Nano-sized CaCO3 Research Articles

An investigation of nano- and micron-sized carriers based on calcium carbonate and polylactic acid for oral administration of siRNA

ABSTRACT Background Oral delivery of small interfering RNAs (siRNAs) draws significant attention, but the gastrointestinal tract (GIT) has many biological barriers that limit the drugs’ bioavailability. The aim of this work was to investigate the potential of micro- and nano-sized CaCO3 and PLA carriers for oral delivery of siRNA and reveal a relationship between the physicochemical features of these carriers and their biodistribution. Research design and methods In vitro stability of carriers was investigated in simulated gastric and intestinal fluids. Toxicity and cellular uptake were investigated on Caco-2 cells. The biodistribution profiles of the developed CaCO3 and PLA carriers were examined using different visualization methods, including SPECT, fluorescence imaging, radiometry, and histological analysis. The delivery efficiency of siRNA loaded carriers was investigated both in vitro and in vivo. Results Micro-sized carriers were accumulated in the stomach and later localized in the colon tissues. The nanoscale particles (100–250 nm) were distributed in the colon tissues. nPLA was also detected in small intestine. The developed carriers can prevent siRNA from premature degradation in GIT media. Conclusion Our results reveal how the physicochemical properties of the particles, including their size and material type can affect their biodistribution profile and oral delivery of siRNA.

Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO3.

The utilization of Bacillus sp. for the production of bio-CaCO3 in concrete crack repair and strength enhancement has attracted considerable attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Here calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial β-oxidation under alkaline were used to generate micro/nano CaCO3. The results indicate that the main crystalline form of the generated precipitated particles is calcite, with a particle size ranging from 0.7 to 10 μm. Minimal heavy metals were found in the supernatant following settling. And at the optimum pH of 8.5-9, carbon capture reached 743 mg L-1, and CaCO3 production reached 1,191 mg L-1, and dominant phylum were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in β-oxidation. Mass balance analysis showed that alkali promotes microbial β-oxidation of organisms to produce CO2 and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.

An integrated airlift loop reactor for continuous production of calcium carbonate from phosphogypsum using a one-step method

Commercial exploitations of phosphogypsum and CO2 are the research hotspots and difficulties. A coupled reaction and separation airlift loop reactor, which integrates four consecutive processes (i.e., dissolution of slightly soluble raw material, impurity separation, product preparation, and product separation) for reactive crystallization, was proposed to continuously prepare high-value products (i.e., (NH4)2SO4 and nano-sized CaCO3) using waste to treat waste (i.e., phosphogypsum and CO2) at ambient conditions by a one-step method. The technical feasibilities of the coupled reactor were verified, and principal influencing factors on the CaCO3 product quality were systematically investigated and optimized. Additionally, the coupled fluid hydrodynamics dependent on the two individual airlift loop reactors were also inspected. This work shed some new light on the practical resource utilization of phosphogypsum and waste CO2 in tandem at a low cost, and a solid basis for the rational design, optimization, and scale-up of such promising reactors was provided.

Strong acid-mediated Ca2+ extraction–CO2 mineralization process for CO2 absorption and nano-sized CaCO3 production from cement kiln dust: Simultaneous treatment of CO2 and alkaline wastewater

Increasing yearly stockpiles of cement kiln dust (CKD) and the associated high landfilling cost require innovative solutions to utilize CKD. This study proposes a strong acid-mediated extraction–mineralization process that utilizes CO2. The process comprises the extraction of Ca2+ from CKD using strong acids, mineralization of CO2 using extracted Ca2+ and alkaline wastewater, and production of Ca carbonate. High Ca2+ leaching efficiency, high Ca2+ extraction efficiency, and high-purity nano-sized CaCO3 production from CKD were achieved under normal operating conditions in an in-situ strong acid solution. The process feasibility was primarily tested via an individual extraction process using aqueous HCl and HNO3 solutions from typical CKD and mineral carbonation experiments using Ca(OH)2 and alkaline wastewater obtained from the extraction process. The process had a Ca2+ leaching efficiency of 94.73%, Ca2+ extraction efficiency of 93.54%, and CaCO3 yield of 1.45 ton/ton CKD in the aqueous HCl solution. Polymorphism and crystal structure analyses showed that CaCO3 obtained after CO2 mineralization was mainly present as calcite. Alkaline wastewater acted as a pH buffer, enhanced the reactivity with CO2, accelerated the conversion of CO2(g) to CO32-(aq), and acted as an accelerator that promoted the nucleation growth of CaCO3 by OH- ions during the mineralization process. The effect of the nucleation and growth of CaCO3 on the particle and crystallite size is highly dependent on the system pH. These results can be applied to CO2 utilization processes by industrial by-products.

Effect of pretreatment procedure on the properties of cementitious materials with limestone cured by CO2

Carbon sequestration in cementitious materials is an effective way to promote sustainable development of the cement industry. Traditionally, specimens are cast and then cured by CO2. Cement particles are first pretreated with CO2 and cast into specimens to study their performance properties are innovatively investigated in this paper. In this study, the carbonation depth, CO2 uptake amount, compressive strength, reaction heat, XRD and SEM/BSE of cementitious materials with and without pretreatment procedure were investigated. The results showed that the pretreatment procedure enhanced the CO2 uptake amount of paste samples and contributed significantly to the carbonation depth, but was not conducive to the development of compressive strength. As seen in the SEM/BSE images, a rim of dense nano-sized CaCO3 was produced around the clinker particle after pretreatment, which was identified as mainly calcite in combination with XRD analysis. The considerable reduction in cumulated heat release of the pretreated cement implied that the rim of dense CaCO3 hinder the subsequent hydration of unreacted clinker particle to some extent. The sample prepared with pretreated cement caused a rim of crack around the clinker particle after 1 day of CO2 curing and 27 days of subsequent water curing. 5%, 10% and 15% limestone powder were added in order to improve the degree of carbonation and hydration of cementitious materials. With the increase of limestone powder addition, the carbonation depth and CO2 uptake amount increased gradually. The compressive strength reached the maximum when its content was 10%.

A novel approach to mineral carbonation using deep eutectic solvents for the synthesis of nano-sized amorphous CaCO3

This paper proposes a novel synthesis method for nanosized amorphous CaCO3 based on advanced mineral carbonation using the macromolecular properties of deep eutectic solvents (DESs). DESs are generally synthesized by mixing hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), and their properties vary depending on the HBDs and HBAs used for the synthesis. To synthesize DESs with CO2-philic properties, monoethanolamine (MEA) was selected as the HBD because it possesses a CO2-active site. However, alkanolamine-based DESs are difficult to use in practical applications because of their high viscosity following CO2 absorption. To mitigate the onset of high viscosity, H2O was added to the synthesized DESs, with the molar ratio HBA:HBD:H2O as 1:5:10 and 1:5:15. In the proposed process, CO2 was captured by the DESs-H2O system and converted into particle-size- and morphology-controlled CaCO3. Nanosized amorphous CaCO3 (ACC) with average particle sizes of 38.1 and 48.0 nm was formed by DESs based on the molar ratio of 1:5:10. The results demonstrated the need for an adequate ratio of H2O to DES to form nanosized ACC, implying that the strength of hydrogen bonding in DES-H2O systems is the primary factor affecting the performance of the solvent. The DES-H2O systems with inter- and intramolecular hydrogen bonding inhibited the crystallization of CaCO3. The findings of this study are applicable to CO2 utilization processes designed for the production of nanosized ACC.

Effect of CO2 capture on the performance of CaO-activated slag pastes and their acid resistance

Carbonation of CaO-activated slag shows great potential in terms of storing CO2, reducing emissions by reducing cement consumption and recycling steel slag. This study investigates the effect of quicklime dosage and CO2 capture time on the performance of CaO-activated slag experimentally. CO2 capture time varies from 0 to 15 min, and the addition of quicklime as CO2 carrier increases from 10 % to 30 %. The fluidity behavior of fresh pastes, and hydration evolution, strength behavior and acid resistance of hardened pastes before and after carbonation were analyzed. The experimental results show that more addition of quicklime and extended CO2 fixation time decrease the fluidity but increase the shear stress and apparent viscosity, which are associated with chemical reaction of quicklime and generation of large amounts of nano-sized CaCO3. Increased addition of quicklime improving the alkaline environment promotes the pozzolanic reaction of CaO-activated slag and enriches the content CO2 carrier. Hence, longer CO2 fixation time improves the filling effect of nanoscale CaCO3 on the hardened matrix obviously, and leads to better mechanical performance. Additionally, both more addition of quicklime and extended CO2 fixation time increase the acid resistance of hardened pastes chemically and physically. Therefore, this study will provide novel carbonated binders, which are benefit to the energy saving, emission reduction and environmental protection.

Preparation of calcium carbonate nanoparticles from waste carbide slag based on CO2 mineralization

This study proposes a novel method for simultaneously dealing with the waste carbide slag (WCS) and CO2 mitigation. In addition, the ultrafine vaterite CaCO3 with high economic value was produced under mild conditions of 25 °C and 0.1 MPa. Ammonium sulfate ((NH4)2SO4) was employed to efficiently extract calcium from WCS into the solid phase calcium sulfate dehydrate (CaSO4·2H2O). Subsequently, it was subjected to “dropwise carbonation” leading to the formation of a calcium carbonate with controllable particle size between 100 nm–1 μm through multiple crystalline phase transformations. The results showed that nano-sized CaCO3 with nearly 90% purity and whiteness was prepared at 25 °C, CO2-500 mL/min, and NH4+/Ca2+ = 2.4 conditions. Results of TG and FTIR analyses confirmed that CaCO3 polymorphs with vaterite and metastable were formed. Based on the calcium conversion ratio of the entire process, treatment with 1 ton of WSC captured ∼0.5 tons of CO2 and yields about 1.15 tons of nano-sized CaCO3 per each cycle operation. This study provides a valuable method for identifying potential application for scale preparation of vaterite nanoparticles from low cost but abundant calcium resource such as WCS and gypsum.

Preparation of environment-friendly ultrafine fly ash based superhydrophobic demoulding coating

The superhydrophobic surface can be used to separate castable concrete materials and moulds instead of waste oil which has the risk of contamination. In this study, a low cost superhydrophobic demoulding coating was prepared using waste materials. Solid waste ultrafine fly ash (UFA) as micron particles. Nano-sized CaCO3 nucleated on the surface of UFA with Ca(OH)2/calcium carbide slag(CCS) slurry under constant CO2 bubbling condition. Fluorosilanes were used to provide low surface energy. Powder coating was used as the base coating to provide intermediate bonding. Through SEM and AFM analysis, it was found that after carbonization, nano-sized CaCO3 particles were distributed on the surface of UFA particles and form large protrusion, and the surface roughness was significantly increased. The contact angle of the coating water was greater than 150° under the optimal condition. Compared with the original UFA, the amount of fluorosilane was reduced from 2% to 0.1%, which reduced the cost. The composite interface between the liquid droplets and the coating surface was formed to intercept air bubbles. The hydrophobic model of the coating met the Cassie theory. The coating can replace the release agent to achieve easy release effect.

Influence of nanosized CaCO3 content in tailoring the structure, the morphology and the thermal and mechanical properties of iPP/PA66/PP-g-MA alloy

Nanocomposites of Polypropylene/Polyamide 66 (iPP/PA66) with a weight ratio of (70/30) filled with stearic acid-treated nanosized CaCO3 were melt compounded in the presence of a fixed amount of grafted polypropylene maleic anhydride (PP-g-MA) in a Brabender mixer. The purpose of this research is to obtain nanocomposites with high-performance structural, morphological, and thermomechanical properties. The obtained properties are discussed in light of the content of nano-CaCO3 and of the induced interfacial bonding properties generated by the insertion of the compatibilizer. The results confirmed that, according to the FTIR spectroscopy analysis, the existence, on one hand of possible interactions between PP-g-MA and PA66 and, on the other hand, between stearic acid and PA66. XRD results show that nanosized CaCO3 particles play the role of nucleating agents in the matrix and thus increasing the crystallinity of the blend. SEM results revealed that the treated nanosized CaCO3 was more homogeneously dispersed in the (iPP/PA66), and a refinement of the morphology and better dispersion of the filler were detected after the addition of PP-g-MA. From the mechanical point of view; the incorporation of CaCO3 increased appreciably the tensile strength at break and the tensile modulus of (iPP/PA66) blend.

Zein coated calcium carbonate nanoparticles for the targeted controlled release of model antibiotic and nutrient across the intestine

In this study, a novel bio-inspired method was used to synthesize calcium carbonate nanoparticles (CaCO3 NPs) using gelatin as a template for the co-delivery of vitamin D and amoxicillin. The synthesized CaCO3 NPs were characterized using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET). XRD and TEM confirmed nanocrystalline nature of CaCO3 in size range of 10−15 nm. Further, CaCO3 NPs encapsulated with vitamin D, coated with zein and finally loaded with amoxicillin as a model drug. The release study of vitamin D and amoxicillin was performed in the simulated gastric fluid (SGF) (pH 1.2) and simulated intestinal fluid (SIF) (pH 6.8) and (pH 7.4) at 37 °C temperature. The encapsulation of hydrophobic vitamin D in CaCO3 NPs with an external zein coating approach enhances their controlled and sustained release property at the target site. The role of gelatin molecule in the synthesis of nano-sized CaCO3 was demonstrated using CD spectroscopy. MTT assay was performed on zein coated CaCO3 NPs at varying concentrations on kidney (HEK) and liver (Hep G2) cell lines after 24 h exposure to ensure its biocompatibility.

Effect of silicate modulus on tensile properties and microstructure of waterproof coating based on polymer and sodium silicate-activated GGBS

Abstract This paper investigated a novel and environmentally-friendly waterproof coating produced by the organic (i.e., styrene-acrylate copolymer) and inorganic (i.e., waterglass and ground granulated blast-furnace slag (GGBS)) compounds. The good cohesion of polymer and sodium silicate-activated GGBS can provide good mechanical properties, and this material also shows a better environmental benefit as no cement was used for coating. In this work, an appropriate proportion of polymer, waterglass and GGBS was given, and the effect of silicate modulus on the macro-performances and microstructures of the waterproof coating was studied. The optimal silicate modulus was 1.75, and the corresponding tensile strength and breaking elongation were 2.20 MPa and 90.48%, respectively. Furthermore, the waterproof coating also exhibited favorable tensile properties, flexibility or water impermeability after subjected to high temperature, alkali, water immersion, low temperature and high water pressure. This new waterproof coating exhibited the favorable tensile properties owing to (i) appropriate reaction rate, (ii) high degree of polymerization of C-S-H gel, (iii) high content of C-S-H gel and CaCO3 crystal, (iv) high reaction degree between emulsion and sodium silicate-activated GGBS, (v) nano-sized CaCO3 crystals and mechanical bond between the CaCO3 particles.

Effect of n-CaCO3 on fresh, hardened properties and acid resistance of granulated blast furnace slag added mortar

Nano size CaCO3 (n-CaCO3) particles were used as an additive into the Ground Granulated Blast Furnace Slag (GGBS) added mortar to investigate their effects on fresh, hardened properties and acid resistance. Setting time, normal consistency, flow diameter, volume stability, flexural and compressive strengths tests were performed in the present study. In addition, to see how n-CaCO3 and GGBS affect the acid resistance of the mortars, the produced mortar samples were stored in the acid solution and their mass losses were determined. Mortars including 20% GGBS (replaced with cement by weight) with 0%, 1% and 2% n-CaCO3 (added by weight of cement) and a control mortar which has no GGBS and n-CaCO3were produced. Experimental results showed that addition of 1% n-CaCO3 were helpful to increase the both flexural and compressive strength and resonance frequency of mortars 11.54%, 11.9% and 10%, respectively and the setting period was shortened, 7.4% according to control sample. XRD analysis showed that the chemical structure of the mortar samples before and after acid attack did not change, significantly.

The crystallization kinetic model of nano-CaCO3 in CO2-ammonia-phosphogypsum three-phase reaction system

Phosphogypsum (PG) as a low-cost calcium resource was used to prepare nano-CaCO3 in a three-phase system by reactions. Based on the population balance equation, nano-CaCO3 crystal nucleation and growth model in the gas (CO2)-liquid (NH3·H2O)-solid (CaSO4) three-phase system was established. The crystallization kinetic model of nano-CaCO3 in CO2-NH3·H2O-CaSO4 reactions system was experimental developed over an optimized temperature range of 20–40 °C and CO2 flow rate range of 138–251 ml/min as rCaCO3=kn32πM2γ33R3ρ2T3(C-C∗)0.8[ln(C/C∗)]3+πρ3Mkg3kn(C-C∗)2t3, where nano-CaCO3 nucleation rate constant was kn=6.24×1019exp-15940RT and nano-CaCO3 growth rate constant was kg=0.79exp-47650RT respectively. Research indicated that nucleation rates and growth rates both increased with the increasing of temperature and CO32– ion concentration. And crystal growth was dependent on temperature more than that of nucleation process because the activation energy of CaCO3 growth was bigger than that of CaCO3 nucleation. Decreasing the reaction temperature and CO2 flow rate was more beneficial for producing nano-size CaCO3 because of the lower CaCO3 growth rates. The deduced kinetic equation could briefly predict the average particle sizes of nano-CaCO3.

Adsorption and Desorption Characteristics of Cd2+ and Pb2+ by Micro and Nano-sized Biogenic CaCO3.

The purpose of this study was to elucidate the characteristics and mechanisms of adsorption and desorption for heavy metals by micro and nano-sized biogenic CaCO3 induced by Bacillus subtilis, and the pH effect on adsorption was investigated. The results showed that the adsorption characteristics of Cd2+ and Pb2+ are well described by the Langmuir adsorption isothermal equation, and the maximum adsorption amounts for Cd2+ and Pb2+ were 94.340 and 416.667 mg/g, respectively. The maximum removal efficiencies were 97% for Cd2+, 100% for Pb2+, and the desorption rate was smaller than 3%. Further experiments revealed that the biogenic CaCO3 could maintain its high adsorption capability for heavy metals within wide pH ranges (3–8). The FTIR and XRD results showed that, after the biogenic CaCO3 adsorbed Cd2+ or Pb2+, it did not produce a new phase, which indicated that biogenic CaCO3 and heavy metal ions were governed by a physical adsorption process, and the high adsorptive capacity of biogenic CaCO3 for Cd2+ and Pb2+ were mainly attributed to its large total specific surface area. The findings could improve the state of knowledge about biogenic CaCO3 formation in the environment and its potential roles in the biogeochemical cycles of heavy metals.

Effect of calcium carbonate particle size on formation and morphology of calcium hexaboride powder synthesized from condensed boric acid-poly(vinyl alcohol) product

Calcium hexaboride (CaB6) powder was synthesized by carbothermal reduction via the transient boron carbide (B4C) formation starting from a condensed boric acid (H3BO3)-poly(vinyl alcohol) (PVA) product. The effect of the size of calcium carbonate (CaCO3) particles on the formation behavior of CaB6 and the obtained particle morphology was investigated in this study. CaB6 powder was prepared using CaCO3 powders with microsize or nanosize particles. The CaB6 formation reaction was accelerated at lower temperature and shorter heat treatment time when using nanosize CaCO3 particles. The complete formation of CaB6 was achieved at 1400 °C for 3 h in an Ar flow. Furthermore, CaB6 powder with nanosize particles was obtained. The precursor powder obtained using nanosize CaCO3 particles transiently formed fine B4C and calcium borate particles, which are reactive species of CaB6, leading to the facile formation of fine CaB6 particles.

Creation of hybrid polymer particles through morphological tuning of CaCO3 crystals in miniemulsion system

We developed a miniemulsion-based nanoreactor system, which can allow for morphological tuning of CaCO3 crystals in nanodroplets and their high encapsulation efficiency in polymer particles.We first obtained nano-sized CaCO3 by using the aqueous nanodroplet as a nanoreactor. In addition, it was found that crystal growth and morphological transformation of CaCO3 from spherical to rod-like crystals were induced by adding 2-hydroxyethyl methacrylate (HEMA) in nanodroplets. Such transformation was also promoted by raising the incubation temperature or increasing the number of nanodroplets in the presence of HEMA. We speculated that crystal growth of CaCO3 crystals was induced by coalescence of nanodroplets and morphological transformation to rod-like shape was undertaken with an assistance of HEMA. In this way, we could tune the shapes of CaCO3 with the well-controlled size and aspect ratio by tuning environments in nanodroplets.Then, subsequent polymerization of HEMA, which was used as a monomer, was carried out for encapsulation of CaCO3 with rod-like morphologies inside polymer nanoparticles. As a result, spherical and spheroidal hybrid nanoparticles, which possessed homogeneity in size and shape, were obtained. Then, by spin-coating of hybrid nanoparticles onto the glass substrate, we could obtain a closely-packed particle monolayer.

Facile preparation of micro and nano-sized CaCO3 particles by a new CO2-storage material

A facile method was designed to synthesize CaCO3 particles with spindle morphology and an average diameter of 300nm from CaCl2 and CO2-storage material (CO2SM), in which CO2SM was used as both CO32– source and crystal modifier to prepare CaCO3 crystals. The effects of CO2SM concentration, Ca2+ concentration, and stirring time on crystallization behavior of CaCO3 were investigated. Except of the rapid production of CaCO3 particles, the filtered solution without CaCO3 precipitate could be reused to prepare CaCO3 particles with the additional CO2 and CaCl2. In addition, a self-assembly formation mechanism of vaterite CaCO3 particles also was proposed.

Cytotoxicity, Uptake Behaviors, and Oral Absorption of Food Grade Calcium Carbonate Nanomaterials.

Calcium is the most abundant mineral in human body and essential for the formation and maintenance of bones and teeth as well as diverse cellular functions. Calcium carbonate (CaCO3) is widely used as a dietary supplement; however, oral absorption efficiency of CaCO3 is extremely low, which may be overcome by applying nano-sized materials. In this study, we evaluated the efficacy of food grade nano CaCO3 in comparison with that of bulk- or reagent grade nano CaCO3 in terms of cytotoxicity, cellular uptake, intestinal transport, and oral absorption. Cytotoxicity results demonstrated that nano-sized CaCO3 particles were slightly more toxic than bulk materials in terms of oxidative stress and membrane damage. Cellular uptake behaviors of CaCO3 nanoparticles were different from bulk CaCO3 or Ca2+ ions in human intestinal epithelial cells, showing efficient cellular internalization and elevated intracellular Ca2+ levels. Meanwhile, CaCO3 nanoparticles were efficiently transported by microfold (M) cells in vitro model of human intestinal follicle-associated epithelium, in a similar manner as Ca2+ ions did. Biokinetic study revealed that the biological fate of CaCO3 particles was different from Ca2+ ions; however, in vivo, its oral absorption was not significantly affected by particle size. These findings provide crucial information to understand and predict potential toxicity and oral absorption efficiency of food grade nanoparticles.

One-pot to fabrication of calcium oxide/carbon foam composites for the adsorption of trace SO2

The trace SO2 in the atmosphere can cause serious degradation in performance of proton exchange membrane fuel cells. To mitigate this problem, calcium oxide/carbon foam composites were designed and fabricated via a facile one-pot method using phenol formaldehyde resin as the carbon precursor, with polyurethane foam as the template and nano-sized CaCO3 as the precursor of CaO. The composite shows a promising retention capacity for trace SO2 and enhanced cycle stability due to the combined effect of well-distributed CaO particles, the hierarchical porous structure and the anchoring effect of the carbon foam matrix. It has been demonstrated that the as-made composite is a promising adsorbent for the efficient removal of the trace SO2 from air, suggesting this composite can be a potential candidate for desulfurization of the air entering proton exchange membrane fuel cells.