Microplastics encapsulation in aragonite: efficiency, detection and insight into potential environmental impacts

Plastic pollution in aquatic ecosystems has become a significant problem especially microplastics which can encapsulate into the skeletons of organisms that produce calcium carbonates, such as foraminifera, molluscs and corals. The encapsulation of microplastics into precipitated aragonite, which in nature builds the coral skeleton, has not yet been studied. It is also not known how the dissolved organic matter, to which microplastics are constantly exposed in aquatic ecosystems, affects the encapsulation of microplastics into aragonite and how such microplastics affect the mechanical properties of aragonite. We performed aragonite precipitation experiments in artificial seawater in the presence of polystyrene (PS) and polyethylene (PE) microspheres, untreated and treated with humic acid (HA). The results showed that the efficiency of encapsulating PE and PE-HA microspheres in aragonite was higher than that for PS and PS-HA microspheres. The mechanical properties of resulting aragonite changed after the encapsulation of microplastic particles. A decrease in the hardness and indentation modulus of the aragonite samples was observed, and the most substantial effect occurred in the case of PE-HA microspheres encapsulation. These findings raise concerns about possible changes in the mechanical properties of the exoskeleton and endoskeleton of calcifying marine organisms such as corals and molluscs due to the incorporation of pristine microplastics and microplastics exposed to dissolved organic matter.

Microbial-mineral interaction experiments and density functional theory calculations revealing accelerating effects for the dolomitization of calcite surfaces by organic components

Carbonates represent major sedimentary rocks in on the continental and oceanic crust of Earth and are often closely related to microbial activities. However, the origin of magnesium-containing carbonates, such as dolomites, has not yet been fully resolved and was debated for many years. In order to reveal the specific role of organic components and microbes on the precipitation of magnesium ions, different dolomitization experiments were carried out with various setups for the presence of eight amino acids and microbes. The Gibbs free energy for dehydration of Mg[6(H2O)]2+ and organic‑magnesium complexes (OMC) at the calcite (101¯4) step edges were calculated by density functional theory (DFT). Combined results of X-ray diffraction (XRD), scanning electron microscope-energy disperse spectroscopy (SEM-EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) indicated that magnesium ions were incorporated into the crystal lattice of calcite after calcite reacting with organic‑magnesium solutions (OMS). Dolomite was formed on the surface of calcite under the presence of microbes. The Gibbs free energy barrier of asp, glu, gly, thr, tyr, lys, ser, and ala bonding to Mg[6(H2O)]2+ were 17.8, 16.2, 14.8, 16.5, 19.2, 14.5, 19.0, 17.0 kcal/mol, those are lower than that of the direct dehydration of Mg[6(H2O)]2+ of 19.45 kcal/mol. The Gibbs free barrier of OMC bonding at the acute step ([481¯] and [4¯41]) of 29.7/34.25 kcal/mol are lower than that of Mg[6(H2O)]2+ of 32.45/36.7 kcal/mol and the Gibbs free barrier of OMC bonding at the obtuse step ([481¯] and [4¯41]) of 42.07/47.6 kcal/mol are lower than that of Mg[6(H2O)]2+ of 55.4/60.34 kcal/mol. The enhancing effects of organic components and microbes on the precipitation of magnesium ions were collectively determined through experimental and theoretical calculation, thus setting up a new direction for future studies of dolomitization with a focus on microbial- mineral interactions.

Inorganic Scaling in Membrane Desalination: Models, Mechanisms, and Characterization Methods

Inorganic scaling caused by precipitation of sparingly soluble salts at supersaturation is a common but critical issue, limiting the efficiency of membrane-based desalination and brine management technologies as well as other engineered systems. A wide range of minerals including calcium carbonate, calcium sulfate, and silica precipitate during membrane-based desalination, limiting water recovery and reducing process efficiency. The economic impact of scaling on desalination processes requires understanding of its sources, causes, effects, and control methods. In this Critical Review, we first describe nucleation mechanisms and crystal growth theories, which are fundamental to understanding inorganic scale formation during membrane desalination. We, then, discuss the key mechanisms and factors that govern membrane scaling, including membrane properties, such as surface roughness, charge, and functionality, as well as feedwater characteristics, such as pH, temperature, and ionic strength. We follow with a critical review of current characterization techniques for both homogeneous and heterogeneous nucleation, focusing on the strengths and limitations of each technique to elucidate scale-inducing mechanisms, observe actual crystal growth, and analyze the outcome of scaling behaviors of desalination membranes. We conclude with an outlook on research needs and future research directions to provide guidelines for scale mitigation in water treatment and desalination.

Extraction and Characterization of Biogenic Silica Obtained from Selected Agro-Waste in Africa

Increased amounts of available biomass residues from agricultural food production are present widely around the globe. These biomass residues can find essential applications as bioenergy feedstock and precursors to produce value-added materials. This study assessed the production of biogenic silica (SiO2) from different biomass residues in Africa, including cornhusk, corncob, yam peelings, cassava peelings and coconut husks. Two processes were performed to synthesize the biogenic silica. First, the biomass fuels were chemically pre-treated with 1 and 5% w/v citric acid solutions. In the second stage, combustion at 600 °C for 2 h in a muffle oven was applied. The characterization of the untreated biomasses was conducted using Inductively coupled plasma—optical emission spectrometry (ICP-OES), thermal analysis (TG-DTA) and Fourier-transform infrared spectroscopy (FTIR). The resulting ashes from the combustion step were subjected to ICP, nitrogen physisorption, Energy dispersive X-ray spectroscopy (EDX) as well as X-ray diffraction (XRD). ICP results revealed that the SiO2 content in the ashes varies between 42.2 to 81.5 wt.% db and 53.4 to 90.8 wt.% db after acidic pre-treatment with 1 and 5 w/v% acid, respectively. The relative reductions of K2O by the citric acid in yam peel was the lowest (79 wt.% db) in comparison to 92, 97, 98 and 97 wt.% db calculated for corncob, cassava peel, coconut husk and cornhusk, respectively. XRD analysis revealed dominant crystalline phases of arcanite (K2SO4), sylvite (KCl) and calcite (CaCO3) in ashes of the biomass fuels pre-treated with 1 w/v% citric acid due to potassium and calcium ions present. In comparison, the 5 w/v% citric acid pre-treatment produced amorphous, biogenic silica with specific surface areas of up to 91 m2/g and pore volumes up to 0.21 cm3/g. The examined biomass residues are common wastes from food production in Africa without competition in usage with focus application. Our studies have highlighted a significant end-value to these wastes by the extraction of high quality, amorphous silica, which can be considered in applications such as catalyst support, construction material, concrete and backing material.

1,1′-Ferrocenedicarboxylic acid/tetrahydrofuran induced precipitation of calcium carbonate with a multi-level structure in water

Multi-molecules co-regulate the orderly morphology and structure of CaCO3 precipitates and the influence of ether bonds on the formation of CaCO3 precipitates.

Mineralization of calcium phosphate controlled by biomimetic self-assembled peptide monolayers via surface electrostatic potentials

The functions of acidic-rich domains in non-collagenous protein during biomineralization are thought to induce nucleation and control the growth of hydroxyapatite. The tripeptide Asp-Ser-Ser (DSS) repeats are the most common acidic-rich repeated unit in non-collagenous protein of dentin phosphoprotein, the functions of which have aroused extensive interests. In this study, biomimetic peptides (DSS)_n (n = 2 or 3) were designed and fabricated into self-assembled monolayers (SAMs) on Au (111) surface as biomimetic organic templates to regulate hydroxyapatite (HAp) mineralization in 1.5 simulated body fluid (1.5 SBF) at 37 °C. The early mineralization processes and minerals deposited on the SAMs were characterized by X-ray diffraction, scanning electron microscope, and Fourier transform infrared spectroscopy analyses. The SAM-DSS9/DSS9G showed the highest capacity to induce HAp nucleation and growth, followed by SAM-DSS6/DSS6G, SAM-COOH, and SAM-OH. The SAM-(DSS)_n had more negative zeta potentials than SAM-COOH surface, indicating that DSS repeats contributed to the biomineralization, which not only provided strong affinity with Ca²⁺ ions through direct electrostatic bonds, but more importantly influence surface electrostatic potentials of the assembled organic template for nucleation.

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Biomimetic peptides designed from DPP and self-assembled to form SAMs.

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Quantitative model for HAp mineralization regulated by non-collagenous protein.

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Extra DSS repeat reduced the zeta potential on the SAM surface.

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The nuclei quantity and mineral size on DSS9/DSS9G were always larger.

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DSS repeats provided surface electrostatic potentials for stronger Ca²⁺ affinity.

The current application of nanotechnology in food and agriculture

The rapid development of nanotechnology has been facilitating the transformations of traditional food and agriculture sectors, particularly the invention of smart and active packaging, nanosensors, nanopesticides and nanofertilizers. Numerous novel nanomaterials have been developed for improving food quality and safety, crop growth, and monitoring environmental conditions. In this review the most recent trends in nanotechnology are discussed and the most challenging tasks and promising opportunities in the food and agriculture sectors from selected recent studies are addressed. The toxicological fundamentals and risk assessment of nanomaterials in these new food and agriculture products are also discussed. We highlighted the potential application of bio-synthesized and bio-inspired nanomaterial for sustainable development. However, fundamental questions with regard to high performance, low toxic nanomaterials need to be addressed to fuel active development and application of nanotechnology. Regulation and legislation are also paramount to regulating the manufacturing, processing, application, as well as disposal of nanomaterials. Efforts are still needed to strengthen public awareness and acceptance of the novel nano-enabled food and agriculture products. We conclude that nanotechnology offers a plethora of opportunities, by providing a novel and sustainable alternative in the food and agriculture sectors.

Surface properties of PM2.5 calcite fine particulate matter in the presence of same size bacterial cells and exocellular polymeric substances (EPS) of Bacillus mucitaginosus

Microorganism cells and spores are the main components of PM2.5 (fine particulate matter) as well as fine mineral particles. In the microscopic system, the microorganisms will affect the minerals through attachment, charge neutralization, and dissolution related to the cell surface structure and metabolite. To explore the process and the results of microbial cells and their extracellular polymeric substances (EPS) acting on the surface properties of minerals of PM2.5 through the metabolism, a common native soil bacterium Bacillus mucitaginosus with abundant extracellular polymers was chosen as the tested strain. Meanwhile, as one of the PM2.5 common minerals, calcite fine particles were taken as the research object to explore the influence of microbial cells and extracellular polymers on its surface properties. High performance liquid chromatography (HPLC), inductively coupled plasma spectrometry (ICP), Zeta potential analysis, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) were used to characterize the composition of EPS, the soluble ions, surface charge, surface groups, crystal form, and surface morphology of calcite residual solid after being treated by the bacterial cells and EPS. The results revealed the EPS of B. mucitaginosus mainly consisted of protein and polysaccharides. Both the whole cell and its EPS could promote the dissolution of calcite particles into calcium ions. Due to the adhesion of organic groups on the calcite surface, the surface potential shifted significantly in the negative direction and the solution pH was clearly increased. The morphology of calcite surface was significantly changed after dissolution and re-crystallization. Experimental results also showed that the existence of the bacteria cells and EPS significantly affected the surface properties of calcite and provide a theoretical basis for the mechanism of PM fine particulate matter on human health impact for further study.

Nanoparticles considered as mixtures for toxicological research

Nanoparticles are used widely in our lives, but the understanding of their impacts on human and environmental health is still limited, at least due in part to the fact that nanoparticles are mixtures. This review describes that "nanotoxicity" is actually a test of the overall effect of a nanoparticle mixture: starting materials for nanoparticle preparation, surface coating agents, surface reaction-generated species, and transformed byproducts of the nanoparticle in biological and environmental media, as well as variations of the intrinsic nanoparticle structures.

DNA action on the growth and habit modification of NaCl crystals

{100} hopper-like NaCl crystals were prepared upon the action of DNA by the solvent evaporation method.

Two competitive nucleation mechanisms of calcium carbonate biomineralization in response to surface functionality in low calcium ion concentration solution

Four self-assembled monolayer surfaces terminated with –COOH, –OH, –NH₂ and –CH₃ functional groups are used to direct the biomineralization processes of calcium carbonate (CaCO₃) in low Ca²⁺ concentration, and the mechanism of nucleation and initial crystallization within 12 h was further explored. On −COOH surface, nucleation occurs mainly via ion aggregation mechanism while prenucleation ions clusters may be also involved. On −OH and −NH₂ surfaces, however, nucleation forms via calcium carbonate clusters, which aggregate in solution and then are adsorbed onto surfaces following with nucleation of amorphous calcium carbonate (ACC). Furthermore, strongly negative-charged −COOH surface facilitates the direct formation of calcites, and the −OH and −NH₂ surfaces determine the formation of vaterites with preferred crystalline orientations. Neither ACC nor crystalline CaCO₃ is observed on −CH₃ surface. Our findings present a valuable model to understand the CaCO₃ biomineralization pathway in natural system where functional groups composition plays a determining role during calcium carbonate crystallization.

Gene expression profiling and mechanism study of neural stem cells response to surface chemistry

To declare the mechanisms of neural stem cells (NSCs) in response to material surface chemistry, NSCs were exposed to the self-assemble monolayers of alkanethiolates on gold surfaces terminated with amine (NH2), hydroxyl (OH) and methyl (CH3) for analysis. The morphological responses of NSCs were recorded; the gene expression profilings were detected by genechips; the gene expressions data of NSCs responded to different chemical groups were declared through the gene ontology term and pathway analyses. It showed that cells behaved dissimilar on the three chemical groups, the adhesion, proliferation and migration were easier on the NH2 and OH groups; the gene expressions of NSCs were induced differently, either, involved in several functional processes and signaling pathways. CH3 group induced genes enriched much in chemistry reactions and death processes, whereas many genes of cellular nucleotide metabolism were down-regulated. NH2 group induced NSCs to express many genes of receptors on membrane, and participated in cellular signal transduction of cell adhesion and interactions, or associated with axon growth. OH group was similar to NH2 group to induce the membrane response, but it also down regulated metabolism of cells. Therefore, it declared the chemical groups affected NSCs through inner way and the NH2, OH and CH3 groups triggered the cellular gene expression in different signaling pathways.