Synthesis of thickness-controllable polydopamine modified halloysite nanotubes (HNTs@PDA) for uranium (VI) removal.

Halloysite nanotubes (HNTs) are considered structurally promising adsorption materials, but their application is limited due to their poor native adsorption properties. Improving the adsorption capacity of HNTs for radioactive U(VI) is of great significance. By controlling the mass ratio of HNTs and dopamine (DA), composite adsorbents (HNTs@PDA) with different polydopamine (PDA) layer thicknesses were synthesized. Characterization of HNTs@PDA demonstrated that the original structure of the HNTs was maintained. Adsorption experiments verified that the adsorption capacity of HNTs@PDA for U(VI) was significantly improved. The effects of solution pH, temperature, and coexisting ions on the adsorption process were investigated. The removal efficiency was observed to be 75% after five repeated uses. The adsorption mechanism of U(VI) by HNTs@PDA can be explained by considering electrostatic interactions and the complexation of C-O, -NH- and C-N/CN in the PDA layer. This study provides some basic information for the application of HNTs for U(VI) removal.

Removal of levofloxacin through adsorption and peroxymonosulfate activation using carbothermal reduction synthesized nZVI/carbon fiber.

Nano zero-valent iron (nZVI) is widely used for decontamination. The main issues associated with nZVI are agglomeration and oxidation in the long term. In this study, the carbothermal reduction of cotton fiber was conducted for the synthesis of nZVI supported on cotton carbon fiber (nZVI/CF) to address the agglomeration and oxidation of nZVI. Synergistic adsorption and peroxymonosulfate (PMS) activation using nZVI/CF for removing levofloxacin (LEV) are reported herein. The nZVI concentration and morphology were conveniently adjusted by soaking cotton fiber in ferric nitrate solutions of various Fe3+ concentrations. The carbothermal reduction of the cotton fiber at 900 °C contributed to the reduction of Fe3+ into nZVI. A nZVI/CF-900-0.3 system was obtained through the carbothermal reduction of cotton fiber soaked in 0.3 M ferric nitrate. Favorable adsorption of nZVI/CF-900-0.3 to LEV facilitated LEV degradation under PMS activation. Approximately 93.83% of LEV (C0 = 20 ppm) was removed within 60 min with 0.2 g/L of the catalyst and 1 mM PMS. It was preferable to use nZVI + CF-900 to activate PMS for degrading LEV, thus confirming the favorable effect of LEV adsorption on further degradation. The nZVI/CF-900-0.3 exhibited excellent long-term stability given that it was able to activate PMS after it was stored for 6 months. ·SO4- played an important role in LEV degradation in the presence of PMS.

Effect of nonionic surfactants on the oxidation of carbaryl by anodic Fenton treatment.

As a potentially promising technology, anodic Fenton treatment (AFT) has been shown to be very successful in pesticide removal. However, the influence of other constituents in the pesticide formulation, such as nonionic surfactants, has not been addressed. In this study, the effect of Triton X (TX) on the degradation kinetics and pathways of carbaryl undergoing AFT was investigated in an effort to facilitate its practical application. The presence of Triton X-100 was found to slow down the carbaryl degradation rate. This result can be attributed to the consumption of hydroxyl radicals ((*)OH) by surfactants and the formation of a carbaryl...TX...Fe(3+) complex, resulting in the unavailability of carbaryl to (*)OH attack. The modified AFT kinetic model previously developed in this laboratory shows an excellent fit to the carbaryl degradation profile (R(2)>0.998), supporting the formation of a carbaryl...TX...Fe(3+) complex. The carbaryl degradation rate decreased as Triton X-100 concentration increased from 20 to 1000 mg L(-1). Both (*)OH consumption by surfactants and complex formation are responsible for the degradation rate reduction below the critical micelle concentration (CMC), whereas the complex and micelle formation becomes a more dominant factor above the CMC. The effect of ethylene oxide (EO) numbers of a given nonionic surfactant mainly lies in the consumption of hydroxyl radicals, which increases with the length of the EO chain, but does not significantly affect the formation of the carbaryl...TX...Fe(3+) complex. Based on the GC-MS and LC-ESI-MS results, no evidence was found that the carbaryl degradation pathway was affected. Carbaryl was typically oxidized to 1-naphthol and 1,4-naphthoquinone similar to what is observed in the absence of surfactants. Triton X-100 was degraded via the breakdown of EO chains and omega-oxidation of the terminal methyl group, which resulted in the production of a series of ethoxylate oligomers.