This study investigated the combustion behavior and evolved greenhouse gases of coal, Scenedesmus microalgae, and coal-Scenedesmus microalgae blends (Coalgae® 5–20%) in air using a thermogravimetric analyzer (TG)-mass spectrometer (MS). Coalgae® refers to a blend of coal fines and microalgae biomass. TG-DTG curves of coal and microalgae confirmed that the combustion behavior of these materials were different. Scanning Electron Micrograph (SEM) morphology images of ash obtained from the combustion of coal and Coalgae® 5–20% confirmed changes in devolatilization and combustion behavior of solid raw fuel. A significant reduction in activation energy of 160.4 kJ/mol, 159.6 kJ/mol, 151.3 kJ/mol, and 134.2 kJ/mol for Coalgae® 5%, Coalgae® 10%, Coalgae® 15% and Coalgae® 20%, respectively, compared to coal (161.3 kJ/mol) was achieved. The lowering of activation energy could be attributed to the relative decrease in fixed carbon. MS data presented a decrease in the emissions of CO₂ (m/e 44), NOx (NO: m/e 30 and NO₂: m/e 46) and SO₂ (m/e 64) from coal to Coalgae® 5–20% due to the complex combustion mechanism in the presence of radicals. The Coalgae® blends showed a synergistic effect due to different combustion characteristics of coal and Scenedesmus microalgae. The results obtained from this work provide a reference to further work on co-combustion of coal and microalgae to some extent.

This study investigated the effect of coal–Scenedesmus microalgae (with blending ratios of 100:0 (coal), 95:5 (Coalgae^® 5%), 90:10 (Coalgae^® 10%), 85:15 (Coalgae^® 15%) and 80:20 (Coalgae^® 20%)) on combustion temperature, mass loss, the formation of CO₂, SO₂ and NOx gases, and ash content under constant atmospheric air flow. Coalgae^® refers to a material formed after blending coal and microalgae. The results showed that NOx came mainly from Coalgae^® 10% and 15%, and this observation could be attributed to a variable air concentration level (O₂ level) in the environment that could influence NOx during the combustion process, irrespective of the blending ratios. CO₂ emission reductions (12%, 17%, 21% and 29%) and SO₂ emission reductions (3%, 12%, 16% and 19%) increased with the increasing coal-microalgae blending ratio (Coalgae^® 5–20%), respectively. Bubble-like morphology was observed in the ash particles of coal–microalgae blends through SEM, while the TEM confirmed the formation of carbon-based sheets and graphitic-based nanocomposites influenced by the microalgae amounts. Ash residues of the coal–microalgae blends contained high amounts of fluxing compounds (Fe₂O₃, K₂O, CaO and MgO), which resulted in an increased base/acid ratio from 0.189 (coal) to 0.568 (Coalgae^® 20%). Based on the above findings, the co-firing of coal–Scenedesmus microalgae led to a reduction in CO₂, SO₂, and NOx emissions. As such, lower Coalgae^® blends can be considered as an alternative fuel in any coal-driven process for energy generation.

Metal-organic frameworks (MOFs) refer to porous materials which have received excessive interest due to their unique structural diversity thus helping them maintain high surface area and porosity. Zirconium-based MOFs (UiO-66) can be easily modified with various functional groups, allowing control over how strongly an analyte binds to the MOF. Amine-functionalized UiO-66 MOFs (UiO-66-NH ₂ ) offers higher surface areas and exceptional porosity with potentially enhanced activity compared to traditionally used materials such as base metal oxides and offer shape/size selectivity, which attracts many applications such as gas storage, gas purification and separation, wastewater treatment. In recent studies, UiO-66-NH ₂ has been incorporated with nanomaterials such as graphene oxide (GO) (UiO-66-NH ₂ /GO) to improve its properties for adsorption applications. In this review, we present the synthetic methods, characteristic properties, and adsorption/separation applications of amine-functionalized zirconium-based metal-organic frameworks as well as incorporation of these MOFs in polymeric membranes. Lastly, challenges and future perspectives of UiO-66-NH ₂ /GO MOFs are discussed.