Transformation of struvite from wastewater to a hydrogen fuel storage compound ammonia borane

Ammonia borane (NH3BH3) is a carrier of hydrogen gas that is known as a carbon-free renewable energy source. A high hydrogen content of ammonia borane and its stability in air at ambient temperatures make it a valuable molecule for its potential use as a hydrogen storage compound. In this study, we investigate a new approach for synthesizing ammonia borane using wastewater-derived ammonia source. Wastewater recycling has always been a global interest towards sustainability. In addition to reclaiming the water, recycling nutrients in wastewater is a topic of interest. Nutrients such as nitrogen, magnesium, and phosphorous are readily recovered from wastewater as struvite (NH4MgPO4·6H2O). This new process involves converting urine into struvite, and then reacting struvite with alkali borohydrides to produce a high-purity ammonia borane. The use of mild reaction conditions without extensive purification process, together with high purity ammonia borane product make this process a desirable course of action for recycling the nitrogen waste. In the course of moving towards a sustainable environment, the energy and wastewater industries will benefit from this combined process of nitrogen removal from wastewater to generate a renewable carbon-free energy molecule.


Table of Contents S1
Thermal analysis of struvite samples by differential scanning calorimeter S2 IR spectrum of ammonia borane (Table 1 entry #1) S3 IR spectrum of ammonia borane (

Figure S14
. Thermogravimetric analysis of ammonia borane synthesized using commercially available struvite from the reaction stopped at 24 hours.A dash line represents crude product and a solid line represents product after purification.

Figure S1 .
Figure S1.DSC curve of struvite purchased from Sigma-Aldrich.Only a single, broad endothermic peak is visible.This corresponds to the major mass loss during heating.The presence of a single peak in the DSC curve indicates that water and ammonia are lost simultaneously from the struvite structure.

Figure S2 .
Figure S2.DSC curve of struvite prepared from wastewater.It is almost identical to the commercially available one from Fig S1.

Figure S4 .
Figure S4.IR spectrum of ammonia borane synthesized from wastewater-derived struvite (Table 1 trial #3).The bands are almost identical to those of Fig S3.

Figure S5 .
Figure S5.IR spectrum of crude ammonia borane synthesized using commercially available struvite from the reaction stopped at 16 hours (before purification).

Figure S6 .
Figure S6.IR spectrum of ammonia borane synthesized using commercially available struvite from the reaction stopped at 16 hours (after purification).The bands are almost identical to those of Fig S3 and Fig S4.

Figure S7 .
Figure S7.IR spectrum of ammonia borane synthesized using commercially available struvite from the reaction stopped at 24 hours (before purification).

Figure S8 .
Figure S8.IR spectrum of ammonia borane synthesized using commercially available struvite from the reaction stopped at 24 hours (after purification).

Figure S9 .
Figure S9.(a) 1 H NMR and (b) 11 B NMR of crude AB from the reaction stopped at 16 hours (c) 1 H NMR and (d) 11 B NMR of purified AB product after ethanol purification (e) 11 B NMR of impure AB from the reaction stopped at 16 hours with integrations to identify and calculate the impurities.A peak at δ4.90 represents borates and the peaks at δ-41 represent borohydride.Samples were dissolved in D2O and spectra acquired at room temperature.

Figure S11 .
Figure S11. 11B NMR spectrum of crude ammonia borane (before purification) synthesized using commercially available struvite from the reaction stopped at 24 hours.Crude yield is 37%.

Figure S12. 1 H
Figure S12. 1 H NMR spectrum of ammonia borane (after purification) synthesized using commercially available struvite from the reaction stopped at 24 hours (after purification).Percent yield is 21%.

Figure S13 .
Figure S13. 11B NMR spectrum of ammonia borane (after purification) synthesized using commercially available struvite from the reaction stopped at 24 hours.Percent yield is 21%.