Reductive Degradation Of Organic Pollutants In Water Via Zero-valent Aluminum

The application of zero-valent metals (ZVMs) have emerged as an efficient technology for the reductive degradation organic pollutants in the water. The iron is the mostly used ZVMs, and other ZVMs include aluminum, zinc, copper and so on. However, the aluminum metal is a strong reducing agent that has a standard reduction potential (E0=-1.662 V) more negative than ZVI (E0=-0.43 V). Also, the ZVA1 has lower weight than the ZVI. Furthermore, the ZVAl has reactivity under both acidic and alkaline condition. This means that the ZVA1 can reduce pollutants under a wider pH range compared to the ZVI. However, the ZVAl is commonly covered with a native oxide layer (Al2O3), which hinders the strong reducing ability of ZVAl. Now, most studies are focused on the oxide layer removal of ZVA1, then using the ZVAI/O2 system to oxidative degradation contaminants. Now, our research is aimed at using the mild ZVAl without any surface pretreatment to reductive degradation of nitrobenzene (NB), acid orange 7 (AO7) which were used as model pollutants. Specific research contents and results are as follows:(1) Because the ZVAl has amphoteric character, we have investigated the ZVAl (without any surface pretreatment) reductive degradation NB under acidic (pH= 1.0-4.0) and alkaline (pH= 8.0-12.0) condition. The results show that ZVAl can reduce NB only under strong acidic condition (pH< 2.0), and the reductive degradation need longer inductive time, and the reductive efficiency is very poor. Under the alkaline condition, although the ZVAl is not pretreated, the ZVAl can react with NB very quickly. The NB can be reduced to AN within 10 minute without any inductive time. Meanwhile the reductive reaction only can happen when the pH value is higher than 11.0. And the reductive efficiency is increased with the pH elevated. The particle size also has great effect on the reductive degradation of NB. The reductive efficiency brings down when the particle size of ZVAl is increased.(2) We have investigated the ZVAl (without any surface pretreatment) reduce the NB under carbonate buffered solution. We also find that the oxide layer of ZVAl can be removed quickly under carbonate buffered solution, then the ZVAl can transfer the electron to NB, and form AN. Under carbonate buffered solution, ZVAl can reduce NB more efficiently compared to that at the equally unbuffered pH. Furthermore, the pH range is wider than that under unbuffered solution:The reductive reaction can occur at pH= 10.3 under the buffered solution. The efficiency is also influenced with the ZVAl’s particle size. We can include that the buffered solution can maintain steady pH. The oxide layer of ZVAl can be removed effectively under the buffered solution, and the reduction efficiency of NB is better by ZVAl.(3) In this part we study the effect of temperature on the NB reduction by 100-200 mesh ZVAl. We find that the temperature can enhance the corrosion of ZVAl, then the ZVAl can reduce the NB more effectively, and the reductive efficiency is better. Furthermore, the temperature also can shorten the inductive time of NB reduction under acidic condition, and the temperature even can expand the pH range of the reductive reaction of NB under alkaline condition. The ZVAl can reduce the NB even at the pH= 8.5-10.0.(4) We can find that the ZVAl (without any surface pretreatment) can effectively reduce the NB under the alkaline condition. So we also investigate the reductive degradation of other organic pollutants for example the typical azo dyes:AO7. The result also shows that the ZVAl also can successfully reduce the AO7.In conclusion, using ZVAl (without any surface pretreaatment) under alkaline condition to reduce the organic pollutants is feasible. Especially, under carbon buffered solution the ZVAl can obtain a significant reduction effect for the organic pollutants. This method provides a new idea for the ZVAl application on the reductive degradation of organic pollutants.