Zhigang Ke

Reduction and Removal of Aqueous Cr(VI) by Glow Discharge Plasma at the Gas-Solution Interface

Aqueous chromium(VI) reduction and removal induced by glow discharge taking place at the gas-solution interface in an argon atmosphere was studied. The effect of initial pH and hydroxyl radical scavenger (ethanol) on the reduction efficiency was examined. High reduction efficiency was obtained when initial pH ≤ 2.0 or ≥ 8.0. In particular, addition of ethanol into the solution substantially increased the reduction efficiency and facilitated chromium removal from the solution in the form of sediment after discharge. The optimum pH values for Cr(VI) removal were within 6.0-7.0. Fourier transform-infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis confirmed that the main constituent of the sediment is chromium hydroxide.

Degradation of microcystin-LR in water by glow discharge plasma oxidation at the gas-solution interface and its safety evaluation.

Microcystin-LR (MC-LR) is one of the most commonly found microcystins (MCs) in fresh water and it poses danger to human health due to its potential hepatotoxicity. In the present study, we employed a novel method by using discharge plasma taking place at the gas-solution interface in gas atmosphere to degrade MC-LR in aqueous solution. The initial degradation rate of MC-LR was fastest under acidic conditions (5.41 ± 0.17 × 10(-3) mM min(-1) at pH 3.04) and decreased to 2.22 ± 0.11 × 10(-3) mM min(-1) and 0.912 ± 0.02 × 10(-3) mM min(-1) at pH 4.99 and 7.02, respectively. The effects of total soluble nitrogen (TN), total soluble phosphorus (TP) and natural organic matter (NOM) on the degradation efficiency were studied. The degradation rate was remarkably affected by TP and TN. Mass spectrometry was applied to identify the products of the reactions. Major degradation pathways are proposed according to the results of liquid chromatography/mass spectrometry (LC/MS) results. It suggests that the degradation of MC-LR is initiated via the attack of hydroxyl radicals on the conjugated carbon double bonds of Adda and on the benzene ring of Adda. Finally, the toxicity of intermediates or end-products from MC-LR degraded by this method was assessed using Caenorhabditis elegans. Our findings demonstrates that discharge plasma oxidation is a promising technology for degradation and removal of MC-LR and it may lead us to a new route to efficient treatment of other cyanotoxins from aqueous solutions.

Non-thermal hydrogen plasma processing effectively increases the antibacterial activity of graphene oxide

Graphene-based materials (GMs) are promising antibacterial agents which provide an alternative route to treat pathogenic bacteria with resistance to conventional antibiotics. To further improve their antibacterial activity, many methods have been developed to functionalize the GMs with chemicals. However, the application of additional chemicals may pose potential risks to the environment and human being. Herein, a radio-frequency-driven inductively coupled non-thermal hydrogen plasma was used to treat and reduce graphene oxide (GO) without using any other chemicals, and we found that the plasma-reduced GO (prGO) is with significantly higher bactericidal activity against Escherichia coli. The mechanism of the increased antibacterial activity of prGO is due to that plasma processing breaks down the GO sheets into smaller layers with more rough surface defects, which can thus induce more destructive membrane damages to the bacteria. This work sets another good example, showing that plasma processing is a gre...

Stainless steel induced DNA damage and reduced by nitrogen plasma immersion ion implantation

Micronuclei tests (MNT) using the Chinese Hamster Ovary (CHO) cells and Chinese Hamster Ovary Mutant cells (XRS5) have been conducted to evaluate the biocompatibility of stainless steel 304 (SS304) and nitrogen plasma-implanted SS 304. SS304 induces high MN ratios of the two cell lines and thus has poor biocompatibility. The MN ratio of CHO cells is higher than background by about 63.9% and the MN ratio of XRS5 cells is even higher by about 100%, suggesting that most of the cellular DNA damages on the SS304 are DNA double-strand breaks (DSBs) and are efficiently repaired by the nonhomologous end-joining (NHEJ) pathway. The surface biocompatibility of SS 304 may be enhanced by nitrogen plasma immersion ion implantation (PIII). The altered oxidized species on the nitrogen plasma-implanted surface block cellular DSB repaired by the NHEJ pathway and decrease the MN ratio of XRS5 cells. Our results suggest that cellular DNA damages on the SS304, Cr and N implantation SS304 are mainly repaired by NHEJ pathway way. While cellular DNA damages can be blocked by SS304 implanted NH3 and N. Our results also suggest that the genotoxicity of cell assay such as MNT and DSB is a valid method to investigate biocompatibility.