Removal of nitrophenols and their derivatives by chemical redox: A review

A facile, environment-friendly route is illustrated for the efficient assembly of stable and uniform silver nanoparticles (AgNPs) on the surface of two-dimensional (2D) silica nanosheets (SiNSs, derived from natural kaolinite mineral) via in-situ reduction using Sn(II) as reductant. Compared to the common reduction method using NaBH4 reductant, the loaded AgNPs on AgNPs/SiNSs nanocomposite showed higher purity, uniformity and stability (antioxygenation). The catalytic reduction of 4-nitrophenol (4-NP) over AgNPs/SiNSs nanocatalyst was almost complete within 40 s without stirring and the apparent kinetic rate constant kapp (80.19 × 10−3 s−1) is much higher than those of other substrate-supported Ag/Au nanocatalysts. The effects of support material and assembly approach of AgNPs on the catalytic performance were discussed in detail. The high turnover frequency (TOF) for AgNPs/SiNSs nanocatalyst (3.52 min−1) indicates that the high-density dispersion of uniform small-sized AgNPs on 2D SiNSs surface is responsible for the excellent catalytic property, which offer many active sites for effective contact with the reactants and fast interfacial electron transfer from the AgNPs surface to 4-NP. It exhibits the great potential of 2D silica nanosheets as support materials for the efficient assembly of uniform noble-metal nanoparticles. Moreover, the 2D AgNPs/SiNSs nanocomposite holds a stable catalytic efficiency (around 100%) over five reaction cycles. The high efficiency and convenience have been demonstrated by purifying the 4-NP polluted water in the “filtering and catalyzing” device, in which the polluted water could become colorless within 10 s.

Green assembly of stable and uniform silver nanoparticles on 2D silica nanosheets for catalytic reduction of 4-nitrophenol

In 2008 we published recommendations on chemicals that would be appropriate to evaluate the sensitivity and specificity of new/modified mammalian cell genotoxicity tests, in particular to avoid misleading positive results. In light of new data it is appropriate to update these lists of chemicals. An expert panel was convened and has revised the recommended chemicals to fit the following different sets of characteristics: • Group 1: chemicals that should be detected as positive in in vitro mammalian cell genotoxicity tests. Chemicals in this group are all in vivo genotoxins at one or more endpoints, either due to DNA-reactive or non DNA-reactive mechanisms. Many are known carcinogens with a mutagenic mode of action, but a sub-class of probable aneugens has been introduced. • Group 2: chemicals that should give negative results in in vitro mammalian cell genotoxicity tests. Chemicals in this group are usually negative in vivo and non-DNA-reactive. They are either non-carcinogenic or rodent carcinogens with a non-mutagenic mode of action. • Group 3: chemicals that should give negative results in in vitro mammalian cell genotoxicity tests, but have been reported to induce gene mutations in mouse lymphoma cells, chromosomal aberrations or micronuclei, often at high concentrations or at high levels of cytotoxicity. Chemicals in this group are generally negative in vivo and negative in the Ames test. They are either non-carcinogenic or rodent carcinogens with an accepted non-mutagenic mode of action. This group contains comments as to any conditions that can be identified under which misleading positive results are likely to occur. This paper, therefore, updates these three recommended lists of chemicals and describes how these should be used for any test evaluation program.

R. DeWire

Papers

Assessment of the genotoxic and carcinogenic risks of p-nitrophenol when it is present as an impurity in a drug product