Percorrer por autor "Gomes, Helder T."
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- Development and characterization of organically grafted clay minerals for the removal of methylene blue from waterPublication . Serikbayeva, Aizhan M.; Roman, Fernanda F.; Gomes, Helder T.; Kalmakhanova, Marzhan S.In recent years, water pollution caused by industrial waste has been a major problem throughout the world. To remove harmful impurities from water, using methylene blue (MB) as a model compound, modified clays were used, as they are capable of adsorbing various substances on their surfaces. The modified clays were obtained by grafting dimethyl sulfoxide (DMSO) and triethanolamine (TEOA) in the space between the layers of Shymkent clay. DMSO was first added to the natural clay; TEOA was also added at a temperature of 180°C and then held at that temperature for 2 h. The resulting modified clays were dried at 60°C for 24 h and characterized by X-ray diffraction (XRD), surface area analysis (SAA), Fourier-transform infrared spectroscopy (FT-IR), elemental analysis, and thermogravimetric analysis (DTA and TGA). Natural and modified clays (0.25–2.5 g L–1, pH=1–12, and 50°C) were used to adsorb MB from an aqueous solution at a concentration of 50 mg L–1. Contact with the adsorbent was maintained for 8 h. As much as 95.9% of the MB was removed from the aqueous solution in as little time as 15 min. Adsorption conditions were optimized, and the clay modified with TEAO showed better results than the natural clay (85% for modified clay vs 40% for original clay, at a clay concentration of 0.5 g L–1); significant adsorption was obtained over a wide pH range (>85% from pH 1 to 12).
- Growth of Carbon Nanotubes on Co(x)‐Ni(1‐x) Ferrites by Chemical Vapor Deposition and Performance on Catalytic Wet Peroxide OxidationPublication . Silva, Adriano S.; Roman, Fernanda F.; Díaz de Tuesta, Jose Luis; Olias, Lola G.; Çaha, Ihsan; Ferreira, Ana P.; Souza, Renata P. de; Deepak, Francis Leonard; Pereira, Ana I.; Silva, Adrián; Gomes, Helder T.Upcycling plastic solid wastes (PSWs) into high-value carbon nanotubes (CNTs) offers a promising approach to sustainable material development. This study explores the synthesis of CNTs via chemical vapor deposition (CVD) using mixed cobalt-nickel-iron oxide catalysts supported on alumina and PSW representative polyolefins as carbon sources. The impact of catalyst composition on the yield, morphology, and textural properties of CNTs was systematically evaluated. Characterization techniques, such as textural properties, transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis (TGA), revealed that increasing cobalt content in the catalyst resulted in thicker CNT walls (9.2-23.6 nm) and different textural properties (SBET = 47-87 m2 g-1). The synthesized CNTs were then tested in catalytic wet peroxide oxidation (CWPO) for the degradation of sulfamethoxazole (SMX) and bisphenol A (BPA) in both single- and multi-component systems. The results indicated that a higher cobalt content in the CNT catalysts enhanced catalytic activity, particularly for BPA degradation, due to improved H2O2 decomposition. However, a higher leaching of Co and Fe was also observed. The CNTs synthesized with a Co/Ni catalyst composition ratio of 7/3 (CNT@Co0.7Ni0.3) exhibited the best balance among the tested materials in terms of CNTs yield, catalytic activity, and stability. These findings provide valuable insights to optimize CNT catalysts derived from waste plastics for environmental remediation applications.
- Oxidative denitrogenation using sustainable carbon nanotubes: Effect of reaction conditions on hydrogen peroxide efficiencyPublication . Roman, Fernanda F.; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Silva, Adrián; Faria, Joaquim L.; Gomes, Helder T.Nitrogenated compounds in fuels contribute significantly to NOₓ emissions, prompting the need for efficient and sustainable removal technologies. Oxidative denitrogenation (ODN) has emerged as an alternative or complement to hydrodenitrogenation (HDN) to remove undesired nitrogenated compounds. While ODN requires significantly milder conditions compared to HDN, it relies on the use of hydrogen peroxide as oxidant source. Most works report the removal of nitrogenated compounds but neglect the rate of consumption and efficiency of use of hydrogen peroxide. In this work, the operational conditions during ODN (hydrogen peroxide concentration, catalyst concentration, temperature, and pH) were optimized to maximize the removal of nitrogenated compound, using quinoline as model compound, from a simulated fuel. Two sustainability-oriented parameters were introduced: (i) the abatement of total organic carbon and (ii) the efficiency of hydrogen peroxide consumption. Under optimum conditions ([H2O2]0 = 12 g L−1, 70 °C, [cat] = 2.5 g L−1, pH0 = 3.0), the process achieved 89 % quinoline removal, 35 % TOC abatement, and more than 77 % H2O2 consumption efficiency. These results demonstrate the potential of ODN to operate under mild conditions while maintaining high oxidant efficiency for model nitrogen-containing fuel compound, contributing to cleaner and more sustainable fuel purification strategies.
- Reactive Materials and Solutions Towards Treatment and Reuse of Waters with Contaminants of Emerging ConcernPublication . Silva, Adriano S.; Roman, Fernanda F.; Silva, Ana P. F.; Díaz de Tuesta, Jose Luis; Kalmakhanova, Marzhan; Snow, D.; Gomes, Helder T.Intense population growth has significantly impacted the quality and access to water, resulting in increased production and release of contaminants of emerging concern (CECs), such as pharmaceutical compounds. Catalytic wet peroxide oxidation (CWPO) is a promising technology for the removal of CECs that relies on the use of solid catalysts to accelerate the reaction, its reactivity and stability depending greatly on the catalyst used. This work aims to compare three typically studied catalysts: a clay-based, a carbon-based and a hybrid material, consisting in carbon-shell metal nanoparticle structure. Hybrid catalysts combine the benefits of metal-based catalysts (high activity) and carbon-based catalysts (low leaching), indicating to be a suitable choice. However, it is highlighted that the development of proper soludons for treatment and reuse of waters must pass through detailed identification and quantification of CECs, allowing better catalyst evaluations under real scenario conditions.
- Synthesis of carbon nanotubes from polyolefin waste: mass balance and gas phase compositionPublication . Roman, Fernanda F.; Silva, Adriano S.; Gomes, Helder T.The valorization of plastic solid waste (PSW) through thermochemical routes has emerged as a sustainable strategy to address the growing accumulation of these materials. Among the most attractive products, carbon nanotubes (CNTs) stand out due to their high added-value and potential applications in catalysis, sensors, and environmental remediation. CNT synthesis from plastics typically involves thermal decomposition of the polymer into a carbon-rich gas fraction, followed by its deposition on metallic nanoparticles to form CNTs. Optimizing this process requires a detailed understanding of both the mass balance and gas composition. In this work, CNTs were synthesized by chemical vapor deposition (CVD) from low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) using a nickel–iron (NiFe) catalyst (synthesis details presented elsewhere [1]). The experiments were performed in a one-chamber reactor, with 1 g of plastic loaded in the upper zone (400–450 °C) and 0.2 g of NiFe in the lower zone (850 °C). The system was heated for 1 h and then held for 0.5 h under a N2 flow (50 cm3 min-1). Generated gases were analyzed in situ by gas chromatography with flame ionization detection (GC-FID). After reaction, solid and liquid fractions were collected and weighed. Characterization of similar CNTs can be consulted in previous publications [1-3]. The results are summarized in Fig. 1. As shown in Fig. 1a, the solid fraction yields were similar for all polymers (35–38%), while HDPE produced a higher liquid fraction than LDPE and PP. The gas fraction dominated in all cases, suggesting catalyst deactivation or an inadequate catalyst-to-plastic ratio. Three major gases were detected (Fig. 1b): methane >> propylene > ethylene. LDPE and PP showed comparable gas distributions, whereas HDPE generated markedly less methane and propylene, consistent with the mass balance trends.