Camilla Henriques Maia de Camargos

Light-colored nanolignin obtained by oxidation through sustainable procedures yields antioxidant and UV-protective materials for cultural heritage applications.

Water scarcity, contamination, and lack of sanitation are global issues that require innovations in chemistry, engineering, and materials science. To tackle the challenge of providing high-quality drinking water for a growing population, we need to develop high-performance and multifunctional materials to treat water on both small and large scales. As modern society and science prioritize more sustainable engineering practices, water treatment processes will need to use materials produced from sustainable resources via green chemical routes, combining multiple advanced properties such as high surface area and great affinity for contaminants. Lignin, one of the major components of plants and an abundant byproduct of the cellulose and bioethanol industries, offers a cost-effective and scalable platform for developing such materials, with a wide range of physicochemical properties that can be tailored to improve their performance for target water treatment applications. This review aims to bridge the current gap in the literature by exploring the use of lignin, both as solid bulk or solubilized macromolecules and nanolignin as multifunctional (nano)materials for sustainable water treatment processes. We address the application of lignin-based macro-, micro-, and nanostructured materials in adsorption, catalysis, flocculation, membrane filtration processes, and antimicrobial coatings and composites. Throughout the exploration of recent progress and trends in this field, we emphasize the importance of integrating principles of green chemistry and materials sustainability to advance sustainable water treatment technologies.

O branqueamento é um procedimento amplamente difundido e empregado na área da restauração de documentos gráficos. É frequentemente realizado com a justificativa de beneficiar, melhorar ou “resgatar” a qualidade estética da obra tratada, oferecendo um aspecto subjetivamente novo, asséptico e imaculado ao papel já amarelecido ou manchado. Mesmo nas justificativas menos enviesadas, pautadas em uma possível recuperação da legibilidade e melhora da fruição estética de obras de arte sobre papel, também imperam os argumentos em favor da execução dessa abordagem restaurativa. Centrando as discussões nesse procedimento controverso, o objetivo do presente artigo é tecer um panorama sobre os métodos de branqueamento – convencionais, menos convencionais ou alternativos –, aventando seus princípios metodológicos e principais aspectos físico-químicos. A partir de tal levantamento crítico-metodológico, que contempla inclusive uma introdução aos fenômenos químicos fundamentais à ação do branqueamento sobre cromóforos-chave presentes na celulose amarelecida, faz-se uma exposição criteriosa dos prós e contras das operações em questão, cotejando o debate da teoria da restauração com a discussão feita por Irene Brückler e Ute Henniges em seu artigo sistemático Thoughts on bleaching guidelines. A proposta é contribuir para o debate acerca do branqueamento, também em língua portuguesa, munindo os conservadores-restauradores de informações sobre os principais critérios a serem considerados e os diversos métodos para a realização segura e racional do procedimento.

In this study, we propose the production of a thin-film composite (TFC) membrane with efficient antimicrobial properties by modifying it with cellulose nanocrystals (CNC) and silver nanoparticles (AgNP). Two approaches (i.e., “one-pot” and “layer-by-layer”) were employed to incorporate CNC and AgNP onto the membrane surface and their impact on the membrane antimicrobial properties was examined. Firstly, the “one-pot” method involved reacting CNC with AgNO₃ and NaBH₄ to form a CNC/Ag hybrid material. This CNC/Ag hybrid was then applied to the TFC drawmembranes using polydopamine (PDA) chemistry, allowing the deposition of both CNC and AgNP in a single step. Secondly, the “layer-by-layer” method involved attaching CNC to the membrane surface using PDA chemistry, which was then followed by an in situ reaction of AgNO₃ and NaBH₄ to deposit the AgNP directly on top of the CNC layer. Membranes modified with a CNC/Ag hybrid using the one-pot method were able to deactivate 75.7 ± 15.6% of attached E. coli cells without detrimental impact to membrane separation performance. The membranes modified using the layer-by-layer assembly demonstrated improved antimicrobial activity when compared to those modified with the one-pot CNC/Ag hybrid, being capable of inactivating 90% of the attached E. coli cells. On the other hand, the layer-by-layer modification method led to a significant loss in the membrane's salt rejection capacity. These water-based, straightforward, and simple functionalization strategies can tailor the antimicrobial and anti-biofouling performance of membranes for water treatment applications.

In this study, we added value to lignocellulosic biomass-derived lignin by converting it into antimicrobial nanoparticles using a simple self-assembling method in solution. Transmission electron microscopy (TEM) and zeta potential analyses showed that the self-assembled lignin nanoparticles (SA-LNPs) had a spherical-like morphology, 80 nm average size, and a surface charge of −29 ± 4 mV. Previous studies have shown that LNPs are toxic to bacteria, though the potential mechanisms of action leading to antimicrobial properties of LNPs are lacking in the literature. Therefore, we conducted a thorough investigation of the antibacterial activity of SA-LNPs using four bacteria strains: Escherichia coli and Pseudomonas aeruginosa (Gram-negative) and Bacillus subtilis and Lactobacillus fermentum (Gram-positive). The antimicrobial assays performed in saline media revealed that SA-LNPs were selectively toxic to Gram-positive bacteria, and no significant antimicrobial effects were found against the Gram-negative strains. Time-kill experiments showed that 25 μg mL⁻¹ SA-LNPs were able to inactivate more than 90% of the Gram-positive bacteria after 30 min exposure. We conducted in vitro and in vivo assays to evaluate the production of reactive oxidative species (ROS), such as glutathione and 2′,7′-dichlorodihydrofluorescein diacetate (H₂DCFA). These assays indicated that oxidative stress was not the underlying mechanism involved in the antimicrobial activity of SA-LNPs. This finding corroborates that SA-LNPs could scavenge radicals of 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazin-1-yl (DPPH), confirming their strong antioxidant property. Although direct oxidative stress was ruled out as the probable mechanism of action, we still cannot dismiss an indirect pro-oxidant effect resulting from the SA-LNPs-containing adsorbed ROS coming into direct contact with the cell wall.