Innovative gas capture technologies with the objective to mitigate CO and CH emissions are discussed in this review. Emphasis is given on the use of nanoparticles (NP) as sorbents of CO and CH, which are the two most important global warming gases. The existing NP sorption processes must overcome certain challenges before their implementation to the industrial scale. These are: i) the utilization of the concentrated gas stream generated by the capture and gas purification technologies, ii) the reduction of the effects of impurities on the operating system, iii) the scale up of the relevant materials, and iv) the retrofitting of technologies in existing facilities. Thus, an innovative design of adsorbents could possibly address those issues. Biogas purification and CH storage would become a new motivation for the development of new sorbent materials, such as nanomaterials. This review discusses the current state of the art on the use of novel nanomaterials as adsorbents for CO and CH. The review shows that materials based on porous supports that are modified with amine or metals are currently providing the most promising results. The FeO-graphene and the MOF-117 based NPs show the greatest CO sorption capacities, due to their high thermal stability and high porosity. Conclusively, one of the main challenges would be to decrease the cost of capture and to scale-up the technologies to minimize large-scale power plant CO emissions.

A novel approach for harvesting Scenedesmus sp. microalgae from real wastewater by using adsorbents of magnetite-based nanoparticles (Fe 3 O 4 NPs) was tested in this study for the first time for this microalgae. Using these NPs, the harvesting efficiency was even higher than 95%. The optimal conditions (0.14 gNPs/L, a short magnetic separation time of only 8 min and 27 min of contact time) were found using the response surface methodology. The best fitting of the adsorption equilibrium results was achieved by the Langmuir isotherm model, and the maximum adsorption capacity for Scenedesmus sp. reached 3.49 g dry cell weight (DCW)/g Fe 3 O 4 NPs. Zeta potential measurements and the Dubinin-Radushkevich isotherm model analysis pointed out that the main adsorption mechanism between Scenedesmus sp. cells and Fe 3 O 4 NPs was electrostatic interaction.Finally, Fe 3 O 4 NPs were six times successfully reused by combining an alkaline treatment with an ultrasonication process, which implies microalgae lysis. The results herein obtained highlight the potential for magnetic separation of microalgae from wastewater, which is capable of reaching a high harvesting efficiency in a very short time.

Highlights• Immobilization of magnetite nanoparticles on cationic polymer was synthesized.• Phosphate removal using magnetite based nanocomposites was tested.• Adsorption isotherms of phosphate at two pH; 5 and 7 were performed.• Different isotherms models were applied for experimental data fitting.• Regeneration and reusability of the magnetite based nanocomposites were carried out. Graphical Abstract 2 AbstractA novel nanocomposite based on magnetite nanoparticles (Fe3O4-NPs) immobilized on the surface of the cationic exchange polymer, C100, using a modification of the coprecipitation method was developed to obtain magnetic nanocomposites (NCs) for phosphate removal and recovery from water. High resolution TEM-EDS, SEM, XRD, and ICP-OES were used to characterize the NCs. The continuous adsorption process by the so-called breakthrough curves was used to determine the adsorption capacity of the Fe3O4 based NC. The adsorption 3 capacity conditions were studied under different conditions (pH, phosphate concentration and concentration of NPs). The optimum concentration of iron in the NC for phosphate removal was 23.59 mgFe/gNC. The sorption isotherms of this material were performed at pHs 5 and 7.Taking into account the real application of this novel material in real water, the experiments were performed at pH 7, achieving an adsorption capacity higher than 4.9 mgPO4-P/gNC.Moreover, Freundlich, Langmuir and a combination of them fit the experimental data and were used for interpreting the influence of pH on the sorption and the adsorption mechanism for this novel material. Furthermore, regeneration and reusability of the nanocomposite were tested obtaining 97.5 % recovery of phosphate for the first cycle and at least 7 cycles of adsorptiondesorption were carried out with more than 40% of recovery. Thus, this work described a novel magnetic nanoadsorbent with promoting properties for phosphate recovery in wastewater.

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Synthesized magnetic core-shell Ce-Ti@FeO nanoparticles were tested, as an adsorbent, for fluoride removal and the adsorption studies were optimized. Adsorption capacity was compared with the synthesized Ce-Ti oxide nanoparticles. The adsorption equilibrium for the Ce-Ti@FeO adsorbent was found to occur in <15min and it was demonstrated to be stable and efficient in a wide pH range of 5-11 with high fluoride removal efficiency over 80% of all cases. Furthermore, isotherm data were fitted using Langmuir and Freundlich models, and the adsorption capacities resulted in 44.37 and 91.04mg/g, at pH7, for Ce-Ti oxides and Ce-Ti@FeO nanoparticles, respectively. The physical sorption mechanism was estimated using the Dubinin-Radushkevich model. An anionic exchange process between the OH group on the surface of the Ce-Ti@FeO nanomaterial and the F was involved in the adsorption. Moreover, thermodynamic parameters proved the spontaneous process for the adsorption of fluoride on Ce-Ti@FeO nanoparticles. The reusability of the material through magnetic recovery was demonstrated for five cycles of adsorption-desorption. Although the nanoparticles suffer slight structure modifications after their reusability, they keep their adsorption capacity. Likewise, the efficiency of the Ce-Ti@FeO was demonstrated when applied to real water to obtain a residual concentration of F below the maximum contaminated level, 1.5mg/L (WHO, 2006).