Qiuya Niu

Removal of cationic dyes from aqueous solution using magnetic multi-wall carbon nanotube nanocomposite as adsorbent.

A magnetic multi-wall carbon nanotube (MMWCNT) nanocomposite was synthesized and was used as an adsorbent for removal of cationic dyes from aqueous solutions. The MMWCNT nanocomposite was composed of commercial multi-wall carbon nanotubes and iron oxide nanoparticles. The properties of this magnetic adsorbent were characterized by scanning electron microscopy, X-ray diffraction and BET surface area measurements. Adsorption characteristics of the MMWCNT nanocomposite adsorbent were examined using methylene blue, neutral red and brilliant cresyl blue as adsorbates. Experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of adsorption dosage and solution pH values on the removal of cationic dyes. Kinetic data were well fitted by a pseudo second-order model. Freundlich model was used to study the adsorption isotherms. The prepared MMWCNT adsorbent displayed the main advantage of separation convenience compared to the present adsorption treatment.

Bioremediation mechanisms of combined pollution of PAHs and heavy metals by bacteria and fungi: A mini review

In recent years, knowledge in regard to bioremediation of combined pollution of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by bacteria and fungi has been widely developed. This paper reviews the species of bacteria and fungi which can tackle with various types of PAHs and heavy metals entering into environment simultaneously or successively. Microbial activity, pollutants bioavailability and environmental factors (e.g. pH, temperature, low molecular weight organic acids and humic acids) can all affect the bioremediation of PAHs and heavy metals. Moreover, this paper summarizes the remediation mechanisms of PAHs and heavy metals by microbes via elucidating the interaction mechanisms of heavy metals with heavy metals, PAHs/PAHs metabolites with PAHs and PAHs with heavy metals. Based on the above reviews, this paper also discusses the potential research needs for this field.

Inactivation performance and mechanism of Escherichia coli in aqueous system exposed to iron oxide loaded graphene nanocomposites.

The challenge to achieve efficient disinfection and microbial control without harmful disinfection byproducts calls for developing new technologies. Magnetic-graphene oxide (M-GO) with magnetic iron oxide nanoparticles well dispersed on graphene oxide (GO) nanosheets exerted excellent antibacterial activity against Escherichia coli. The antibacterial performance of M-GO was dependent on the concentration and the component mass ratio of M/GO. The synergetic antibacterial effect of M-GO was observed with M/GO mass ratio of 9.09. TEM images illustrated the interaction between E. coli cells and M-GO nanocomposites. M-GO nanomaterials were possible to deposit on or penetrate into cells leading to leakage of intercellular contents and loss of cell integrity. The inactivation mechanism of E. coli by M-GO was supposed to result from both the membrane stress and oxidation stress during the incubation period. M-GO with excellent antibacterial efficiency against E. coli and separation-convenient property from water could be potent bactericidal nanomaterials for water disinfection.

Shellac-coated iron oxide nanoparticles for removal of cadmium(II) ions from aqueous solution.

This study describes a new effective adsorbent for cadmium removal from aqueous solution synthesized by coating a shellac layer, a natural biodegradable and renewable resin with abundant hydroxyl and carboxylic groups, on the surface of iron oxide magnetic nanoparticles. Transmission Electron Microscopy (TEM) imaging showed shellac-coated magnetic nanoparticle (SCMN) adsorbents had a core-shell structure with a core of 20 nm and shell of 5 nm. Fourier Transform Infrared Spectroscopic analysis suggested the occurrence of reaction between carboxyl groups on the SCMN adsorbent surface and cadmium ions in aqueous solution. Kinetic data were well described by pseudo second-order model and adsorption isotherms were fitted with both Langmuir and Freundlich models with maximum adsorption capacity of 18.80 mg/g. SCMN adsorbents provided a favorable adsorption capacity under high salinity conditions, and cadmium could easily be desorbed using mild organic acid solutions at low concentration.

Polyvinyl alcohol-immobilized Phanerochaete chrysosporium and its application in the bioremediation of composite-polluted wastewater.

A novel biosorbent, polyvinyl alcohol (PVA)-immobilized Phanerochaete chrysosporium, was applied to the bioremediation of composite-polluted wastewater, containing both cadmium and 2,4-dichlorophenol (2,4-DCP). The optimum removal efficiency achieved was 78% for Cd(II) and 95.4% for 2,4-DCP at initial concentrations of 20 mg/L Cd(II) and 40 mg/L 2,4-DCP. PPBs had significantly enhanced the resistance of P. chrysosporium to 2,4-DCP, leading to the degradation rates of 2,4-DCP beyond 90% with varying initial 2,4-DCP concentrations. This research demonstrated that 2,4-DCP and secreted proteins might be used as carbon and nitrogen sources by PVA-immobilized P. chrysosporium beads (PPBs) for Cd(II) removal. Fourier transform infrared spectroscopy analysis showed that hydroxyl and carboxyl groups on the surface of PPBs were dominant in Cd(II) binding. The mechanism underlying the degradation of 2,4-DCP into fumaric acid and 1-hexanol was investigated. The adsorption-desorption studies indicated that PPBs kept up to 98.9% of desorption efficiency over three cycles.

Green-emitting fluorescence Ag clusters: facile synthesis and sensors for Hg2+ detection

Bovine serum albumin (BSA) has proven to be particularly effective for the synthesis of Ag clusters due to its free cysteine residue in an alkaline environment. However, the currently used BSA-directed synthesis method is still complicated and uses BSA only as a stabilizing agent. In this study, we developed a simpler method for the synthesis of new fluorescent Ag clusters using BSA as a reducing and stabilizing agent. The as-prepared Ag clusters exhibited high green fluorescence emission (∼548 nm). Different changes in the pH were used for the synthesis of Ag clusters with different sizes. The results indicated that higher pH led to a smaller size. Furthermore, the Ag clusters were successfully applied in Hg2+ detection. The lowest detectable concentration was estimated to be 4.0 nM with a large range from 4.0 nM to 400.0 nM. MTT assays showed that the biotoxicity of the as-prepared Ag clusters was significantly lower than that of NaBH4-reduced nano-silver.

Time-gated fluorescence sensor for silver ions using Mn:CdS/ZnS quantum dots/DNA/gold nanoparticle complexes

A fluorescent sensor for the determination of Ag+ by time-gated mode is proposed. The method is based on Ag+-induced formation of quantum dot/DNA/gold nanoparticle complexes. Two ssDNA strands (strand A and strand B) are designed which contain C–C mismatched base pairs that can specifically react with Ag+. The water-soluble long-lifetime fluorescence quantum dots (Mn:CdS/ZnS) functionalized with strand A are selected as the fluorophore. The gold nanoparticles (GNPs) which are labeled with strand B, acted as the quencher. When Ag+ is absent in the sample solution, DNA-modified GNPs and Mn:CdS/ZnS were in the freedom state, the fluorescence signal of Mn:CdS/ZnS is obviously strong. When Ag+ are present in the sample solution, a DNA duplex is formed because of the strong binding ability between Ag+ and cytosine bases and formed stable C–Ag+–C structures. As a result, the Mn:CdS/ZnS and the GNPs are brought into close proximity, which caused the fluorescence quenching of the Mn:CdS/ZnS due to the nanometal surface energy transfer (NSET) between the Mn:CdS/ZnS and GNPs. This fluorescent sensor could present a satisfactory specificity and selectivity for Ag+. Meanwhile, the detection limit of Ag+ was estimated to be 7.9 nM.

Effect of Pb(II) on phenanthrene degradation by new isolated Bacillus sp. P1

A polycyclic aromatic hydrocarbon (PAH)-degrading microbe was isolated and the effect of Pb(II) on the degradation of phenanthrene (PHE) by this microbe was studied in this research. The changes in the metabolism, protein content, enzyme activity and PHE degradation induced by Pb(II) were investigated to elucidate the effect of Pb(II) on the degradation of PHE. The protein content, catechol 2,3-dioxygenase activity and phenanthrene-degrading ability of the enzymes were all enhanced at low concentrations of Pb(II) (below 50 mg L−1) but decreased at relatively higher concentrations (100 to 300 mg L−1) of Pb(II). These results indicate that the presence of Pb(II) is relevant to enzymatic changes in this PAH-biodegrading microbe: it helps the process of PHE biodegradation at low concentrations, but impairs PHE biodegradation at excessive concentrations.