Geopolymers produced from an aluminosilicate precursor and an alkaline activating solution have emerged as low carbon alternative binders which can substitute for Portland cement (PC) in many ...applications. The presence of soluble silicate in the activating solution of a geopolymer is known to yield a denser and more compact material with higher mechanical strength compared to hydroxide-activated geopolymers. However, these silicate solutions are the most expensive component of geopolymer cements, as well as the highest contributors to their environmental impacts in most life cycle categories. Geopolymers are widely accepted as a more environmental friendly material due to their claimed lower CO2 emissions due to their synthesis from industrial by-products or wastes, as well the low energy demand during their production. However, the use of alkali-silicate activators can significantly increase other environmental impacts, leading to controversies regarding whether geopolymers can really be considered as a more sustainable material. Thus, this study evaluates the life cycle impacts of a geopolymer produced from a kaolin sludge residue from the Brazilian mining industry. Alkaline solutions derived from sodium hydroxide solutions and two different soluble silica sources were used as activators: a commercial sodium silicate (waterglass), and chemically modified rice husk ash (RHA). The processes which contribute the most to the life cycle impacts of geopolymers are thermal curing, waterglass production, and sodium hydroxide production. The use of RHA-derived sodium silicate may reduce environmental impacts by more than 60% in 6 of the 9 categories assessed, indicating that this is a favourable alternative where RHA is locally available. Although the binders evaluated here have differences in mechanical properties, those using RHA-derived activators exhibit impacts lower than PC for 4 of the 8 categories evaluated, and a reduction of more than 70% in global warming potential. RHA-based activators are identified as a promising alternative for impact reduction in geopolymer production, and more detailed assessments of the performance and reactivity of these activators should be conducted.
•Life cycle impacts of a geopolymer based on kaolin sludge residue are evaluated.•Chemically modified rice husk ash applied as alternative to sodium silicate.•RHA-based activators are an alternative for impact reduction in GP production.
Aim
The calibration area (CA) corresponds to the geographic region used by different algorithms that estimate the species' environmental preferences and delimit its geographic distribution. This ...study intended to identify, test and compare current literature's most commonly employed approaches and methods for CA creation, highlighting the differences with the accessible area (M), a frequently misapplied concept.
Location
Global.
Taxon
Arthropods, amphibians, reptiles, birds and mammals.
Methods
We conducted a literature review and analysed 129 recent articles on species distribution that use correlative models to identify the methods used to establish the CA and their frequency. We also evaluated seven of the most widely used methods for 31 species from different taxa.
Results
We found that the most frequently used methods in literature corresponded to biogeographic entities (BE). Moreover, according to our evaluation, those methods that seek to establish the CA through the accessible area approach (including BE and ‘grinnell’) were the best evaluated. Finally, we highlight the advantages and disadvantages of the analysed methods in selecting CA.
Main Conclusions
Although we cannot fail to recognize the usefulness and validity of the different methods to establish CAs, we suggest calibrating ecological niche and species distribution models in light of explicit a priori hypotheses regarding the extent of accessible areas (M) as a delimitation of the CA, which theoretically includes the species' dispersal ability and its barriers. We recommend using the BE method, which is simple to establish and highly operational.
The genetic regulation underlying the effect of arsenic (As(III)) on the model symbiosis Medicago–Ensifer was investigated using a combination of physiological (split‐roots), microscopy and genetic ...(microarrays, qRT‐PCR and composite plants) tools. Nodulation was very sensitive to As(III) (median inhibitory dose (ID50) = 20 μM). The effect on root elongation and on nodulation was local (nonsystemic). A battery of stress (salt, drought, heat shock, metals, etc.)‐related genes were induced. Glutathione played a pivotal role in tolerance/detoxification, together with secondary metabolites ((iso)flavonoids and phenylpropanoids). However, antioxidant enzymes were not activated. Concerning the symbiotic interaction, molecular evidence suggesting that rhizobia alleviate As stress is for the first time provided. Chalcone synthase (which is involved in the first step of the legume–rhizobia cross‐talk) was strongly enhanced, suggesting that the plants are biased to establish symbiotic interactions under As(III) stress. In contrast, 13 subsequent nodulation genes (involved in nodulation factors (Nod factors) perception, infection, thread initiation and progression, and nodule morphogenesis) were repressed. Overexpression of the ethylene responsive factor ERN in composite plants reduced root stress and partially restored nodulation, whereas overexpression of the early nodulin ENOD12 enhanced nodulation both in the presence and, particularly, in the absence of As, without affecting root elongation. Several transcription factors were identified, which could be additional targets for genetic engineering aiming to improve nodulation and/or alleviate root stress induced by this toxic.
The SARS-CoV-2 health crisis has temporarily forced the lockdown of entire countries. This work reports the short-term effects on air quality of such unprecedented paralysis of industry and transport ...in different continental cities in Spain, one of the countries most affected by the virus and with the hardest confinement measures. The study takes into account sites with different sizes and diverse emission sources, such as traffic, residential or industrial emissions. This work reports new field measurement data for the studied pandemic period and assesses the air quality parameters within the historic trend of each pollutant and site. Thus, 2013–2020 data series from ground-air quality monitoring networks have been analysed to find out statistically significant changes in atmospheric pollutants during March–June 2020 due to this sudden paralysis of activity. The results show substantial concentration drops of primary pollutants, including NOx, CO, BTX, NMHC and NH3. Particulate matter changes were smaller due to the existence of other natural sources. During the lockdown the ozone patterns were different for each studied location, depending on the VOCs-NOx ratios, with concentration changes close to those expected from the historical series in each site and not statistically attributable to the health crisis effects. Finally, the gradual de-escalation and progressive increase of traffic density within cities reflects a slow recovery of primary pollutants. The results and conclusions for these cities, with different sizes and population, and specific emission sources, may serve as a behavioural model for other continental sites and help understand future crises.
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•SARS-CoV-2 lockdown and de-escalation’s effects on air quality in different size cities in Spain.•Significant and fast reduction of NOx, CO, BTXs, NMHC and NH3 have been observed.•Lower changes in PM were found during the crisis and not clear trends for O3.•Pollutant levels remained below pre-lockdown values despite gradual de-escalation.
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•Innovative design for producing skinless polymer foams by gas dissolution foaming.•The gas diffusion barrier maintains high gas concentration in the polymer edges.•Achievement of ...skinless polymer foams by using the gas diffusion barrier approach.•Thin films with homogenous structures were completely foamed without solid skins.•Porous in the outer layers expose the inner cellular structure to external medium.
An innovative approach to reduce and eliminate the non-foamed solid skins of the cellular polymers fabricated by gas dissolution foaming is presented in this work. The incorporation of a flexible gas diffusion barrier on the polymer surfaces during the saturation and foaming processes provided significant reduction or even hindered the appearance of the non-foamed solid skins while enabling appropriate expansions in several polymers (PMMA, PS, PC, and PCL). Besides, this approach has allowed to achieve significant expansions by foaming polymer samples with thicknesses in the order of magnitude of the non-foamed solid skins, i.e., thin films (<100 µm). This paper discusses how the gas diffusion barrier allows reducing the solid skins, the mechanisms involved in the gas diffusion process, and the possibility of interconnecting the inner cellular structure with the external medium.
Efflorescence can be harmful to material performance as a consequence of microstructural changes due to leaching and carbonation of alkalis. This article identifies mechanisms of efflorescence in ...metakaolin-based geopolymers, and approaches to reduce free/mobile alkali cations and pore network connectivity, and hence reduce efflorescence. Mechanical, mass transport and microstructural properties are assessed in metakaolin-based geopolymer cements produced using different alkali concentrations in the alkali activator and substitution/addition of blast furnace slag, silica fume, calcium aluminate cement, silicone oil and a dispersive admixture. The most effective strategy to reduce efflorescence results from increasing Si/Al in the geopolymer gel by addition of soluble silicate, silica fume or silicone oil. Addition of calcium aluminate cement or a dispersive admixture also reduce efflorescence, but are less effective. These results confirm that efflorescence may be reduced by controlling the amount of soluble silicates and reducing free alkali cations in geopolymers, providing enhanced performance and durability.
This work shows that biosphere reserves, national parks and other protected natural areas require in situ tools to monitor and detect local and remote air pollution sources which are a threat to ...flora, fauna water and soil. Industries in surrounding areas, traffic and long-range transport of air pollution, can change with time and meteorology and so each national park should also have a historical database of the air quality in the site. This study reports surface measurements of ozone, NO, NO2, CO, SO2 and PM2.5 acquired from March 2020 to July 2021 in “Las Tablas de Daimiel”, a wetland Mediterranean National Park bordered by different cities and new industries in the field of the revalorization of agricultural wastes. Simultaneous data from a background station in a rural area isolated from air pollution are considered as reference.
Twelve campaigns of one week duration were also performed to sample air in sorbent tubes to analyse volatile organic compounds from anthropogenic sources. Data are discussed considering meteorology, especially wind speed and direction together with the assessment of back-trajectories of air masses from distant sources. The results show that the effects of pollution from local and faraway sources on air quality in the park were weak. Thus, except for the high levels of ozone, with a mean value of 71 μg.m−3, measured mass loadings for pollutants were low and not in exceedance of the air quality standards. Saharan dust events were frequent and contributed to PM2.5 levels in the site. NOx and SO2 average concentrations (3.2 and 0.4 μg.m−3, respectively) were below the recommended critical levels for vegetation and all the quantified VOCs were found in average concentration levels below 0.5 μg.m−3.
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•Natural areas are increasingly threatened by cities and emerging industrial parks.•Weekend effect show a weak anthropogenic impact on the air quality of the area.•Several anthropogenic VOCs have been found in average concentration below 0.5 μg.m−3.•Except for ozone, criteria pollutants' levels in the area are still low.•Saharan dust intrusions were frequent and contributed to PM2.5 levels in the park.
Organic dyes constitute one of the main pollutants existing in wastewater, perturbing aquatic life and causing environmental problems. Photocatalytic oxidation represents an alternative process for ...effective and easy degradation of dyes. In this study, the synthesis of novel silver and bismuth tungstate-based nanostructures with high photocatalytic activity for photodegrading methylene blue (MB) dye is described. The novel, as-prepared, Ag
8
W
4
O
16
/AgBiW
2
O
8
/Bi
2
WO
6
photocatalyst improved MB decomposition efficiency achieving a photodegradation of 82.50% within 40 min under UV irradiation. Herein, the holes (
h
+
) are the main oxidative species in the MB degradation process. Moreover, the photocatalytic mechanisms of MB degradation by using the AgBiW
2
O
8
/Bi
2
WO
6
and Ag
8
W
4
O
16
/AgBiW
2
O
8
/Bi
2
WO
6
heterojunctions is postulated. The synthesis is conducted by a green and combined methodology that includes the use of a metathesis reaction (double displacement reaction)/molten salt procedure. This methodology is simple, effective, high-yield (95%), and intermediate temperature, carried out in normal atmospheric conditions and using simple equipment. The particles were obtained in NaNO
3
at 350 °C (2 h) showing spherical-like shapes with sizes from 10 to 59 nm according to the Ag content in samples.
S
BET
and
D
p
values obtained for samples varied from 8.1 to 10.2 m
2
g
−1
and 17.67 to 32.15 nm, respectively. The Ag load in samples showed an important role in the phase composition of photocatalysts obtaining AgBiW
2
O
8
/Bi
2
WO
6
and Ag
8
W
4
O
16
/AgBiW
2
O
8
/Bi
2
WO
6
-type heterostructures.
Graphical Abstract
The charge transfer of the photogenerated carriers (
e
−
and
h
+
) in the novel as-prepared Ag
8
W
4
O
16
/AgBiW
2
O
8
/Bi
2
WO
6
heterostructure for degrading MB dye under UV light irradiation: the
e
−
transfers from Ag
8
W4O
16
to Bi
2
WO
6
and then to the AgBiW
2
O
8
, whereas the
h
+
was relocated from AgBiW
2
O
8
to Bi
2
WO
6
.
A novel device, called quantum sensor, has been conceived to measure the mass of a single ion with ultimate accuracy and unprecedented sensitivity while the ion is stored and cooled in a trap. The ...quantum sensor consists of a single calcium ion as sensor, which is laser cooled to mK temperatures and stored in a second trap connected to the trap for the ion under study by a common endcap. The cyclotron motion of the ion under investigation is transformed into axial motion along the magnetic field lines and coupled to the sensor ion by the image current induced in the common endcap. The axial motion of the sensor ion in turn is monitored spatially resolved by its fluorescence light. In this way the detection of phonons can be upgraded to a detection of photons. This device will allow one to overcome recent limitations in high-precision mass spectrometry.
The effect of different microstructural factors on crack growth and fatigue fracture mechanisms in dual‐phase (DP) steels has yet to be fully understood. The present research examines the ...relationship between crack growth, microstructure, and fracture mechanisms. The samples were intercritically annealed at different temperatures to produce three different martensite volume fractions (MVFs). The results show that the mechanical incompatibility of ferrite and martensite promotes continuous crack tip deflection. MVF increases are associated with elevated fracture tortuosity, more significant fracture energy surface formation, and higher Paris law exponent m values. The interaction of the microstructure with the crack tip, the strain energy density, and the softening caused by secondary microcrack propagation are all illustrated by Electron backscatter diffraction (EBSD) maps. Increasing MVF promotes slow crack growth and a fracture energy increase of 22.9% between the as‐received and heat‐treated steels.
Highlights
Martensite content in dual‐phase steels generate greater crack propagation resistance.
Martensite volume increase produces a more significant number and extension of secondary microcracks.
Differences in ferrite and martensite phases promote continuous crack tip deflection.
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