Daniel Sutiman

One step synthesis of fluorescent carbon dots through pyrolysis of N-hydroxysuccinimide

Fluorescent carbon dots were prepared via a simple and straightforward one-step pyrolytic process using N-hydroxysuccinimide. The prepared C-dots present remarkable photoluminescence with blue to green shifting emission and absolute quantum yields varying from 14 to 31% as a function of the excitation wavelength and selected dispersion media. Interestingly, up-conversion from NIR to the visible range was not only instrumentally recorded but even visually observable. Further, the composition and morphology of the prepared C-dots were studied using XPS, FT-IR, Raman, P-XRD, DLS and AFM as investigation methods. Since the majority of C-dot studies are biased towards fluorescent labeling in cellular imaging, their photoluminescence properties, physicochemical stability and ease of fabrication are expected to play a key role in applications ranging from sensors to efficient solar energy conversion or high performance optoelectronic devices.

Removal of heavy metal ions from aqueous solutions using low-cost sorbents obtained from ash

This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu2+ per g of sorbent, 303 mg of Ni2+ per g of sorbent, and 1111 mg of Pb2+ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.

Highly luminescent europium and terbium complexes based on succinimide and N-hydroxysuccinimide

Abstract The preparation of two highly luminescent europium(III) and terbium(III) complexes with succinimide (SI) and N-hydroxysuccinimide (NHSI) were reported, which were further investigated through elemental chemical analysis, thermal analysis, FT-IR, powder X-ray diffraction, SEM and fluorescence spectroscopy. Data collected through these analysis revealed the formation of the Eu(III) and Tb(III) complexes with the above mentioned ligands at a metal to ligand (M:L) molar ratio of 1:3. Interesting conclusions regarding the efficient sensitization through the coordination site of the lanthanide luminescent centers were retained from the photoluminescent spectra investigation. Strong luminescence emission was observed in case of Eu(III)-SI and Tb(III)-NHSI complexes while the corresponding Eu(III)-NHSI and Tb(III)-SI complexes exhibited no photo luminescent properties. Newly obtained luminescent lanthanide complexes may be of particular interest for various applications in optoelectronics.

Removal of cadmium(II) from aqueous solution by adsorption onto modified algae and ash

Pollution with cadmium ions has serious negative consequences on human health and environment. Adsorption of low-cost materials represents a viable option for the removal of cadmium ions from aqueous media. In this study are comparatively discussed the adsorption behaviour of cadmium(II) on two low-cost materials, one of biologic nature (marine algae) and other of inorganic nature (ash), after their treatment with alkaline solution. The influence of contact time and initial cadmium ions concentration was studied in batch system, for each type of adsorbent. In optimum experimental conditions (solution pH of 5.0; adsorbent dose of 8 g L−1 ) and an initial cadmium concentration of 360mg L−1, the obtained uptake capacities reach to 34.15mg g−1 for the modified algae and to 43.12mg g−1 for the modified ash, respectively. The uptake data were analyzed using two isotherm models (Langmuir and Freundlich) and the models’ parameters were evaluated. The results indicate that t heLangmuir model provides the best correlation of experimental data for both adsorbents, and the maximum adsorption capacities were 41.8mg g−1 for modified algae and 48.0 mg g−1 for modified ash, respectively. The kinetics of the cadmium uptake was modelled using the pseudofirst order, pseudo-second order and intra-particle diffusion model equations. It was shown that the pseudo-second order kinetic equation could best describe the adsorption kinetics of cadmium ions, whatever the nature of adsorbent.

Electrochemical behaviour of Ti alloys containing Mo and Ta as β-stabilizer elements for dental application

Abstract Corrosion behaviour of the studied Ti12Mo and Ti60Ta alloys with the same Mo equivalent values (12%, mass fraction) together with the currently used metallic biomaterials Cp-Ti were investigated for dental applications. The electrochemical properties of the samples were examined using electrochemical techniques: such as open-circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS), in two electrochemical media of artificial saliva and fluoridated artificial saliva (0.1% fluoride ions, F − ) at 37 °C. Fluoride is commonly included in toothpastes, odontological gels and dental rinses to prevent dental caries and relieve dental sensitivity. The passive behaviour for all the titanium samples is observed for both solutions. The Ti60Ta alloy appears to possess superior corrosion resistance than the Ti12Mo and Cp-Ti in both electrochemical media.

Synthesis and Study of Some New Co(II) Polyphosphinates Determination of the Kinetic Parameters for the Thermal Decomposition Reactions

This paper reports the synthesis and study of some Co(II) coordination polymers with the following acids as ligands: 2,8-dimethylphenoxyphosphinic, diphenyloxyphosphinacetic, diphenylthiophosphinacetic and dihexylphosphinic acids. The study was performed by means of chemical analysis, gel chromatography, IR spectroscopy, ESR, X-ray diffraction, thermogravimetry and electric resistance measurements. The experimental results were used to propose the structural formulae of these compounds and to calculate the kinetic parameters of the thermal decomposition reactions.

Photoluminescent red, green and blue monoliths of new Eu(III), Tb(III) and Y(III) complexes embedded in silica matrix

Large transparent photoluminescent monoliths were prepared by embedding newly synthesized Eu(III), Tb(III) and Y(III) complexes with 2-(1H-1,2,4-Triazol-3-yl)pyridine ligand in silica matrices through a modified sol-gel process. The remarkable luminescent properties of the free complexes were preserved in silica matrix, resulting in red, green and blue monoliths with a shape that may be tailored during the gelation process according to specific applications. Prior to embedment, the complexes prepared at 1/3 metal to ligand ratio were investigated through elemental analysis, thermal analysis, FT-IR, mass and fluorescence spectroscopy while the obtained silica monoliths were supplementary investigated through SEM and fluorescence spectroscopy. The emission peaks are located at 612 nm for the monolithic silica embedded Eu(III) complex, at 542 nm for the monolithic silica embedded Tb(III) complex and at 482 nm respectively for the silica monolith containing the Y(III) complex. Their excellent photoluminescent properties may recommend them as photonic conversion materials in various optoelectronic applications.

Influence of caffeine and temperature on corrosion-resistance of CoCrMo alloy

The inhibitory activity of caffeine (1,3,7-trimethyl xanthine) on artificial saliva was studied on a CoCrMo alloy using different electrochemical methods: open circuit potential (OCP), potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). The results show that caffeine produces an inhibitory effect on the anodic currents due to its adsorption on the surface of the alloy. Temperature is another parameter with an influence on corrosion processes, so thermodynamic data were obtained from Arrhenius plots and Langmuir adsorption isotherms. The protective action of caffeine is enhanced at high temperatures at OCP, while for potentiodynamic experiments high temperatures block the inhibitory activity of caffeine and the corrosion rate increases. The process may also be studied by a simulation, determining the functional dependence between OCP, corrosion current density (icorr), corrosion potential (Ecorr), breakdown potential (Ebd) and temperature and amount of caffeine in artificial saliva, for Heraenium® CE. The neural network-based methodology applied in this work provides accurate results, thus proving to be an efficient modelling technique.

Experimental densities of binary mixtures: Acetic acid with benzene at several temperatures

Hydrocarbons are the most commonly used chemicals in the hydrocarbon processing industries. The knowledge of thermodynamic properties of various binary organic or inorganic mixtures is essential in many practical aspects concerning the mass transport and fluid flow. Such properties are important from the fundamental point of view to understand their mixing behaviour (molecular interactions), as well for practical applications (e.g. in the petrochemical industry). The density of acetic acid‐benzene mixtures at several temperatures (T = 296.15, 302.15, 308.15, 314.15 and 319.15 K) were measured over the whole composition range and atmospheric pressure, along with the physical‐chemical properties of the pure components (e.g. density, viscosity, refractive index at 298.15 K). The excess molar volumes at the above‐mentioned temperatures were calculated from experimental data and fitted by using a new polynomial equation comparing the results with the known equation of Redlich‐Kister. The excess volumes for ace...

ELECTROCHEMICAL AND SEM CHARACTERIZATION OF YsZ COATED CoCrMo ALLOY PROCESSED BY PLASMA SPRAYED TECHNIQUE

The CoCrMo alloys have been widely used in artificial knee or hip joints. It is well known that these materials have a good corrosion resistance and acceptable biocompatibility properties. Zirconia as a ceramic biomaterial facilitates the osteoconductivity and tissue osteogenetic capacity in new bone formation around implant. Linear polarization and electrochemical impedance spectroscopy (EIS) were employed to characterize the electrochemical behavior of plasma sprayed yttrium oxide stabilized zirconium oxide (YsZ) coated CoCrMo alloy in Ringer solution. Surface characterization before and after electrochemical testing was performed used scanning electron microscopy (SEM). YsZ-coated showed higher zero corrosion potential (ZCP) and lower corrosion current density (icorr) compared with the CoCrMo substrate. The electrochemical properties of the coated CoCrMo sample at the open circuit potential at different immersion time in Ringer solution were studied by EIS. Equivalent circuit (EC) was used to modeling EIS data, in order to characterize YsZ-coated CoCrMo surface.