Liana Alvares Rodrigues

The electrochemical production of hydroperoxide (HO ₂ ⁻ ) via the two-electron oxygen reduction reaction (2e ⁻ ORR) is a sustainable alternative to the conventional anthraquinone process.

This study investigates the valorization of residual microalgal biomass into functional biochar for lipase immobilization and enzymatic biodiesel production. Microalgal residue remaining after pigment and lipid extraction underwent pyrolysis at different temperatures and treatment strategies, and the most suitable support was obtained by pyrolysis at 500 °C followed by nitric acid modification and silanization. These treatments enhanced biochar physicochemical properties, providing superior textural and chemical characteristics, including higher surface area and enhanced enzyme affinity. Burkholderia cepacia lipase (BCL) was immobilized on biochar by covalent bonding and physical adsorption. Among the evaluated conditions, covalent immobilization on chemically modified biochar resulted in the highest catalytic activity (4052.11 U g ^− 1 ) and immobilization yield (78%), demonstrating the positive effect of support functionalization on enzyme-support interactions. The biocatalysts were characterized by kinetic and thermal analyses, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy (FTIR). These techniques confirmed the biochar porous morphology, successful enzyme attachment, and functional groups favorable for immobilization. Kinetic analysis revealed increased substrate affinity for the covalently immobilized enzyme, while thermal stability tests showed that both immobilization strategies preserved approximately 85% of enzymatic activity after 240 min at 45 °C. The biocatalysts were then applied to biodiesel synthesis from babassu oil. BCL immobilized by covalent bonding on chemically modified biochar achieved complete conversion into ethyl esters and produced biodiesel with viscosity within fuel-standard limits. Reusability assays showed that the immobilized derivative retained more than 60% conversion after four consecutive cycles, corresponding to an operational half-life of 301 h. Overall, microalgal biochar proved to be a robust, renewable, and effective support for enzyme immobilization, contributing to sustainable biodiesel production and residue valorization.

Pulverized activated carbon (PAC) adsorption is an effective complementary technique for removing pesticides in conventional water treatment. However, the high cost and residue generation associated with PAC use are significant drawbacks. This study evaluates the adsorption and desorption performance of atrazine (ATZ), simazine (SMZ), and diuron (DIU) using magnetized pulverized activated carbon (PACmag) for potential reuse in water treatment plants (WTPs). PAC16mag was identified as the adsorbent with the highest adsorption and desorption efficiencies. Under extreme contamination conditions, the process achieved removal efficiencies of 49.5% for ATZ, 53.8% for SMZ, and 69.1% for DIU, corresponding to residual concentrations of 712.9 μg L-1, 572.6 μg L-¹, and 7,254.2 μg L-¹, respectively, from initial concentrations of 1,411.1 μg L-¹, 1,240.2 μg L-¹, and 23,410.4 μg L-¹. Kinetic studies revealed that the Elovich model best describes the adsorption process, highlighting heterogeneous surface interactions. Adsorption isotherms indicated that the Sips model provided the best fit, particularly for DIU, suggesting multilayer adsorption. The point of zero charge (pHPZC) of PAC16mag was determined to be 7.1, indicating a near-neutral surface charge that facilitates adsorption through hydrophobic and π-π interactions. The desorption process reached 100%, with methanol (MeOH) exhibiting the best desorption efficiency. Although the magnetization process reduces PAC porosity indices, Fourier-transform infrared spectroscopy (FTIR) analyses revealed that Fe-O functional groups from magnetization enhance adsorptive efficiencies and facilitate material recovery. These findings suggest that magnetization is a promising technique for improving PAC performance and enabling its regeneration for reuse in WTPs.

For decades, lead-acid batteries have been supplying power to electrical systems through redox reactions involving Pb and PbO₂. However, the energy supply capacity is inherently constrained by low energy density and challenges associated with charge/discharge cycles. Studies have indicated that additions of C to the composition of the active mass improve the electrochemical properties of batteries. This work aims to produce, characterize the microstructure and evaluate the electrochemical properties of Pb-Carbon composites, comparing different types of C (graphite, graphene and xerogel). The samples were produced through powder metallurgy, pressed at 550 MPa and sintered at 320°C-48 h. The microstructure was characterized by XRD, SEM/EDS, and Vickers microhardness. Electrochemical analyses were evaluated through OCP, polarization, and cyclic voltammetry (CV) measurements in a solution of 4.91 mol•L^-1 of H₂SO₄. Microstructural characterizations revealed dispersions of C particles in the Pb matrix and an increase in the microhardness of the composites. Electrochemical analyses showed an increase in polarization resistance and a reduction in the corrosion rate compared to Pb. CV curves, demonstrated that C particles enhanced electrical conductivity for the formation of PbSO₄ and PbO₂, allowing greater absorption of electrical overpotentials when compared to Pb, thereby improving charge/discharge cycles in positive grids.

This paper proposes the study of a solar-based photocatalytic ozonation process for the degradation of salicylic acid (SA) using a novel S-scheme ZnO/Cu₂O/CuO/carbon xerogel photocatalyst. The incorporation of CuO and Cu₂O aims to enhance charge mobility through the formation of p-n heterojunctions with ZnO, whereas the carbon xerogel (XC) was selected due to its eco-friendly nature, capacity to stabilize S-scheme heterojunctions as a solid-state electron mediator, and ability to function as a reducing agent under high temperatures. The characterization of the composites demonstrates that the presence of the XC during the calcination step led to the reduction of a fraction of the CuO into Cu₂O, forming a ternary semiconductor heterojunction system. In terms of photocatalysis, the XC/ZnO-Cu_xO 5% composite achieved the best efficiency for salicylic acid degradation, mainly due to the stabilization of the S-scheme charge transfer pathway between the ZnO/CuO/Cu₂O semiconductors by the XC. The total organic carbon (TOC) removal during heterogeneous photocatalysis was 80% for the solar-based process and 68% for the visible light process, after 300 min. The solar-based photocatalytic ozonation process was highly successful regarding the degradation of SA, achieving a 75% increase in the apparent reaction rate constant when compared to heterogeneous photocatalysis. Furthermore, a 78% TOC removal was achieved after 150 min, which is half the time required by the heterogeneous photocatalysis to obtain the same result. Temperature, salinity, and turbidity had major effects on the efficiency of the photocatalytic ozonation process; the system’s pH did not cause any major performance variation, which holds relevance for industrial applications.