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- Catalytic wet peroxide oxidation of paracetamol using carbon nanotubes synthesized from low-density polyethylene as model plastic wastePublication . Roman, Fernanda; Lopes, Jéssica Paula Marim; Silva, Ana P. F.; Díaz de Tuesta, Jose Luis; Lenzi, Giane G.; Silva, Adrián; Gomes, HelderOne of the ongoing concerns related with wastewater treatment is the presence of micropollutants on water bodies, since they accumulate due to its recalcitrant behavior and its constant introduction in the system [1]. Catalytic Wet Peroxide Oxidation (CWPO) is a wastewater treatment technology based on the generation of powerful oxidants (hydroxyl radicals) from the decomposition of H2O2, providing that suitable solid catalysts are used, with promising results being reported in the removal of pharmaceuticals [2]. On the other hand, plastic waste is an actual concern in waste management, and alternatives to its post-use should be sought [3]. This study aims at the CWPO of paracetamol (PCM) as model micropollutant, using as catalysts carbon nanotubes (CNTs) synthesized from low-density polyethylene, as representative polymer found in municipal plastic solid waste streams. The CNTs were synthesized by chemical vapor deposition at 800 ºC, considering three catalyst based on Ni, Fe and Al prepared by coprecipitation and wet impregnation methods. The synthesized CNTs were further tested on the CWPO of PCM (100 mg L-1 of PCM, pH0 3.5, 474 mg L-1 H2O2, Ccatalyst = 2.5 g L-1 and 80 °C). All catalysts tested led to the complete conversion of both PCM and H2O2 after 24 h of reaction time (Figure 1(a,b)), with a contribution of 23-42% of adsorption according to pure adsorption tests performed at the same operating conditions (Figure 1(d)). The CNT synthesized on the catalyst prepared by the impregnation method shows a lower contribution of adsorption and led to a mineralization of 70% after 24 h of reaction time, with the highest efficiency of H2O2 consumption (determined as TOC conversion divided by H2O2 conversion).
- Production of catalysts for the valorization of plastic waste, and for the wet peroxide oxidation of paracetamolPublication . Silva, Ana P. F.; Gomes, Helder; Bineli, Aulus Roberto; Tuesta Triviño, José Luis Diaz deThe efficient treatment of waste plastics and pharmaceutical pollutants is of conspicuous environmental, social and economic benefits. Therefore, here it is approached the application of catalysts that can be efficient in mitigating both environmental problems. In this work, four different catalysts were prepared. Three of them were synthesized by co-precipitation of Ni, Al and Fe nitrates with different mass ratios (5%Ni:95%Al, 20%Ni:80%Al and 10%Ni10%Fe80%Al). The fourth catalyst was prepared by wet impregnation of nickel on alumina. Then fresh catalysts were characterized by Fourier Transformed Infrared Spectroscopy and X-ray diffraction to observe crystalline phases. Carbon structures were prepared from low-density polyethylene, used as representative compound of plastic solid waste by Chemical Vapor Deposition over 20% Ni/Al catalyst in a tubular furnace. Scanning Electron Microscopy analyses were performed, identifying the carbon nanostructures with size variation (1 μm to 4 μm). For paracetamol (PCM) removal Catalytic Wet Peroxide Oxidation was assessed with 20%Ni:80%Al, 10%Fe:10%Ni:80% and commercial Al2O3 catalysts. The conversion of paracetamol, hydrogen peroxide and Total Organic Carbon (TOC) were monitorized by High-Performance Liquid Chromatography, UV-Vis spectrophotometer and TOC analyzer, respectively. The iron-containing catalyst showed the highest catalytic activity in the CWPO of PCM satisfactory conversions (complete removal of PCM after 4 h of reaction time under the following operating conditions: Ccat = 2.5 g/L, CPCM,0 = 100 mg/L, pH0 = 3.5, and CH2O2 = 472.4 mg/L).
- Breakthrough Curves for the Continuous Adsorption of Micropollutants on Activated Carbon/Geopolymer MixturesPublication . Baldo, Arthur P.; Silva, Ana P. F.; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Marin, Pricila; Peres, José A.; Gomes, Helder T.Breakthrough curves are key for designing continuous flow adsorption systems, typically obtained experimentally or through modeling [1]. In this study, a mixture of activated carbon (AC) and geopolymers (GP) was tested in a continuous treatment system for the removal of model contaminants from waters in a single-component system composed of sulfamethoxazole (SMX), acetaminophen (ACT), or gallic acid (GA). In addition, the adsorbent materials were also tested in a multi-component water matrix to evaluate the interactions between adsorbates and adsorbents. Adsorption tests were conducted using 1g of GP and 0.5g of AC, filled with glass beads. The experiments were carried out at room temperature, considering 100 mg/L for all contaminants and natural pH of the solutions. The flow was set to 1 mL/min and controlled by a peristaltic pump. The breakthrough curves are shown in Figure 1. Based on the experimental data, the useful operating times were calculated, assuming that the effluent concentration should not exceed 5% of the initial concentration [2], yielding 228 minutes for ACT, 46 minutes for SMX, and 53 minutes for GA in the multi-component system. A reduction in time was observed when compared to the single-component system due to faster saturation caused by competition for active sites. The useful adsorption capacities were also calculated, with values of 45.7 mg/g for ACT, 9.2 mg/g for SMX, and 10.7 mg/g for GA in the multicomponent system. The overall results indicated that the column was efficient, as the contaminating compounds were removed up to the system breakthrough. In conclusion, this preliminary study suggests that these materials can be effectively combined and applied in tertiary wastewater treatments, as permeable reactive barriers.
- Synthesis and Characterization of Activated Carbons, Geopolymers, and Carbon Nanotubes from Waste-Derived SourcesPublication . Baldo, Arthur P.; Silva, Ana P. F.; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Marin, Pricila; Peres, José A.; Gomes, Helder T.Circular Economy implies strategies for waste valorization and reuse to produce higher-value products [1]. In this context, exhausted olive pomace, a waste biomass derived from olive industry was used to synthesize activated carbon (AC) through slow pyrolysis, followed by activation with CO2 to optimize the adsorbent's porosity. The pyrolysis furnace was initially maintained under an inert atmosphere with a nitrogen flow rate of 100 NmL/min, considering three different temperature stages reached through the application of a heating ramp of 5ºC/min up to 400°C and 600°C (maintained 1 hour each) and up to 800°C. Activation with CO2 occurs in the first hour at this temperature, followed by 3 hours in a nitrogen atmosphere, completing the process in 9 hours. The geopolymer (GP) was synthesized using 10 g of fly ash, a byproduct of the combustion of municipal solid waste, mixed with an alkaline solution, a mixture of 5,67g of sodium silicate and 2,27g of sodium hydroxide (10M), to initiate the geopolymerization reaction. The synthesis of carbon nanotubes (CNTs) was based on the methodology of Díaz de Tuesta et al. [2], by chemical vapor deposition with plastic waste as the precursor. The results obtained for textural characterization are presented in Table 1. AC showed the highest surface area (527 m²/g) and a pore volume of 0.318 cm³/g, can be advantageous for adsorption, while CNT functions effectively as a catalyst despite its lower surface area. Acid-base characterization showed that AC possesses high basicity (1250 μmol/g), enhancing its ability to adsorb acidic contaminants, while CNT and GP demonstrated balanced acid and basic properties, with point of zero charge (pHpzc) values of 9.86 for AC, 6.9 for CNT, and 7.6 for GP. Elemental analysis (CHNS) revealed that AC contained 63.0% C, 0.8% H, 18.0% O, and 16.4% ash. CNT, in contrast, had a higher carbon content of 92.5% and 6.0% ash.
- 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.
- 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.
- Response surface method-driven design of experiments for the synthesis of fly ash-based geopolymers in the gallic acid optimized removal from wastewaterPublication . Silva, Ana P. F.; Natal, Ana Paula Silva; Baldo, Arthur Pietrobon; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Marin, Pricila; Peres, José A.; Gomes, HelderThe growing need for sustainable wastewater treatment solutions has led to exploring alternative materials to explore large-scale and reliable technologies. This study focuses on optimizing the synthesis of geopolymers based on fly ash using a Box-Behnken experimental design to enhance their adsorption efficiency for phenolic compounds, as gallic acid model pollutant which are widely found in wastewater leaching from landfills. Fifteen geopolymer samples were synthesized, characterized, and tested for adsorption performance. Various techniques were employed, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy. The optimization process highlighted the significance of the Si/Al mass ratio, NaOH molar concentration, and Na₂SiO₃/NaOH as variables in the geopolymers production. Geopolymer samplesdemonstrated significant adsorption capacities, with GP_2.0_10_2.5 achieving a maximum adsorption capacity of 75.8 mg g-1. Kinetic studies indicated that the pseudo-first-order model best described the adsorption process. At the same time, equilibrium data fitted well with both Langmuir and Freundlich isotherms, with GP_2.0_10_2.5 showing the best fit for the Langmuir model. These findings reveal the potential of geopolymers derived from fly ash as cost-effective adsorbents in wastewater treatment, promoting the reuse of industrial waste within the framework of a Circular Economy.
- Simultaneous removal of o-and p-nitrophenol from contaminated water by wet peroxide oxidation using carbon-coated magnetic ferrite as catalystPublication . Dias, Arnaldo; Silva, Adriano S.; Silva, Ana P. F.; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Oliveira, Jéssica; Ferrari, Ana M.; Lenzi, Giane G.; Gomes, Helder; Oliveira, JessícaGroundwater is the most common source of drinking water worldwide and is currently facing contamination problems with the discharge of pollutants into aquatic systems through different means, namely through municipal, industrial and agricultural activities. Contaminants, such as herbicides, pharmaceuticals, phenolic compounds and personal care products are not removed by conventional treatments from wastewater treatment plants, leading to their accumulation in the environment. In this regard, o-nitrophenol (o-NP) and p-nitrophenol (p-NP), commonly used as raw materials in chemical and pharmaceutical engineering, represent a severe risk to humans and aquatic life, leading to the necessity to properly treat wastewaters containing these contaminants before discharge into the aquatic environment. Catalytic wet peroxide oxidation (CWPO) showed promising results for removing nitrophenols from wastewater in previous works. In this technology, H2O2 is used as an oxidant, and its interaction with a suitable catalyst leads to the formation of hydroxyl radicals under determined conditions already established in literature (pH and temperature have a strong influence) [1]. Typical catalysts employed have a transition metal in its structure. Carbon-based catalysts also have activity in this technology, mostly ascribed to the electronic properties of the carbonaceous surface. Furthermore, carbon-coated metal oxide materials (hybrid) have also demonstrated potential applications in CWPO. Those structures combine carbon and metal activities with the advantage of protecting the metal core from leaching, increasing the efficiency and stability of the catalysts.
- Magnetic carbon nanotubes prepared from LDPE, HDPE and PPPublication . Sanches, Lucas Fenato; Silva, Adriano S.; Roman, Fernanda; Silva, Ana P. F.; Díaz de Tuesta, Jose Luis; Silva, Fernando Alves; Silva, Adrián; Faria, Joaquim; Gomes, HelderPlastics are among the most generated solid wastes, predominantly composed by polymers, as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP).1 This work deals with the preparation of magnetic carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering LDPE, HDPE and PP as carbon precursors representative of urban plastic solid waste in a perspective of circular economy.1 Magnetite supported in alumina nanoparticles previously synthesized by sol-gel were used as catalysts in the CCVD process. Afterward, each synthesized CNT was washed with 50% H2SO4 at 140 °C during 3 h to remove the remaining magnetite, following methods previously described.2 The successful removal of the magnetite particles was assessed measuring the ashes content of the CNTs, removals higher than 83% being achieved (ashes content of final CNT products ranging from 4.2 to 7.9%). The remaining catalyst was located inside the CNTs, conferring magnetic properties to the materials even after washing (Figure 1). BET specific surface areas of 94, 75, and 66 m2 g-1 were found for CNT_LDPE, CNT_HDPE and CNT_PP, respectively, and a slight increase of 1-5 m2 g-1 was observed after washing the materials with acid.