Biological and composting processes used in the treatment of municipal solid waste typically are sources of odour pollution (gaseous pollutants include SO2, NH3, H2S and other toxic air pollutants). In this work, the removal of NH3 present in odorous composting leachate was assessed for the first time in a fixed-bed column loaded with carbonaceous adsorbents prepared by hydrothermal carbonization (HTC) assisted with sulphuric acid and by pyrolysis of carbon precursors (olive stone and malt bagasse). The resultant adsorbents were characterized to study their surface chemistry and textural properties. Scarce work studying the HTC in presence of additives, but H2SO4-assisted HTC allow to obtain acid hydrochars with accuracy properties for NH3 adsorption. In this work, the hydrochar prepared from olive stone by H2SO4-assisted HTC shows the highest NH3 adsorption capacity (11.4 mg g-1), evidencing that acidity contributes more significantly to the removal of NH3 than the specific surface area of the adsorbents. The NH3-saturated hydrochar was regenerated by washing with distilled water and subsequently re-used in the adsorption of NH3, obtaining satisfactory performance (68% of the mean NH3 adsorption capacity of its respective first use).

Carbon nanotubes (CNTs) were tested as catalysts in the selective denitrification of 4-nitrophenol (4-NP) from oily wastewater by catalytic wet peroxide oxidation (CWPO). The CNTs were prepared by chemical vapor deposition, feeding sequentially ethylene (E) and/or acetonitrile (A) during different times until 20 min, resulting in samples E20, A20 and E10A10, the number denoting the time feeding of each precursor and the order of appearance of the letter indicating the order of each precursor. The synthesized CNTs were tested in the CWPO of 4-NP in aqueous solutions and in simulated oily wastewater (2,2,4-trimethylpentane and water) at 80 ºC, initial pH 3.5, C4-NP = 1 g L-1, CH2O2 = 3.56 g/L and Ccatalyst = 2.5 g L-1. The catalyst A20 promoted a faster decomposition of H2O2 and a lower degradation of 4-NP in the aqueous system, whereas the catalyst E20 displayed the opposite trend, since E20 was able to remove 99% of the pollutant and A20 only 69% after 8 h of reaction. E10A10 in biphasic L-L media presented the highest conversion of 4-NP after 24 h in the oily phase (51%), followed by A20 (38%) and then E20 (25%). This tendency may be ascribed to the formation of Pickering emulsions by E10A10. The amphiphilic carachteristic of this material ensures a closer contact between the liquid phases, allowing higher mass transfer.

This work focuses the use of carbon-coated magnetic cobalt ferrite nanoparticles as catalysts for catalytic wet peroxide oxidation (CWPO) of the emerging pollutant paracetamol. A magnetic core composed of CoFe2O4 is developed by a sol-gel method. The core is subsequently coated with a formaldehyde-resorcinol resin and TEOS, further carbonized at 600 ºC, and etched with NaOH to create a yolk-shell structure denoted as CoFe2O4@void@C. XRD, TEM, and FTIR analysis revealed that the uncoated core is composed by a CoFe2O4 cubic spinel structure with a crystallite size of 53 nm calculated using the W-H method, matching very well the average size observed by TEM (53.51  4.2 nm). Comparing the performances of CoFe2O4@void@C and of the bare CoFe2O4 in the CWPO of paracetamol, TOC removals of 46 and 58% are obtained respectively after 24 h of reaction. An empirical kinetic model based on second-order and autocatalytic expressions was developed to suitably describe the decomposition of H2O2 and the removal of paracetamol using CoFe2O4@void@C as catalyst.

This work presents the development of magnetic carbon nanotubes (MCNTs) from plastic solid waste (PSW). For this purpose, diverse catalytic nanoparticles based on Fe, Ni and Al were prepared by impregnation of alumina or co-precipitation of Ni, Fe and Al nitrate salts with NH4OH, followed by calcination at 800 ºC. These magnetic nanoparticles were then used as catalysts in the growth of carbon nanotubes by chemical vapour deposition in a tubular furnace using low-density polyethylene as carbon precursor and as representative polymer composing PSW. MCNTs were characterized by transmission electron microscopy (TEM) and X-ray diffraction. The morphology and dimensions of the MCNTs were observed by TEM, concluding that large multiwalled MCNTs were prepared with magnetic nanoparticles inside (spacing of ~0.2 nm) and with a carbon interlayer spacing of ~0.34 nm. In conclusion, the synthesis of MCNTs from polyolefins is evidenced and can lead to technological alternatives in the treatment of PSWs.

The performance of metal-free carbonaceous catalysts was evaluated in the removal of paracetamol, chosen as model pharmaceutical micropollutant, by catalytic wet peroxide oxidation (CWPO). The carbon materials were prepared from pentaerythritol tetraacrylate and divinylbenzene copolymer with bis(2-ethylhexyl) phthalate as porogen followed by subsequent carbonization at 900 ºC under N2 atmosphere. The synthesized material was grinded to powder and separated into different samples, according to its granulometry. The sample with particle sizes between 53 and 106 µm (catalyst Mon11) was further functionalized with nitric acid 5 M at 120 °C for 3 h (catalyst Mon11F) to increase the hydrophilicity of the original material. Both catalysts revealed high activity in CWPO, completely removing the pharmaceutical compound within 6 and 24 h of reaction at 80 ºC, when Mon11 and Mon11F were used, respectively. Total organic carbon (TOC) conversion achieved values of 86.8 and 75.8% with Mon11 and Mon11F, respectively. Adsorption tests at the same operating conditions resulted in removals of paracetamol after 24 h around 29% for Mon11 and 11% for Mon11F, confirming the predominance of catalytic removal of the pollutant in the CWPO runs.