Zuliang Chen

Removal of Chromium (VI) from wastewater using bentonite-supported nanoscale zero-valent iron

Bentonite-supported nanoscale zero-valent iron (B-nZVI) was synthesized using liquid-phase reduction. The orthogonal method was used to evaluate the factors impacting Cr(VI) removal and this showed that the initial concentration of Cr(VI), pH, temperature, and B-nZVI loading were all importance factors. Characterization with scanning electron microscopy (SEM) validated the hypothesis that the presence of bentonite led to a decrease in aggregation of iron nanoparticles and a corresponding increase in the specific surface area (SSA) of the iron particles. B-nZVI with a 50% bentonite mass fraction had a SSA of 39.94 m(2)/g, while the SSA of nZVI and bentonite was 54.04 and 6.03 m(2)/g, respectively. X-ray diffraction (XRD) confirmed the existence of Fe(0) before the reaction and the presence of Fe(II), Fe(III) and Cr(III) after the reaction. Batch experiments revealed that the removal of Cr (VI) using B-nZVI was consistent with pseudo first-order reaction kinetics. Finally, B-nZVI was used to remediate electroplating wastewater with removal efficiencies for Cr, Pb and Cu > 90%. Reuse of B-nZVI after washing with ethylenediaminetetraacetic acid (EDTA) solution was possible but the capacity of B-nZVI for Cr(VI) removal decreased by approximately 70%.

Kaolinite-supported nanoscale zero-valent iron for removal of Pb2+ from aqueous solution: Reactivity, characterization and mechanism

The use of nanoscale zero-valent iron (nZVI) to remediate contaminated groundwater is limited due to its lack of durability and mechanical strength. To address this issue, 20% (w/w) nZVI was loaded onto kaolinite as a support material (K-nZVI). More than 96% of Pb(2+) was removed from aqueous solution using K-nZVI at an initial condition of 500 mg/L Pb(2+) within 30 min under the conditions of 10 g/L of K-nZVI, pH 5.10 and a temperature of 30 °C. To understand the mechanism of removal of Pb(2+), various techniques were implemented to characterize K-nZVI. Scanning electron microscopy (SEM) indicated that K-nZVI had a suitable dispersive state with a lower aggregation, where the mean specific surface area and average particle size as determined by the BET-N(2) method and X-ray diffraction (XRD), were 26.11 m(2)/g and 44.3 nm, respectively. The results obtained from XRD, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) indicated that a small number of iron oxides formed on the surface of K-nZVI, suggesting that free Pb(2+) was adsorbed onto K-nZVI and subsequently reduced to Pb(0).

Removal of methyl orange from aqueous solution using bentonite-supported nanoscale zero-valent iron.

Zero-valent iron (ZVI) nanoparticles tend to agglomerate, resulting in a significant loss in reactivity. To address this issue, synthesized bentonite-supported nanoscale zero-valent iron (B-nZVI) was used to remove azo dye methyl orange (MO) in aqueous solution. Batch experiments show that various parameters, such as pH, initial concentration of MO, dosage, and temperature, were affected by the removal of MO. Scanning electron microscopy (SEM) confirmed that B-nZVI increased their reactivity and a decrease occurred in the aggregation of iron nanoparticles for the presence of bentonite (B). Using B-nZVI, 79.46% of MO was removed, whereas only 40.03% when using nZVI after reacting for 10 min with an initial MO concentration of 100 mg/L (pH=6.5). Furthermore, after B-nZVI reacted to MO, XRD indicated that iron oxides were formed. FTIR showed that no new bands appeared, and UV-vis demonstrated that the absorption peak of MO was degraded. Kinetics studies showed that the degradation of MO fitted well to the pseudo first-order model. A degradation mechanism is proposed, including the following: oxidation of iron, adsorption of MO to B-nZVI, formation of Fe(II)-dye complex, and cleavage of azo bond. Finally, the removal rate of MO from actual wastewater was 99.75% when utilizing B-nZVI.

Removal of Pb(II) from aqueous solution using modified and unmodified kaolinite clay.

Modified kaolinite clay with 25% (w/w) aluminium sulphate and unmodified kaolin were investigated as adsorbents to remove Pb(II) from aqueous solution. The results show that amount of Pb(II) adsorbed onto modified kaolin (20mg/g) was more than 4.5-fold than that adsorbed onto unmodified kaolin (4.2mg/g) under the optimized condition. In addition, the linear Langmuir and Freundlich models were used to describe equilibrium isotherm. It is observed that the data from both adsorbents fitted well to the Langmuir isotherm. The kinetic adsorption of modified and unmodified kaolinite clay fitted well to the pseudo-second-order model. Furthermore, both modified and unmodified kaolinite clay were characterized by X-ray diffraction, Fourier transform infrared (FT-IR) and scanning electron microscope (SEM). Finally, both modified and unmodified kaolinite clay were used to remove metal ions from real wastewater, and results show that higher amount of Pb(II) (the concentration reduced from 178 to 27.5mg/L) and other metal ions were removed by modified kaolinite clay compared with using unmodified adsorbent (the concentration reduced from 178 to 168 mg/L).

Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite.

Adsorption of cationic methylene blue and anionic orange II onto unmodified and surfactant-modified zeolites was studied using a batch equilibration method. The effects of equilibrium time, solution pH, and sorption temperature were examined. The results suggested that 2% sodium dodecyl benzenesulfonate (SDBS)- and 3% sodium dodecyl sulfate (SDS)-modified zeolites had higher adsorption capacities for methylene blue than the unmodified zeolite, while 2% cetylpyridinium bromide hexadecyl (CPB)- and 2% hexadecylammonium bromide (HDTMA)-modified zeolites were the best adsorbents for orange II. The adsorption conditions were optimized, and the mechanisms of adsorption are briefly discussed.

Green synthesis of Fe nanoparticles using eucalyptus leaf extracts for treatment of eutrophic wastewater

Iron nanoparticles were firstly synthesized through a one-step room-temperature biosynthetic route using eucalyptus leaf extracts (EL-Fe NPs). Scanning electron microscopy (SEM) and X-ray energy-dispersive spectrometer (EDS) confirmed the successful synthesis of the spheroidal iron nanoparticles. Furthermore, X-ray diffraction (XRD) and Fourier Transform Infrared spectrometer (FTIR) indicated that some polyphenols are bound to the surfaces of EL-Fe NPs as a capping/stabilizing agent. Reactivity of EL-Fe NPs was evaluated for the treatment of swine wastewater and results indicated that 71.7% of total N and 84.5% of COD were removed, respectively. This demonstrated the tremendous potential of EL-Fe NPs for in situ remediation of eutrophic wastewater.

Heterogeneous Fenton-like oxidation of monochlorobenzene using green synthesis of iron nanoparticles

Iron nanoparticles (Fe NPs) were synthesized using tea extracts as a catalyst for the Fenton-like oxidation of monochlorobenzene (MCB), where 69%, 53%, and 39% of MCB were, respectively, degraded by Fe NPs synthesized using green tea extracts, oolong tea extracts, and black tea extracts. Fe NPs synthesized using green tea extracts (GT-Fe NPs) demonstrated the best degradation since green tea contains a high concentration of caffeine/polyphenols used as both reducing and capping agents in the synthesis of Fe NPs. This was confirmed by SEM image, EDS, and XRD pattern of GT-Fe NPs. In addition, batch experiments show that the oxidation of MCB and the removal of chemical oxygen demand (COD) using GT-Fe NPs were 81% and 31%, respectively, at optimal conditions, where dosages were 0.6g/L GT-Fe NPs, 0.045 mol/L H2O2, and initial pH of 3.0. Compared to homogeneous Fenton oxidation of MCB, GT-Fe NPs as a heterogeneous catalyst indicate that Fe(2+) and Fe(3+) leached from GT-Fe NPs nanoparticles and consequently reduced the formation of iron sludge. Finally, GT-Fe NPs were successful in removing MCB from wastewaters, and the possible Fenton-like oxidative mechanism of MCB was proposed. The proposition was based on adsorption of MCB on the surface of GT-Fe NPs, decomposition of H2O2, generation of hydroxyl radicals, and oxidation of MCB.

Is photosynthesis related to concentrations of nitrogen and Rubisco in leaves of Australian native plants

The relationships among light-saturated photosynthesis and concentrations of nitrogen and ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in Australian native plants are poorly known, primarily due to the difficulty of extracting and analysing Rubisco from such species. Rubisco may be rapidly quantified in crude extracts of plant tissue by capillary electrophoresis (CE); however, the presence of phenolic compounds in many Australian native plants limits the use of these methods. The addition of insoluble polyvinylpolypyrrolidone (PVPP) during leaf extractions effectively removed phenols permitting quantitation of Rubisco. Relationships among maximum rates of photosynthesis and concentrations of nitrogen and Rubisco were then investigated in ten species native to Australia. Total nitrogen and the major pools of N in foliage varied greatly between species. Equally, within species N-partitioning was highly plastic, as affected by different concentrations and forms of N applied in sand culture (0.5 or 8 mM, nitrate or ammonium). In Hakea prostrata, for example, the proportion of total N present as soluble proteins varied between 43 and 71%, while the proportion of total N present as Rubisco N ranged between 9.4 and 30.0%, and the contribution of Rubisco to soluble proteins varied between 21 and 42%. The measured concentration of Rubisco varied between 40% and 600% of that estimated from enzyme kinetics and measured rates of photosynthesis. Generally there was a large ‘excess’ of Rubisco, and in only two cases was the measured concentration of Rubisco significantly less than predicted. Total N, soluble protein and Rubisco concentrations were poorly related to maximum rates of photosynthesis, while the relationship between photosynthesis and Rubisco was worse than that with N, primarily due to the plants’ variable over-investment in Rubisco.

Spectroscopic study of aluminium speciation in removing humic substances by Al coagulation

Removal of humic substances (HS) isolated from swamp water, surface soil, peat and brown coal by aluminium (Al) coagulation under different conditions was studied using the jar test method and spectroscopic techniques. At lower pHs<4.5, humic substances formed soluble complexes with Al3+ and the amounts of these HS–Al complexes increased with increasing concentration of the humic substances. Maximum removal of the humic substances was found to occur in the pH range from 5.0 to 7.0, due to the adsorption of humic substances on the surface of Al(OH)3(s) crystal. Sequential extraction of the humic substances adsorbed on Al(OH)3(s) using the Soxhlet technique with different solvents showed that the adsorption forces involved were great. The effects of humic substances on the Al speciation are discussed and a model is proposed to explain the mechanism for the removal of humic substances during the Al coagulation process.

Biodegradation of naphthalene by strain Bacillus fusiformis (BFN)

Bacterial strains isolated from oil refining wastewater sludge (Fuzhou, China) were used to biodegrade naphthalene in cultured medium. Bacillus fusiformis (BFN) strain was identified using 16S rDNA gene sequence analysis. Optimal conditions for the biodegradation of naphthalene included: temperature of 30 degrees C, pH 7.0, 0.2% inoculum size and a C/N ratio of 1.0. Under these conditions and initial naphthalene concentration of 50 mg/L, more than 99.1% was removed within 96 h. Of those factors influencing the biodegradation of naphthalene, salinity and inoculum concentration were of greatest importance. Furthermore, the biodegradation kinetics of naphthalene corresponded with the first-order rate model. Degradation metabolites identified using GC-MS, included o-phthalic acid and benzoic acid, suggesting possible metabolic pathways. Finally, given these metabolites are water-soluble and non-toxic, the findings suggest a potential bioremediation role of Bacillus fusiformis (BFN) in the removal of naphthalene from wastewaters.