A novel approach for continuous synthesis of calcium carbonate using sequential operation of two sonochemical reactors

A novel continuous process for the synthesis of calcium carbonate based on precipitation reaction has been developed involving the sequential operation of two sonochemical reactors for the first time. The reactors were also operated as control (conventional approach without ultrasound) to clearly establish the process intensification benefits due to the use of ultrasound. The effect of different operating parameters such as Ca(OH)₂ concentration, CO₂ flow rate and Ca(OH)₂ slurry flow rate on the particle size has been investigated. The obtained calcite particles were characterized using Fourier transform infrared (FTIR), wide angle X-ray diffraction (XRD) and particle size distribution (PSD) analysis. The morphology of the obtained particles was also analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was established that the average particle size obtained in the presence of ultrasound was smaller with much narrow size distribution as compared to the conventional approach. Further, the average particle size was established to decrease with an increase in the Ca(OH)₂ slurry concentration and CO₂ flow rate with the optimum conditions giving a particle size of 164nm. The particle size was also influenced by the Ca(OH)₂ slurry flow rate and under optimum condition of Ca(OH)₂ slurry flow rate as 24mL/min, particle size of 135nm was obtained. Only calcite phase of CaCO₃ was observed to be formed as established based on the XRD analysis during both the synthesis approaches confirming the stability of the obtained particles. It was also observed that the shape of the crystals varied with the method of synthesis. Rhombohedral calcite particles were formed in the presence of ultrasound whereas the conventional stirring method resulted in spindle shaped particles. Overall, the utility of the ultrasound assisted approach has been clearly established with novel results based on the use of sonochemical reactors in series.

Shape control of inorganic nanoparticles from solution

Inorganic materials with controllable shapes have been an intensely studied subject in nanoscience over the past decades. Control over novel and anisotropic shapes of inorganic nanomaterials differing from those of bulk materials leads to unique and tunable properties for widespread applications such as biomedicine, catalysis, fuels or solar cells and magnetic data storage. This review presents a comprehensive overview of shape-controlled inorganic nanomaterials via nucleation and growth theory and the control of experimental conditions (including supersaturation, temperature, surfactants and secondary nucleation), providing a brief account of the shape control of inorganic nanoparticles during wet-chemistry synthetic processes. Subsequently, typical mechanisms for shape-controlled inorganic nanoparticles and the general shape of the nanoparticles formed by each mechanism are also expounded. Furthermore, the differences between similar mechanisms for the shape control of inorganic nanoparticles are also clearly described. The authors envision that this review will provide valuable guidance on experimental conditions and process control for the synthesis of inorganic nanoparticles with tunable shapes in the solution state.

Application of ionomics to plant and soil in fields under long-term fertilizer trials

Ionomics is the study of elemental accumulation in living organisms using high-throughput elemental profiling. In the present study, we examined the ionomic responses to nutrient deficiency in maize grown in the field in long-term fertilizer trials. Furthermore, the available elements in the field soils were analyzed to investigate their changes under long-term fertilizer treatment and the ionomic relationships between plant and soil. Maize was cultivated in a field with the following five long-term fertilizer treatments: complete fertilization, fertilization without nitrogen, without phosphorus, without potassium, and no fertilization. Concentrations of 22 elements in leaves at an early flowering stage and in soils after harvest were determined. The fertilizer treatments changed the availabilities of many elements in soils. For example, available cesium was decreased by 39 % and increased by 126 % by fertilizations without nitrogen and potassium, respectively. Effects of treatments on the ionome in leaves were evaluated using the translocation ratio (the concentration in leaves relative to the available concentration in soils) for each element. Nitrogen deficiency specifically increased the uptake ability of molybdenum, which might induce the enhancement of nitrogen assimilation and/or endophytic nitrogen fixation in plant. Potassium deficiency drastically enhanced the uptake ability of various cationic elements. These elements might act as alternatives to K in osmoregulation and counterion of organic/inorganic anions. Two major groups of elements were detected by multivariate analyses of plant ionome. Elements in the same group may be linked more or less in uptake and/or translocation systems. No significant correlation between plant and soil was found in concentrations of many elements, even though various soil extraction methods were applied, implying that the interactions between the target and other elements in soil must be considered when analyzing mineral dynamics between plant and soil.