News from China

Effect of C₆₀ nanocrystalline dispersion on its photochemical properties¹

Considering the wide range of industrial applications of fullerene C₆₀, its release into the aquatic environment and accumulation with other contaminants is inevitable, which has elicited concerns regarding its potential environmental and health effects. It has been reported that the physicochemical properties and the behavior in the environment of nC₆₀ nanoparticles, including the aggregates size, morphology and surface zeta potential, were sensitive to complex hydrological conditions, and they usually vary with changes in conditions, such as alkalinity, ionic strength or contact with other pollutants. That means, the transport and fate of nC₆₀ as well as ecological effects are complicated and largely unknown. Therefore, evaluating the environmental impact of nC₆₀ requires careful and thorough characterization of its physicochemical properties in the natural aqueous environment. The nonionic surfactant (TX100) can induce nC₆₀ to restore photoactivity, according to research published in Chinese Environmental Chemistry (2011, 30, 1534–1538), which makes the mechanisms of C₆₀'s transformation and toxicity more complicated.

The type of surfactant has an important influence on the dispersive–aggregative status of nC₆₀ aggregates, which plays a key role in whether nC₆₀ can have photochemical reactivity, explains Prof. Bo Zhang, an environmental chemist at the School of Environmental Science and Engineering, Shanghai Jiaotong University, China. In Prof. Zhang's study, FFA, as a scavenger of ¹O₂, was selected to detect the production of ¹O₂ by nC₆₀ aggregates in the presence or absence of surfactants under UVA irradiation. The nC₆₀ aggregates and CTAB, SDS, and TX100 solution themselves cannot produce ¹O₂. The production of ¹O₂ was observed only in the presence of TX100 above its CMC, while for nC₆₀ aggregates with CTAB and SDS, ¹O₂ cannot be produced. Both TEM and DLS analysis show the nC₆₀ aggregates in the presence of TX100 become more dispersed with the Z_ave decreasing to 22 nm, compared to SDS and CTAB. That means restoration of nC₆₀'s photochemical reactivity in the presence of TX100 was related to the change in dispersion status of nC₆₀ during this physical interaction process between TX100 and nC₆₀.

Human exposure to nanoparticles is directly related to their environmental behavior. The fate of C₆₀ nanoparticles in water depends on their dispersive–aggregative status. This study illustrates that C₆₀ can restore its molecular photochemical reactivity with TX100, which suggests surfactants, as common environmental pollutants, can change the environmental fate of nC₆₀ in water environments and increase the environmental risk due to the change in the dispersive–aggregative status of nC₆₀ aggregates. Thus accurate characterization of physicochemical properties of nC₆₀ aggregates is necessary for evaluating their environmental behaviour and fate in the environment.

(Contributed by the editorial office of “Chinese Environmental Chemistry”)

Effect of gold nanoparticles on the efficiency and specificity of polymerase chain reaction²

Gold nanoparticles (AuNPs) modified with different chemical groups are widely used in many fields, particularly in biological analysis, detection and biomedical research. With AuNPs increasingly applied in biomedicine, the interactions between surface-modified AuNPs and biological macromolecules cannot be ignored, since they are potentially hazardous to human health. Studies on the effect of AuNPs on the efficiency and specificity of polymerase chain reactions (PCR) may establish a simple method to evaluate the potential toxic effects of various surface-modified AuNPs, according to the research published in a recent issue of Chinese Environmental Chemistry (2012, 31, 1–8).

“The size, concentration and the surface properties of AuNPs can affect the efficiency and specificity of PCR significantly”, explains Associate Prof. Yong Liang, an environmental toxicologist at the School of Medicine, Jianghan University, China. Recent studies showed that diverse surface-modified AuNPs have different toxic effects to various types of cells, which are mainly caused by their interactions with biological macromolecules. However, the inherent molecular mechanisms remain unclear. The researchers from Jianghan University prepared three types of AuNPs by the methods of sodium citrate (Na₃Ct) reduction, polyvinylpyrrolidone (PVP) surface coating, and mercaptopropionic acid–homocysteine (MPA–HCys) surface coating, and compared their effects on PCR. Furthermore, they applied competitive primers to compare the effect of the three AuNPs on PCR specificity, and to clarify the main factors that affected PCR specificity and yield.

It turned out that the three types of AuNPs significantly enhanced PCR efficiency in the order of Na₃Ct–AuNPs (12 nm) > MPA–HCys–AuNPs (12 nm) > PVP–AuNPs (4 nm), and the enhancement was dependent on their concentration and size. Furthermore, by comparing the two nanoparticles of similar size (Na₃Ct–AuNPs and MPA–HCys–AuNPs), Na₃Ct–AuNPs improved the PCR efficiency more profoundly, indicating that the surface properties are also important factors in influencing the PCR efficiency. In addition, the three AuNPs effectively eliminated the inhibition of the competitive primer on PCR in a concentration-dependent manner. These results indicate that the three AuNPs can dramatically enhance the efficiency and specificity of PCR, and this effect is related to its concentration, size and surface properties.

(Contributed by the editorial office of “Chinese Environmental Chemistry”)

Visible light photocatalytic properties of iodine/cerium co-doped nano TiO₂

Photocatalytic reactions have drawn intensive research interest due to their significance in a variety of processes such as solar energy conversion and environmental contaminant degradation. Titanium oxide (TiO₂) is a semiconductor material frequently employed in photocatalytic reactions. However, due to its wide band gap, utilization of visible light by TiO₂ is very limited. It has been recognized that doping of TiO₂ with other elements can enhance its absorption of visible light. In a recent report from the research group of Prof. Yingping Huang, China Three Gorges University, an iodine/cerium (I/Ce) co-doped nano TiO₂ photocatalyst was synthesized, and the effect of co-doping on the structure and visible light photocatalytic activity was studied.³

Un-doped, Ce-doped and I\Ce co-doped TiO₂ nanoparticles with two different doping ratios were synthesized by the sol–gel method, and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible diffuse reflection spectroscopy. The TEM images showed that all the particles were well dispersed and uniformly distributed with a size of 10 nm diameter. Based on XRD data, all the crystals were anatase after calcination at 450 °C. Ce and I atoms possibly entered the crystal lattice to form I–Ce–O and O–Ti–I bonds. UV-visible diffuse reflection spectroscopy revealed that the band gap of the co-doped TiO₂ was 2.76 eV, which is significantly narrower than pure TiO₂ (3.14 eV).

The degradation of rhodamine B (RhB) and salicylic acid (SA) were used as the model reactions to determine the optimal concentration of Ce and I. The results indicated that the optimal molar ratio was n_Ce : n_I : n_Ti = 0.04 : 0.05 : 1, and the I_0.05Ce_0.04TiO₂ catalyst had 2 and 3 times higher activity respectively than Ce–TiO₂ and TiO₂ under visible light irradiation (λ > 420 nm). The photocatalytic process was proposed mainly as the hole oxidation mechanism along with the formation of ˙OH, O₂˙⁻ and H₂O₂. I\Ce co-doping efficiently decreased the recombination rate of the electron–hole pairs in the semiconductor.

(Contributed by the editorial office of “Chinese Environmental Chemistry”)

References

1. M. Ni, B. Zhang, Y. He, J. Kim and J. B. Hughes, Chinese Environmental Chemistry, 2011, 30, 1533–1538.
2. J. Yao, Y. Lin, J. Li, Q. Zhou and Y. Liang, Chinese Environmental Chemistry, 2012, 31, 1–8.
3. Y. Fang, T. Lan, Y. Zheng, J. Yang, A. Deng, A. Zhang and Y. Huang, Chinese Environmental Chemistry, 2012, 31, 135–142.

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