K. Byrappa

Nanoparticles synthesis using supercritical fluid technology - towards biomedical applications.

Supercritical fluid (SCF) technology has become an important tool of materials processing in the last two decades. Supercritical CO(2) and H(2)O are extensively being used in the preparation of a great variety of nanomaterials. The greatest requirement in the application of nanomaterials is its size and morphology control, which determine the application potential of the nanoparticles, as their properties vary significantly with size. Although significance of SCF technology has been described earlier by various authors, the importance of this technology for the fabrication of inorganic and hybrid nanomaterials in biomedical applications has not been discussed thoroughly. This review presents the nanomaterial preparation systematically using SCF technology with reference to the processing of biomedical materials. The basic principles of each one of the processes have been described in detail giving their merits and perspectives. The actual experimental data and results have been discussed in detail with respect to the selected nanomaterials for biomedical applications. The SCF synthesis of nanoparticles like phosphors, magnetic materials, carbon nanotubes, etc. have been discussed as they have potential applications in bio-imaging, hyperthermia, cancer therapy, neutron capture therapy, targeted drug delivery systems and so on. The more recent approach towards the in situ surface modification, dispersibility, single nanocrystal formation, and morphology control of the nanoparticles has been discussed in detail.

Mechanochemical-hydrothermal synthesis of carbonated apatite powders at room temperature

Crystalline carbonate- and sodium-and-carbonate-substituted hydroxyapatite (CO3HAp and NaCO3HAp) powders were prepared at room temperature via a heterogeneous reaction between Ca(OH)2/CaCO3/Na2CO3 and (NH4)2HPO4 aqueous solution using the mechanochemical hydrothermal route. X-ray diffraction, infrared spectroscopy, thermogravimetry, and chemical analysis were performed. Room temperature products were phase-pure CO3HAp and NaCO3HAp containing 0.8-12 wt% of carbonate ions in the lattice. Dynamic light scattering revealed that the median agglomerate size of the room temperature CO3HAp and NaCO3HAp powders was in the range of 0.35-1.6 microm with a specific surface area between 82 and 121 m2/g. Scanning and transmission electron microscopy confirmed that the carbonated HAp powders consisted of mostly submicron aggregates of nanosized, approximately 20 nm crystals. The synthesized carbonated apatite powders exhibit chemical compositions and crystallinities similar to those of mineral constituents of hard tissues and therefore are promising for fabrication of bone-resembling implants.

Photocatalytic degradation of rhodamine B dye using hydrothermally synthesized ZnO

The sunlight mediated photocatalytic degradation of rhodamine B (RB) dye was studied using hydrothermally prepared ZnO (T = 150°C andP ∼ 20–30 bars). Zinc chloride was used as the starting material along with sodium hydroxide as a solvent in the hydrothermal synthesis of ZnO. Different durations were tried to obtain pure ZnO phase, which was later confirmed through powder X-ray diffraction. The photocatalytic behaviour of the prepared ZnO was tested through the degradation of RB. The disappearance of organic molecules follows first-order kinetics. The effect of various parameters such as initial dye concentration, catalyst loading, pH of the medium, temperature of the dye solution, on the photo degradation of RB were investigated. The thermodynamic parameters of the photodegradation of RB, like energy of activation, enthalpy of activation, entropy of activation and free energy of activation revealed the efficiency of the process. An actual textile effluent containing RB as a major constituent along with other dyes and dyeing auxiliaries was treated using hydrothermally synthesized ZnO and the reduction in the chemical oxygen demand (COD) of the treated effluent revealed a complete destruction of the organic molecules along with colour removal.

Solution synthesis of hydroxyapatite designer particulates

Abstract This paper reviews our research program for intelligent synthesis of hydroxyapatite (HAp) designer particulates by low-temperature hydrothermal and mechanochemical–hydrothermal methods. Our common starting point for hydrothermal crystallization is the generation and validation of equilibrium diagrams to derive the relationship between initial reaction conditions and desired phase assemblage(s). Experimental conditions were planned based on calculated phase boundaries in the system CaO–P2O5–NH4NO3–H2O at 25–200 °C. HAp powders were then hydrothermally synthesized in stirred autoclaves at 50–200 °C and by the mechanochemical–hydrothermal method in a multi-ring media mill at room temperature. The synthesized powders were characterized using X-ray diffraction, infrared spectroscopy, thermogravimetry, chemical analysis and electron microscopy. Hydrothermally synthesized HAp particle morphologies and sizes were controlled through thermodynamic and non-thermodynamic processing variables, e.g. synthesis temperature, additives and stirring speed. Hydrothermal synthesis yielded well-crystallized needle-like HAp powders (size range 20–300 nm) with minimal levels of aggregation. Conversely, room-temperature mechanochemical–hydrothermal synthesis resulted in agglomerated, nanosized (∼20 nm), mostly equiaxed particles regardless of whether the HAp was stoichiometric, carbonate-substituted, or contained both sodium and carbonate. The thermodynamic model appears to be applicable for both stoichiometric and nonstoichiometric compositions. The mechanochemical–hydrothermal technique was particularly well suited for controlling carbonate substitution in HAp powders in the range of 0.8–12 wt.%. The use of organic surfactants, pH or nonaqueous solvents facilitated the preparation of stable colloidal dispersions of these mechanochemical–hydrothermal-derived HAp nanopowders.

Decomposition of silicon carbide in the presence of organic compounds under hydrothermal conditions

The synthesis of different carbon polymorphs such as under hydrothermal conditions through decomposition of graphite, diamond, amorphous carbon or diamond-like silicon carbide in the presence of organic compounds carbon, fullerenes, carbon nanotubes, etc., has attracted instead of pure water. The organic compounds decompose considerable interest for a long time because of their into various C–O–H fluids; the main components are CO, importance in science and technology. There are great OH, CO , and C H radicals. It is very well known that 2 1 x uncertainties about the phase stabilities of these polythese fluids play a significant role in creating a highly morphs as some of them do not find a place in the carbon reducing environment in the system and also assist in the pressure–temperature (P–T ) diagram and are also known dissociation of silicon carbide and precipitation of the for their contrasting physical properties. The exact carbon phase. physico–chemical phenomena responsible for their formaHydrothermal experimental runs were carried out in the tion are yet to be understood. Attempts to synthesize these pressure–temperature range of 100–200 MPa and 600– forms with varied conditions and techniques, sometimes 8508C employing conventional Roy–Tuttle reactor vessels even violating the thermodynamic principles, have met and gold tubes. The starting materials such as silicon with a fair amount of success. The stabilities of graphite carbide and organic compounds in 1:1 mol were encapsuand diamond in nature were mainly controlled by P–T– lated in gold tubes and placed them in the reactor vessels fO in the C–O–H system [1–6]. The role of C–O–H after ensuring for any leakage. The silicon carbide used in 2 fluids [7,8], as well as the hydrothermal and organic origin the present study is fine grained b-SiC powder with a 2 21 [9,10] of these polymorphs, especially with reference to specific area of less than 8 m g , and the organic diamond genesis, prompted the material scientists to compounds used in the present investigation are malonic explore the possibility of synthesizing them at fairly low acid, glycolic acid, citric acid, sucrose, formic acid, acetic pressure and temperature conditions. The hydrothermal acid, ascorbic acid, succinic acid and malic acid. All these technique is highly promising for reactions involving compounds are of pure reagent grade chemicals from volatiles as they attain the supercritical fluid state and Wako and Kanto, Japan. The experiments were quenched supercritical fluids are known for their greater ability to after 40–80 h. The capsules were cut open and the run dissolve non-volatile solids [11]. Silicon carbide powder products were dried and examined under an optical microhas been used for the synthesis of carbon polymorphs scope. It is interesting to note that sufficient gas evolved [12–14], and Gogotsi et al. [15] have reported decomposiwith a pungent smell while opening the capsule, which tion of silicon carbide in supercritical water and discussed indicates the capsule was intact during the run and possibly the formation of various carbon polymorphs. Here we the presence of CH (methane) as one of the gas phases 4 explore the possibility of producing carbon polymorphs inside the capsule. The run products were further characterized by Cu K X-ray diffraction (XRD), scanning a electron microscopy (SEM) and micro Raman spectros*Corresponding author. 1 E-mail address: bbmysore@yahoo.com (B. Basavalingu). copy (Ar laser).

Synthesis, characterization, and dispersion properties of hydroxyapatite prepared by mechanochemical–hydrothermal methods

Thermodynamic modeling was utilized to identify reaction conditions to prepare phase-pure hydroxyapatite particulates (HA) by mechanochemical–hydrothermal (M–H) methods using Ca(OH)2 and (NH4)2HPO4 as precursors. The resulting HA powders were characterized by X-ray diffraction, infra-red spectroscopy, thermogravimetry, and transmission electron microscopy, nitrogen adsorption and dynamic light scattering methods. Choosing reaction conditions in the 99% yield region of the CaO–P2O5–NH4OH–H2O phase-pure equilibrium system, nearly stoichiometric and nanostructured HA powders were prepared at room temperature in as little as 1 h. The minimum time to obtain phase-pure HA was 8 h from the conventional attrition mill. As-prepared powders were found to be highly agglomerated with a mass-weighted mean diameter of 2.6 µm in deionized water and average agglomeration number (AAN) as high as 4.5 × 106. Dispersion studies revealed that the appropriate use of dispersants could reduce the mass-weighted mean diameter and AAN. In the presence of sodium polyacrylate, the mass-weighted mean diameter and AAN were 217 nm and 1600, respectively.

Crystallization and characterization of Na2(La,Me)Zr(PO4)3.

Na2(La, Me)Zr[PO4]3 (where Me=Co, Al, Cr) crystals have been grown by three methods: by chemical reaction; from highly concentrated phosphoric acid solutions; and by a hydrothermal technique. The advantages and disadvantages of each method to obtain these crystals have been discussed. Morphological, X-ray, chemical analysis and IR-spectral studies were performed on these crystals.

Photocatalytic treatment of municipal wastewater using modified neodymium doped TiO2 hybrid nanoparticles.

Photocatalytic degradation of municipal wastewater was investigated using reagent grade TiO2 and modified neodymium doped TiO2 hybrid nanoparticles. For the first time, surface modification of Nd3 + doped TiO2 hybrid nanoparticles were carried out with n-butylamine as surface modifier under mild hydrothermal conditions. The modified nanoparticles obtained were characterized by Powder XRD, FTIR, DLS, TEM, BET surface area, zeta potential and UV-Vis Spectroscopy. The characterization results indicated better morphology, particle size distribution and low agglomeration of the nanoparticles synthesized. It was found that photodegradation of wastewater using surface modified neodymium doped TiO2 nanoparticles was more compared to pure TiO2, which can be attributed to the doping and modification with n-butylamine.

Hydrothermal Preparation of TiO2 and Photocatalytic Degradation of Hexachlorocyclohexane and Dichlorodiphenyltrichloromethane

Photocatalytic TiO2 was prepared as monodispersed fine particles under mild hydrothermal conditions (T = 150°C, P = ∼ 40 bars). Active elements like W, were introduced into the structure of TiO2 up to 10 wt% in order to obtain enhanced photocatalytic activity in the title compound. The influence of various growth parameters such as pH of the media, crystallization temperature, type of solvent, % fills (pressure) and the type of starting material were studied with reference to the quality of the resultant product and its photocatalytic activity. The disintegration of hexachlrocyclohexane (HCCH) and dichlorodiphenyltrichloroehtane (DDT) was studied using TiO2, and we have proposed the photocatalytic reaction mechanism for the first time. Natural sunlight was used as the main light source in the photocatalytic reaction.

Hydrothermal synthesis of mixed phosphates of neodymium and alkaline metals (Me2O·Nd2O3·4P2O5)

The phase formation in the system Me2O-Nd2O3-P2O5-H2O (where Me = Li, Na, K, Rb and Cs) has been studied under hydrothermal conditions in the temperature and pressure range 300 to 700‡ C and 0.5 to 600 atm, respectively, using vitreous carbon glass liners. A composition diagram showing the possible fields of crystallization of different phases under equilibrium conditions is given. AB-diagrams of fields of crystallization of different phases in the system investigated are given. These diagrams are in correspondence with the theoretical composition diagram. The advantages and disadvantages of different methods employed in the growth of MeNd-phosphates are discussed. The crystals obtained were characterized by various methods.