Iron-doped carbon nanotubes with magnetic enhanced Fe(VI) degradation of arsanilic acid and inorganic arsenic: Role of intermediate iron species and electron transfer.

Arsanilic acid (p-AsA), a prevalently used feed additive, is frequently detected in environment posing a great threat to humans. Potassium ferrate (Fe(VI)) was an efficient way to tackle arsenic contamination under acid and neutral conditions. However, Fe(VI) showed a noneffective removal of p-AsA under alkaline conditions due to its oxidation capacity attenuation. Herein, a magnetic iron-doped carbon nanotubes (F-CNT) was successfully prepared and further catalyzed Fe(VI) to remove p-AsA and total As species. The Fe(VI)/F-CNT system showed an excellent capability to oxidize p-AsA and adsorb total As species over an environment-related pH range of 6-9. The high-valent iron intermediates Fe(V)/Fe(IV) and the mediated electron-transfer played a significant part in the degradation of p-AsA according to the probes/scavengers experiments and galvanic oxidation process. Moreover, the situ formed iron hydroxide oxide and F-CNT significantly improved the adsorption capacity for total As species. The electron-donating groups (semiquinone and hydroquinone) and high graphitization of F-CNT were responsible for activating Fe(VI) based on the analysis of X-ray photoelectron spectroscopy (XPS). Density functional theory calculations and the detected degradation products both indicated that the amino group and the C-As bond of p-AsA were main reactive sites. Notably, Fe(VI)/F-CNT system was resistant to the interference from Cl-, SO42-, and HCO3-, and could effectively remove p-AsA and total As species even in the presence of complex water matrix. In summary, this work proposed an efficient method to use Fe(VI) for degrading pollutants under alkaline conditions and explore a new technology for livestock wastewater advanced treatment.

Degradation of tetracyclines via calcium peroxide activation by ultrasonic: Roles of reactive species, oxidation mechanism and toxicity evaluation.

Tetracyclines (TC) frequently detected in the aqueous environment pose threats to humans and ecosystems. The synergistic technology coupling ultrasound (US) and calcium peroxide (CaO2) has a great potential to abate TC in wastewater. However, the degradation efficiency and detailed mechanism of TC removal in the US/CaO2 system is unclear. This work was carried out to assess the performance and mechanism of TC removal in the US/CaO2 system. The results demonstrated that 99.2% of TC was degraded by the combination of 15 mM CaO2 with ultrasonic power of 400 W (20 kHz), but only about 30% and 4.5% of TC was removed by CaO2 (15 mM) or US (400 W) alone process, respectively. Experiments using specific quenchers and electron paramagnetic resonance (EPR) analysis indicated that the generation of hydroxyl radicals (•OH), superoxide radicals (O2-•), and single oxygen (1O2) in the process, whereas •OH and 1O2 were mainly responsible for the degradation of TC. The removal of TC in the US/CaO2 system has a close relationship with the ultrasonic power, the dosage of CaO2 and TC, and the initial pH. The degradation pathway of TC in the US/CaO2 process was proposed based on the detected oxidation products, and it mainly included N,N-dedimethylation, hydroxylation, and ring-opening reactions. The presence of 10 mM common inorganic anions including chloridion (Cl-), nitrate ion (NO3-), sulfate ion (SO42-), and bicarbonate ion (HCO3-) showed negligible influences on the removal of TC in the US/CaO2 system. The US/CaO2 process could efficiently remove TC in real wastewater. Overall, this work firstly demonstrated that •OH and 1O2 mainly contributed to the removal of pollutants in the US/CaO2 system, which was remarkable for understanding the mechanisms of CaO2-based oxidation process and its future application.

A colorimetric fluorescent probe for rapid and specific detection of nitrite.

The method of fluorescent probes has been an important technique for detection of nitrite (NO2 - ). As an important inorganic salt, excessive nitrite would threaten humans and the environment. In this paper, a colorimetric fluorescent probe P-N (1,2-diaminoanthraquinone) with rapid response and high selectivity, which could detect NO2 - by visual colour changes and fluorescence spectroscopy is presented. The probe P-N solution (pH 1) changed from pink to colourless with the addition of NO2 - and fluorescence intensity at 639 nm clearly decreased. Good linear exists between fluorescence intensities and NO2 - concentrations for the range 0-16 µM, and the detection limit was 54 nM (based on a 3σ/slope). Moreover, probe P-N could also detect NO2 - in real water samples, and results were all satisfactory. Probe P-N shows great practical application value for detecting NO2 - in the environment.

Investigation of long wavelength mid-infrared generation in the tight focusing limit.

An ultrafast coherent long wavelength MIR source based on difference frequency generation was demonstrated. An average power of 2.5 mW at ∼18 µm was achieved. The angular distribution of the generated MIR source under the condition of tight-focusing limit shows the onset of conical emission of the MIR beam due to on-axis phase mismatching.

Highly selective and sensitive fluorescent probe for the rapid detection of mercury ions.

Mercury (Hg) is one of the major toxic heavy metals, harmful to the environment and human health. Thus, it is significantly important to find an easy and quick method to detect Hg2+. In this study, we designed and synthesized a simple fluorescent probe with excellent properties, such as high sensitivity and selectivity, rapid response, and outstanding water solubility. When Hg2+ (5 µM) was added to the probe solution, it exhibited a very large fluorescent enhancement (about 350-fold stronger than the free probe) with the help of hydrogen peroxide (H2O2). Probe HCDC could quantitatively detect Hg2+ in the range of 0-10 µM using the fluorescence spectroscopy method and the detection limit was measured to be about 0.3 nM (based on a 3σ/slope). Analytical application was also studied, and the probe HCDC exhibited excellent response to Hg2+ with the addition of H2O2 in real water samples. So, our proposed probe HCDC provided a practical and promising method for determining Hg2+ in the environment.

A new colorimetric and far-red fluorescent probe for hydrazine with a large red-shifted absorption spectrum.

Recently, growing attention has been paid to the detection of hydrazine (NH2 NH2 ) because of its important roles in industrial chemical and high toxicity to human beings. Herein, we have constructed a new colorimetric and far-red fluorescent probe containing a receptor of 4-bromobutanoate to selectively detect hydrazine. The probe could detect hydrazine quantitatively in the range of 40-500 µM with the detection limit of 2.9 µM. In addition, the probe could monitor hydrazine by the ratiometric method with a large (185 nm) red-shifted absorption spectrum, and the color changes from yellow to blue make it as a 'naked-eye' indicator for hydrazine. Consequently, our proposed probe would be of great benefit for monitoring hydrazine in aqueous solution.