Photocatalyzed hydrodecarboxylation of fatty acids: a prospective method to produce drop-in biofuels.

A direct and practical method for photocatalyzed hydrodecarboxylation of fatty acids is reported herein. The catalytic system consists of a commercially available acridinium salt as the photocatalyst and thiophenol as the Hydrogen Atom Transfer (HAT) co-catalyst. Results evidenced that Cn-1 alkanes were obtained in yields up to 77%. Furthermore, the protocol was employed for a complex mixture of fatty acids bio-derived from a real sample of licuri oil to obtain hydrocarbons in the range of C9-C17 with high selectivity and excellent conversion (>90%). This work provides a powerful strategy for producing drop-in biofuels under mild conditions. Finally, an energetic assessment of our proposed protocol (∼22.9 kW h) reveals the benefit of a sustainable production of renewable hydrocarbons.

Sulphate-based electrochemical processes as an alternative for the remediation of a beauty salon effluent‡.

Beauty salons (BS) are places that deal with a wide range of cosmetics with potentially hazardous chemicals, and their effluent should be properly treated before going to the sewage system, once it represents characteristics of industrial wastewater. This work provides an extensive characterization of a BS effluent and its respective electrochemical treatment by comparing NaCl, Na2SO4, and Na2S2O8 as supporting electrolytes with a boron-doped diamond (BDD) as anode, applying 10 or 30 mA cm-2 of current density (j). The inclusion of UVC irradiation was also performed but the improvements achieved in removing the organic matter were null or lower. The analysis of chemical oxygen demand (COD) removal, energy consumption, and total current efficiency (TCE) was required to prove the efficacy of the processes and the comparative study of the performance of different technologies. Precipitate analysis was also done due to the high turbidity of the raw effluent and the appearance of a precipitate before and during the electrolysis, mainly with Na2S2O8. The precipitate confirmed the presence of silicates and small amounts of heavy metals. The results clearly showed that 6 h of treatment with Na2SO4 achieved 58% of COD removal with an energy consumption of about 0.52 kWh m-3, being the best electrolyte option for treating BS effluent by applying 10 mA cm-2. Under these experimental conditions, the final wastewater can be directly discharged into the sewage system with a lower amount of visible precipitate, and with 73% less turbidity. The treatment here proposed can be used as an alternative to decision-makers and governments once it can be a step further in the implementation of better and advanced politics of water sanitation.

Photocatalytic Hydrodecarboxylation of Fatty Acids for Drop-in Biofuels Production.

A mild, practical, and environmentally friendly method for the hydrodecarboxylation of fatty acids using an acridine-based photoredox catalyst and thiophenol was developed. Cn-1 alkanes were synthesized in good to excellent yields (up to 99 %) from C10-C18 saturated fatty acids under visible light irradiation (405 nm). The developed protocol was employed for a mixture of fatty acids obtained from the hydrolysis of Licuri oil, affording a mixture of C9-C17 hydrocarbons in quantitative yield, which demonstrates the potential application of the method to produce drop-in biofuels.

Cost-effective smartphone-based method for low range chemical oxygen demand analysis.

Aiming the decentralization of monitoring policies and to facilitate the work of researchers, mainly in developing countries, the present method deals with the explanation of a simple and rapid protocol for chemical oxygen demand (COD) analysis through the use of digital smartphone devices coupled with a camera and a free app available for Android operating system that recognizes HSV (hue, saturation, value). The calibration of the method is done based on the theoretical values of potassium hydrogen phthalate for a proper and reliable build of the calibration curve by using the smartphone-based technique and the digested samples of COD. The coefficient of determination (R2) attained a value upper than 0.99, providing a high confidence levels, and the method achieved 97% of average accuracy in samples with COD values ranging from 0 to 150 mg L-1. Finally, the procedure here presented can be a great support for scientific laboratories and monitoring policies, once it can efficiently substitute expensive spectrophotometers and can improve and ensure the sustainable management of water sanitation, which is one of the sustainable goals proposed by the United Nations.•COD measurements, based on the use of a simple smartphone with a camera, can be a promising way for environmental analysis when spectrophotometers are not available, such as decentralized approaches.•The use of smartphone protocol is a novel initiative to fulfill sustainable development goal 6 on clean water and sanitation.•The smartphone is capable to read the difference of HSV values efficiently and can substitute the use of expensive spectrophotometers.

Decentralized environmental applications of a smartphone-based method for chemical oxygen demand and color analysis.

This study is focused on a proposal of a smartphone imaging-based quantification for providing a simple and rapid method for the analysis of chemical oxygen demand (COD) and color throughout the use of the HSV and/or RGB model in digital devices. For COD, calibration curves were done based on the theoretical values of potassium biphthalate for a proper comparison between the spectrophotometer and the smartphone techniques. The smartphone camera and application attain an average accuracy higher than the analysis in the spectrophotometer (98.3 and 96.2%, respectively). In the color analysis, it was demonstrated that only the UV-vis bands measurement is not feasible to perform the real abatement of the dye in the water because the limiting concentration that allows obtaining a linear relationship in this equipment related to the dye concentration is about 10 mg L-1. Above this value, the spectrophotometer can not reach the real difference of color in the solution. Meanwhile, the smartphone method by using the camera reaches linearity until 50 mg L-1. From an environmental point of view, smartphones have been used for monitoring several organic and inorganic pollutants, however, no attempts have been published related to their use to evaluate the color and COD during wastewater treatment. Therefore, this investigation also aims to assess the utilization of these methods, for the first time, when high-colored water polluted by methylene blue (MB) was electrochemically treated by using a boron-dopped diamond (BDD) as the anode, with different current densities (j = 30, 45, 60, and 90 mA cm-2). COD and color abatement results clearly showed that different organic matter/color removal efficiencies were achieved, depending on the j used. All the results are aligned with the studies already available in the literature, with the total removal of color in 120 min of electrolysis with 60 and 90 mA cm-2, and almost 80% of COD abatement with the higher j. Moreover, samples of real effluent from beauty salons were compared, with standard deviation varying from only 3 to 40 mg O2 L-1, which is acceptable for COD values close to 2000. Finally, the methods here presented can be a great benefit for public water monitoring policies, since it is cheap and has a decentralized characteristic, given that smartphones are very common and portable devices.

Combining Soil Vapor Extraction and Electrokinetics for the Removal of Hexachlorocyclohexanes from Soil.

This paper focuses on the evaluation of the mobility of four hexachlorocyclohexane (HCH) isomers by soil vapor extraction (SVE) coupled with direct electrokinetic (EK) treatment without adding flushing fluids. SVE was found to be very efficient and remove nearly 70 % of the four HCH in the 15-days of the tests. The application of electrokinetics produced the transport of HCH to the cathode by different electrochemical processes, which were satisfactorily modelled with a 1-D transport equation. The increase in the electric field led to an increase in the transport of pollutants, although 15 days was found to be a very short time for an efficient transportation of the pollutants to the nearness of the cathode. Loss of water content in the vicinity of the cathode warns about the necessity of using electrokinetic flushing technologies instead of simple direct electrokinetics. Thus, results point out that direct electrokinetic treatment without adding flushing fluids produced low current intensities and ohmic heating that contributes negatively to the performance of the SVE process. No relevant differences were found among the removal of the four isomers, neither in SVE nor in EK processes.

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater.

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm-2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm-2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na2SO4 L-1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na2SO4 L-1 and by applying 15 mA cm-2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Photovoltaic Electrochemically Driven Degradation of Calcon Dye with Simultaneous Green Hydrogen Production.

In this study, for the first time, the production of green hydrogen gas (H2) in the cathodic compartment, in concomitance with the electrochemical oxidation (EO) of an aqueous solution containing Calcon dye at the anodic compartment, was studied in a PEM-type electrochemical cell driven by a photovoltaic (PV) energy source. EO of Calcon was carried out on a Nb/BDD anode at different current densities (7.5, 15 and 30 mA cm-2), while a stainless steel (SS) cathode was used for green H2 production. The results of the analysis by UV-vis spectroscopy and total organic carbon (TOC) clearly showed that the electrochemical oxidation (EO) of the Calcon dye after 180 min of electrolysis time by applying 30 mA cm-2 reached up to 90% of degradation and 57% of TOC removal. Meanwhile, under these experimental conditions, a green H2 production greater than 0.9 L was achieved, with a Faradaic efficiency of 98%. The hybrid electrolysis strategy is particularly attractive in the context of a circular economy, as these can be coupled with the use of more complex water matrices to transform organic depollution into an energy resource to produce H2 as a chemical energy carrier.

Application of electro-Fenton and photoelectro-Fenton processes for the degradation of contaminants in landfill leachate.

Worldwide, most solid waste ends its life in landfill sites, which have a significant environmental impact in several respects. In particular, rainfall over landfill sites results in the production of an aqueous leachate containing compounds having low biodegradability, high toxicity, and a high organic load. For this reason, this study aims to investigate the applicability of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes as alternative for treating a local landfill effluent with high organic content (chemical oxygen demand (COD) = 2684.7 mg-O2 L -1) in a continuous-flow reactor (using, for first time, this kind of system with higher electrodes area of 35 cm2) using boron-doped diamond anode (Nb/BDD) and a carbon felt cathode (FC) electrodes. The effects of current density j (30, 60 and 90 mA cm-2) and UV radiation wavelength (UVA and UVC) were studied to evaluate the treatment efficiency as well as the energy consumption. Results clearly showed that, the best efficiencies removing organic matter, in terms of COD, were about 66%, 68% and 89% with an energy consumption of only 19.41, 17.61 and 17.59 kWh kg COD-1 for EF, PEF-UVA and PEF-UVC respectively, at 90 mA cm-2 after 4 h of operation. The treatment of this kind of effluent produced organic and inorganic by-products, the acetic and formic acids as well as NO2-, NO3-, and NH4+, being assessed their concentrations.

Enhancing soil vapor extraction with EKSF for the removal of HCHs.

This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm-1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested.

Green Composite Sensor for Monitoring Hydroxychloroquine in Different Water Matrix.

Hydroxychloroquine (HCQ), a derivative of 4-aminoquinolone, is prescribed as an antimalarial prevention drug and to treat diseases such as rheumatoid arthritis, and systemic lupus erythematosus. Recently, Coronavirus (COVID-19) treatment was authorized by national and international medical organizations by chloroquine and hydroxychloroquine in certain hospitalized patients. However, it is considered as an unproven hypothesis for treating COVID-19 which even itself must be investigated. Consequently, the high risk of natural water contamination due to the large production and utilization of HCQ is a key issue to overcome urgently. In fact, in Brazil, the COVID-19 kit (hydroxychloroquine and/or ivermectin) has been indicated as pre-treatment, and consequently, several people have used these drugs, for longer periods, converting them in emerging water pollutants when these are excreted and released to aquatic environments. For this reason, the development of tools for monitoring HCQ concentration in water and the treatment of polluted effluents is needed to minimize its hazardous effects. Then, in this study, an electrochemical measuring device for its environmental application on HCQ control was developed. A raw cork-graphite electrochemical sensor was prepared and a simple differential pulse voltammetric (DPV) method was used for the quantitative determination of HCQ. Results indicated that the electrochemical device exhibited a clear current response, allowing one to quantify the analyte in the 5-65 µM range. The effectiveness of the electrochemical sensor was tested in different water matrices (in synthetic and real) and lower HCQ concentrations were detected. When comparing electrochemical determinations and spectrophotometric measurements, no significant differences were observed (mean accuracy 3.0%), highlighting the potential use of this sensor in different environmental applications.

Applicability of Cork as Novel Modifiers to Develop Electrochemical Sensor for Caffeine Determination.

This study aims to investigate the applicability of a hybrid electrochemical sensor composed of cork and graphite (Gr) for detecting caffeine in aqueous solutions. Raw cork (RAC) and regranulated cork (RGC, obtained by thermal treatment of RAC with steam at 380 °C) were tested as modifiers. The results clearly showed that the cork-graphite sensors, GrRAC and GrRGC, exhibited a linear response over a wide range of caffeine concentration (5-1000 µM), with R2 of 0.99 and 0.98, respectively. The limits of detection (LOD), estimated at 2.9 and 6.1 µM for GrRAC and GrRGC, suggest greater sensitivity and reproducibility than the unmodified conventional graphite sensor. The low-cost cork-graphite sensors were successfully applied in the determination of caffeine in soft drinks and pharmaceutical formulations, presenting well-defined current signals when analyzing real samples. When comparing electrochemical determinations and high performance liquid chromatography measurements, no significant differences were observed (mean accuracy 3.0%), highlighting the potential use of these sensors to determine caffeine in different samples.