Antonio Machado Netto

Alkali-metal niobates MNbO₃ (M = Na, Li) decorated with platinum (Pt) nanoparticles (NPs) are innovatively utilized as catalytic supports for hydrogen (H₂) evolution from sodium borohydride (NaBH₄). Notably, a direct comparison between sodium niobate (NaNbO₃) and lithium niobate (LiNbO₃) in their efficiency for H₂ evolution from NaBH₄ was conducted for the first time, highlighting the distinct catalytic performance of these materials. The synthesis was confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The deposited Pt nanoparticles remain below 10 nm. In this study, different transition-metal nanoparticles (M = Co, Ni, Pd, Pt) supported on NaNbO₃ and LiNbO₃ were evaluated as catalysts. The Pt NPs/NaNbO₃ and Pt NPs/LiNbO₃ catalysts demonstrated optimized performance, producing H₂ at similar rates of 2044.9 and 2303.7 mL min^–1 g_cat^–1 at 293.15 K. Arrhenius plots indicate activation energies (E_a) of 35.54 ± 1.32 kJ mol^–1 for Pt NPs/NaNbO₃ and 35.04 ± 1.32 kJ·mol^–1 for Pt NPs/LiNbO₃. Additionally, the materials exhibited consistent stability, with an efficiency loss of less than 20% after the 10th cycle of use. These results underscore the potential of these catalysts for H₂ generation applications.

The pulp and paper industry generates large amounts of biological sludge, which can be valorized into activated biochar (A-BC), offering environmental and economic benefits. In this work, A-BCs were produced from this residue using H₃PO₄ as an activating agent and subjected to different pyrolysis temperatures (400 to 550 °C). H₃PO₄ was selected for its superior activation performance over KOH, enhancing porosity and surface functionalization, while the temperature was chosen to match the main thermal degradation of the sludge’s lignocellulosic matrix. The A-BCs were characterized by proximate and elemental analysis (fixed carbon content ∼30%), FTIR (CO, O–H, O–Si–O, and PO functional groups), XRD (predominantly amorphous structure), and Raman spectroscopy (D and G bands). Furthermore, BET surface areas from 7.68 to 1.52 m² g^–1, a higher heating value (HHV) from 3788 to 4750 kcal kg^–1, and a point of zero charge (pH_PZC) from 3.31 to 6.15 were obtained. Increasing the temperature from 400 to 450 °C increases surface area via pore formation, while higher temperatures reduce porosity due to pore collapse and lignin condensation. The A-BC produced at 450 °C (A-BC2) exhibited more than double the surface area and higher methylene blue (MB) removal efficiency than the other samples, consistent with the characterization results. The adsorption assays indicated that the maximum adsorption capacity was 390.73 mg g^–1, with the Langmuir model fitting the experimental data best (R ² = 0.996, R ² _adj = 0.995, and χ² = 1.62). The adsorption kinetics followed the pseudo-second-order model (R ² = 0.982, R ² _adj = 0.981, and χ² = 7.78), indicating a chemisorption-controlled mechanism involving electron sharing or exchange between cationic dyes and oxygenated biochar surface groups. The study demonstrates that A-BC from cellulose industry sludge is a viable, sustainable option for dye-containing effluent treatment, supporting circular economy principles.

Background Biochar has emerged as a sustainable and efficient alternative for water and wastewater treatment due to its high surface area, porosity, chemical stability, and adsorption capacity. Over time, numerous studies have proposed methods for removing contaminants from water and wastewater to enable their reuse in accordance with Sustainable Development Goals (SDGs) 6 and 14. Among the techniques reported as effective in this context is the use of biochar. Therefore, the aim of the present study was to examine the state of the art and current trends regarding the use of biochar in water and wastewater treatment. To achieve this, a bibliometric analysis was conducted using the Scopus scientific database to identify the research landscape involving biochar for water and wastewater treatment. Results The use of residual agroforestry biomass for biochar production was predominant, including coffee husks, açaí seeds, bamboo, wood, rice husks, corn cobs, and forest residues. In addition, muffle furnaces were the most commonly used systems in thermal degradation processes. The pharmaceutical and textile industries, followed by water treatment facilities, were identified as the sectors with the greatest research interest involving biochar-based adsorbents. Conclusion Biochar demonstrated significant potential and efficiency for water and wastewater treatment due to its performance in removing contaminants such as pharmaceutical compounds, dyes, heavy metals, and emerging micropollutants. The successful removal of pollutants was mainly attributed to the adsorption mechanism associated with biochar, with improved performance observed after chemical activation. Therefore, biochar stands out not only as an adsorbent material, but also as a technology aligned with environmental remediation strategies, waste valorization, and sustainable water resource management.

The application of circular economy principles to the sustainable management of waste from the pulp industry presents significant environmental challenges. In this context, using biological sludge as a raw material for producing activated biochar (BC) emerges as a promising and sustainable alternative. This study evaluated the valorization of biological sludge through the synthesis of activated BC for the removal of color, chemical oxygen demand (COD), and conductivity from the industry’s effluent. BC was produced using chemical activation with phosphoric acid (H₃PO₄) and potassium hydroxide (KOH), followed by pyrolysis at 500 °C and 450 °C, respectively. A central composite rotational design (CCRD) was applied to optimize the process. The optimized BCs were characterized by proximate analysis, FTIR, BET surface area, higher heating value (HHV), and SEM. Adsorption assays showed that H₃PO₄-activated BC achieved removal efficiencies of 52.2% for color, 23.9% for COD, and 46.2% for conductivity at a dosage of 5 g L⁻¹. Conversely, KOH-activated BC did not perform effectively. The results highlight the influence of activation and pyrolysis on BC properties and confirm the potential of this approach for the tertiary treatment of industrial effluents, contributing to waste valorization and environmental sustainability.

Sewage sludge serves as a promising raw material for producing activated biochar (BC), offering both environmental and economic benefits. This work aimed to optimize the synthesis of biochar (BC) from cosmetic industry sludge using response surface methodology (RSM) with central composite rotational design (CCRD) and to assess its effectiveness in removing the antibiotic enrofloxacin (ENR) from synthetic effluents. The input variables considered were (i) residence time in the reactor and (ii) impregnation ratio (NaOH/biomass). The response for optimization was the iodine number. The sludge underwent pyrolysis at 550 °C under a nitrogen atmosphere. The optimized biochar (OBC) had a macroporous structure with a specific surface area of 46.1 m2 g–1 and a calorific value of 4146 kcal kg–1. The bio-oil contained nitrogenous compounds and alcohols. The effectiveness of the OBC in adsorbing ENR in aqueous systems was assessed. Kinetic assays showed an equilibrium time of 90 min, with the pseudo-second-order model best fitting the experimental data. The Langmuir isotherm model best described the adsorption (qmax = 15.83 mg g–1). The material is competitive with commercial adsorbents. This work underscores the potential of industrial sludges as a sustainable source for BC, contributing to pollution reduction and promoting circular economy practices.