Abstract
Nitrate reduction by zero-valent iron-based materials has been extensively studied. However, the aggregation of nanoparticles and the preference for unfavored ammonia products limit the application of this technology. To overcome this issue, this study introduced a novel synthesized nanoscale palladized zero-valent iron graphene composite (nZVI-Pd/NG) and explored its nitrate reduction efficiency. A nitrate removal rate of 97.0% was achieved after 120 min of reaction for an initial nitrate concentration of 100 mg N/L. The nitrogen gas selectivity was enhanced from 0.4% to 15.6% at the end point compared to nanoscale zero-valent iron (nZVI) particles under the same conditions. Further analyses revealed that zero-valent metal nanoparticles spread uniformly on the graphene surface, with a thin layer of iron (hydr)oxides dominated by magnetite. The nZVI-Pd/NG exhibited good catalytic activity with the associated activation energy of 17.6 kJ/mol being significantly lower than that with nZVI (42.8 kJ/mol). The acidic condition promoted a higher nZVI utilization rate, with the excess dosage of nZVI-Pd/NG ensuring a high nitrate removal rate for a wide pH range. This study demonstrates an improvement in nitrate reduction efficiency in a nZVI system by combining the exceptional properties of graphene and palladium.
Highlights
Nitrate is a major environmental pollutant in surface and ground water systems[1,2]
This study introduces a novel synthesized nanoscale palladized zero-valent iron graphene composite, and its nitrate removal efficiency was investigated through batch experiments
Were investigated through BET, SEM, energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, with fresh nanoscale zero-valent iron (nZVI) and graphene characterized for comparison
Summary
Nitrate is a major environmental pollutant in surface and ground water systems[1,2]. Nitrate overload in water causes eutrophication and poses a threat on human health when consumed[3,4,5]. The microscale particles formed are considered to behave like the microscale ZVI20 It has been reported in many studies that as reaction proceeds, iron corrosion products (such as maghemite, lepidocrocite, magnetite, akaganeite, goethite) may cover the core-shell structure of nZVI, preventing subsequent reactions[21,22]. The deposition of nZVI on supports improves denitration performance by relieving their self-agglomeration and offering a high surface area for mass transfer[33]. To the best of our knowledge, bimetal nanoparticles (i.e., zero-valent iron and palladium) embedded in graphene for nitrate removal have not yet been reported, with the synergistic effect of graphene and a catalyst on nitrate reduction lacking comprehensive studies
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