Nucleation and growth kinetics of CaCO3 crystals in the presence of foreign monovalent ions

The aim of this work is to study the effect of the presence of different monovalent ions (Na+, NH4+ and K+) on the nucleation and growth rates of CaCO3 precipitation. There is currently great interest in the precipitation of CaCO3 particles reusing CO2 rich flue gases and calcium-rich wastes, which implies the presence of foreign ions that can affect the crystallization process. Unseeded and seeded tests were carried out in a batch system to estimate the nucleation and growth kinetics, respectively. Tests with Na2CO3 and CaCl2 as precursors led to the classical calcite crystallization mechanism via vaterite formation at high supersaturations. On the other hand, the use of (NH4)2CO3 entailed lower pH and the presence of NH4+, which stabilized the vaterite and avoided its transformation into stable calcite crystals. Thus, faster nucleation kinetics by using Na2CO3 were obtained. To estimate the growth rate, tests with two initial seed loadings and types (micro and nano seed) were performed. The growth rate increased with the crystal size and decreased with the magma density. The results indicate that the ion effect on the growth rate seems to be related to the ionic radius of the foreign ion

Optimization of CaCO3 synthesis through the carbonation route in a packed bed reactor

This article presents an investigation on the recovery of CO2 from the combustion gases of the cement industry through a carbonation route in order to obtain Calcium Carbonate Nanoparticles (CCnP), which could find application as either polymer or cement fillers. Two different experimental setups, a Continuously Stirred Bubbling Reactor (CSBR) and a Packed Bed Reactor (PBR), were studied in order to improve the final product and enhance the process yield. The influence of the experimental parameters on the particle size and morphology was tested for both reactors. The process was intensified by employing the PBR, where cubic calcite particles smaller than 300 nm were synthesized and higher CO2 conversions were obtained with respect to the CSBR performance

Closing the loop: Analysis of biotechnological processes for sustainable valorisation of textile waste from the fast fashion industry

The textile industry currently stands as one of the most polluting sectors globally. The proliferation of fast fashion has led to an unprecedented increase in textile production and waste generation, marked by mixed material compositions and significant reduction in the lifespan of each garment. These factors contribute to the creation of complex mixed waste streams, with a majority ending up in landfills. In agreement with international sustainability directives, the textile sector has emerged as a prime candidate for harnessing valuable raw materials from waste. This review specifically targets the transformation of the prevailing linear production model into a more circular one. It focuses on utilizing biotechnological processes to convert textile waste into secondary raw materials to produce platform chemicals and added-value products, able to replace petrochemical-derived materials. The review begins with an extensive analysis of the state-of-the-art and the determination of technically feasible, economically viable, and environmentally sustainable waste valorisation techniques. The focus is on the pre-treatment phases of hydrolysis and fermentation of textile waste to produce industrially promising building blocks. Cotton and cotton-polyester blends, the two most common waste materials in fast fashion, were selected as the primary research materials. Significant variables affecting the efficiency of pre-treatment and hydrolysis methods are identified, highlighting the importance of pre-treatment and the potential use of enzymes for textile hydrolysis. Following the selected studies, the review defines the environmental and economic interests of the projects. These assessments provide essential insights into the sustainability and financial feasibility of the proposed waste valorisation methods

Toxicological profile of calcium carbonate nanoparticles for industrial applications.

Calcium carbonate nanoparticles (CaCO3NPs) derived from CO2 are promising materials for different industrial applications. It is imperative to understand their toxicological profile in biological systems as the human and environmental exposures to CaCO3NPs increases with growing production. Here, we analyse the cytotoxicity of CaCO3NPs synthesized from a CaO slurry on two cell lines, and in vivo on zebrafish (Danio Rerio). Our results demonstrate the CaCO3NPs in vitro safety as they do not cause cell death or genotoxicity. Moreover, zebrafish treated with CaCO3NPs develop without any abnormalities, confirming the safety and biocompatibility of this nanomaterial

Nano CaCO3 particles in cement mortars towards developing a circular economy in the cement industry

Abstract This paper calls into question the effects of incorporating nano calcium carbonate (CaCO3) particles in cement mortars, as they are interesting additive materials already successfully tested as cement nanofiller. These nanoparticles could potentially be prepared through the carbonation route using CO2 from combustion gases from the cement industry. This could enable a circular-economy approach for carbon capture and its re-use within the cement industry, in a sustainable and synergistic manner. In this study, part of the cement content was substituted with commercial nano CaCO3 particles to investigate their effects on the flexural and compressive strength of the resulting cement mortars, after curing for 7 and 28 days. Decreasing the cement content could lead to a reduction in the carbon footprint of cement, which is responsible for approximately 8% of global carbon dioxide emissions. Preliminary results using synthesized CaCO3 particles as nanofillers showed that, after 7 days of curing, mechanical properties of cement mortars improved. This indicates that hydration reaction was accelerated since CaCO3 acts as seeding for this reaction. By contrast, after 28 days of curing, no major improvement was observed. A higher content of calcium carbonate nanoparticles may have reduced the filler effect of these particles due to aggregation phenomena. In the present work, the effects of commercial nano CaCO3 particles on cement hydration were investigated. Mechanical tests showed promising results both after 7 and 28 days of curing. This could lead to the reduction of the carbon footprint of cement manufacturing and produce increasingly better performing building materials. Thus, the development of a circular economy in the cement industry could be achieved

Optimization of BiVO4 photoelectrodes made by electrodeposition for sun-driven water oxidation

In this work, the synthesis of cheap BiVO4 photoanodes for the photoelectrochemical water splitting reaction was optimized via the scalable thin film electrodeposition method. Factors affecting the photoelectrochemical activity, such as the electrodeposition time, the ratio of the Bi-KI to benzoquinone-EtOH in the deposition bath, and the calcination temperature, have been investigated by using the Central Composite Design of Experiments. Pristine monoclinic scheelite BiVO4 photoanodes having a photocurrent density of 0.45 ± 0.05mA/cm2 at 1.23 V vs RHE have been obtained. It was shown that a high photocurrent density is generally dictated by the following physico-chemical properties: a higher crystallite size, optimal thickness and a porous morphology, which give rise to a low charge transfer resistance, low onset potential and a high donor density. Moreover, to the best of our knowledge, this is the first report on the depth profile XPS analysis performed in BiVO4 photoanodes made by electrodeposition technique, from which it was concluded that the surface V species exist as V4+ while the bulk V species are V5+. The V4+ induces a higher amount of surface oxygen vacancies, which was found to be beneficial for the photoactivity

Towards the sustainable hydrogen production by catalytic conversion of C-laden biorefinery aqueous streams

An extensive screening of representative molecules of a post-hydrothermal process side stream has been performed with the aim of producing a gas mixture rich in hydrogen by catalytic aqueous phase reforming. The survey enlightens possible routes of valorisation of these by-products, scarcely investigated with other processes so far. The influence of reaction temperature was studied in the 230–270 °C range, looking at both the composition of the gas phase and the characterization of the liquid products. Indeed, the information coming from the condensed phase may provide relevant insights on the components that are not easily reformed, and that should be studied to improve the performance of the process. Binary and ternary mixtures of four selected compounds were tested to investigate synergistic and inhibiting effects, going towards the direction of a real biorefinery stream. The spent alumina-supported catalyst was characterized, outlining possible deactivation mechanisms of the catalytic system, and reused in two successive tests

FIRB "SQUARE" project: nano-structured sensors for the detection of the polluting in engine exhaust gases and for indoor air quality monitoring

The present work is a final dissemination of activities carried out and main results obtained in the national founded project Firb "Square". The project is leaded by Centro Ricerche Fiat and it involves the most qualified national public Research Institutes and Universities active in the fields of nanomaterials synthesis, nanotechnology and gas sensors development