High-gravity Method Research Articles

Preparation of Mn-FeOX/ZSM-5 by high-gravity method for heterogeneous catalytic ozonation of nitrobenzene

Mn-FeOX/ZSM-5 is a good catalyst for wastewater treatment, but the conventional methods for preparing Mn-FeOX/ZSM-5 have the problems of non-uniform dispersion of active components and long preparation time. As the liquid-solid mass transfer process could be effectively increased in a high-gravity field, Mn-FeOX/ZSM-5 was prepared by high-gravity method in this study, and its properties were characterized by XRD, FTIR and SEM. The stability of Mn-FeOX/ZSM-5 and the loss of active components were investigated, and the mechanism of Mn-FeOX/ZSM-5 catalyzed the ozonation of nitrobenzene (NB) was also discussed. The results show that the specific surface area of Mn-FeOX/ZSM-5-h is 292.103 m2/g and the active components are well dispersed. Mn-FeOX/ZSM-5-h has the best catalytic activity under the conditions of precursor solution concentration = 0.3 mol/L, liquid flow rate = 60 L/h, and high gravity factor β = 30, and the removal efficiency of TOC reaches 87.5% within 25 min. The catalyst has good stability and only 1.10% of Mn and 0.63% of Fe are lost on average after 5 cycles. However, the removal rate of NB is significantly reduced with the addition of tert-butyl alcohol (TBA), implying that ·OH plays a dominant role in catalytic ozonation of NB by Mn-FeOX/ZSM-5. The electron paramagnetic resonance results confirm that ·OH is produced in the degradation process. In conclusion, Mn-FeOX/ZSM-5-h prepared by high-gravity method is a good catalyst for catalytic ozonation of NB because of its high catalytic activity and stability.

Preparation of Fe-MnOX/AC by high gravity method for heterogeneous catalytic ozonation of phenolic wastewater

• The preparation of Fe-MnO X /AC by high gravity technology was firstly proposed. • Fe-MnO X /AC(RPB) had more uniform active components compared with Fe-MnO X /AC(STR). • The redox cycle of Mn(IV)/Mn(III) and Fe(III)/Fe(II) synergistically activated O 3. • The catalytic process followed ·OH mechanism and was verified by EPR technology. • The η TOC of Fe-MnO X /AC/O 3 (RPB) was 7% higher than that of Fe-MnO X /AC/ O 3 (STR). In this study, activated carbon (AC) -supported Fe-Mn oxides (Fe-MnO X /AC) were prepared by high gravity method for heterogeneous catalytic ozonation of phenolic wastewater. The properties, catalytic performance and mechanism of Fe-MnO X /AC were investigated. It was found that Mn and Fe were successfully loaded on the surface of AC in the form of Fe 2 O 3 , Fe 3 O 4 and MnO 2 . The metal oxides were well dispersed and had a uniform particle size distribution, and the catalyst had a unique microporous structure. The mineralization rate of phenol by Fe-MnO X /AC/O 3 (RPB) was increased by 56% and 7% compared with that by ozone alone and Fe-MnO X /AC/O 3 (STR), respectively. The treatment time was only 45 min for Fe-MnO X /AC(RPB) but 10 h for Fe-MnO X /AC(STR). The high gravity technology enhanced the interphase mass transfer and the preparation efficiency of the catalyst because of its excellent micromixing performance. The XPS results showed charge transfer between Mn(IV)/Mn(III), Mn(III)/Mn(II) and Fe(III)/Fe(II). Mn(IV) and Fe(III) were the active sites that could generate oxygen vacancies to promote the adsorption and decomposition of O 3 . The electron paramagnetic resonance (EPR) detected the ·OH signal peak by comparing the intensity of free radicals. Fe-MnO X /AC(RPB) enhanced the production of ·OH from O 3 , supporting the catalytic mechanism of Fe-MnO X /AC(RPB) on O 3 . In conclusion, the high gravity method provides a new means for industrial production of supported catalysts.

Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300±70nm to 90±20nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80±10nm to 13±5nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO3) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.

Synthesis of Ultrafine SrCO<sub>3</sub> Powders by High Gravity

A new synthetic technology of Strontium carbonate with high gravity is introduced in this paper. We got ultrafine SrCO3 powders with Sr(NO3)2 and NaCO3 or CO2 as raw material by high gravity method. We studied flows, the rotating speed, additives and CO2 as the reactants on the morphology of strontium carbonate. The results show that the presence of additive-free, we got rod-like structure of strontium carbonate. Added EDTA, we got a good dispersion of spherical particles of narrow particle size distribution. The presence of EDTA, the average particle size of spherical particles decreases with the speed increases. CO2 alternative Na2CO3 as the reactants, the presence of additive-free, we got the bundle structure of strontium carbonate. The presence of EDTA, we got spherical particles, but the particle dispersion is not well, gathered together.

Template-Free Growth of Novel Hydroxyapatite Nanorings: Formation Mechanism and Their Enhanced Functional Properties

Template-free, single crystalline novel hydroxyapatite (HAp) nanorings with an inner diameter of 70 nm were grown by a combined high gravity and hydrothermal approach. Nanodisks were suggested to be formed by oriented aggregation and Ostwald ripening of mostly calcium pyrophosphate nanospheres prepared initially by the high gravity method with a stepwise increase of flow rate of phosphate solution. The prolonged hydrothermal treatment of nanodisks appeared to induce the nanoring formation via acid penetration along the dislocations in HAp nanodisks. The presence of edge dislocations in the central region of nanodisks was confirmed by high resolution transmission electron microscopy. The mechanical evaluation of high molecular weight polyethylene (HMWPE) composite with various shaped HAp nanocrystals and in vitro cellular analysis of HAp nanocrystals revealed that mechanical and bioactive performances improved with an increase of the specific surface area of HAp nanocrystals. The enhanced mechanical performance of HMWPE/HAp nanoring composite and the excellent cell viability for HAp nanorings are attributed to the superior interface bonding and cell activity, respectively, both of which are enhanced by the high specific surface area.

Multifunctional properties of hydroxyapatite/titania bio-nano-composites: bioactivity and antimicrobial studies

Hydroxyapatite/titania bio-nano-composites with different ratios have been successfully synthesized by combined high gravity and hydrothermal approaches. Initial colloidal nanoparticles were prepared by high gravity method and then the nanoparticles were treated hydrothermally. Detailed characterization was carried out by using XRD, FESEM and TEM analysis. Bioactive nature of the nanocomposites was analyzed by using osteoblast-like Chinese hamster ovary cells (CHO-K1, Korean Collection for Type Cultures). HAp/TiO2 nanocomposites showed good bioactivity for higher HAp content. Antimicrobial property of the bio-nano-composite was carried out by well-diffusion method against pathogenic organisms such as Escherichia coli (E. coli-Gram negative) and Staphylococcus aureus (S. aureus‐Gram positive). The antimicrobial property increased upon the increase of the TiO2 concentration, but at a particular composition the property was better than the pure TiO2. Also the antimicrobial property was more pronounced with the positive bacteria than the negative one. The results showed that the bioactivity and antimicrobial property changed inversely depending upon the HAp/TiO2composite ratio.

Large scale synthesis of hydroxyapatite nanospheres by high gravity method

Hydroxyapatite (HAp) nanospheres were synthesized in large scale using high gravity method. The effects of flow rates (300, 500 and 700 mL/min) and rotating speeds (1000, 2000 and 3000 rpm) on the size, distribution and morphology of nanoparticles were studied. The liquid flow rate and rotation speed was found to have a great influence on the formation of nanoparticles and uniform size distribution. The particle size decreased with an increase in the rotation speed of the RPB. The particle size was observed to be smaller at a lower liquid flow rate compared to that of the high liquid flow rate. TEM images of the granular HAp nanoparticles clearly displayed the spherical shape of nanoparticles. Densely assembled arranged nanospheres with diameters of 20–40 nm were observed at various rpm values. The obtained nanospheres appeared to be single crystalline from the image and SAED pattern analyses. In vitro cellular analysis showed very good improvement in the cell adhesion. For mechanical analysis, HAp/HMWPE composite was fabricated. The smaller size of HAp particles provided a relatively homogenous mixture of HAp and HMWPE which ensured the good mechanical strength.

Synthesis of nanosized Y-type TiOPc by a high gravity method

Oxotitanium phthalocyanine (TiOPc) is an ideal photoconductive material and electrophotographic photoreceptor since it exhibits remarkable absorption and photosensitivity properties in the visible and near-infrared wavelength region, which lead to the generation of free carriers with a high quantum yield [1]. It was reported that Y-type TiOPc had the most excellent photosensitive properties among five typical crystal forms of TiOPc [2–7]. In conventional routes, TiOPc of other crystal forms are usually synthesized and then transformed to Y-type TiOPc by processes such as thermomechanical, solvent, acid treatment and mechanical grinding. Solvent treatment is preferred among these processes due to its convenience and high efficiency where TiOPc is subjected to crystal transformation in the presence of water, aromatic compounds, alcohol, ketone, ether and their derivatives. Since Chen et al. [8] reported that photoconductivity of TiOPc depended on particle size, many works have been directed to obtaining nanosized Y-type TiOPc by different methods. In this paper, Y-type TiOPc is synthesized under high gravity environment created by a rotating packed bed (RPB) reactor, which can greatly intensify micromixing and mass transfer between fluids. Advantages of the high gravity method in synthesizing nanosized inorganic materials have been reported in our previous works [9, 10].

Synthesis and application of nanoparticles by a high gravity method

Synthesis and application of nanoparticles by a high gravity method