Development of activated carbons derived from wastes: coffee grounds and olive stones as potential porous materials for air depollution.

Agro-industrial byproducts and food waste necessitate an environmentally friendly way of reducing issues related to their disposal; it is also necessary to recover as much new raw material from these resources as possible, especially when we consider their potential usage as a precursor for preparing depolluting materials, such as activated carbon. In this work, coffee grounds and olive stones were chosen as precursors and the adsorption capacity of the obtained porous carbons for volatile organic compounds (VOCs) was studied. Microporous activated carbons (ACs) were prepared using chemical (K2CO3) and physical (CO2) activation. The influence of the activation process, type, and time of activation was also investigated. Measurements of VOCs adsorption were performed, and methyl-ethyl-ketone (MEK) and toluene were chosen as the model pollutants. The surface areas and total pore volumes of 1487 m2/g and 0.53 cm3/g and 870 m2/g and 0.22 cm3/g for coffee ground carbons and olive stone carbons, respectively, were obtained via chemical activation, whereas physical activation yielded values of 716 m2/g and 0.184 cm3/g and 778 cm2 g-1 and 0.205 cm3/g, respectively. As expected, carbons without activation (biochars) showed the smallest surface area, equal to 331 m2/g and 251 m2/g, and, hence, the lowest adsorption capacity. The highest adsorption capacity of MEK (3210 mg/g) and toluene (2618 mg/g) was recorded for chemically activated coffee grounds. Additionally, from the CO2 isotherms recorded at a low pressure (0.03 bar) and 0 °C, the maximum CO2 adsorption capacity was equal to 253 mg/g.

Highly Stable Self-Cleaning Paints Based on Waste-Valorized PNC-Doped TiO2 Nanoparticles.

Adding photocatalytically active TiO2 nanoparticles (NPs) to polymeric paints is a feasible route toward self-cleaning coatings. While paint modification by TiO2-NPs may improve photoactivity, it may also cause polymer degradation and release of toxic volatile organic compounds. To counterbalance adverse effects, a synthesis method for nonmetal (P, N, and C)-doped TiO2-NPs is introduced, based purely on waste valorization. PNC-doped TiO2-NP characterization by vibrational and photoelectron spectroscopy, electron microscopy, diffraction, and thermal analysis suggests that TiO2-NPs were modified with phosphate (P=O), imine species (R=N-R), and carbon, which also hindered the anatase/rutile phase transformation, even upon 700 °C calcination. When added to water-based paints, PNC-doped TiO2-NPs achieved 96% removal of surface-adsorbed pollutants under natural sunlight or UV, paralleled by stability of the paint formulation, as confirmed by micro-Fourier transform infrared (FTIR) surface analysis. The origin of the photoinduced self-cleaning properties was rationalized by three-dimensional (3D) and synchronous photoluminescence spectroscopy, indicating that the dopants led to 7.3 times stronger inhibition of photoinduced e-/h+ recombination when compared to a benchmark P25 photocatalyst.

Operando monitoring of a room temperature nanocomposite methanol sensor.

The sensing of volatile organic compounds by composites containing metal oxide semiconductors is typically explained via adsorption-desorption and surface electrochemical reactions changing the sensor's resistance. The analysis of molecular processes on chemiresistive gas sensors is often based on indirect evidence, whereas in situ or operando studies monitoring the gas/surface interactions enable a direct insight. Here we report a cross-disciplinary approach employing spectroscopy of working sensors to investigate room temperature methanol detection, contrasting well-characterized nanocomposite (TiO2@rGO-NC) and reduced-graphene oxide (rGO) sensors. Methanol interactions with the sensors were examined by (quasi) operando-DRIFTS and in situ-ATR-FTIR spectroscopy, the first paralleled by simultaneous measurements of resistance. The sensing mechanism was also studied by mass spectroscopy (MS), revealing the surface electrochemical reactions. The operando and in situ spectroscopy techniques demonstrated that the sensing mechanism on the nanocomposite relies on the combined effect of methanol reversible physisorption and irreversible chemisorption, sensor modification over time, and electron/O2 depletion-restoration due to a surface electrochemical reaction forming CO2 and H2O.

New Materials and Technologies for Durability and Conservation of Building Heritage.

The increase in concrete structures' durability is a milestone to improve the sustainability of buildings and infrastructures. In order to ensure a prolonged service life, it is necessary to detect the deterioration of materials by means of monitoring systems aimed at evaluating not only the penetration of aggressive substances into concrete but also the corrosion of carbon-steel reinforcement. Therefore, proper data collection makes it possible to plan suitable restoration works which can be carried out with traditional or innovative techniques and materials. This work focuses on building heritage and it highlights the most recent findings for the conservation and restoration of reinforced concrete structures and masonry buildings.

Transformation of industrial and organic waste into titanium doped activated carbon - cellulose nanocomposite for rapid removal of organic pollutants.

Production of cost-efficient composite materials with desired physicochemical properties from low-cost waste material is much needed to meet the growing needs of the industrial sector. As a step forward, the current study reports for the first time an effective utilization of industrial metal (inorganic) waste as well as fall leaves (organic waste), to produce three types of nanomaterials at the same time; "Titanium Doped Activated Carbon Nanostructures (Ti-ACNs)", "Nanocellulose (NCel)", and combination of both "Titanium Doped Activated Carbon Cellulose Nanocomposite (Ti-AC-Cel-NC)". X-ray diffraction (XRD), transmission electron microscopy (TEM) and microanalysis (EDXS) measurements reveal that the Ti-ACNs material is formed by Ti-nanostructures, generally poorly crystalized but in some cases forming hexagonal Ti-crystallites of 15 nm, embedded in mutated graphene clouds. Micro- Fourier transform infrared spectroscopy (micro-FTIR) confirms that the chemical structure of NCel with bond vibrations between 1035 to 2917 cm-1 remained preserved during Ti-AC-Cel-NC formation. The prepared materials (Ti-ACNs, Ti-AC-Cel-NC) have demonstrated rapid removal of organic pollutants (Crystal Violet, Methyl Violet) from wastewater through surface adsorption and photocatalysis. In the first 20 min, Ti-ACNs have adsorbed ≈87% of the organic pollutants and further photocatalyzed them up to ≈96%. When Ti-ACNs are combined with NCel, their efficiency is increased of about four times. This performance originates from the adsorption by mutated graphene-like carbon and assisted photocatalysis by Ti nanostructures as well as the good supporting capacity of NCel for the homogenous Ti-ACNs distribution.

Characterization and Filtration Efficiency of Sustainable PLA Fibers Obtained via a Hybrid 3D-Printed/Electrospinning Technique.

The enormous world demand for personal protective equipment to face the current SARS-CoV-2 epidemic has revealed two main weaknesses. On one hand, centralized production led to an initial shortage of respirators; on the other hand, the world demand for single-use equipment has had a direct and inevitable effect on the environment. Polylactide (PLA) is a biodegradable, biocompatible, and renewable thermoplastic polyester, mainly derived from corn starch. Electrospinning is an established and reproducible method to obtain nano- and microfibrous materials with a simple apparatus, characterized by high air filtration efficiencies. In the present work, we designed and optimized an open-source electrospinning setup, easily realizable with a 3D printer and using components widely available, for the delocalized production of an efficient and sustainable particulate matter filter. Filters were realized on 3D-printed PLA support, on which PLA fibers were subsequently electrospun. NaCl aerosol filtration tests exhibited an efficiency greater than 95% for aerosol having an equivalent diameter greater than 0.3 µm and a fiber diameter comparable to the commercially available FFP2 melt-blown face mask. The particulate entrapped by the filters when operating in real environments (indoors, outdoors, and working scenario) was also investigated, as well as the amount of heavy metals potentially released into the environment after filtration activity.

Post-digestate composting benefits and the role of enzyme activity to predict trace element immobilization and compost maturity.

The current study evaluated the quality of agricultural waste digestate by composting or co-composting with biogas feedstock (maize silage, food processing waste, or poultry litter). Temperature, phytotoxicity, C/N ratio, water extractable trace elements, and 14 enzyme activities were monitored. Temperature dropped earlier in digestate and maize silage co-composting pile, reducing time to maturity by 20 days. Composting and co-composting reduced phytotoxicity and C/N ratio, but increased immobilization of Al, Ba, Fe, Zn, and Mn at least by 40% in all piles. All the enzyme activities, except arylsulfatase and α-glucosidase, increased at the maturity phase and negatively correlated with organic matter content and most of trace elements. Post-digestate composting or co-composting with biogas feedstock is a promising strategy to improve digestate quality for fertilizer use, and selected enzyme activities can be indicators of compost maturity and immobilization of trace elements.

The Critical Raw Materials Issue between Scarcity, Supply Risk, and Unique Properties.

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements' formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology).

Microstructural Features in Multicore Cu-Nb Composites.

The study is devoted to heavily drawn multicore Cu-18Nb composites of cylindrical and rectangular shapes. The composites were fabricated by the melt-and-deform method, namely, 600 in situ rods of Cu-18%Nb alloy were assembled in a copper shell and cold-drawn to a diameter of 15.4 mm (e = 10.2) and then rolled into a rectangular shape the size of 3 × 5.8 mm (e = 12.5). The specimens were analyzed from the viewpoints of their microstructure, microhardness, and thermal stability. The methods of SEM, TEM, X-ray analysis, and microhardness measurements were applied. It is demonstrated that, at higher strain, the fiber texture 110Nb∥ 111Cu∥ DD (drawing direction), characteristic of this material, becomes sharper. The distortions of niobium lattice can be observed, namely, the 110 Nb interplanar distance is broadened in longitudinal direction of specimens and compacted in transverse sections. The copper matrix lattice is distorted as well, though its distortions are much less pronounced due to its recrystallization. Evolution of microstructure under annealing consists mainly in the coagulation of ribbon-like Nb filaments and in the vanishing of lattice distortions. The structural changes in Nb filaments start at 300-400 °C, then develop actively at 600 °C and cause considerable decrease of strength at 700-800 °C.

Cigarette butts, a threat for marine environments: Lessons from benthic foraminifera (Protista).

Cigarette butts are the most common form of litter in the world and their environmental impact is related to both persistence and potential toxic effects for chemical composition. The objective of this study was to assess the acute toxicity (LC50-48 h) of human-smoked cigarette butts leachate on 3 cultured genera of benthic foraminifera: the calcareous perforate Rosalina globularis, the calcareous imperforate Quinqueloculina spp., and the agglutinated Textularia agglutinans. The specimens were exposed to 16, 8, 4, 2, and 1 cigarette butts/L concentrations that prove to be acutely toxic to all taxa. Starting from 4 cigarette butts/L, both calcareous genera showed shell decalcification, and death of almost all the individuals, except for the more resistant agglutinated species. These results suggest the potential harmfulness of cigarette butts leachate related to pH reduction and release of toxic substances, in particular nicotine, which leads to physiology alteration and in many cases cellular death.

Tailoring Electro/Optical Properties of Transparent Boron-Doped Carbon Nanowalls Grown on Quartz.

Carbon nanowalls (CNWs) have attracted much attention for numerous applications in electrical devices because of their peculiar structural characteristics. However, it is possible to set synthesis parameters to vary the electrical and optical properties of such CNWs. In this paper, we demonstrate the direct growth of highly transparent boron-doped nanowalls (B-CNWs) on optical grade fused quartz. The effect of growth temperature and boron doping on the behavior of boron-doped carbon nanowalls grown on quartz was studied in particular. Temperature and boron inclusion doping level allow for direct tuning of CNW morphology. It is possible to operate with both parameters to obtain a transparent and conductive film; however, boron doping is a preferred factor to maintain the transparency in the visible region, while a higher growth temperature is more effective to improve conductance. Light transmittance and electrical conductivity are mainly influenced by growth temperature and then by boron doping. Tailoring B-CNWs has important implications for potential applications of such electrically conductive transparent electrodes designed for energy conversion and storage devices.

DGT use in contaminated site characterization. The importance of heavy metal site specific behaviour.

The objective of this study is to provide an insight into the techniques for measuring the lability of heavy metals in solid-phase pool of soils in order to assess the environmental risk arising from pollution. The technique of diffusive gradients in thin films (DGT) and a sequential extraction procedure were used to quantify the labile pools of Cu, Fe, Mn and Ni. These results were compared to metal concentrations in groundwater, measured directly using the in situ piezometers, and to the total concentration of metal in the soils. High concentrations of metal in the directly analysed soil solution compared to DGT measurement were attributed to the presence of colloidal metal. The use of DGT allowed only to calculate leaching parameters of the free ions and labile fractions of the metals. For this reason DGT technique needs preliminary investigation on metal speciation in soil solution before its application as a good tool in the characterization procedure of contaminated sites.

A Novel Method for the Combined Photocatalytic Activity Determination and Bandgap Estimation.

The ability of a photocatalyst to degrade a target pollutant is a commonly used method to assess its effectiveness for environmental applications, while ultraviolet-visible (UV-vis) spectroscopy and spectroscopic ellipsometry are conventional techniques for the estimation of a semiconductor band gap. In this work, an array of six light-emitting diodes (LEDs), characterized by different emission peaks between 470-370 nm and absorbed power of 3 W, was implemented into an existing standard testing apparatus for the testing of nitrogen oxides degradation in air. The abatement indexes, obtained under different LEDs irradiation, were firstly compared to the ones determined according the standard and, secondly, correlated with the measured LED emission spectrum, in order to estimate the photocatalyst band gap. Results suggest that this expeditious technique can be easily implemented into existing testing apparatus for the estimation of the band gap and for the appraisal of photocatalytic materials under realistic conditions.

Appraisal of a hybrid air cleaning process.

Nowadays, there is an amplified interest in maintaining suitable indoor air quality (IAQ). Besides a wide range of available interventions, air cleaners are considered a valuable tool, since based on inexpensive and easily implementing technologies to improve IAQ. The purpose of this work is to combine the TiO2-photocatalysis with the electrostatic and adsorption processes, in order to improve efficiency and reliability. A TiO2-photocatalytic oxidation combined with an electrostatic filter has been studied. Nitrogen oxides reduction and degradation of many VOC over different catalyst support were monitored jointly with CO and CO2 production. The coupling of photocatalysis with an external electric field enhances efficiency of the process. The choice of materials with diversified adsorptive characteristics plays an important role in the durability of the process over time.

Influence of Binders and Lightweight Aggregates on the Properties of Cementitious Mortars: From Traditional Requirements to Indoor Air Quality Improvement.

Innovative and multifunctional mortars for renders and panels were manufactured using white photocatalytic and non-photocatalytic cement as binder. Unconventional aggregates, based on lightweight materials with high specific surface and adsorbent properties, were adopted in order to investigate the possible ability to passively improve indoor air quality. The reference mortar was manufactured with traditional calcareous sand. Results show that even if the mechanical properties of mortars with unconventional aggregates generally decrease, they remain acceptable for application as render. The innovative mortars were able to passively improve indoor air quality in terms of transpirability (70% higher), moisture buffering ability (65% higher) and depolluting capacity (up to 75% higher) compared to traditional ones under the current test conditions.

Solutions for Critical Raw Materials under Extreme Conditions: A Review.

In Europe, many technologies with high socio-economic benefits face materials requirements that are often affected by demand-supply disruption. This paper offers an overview of critical raw materials in high value alloys and metal-matrix composites used in critical applications, such as energy, transportation and machinery manufacturing associated with extreme working conditions in terms of temperature, loading, friction, wear and corrosion. The goal is to provide perspectives about the reduction and/or substitution of selected critical raw materials: Co, W, Cr, Nb and Mg.

Surfactant effects on electrokinetic processes in clay-rich soils remediation.

The present work concerns the realisation of an equipment suitable for the choice of surfactants to be employed in the remediation of polluted soils by soil washing processes. The experimental activity has been focused to verify the surfactants efficiency in electrokinetic processes applied in low porosity soils, polluted with used vehicle oil. The equipment consents to estimate low electroosmotic permeabilities, electrical current and to analyse the electrolytic solutions. The concentration of the chemical species reached in both anodic and cathodic cells allows a more accurate evaluation of the ion mobility through the soil. The apparatus realised has been shown to be a useful instrument capable of providing directions for the choice of surfactants in electrokinetic soil remediation. The choice of an anionic surfactant for the oil removal has shown promising result.

Design and calibration of an organic diffusive probe to extend the diffusion gradient technique to organic pollutants.

The objective of this study was to develop a method for measuring the mobility of persistent organic pollutants in the solid phase of soils within the context of environmental pollution risk assessment. A new diffusive probe, purposely designed by adapting the diffusive gradient technique method, measures labile organic species by immobilizing them after diffusion through a thin deionized water layer. The measure of the mass accumulated is used to calculate the flow of pollutant from solid phase to pore water. Naphthalene was chosen as a model persistent organic pollutant. The probe was calibrated at different temperatures and was then tested in several microcosms at different porosity and reactivities with naphthalene (one clay soil, two sandy soils and one natural soil). The probe response showed good agreement with the expected different abilities of the solid phases in restoring the solution phase. The concentration of naphthalene in the pore water was well buffered by rapid equilibria with the solid phase in the investigated natural soil. In contrast, pore water concentration in the sandy soils decreased rapidly and the flow was slackened, especially for the sandy soil with finer particles. In clay, only a fraction of the total naphthalene content was present in the labile fraction, while the remaining was tightly bound and was not released to the pore water. Therefore, this first stage of testing points out that the diffusive gradient technique, if optimized, can properly quantify the mobility of organic pollutants in soil.