Issue 54, 2015

Bromate reduction in water by catalytic hydrogenation using metal–organic frameworks and sodium borohydride

Abstract

Catalytic hydrogenation of bromate is a promising approach to remove bromate from water considering that this approach not only removes bromate but also converts it to bromide. However, the reduction of metal catalysts and bromate reduction using a continuous H2 purge inevitably leads to waste of H2 gas. Thus, using solid H2-releasing compounds (e.g., NaBH4) to generate H2 in situ seems to be more advantageous because solid H2-releasing compounds are relatively safe and easy to handle. Recently, Metal–Organic Frameworks (MOFs) have attracted enormous attention owing to their superior physical and chemical characteristics in CO2 capture and H2 storage. Some non-noble-metal MOFs also have been extensively used as catalysts, including hydrolysis of NaBH4 for H2 production. Nevertheless, few studies have studied using MOFs as heterogeneous catalysts to produce hydrogen in situ and then reduce bromate. In fact, metallic catalysts coupled with NaBH4 have not been evaluated for bromate reduction. Thus, this study aims to investigate whether MOFs/NaBH4 can be an effective system to reduce bromate. The iron-bearing MOF, MIL-88A, and the cobalt-bearing MOF, ZIF-67, were selected owing to their non-noble metallic contents. While NaBH4 alone was found to reduce bromate, the combination of MOFs/NaBH4 considerably accelerated the hydrolysis of NaBH4, thereby reducing bromate to bromide. The effect of NaBH4 dosage was found to be the most influential on the removal efficiency and kinetics, while the effect of MOF loading was insignificant. Elevated temperatures and relatively acidic conditions were also more favorable for the bromate reduction. In the presence of other anions, MOFs/NaBH4 still successfully reduced bromate to bromide. MOFs/NaBH4 can be also re-used for the bromate reduction and ZIF-67/NaBH4 even exhibited almost 100% recyclability after 5 cycles. The above-mentioned results indicate that MOFs can successfully facilitate the hydrolysis of NaBH4 and subsequently reduce bromate to bromide in water.

Graphical abstract: Bromate reduction in water by catalytic hydrogenation using metal–organic frameworks and sodium borohydride

Supplementary files

Article information

Article type
Paper
Submitted
31 Mar 2015
Accepted
08 May 2015
First published
08 May 2015

RSC Adv., 2015,5, 43885-43896

Author version available

Bromate reduction in water by catalytic hydrogenation using metal–organic frameworks and sodium borohydride

K. Andrew Lin and S. Chen, RSC Adv., 2015, 5, 43885 DOI: 10.1039/C5RA05705A

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