R.M.G. Rajapakse

Facile synthesis of both needle-like and spherical hydroxyapatite nanoparticles: effect of synthetic temperature and calcination on morphology, crystallite size and crystallinity.

Synthetic hydroxyapatite (HA) nanoparticles, that mimic natural HA, are widely used as biocompatible coatings on prostheses to repair and substitute human bones. In this study, HA nanoparticles are prepared by precipitating them from a precursor solution containing calcium sucrate and ammonium dihydrogen orthophosphate, at a Ca/P mole ratio of 1.67:1, at temperatures, ranging from 10°C to 95°C. A set of products, prepared at different temperatures, is analyzed for their crystallinity, crystallite size, morphology, thermal stability and composition, by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopic techniques, while the other set is analyzed after calcining the respective products, soon after their synthesis, for 3h, at 700°C. The as-prepared products, after 2h of drying, without any calcination, are not crystalline, but they grow very slowly into needle-like morphologies, as they are ripened with time. The percentage crystallinity of the final products increases from 15% to 52%, with increasing the preparative temperature. The calcined samples always produce spherical nanoparticles of essentially the same diameter, between 90 nm and 100 nm, which does not change due to aging and preparative temperatures. Therefore, the same method can be utilized to synthesize both spherical and needle-like nanoparticles of hydroxyapatite, with well-defined sizes and shapes. The ability to use readily available cheap raw materials, for the synthesis of such well-defined crystallites of hydroxyapatite, is an added advantage of this method, which may be explored further for the scaling up of the procedures to suit to industrial scale synthesis of such hydroxyapatite nanoparticles.

Preparation of bone-implants by coating hydroxyapatite nanoparticles on self-formed titanium dioxide thin-layers on titanium metal surfaces

Preparation of hydroxyapatite coated custom-made metallic bone-implants is very important for the replacement of injured bones of the body. Furthermore, these bone-implants are more stable under the corrosive environment of the body and biocompatible than bone-implants made up of pure metals and metal alloys. Herein, we describe a novel, simple and low-cost technique to prepare biocompatible hydroxyapatite coated titanium metal (TiM) implants through growth of self-formed TiO2 thin-layer (SFTL) on TiM via a heat treatment process. SFTL acts as a surface binder of HA nanoparticles in order to produce HA coated implants. Colloidal HA nanorods prepared by a novel surfactant-assisted synthesis method, have been coated on SFTL via atomized spray pyrolysis (ASP) technique. The corrosion behavior of the bare and surface-modified TiM (SMTiM) in a simulated body fluid (SBF) medium is also studied. The highest corrosion rate is found to be for the bare TiM plate, but the corrosion rate has been reduced with the heat-treatment of TiM due to the formation of SFTL. The lowest corrosion rate is recorded for the implant prepared by heat treatment of TiM at 700 °C. The HA-coating further assists in the passivation of the TiM in the SBF medium. Both SMTiM and HA coated SMTiM are noncytotoxic against osteoblast-like (HOS) cells and are in high-bioactivity. The overall production process of bone-implant described in this paper is in high economic value.

Encapsulation of anticancer drug copper bis(8-hydroxyquinoline) in hydroxyapatite for pH-sensitive targeted delivery and slow release

There is a conspicuous progress in increasing anticancer drug delivery through the utilization of nanoparticles (NPs) as drug delivery agents. Hydroxyapatite (HA) gives improved clinical effectiveness of drugs by reducing systemic toxicity and broadening the spectrum of drug delivery since it is biocompatible and it can be targeted towards tumor cells. Herein, investigation of the potential of enhancing controlled drug release of the template model drug, copper bis-(8-hydroxyquinoline), by encapsulating it in hollow hydroxyapatite nano-carriers, is presented. Hydroxyapatite nanoparticles are synthesized by following four different routes to optimize its efficacy of drug loading. Copper bis-(8-hydroxyquinoline) is encapsulated by Method (a) which was effected by stirring the model drug and porous HA NPs in colloidal solution and Method (b) which was done during synthesis of hydroxyapatite nanoparticles in a solution of the model drug. In synthesizing nanoporous HA NPs, calcium carbonate is used as a template to create voids in HA. In each method, Ca/P ratio was ensured to be kept at 1.67:1. Appealing results are reported for the encapsulated product which was prepared by Method (a2). Method (a) was done at three different molar ratios of PO43-:CO32- and best result was obtained for that utilized 2.003:1 molar ratio (Method (a2).). It produced 98.67% of encapsulation efficiency and 2.9522mg/g of drug loading capacity. Release kinetics was studied at a range of pH values; the lower the pH of the medium the higher is the drug release. For instance, when considering the product which exhibited high encapsulation efficiency and high drug loading capacity, at pH3.5 during the first 8h it elicited about 13% of release, at pH5.0 about 8% release while at pH6.0 it was just 2.5%. During the 24-hour span, pH3.5 exhibited about 23.8%, at pH5.0 approximately 9% with an increasing trend of release and at pH6.0 showed a value just above 2.5%. As such, acidity of the cancerous cells can be made use to increase the drug slow-release kinetics at the vicinity of the cancer cells.

Improved performance of dye-sensitized solar cells using a diethyldithiocarbamate-modified TiO 2 surface

The surface modification of a TiO2 electrode with diethyldithiocarbamate (DEDTC) in dye-sensitized solar cells (DSSCs) was studied. Results fromX-ray photoelectron spectroscopy (XPS) indicate that over half of the sulfur atoms become positively charged after the DEDTC treatment of the TiO2 surface. DSSCs were fabricated with TiO2 electrodes modified by adsorbing DEDTC using a simple dip-coating process. The conversion efficiency of the DSSCs has been optimized to 6.6% through the enhancement of the short-circuit current density (JSC = 12.74 mA/cm2). This is substantially higher compared to the efficiency of 5.9% (JSC = 11.26 mA/cm2) for the DSSCs made with untreated TiO2 electrodes.

Urea-assisted synthesis of hydroxyapatite nanorods from naturally occurring impure apatite rocks for biomedical applications

Hydroxyapatite (HA) nanoparticles are heavily used materials in biomedical applications. Therefore, identification of cheap and readily available raw-materials for the synthesis of HA nanoparticles is very important to fulfill the current demand. Herein, for the first time, we have developed a novel method to convert readily available, extensively distributed, naturally occurring apatites into nontoxic hydroxyapatite nanoparticles for biomedical applications. In this method, powdered apatite is digested and combusted to produce calcium phosphate nanoparticles and hydrothermally treated to convert them into high purity HA. HA nanoparticles are characterized using X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Synthesized HA nanoparticles are nontoxic according to the cytotoxicity results which confirm their potential usage in biomedical applications. Therefore, this method is very important to fulfill the current demand of HA nanoparticles and for value-addition to natural apatite.

Preparation, characterization and oxygen reduction catalytic activities of nanocomposites of Co(II)/montmorillonite containing polypyrrole, polyaniline or poly(ethylenedioxythiophene)

Electronically conducting composites of cobalt(II)/conducting polymer/montmorillonite are synthesized through ion exchange of montmorillonite (MMT) followed by oxidative polymerization of the monomers such as aniline, pyrrole or ethylenedioxythiophene within the interlayer spaces of the clay particles using Co(III) as the oxidant. In these syntheses, bentonite clay is purified to obtain pure MMT containing Na+ interlayer cations. Then, cobalt(III) ions are exchanged for Na+ ions present within the interlayer spaces. Monomers (aniline, pyrrole or 3,4-ethylenedioxythiophene) are then added to the ion-exchanged MMT dispersions. Co(III) is then reduced to Co(II) while oxidatively polymerizing aniline, pyrrole or 3,4-ethylenedioxythiophene monomers to polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiphene) (PEDOT) respectively, thus forming Co(II)/MMT/PANI, Co(II)/MMT/PPY and Co(II)/MMT/PEDOT composite materials. These composites are characterized using XRD, XRF, FTIR, XPS, SEM and TGA analyses. These analyses show that in Co(II)/MMT/PANI and Co(II)/MMT/PPY composites the respective polymer and Co(II) ions are intercalated within the interlayer spaces of MMT while Co(II)/MMT/PEDOT shows exfoliated MMT platelets in the polymer/Co(II) matrix. The materials are also characterized for their electrical conductivities through DC conductivity measurements and AC impedance analyses and Co(II)/MMT/PANI, Co(II)/MMT/PPY and Co(II)/MMT/PEDOT have conductivities of 0.38 S m−1, 0.78 S m−1 and 0.32 S m−1 respectively. Electrochemical data depict that all three composites are good catalysts for the oxygen reduction half-reaction, and particularly Co(II)/MMT/PPY and Co(II)/MMT/PEDOT show good catalytic properties comparable to those of conventional and expensive C/Pt catalysts that are currently used in fuel cells. As such, very low-cost oxygen reduction catalysts for fuel cell applications can be realized with these clay/polymer/Co(II) systems.

Fabrication of ZnO nanoarchitectured fluorine-free robust superhydrophobic and UV shielding polyester fabrics for umbrella canopies

Mechanically robust, durable, fluorine-free superhydrophobic and UV shielding surfaces are fabricated on polyester umbrella canopy fabrics by self-assembly of stearic acid on zinc oxide (ZnO) nanoarchitectures on polyester fabrics. Drawbacks of conventional umbrella canopies including rain water penetration through the canopy during heavy rains, wet canopies taking too long to dry, and limited blockage of harmful UV radiation have been overcome with the surface modified canopy fabrics in the present study. Herein, in the typical synthesis, the polyester fabric is dipped in Zn(NO3)2u2006:u2006hexamethylenetetraamine (HMT), at 1u2006:u20061 molar ratio solution and heated at 100 °C for 2 h to grow ZnO nanoarchitectures on the fabric surface. Stearic acid is allowed to self-assemble by dipping the fabric in 1 g dm−3 stearic acid solution. The modified fabrics are characterized using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray fluorescence spectroscopic techniques. The modified fabrics show superhydrophobicity characterized by water contact angles over 150° with the optimum analyzed conditions. The superhydrophobic layer formed on the fabric is resistant to acid rain and stayed durable throughout 50 abrasion cycles and under 1.5 h strong surfactant washing. The developed method is useful to fabricate a smart umbrella canopy with acid rain resistant, durable, robust superhydrophobic and UV blocking properties.

Preparation and characterization of mesoporous hydroxyapatite with non-cytotoxicity and heavy metal adsorption capacity

Mesoporous hydroxyapatite (MPHA) particles have recently gained a great deal of interest in a broad range of fields including biomedical fields, wastewater treatment and catalysis. In this paper, we describe a novel and convenient route to synthesise MPHA particles using calcium carbonate nanoparticle templates for the formation of mesopores in HA. In this method, both nano-CaCO3 templates and HA are prepared simultaneously using calcium sucrate as a precursor by allowing the nano-CaCO3 to embed in HA. Mesopores in HA are obtained by removing the template. The porosity of HA is confirmed by Brunauer–Emmett–Teller (BET) analysis and the average pore size (below 50 nm) is determined from Transmission Electron Microscopy (TEM) images. The synthesized material is noncytotoxic as confirmed by cytotoxicity studies, which makes it a potential candidate as a biomaterial for biomedical applications. Furthermore, the MPHA shows a superior adsorption ability towards Pb2+ Ni2+ and Cd2+ in aqueous solutions, and could also be used as an environmental-friendly material for wastewater treatment and water purification. Therefore, we believe that this simple and novel synthesis route for the fabrication of porous HA could be useful in fulfilling the current demand for HA in biomedical and water purification applications.

Efficient dye-sensitized solar cells from mesoporous zinc oxide nanostructures sensitized by N719 dye

Dye-sensitized solar cells (DSCs) have attracted a great deal of attention due to their low-cost and high power conversion efficiencies. They usually utilize an interconnected nanoparticle layer of TiO2 as the electron transport medium. From the fundamental point of view, faster mobility of electrons in ZnO is expected to contribute to better performance in DSCs than TiO2, though the actual practical situation is quite the opposite. In this research, we addressed this problem by first applying a dense layer of ZnO on FTO followed by a mesoporous layer of interconnected ZnO nanoparticle layer, both were prepared by spray pyrolysis technique. The best cell shows a power conversion efficiency of 5.2% when the mesoporous layer thickness is 14 μm and the concentration of the N719 dye in dye coating solution is 0.3 mM, while a cell without a dense layer shows 4.2% under identical conditions. The surface concentration of dye adsorbed in the cell with a dense layer and that without a dense layer are 5.00 × 10−7 and 3.34 × 10−7 mol/cm2, respectively. The cell with the dense layer has an electron lifetime of 54.81 ms whereas that without the dense layer is 11.08 ms. As such, the presence of the dense layer improves DSC characteristics of ZnO-based DSCs.

Heterogeneous photocatalytic degradation of toluene in static environment employing thin films of nitrogen-doped nano-titanium dioxide

Photocatalytic semiconductor thin films have the ability to degrade volatile organic compounds (VOCs) causing numerous health problems. The group of VOCs called “BTEX” is abundant in houses and indoor of automobiles. Anatase phase of TiO2 has a band gap of 3.2xa0eV and UV radiation is required for photogeneration of electrons and holes in TiO2 particles. This band gap can be decreased significantly when TiO2 is doped with nitrogen (N-TiO2). Dopants like Pd, Cd, and Ag are hazardous to human health but N-doped TiO2 can be used in indoor pollutant remediation. In this research, N-doped TiO2 nano-powder was prepared and characterized using various analytical techniques. N-TiO2 was made in sol–gel method and triethylamine (N(CH2CH3)3) was used as the N-precursor. Modified quartz cell was used to measure the photocatalytic degradation of toluene. N-doped TiO2 nano-powder was illuminated with visible light (xenon lamp 200xa0W, λu2009=u2009330–800xa0nm, intensityu2009=u20091 Sun) to cause the degradation of VOCs present in static air. Photocatalyst was coated on a thin glass plate, using the doctor-blade method, was inserted into a quartz cell containing 2.00xa0µL of toluene and 35xa0min was allowed for evaporation/condensation equilibrium and then illuminated for 2xa0h. Remarkably, the highest value of efficiency 85% was observed in the 1 μm thick N-TiO2 thin film. The kinetics of photocatalytic degradation of toluene by N-TiO2 and P25-TiO2 has been compared. Surface topology was studied by varying the thickness of the N-TiO2 thin films. The surface nanostructures were analysed and studied with atomic force microscopy with various thin film thicknesses.