Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag

Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100% and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively

Tailoring the thermal conductivity of rubber nanocomposites by inorganic systems: Opportunities and challenges for their application in tires formulation

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon‐based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires

Localizing the cross-links distribution in elastomeric composites by tailoring the morphology of the curing activator

The localization of the rubber vulcanization reaction close to the silica filler surface was investigated in isoprene rubber composites (IR NCs): the main goal was to highlight the role of curing agents’ dispersion and filler surface features on the spatial propagation of the rubber cross-links and the resulting mechanical behavior of the material. The study was realized by tailoring the morphology of the curing activator, i.e. by vulcanizing IR NCs with Zn@SiO2 double function filler, composed of Zn(II) single sites anchored on SiO2 filler, in comparison to silica filled IR NCs vulcanized with microcrystalline ZnO (m-ZnO). The microscopic cross-links distribution was measured by Transmission Electron Microscopy for network visualization (NVTEM) and Time Domain Nuclear Magnetic Resonance (TD-NMR). Besides the NCs mechanical behavior was characterized both at small strain and at fracture. In the presence of Zn@SiO2, higher cross-link density in proximity to SiO2 particles was evidenced, which gradually spreads from the filler surface to the bulk, induced by localization of the Zn(II) centers. IR NCs with Zn@SiO2 resulted stiffer (+45%) and with a lower fracture toughness (less than one third), compared to m-ZnO based NCs, which shows a quite homogeneous structure of the rubber cross-links network. The results highlighted the correlation between the composites structural features and their macroscopic behavior, paving the way to modulating the mechanical properties of elastomeric materials by tuning the nature of the curing agents

Hazardous o-toluidine mineralization by photocatalytic bismuth doped ZnO slurries

Photocatalytic mineralization of o-toluidine in aqueous media under UV/solar irradiation was achieved by bare and bismuth doped zinc oxide nanoparticles. By adopting different analytical approaches a reaction mechanism is proposed, explaining the differences in photodetoxification performances

o-Toluidine photodetoxification by bismuth doped ZnO nanopowders

Nowadays environmental pollution has become a very diffuse topic for scientific research and several articles deal with the development of innovative techniques and materials for treatments of both wastewaters and polluted air. In this context, photocatalysis has a great potential as green technique for the depollution of several organic and inorganic toxic molecules. Zinc oxide has been introduced in heterogeneous photocatalytic treatments as an alternative material to TiO2, thanks to its similar properties: high photosensitivity, non-toxicity, low cost, competitive photocatalytic activity (band gap of 3.37 eV). Recently, along with their traditional application fields (e.g. coatings, cosmetics), ZnO nanopowders have been used as photocatalysts (second only to TiO2) for environmental remediation both in aqueous and gas phases [1-4]. The best performances for nanosized ZnO can be reached either modifying the strategy of synthesis or doping the material with different species, including transition metals (Mn, Cu) but also rare earth elements (La, Er) [5,6]. Also bismuth has been tested as dopant, proving its ability to shift the adsorption edge of ZnO (reducing the band gap of the material) to lower energy, exploiting solar light and modifying the separation rate of photoinduced charge carriers [7-9] In the present paper photocatalytic mineralization of o-toluidine in aqueous media under UV/solar irradiation was achieved by bare and bismuth doped zinc oxide nanoparticles. By adopting different analytical approaches a reaction mechanism is proposed, explaining the differences in photodetoxification performances

Electron and Energy Transfer Mechanisms: The Double Nature of TiO2 Heterogeneous Photocatalysis

Photocatalytic chemical transformations in the presence of irradiated TiO2 are generally considered in terms of interfacial electron transfer. However, more elusive energy-transfer-driven reactions have been also hypothesized to occur, mainly on the basis of the indirect evidence of detected reaction products whose existence could not be justified simply by electron transfer. Unlike in homogeneous and colloidal systems, where energy transfer mechanisms have been investigated deeply for several organic syntheses, understanding of similar processes in heterogeneous systems is at only a nascent level. However, this gap of knowledge can be filled by considering the important achievements of synthetic heterogeneous photocatalysis, which bring the field closer to industrial exploitation. The present manuscript summarizes the main findings of previous literature reports and, also on the basis of some novel experimental evidences, tentatively proposes that the energy transfer in TiO2 photocatalysis could possess a Förster-like nature

Tailored routes for home-made Bi-doped ZnO nanoparticles : Photocatalytic performances towards o-toluidine, a toxic water pollutant

Herein we report the photodegradation of highly toxic o-toluidine in aqueous media (under UV irradiation), by using home-made bare and bismuth-doped ZnO nanoparticles. The latter powder was prepared by both a traditional impregnation method and by an innovative sol-gel synthesis, obtained using bismuth nitrate as precursor. Moreover, synthetic conditions (such as zinc salts and medium acidity) were varied in order to obtain different semiconductor nanopowders with diverse physicochemical properties and, hence, photocatalytic performances. Both the disappearance and the mineralization of the pollutant molecule were followed by Linear Sweep Voltammetry and Total Organic Carbon techniques, respectively. Photocatalysis by-products were then identified by HPLC-MS (on eluates, after 3h and 6 h) and ATR-FTIR (on used nanopowders) analyses. Thus, a new photodegradation pathway (with azo dimer derivatives in the first step) has, been proposed. Bi-impregnated samples show high degree of mineralization, reducing the stability of the intermediates

From UV to Solar Irradiation Sources: ZnO Versus Bi2O3 Photocatalytic Performances

Highly toxic o-toluidine pollutant was photo-degraded in aqueous media, under UV/solar light, by using commercial pure and Bi-doped ZnO and Bi2O3 nanopowders synthesized by precipitating method (with the addition of a dispersing agent). All the synthesized nanopowders were deeply characterized on structural, morphological, surface and optical points of view. For all the tests, the disappearance and the relative mineralization of o-toluidine molecules were followed by Linear Sweep Voltammetries (LSVs) and TOC determinations, respectively. Hence, correlations between their properties and the photocatalytic performances were drawn