial: Preparation and application in removal of phosphate from water

La-EDTA-Fe3O4 was prepared by a chemical co-precipitation method. The magnetic composite was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the adsorption properties of La-EDTA-Fe3O4 toward phosphate in water were investigated. The uptake rate of phosphate in water by La-EDTA-Fe3O4 was 3-1000 times than that of EDTA-Fe3O4, and reached 97.8% at 7 hr. The adsorption process agreed well with the Freundlich model and kinetics studies showed that the adsorption of phosphate proceeds according to pseudo second-order adsorption kinetics. The maximum removal rate was achieved at pH 6.0-7.0. The La-EDTA-Fe3O4 had good adsorption properties and could be separated well from aqueous solution by a permanent magnet. Therefore, this nanomaterial has potential application for the removal of phosphate from large water bodies.

Removal of Trace As(V) from Water with the Titanium Dioxide/ACF Composite Electrode

The novel titanium oxide/active carbon fiber (TiO2/ACF) electrode was prepared, and electrosorptive properties for As(V) in aqueous solution were investigated. The structure of TiO2/ACF was characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Furthermore, the As(V) electrosorptive properties of TiO2/ACF electrodes with calcination temperature, ionic species, and loaded amount of TiO2 were measured, and the electrosorption isotherm and kinetics were investigated at the applied voltage of 1.5xa0V. The optimal load quality of TiO2 was 0.80xa0g per ACF electrode (length × width × heightu2009=u20092xa0cmu2009×u20091xa0cmu2009×u20090.4xa0cm, 0.30xa0g), and optimum calcination temperature was 450xa0°C. The maximum electrosorption capacity of TiO2/ACF was 8.09xa0mg/g, about 200xa0% higher than that of ACF. Moreover, the electrode performance was stable than other materials such as pure ACF, manganese oxide/ACF, and iron oxides/ACF. It can process 100xa0ppb As(V) of water to 6xa0ppb (reach the drinking water standards of WHO), demonstrating that our novel electrode is with potential practical application.

Analysis of microbial diversity by pyrosequencing the small-subunit ribosomal RNA without PCR amplification

To avoid the biases associated with PCR amplification in analysis of microbial communities, a new method has been tested for direct sequencing of the cDNA of full-length Small-subunit Ribosomal RNA withOut specific PCR amplification (SROP). In silico analysis of the SROP method demonstrated that more than 99xa0% of the SROP sequences could be correctly annotated. Two environmental samples (activated sludge and anaerobic sludge) with complex microbial communities were used for comparison in this study. The SROP results demonstrated that the families Rhodocyclaceae and Nitrosomonadaceae in activated sludge and the phyla Synergistetes and Spirochaetes in anaerobic sludge were underestimated by PCR-based detection. One third of the 16S ribosomal RNA (rRNA) sequences obtained by the SROP method covered the V3 amplicon region, and they are suitable for phylogenetic and diversity index analyses. The microbial diversity index calculated from the rRNA sequences by the SROP was much higher than that calculated by conventional PCR, particularly for the anaerobic sludge. The metatranscriptome-based SROP method will contribute to our better understanding of the diversity of complex microbial communities.

Differential responses of ammonia/ammonium-oxidizing microorganisms in mangrove sediment to amendment of acetate and leaf litter.

The effects of acetate and leaf litter powder on ammonia/ammonium-oxidizing microorganisms (AOMs) in mangrove sediment were investigated in a laboratory incubation study for a period of 60xa0days. The results showed that different AOMs responded differently to the addition of acetate and leaf litter. A higher diversity of anaerobic ammonium-oxidizing (anammox) bacteria was observed when acetate or leaf litter was added than the control. However, acetate and leaf litter generally inhibited the growth of anammox bacteria despite that leaf litter promoted their growth in the first 5xa0days. The inhibitory effects on anammox bacteria were more pronounced by acetate than by leaf litter. Neither acetate nor leaf litter affected ammonia-oxidizing archaea (AOA) community structures, but promoted their growth. For ammonia-oxidizing bacteria (AOB), the addition of acetate or leaf litter resulted in changes of community structures and promoted their growth in the early phase of the incubation. In addition, the promoting effects by leaf litter on AOB growth were more obvious than acetate. These results indicated that organic substances affect AOM community structures and abundances. The study suggests that leaf litter has an important influence on the community structures and abundances of AOMs in mangrove sediment and affects the nitrogen cycle in such ecosystem.

Higher Abundance of Ammonia Oxidizing Archaea than Ammonia Oxidizing Bacteria and Their Communities in Tibetan Alpine Meadow Soils under Long-term Nitrogen Fertilization

Increasing usage of nitrogen fertilizer for food production has resulted in severely environmental problems of nutrients enrichment. This study aimed to examine the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to a long-term nitrogen fertilization in Tibetan alpine meadow. The abundance and composition of both AOB and AOA were assessed using quantitative real-time PCR, cloning and sequencing techniques based on amoA gene under different fertilization gradient (0, 30, 60, 90, and 120 g m−2 year−1). Our results showed that, abundances of AOA amoA genes (ranging from 1.48 × 109 to 2.00 × 109 copies per gram of dry soil) were significantly higher than those of AOB amoA genes (1.25 × 107 to 2.62 × 108 copies per gram of dry soil) under fertilization scenario. The abundance of AOB amoA genes increased with increasing nitrogen fertilization, whereas fertilization had little effect on AOA abundance. Sequences of clone libraries of the different treatments revealed that AOB communities were dominated by representatives of Cluster 4, constituting 48.94–64.44% in each clone library. Sequences of Clusters 9, 1 and 2 were prevalent in soils under higher fertilization. All archaeal amoA sequences recovered were affiliated with the soil/sediment clade and marine sediment clade, and no significant difference was observed on the community structure among different fertilization treatments. Variations in the AOB community structure and abundance were linked to ammonium-N and soil pH induced by different fertilization treatments. These results showed that the abundance and structure of the AOB community respond to the fertilization gradient, not AOA.

Removal of trace Cd(II) from water with the manganese oxides/ACF composite electrode

The Manganese oxide/active carbon fiber (MO/ACF) was prepared and its electrosorptive properties of Cd(II) in aqueous solution were investigated. The structure of MO/ACF was characterized with transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Furthermore, the Cd(II) electrosorptive properties of MO/ACF electrodes with different bias potentials, ionic strengths, and loaded amount of manganese oxides were measured and the electrosorption isotherm and kinetics were investigated. The Cd(II) electrosorptive capacity of MO/ACF was 6 times higher than that of pure ACF. The optimal adsorptive bias voltage was 1.5xa0V and the optimal electrolyte concentration of NaCl was 0.1xa0mol/L. The adsorption isotherm was agreed well with the Freundlich adsorption model and its maximum electrosorption capacity was 14.88xa0mg/g by Langmuir model. The higher adsorptive capacity of MO/ACF than that of pure ACF is attributed to higher capacitance and more adsorptive sites of MO/ACF.