Quoc Cuong Do

The emerging H2 economy faces storage and transport challenges, and the use of ammonia (NH3) as a COx-free source of H2 via NH3 decomposition has recently attracted attention. Noble Ru-based catalysts are considered the best choice for highly efficient NH3 decomposition; however, their high cost and limited availability are disadvantages in large-scale applications. Otherwise, among non-noble metal-based catalysts, Ni-based catalysts are the most active, and Ni is considered a good alternative candidate material for NH3 decomposition because of its low cost. At present, some challenges remain in efforts to improve the efficiency of both Ru- and Ni-based systems. This review covers recent developments regarding these catalysts and can serve as a comprehensive work for evaluating effective long-term strategies.

Livestock wastewater effluent generated after the anaerobic treatment process contains the considerable amount of color-causing organic matter. In this study, a quantitative comparison of three carbon-based adsorbents included granular activated carbon (GAC), expanded graphite (EG), and multi-walled carbon nanotubes (MWNTs) was carried out for the potential application to the removal of color substances, and their mechanism was proposed. Although GAC showed the highest specific dissolved organic carbon (DOC) adsorption capacity, the color removal efficiency was the smallest among three adsorbents. The selective color removal ratios of EG and MWNTs reached 22.7 ± 0.1 PtCo/mg-DOC-removed and 21.2 ± 0.1 PtCo/mg-DOC-removed, respectively, while that of GAC was only 12.3 ± 0.1 PtCo/mg-DOC-removed. The selective adsorption of color substances by graphene-based carbon materials was due to the aromatic π–π interaction between organic matter and the hexagonal carbon lattice of graphene. The analysis of molecular weight distribution also confirmed that the exposed surface area and macro-pores were responsible for the adsorption of high molecular weight color substances. The chemical regeneration of three adsorbents was examined using 1% NaOCl solution and MWNTs showed almost complete recovery of the initial color removal capacity. In conclusion, MWNTs were the most suitable carbon nanomaterial for the selective color removal from livestock wastewater effluent.

In this study, expanded graphite (EG) was decorated with manganese oxide nanoparticles (MONPs) by the hydrothermal method, and the newly formed composite (MONPs-EG) was applied as adsorbent for the removal of heavy metals from aqueous solutions. The comparative and competitive adsorption of Pb²⁺ and Ni²⁺ (0.01–1.00 mM) on MONPs-EG was investigated. Data from isothermal adsorption of single and binary systems suggested that both Pb²⁺ and Ni²⁺ were well described by the Langmuir isotherm, and the maximum adsorption capacities at 298 K were calculated at 0.278 and 0.113 mmol/g for Pb²⁺ and Ni²⁺, respectively. In binary systems, a dramatic decrease in adsorption capacity of Ni²⁺ was observed, while the adsorption capacity of Pb²⁺ was almost stable, indicating the favorable adsorption of Pb²⁺ over Ni²⁺ onto the prepared adsorbent. Kinetics studies of single and binary systems showed that a pseudo-second order model could explain the adsorption processes well. Thermodynamic analysis results demonstrated that the adsorption of these metal ions on the prepared adsorbent is spontaneous and exothermic in nature. The adsorption capacity of MONPs-EG increased significantly in the presence of humic acids. Overall, the results of this study suggest that MONPs-EG can be used effectively as an adsorbent for heavy metals removal from aqueous solutions.