Efficient Removal of Nitrate in Neutral Solution Using Zero-Valent Al Activated by Soaking

Yi-Gong Dai; Xiao-Han Guo; Gen-Wang Ma; Wei-Zhuo Gai; Zhen-Yan Deng

doi:10.1021/acsomega.3c01347

Efficient Removal of Nitrate in Neutral Solution Using Zero-Valent Al Activated by Soaking

ACS Omega. 2023 Jul 10;8(28):24922-24930. doi: 10.1021/acsomega.3c01347. eCollection 2023 Jul 18.

Authors

Yi-Gong Dai^{1

2}, Xiao-Han Guo^{1

2}, Gen-Wang Ma^{1

2}, Wei-Zhuo Gai³, Zhen-Yan Deng^{1

2}

Affiliations

¹ Energy Materials & Physics Group, Department of Physics, Shanghai University, Shanghai 200444, China.
² Institute of Low-Dimensional Carbon and Device Physics, Shanghai University, Shanghai 200444, China.
³ College of Physics and Electronic Information & Henan Key Laboratory of Electromagnetic Transformation and Detection, Luoyang Normal University, Luoyang 471934, China.

Abstract

Nitrate is a contaminant widely found in surface water, and a high concentration of nitrate can pose a serious threat to human health. Zero-valent iron is widely used to reduce nitrate in aqueous solution, but an acidic condition is required. Zero-valent aluminum has a much lower redox potential (E₀(Al³⁺/Al⁰) = -1.662 V) than zero-valent iron (E₀(Fe²⁺/Fe⁰) = -0.44 V), making it a better choice for reduction of nitrate. However, a passive oxide film covering on Al surfaces inhibits its electron transfer. In this work, metal Al powder was activated by a soaking procedure in deionized water. It was found that nitrate in neutral solution can be efficiently and completely reduced by soaked Al, even if the concentration of nitrate-N was up to 100 mg L^-1. Using an optimal soaking time, the soaked Al can remove >90% of nitrate in aqueous solution within ∼2 h at 50 °C. Furthermore, the nitrate reduction efficiency increased with increasing reaction temperature and dosage of Al powder. After reaction, only ∼50% of pristine N content was left in the form of ammonia ions (NH₄⁺) in aqueous solution. Mechanism analyses showed that after soaking, Al particle surfaces were covered by a layer of loose and fine Al(OH)₃ grains, which can shorten the induction time for the beginning of the reaction between inner Al and outside ions or molecules. This is the reason why soaked Al has a high efficiency for nitrate removal. The present results indicate that soaking is an effective way to activate Al to remove nitrate in water.