Resumo em Inglês:

Carbon dioxide capture and conversion is gaining increased attention due to climate change issues. The direct air capture of CO2 may be accomplished with functionalized adsorbents that can work at atmospheric pressure and room temperature. The captured CO2 may be converted into fuels and chemicals. CO2 can be hydrogenated to methanol, which is a commodity used in the fuel and chemical sectors, over Cu.ZnO-based catalysts. Improvements to catalyst formulation are still needed to operate at lower temperatures. Dimethyl ether can be directly produced from CO2 and H2 through the use of bifunctional catalysts. Organic carbonates appear as promising compounds of wide use in the chemical sector. Cyclic carbonates may be produced from CO2 and epoxides with the use of Lewis acids catalyst. Zeolites impregnated with metal halides appear to be a promising system to achieve high conversion and selectivity. Aliphatic organic carbonates can be produced from CO2 and alcohols, but the reaction presents thermodynamic limitations. The role of oxygen vacancies on CeO2-based catalysts and use of dehydrating agents in the production of dimethyl carbonate will be discussed in this account. The challenges and future perspectives for the direct air CO2 capture and conversion into fuels and chemicals will be addressed.

Resumo em Inglês:

The use of non-conventional solvent systems, such as deep eutectic solvents (DES), for biomass processing is a growing interest. DES are formed by two or more components, usually solids at room temperature, which can interact with each other via hydrogen bonding, from a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), resulting in a liquid phase. The most studied HBA in the literature is choline chloride with several HBD and their use have been extensively reviewed. However, other abundant and natural HBA can be successfully applied on the preparation of different DES, e.g., amino acids. These amino acid-based DES have been used in biomass pretreatment, providing the fractionation of the main macromolecular components by lignin solubilization. In addition, amino acid-based DES can be applied in biomass chemical conversion to obtaining platform chemicals such as furanic derivatives. Bearing this in mind, this review focuses on exploring the use of amino acid-based DES on biomass processing, from pretreatment to chemical conversion.

Resumo em Inglês:

Hydrogen (H2) was one of the first molecules discovered by our society, being the most abundant element in the whole universe. Thus, H2 has gained a lot of attention throughout the years, and it has lots of applications in different areas, especially since it offers ways to decarbonize a lot of sectors, mainly the ones where it has been proved to be very difficult to meaningfully reduce those carbon emissions. Herein, the main aspects of the hydrogen economy and its main applications for energy, transportation and industries are described. These main areas outline how important is H2 for our society highlighting how H2 can make those well-known processes more sustainable and greener. By the end, a brief discussion on these applications with future perspectives is presented.

Resumo em Inglês:

Green hydrogen is a fuel capable of promoting sustainable energy development and is gaining attention in the current global energy transition framework. The global shift toward decarbonization has triggered a substantial boost in the hydrogen industry. This study presents an overview of the current status of hydrogen production, regulation of the green hydrogen segment, hydrogen storage, distribution, and transportation, and final use and application. We also critically discuss the viability of adopting green hydrogen in terms of possible economic and environmental impacts as well as the main challenges and opportunities it represents for the Chemical Sciences.

Resumo em Inglês:

Biosurfactants are amphipathic molecules produced by plants, animals, and microorganisms, that present emulsifying properties and may act reducing surface and interfacial tensions. When compared to synthetic surfactants, these biological analogues have high biodegradability potential, and may be produced from renewable raw materials within overall biotechnological processes involving low generation of residues. The production and application of microbial surfactants have been recently considered in several industrial sectors, as these low toxicity versatile compounds find applications in food, pharmaceutical, cosmetic, and petrochemical products, in nanotechnology and agriculture, and in the bioremediation of xenobiotic-contaminated areas. Herein, the main conceptual aspects and physicochemical properties, as well as the classifications of biosurfactants according to their origin and their chemical structures, are addressed. The production of microbial biosurfactants through sustainable processes are also described, with particular focus on new applications and on the increasing relevance of such bioproducts for the sustainable development of modern society.

Resumo em Inglês:

Forming semiconductor heterojunction is promising for improved photocatalytic performance due to synergistic combination of the best properties of each material. The present study reports a simple hydrothermal strategy to form n-n heterojunction of Ta2O5 nanotubes and BiVO4 microstructures. The Ta2O5/BiVO4 heterojunctions were characterized by Raman spectroscopy, UV Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and their photocatalytic activity was evaluated by hydrogen production and photodegradation of methylene blue (MB) dye in aqueous medium under AM 1.5 G (100 mW cm2) condition. The heterojunctions have optical absorption in the visible region (200 500 nm) with crystal structures defined as monoclinic for BiVO4 and orthogonal for Ta2O5. For MB photodegradation, the Ta2O5/BiVO4 obtained via hydrothermal route showed a photodegradation of 72.3%, compared to 28.3% presented by the sample produced through the mechanical mixture, with the maintenance of 86.4% of its photocatalytic performance after 3 cycles of photodegradation. For H2 production, hydrothermally prepared Ta2O5/BiVO4 generated 10.2 μmol g-1 of H2 in 3 h; while Ta2O5 nanotubes and mechanical Ta2O5/BiVO4 mixture shows 6.82 and 2.80 μmol g-1, respectively. The results suggest that Ta2O5/BiVO4 is a promising material for applications in photocatalysis, promoting sustainable energy production through hydrogen and for the treatment of effluents containing cationic dyes.

Resumo em Inglês:

Cupuaçu husk (CH) is the waste of a common fruit from a native species of the Brazilian Legal Amazon. The current study investigated the influence of ultrasound (US) combined with aqueous, acid, alkaline, and ionic liquid (IL) pretreatments on the chemical and physical aspects of CH and the yield of chemical platforms production, 5-hydroxymethylfurfural (HMF) and furfural (FF), using IL. Scanning electron microscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy were used to feature the raw and pretreated biomass. The highest levels of glucose (9.90 g L-1) were observed in the liquid fraction resulting from the acid + US pretreatment followed by acid hydrolysis. The IL + US pretreatment recorded the best performance in removing lignin. Based on XRD analyses, ultrasound increased crystallinity of all pretreated samples as a result of the removal of cellulose’s amorphous fraction. However, it promoted accessibility to adopted reagents by increasing biomass exposure due to cavitation. The best yields of HMF and FF were recorded from hydrolysis of the solid fraction resulting from the acid + US (12.94%) and alkaline + US (48.84%) pretreatment, respectively. These results indicate satisfactory performance of ultrasound assisted pretreatments to the simplified and economic conversion of biomass into value-added products.

Resumo em Inglês:

In this work, different metal oxides containing Ti, Zr and Al were prepared and characterized and their catalytic activities for cracking, transesterification, and hydroesterification reactions of soybean oil were evaluated. It is described the synthesis of the solids by co-precipitation, and their characterization by thermogravimetry, X-ray diffraction, Brunauer-Emmet-Teller surface area determination, Fourier-transformed Raman spectroscopy, and the determination of Lewis and Brønsted acid sites by pyridine adsorption and detection through Fourier transform infrared spectroscopy (FTIR). The hydrocarbons obtained by soybean pyrolysis were analyzed by fractional distillation, acid number, FTIR, density (at 20 °C), viscosity (at 40 °C), and calculation of the cetane number. The results suggest that all of the solids exhibit catalytic activity at the second stage of the cracking reaction (deoxygenation), lowering the final acidity of the products. The solids also exhibited catalytic activity for transesterification and hydroesterification of triacylglycerides, leading to good yields in methyl fatty acid esters.

Resumo em Inglês:

Triazine herbicides are widely used both in Brazil and internationally and are frequently detected in natural environments and drinking water. This study assesses atrazine degradation through solar radiation under tropical conditions and determines the toxicity of the intermediates. Atrazine degradation is tested through ultrapure water, humic acid solution and natural water experiments, with exposure to sunlight to simulate a natural environment. A yeast estrogen screen (YES) assay and Artemia salina test are carried out during the abiotic degradation. The atrazine degradation depends on the radiation intensity, since the experiments conducted in the summer reached 50% after ca. 17 days. No significant variations in this herbicide concentration are observed after 90 days of exposure in the fall. Atrazine degradation is observed only in humic acid and is responsible for indirect photolysis. Intermediates, namely, desethylatrazine (DEA) and deisopropylatrazine (DIA), are identified and quantified at the μg L-1 level. Thus, with the degradation of atrazine in water, the medium toxicity may decrease, since DEA and DIA have mean effective concentrations that kill 50% of Artemia salina (EC50) similars to atrazine (13 mg L-1). No estrogenic activity in the YES is detected for atrazine and its metabolites. These findings evidence that radiation intensity and organic substances in tropical countries influence the half-life of pesticides in aquatic environments.

Resumo em Inglês:

This work uses new waste feedstock, essential to increase the range of new biomasses, demonstrating experimentally and numerically the economic potential of coconut husk residues to produce renewable biofuels (pyrolytic oil and biochar) through slow pyrolysis. The samples were submitted to a pyrolysis process (500 ºC for 30 min, with a heating rate of 20 ºC min-1, using water vapor as carrier gas), where the biochar and bio-oil yields reached were 31 and 30%, respectively. The main components found in bio-oil were furfural (29.23%), phenol (22.18%), and isoeugenol (10.26%). The surface area values (Brunauer-Emmett-Teller (BET) and Langmuir) found for biochar were greater than 300 m2 g-1 and a micropore volume of 0.11 cm3 g-1. The estimated theoretical energy potential of biochar and bio-oil were 208,107,180 MJ and 190,205,438 MJ, equivalent to 3,729,518.4 tons of coconut husks. Thus, this study brings as a novelty a new feedstock associated with bioprocess technological models that will pave sustainable avenues for the development of biorefineries, offering a sustainable green option to produce bioproducts and bioenergy. In the proposed model, the wastes are valorized using various processes addressing economy.

Resumo em Inglês:

The development of visible-light active photocatalysts is vital to harvest the solar irradiation and build efficient photoelectrochemical devices. Bismuth oxyhalide (BiOCl, BiOBr and BiOI) materials stand out due to their remarkable properties, e.g., the band gap energy can be tuned from 1.9 to 3.4 eV depends on the halide employed. However, the hydrothermal synthesis of this material class was not properly investigated and compared. Then, we evaluated the effect of the hydrothermal treatment in the BiOX’s structural, electronic, morphological and textural properties and the relationship with their photocatalytic performance. Methylene blue (MB) dye was used as probe for photocatalytic performance evaluation under ultraviolet (UV) and visible (Vis) radiation. BiOCl and BiOBr samples showed a good photoactivity under both UV and visible radiation, on other hand the BiOI samples was not active, likely due to the fast charge recombination. BiOCl and BiOBr samples exhibit a favorably interaction with MB dye, because their surfaces are negatively charged. BiOCl samples were able to promote around 40 and 80% of the MB dye degradation under visible and UV radiation, respectively. The samples were also employed as photoanode for O2 evolution, BiOI sample exhibited the best performance, due to the synergistic effect of photocatalysis and electrocatalysis.

Resumo em Inglês:

Metal-organic framework (MOF) UiO-66 was synthesized and evaluated as solid-phase extractor support for cadmium preconcentration in a micro-flow injection system coupled to thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) detection. The adsorbent was characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Raman spectroscopy, and textural data from N2 adsorption/desorption isotherm data. The optimized conditions were achieved by loading 10.0 mL of a sample, containing 0.05 mol L-1 of phosphate buffer solution at pH 8.0, at a high flow rate of 10.0 mL-1 through 20.0 mg of UiO-66 packed into a mini-column, followed by elution with 1.0 mol L-1 HCl. At these conditions, the method presented a preconcentration factor of 35.7, limit of detection of 0.03 µg L-1 and a dynamic linear range from 0.1 to 8.0 µg L-1. The adsorption performance of UiO-66 towards cadmium was not influenced by Pb2+, Hg2+, Fe2+, Co2+, Cu2+, Ni2+, Zn2+, Mg2+ and Ca2+ ions. Analysis of different waters samples (tap water, physiological solution, mineral water, and lake water) was carried out without matrix interference, yielding recovery values ranging from 92.0 to 111.9%.

Resumo em Inglês:

In this work, we describe a sustainable alternative to recover iron from two iron ore tailings (IOT) using hydrogen reduction at relatively low temperatures followed by magnetic separation. X-ray powder diffraction (XRD), inductively coupled plasma (ICP), atomic absorption (AA), Mössbauer, scanning electron microscopy (SEM/EDS), Raman and thermogravimetry (TG) analyses indicated that the Fe oxide present in the IOTs (sandy tailing (ST) and mud tailings (MT)), can be reduced with H2 at 500 ºC to produce α-Fe. Upon magnetic separation the mud tailing produced a 77 wt.% magnetic fraction increasing the Fe content from 19.2 to ca. 56 wt.% of Fe. On the other hand, the sandy tailing resulted in a 15 wt.% magnetic fraction increasing the Fe content from 19.2 to 70 wt.%. These results indicate that up to 86% of iron can be recovered from the IOT wastes already in the metallic form which can be very interesting for the steel industry.

Resumo em Inglês:

The widespread use of the trace metal chromium in industrial processes and the known toxicity of CrVI species have stimulated interest in chromium speciation analysis. However, some analytical detection systems are not suitable for the quantification of CrIII and CrVI species. In the present study, an aqueous biphasic system (ABS) was employed as an environmentally safe, simple, and economical alternative. The ABS allows the implementation of an efficient separation step before quantifying of the species of interest by flame atomic absorption spectrometry. A robust speciation and preconcentration method was developed, which can be applied to samples with a wide concentration range, without the use of any extractants and interconversion of the species during the procedure. The proposed method was successfully used to determine the chromium species present in tap, treatment plant, river, and electroplating wastewater samples. Recovery percentages of 87.9-107% were achieved, suggesting minor water matrix interference. The proposed method had acceptable limits of detection and quantification of 5.38 and 16.3 µg kg-1, respectively.

Resumo em Inglês:

Alginate (ALG) is a natural polymer used in a wide range of applications. Cerium is a sustainable corrosion inhibitor for many metal substrates. In this study, ALG/Ce3+ hydrogel microparticles are presented as an innovative cerium(III) reservoir system for the smart release of cerium ions. The active corrosion inhibition capacity of the ALG/Ce3+ complex was investigated. Tests using ALG/Ce3+ macrogels (beads) and electrochemical experiments showed that, in saline media, ALG/Ce3+ hydrogel was able to release Ce3+, which was subsequently exchanged with Al3+, Fe2+ and Fe3+ and, thus slowing the corrosion process of AA2024 (aluminum alloy) and AISI1020 (carbon steel) substrates, respectively. It is suggested that the presence of metal ions originated from the corrosion process triggers the cerium release. The corrosion protection of ALG/Ce3+ of the aluminum alloy was confirmed by polarization curves, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) and the protection of the carbon steel was demonstrated by EIS experiments. To the best of our knowledge, this is the first time that an alginate-based complex has been reported as an ion exchange corrosion-inhibiting system for metal substrates.

Resumo em Inglês:

Sustainable energy generation has been a growing concern worldwide due to the alarming effects of climate changes in the last few decades. In this scenario, perovskite solar cells hold great promise in contributing for a greener global energy matrix. Despite the great potential of this technology, several difficulties to deploy perovskite solar panels are yet to be overcome, being their long-term stability one of the most critical. In this sense, this work offers an alternative to improve the long-term, operational stability of the devices by passivating the CsFAMA perovskite active layer with a mixture of N-(2-aminoethyl)naphthalimide and mercaptopropionic acid. These modifications improved the perovskite and device stability under ambient conditions. The solar cells without encapsulation and with post-treatment with 5 mM modifier solution retained ca. 90% of its initial power conversion efficiency (PCE) after 500 h exposed to ambient conditions, while standard solar cells retained ca. 58%. Our approach offers a simple new method to improve the stability of perovskite solar cells using an unexplored combination of passivating molecules.

Resumo em Inglês:

A sensitive method is proposed to determine antimony species using vortex-assisted ionic liquid-based liquid-phase microextraction and digital imaging colorimetry. SbIII forms a ternary complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol, ascorbic acid, and iodide in an acid medium. The acceptor phase consists of the ionic liquid 1-butyl-3-methylimidazole hexafluorophosphate, dispersed in the aqueous solution with a vortex stirrer. After centrifugation, SbIII was determined directly in the rich phase. SbV can also be measured by converting to reduced species. The method presented a limit of detection of 1.4 and 4.2 μg L-1 and an enrichment factor of 360. The precision (relative standard deviation) of the method is 7.0%. The procedure was applied to the speciation of antimony in river water and mineral water samples. Some results were compared with those obtained by electrothermal atomic absorption spectrometry (ET AAS). The method is an attractive alternative for determining antimony species, considering the aspects of green analytical chemistry.