http://repositorio.ufc.br/handle/riufc/419 2026-09-12T07:34:23Z http://repositorio.ufc.br/handle/riufc/87940 Título: Green synthesis of CoFe2O4 nanoparticles and their application as bifunctional electrocatalysts in water electrolysis Autor(es): Bampoky, Nayuca Alberto Abstract: The development of efficient and sustainable electrocatalysts based on earth-abundant elements is essential for advancing green hydrogen production through water electrolysis. This doctoral thesis investigates cobalt ferrite (CoFe2O4) nanoparticles synthesized by environmentally friendly routes and evaluates their performance as bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. The study was conducted in two stages: (i) optimization of the sonochemical synthesis by varying the ultrasonic power and (ii) comparison of the optimized sonochemical route with hydrothermal and protein-assisted sol–gel methods. The results demonstrate that increasing the ultrasonic power promotes structural disorder and a higher density of surface defects, as evidenced by Mössbauer spectroscopy, leading to a significant increase in the electrochemically active surface area and improved electrocatalytic kinetics. The optimized sample, synthesized at 60% ultrasonic power (designated as CoFe2O4-60), exhibited the best overall performance for both HER and OER. Comparative analyses revealed that the protein-assisted sol–gel route produced smaller nanoparticles with intrinsic lattice strain, whereas the hydrothermal route resulted in incomplete phase formation with hematite impurities. In contrast, the sonochemical method yielded highly pure spinel CoFe2O4 nanoparticles without requiring post-synthesis calcination. Electrochemical measurements confirmed the superior catalytic activity and long-term stability of the sonochemically synthesized material compared with the hydrothermal and protein-assisted sol–gel counterparts. These findings demonstrate that sonochemical synthesis is an effective route for tailoring the structural properties of CoFe2O4 and producing highly active bifunctional electrocatalysts for alkaline water electrolysis. The work provides a sustainable and scalable approach to developing low-cost alternatives to noble-metal-based catalysts for green hydrogen production. Tipo: Tese 2026-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/87937 Título: Anaerobic digestion of the liquid fraction of fruit and vegetable waste: two-stage versus single-stage process Autor(es): Silva Júnior, Francisco das Chagas Gomes da; Almeida, Priscilla de Souza; Menezes, Camila Aparecida de; Duarte, Maíra Saldanha; Silva, Thobias Pereira; Santos, André Bezerra dos; Zaiat, Marcelo; Leitão, Renato Carrhá Abstract: This study evaluated the anaerobic digestion of the liquid fraction of fruit and vegetable waste to optimize energy recovery through sequential hydrogen and methane production. Two configurations were tested: a single-stage (SS) system using an upflow anaerobic sludge blanket (UASB) reactor and a twostage (TS) system combining an anaerobic structured bed reactor (AnStBR) with a UASB reactor. The objective was to identify the most efficient configuration under various organic loading rates (OLR). In the AnStBR, OLR ranged from 40 to 80 g COD/Lreactor·day, while in UASB reactors, the OLR range was from 1.5 to 22.0 g COD/Lreactor·day. The TS outperformed the SS in methane production, achieving 3.6 NL CH4/Lreactor·day at an OLR of 22.0 g of COD/Lreactor·day. It also demonstrated a higher energy potential, generating a total of 1554.9 KJ/day� 35.7% more efficient than the SS. Additionally, the UASB-TS reactor maintained stability throughout the study, with minimal acid accumulation and an intermediate alkalinity/partial alkalinity ratio (IA:PA) consistently below 0.4, even at elevated OLR. In contrast, the UASB-SS reactor showed signs of acidification at higher OLR. These findings suggest that TS anaerobic digestion offers a more robust and efficient solution for treating high-strength organic waste, enhancing both energy recovery and process stability. Tipo: Artigo de Periódico 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/87919 Título: Influence of Granular Activated Carbon Addition on Methane Production in Dry and Semidry Anaerobic Digestion of Swine Manure Autor(es): Silva, Amanda de Sousa e; Santos, Amanda Lima Moraes dos; Malveira, Isabele Clara Cavalcante; Girão, Bianca Holanda Albano; Santos, André Bezerra dos Abstract: This work investigated the effect of granular activated carbon (GAC) on methane-rich biogas production in semidry (10% total solids, TS) and dry (15% TS) anaerobic digestion (AD) of swine manure. The conductive material GAC can improve methane production exponentially in AD, even without pretreatment. However, in semidry and dry conditions, there was no significant difference in methane production yield when using raw or pretreated swine manure with the addition of 20 g/L GAC. For this condition, when using the pretreated substrate, the main observed effect was related to the lag phase increase from 6.5 to 10.6 days and from 10.4 to 32.0 days at 10 and 15% TS, respectively. In semidry AD, with pretreated manure, 10 g/L GAC addition yielded 190 mL CH4/gVS, a value 21% higher than with 20 and 30 g/L GAC. In dry AD, the best condition was with 30 g/L GAC (157 mL CH4/gVS), followed by 20 and 10 g/L GAC (127 and 18 mL CH4/gVS, respectively). Therefore, the TS content influences the ideal GAC concentration. About microbiology, the increase in the abundance of phyla Acidobacteriota, Bacteroidota, Chloroflexi, and Firmicutes was linked to greater methane production when using raw manure. The dominant genus of bacteria in most reactors was Georgenia, and the main abundances of archaea were Methanobacterium (slightly more favored with GAC addition) and Methanosaeta. Therefore, GAC increases methane production not only by favoring certain important species in AD but also mainly by promoting Direct Interspecies Electron Transfer (DIET) and adsorbing inhibitory compounds, thereby improving methane-rich biogas production. Tipo: Artigo de Periódico 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/87916 Título: Engineering aerobic granular sludge for enhanced curdlan biosynthesis: the impact of organic loading rate, carbon-to‑nitrogen ratio, and feeding strategy Autor(es): Adekunle, Adedoyin; Nabaterega, Resty; Santos, André Bezerra dos; Iorhemen, Oliver Terna Abstract: This study reports, for the first time, the recovery of curdlan from aerobic granular sludge (AGS) wastewater systems. Nine bench-scale experiments were conducted to evaluate the effects of organic loading rate (OLR), carbon-to-nitrogen ratio (C/N), and feeding strategy on curdlan biosynthesis during wastewater treatment. At OLR = 2.1 kg COD/m3∙d with C/N = 10 and 30 min feeding/30 min stationary phase, curdlan yield reached 74 ± 6 mg/g biomass, while at OLR = 2.1 kg COD/m3∙d with C/N = 30 and 10 min feeding/50 min stationary phase, curdlan yield was 69 ± 11 mg/g biomass. Univariate statistical analysis showed that there was a statistically significant association between curdlan production and OLR, and between curdlan production and feeding strategy at α = 0.05. Although synthetic wastewater was used for controlled bench-scale experiments, the complex composition of municipal wastewater may further affect microbial dynamics and curdlan biosynthesis. These findings highlight AGS as a promising platform for integrating curdlan recovery into wastewater biorefinery. Tipo: Artigo de Periódico 2025-01-01T00:00:00Z