Peroxymonosulfate activation by walnut shell activated carbon supported nano zero-valent iron for the degradation of tetracycline: Performance, degradation pathway and mechanism

In this study, activated carbon (WS-AC) was prepared from walnut shell. Nano-zero-valent iron (nZVI) was loaded on walnut shell activated carbon by liquid phase reduction method and used as catalyst (WS-AC/nZVI) to activate peroxymonosulfate (PMS) to efficiently degrade tetracycline (TC) in solution. The composite material with a mass ratio of WS-AC to nZVI of 1:1 has the highest catalytic performance for activating PMS to degrade TC. The results showed that under the conditions of TC concentration of 100 ppm, PMS dosage of 0.2 mM and WS-AC/nZVI dosage of 0.1 g/L, the removal efficiency of TC could reach 81%. Based on quenching experiments and electron spin resonance (EPR), it was verified that •OH, SO4•- and 1O2 bound on the catalyst surface were the main reactive oxygen species during the reaction. The intermediate products of TC were identified by liquid chromatography-mass spectrometry (HPLC-MS) and DFT calculation, and the possible degradation pathway of TC was proposed. The catalyst still maintained high removal efficiency of TC after four cycles of experiments, and the minimal iron loss on the surface of the catalyst indicated that it had good stability. The efficient and stable WS-AC/nZVI activated PMS showed great potential in the degradation of antibiotics.

Efficient treatment of ammonia-nitrogen contaminated waters by nano zero-valent iron/zeolite composite

The aim of the present study is developing a magnetic nanoscale zero-valent iron/zeolite (nZVI/Z) composite towards the efficient removal of ammonia-nitrogen (NH₄⁺-N) from aqueous solutions. Series of batch experiments were conducted to investigate the effect of different factors on the removal efficiency, including pH effect, aerobic/anaerobic, NH₄⁺-N initial concentration, and temperature. The mixing mass ratio of nZVI/Z was optimized to reach the optimal ratio (0.25 g nZVI: 0.75 g zeolite), corresponding to the best removal efficiency of 85.7% after 120 min of reaction. Results revealed that nZVI/Z is efficient for NH₄⁺-N removal from water at a wide pH range (3.0-10.0), with superiority to the neutral conditions. Moreover, aerobic ambient and normal temperature of 25 °C were the optimal conditions for the removal process of NH₄⁺-N. Removal mechanisms involved electrostatic attraction, ion exchange, and adsorption. Generally, nZVI/Z has great potential towards the practical applications of NH₄⁺-N removal from water.

Ultrasound-assisted heterogeneous activation of persulfate by nano zero-valent iron (nZVI) for the propranolol degradation in water

This study investigated the degradation of propranolol (PRO), a beta (β)-blockers, by nano zero-valent iron (nZVI) activated persulfate (PS) under ultrasonic irradiation. Effects of several critical factors were evaluated, inclusive of PS concentration, nZVI dosage, ultrasound power, initial pH, common anions, and chelating agent on PRO degradation kinetics. Higher PS concentration, nZVI dosage and ultrasound power as well as acidic pH favored the PRO degradation. Conversely, anions and chelating agent took on the inhibitory effect towards PRO degradation to different extents. Furthermore, the variations of morphology and surface composition of nZVI before and after the reaction were characterized by TEM, XRD and XPS. Finally, on the basis of identified degradation intermediates by LC/MS/MS analysis, this work tentatively proposed the degradation pathways. These encouraging results suggest that US/nZVI/PS process is a promising strategy for the treatment of PRO-induced water pollutant.