Microalgae-mediated biofixation as an innovative technology for flue gases towards carbon neutrality: A comprehensive review.

Microalgae-mediated industrial flue gas biofixation has been widely discussed as a clean alternative for greenhouse gas mitigation. Through photosynthetic processes, microalgae can fix carbon dioxide (CO2) and other compounds and can also be exploited to obtain high value-added products in a circular economy. One of the major limitations of this bioprocess is the high concentrations of CO2, sulfur oxides (SOx), and nitrogen oxides (NOx) in flue gases, according to the origin of the fuel, that can inhibit photosynthesis and reduce the process efficiency. To overcome these limitations, researchers have recently developed new technologies and enhanced process configurations, thereby increased productivity and CO2 removal rates. Overall, CO2 biofixation rates from flue gases by microalgae ranged from 72 mg L-1 d -1 to over 435 mg L-1 d-1, which were directly influenced by different factors, mainly the microalgae species and photobioreactor. Additionally, mixotrophic culture have shown potential in improving microalgae productivity. Progress in developing new reactor configurations, with pilot-scale implementations was observed, resulting in an increase in patents related to the subject and in the implementation of companies using combustion gases in microalgae culture. Advancements in microalgae-based green technologies for environmental impact mitigation have led to more efficient biotechnological processes and opened large-scale possibilities.

Combustion characteristics and gasification kinetics of Brazilian municipal solid waste subjected to different atmospheres by thermogravimetric analysis.

This study examines the gasification kinetics of Brazilian municipal solid waste (MSW) and its components under air, CO2, and air/CO2 (70/30 vol%) atmospheres. The ignition indices of paper and plastic are 6 and 3 times that of food waste, which are 38.6 × 10-3 %/min3 and 19.6 × 10-3 %/min3, respectively, implying a faster separation of volatile compounds from the paper and plastic. The minimum Eα values of 132 kJ/mol and 140 kJ/mol have been obtained for paper waste under air and air/CO2, respectively. On CO2 condition, MSW has an average Ea value of 96 kJ/mol. Under an air/CO2 atmosphere, a high synergistic ΔW of -4.7 wt% has been identified between individual components. The presence of air and CO2 improves the oxidation and char gasification process, thus resulting in better combustion. Hence, the gasification of MSW under an air/CO2 atmosphere would improve the waste-to-energy plant's performance and minimize the CO2 emission.

Dependence of n-Type Metal-Oxide Gas Sensor Response on the Pressure of Oxygen and Reducing Gases.

The adsorption of oxygen and its reaction with target gases are the basis of the gas detection mechanism by using metal oxides. Here, we present a theoretical analysis of the sensor response, within the ionosorption model, for an n-type polycrystalline semiconductor. Our goal of our work is to reveal the mechanisms of gas sensing from a fundamental point of view. We revisit the existing models in which the sensor response presents a power-law behavior with a reducing gas partial pressure. Then, we show, based on the Wolkenstein theory of chemisorption, that the sensor response depends not only on the reducing gas partial pressure but also on the oxygen partial pressure. We also find that the obtained sensor response does not explicitly depend on the grain size, and if it does, it is exclusively through the rate constants related to the involved reactions.

Venous blood gases and electrolyte values of captive red foot tortoise (Chelonoidis carbonarius).

Blood gas analysis reflects the exchange of oxygen and carbon dioxide in the lungs. This test provides important information, since the relationship between these gases has a direct impact on the acid-basic balance in the body. Given the significance of blood gas analysis in Brazilian reptiles, this study set out to establish temperature-corrected and uncorrected reference intervals for venous blood gas measurements in Chelonoidis carbonarius, and to compare values between females and males. In this study, 19 animals were used, 8 males and 11 females. Blood samples were collected from the dorsal coccygeal vein, and the analyses were performed immediately after blood sample collection. The following parameters were measured: pH, PO2, HCO3-, TCO2, BEecf, Na, K, ICa, and Glu, and were compared between females and males. Additionally, pH, pCO2, and pO2 values were compared with and without temperature correction. Oxygen saturation and Na levels were significantly higher (p<0.05) in males. Furthermore, it was possible to infer that the lower the body temperature relative to the environmental temperature, the larger the difference in pH following temperature correction.

Estimation of the main air pollutants from different biomasses under combustion atmospheres by artificial neural networks.

The production of biofuels to be used as bioenergy under combustion processes generates some gaseous emissions (CO, CO2, NOx, SOx, and other pollutants), affecting living organisms and requiring careful assessments. However, obtaining such information experimentally for data evaluation is costly and time-consuming and its in situ obtaining for regional biomasses (e.g., those from Northeast Brazil (NEB) is still a major challenge. This paper reports on the application of artificial neural networks (ANNs) for the prediction of the main air pollutants (CO, CO2, NO, and SO2) produced during the direct biomass combustion (N2/O2:80/20%) with the use of ultimate analysis (carbon, hydrogen, nitrogen, sulfur, and oxygen). 116 worldwide biomasses were used as input data, which is a relevant alternative to overcome the lack of experimental resources in NEB and obtain such information. Cross-validation was conducted with k-fold to optimize the ANNs and performance was analyzed with the use of statistical errors for accuracy assessments. The results showed an acceptable statistical performance for all architectures of ANNs, with 0.001-12.41% MAPE, 0.001-5.82 mg Nm-3 MAE, and 0.03-52.30 mg Nm-3 RMSE, highlighting the high precision of the emissions studied. On average, the differences between predicted and real values for CO, CO2, NO, and SO2 emissions from NEB biomasses were approximately 0.01%, 10-6%, 0.14%, and 0.05%, respectively. Pearson coefficient provided consistent results of concentration of the ultimate analysis in relation to the emissions studied and effectiveness of the test set in the developed models.

Prefeasibility analysis of biomass gasification and electrolysis for hydrogen production.

Hydrogen is a key energy vector to accomplishing energy transition and decarbonization goals proposed in the transport and industrial sectors worldwide. In recent years, research has focused on analyzing, designing, and optimizing hydrogen production, searching to improve economic prefeasibility with minimal emissions of polluting gases. Therefore, the techno-economic analysis of hydrogen production by electrolytic and gasification processes becomes relevant since these processes could compete commercially with industrial technologies such as SMR - Steam methane reforming. This work aims to analyze hydrogen production in stand-alone processes and energy-driven biorefineries. The gasification and electrolysis technologies were evaluated experimentally, and the yields obtained were input data for scaling up the processes through simulation tools. Biomass gasification is more cost-effective than electrolytic schemes since the hydrogen production costs were 4.57 USD/kg and 8.30 USD/kg at an annual production rate of 491.6 tons and 38.96 tons, respectively. Instead, the electrolysis process feasibility is strongly influenced by the recycled water rate and the electricity cost. A sensitivity analysis was performed to evaluate the temperature, pressure, and current density variability on the hydrogen production rate. The increase in pressure and current density induces parasitic currents while the temperature increases hydrogen production. Although higher hydrogen production rates from gasification, the syngas composition decreases the possibility of being implemented in applications where purity is critical.

Control of selectivity in the oxidation of 5-hydroxymethylfurfural to 5- formyl-2-furancarboxylic acid catalyzed by laccase in a multiphasic gas-liquid microbioreactor.

The selectivity of 5-formyl-2-furancarboxylic acid (FFCA) was studied in a batch bioreactor and microbioreactors with different internal diameters (ID). Using microbioreactors, the effect of the flow rate of the liquid and gas phase on the yield, space time yield (STYFFCA), and gas-liquid mixture velocity (UM) of the reaction was evaluated. The biooxidation in flow microbioreactors, a selectivity of 100 % for FFCA was achieved, while with the batch bioreactor at the same substrate concentration a selectivity of 6.7 % was obtained. The highest yield (30 %) with 15 mM of 5-hydroxymethylfurfural (HMF) was reached at a gas-liquid flow rate of 0.5 µL/min and the highest STYFFCA (0.07 mol m-3 min-1) was achieved at a gas-liquid flow rate of 1.5 µL/min with the microbioreactor with an ID of 0.5 mm. The UM values (0.5 to 1.6 cm min1) indicated that the reaction takes place under a kinetic regime without mass transfer limitations.

Targeting Biomechanical Endurance of Dental-Implant Abutments Using a Diamond-Like Carbon Coating.

Abutment components (i.e., fixtures associated with oral implants) are essentially made of titanium (Ti), which is continuously exposed to the hash oral environment, resulting in scratching. Thus, such components need to be protected, and surface treatments are viable methods for overcoming long-term damage. Diamond-like carbon (DLC), an excellent protective material, is an alternative surface-treatment material for Ti abutments. Here, we demonstrate that a silicon interlayer for DLC film growth and the pulsed-direct current plasma-enhanced chemical vapor deposition (DC-PECVD) method enables the deposition of an enhanced protective DLC film. As a result, the DLC film demonstrated a smooth topography with a compact surface. Furthermore, the DLC film enhanced the mechanical (load-displacement, hardness, and elastic modulus) and tribological properties of Ti as well as increased its corrosion resistance (16-fold), which surpassed that of a bare Ti substrate. The biofilm formed (Streptococcus sanguinis) after 24 h exhibited an equal bacterial load (∼7 Log colony-forming units) for both the groups (Ti and DLC). In addition, the DLC film exhibited good cytocompatibility, owing to its noncytotoxicity toward human gingival fibroblast cells. Therefore, DLC deposition via DC-PECVD can be considered to be a promising protective and cytocompatible alternative for developing implant abutments with enhanced mechanical, tribological, and electrochemical properties.

An overview of oxygen transport in plants: diffusion and convection.

The movement of gases within plants is crucial for species that live in flood-prone areas with limited soil oxygen. These plants adapt to hypoxia/anoxia not by using oxygen more efficiently, but by ensuring a steady oxygen supply to their cells. Wetland plants typically form gas-filled spaces (aerenchyma) in their tissues, providing a low-resistance pathway for gas movement between shoots and roots, especially when the shoots are above water, and the roots are submerged. Oxygen movement in plant roots is mainly through diffusion. However, in certain species, such as emergent and floating-leaved plants, pressurized flows can also facilitate the movement of gases within their stems and rhizomes. Three types of pressurized (convective) flows have been identified: humidity-induced pressurization (positive pressure), thermal osmosis (positive pressure with air flow against the heat gradient), and venturi-induced suction (negative pressure) caused by wind passing over broken culms. A clear diel variation in pressurized flows exists, with higher pressures and flows during the day and negligible pressures and flows during the night. This article discusses some key aspects of these mechanisms for oxygen movement.

Curcuma longa-Based Optical Sensor for Hydrochloric Acid and Ammonia Vapor Detection.

In this research, we present a prototype optical system that offers significant advances in detecting hydrochloric acid (HCl) and ammonia (NH3) vapors. The system utilizes a natural pigment sensor based on Curcuma longa that is securely attached to a glass surface support. Through extensive development and testing with HCl (37% aqueous solution) and NH3 (29% aqueous solution) solutions, we have successfully demonstrated the effectiveness of our sensor. To facilitate the detection process, we have developed an injection system that exposes C. longa pigment films to the targeted vapors. The interaction between the vapors and the pigment films triggers a distinct color change, which is then analyzed by the detection system. By capturing the transmission spectra of the pigment film, our system allows a precise comparison of these spectra at different concentrations of the vapors. Our proposed sensor exhibits remarkable sensitivity, allowing the detection of HCl at a concentration of 0.009 ppm using only 100 µL (2.3 mg) of pigment film. In addition, it can detect NH3 at a concentration of 0.03 ppm with a 400 µL (9.2 mg) pigment film. Integrating C. longa as a natural pigment sensor in an optical system opens up new possibilities for detecting hazardous gases. The simplicity and efficiency of our system, combined with its sensitivity, make it an attractive tool in environmental monitoring and industrial safety applications.

Substitutional Coinage Metals as Promising Defects for Adsorption and Detection of Gases on MoS2 Monolayers: A Computational Approach.

Defective molybdenum disulfide (MoS2) monolayers (MLs) modified with coinage metal atoms (Cu, Ag and Au) embedded in sulfur vacancies are studied at a dispersion-corrected density functional level. Atmospheric constituents (H2, O2 and N2) and air pollutants (CO and NO), known as secondary greenhouse gases, are adsorbed on up to two atoms embedded into sulfur vacancies in MoS2 MLs. The adsorption energies suggest that the NO (1.44 eV) and CO (1.24 eV) are chemisorbed more strongly than O2 (1.07 eV) and N2 (0.66 eV) on the ML with a cooper atom substituting for a sulfur atom. Therefore, the adsorption of N2 and O2 does not compete with NO or CO adsorption. Besides, NO adsorbed on embedded Cu creates a new level in the band gap. In addition, it was found that the CO molecule could directly react with the pre-adsorbed O2 molecule on a Cu atom, forming the complex OOCO, via the Eley-Rideal reaction mechanism. The adsorption energies of CO, NO and O2 on Au2S2, Cu2S2 and Ag2S2 embedded into two sulfur vacancies were competitive. Charge transference occurs from the defective MoS2 ML to the adsorbed molecules, oxidizing the later ones (NO, CO and O2) since they act as acceptors. The total and projected density of states reveal that a MoS2 ML modified with copper, gold and silver dimers could be used to design electronic or magnetic devices for sensing applications in the adsorption of NO, CO and O2 molecules. Moreover, NO and O2 molecules adsorbed on MoS2-Au2s2 and MoS2-Cu2s2 introduce a transition from metallic to half-metallic behavior for applications in spintronics. These modified monolayers are expected to exhibit chemiresistive behavior, meaning their electrical resistance changes in response to the presence of NO molecules. This property makes them suitable for detecting and measuring NO concentrations. Also, modified materials with half-metal behavior could be beneficial for spintronic devices, particularly those that require spin-polarized currents.

On the correlation between thermal imagery and fugitive CH4 emissions from MSW landfills.

Landfill gas (LFG) is related to the biochemical processes generating heat and releasing CH4, CO2, and other gases in lower concentrations, which result in environmental impacts and risk of local explosion. Thermal infrared imagery (TIR) is employed to detect CH4 leakage as a risk control approach. However, the challenge for LFG leakage detection using TIR is establishing a relation between the gas flux and the ground temperature. This study evaluates the problem of a heated gas flowing through a porous medium column where the upward surface exchanges heat by radiation and convection to the environment. A heat transfer model that considers the upward LFG flow is proposed, and a sensibility analysis is developed to relate the flux to the ground temperature level in the condition of non-income solar radiation. An explicit equation to predict CH4 fugitive flow as a function of temperature anomalies of the ground was presented for the first time. The results show that the predicted ground surface temperatures are consistent with the literature's experimental observations. Moreover, the model was complementarily applied to a Brazilian landfill, with in situ TIR measurements in an area with a slightly fractured cover. In this field observation, the predicted CH4 flux was around 9025 g m-2 d-1. Model limitations concerning the soil homogeneity, the transient variation of atmospheric conditions or local pressure, and soil temperature difference in low-flux conditions (related to TIR-cameras accuracy) require further validation. Results could help landfill monitoring in conditions of a high-temperature ground anomaly in dry seasons.

Photosynthetic gas exchange and chlorophyll fluorescence of female hemp plants during sexual reversal treatments / Intercambio gaseoso y fluorescencia de la clorofila en plantas femeninas de Cannabis durante tratamientos de reversión sexual

Sexual reversal methods are commonly used in plant breeding programs, allowing male flowers from female plants or vice versa. This work evaluated sexual reversal methods in female Cannabis plants and their effect on gas exchange activity. Plants treated with 1, methyl-cyclopropene (1-MCP), and aminoetoxyvinylglycine (AVG) showed differences in net photosynthesis (A) and stomatal conductance (gs) between the periods before and after sexual reversal treatments. Quantum yield (Qy), electron transport rate (ETR), and non-photochemical quenching (NPQ) did not show a relationship to the treatments, an increase in Qy and ETR, and a reduction in NPQ were observed after applying treatments. 1-MCP, AVG, and STS (silver thiosulfate) were effective in sexual reversal, while photoperiod changes did not induce the formation of male flowers. Induction of sexual reversion in Cannabis plants did not generate variations in energy dissipation mechanisms through photosystems.

Los métodos de reversión sexual se utilizan comúnmente en los programas de fitomejoramiento, permitiendo la formación de flores masculinas a partir de plantas femeninas y viceversa. Este trabajo tuvo como objetivo evaluar métodos de reversión sexual en plantas femeninas de Cannabis y su efecto sobre el intercambio de gases. Plantas tratadas con 1-metil-ciclopropano (1-MCP) y aminoetoxivinilglicina (AVG) mostraron diferencias en fotosíntesis neta (A) y conductancia estomática (gs) entre los periodos antes y después de los tratamientos de reversión sexual. El rendimiento cuántico (Qy), la tasa de transporte de electrones (ETR) y la disipación no fotoquímica (NPQ) no mostraron relación con los tratamientos, se observó un incremento en Qy y ETR y una reducción en NPQ después de la aplicación de los tratamientos. 1-MCP, AVG y STS (tiosulfato de plata) fueron efectivos en la reversión sexual, mientras que los cambios en el fotoperiodo no indujeron la formación de flores masculinas. La inducción de la reversión sexual en plantas de Cannabis no generó variaciones en los mecanismos que disipan la energía a través de los fotosistemas.

Pictograms to assess bloating and distension symptoms in the general population in Mexico: Results of The Rome Foundation Global Epidemiology Study.

BACKGROUND: There is no term for bloating in Spanish and distension is a very technical word. "Inflammation"/"swelling" are the most frequently used expressions for bloating/distension in Mexico, and pictograms are more effective than verbal descriptors (VDs) for bloating/distension in general GI and Rome III-IBS patients. However, their effectiveness in the general population and in subjects with Rome IV-DGBI is unknown. We analyzed the use of pictograms for assessing bloating/distension in the general population in Mexico. METHODS: The Rome Foundation Global Epidemiology Study (RFGES) in Mexico (n = 2001) included questions about the presence of VDs "inflammation"/"swelling" and abdominal distension, their comprehension, and pictograms (normal, bloating, distension, both). We compared the pictograms with the Rome IV question about the frequency of experiencing bloating/distension, and with the VDs. KEY RESULTS: "Inflammation"/"swelling" was reported by 51.5% and distension by 23.8% of the entire study population; while 1.2% and 25.3% did not comprehend "Inflammation"/"swelling" or distension, respectively. Subjects without (31.8%) or not comprehending "inflammation"/"swelling"/distension (68.4%) reported bloating/distension by pictograms. Bloating and/or distension by the pictograms were much more frequent in those with DGBI: 38.3% (95%CI: 31.7-44.9) vs. without: 14.5% (12.0-17.0); and in subjects with distension by VDs: 29.4% (25.4-33.3) vs. without: 17.2% (14.9-19.5). Among subjects with bowel disorders, those with IBS reported bloating/distension by pictograms the most (93.8%) and those with functional diarrhea the least (71.4%). CONCLUSIONS & INFERENCES: Pictograms are more effective than VDs for assessing the presence of bloating/distension in Spanish Mexico. Therefore, they should be used to study these symptoms in epidemiological research.

Degradation of antibiotic amoxicillin from pharmaceutical industry wastewater into a continuous flow reactor using supercritical water gasification.

In recent years the concern with emerging pollutants in water has become more prominent, especially pharmaceutical residues, such as antibiotics due to the influence to increase antibacterial resistance. Further, conventional wastewater treatment methods have not demonstrated efficiency for the complete degradation of these compounds, or they have limitations to treat a large volume of waste. In this sense, this study aims to investigate the degradation of amoxicillin, one of the most prescribed antibiotics, in wastewater via supercritical water gasification (SCWG) using a continuous flow reactor. For this purpose, the process operating conditions of temperature, feed flow rate, and concentration of H2O2 was evaluated using Experimental Design and Response Surface Methodology techniques and optimized by Differential Evolution methodology. Total organic carbon (TOC) removal, chemical oxygen demand (COD) degradability, reaction time, amoxicillin degradation rate, toxicity of degradation by-products, and gaseous products were evaluated. The use of SCWG for treatment achieved 78.4% of the TOC removal for the industrial wastewater. In the gaseous products, hydrogen was the majority component. Furthermore, high-performance liquid chromatography analyses demonstrated that the antibiotic amoxicillin was degraded. For a mass flow rate of 15 mg/min of amoxicillin fed into the reaction system, 14.4 mg/min was degraded. Toxicity tests with microcrustacean Artemia salina showed slight toxicity to treated wastewater. Despite that, the outcomes reveal the SCWG has great potential to degrade amoxicillin and may be applied to treat several pharmaceutical pollutants. Aside from this, carbon-rich effluents may lead to a significant energy gaseous product, especially, hydrogen and syngas.

Treatment of gaseous streams polluted with H2S: Comparison of electrolytic and electro-Fenton assisted absorption processes.

H2S is a gaseous compound that contributes to air pollution. In this work, the electrochemical oxidation treatment of gaseous streams polluted with H2S is evaluated using a jet mixer and electrochemical cell device, in which the performance of electrolytic and electro-Fenton assisted absorption processes are compared. Results demonstrate the feasibility of both processes to remove H2S, reaching coulombic efficiencies of nearly 100% in the electrolytic assisted absorption, and 70-80% in the electro-Fenton assisted absorption. Aqueous solutions containing phosphate salts as electrolyte were found to be suitable as absorbents for the process. Efficiency in the cathodic production of H2O2 in these solutions using the experimental device was found to be as high as 32.8% (1.184 mgH2O2/min) at 12 °C and atmospheric pressure. Sequential formation of SO2 and SO3 is obtained by the oxidation of H2S contained in the gas. These species are hydrolysed, and a part remained in the absorbent as SO32- and SO42-, while the rest is dragged in the outlet gas. SO3 production is promoted by electrolytic assisted absorption and polysulphides by the electro-Fenton technology. Low concentrations of elemental sulphur are detected in the solid suspensions formed during the process.

Application of Pyrolysis for the Evaluation of Organic Compounds in Medical Plastic Waste Generated in the City of Cartagena-Colombia Applying TG-GC/MS.

In this study, the thermal degradation and pyrolysis of hospital plastic waste consisting of polyethylene (PE), polystyrene (PS), and polypropylene (PP) were investigated using TG-GC/MS. The identified molecules with the functional groups of alkanes, alkenes, alkynes, alcohols, aromatics, phenols, CO and CO2 were found in the gas stream from pyrolysis and oxidation, and are chemical structures with derivatives of aromatic rings. They are mainly related to the degradation of PS hospital waste, and the alkanes and alkenes groups originate mainly from PP and PE-based medical waste. The pyrolysis of this hospital waste did not show the presence of derivatives of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, which is an advantage over classical incineration methodologies. CO, CO2, phenol, acetic acid and benzoic acid concentrations were higher in the gases from the oxidative degradation than in those generated in the pyrolysis with helium. In this article, we propose different pathways of reaction mechanisms that allow us to explain the presence of molecules with other functional groups, such as alkanes, alkenes, carboxylic acids, alcohols, aromatics and permanent gases.

Arterial Blood Gases in Normal Subjects at 2240 Meters Above Sea Level: Impact of Age, Gender, and Body Mass Index.

Background: The values of arterial blood gases (ABG) change with altitude above sea level; empirical verification is essential because ventilatory acclimatization varies with ethnicity and a population's adaptation. Objective: The aim of the study was to describe ABG in a healthy population residing at 2,240 meters above sea level, to identify the mean level of alveolar ventilation (PaCO2), and to know whether a progressive increase in PaCO2 occurs with age and the impact of increasing body mass index (BMI). Methods: We conducted a cross-sectional study in a referral center for respiratory diseases in Mexico City. Associations among variables with correlation coefficient and regression models of PaO2, SaO2, and P(A-a)O2 as dependent variables as a function of age, BMI, minute ventilation, or breathing frequency were explored. Results: Two hundred and seventeen healthy subjects were evaluated with a mean age of 40 ± 15 years, mean of the PaO2 was 71 ± 6 mmHg, SaO2 94% ± 1.6%, PaCO2 30.2 ± 3.4 mmHg, HCO3 20 ± 2 mmol/L, BE-2.9 ± 1.9 mmol/L, and the value of pH was 7.43 ± 0.02. In a linear regression, the main results were PaO2 = 77.5-0.16*age (p < 0.0001) and with aging P(A-a)O2 tended to increase 0.12 mmHg/year. PaCO2 in women increased with age by 0.075 mmHg/year (p = 0.0012, PaCO2 =26.3 + 0.075*age). SaO2 and PaO2 decreased significantly in women with higher BMI 0.14% and 0.52 mmHg per kg/m2, (p = 0.004 and 0.002 respectively). Conclusion: Mean PaCO2 was 30.7 mmHg, implying a mean alveolar ventilation of around 30% above that at sea level.

CVD Growth of Hematite Thin Films for Photoelectrochemical Water Splitting: Effect of Precursor-Substrate Distance on Their Final Properties.

The development of photoelectrode materials for efficient water splitting using solar energy is a crucial research topic for green hydrogen production. These materials need to be abundant, fabricated on a large scale, and at low cost. In this context, hematite is a promising material that has been widely studied. However, it is a huge challenge to achieve high-efficiency performance as a photoelectrode in water splitting. This paper reports a study of chemical vapor deposition (CVD) growth of hematite nanocrystalline thin films on fluorine-doped tin oxide as a photoanode for photoelectrochemical water splitting, with a particular focus on the effect of the precursor-substrate distance in the CVD system. A full morphological, structural, and optical characterization of hematite nanocrystalline thin films was performed, revealing that no change occurred in the structure of the films as a function of the previously mentioned distance. However, it was found that the thickness of the hematite film, which is a critical parameter in the photoelectrochemical performance, linearly depends on the precursor-substrate distance; however, the electrochemical response exhibits a nonmonotonic behavior. A maximum photocurrent value close to 2.5 mA/cm2 was obtained for a film with a thickness of around 220 nm under solar irradiation.

Metal Oxide Gas Sensors to Study Acetone Detection Considering Their Potential in the Diagnosis of Diabetes: A Review.

Metal oxide (MOx) gas sensors have attracted considerable attention from both scientific and practical standpoints. Due to their promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared with conventional techniques, these devices are expected to play a key role in home and public security, environmental monitoring, chemical quality control, and medicine in the near future. VOCs (e.g., acetone) are blood-borne and found in exhaled human breath as a result of certain diseases or metabolic disorders. Their measurement is considered a promising tool for noninvasive medical diagnosis, for example in diabetic patients. The conventional method for the detection of acetone vapors as a potential biomarker is based on spectrometry. However, the development of MOx-type sensors has made them increasingly attractive from a medical point of view. The objectives of this review are to assess the state of the art of the main MOx-type sensors in the detection of acetone vapors to propose future perspectives and directions that should be carried out to implement this type of sensor in the field of medicine.