Exploration of the degradation mechanism of ciprofloxacin in water by nano zero-valent iron combined with activated carbon and nickel

The addition of second transition metal element has been proven to be one of the most efficient methods to enhance removal efficiency of nano zero-valent iron (nZVI). Here, activated carbon-supported nano zero-valent iron/nickel bimetal composite (AC-nZVI/Ni) as efficient adsorbents to remove ciprofloxacin (CIP) in water is reported. The dispersity of nZVI is dramatically improved by AC. Mass ratio of iron to nickel (50:1) endows AC-nZVI/Ni excellent removal efficiency (98.5% at 120 min), which can be achieved in a wide range of pH. The investigations on degradation kinetics show kinetic behavior is affected by Ni element because the reaction order is changed from pseudo-first-order (AC-nZVI) to pseudo-second-order (AC-nZVI/Ni). At the same time the apparent active energy (Ea) is decreased from 61.06 to 47.11 kJ/mol, which is beneficial for rapid removal of CIP. With the help of AC, the oxidation resistance of AC-nZVI/Ni is the highest one among experimental samples in 100 days, suggesting a good long-term stability. Eventually, three possible degradation paths and ten degradation products of CIP are proposed depending on the analysis of Liquid chromatography-mass spectrometry (LC-MS). These findings may provide a new perspective on evaluating the roles of second metal and supported material to enhance the removal efficiency of nZVI, which is helpful to tailor and create high-efficiency adsorbent material based on nZVI for wastewater fields.