Percorrer por autor "Gomes, Helder T."
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- Carbon-Coated Magnetic Catalysts for Enhanced Degradation of Nitrophenols: Stability and Efficiency in Catalytic Wet Peroxide OxidationPublication . Baldo, Arthur P.; Bezerra, Ana J.B.; Silva, Adriano S.; Silva, Ana P. F.; Roman, Fernanda F.; Çaha, Ihsan; Bañobre-López, Manuel; Deepak, Francis Leonard; Gomes, Helder T.Nitrophenols are persistent organic pollutants that pose serious environmental and health risks due to their toxic and lipophilic nature. Their persistence arises from strong aromatic stability and resistance to biodegradation, while their lipophilicity facilitates bioaccumulation, exacerbating ecological and human health concerns. To address this challenge, this study focuses on the synthesis and characterization of two different types of hybrid multi-core magnetic catalysts: (i) cobalt ferrite (Co-Fe2O4), which exhibits ferrimagnetic properties, and (ii) magnetite (Fe3O4), which demonstrates close superparamagnetic behavior and is coated with a novel and less hazardous phloroglucinol–glyoxal-derived resin. This approach aims to enhance catalytic efficiency while reducing the environmental impact, offering a sustainable solution for the degradation of nitrophenols in aqueous matrices. Transmission electron microscopy (TEM) images revealed the formation of a multi-core shell structure, with carbon layer sizes of 6.6 ± 0.7 nm for cobalt ferrite and 4.2 ± 0.2 nm for magnetite. The catalysts were designed to enhance the stability and performance in catalytic wet peroxide oxidation (CWPO) processes using sol–gel and solution combustion synthesis methods, respectively. In experiments of single-component degradation, the carbon-coated cobalt ferrite (CoFe@C) catalyst achieved 90% removal of 2-nitrophenol (2-NP) and 96% of 4-nitrophenol (4-NP), while carbon-coated magnetite (Fe3O4@C) demonstrated similar efficiency, with 86% removal of 2-NP and 94% of 4-NP. In the multi-component system, CoFe@C exhibited the highest catalytic activity, reaching 96% removal of 2-NP, 99% of 4-NP, and 91% decomposition of H2O2. No leaching of iron was detected in the coated catalysts, whereas the uncoated materials exhibited similar and significant leaching (CoFe: 5.66 mg/L, Fe3O4: 12 mg/L) in the single- and multi-component system. This study underscores the potential of hybrid magnetic catalysts for sustainable environmental remediation, demonstrating a dual-function mechanism that enhances catalytic activity and structural stability.
- A comprehensive mechanical and physico-chemical characterization of fly ash-based geopolymersPublication . Silva, Ana P. F.; Natal, Ana Paula S.; Oliveira, Isaac; Bezerra, Ana J.B.; Baldo, Arthur P.; Silva, Adriano S.; Diaz de Tuesta, Jose Luis; Peres, José A.; Ferreira, Débora; Gomes, Helder T.This work focuses on developing a predictive optimization method for geopolymer concrete, addressing both mechanical strength and water absorption. Despite numerous formulations proposed in the literature, no systematic method has been established to evaluate these properties simultaneously. This research addresses this gap by employing a Design of Experiments approach to systematically explore the effects of key variables such as NaOH molar concentration, sodium silicate-to-sodium hydroxide ratio, and alkaline solution-to-fly ash ratio. After 28 days, geopolymer concrete exhibits competitive compressive strength (geopolymer concrete: 25 MPa, reference Ordinary Portland concrete: 27 MPa), and after 365 days, its compressive strength surpasses that of traditional Ordinary Portland concrete (geopolymer concrete: 56 MPa, reference Ordinary Portland concrete: 27 MPa). Moreover, through Response Surface Methodology, an optimization model indicates that geopolymer concrete compressive strength can reach up to 64 MPa, with a strong influence from the alkaline solution-to-fly ash ratio. Additionally, the materials were characterized in terms of crystalline phases, surface chemistry, thermal stability, and surface area to gain a deeper understanding of the behaviour of these materials.
- 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).
- Enhancing single and multi-component adsorption efficiency of pharmaceutical emerging contaminants using bio waste-derived carbon materials and geopolymersPublication . Silva, Ana P. F.; Baldo, Arthur P.; Silva, Adriano S.; Natal, Ana Paula S.; Bezerra, Ana J.B.; Tuesta, Jose L. Diaz de; Marin, Pricila; Peres, José A.; Gomes, Helder T.Water contamination with pharmaceuticals like acetaminophen (ACT), sulfamethoxazole (SMX), and phenolic compounds such as gallic acid (GA), have become a global concern. These contaminants are persistent environmental pollutants that threaten aquatic life and human health. Adsorption is recognized as an efficient and low-cost solution to tackle water pollution. In this study, the efficiency of three adsorbents—activated carbon (AC), geopolymer (GP), and carbon nanotubes (CNT) prepared from solid wastes for the removal of ACT, SMX, and GA by adsorption is assessed. AC, GP and CNT are synthesized from real wastes to address solid waste management needs. Physisorption confirmed AC superior BET surface area (527 m2 g 1), followed by CNTs (66 m2 g 1) and GPs (30 m2 g 1), allowing to achieve the highest adsorption capacity: 126.8 mg g 1 for ACT, 54.9 mg g 1 for SMX, and 151.5 mg g 1 for GA, with respective breakthrough times of 314, 66, and 68 min. Kinetic and isotherm adsorption models are fitted for all pair pollutant-adsorbent reaching 33 equations to accurately predict adsorption process, concluding that pseudo-second-order kinetic and Freundlich model best fit experimental data, demonstrating a strong adsorbent-adsorbate affinity. The findings suggest that these sustainable materials offer promising solutions for treating contaminated water.
- 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.
- Interface-Controlled GO–CoFe2O4–Silicone Nanocomposite with Magnetic and Adsorptive FunctionalityPublication . Kudaibergenova, Rabiga M.; Anar, Aitekova R.; Demeuova, Gulzat K.; Murzakasymova, Nazgul S.; Kalmakhanova, Marzhan S.; Orynbayev, Seitzhan A.; Gomes, Helder T.; Sugurbekova, Gulnar K.The development of interface-engineered, multifunctional nanostructured materials with controllable surface and magnetic properties remains a critical challenge in wastewater treatment and environmental remediation. In this work, a novel GO-CoFe2O4-Silicone Magnetic Sponge was successfully fabricated through the integration of graphene oxide and CoFe2O4 magnetic nanoparticles within a silicone-modified porous sponge matrix. The resulting material combines superhydrophobicity, oleophilicity, high adsorption capacity, and magnetic responsiveness in a single architecture. The prepared sponge exhibited a high water contact angle of 161.5 degrees, confirming its superhydrophobic nature, while maintaining excellent structural integrity during repeated use. Vibrating sample magnetometry revealed clear ferrimagnetic behavior, enabling rapid magnetic manipulation and efficient recovery of the sponge from aqueous media. The GO-CoFe2O4-Silicone Magnetic Sponge demonstrated strong adsorption performance toward a wide range of oils and organic solvents, including chloroform, olive oil, toluene, ethanol, acetone, gasoline, and hexane, with adsorption capacities remaining stable over multiple cycles. Furthermore, the sponge showed outstanding separation efficiency exceeding 98.3% for various oil/water and organic solvent/water mixtures, both in batch and continuous vacuum-assisted separation systems. The adsorption capacity and separation efficiency were retained after repeated adsorption-desorption cycles, indicating excellent reusability and durability. Owing to its synergistic combination of surface chemistry, porous structure, and magnetic functionality, the GO-CoFe2O4-Silicone Magnetic Sponge represents a promising candidate for practical applications in oil spill cleanup and wastewater treatment.
- 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.
- Permeable Reactive Barriers in Groundwater Remediation: A Review of Efficiency in Removing Pharmaceuticals and Heavy MetalsPublication . Kalmakhanova, Marzhan S.; Reimbayev, Yerbol K.; Karimbayeva, Zhanbike E.; Silva, Ana P. F.; Gomes, Helder T.Global water pollution driven by industrial and agricultural expansion has resulted in the widespread occurrence of persistent contaminants, particularly pharmaceuticals and heavy metals, in groundwater systems. Conventional treatment methods often prove inefficient, costly, and environmentally unsustainable, highlighting the need for innovative in situ remediation technologies. Permeable Reactive Barriers (PRBs) have emerged as a promising and energy-efficient solution for the long-term purification of contaminated aquifers. Their efficiency arises from passive operation, relying on natural groundwater flow to promote pollutant removal through adsorption, ion exchange, precipitation, and redox-driven transformations. This review emphasizes the superior performance of materials such as Activated Carbon, Biochar, Zeolites, and Zero-Valent Iron (ZVI) in the immobilization and reduction in pharmaceuticals and metal ions. Key challenges to PRB longevity include permeability loss and reactive media depletion due to mineral precipitation and biofouling. Advances in hybrid PRB configurations, coupled with electrokinetic (EK) and bioreactor systems, and predictive modeling, particularly Artificial Neural Networks (ANNs), offer pathways to enhance performance, optimize design, and ensure sustainable operation. Overall, PRBs represent a scalable and environmentally sound approach to groundwater remediation, with future progress relying on the development of multifunctional, regenerable materials and integrated design strategies.
- Plastic waste-derived carbon nanotubes: Influence of growth catalyst and catalytic activity in CWPOPublication . Roman, Fernanda F.; Silva, Adriano S.; Tuesta, Jose L. Diaz de; Baldo, Arthur P.; Lopes, Jessica P.M.; Gonçalves, Giane; Pereira, Ana I.; Praça, Paulo; Silva, Adrián; Faria, Joaquim L.; Bañobre-López, Manuel; Gomes, Helder T.Low-density polyethylene (LDPE) was used in this work to grow carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over catalysts based on Ni, Fe and Al, synthesized either by co-precipitation (C) or wet impregnation (I) methods, with CNT yields in the range of 16–33 %. The morphology of the CNTs was directly influenced by the route used for the CVD catalyst synthesis, with co-precipitation-derived CVD catalysts resulting in CNT samples with curly walls. CNTs were purified with H2SO4 (10–50 wt.%) to remove attached metal particles. All synthesized materials (CVD-catalysts, as-synthesized CNTs, and purified CNTs) were tested as catalysts in the catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM), chosen as a model pharmaceutical compound. Removals of 100 % of PCM in 8 h and 71 % of total organic carbon (TOC) in 24 h were achieved, with an H2O2 consumption efficiency of 76 % in 24 h for purified CNT (CNT@NiFeAl-C-P). The same CVD-catalyst (NiFeAl-C) was used to grow CNTs using real LDPE waste, and it was tested under the same reaction conditions, resulting in a PCM and TOC abatement of 90 % and 65 %, respectively. The synthesis of CNTs using LDP waste was a good alternative, given the environmental benefits associated with its reintroduction into the economic cycle as a material with higher value than initially (upcycling).
- Polyolefin and Polystyrene‐Derived Carbon Nanotubes: Catalysts for Oxidative Desulfurization Under a Biphasic SystemPublication . Roman, Fernanda F.; Batista, Maria C.; Silva, Adriano S.; Bezerra, Ana J.B.; Tuesta, Jose L. de Diaz de; Mambrini, Raquel V.; Silva, Adrián; Faria, Joaquim L.; Gomes, Helder T.The conversion of plastic solid waste into carbon nanotubes (CNTs) via chemical vapor deposition (CVD) and the effectiveness of these CNTs as catalysts for oxidative desulfurization (ODS) of a simulated fuel were investigated. The primary focus is on the use of CNTs synthesized from various polymer sources, including polyolefins and polystyrene (PS), to remove sulfur compounds using hydrogen peroxide (H 2 O2 ) as an oxidant. The surface modification of CNTs by using acids (H2 SO4 or HNO3 ), the influence of the carbon feedstock (polyolefins vs PS), the use of co-catalysts, and the effect of the extractant phase were all evaluated on the oxidative removal of dibenzothiophene from a simulated fuel. Results revealed that CNTs derived from polyolefins displayed higher desulfurization efficiency (up to 77% in 8 h), with nitric acid-treated CNTs showing the best performance under oil-water biphasic systems. Replacing water with acetonitrile and adding a co-catalyst (formic acid) resulted in a desulfurization of 91% in 2 h of reaction. Under certain conditions, C─S bond cleav-age was observed. This research contributes to the valorization of plastic solid waste and the reduction of atmospheric pollution, promoting circular economy practices and environmental sustainability.