Nickel and Its Oxide-Modified Biochar for Enhanced Removal of Ammonia: Theoretical Study and Practical Application

A series of metal- and metal oxide-modified biochars were prepared to remove ammonia (NH3). Maize straw was used as the precursor to fabricate biochar, four kinds of biochar with different metal modification were prepared by impregnation method, and the part of metal on the surface of biochar was converted to metal oxide after secondary pyrolysis. It was found that adsorption capacity of BC-Ni-O on NH3 was the highest (118.6 mg/g), which was due to the strong coordination and complexation between metal nickel and ammonia molecules. BC-Ni-O also shows good cycling performance. The mechanism analysis shows that the formation of metal oxides can increase the specific surface area of the adsorbent which plays an important role in the adsorption. The formation of NiO and Ni2+ in secondary pyrolysis plays a major role in the adsorption process, and their contribution is about 86%. To assess the reliability of adsorbent in practical application, the air purification experiment was conducted in a 30-m(3) air chamber. High removal rate of ammonia is recorded 85.9% in single-component gas, and it still maintained at 72.6% in a mixed-component gas (the concentration of toluene, formaldehyde, and ammonia is 1 mg/m(3), 1 mg/m(3), and 1.5 mg/m(3), respectively).

Automated summary

Metal- and metal oxide-modified biochars were used to remove ammonia efficiently. The metal modification and formation of metal oxides increased the specific surface area of the adsorbent, enhancing its adsorption capacity. The experimental results showed that the modified biochar had a high removal rate for ammonia and maintained good removal efficiency in a mixed gas environment.