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There has been an upsurge of green reductants for the preparation of graphene materials taking consideration of human health and the environment in recent years. In this paper, reduced graphene oxides (RGOs) were prepared by chemical reduction of graphene oxide (GO) with three green reductants, L-ascorbic acid (L-AA), D-glucose (D-GLC) and tea polyphenol (TP), and comparatively characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectra, Raman spectra and electrical conductivity analysis. Results showed that all these three reductants were effective to remove oxygen-containing functional groups in GO and restore the electrical conductivity of the obtained RGO. The RGO sample with L-ascorbic acid as a reductant and reduced with the existence of ammonia had the highest electrical conductivity (9.8 S·cm(-1)) among all the obtained RGO samples. The mechanisms regarding to the reduction of GO and the dispersion of RGO in water were also proposed. It is the good dispersibility of reduced graphene oxide in water that will facilitate its further use in composite materials and conductive ink.

The reduced form of graphene oxide (r-GO) represents a versatile precursor to obtain graphene derivatives. Graphene oxide (GO) consists of a layered material based on a carbon skeleton functionalized by different oxygen-containing groups, while r-GO is obtained by the almost complete removal of these oxygen-containing functional groups. The r-GO has mechanical, electrical, and optical properties quite similar to graphene, thus, it proves to be a convenient 2D material useful for many technological applications. Nowadays, the most important aspects to consider in producing r-GO are: (i) the possibility of obtaining the highest reduction grade; (ii) the possibility of improving the dispersion stability of the resulting graphene using surfactants; (iii) the use of environmentally friendly and inexpensive reducing agents. Consequently, the availability of effective soft-chemistry approaches based on a green reducing agent for converting GO to r-GO are strongly needed. Among the green reductants, the most suitable is L-ascorbic acid (L-aa). Different studies have revealed that L-aa can achieve C/O ratio and conductivity values comparable to those obtained by hydrazine, a typical reducing agent. These aspects could promote an effective application strategy, and for this reason, this review summarizes and analyzes, in some detail, the up-to date literature on the reduction of GO by L-aa. The results are organized according to the two most important approaches, which are the reduction in liquid-phase, and the reduction in gel-phase. Reaction mechanisms and different experimental parameters affecting the processes were also compared.

Background Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes that catalyze oxidative depolymerization of industrially relevant crystalline polysaccharides, such as cellulose, in a reaction that depends on an electron donor and O2 or H2O2. While it is well known that LPMOs can utilize a wide variety of electron donors, the variation in reported efficiencies of various LPMO-reductant combinations remains largely unexplained. Results In this study, we describe a novel two-domain cellulose-active family AA10 LPMO from a marine actinomycete, which we have used to look more closely at the effects of the reductant and copper ions on the LPMO reaction. Our results show that ascorbate-driven LPMO reactions are extremely sensitive to very low amounts (micromolar concentrations) of free copper because reduction of free Cu(II) ions by ascorbic acid leads to formation of H2O2, which speeds up the LPMO reaction. In contrast, the use of gallic acid yields steady reactions that are almost insensitive to the presence of free copper ions. Various experiments, including dose–response studies with the enzyme, showed that under typically used reaction conditions, the rate of the reaction is limited by LPMO-independent formation of H2O2 resulting from oxidation of the reductant. Conclusion The strong impact of low amounts of free copper on LPMO reactions with ascorbic acid and O2, i.e. the most commonly used conditions when assessing LPMO activity, likely explains reported variations in LPMO rates. The observed differences between ascorbic acid and gallic acid show a way of making LPMO reactions less copper-dependent and illustrate that reductant effects on LPMO action need to be interpreted with great caution. In clean reactions, with minimized generation of H2O2, the (O2-driven) LPMO reaction is exceedingly slow, compared to the much faster peroxygenase reaction that occurs when adding H2O2.

Silver nanoparticles (AgNPs) are known mainly because of their bactericidal properties. Among the different types of synthesis, there is the biogenic synthesis, which allows the synergy between the nanocomposites and substances from the organism employed for the synthesis. This study describes the synthesis of AgNPs using infusion of roots (AgNpR) and extract (AgNpE) of the plant Althaea officinalis . After the synthesis through reduction of silver nitrate with compounds of A . officinalis , physico-chemical analyzes were performed by UV-Vis spectroscopy, nanoparticles tracking analysis (NTA), dynamic light scattering (DLS) and scanning electron microscopy (SEM). Toxicity was evaluated through Allium cepa assay, comet test with cell lines, cell viability by mitochondrial activity and image cytometry and minimal inhibitory concentration on pathogenic microorganisms. Biochemical analyzes (CAT - catalase, GPx - glutathione peroxidase e GST - glutationa S-transferase) and genotoxicity evaluation in vivo on Zebrafish were also performed. AgNpE and AgNpR showed size of 157 ± 11 nm and 293 ± 12 nm, polydispersity of 0.47 ± 0.08 and 0.25 ± 0.01, and zeta potential of 20.4 ± 1.4 and 26.5 ± 1.2 mV, respectively. With regard to toxicity, the AgNpE were the most toxic when compared with AgNpR. Biochemical analyzes on fish showed increase of CAT activity in most of the organs, whereas GPx showed few changes and the activity of GST decreased. Also regarding to bactericidal activity, both nanoparticles were effective, however AgNpR showed greater activity. Althaea officinalis can be employed as reducing agent for the synthesis of silver nanoparticles, although it is necessary to consider its potential toxicity and ecotoxicity.

2-nitroaniline (2-NA) is highly toxic and environmental contaminant. It is reduced to less toxic and environmental benign product o -phenylenediamine by using different reducing agents like sodium borohydride, potassium borohydride, or hydrazine hydrate in the presence of various catalytic systems. These catalytic systems have various advantages and drawbacks. Silica-supported gold nanoparticles are frequently reported catalyst for the reduction of 2-nitroaniline in aqueous medium. In this review article, different catalytic systems reported for reduction of o -nitroaniline under various reaction conditions have been discussed. The critical review of the recent research progress for development of novel catalysts used for the reduction of 2-nitroaniline has been provided here.

Under various concentration conditions of reducing agents during the green synthesis of gold nanoparticles (AuNPs), we obtain the various geometry (morphology and size) of AuNPs that play a crucial role in their catalytic properties. Through both theoretical and experimental approaches, we studied the relationship between the concentration of reducing agent (caffeic acid) and the geometry of AuNPs. As the concentration of caffeic acid increases, the sizes of AuNPs were decreased due to the adsorption and stabilizing effect of oxidized caffeic acids (OXCAs). Thus, it turns out that optimal concentration exists for the desired geometry of AuNPs. Furthermore, we investigated the growth mechanism for the green synthesis of AuNPs. As the caffeic acid is added and adsorbed on the surface of AuNPs, the aggregation mechanism and surface free energy are changed and consequently resulted in the AuNPs of various geometry.

The application environment for concrete is becoming increasingly complex, accompanied by an intensification of its functional requirements. This paper presents a method for developing self-compacting concrete with conductive properties using limonite and graphite as the concrete conductive phases. In the process of concrete preparation, the limonite is initially treated by a pre-wetting method to prevent the surface depression caused by the addition of limonite during the concrete curing process. The second stage of the process involved optimising different proportions of limonite and graphite and different dosages of water-reducing agent, defoamer and dispersant to prepare concrete. The influence of different dosages of limonite and graphite and different dosages of water-reducing agent on the mechanics and electrical conductivity of concrete was studied in order to obtain self-compacting conductive concrete with performance indicators meeting the requirements of self-compacting and electrical conductivity. The results demonstrate that the mechanical and electrical properties of self-compacting conductive concrete prepared with polycarboxylic acid superplasticizer and retarding superplasticizer combined with superplasticizer are satisfactory, and the composite superplasticizer can function in conjunction with dispersant. The self-compaction index, slump expansion, expansion time T50 and J-ring expansion of fluid concrete meet the requisite standards. Once the concrete has reached the designated curing age, its compressive strength and flexural strength align with the anticipated design expectations, while its resistivity meets the stipulated conductivity index requirements.

The absence of a universal reducing agent distinguishes the Prx6‐type subfamily of peroxiredoxins from the structurally similar Prx1‐type subfamily. A likely explanation for the lack of reactivity of Prx6‐type enzymes with common reducing agents is that a histidyl residue at the bottom of the active‐site pocket traps the oxidized enzyme in an inaccessible fully‐folded protein conformation. Here, we analyzed the reduction of oxidized PfPrx6 from Plasmodium falciparum and human PrxVI by the hydrosulfide ion, HS − , as the smallest possible sulfur‐containing universal electron donor. We show that HS − rapidly reacts with oxidized wild‐type PfPrx6 or human PrxVI (but not the histidyl mutants PfPrx6 H39Y or hPrxVI H39Y ) with a second‐order rate constant of > 10 8 m ‒1 s ‒1 at pH 7.4. The obtained protein‐hydropersulfide species is neither reduced by thioredoxin nor glutaredoxin and glutathione, but further reacts with an excess of HS − with a second‐order rate constant around 10 4 m ‒1 s ‒1 , yielding the reduced enzyme. In summary, we identified HS − as a highly reactive, potential universal electron donor for Prx6‐type enzymes. This study marks the starting point for the characterization of the complex reduction pathway of Prx6‐type enzymes with implications for H 2 S detoxification and redox signaling as well as iron‐sulfur and persulfide metabolism.

Rice husk extract, obtained using acid and alkali pretreatment extraction (AAPE), contains bioactive compounds and exhibits reducing abilities. Phenolic composition in rice husk extract was analyzed and the mechanism of silver nanoparticle (AgNP) biosynthesis by using AAPE rice husk extract was investigated in this study. Stable and spherically shaped AgNPs with a size of <15 nm were prepared under the following conditions: 0.001 M AgNO3, AAPE rice husk extract diluted 10 times, pH 10, and reacted at 25 °C for 60 min. Synergistic effects among phenolic acids contributed to the formation of AgNPs, with the acids acting as excellent reducing agents (owing to their abundant hydroxyl groups) and excellent dispersants (owing to their derived CO groups), which enhanced the NPs' stability. Caffeic acid (CA) was demonstrated to synthesize AgNPs independently and is suggested to be the most crucial compound for reducing Ag+ during the biosynthesis with rice husk extract. A possible mechanism and reaction process for the formation of AgNPs synthesized using CA in rice husk extracts is proposed. [Display omitted] Mechanism and reaction process for the formation of AgNP synthesized using CA in rice husk extracts. •AAPE rice husk extract contains sufficient phenolic acids to biosynthesize AgNPs.•CA is the dominant compound in rice husk extract contributing to reduce Ag+ to AgNPs.•Stable dispersion AgNP solution is obtained by steric hindrance of phenolics-derived quinones.•Characters of AgNPs can be manipulated by adjusting synthesis conditions.

Abstract Silver nanoparticles (AgNPs) have gained significant attention in antimicrobial treatments due to their potent antibacterial properties and potential applications in combating antibiotic-resistant pathogens. Green synthesis of AgNPs using natural extracts provides an eco-friendly and scalable alternative to chemical methods, leveraging plant bioactive compounds to enhance nanoparticle efficacy. Coffee extract, rich in polyphenols, effectively reduces mixed silver ions into pure silver nanoparticles at the nanoscale. This process not only provides an eco-friendly and sustainable method for AgNP synthesis but also ensures the production of high-quality nanoparticles with enhanced antibacterial properties, making it a promising alternative to traditional chemical reduction methods. This study investigates the biosynthesis of AgNPs using robusta, excelsa, and arabica coffee extracts as bioreductors, capitalizing on coffee’s abundance and richness in polyphenols to produce efficient, customizable nanoparticles with improved antibacterial properties. The synthesized AgNPs were characterized using Ultraviolet-Visible (UV-Vis) spectroscopy and a Particle Size Analyzer (PSA). Antimicrobial photodynamic therapy (aPDT) with red laser exposure was employed to evaluate the effect of various energy densities on bacterial samples. Antibacterial efficacy was assessed using the diffusion well and Total Plate Count (TPC). The UV-Vis analysis revealed peak absorbance wavelengths of 425 nm, 450 nm, and 500 nm for robusta, arabica, and excelsa coffee extracts, respectively. PSA results indicated particle sizes at D50 of 73.08 nm (AgNPs-Arabica), 67.85 nm (AgNPs-Robusta), and 67.67 nm (AgNPs-Excelsa), confirming their nanoscale range (1–100 nm). Antibacterial tests showed the highest Escherichia coli bacterial death rate (95.73%) with AgNPs-Arabica and red laser treatment. Compared, Staphylococcus aureus bacterial death peaked at 94.97% with AgNPs-Excelsa and red laser treatment. These findings highlight the potential of green-synthesized AgNPs as effective antimicrobial agents, particularly when combined with laser-based therapies, offering innovative approaches for treating bacterial infections. Resumo Nanopartículas de prata (AgNPs) ganharam atenção em tratamentos antimicrobianos devido às suas potentes propriedades antibacterianas e potenciais aplicações no combate a patógenos resistentes a antibióticos. A síntese verde de AgNPs usando extratos naturais fornece uma alternativa ecológica e escalável aos métodos químicos, aproveitando compostos bioativos vegetais para aumentar a eficácia das nanopartículas. O extrato de café, rico em polifenóis, reduz efetivamente os íons de prata mistos em nanopartículas de prata pura na escala nanométrica. Esse processo não apenas fornece um método ecológico e sustentável para a síntese de AgNP, como também garante a produção de nanopartículas de alta qualidade com propriedades antibacterianas aprimoradas, tornando-o uma alternativa promissora aos métodos tradicionais de redução química. Este estudo investiga a biossíntese de AgNPs usando extratos de café das variedades robusta, excelsa e arábica como biorredutores, aproveitando a abundância e a riqueza dos polifenóis do café para produzir nanopartículas eficientes e personalizáveis com propriedades antibacterianas aprimoradas. As AgNPs sintetizadas foram caracterizadas usando espectroscopia ultravioleta-visível (UV-Vis) e um analisador de tamanho de partícula (PSA). A terapia fotodinâmica antimicrobiana (aPDT) com exposição a laser vermelho foi empregada para avaliar o efeito de várias densidades de energia em amostras bacterianas. A eficácia antibacteriana foi avaliada usando o poço de difusão e a contagem total de placas (TPC). A análise UV-Vis revelou comprimentos de onda de absorção de pico de 425 nm, 450 nm e 500 nm para extratos de café das variedades robusta, arábica e excelsa, respectivamente. Os resultados do PSA indicaram tamanhos de partículas em D50 de 73,08 nm (AgNPs-Arábica), 67,85 nm (AgNPs-Robusta) e 67,67 nm (AgNPs-Excelsa), confirmando sua faixa nanométrica (1–100 nm). Os testes antibacterianos mostraram a maior taxa de mortalidade bacteriana de Escherichia coli (95,73%) com AgNPs-Arábica e tratamento com laser vermelho. Em comparação, a morte bacteriana de Staphylococcus aureus atingiu o pico de 94,97% com AgNPs-Excelsa e tratamento com laser vermelho. Essas descobertas destacam o potencial de AgNPs sintetizados de forma verde como agentes antimicrobianos eficazes, particularmente quando combinadas com terapias baseadas em laser, oferecendo abordagens inovadoras para o tratamento de infecções bacterianas.