Jiajiang Lin

Functional kaolin supported nanoscale zero-valent iron as a Fenton-like catalyst for the degradation of Direct Black G

Kaolin supported nanoscale zero-valent iron (K-nZVI) is synthesized and applied as the Fenton-like oxidation catalyst to degrade a model azo dye, Direct Black G (DBG). The characterization of K-nZVI by the high resolution transmission electronmicroscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy Diffraction Spectrum (EDS) and X-ray diffraction (XRD) show that kaolin as a support material not only reduces the aggregation of zero-valent iron (nZVI) but also facilitates the Fenton-like oxidation by increasing the local concentration of DBG in the vicinity of nZVI. Pseudo first-order and pseudo second-order kinetic models are employed to reveal the adsorption and degradation of the DBG using K-nZVI as the catalyst. A better fit with pseudo second-order model for the adsorption process and equal excellent fits with pseudo first-order and pseudo second-order models for the degradation process are observed; the adsorption process is found to be the rate limiting step for overall reactions. The adsorption, evaluated by isotherms and thermodynamic parameters is a spontaneous and endothermic process. High-performance liquid chromatography-mass spectrometry (LC-MS) analysis was used to test degraded products in the degradation of DGB by K-nZVI. A removal mechanism based on the adsorption and degradation is proposed, including (i) prompt adsorption of DBG onto the K-nZVI surface, and (ii) oxidation of DBG by hydroxyl radicals at the K-nZVI surface. The application of K-nZVI to treat real wastewater containing azo dyes shows excellent degradation efficiency.

Vertical Profiles of Pentachlorophenol and the Microbial Community in a Paddy Soil: Influence of Electron Donors and Acceptors

Vertical variations of pentachlorophenol (PCP) dissipation and microbial community were investigated in a paddy soil with the addition of electron acceptors (NO3(-), SO4(2-)) and donors (crop residues). Crop residues enhanced PCP dissipation by supplying dissolved organic carbon (DOC) as an electron donor, whereas NO3(-) and SO4(2-) inhibited it. The dissipation of PCP in electron donor treatments resulted in the accumulation of 3,4,5-trichlorophenol (3,4,5-TCP) except for wheat residues. The abundance and diversity of phospholipid fatty acids (PLFAs) decreased with increasing soil depth. The succession of predominant PLFAs shifted from aerobic bacteria to anaerobic bacteria when electron acceptors were changed to electron donors. The saturated/monounsaturated fatty acids (S/M) ratio increased with soil depth, which probably implied that nutrient turnover rate declined after the accumulation of 3,4,5-TCP. The results showed that the addition of electron donors and acceptors modified the microbial communities, which then further influenced the degradation pathway of PCP.

Biosynthesized iron oxide nanoparticles used for optimized removal of cadmium with response surface methodology

To effectively reuse adsorbent in removal of Cd (II), magnetic modification was considered as an alternative. In this study, iron oxide nanoparticles (IONPs) synthesized from the extract of Excoecaria cochinchinensis Lour leaves were modified by low-temperature calcination, and used to remove Cd (II). Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and magnetic properties analysis confirmed the successful synthesis of nanoscale magnetic FeOC composite. Response surface methodology (RSM) served to optimize the adsorption of Cd (II) by IONPs based on Box-Behnken design (BBD). According to the quadratic model, the effect of each factor on the removal of Cd (II) by IONPs was: pH > dosage > ionic strength > temperature. In percentage terms, 98.50% of Cd (II) (10 mg L-1) was removed when the pH, absorbent dosage, temperature and ionic strength conditions were 8.07, 2.5 g L-1, 45 °C, and 0.07 mol L-1, respectively. The adsorption of Cd (II) by IONPs is consistent with pseudo-second order kinetics and Langmuir adsorption isotherm models, indicating that the process of adsorption of Cd (II) by IONPs belongs to monolayer chemical adsorption. The -COOH, -COH, Cπ electron and ≡FeOH may be the binding sites for Cd (II) on the surface of IONPs. Overall, IONPs can be used to remove Cd (II) effectively from aqueous solution in a wide range of conditions.

The toxicity of graphene and its impacting on bioleaching of metal ions from sewages sludge by Acidithiobacillus sp.

The increasing production of graphene raised concerns about their releasing into sewage sludge, however, there is little information about graphene impacting on the growth of bacteria and hence their bioleaching of metal ions from sewages sludge. In this study, we reported that Acidithiobacillus sp., isolated from sewages, were used to bioleach Cu2+ and Zn2+ from sewages sludge in the presence of graphene. The negative effect on the growth of Acidithiobacillus sp. and dose-dependent were observed in presence of graphene, where the optical density (OD420) of the culture decreased from 0.163 to 0.045, while the bioleaching efficiency of Cu2+ (70%-16%) and Zn2+ (80%-48%) were also reduced when the graphene dose decreased from 50 mg L-1 to 1 mg L-1. Furthermore, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed that the direct contacts between graphene and cell at 1 mg L-1 graphene caused cell membrane disruption, while Acidithiobacillus sp. grew better by forming dense biofilms around the suspended graphene at a 50 mg L-1. LIVE/DEAD staining further demonstrated that almost no live cells were detected at 1 mg L-1 graphene. The toxicity of graphene could generally be explained by depending on the concentration of graphene. The new findings provide an insight into dose dependence, which impacted on the growth of Acidithiobacillus sp. and their bioleaching of metal ion from sludge.