Low Specific Area Research Articles

The vertical electrical sounding (VES) of the epikarst: A case study of the covered karst of the Bakony region (Hungary)

The epikarsts of five covered karst areas in the Bakony region are compared. The comparison is based on the specific resistances of the bedrock resistance averages measured by vertical electrical sounding (VES). The average largest specific resistance differences (per area) and the mean values (per profile) were calculated to investigate the characteristics of the epikarst. The mean values of specific resistance were compared using analysis of variance (ANOVA) to determine whether the specific resistances of the areas showed significant differences. The studied karst areas can be categorised as high or low specific resistance areas, and the ANOVA method could be applied to three areas based on the available data. It can be concluded that the mean values of their specific resistances are significantly different. The mean values and standard deviation of the specific resistances of the different areas were analysed. It is described that the karst receives less water in the case of areas with lower specific resistance, while it receives more water in the case of areas with higher specific resistance. Areas with a high specific resistance are less karstified, while areas with a low specific resistance are more karstified. Low specific resistances and small mean values indicate a higher degree of cavity formation in the epikarst, while the decrease in mean values and standard deviation indicates increasing uniformity of the degree of cavity formation in the epikarst. The different degree of cavity formation is explained by the different karstification rates and the exposure of different time of certain areas.

Valorization of calcium hypochlorite precipitate as a new source of heterogeneous catalyst development for biodiesel production: A preliminary experiment

One of the main problem related with liquid bleach production from calcium hypochlorite is the amount of precipitates generated and its consequent management. As a result, academic and industrial communities have been challenged with searching of a means for its valorization. Therefore, this research explores the application of the precipitate as a viable source of Ca-based heterogeneous catalyst development for the production of waste cooking oil methyl esters for the first-time. The catalyst was prepared by dividing the precipitates into three forms, viz. raw untreated (RC), heat treated (RC-TB), and NaOH impregnated plus thermally activated (RC-ITB). The prepared catalysts were efficiently characterized by XRF, XRD, FTIR, SEM, and BET techniques. The characterization results indicated that the catalysts are mainly composed of calcium metal in the form of oxides (CaO), calcite (CaCO3) and Portlandite (Ca(OH)2), which are the promising constituents of basic catalysts. The BET inspection of RC, RC-TB, and RC-ITB revealed the specific surface area of 8.509, 9.089, and 9.312 m2/g, respectively. At the same reaction conditions, the maximum biodiesel yield of 76.05 % was achieved by RC-ITB compared to RC-TB (62.57 %) and RC (19.74 %), because it's larger specific surface area and highest basic nature (pH = 12.65 at 1:5 w/v) improves the reaction catalysis through better catalyst-substrates interactions. The lower biodiesel yield was attained through the RC catalyst due to its untreated surface, lower specific area, and weak alkaline nature (pH value = 10.66 at 1:5 w/v). Furthermore, regardless of the amount of yield, almost similar fuel properties and functional groups of the products over the coded catalysts were observed. Generally, the possibility of calcium hypochlorite precipitate as a precursor of Ca-based heterogeneous catalyst has been effectively proven in this research, which could be very important for environmental safety and industrial resource integration.

Recovery of a synthetic dye through adsorption using malt bagasse, a by-product of brewing industry: Study in batch and continuous systems

Reactive dyes are widely used in the textile industry and are known for their toxic and recalcitrant characteristic due to the NN group and the complex aromatic structure. Improper disposal of such compounds in water bodies were linked to respiratory impairments in aquatic animals, photosynthesis reduction in plants, and carcinogenic properties in humans. In addition to the environmental concern, reactive dyes are valuable resources that could be recovered from textile wastewater by means of adsorption. On the other hand, the brewing industry generates about 20 kg of malt bagasse for every 100 L of produced beer. Therefore, this manuscript reports the adsorption of yellow Reafix-B8G (YR-B8G), a synthetic reactive dye, using malt bagasse in batch and continuous systems, aligning the conversion of a by-product of brewing industry into a valuable resource and the resource recovery of synthetic dye, supporting the circular economy. Malt bagasse with minimal processing, i.e., biomass dried at 303 K upon delivery from brewery industry, was effective for adsorption of YR-B8G in acidic pH. The possible adsorption mechanism of YB-B8G on malt bagasse is adsorption in the binding sites of the hydroxyl groups of adsorbent with physisorption was the main interaction. The malt bagasse was characterized as a lignocellulosic material with fibrous structure and low specific area (60.35 m2 g−1). Even though the malt bagasse has low surface area, it is a waste material used without minimal processing and does not require chemical activation or further costly treatments to achieve adsorption capacity of 164.34 mg g−1 for YB-B8G. Dye recovery from malt bagasse was best achieved using 50 % (v/v) ethyl alcohol as desorption solution with ∼94 % of dye recovery. Adsorption in continuous system presented removal capacity superior to the batch removal, with the breakthrough curves strongly affected by the operating conditions. Malt bagasse has potential to be applied as part of the removal and recovery efforts of reactive dyes, contributing to the application of waste materials as valuable resources in the mitigation of organic contaminants in wastewater.

Gill function in an early arthropod and the widespread adoption of the countercurrent exchange mechanism.

Rising but fluctuating oxygen levels in the Early Palaeozoic provide an environmental context for the radiation of early metazoans, but little is known about how mechanistically early animals satisfied their oxygen requirements. Here we propose that the countercurrent gaseous exchange, a highly efficient respiratory mechanism, was effective in the gills of the Late Ordovician trilobite Triarthrus eatoni. In order to test this, we use computational fluid dynamics to simulate water flow around its gills and show that water velocity decreased distinctly in front of and between the swollen ends, which first encountered the oxygen-charged water, and slowed continuously at the mid-central region, forming a buffer zone with a slight increase of the water volume. In T. eatoni respiratory surface area was maximized by extending filament height and gill shaft length. In comparison with the oxygen capacity of modern fish and crustaceans, a relatively low weight specific area in T. eatoni may indicate its low oxygen uptake, possibly related to a less active life mode. Exceptionally preserved respiratory structures in the Cambrian deuterostome Haikouella are also consistent with a model of countercurrent gaseous exchange, exemplifying the wide adoption of this strategy among early animals.

Soil C dynamics after deforestation and subsequent conversion of arable cropland to grassland in humid temperate areas

Land use and plant-soil management influence soil organic C stocks and soil properties. This study aimed to identify the main mechanisms by which these factors alter soil organic matter (SOM) dynamics and stocks. Changes in the organic C pools and biochemical quality in different OM compartments were assessed: a) after deforestation and intensive cultivation (SOM loss) and then, b) after the conversion of cropland to grassland (SOM replenishment) in a chronosequence of recovery (1–45 years). Topsoil samples were subjected to physical fractionation to assess the distribution of free particulate OM (POM) and mineral associated OM (MAOM). SOM quality was characterized by 13C NMR spectroscopy, thermal analysis (DSC/TG), and microbial activity was monitored by isothermal microcalorimetry.Deforestation and intensive cultivation led to the loss of 80 % of the C stored in the upper mineral soil (up to 30–35 cm). The POM was almost depleted, MAOM underwent significant losses (>40 %) and all OM compounds, including the aromatic C, were affected. The large and unexpected loss of MAOM can be attributed to the low specific surface soil area and also to the labile (biodegradable) nature of the OM in this fraction. After 45 years, conversion of cropland to grassland recovered 68 % of the C lost in the mineral soil (mainly as MAOM), at an annual rate of 1.25 Mg C ha−1. The present findings showed that the persistence of long-term OM depends on how strongly organic compounds are adsorbed onto mineral surfaces (i.e., the specific surface area) and the biochemical nature of OM compounds. Adequate plant-soil management favoured the replenishment of the MAOM under these experimental conditions, and this fraction was an active pool in terms of C storage and biochemical quality. This study served to test current theories about changes in soil C fractions due to land use changes and soil-plant management.

Controllable generation of multi-row bubbly flow in coupled microstructures and its boosting of photocatalytic decarboxylative carbonylation

Continuous-flow microreactor technology has emerged as a powerful driver of process innovation in photocatalysis. However, microfluidic schemes that are ideal for gas–liquid photoreactions are still limited by the low specific interfacial area. Herein, we invent for the first time a coupled microstructure comprising sudden contraction, shearing, and sudden expansion parts, which can generate microbubbles with smaller sizes under lower flow rates compared with the conventional T-junction. Based on bubble dynamics studies, a predictive model for the bubble size, with prediction errors of less than 10%, is established. Interestingly, the generated microbubbles can be induced by the expansion flow to form a multi-row bubbly flow. Additionally, predictive models for the row number are proposed to guide its controlled production. Computational fluid dynamics simulations show a 22.8-fold increase in specific interfacial area for the five-row bubbly flow compared to the segmented flow. Moreover, the average dissolved oxygen concentration at a given time increases by 34.0 times. Further, photocatalytic decarboxylative carbonylation limited by oxygen mass transfer is employed as the model reaction, demonstrating the excellent performance of multi-row bubbly flow in enhancing the gas–liquid photocatalysis, and the stronger enhancement at higher row number. Subsequently, the phototransformation achieves 96.3% yield within 19 min at a six-row bubbly flow, and the space–time yield reaches 6.82 gL–1 h−1, thus indicating the high efficiency of the developed microdevice. The multi-row bubbly flow enabled by this coupled microstructure provides a new process window for continuous, efficient, and controllable gas–liquid photocatalysis.

Distinct nature of biochar and activated carbon from pyrolysis-activation of vegetable (lettuce) and staple food (noodles) in food waste

Food waste contains generally not a single component but a mixture of vegetables like lettuce and staple food like noodles. Vegetables and staple food are distinct in biological structures, and their pyrolysis or activation might generate biochar and activated carbon with varied properties. This was investigated in this study via conducting the initial pyrolysis of lettuce and noodles at 350 or 550 °C, and the subsequent activation of the biochar with K2C2O4 at 800°C. The results showed that it was much easier to crack/gasify the organic components in lettuce, producing more gases. The aromatization reactions could take place to a higher extent in pyrolysis of noodles, producing the activated carbon with lower specific area. The activation of the biochar produced at 350°C generated higher overall yields of activated carbon with more developed pore structures. Additionally, the environmental impact of pyrolysis and activation of noodles was milder than that of lettuce.

Characterization of Liquid‐Vapor Interfaces in Pores During Evaporation

AbstractThe evolution of the liquid‐vapor interface plays a key role in multiphase flow, heat and mass transfer, and fluid phase change in porous media. In the soil water evaporation process, the vaporization occurs only on the liquid‐vapor interfaces rather than the apparent soil surface. Yet, the interfaces evolve with high distortion and great complexity along the drying path. Hence the microscale characteristics of interfaces especially geometrical and topological features in soil water evaporation are barely investigated. In this work, we scanned glass bead samples using X‐ray micro tomography and scrutinized the development of liquid‐vapor interfaces with different degrees of saturation. The liquid‐vapor interfaces are identified by morphological operations and extracted using the watershed segmentation technique. The liquid phase disperses into individual ganglia and distributes wildly in the pores as the saturation decreases, leading to low specific interface areas at saturated and dry state but a maximum value at a threshold saturation around 30%. The topological analysis reveals that the liquid and vapor phases present complementary connectivity behaviors quantified by normalized Euler characteristic numbers. The local mean curvature distribution of each typical individual interface cluster quantitatively describes the intricate progression of interface geometry and morphology along with drying. The overall mean curvature evolution of the sample separates the negative curvature component and confirms the capillary pressure increase during the pore water evaporation. The interfacial area and curvature analysis provide a cornerstone to determine the authentic interfacial evaporation rate for the soil under drying.

Household Food Security and Associated Factors among Portuguese Children

ABSTRACT This study investigated the household food insecurity (HFI) among Portuguese children following the last world financial crisis. A cross-sectional study was conducted on 4737 Portuguese children (3–11 yrs). Socio-demographics, food insecurity, and household geographic location were assessed via questionnaire. Nutritional status was measured. Following the economic crisis, 14.2% of school children and 12.0% of preschool children experienced HFI. Preschool children having parents with low and medium parental education (paternal: OR = 4.4; 95% CI 2.7–7.1 and OR = 2.4; 95% CI 1.5–3.6; maternal: OR = 2.2; 95% CI 1.4–3.5 and OR = 1.6; 95% CI 1.1–2.3), living in the south (OR = 1.4; 95% CI 1.0–2.0) and being overweight/obese (OR = 1.1; 95% CI 0.7–1.3) were more likely to experience HFI than food secure household peers. Higher OR of belonging to a food insecure household were observed in school-aged children with low and medium parental education (paternal: OR = 2.9; 95% CI 1.9–4.6 and OR = 1.7; 95% CI 1.1–2.5; maternal: OR = 2.5; 95% CI 1.6–3.9 and OR = 2.3; 95% CI 1.6–3.3), living in Coimbra (OR = 1.7; 95% CI 1.1–2.6) and being overweight/obese (OR = 1.3; 95% CI 0.8–1.5) compared to food secure household peers. Data are instructive and support the need to increase awareness of HFI, reduce its incidence in overweight/obese children from low socio-economic status families and specific geographic areas, and increase food availability based on local ecology.

The Development of a New Phosphogypsum-Based Construction Material: A Study of the Physicochemical, Mechanical and Thermal Characteristics.

Phosphogypsum (PG) is a waste (or by-product) of the production of phosphoric acid, a basic constituent in the manufacturing of modern fertilizers. The annual production of phosphogypsum in Tunisia is currently estimated to be 10 million tons. Its storage in slag in close proximity to production plants generates pollution problems; however, valorization may be a solution. The present paper proposes a simple process for the valorization of this by-product into a construction material. Several physicochemical characterizations are used to prove the characteristics of samples. The chemical composition shows that PG is a gypsum compound with several impurities. The morphological analyses show that the powder materials are mesoporous with a lower specific area. The structural characterizations show that these solids play the role of a water pump as the degree of hydration changes from 2 to 0 and vice versa, depending on the temperature. Mechanical and thermal analyses show that the prepared formulation is brittle and insulating, which presents opportunities for it to be used as a decoration material.

Large inorganic monolithic nanomaterials with a significant rigid hierarchical pore structure

Although there are many methods for preparing macroscopic nanomaterials, it is difficult to directly and completely maintain the structure from nanometer to macroscopic because of the insufficient structural strength. Here, large inorganic monolithic nanomaterials (LNMs) were directly synthesized by the complex nanostructure reinforced nanofilms self-regulating grown along with the bicontinuous emulsion (BE) interface in a three-dimensional bicontinuous film (3DBF) rigid structure. The Zn(OH)2/SiO2 nanofilms have complex nanostructures divided into the nanofoam structure woven by Zn(OH)2 nanoribbons in ionic bonds, and the silica aerogel cross-linked in covalent bonds, significantly strengthening the hard nanofilms. Therefore, the LNMs' structural strength is sufficient to directly overcome the surface tension and capillary pressure and completely maintain the structure from nanometer to macroscopic. Prepared with controllable shapes under mild condition, LNMs not only have the characteristics of traditional nanomaterials such as low density (0.0849 g mL−1) and high specific area (359.43 m2 g−1), but also have new advantages such as high structural strength (compressive strength, 62555 Pa), low-shrinkage (2.97%), hierarchical pores (1 nm ~ >100 μm), and high permeability. Moreover, the Zn(OH)2/SiO2 LNM columns (4 cm3) in a rigid hierarchical pore structure not only has the traditional catalytic and adsorption properties but also overcome fluid erosion and avoid the loss of nanoparticles, that the total Zn in the effluent without separation is 0.89 mg L−1. Therefore, this new method significantly facilitates the commercial synthesis and application of LNMs as convenient, safe, efficient, and stable components.

Biogas dry reforming using Ni–Al-LDH catalysts reconstructed with Mg and Zn

The reconstruction of NiAl-LDH by incorporating Mg or Zn using a memory effect was investigated aiming to improve the basic properties of the catalysts and evaluated in the dry reforming of Biogas. Samples were characterized by XRD, CO2−TPD, N2-physisorption, TPR, and TPO. Biogas dry reforming experiments were carried out using a feed of CH4/CO2/N2 = 1.5/1/7.5 in the temperature range of 500–750 °C with in situ reduced samples. The washing step strongly influences the LDH reconstruction. The unwashed samples showed the reconstruction of the LDH structure, presented a low specific area, and high basicity, responsible for decreasing carbon formation during reactions. The washed samples did not exhibit the LDH reconstruction property but showed a high specific area and low basicity. The metal used in the reconstruction influences the crystallinity, basicity, and reducibility of the materials. Samples with Zn showed higher crystallinity and reducibility, whereas the samples with Mg showed higher basicity. Among all the catalysts, reconstruction with Zn and subsequent washing leads to the best results with CH4 and CO2 conversion of 73% and 90%, respectively, and an H2/CO ratio of approximately 2. This can be attributed to the Ni–Zn alloy formation and to the reducing properties suitable for the range between 600 and 700 °C. This catalyst showed the highest resistance to sintering in the stability test at 700 °C.

Synthesis of a Novel Co-B/CTAB Catalyst via Solid-state-reaction at Room Temperature for Hydrolysis of Ammonia-borane

Cobalt-boride(Co-B) is emerging as one of the promising materials in the base-hydrolytic dehydrogenation of ammonia-borane(AB). In order to avoid the low specific area and poor catalytic capacity of Co-B catalyst caused by aggregation arising from the strong reducing property and rapid reaction condensation of sodium borohydride(NaBH4), novel cobalt boride/cetyltrimethylammonium bromide(Co-B/CTAB) catalyst was obtained via solidstate grinding at room temperature, and the catalyst was further characterized by XRD, SEM, XPS and BET. The hydrogen generation rate(HGR) was then determined by the hydrolysis reaction of AB. The SEM images indicate that a lot of irregular folds and curled edges are formed on the sample with a maximum surface area of 145.57 m2/g, thus possibly resulting in the high hydrogen production(HGR was 10.68 L·min−1·g−1), which may be attributed to CTAB that provide favorable large specific surface area and abundant porous structure. Additionally, catalyst will not be affected by solvants during solid-state reaction. As a diluent, the surfactant CTAB hindered the reaction rate of sodium borohydride reduction to cobalt boride and obtained the novel catalyst with a large specific surface area.

Molten Lithium-Brass/Zinc Chloride System as High-Performance and Low-Cost Battery

Summary Batteries with high safety, low cost, and reasonable energy density are essential for grid-scale energy storage and still remain elusive. Here, we report a solid electrolyte-based liquid lithium-brass/zinc chloride (SELL-brass/ZnCl2) battery using garnet-type lithium-ion solid electrolyte, lithium anode, and brass/ZnCl2 cathode. The chemistry of the cell reaction and the ability of being assembled in discharged state ensures a high safety. The use of low-cost ZnCl2 cathode can realize a low cell material cost of $16 kWh−1. The adoption of lithium anode guarantees a high theoretical energy density of 750 Wh kg−1 and 2,250 Wh L−1. Moreover, by using brass powder as a Zn source in the cathode, the Zn particle growth issue is successfully solved, and a good cycling stability of the battery can be obtained. As full cell performance and scalability are also verified, our SELL-brass/ZnCl2 battery shows a high potential for practical use in grid energy storage.

Hydrothermally derived three-dimensional porous hollow double-walled Mn2O3 nanocubes as superior electrode materials for supercapacitor applications

Although Mn2O3 has been widely used as an electrode material for lithium-ion batteries, it has not been explored as a supercapacitor electrode material due to its low specific area, irregular morphology, low porosity, and low ionic conductivity. Targeting this gap, in this study, we attempted to develop regular and porous hollow double-walled Mn2O3 cubes, which can simultaneously provide a large surface area and enhance charge diffusion to result in a high capacitance. We synthesized cube-like 3D hierarchically porous double-walled Mn2O3 (c-HDW-Mn2O3) using a simple hydrothermal method followed by calcination. The optimized electrode material c-HDW-Mn2O3@9 exhibited excellent capacitance and 90% retention over 3000 consecutive charge-discharge cycles at a fixed current density. Such high performance and good stability can be attributed to the porous and crystalline structure and high surface area of the optimized electrode. Finally, these hierarchically porous nanocubes can be considered as suitable materials for energy-storage applications.

Synthesis of hybrid magnetic molecularly imprinted polymers for the selective adsorption of volatile fatty acids from anaerobic effluents

AbstractA novel magnetic, structured (with ordered pores) and hybrid imprinted polymer (HMMIP) was synthesized to selectively adsorb volatile fatty acids (VFAs) from aqueous matrices. Usual characterization techniques showed that a mesoporous adsorbent was obtained with relatively low specific areas but that could selectively (imprinting factor of 1.64) remove isovaleric acid (used as template) from aqueous solutions and effluents containing VFAs with a good capacity (Qe ~ 50 mg g−1). From kinetic studies a pseudo‐nth‐order model showed the best fit to the experimental data and resulted in k n = 3 equal to 8 × 10−4 g mg−1 min−1 whereas thermodynamic studies indicated that the adsorption of isovaleric acid onto HMMIP was endothermic and entropically driven. Reuse studies indicated that HMMIP loaded with VFA could be efficiently regenerated with acetone–water solution which led to an adsorption loss of ca 10% after three regeneration/reuse cycles and that the magnetic and specific adsorbent could be removed from complex matrices with an efficiency of ca 77%. Biochemical methane production assays showed that the addition of HMMIP to anaerobic batch reactors increased by four times the methane production due to the selective adsorption of VFAs. © 2020 Society of Chemical Industry

Determining roles of in-situ measured surface potentials of phase controlled synthesized MnO2 nanostructures for superficial adsorption

Adsorption is one of options for environmental remediation. Current works focused on designing nanostructures, and ex-situ measured specific area and zeta potential were main descriptors for the adsorption performance, leaving the materials’ intrinsic features irrelevant to adsorption. Herein, to investigate the adsorption performance and adsorbent inherent characteristics, an in-situ measurement of zeta potential was presented by taking MnO2 adsorbing methylene blue (MB) as an example. The performance was randomly related between ex-situ measured specific areas and zeta potentials of MnO2, but the in-situ measured MnO2 zeta potentials in 10 and 100 mg·L−1 MB solutions both showed nonlinear hyperbolic relationship with the performance, confirming the significant role of in-situ zeta potentials. Furthermore, adsorption enhancement in low pH conditions was observed, for Mn(IV) oxidability promoted by acidic solutions, where MB redox was oxidized to the positively charged oxidized form, facilitating adsorption onto negatively charged MnO2. The adsorption performance of MnO2 with considerably low specific area was comparable to reported nanostructured metal oxide adsorbents, showing the importance of surface zeta potentials and oxidability. An insight into the adsorption affecting factors within the inherent features of adsorbents was presented through in-situ measured zeta potentials and pH dependent adsorption.

Synthesis, characterization and evaluation of niobium catalysts in the flash pyrolysis of glycerol

Niobium catalysts supported on sodium vermiculite (Nb2O5/V0) and vermiculite treated with hydrochloric acid (Nb2O5/V3) were prepared by the incipient impregnation method. The unsupported catalyst, niobium pentoxide, was also synthesized. The catalysts were characterized by X-ray diffraction, adsorption-desorption of nitrogen, scanning electron microscopy coupled with energy dispersive spectroscopy, UV–vis diffuse reflectance spectroscopy and Raman spectroscopy. The characterization techniques used in the analysis of the physico-chemical properties of the catalysts showed the presence of Nb2O5 on sodium vermiculite (V0) and activated vermiculite (V3) in different phases. The best dispersion of niobium oxide, as expected, was on the V3 support (SBET = 464.5 m2 g−1), due to its greater specific area compared to V0 (SBET = 0.7 m2 g−1). The rapid pyrolysis of the glycerol in the presence of catalysts Nb2O5/V0, Nb2O5/V3 and Nb2O5 was investigated using Py-GC–MS. The results showed high decomposition of glycerol with Nb2O5 (82.2%), with higher yields of oxygenated products such as organics acids (25.1%), alcohols (19.8%) and esters (23.7%). In comparison, in the presence of Nb2O5/V3 decarboxylation was greater (CO2 = 6.4%), no esters were identified, and production of organics acids (15.9%), alcohols (19.7%) and aldehyde (10.8%) were favored. Nb2O5/V0 formed products similar to pyrolysis, probably because the catalyst has low acidity and small specific area. Thus, the results of glycerol pyrolysis application showed better performance of Nb2O5 and Nb2O5/V3, due to the efficiency in obtaining oxygenated products with industrial applicability through glycerol.

A facile method to produce TiO2 nanorods for high-efficiency dye solar cells

Highly ordered TiO2 nanorods are considered promising for photoanodes in dye-sensitized solar cells due to their high charge transfer rate of photo-generated electrons, but they often suffer from low specific area, which may lead to a low conversion efficiency. Here, we produce long vertical single-crystalline rutile TiO2-nanorod arrays on fluorine-doped tin oxide conductive glass substrates(FTO)by the hydrothermal method. To further increase the specific area, the TiO2-nanorod arrays are etched in a secondary hydrothermal process by hydrochloric acid. The etching time have a major effect on the nanorod microstructure and on the dye-sensitized solar cells efficiency. The best result is reached with 8 h of etching, which results in a record high conversion efficiency of 11.14 ± 0.12% (certified efficiency 10.3%) under full sunlight illumination (AM 1.5 G, 100 mW/cm2). The record cell has an open voltage of 0.79 V and a short current density of 21.59 mA/cm2. The proposed manufacturing approach of TiO2 nanorods is highly potential for producing high-efficiency dye-sensitized solar cells.

Optimization of the Production Parameters of Composites from Sugarcane Bagasse and Iron Salts for Use in Dye Adsorption.

In this study, mechanical mixtures of sugarcane bagasse and iron salts (nitrate, acetate, or a mixture of both) were subjected to thermal decomposition for producing iron oxide and carbonaceous composite materials, which were evaluated as adsorbents for removing dyes from water using methylene blue (MB) as a model system. Aiming to optimize the conditions for obtaining composite adsorbents, the Box-Behnken design (BBD) was used to study the effects of mass sugarcane bagasse/mass iron salt, type of mixture of sugarcane bagasse/iron salt, and temperature on the response to be obtained (adsorption capacity, qe) before the execution of the adsorption tests. The synthesized composites were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The relationship between the characteristics of different materials, based on the processing of statistical data and the results of the adsorption tests, helped determine the routes that led to formation of composites with the most suitable properties for the removal of MB dye. Different phases, such as magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) and iron carbide (Fe3C), were formed. The composites that presented the highest qe values were SB/IN 1:1 (600°C) and SB/IN-IA 1:2 (400°C). The first, which contained iron carbide (Fe3C), according to the XRD results, also showed larger BET surface area than the other composites. These properties may have contributed to the higher MB adsorption efficiency of this material in aqueous medium. The sample SB/IN-IA 1:2 (400°C) had lower specific area and was composed of magnetite and/or maghemite phases. In this case, the high qe was probably associated with the surface properties promoted by combination with the carbonaceous material, favoring interactions with MB.