Journal
CHEMICAL ENGINEERING JOURNAL
Volume 430, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2021.133133
Keywords
Nanoscale zero-valent iron; Nitrate reduction; N-2 selectivity; Pd@Fe; DFT calculation
Categories
Funding
- National Natural Science Foundation of China [51978110]
- Natural Science Foundation of Chongqing Science & Technology Commission [cstc2019jcyj-msxmX0260]
- Science and Technology Research Program of Chongqing Municipal Education Commission [KJQN201900837]
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The research demonstrates that nanoscale zero-valent iron-based nanoparticles have low N-2 selectivity in nitrate removal, but after surface modification with Pd, the N-2 selectivity and NO3- removal efficiency can be improved. The theoretical calculations reveal that Pd plays a crucial role in weakening the binding strengths of H* and N* on the catalyst surface, promoting the formation of N-2.
Nitrate (NO3-) removal on nanoscale zero-valent iron-based nanoparticles (nFe(0) particles) represents one efficient and green technology for nitrate pollution abatement, but its development is hindered by the low product selectivity towards harmless N-2. Herein we demonstrate the inferior performance of nFe(0) in N-2 production originates from its over-strong affinity with both the H* and the N-intermediates (denoted as N*), leading to a low N/H molar ratio and a poor mobility of N* on Fe surface that facilitates the formation of NH3 rather than N-2. Increasing NO3- feeding concentration or lowing nFe(0) dose can uplift the N-2 selectivity up to 41.9% (vs. 19.3% by single nFe(0) in removing 20 mg L-1 NO3--N), but has to sacrifice NO3- removal efficiency and yield more toxic NO2-. The nFe(0) surface modification by 12.0 wt% palladium (Pd) gives rise to a N-2 selectivity of 46.0% and a NO3- removal efficiency above 90% (vs. 100% by single nFe(0)). Theoretical calculations reveal the critical role of Pd in weakening the binding strengths of H* and N* on catalyst, which enables to reduce the H* adsorption and promote the migration of N* that increases the N*-N* encountering possibility for N-2 formation. This correlation between surface chemistry and NO3- conversion may guide the design of improved Fe-0-based materials for practical nitrate remediation.
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