Patrick Ndungu

Pharmaceutical residues in water and sediment of Msunduzi River, KwaZulu-Natal, South Africa

The little data about pharmaceutical residue contamination in African water bodies motivated our study on the occurrence of pharmaceutical residues in the water and sediment of Msunduzi River in the KwaZulu-Natal province of South Africa; and in the Darvill wastewater treatment plant found in Msunduzi catchment. Samples collected along the River and wastewater treatment plant were extracted and analysed for pharmaceutical residues selected based on statistics of drug usage in South Africa i.e. antipyretics, antibiotics, caffeine, an antiepileptic and an antipsychotic drug were determined using HPLC-MS/MS. In all the matrices investigated, the antipyretic ibuprofen had the highest concentration of up to 117 μg L(-1), 84.60 μg L(-1) and 659 ng g(-1) in wastewater, surface water and sediment respectively. Antibiotics were detected in generally low concentrations of<10 μg L(-1) in surface water samples and up to 34.50 μg L(-1) in wastewater; moreover they were not completely removed during wastewater treatment. The percentage removal efficiency of the studied group was 6.55-98.00% for antipyretics, 73.33-98.90% for antibiotics, 48.80% for the anti-epileptic drug and 86.40% for Caffeine. Clozapine exhibited a negative removal. In surface water, Henley dam exhibited a high concentration of the pharmaceutical residues and the highest concentration of metronidazole in sediment (up to 1253.50 ng g(-1)) detected. Metronidazole was only detected in sediment and bio-solids.

Pyrrolic nitrogen-doped carbon nanotubes: physicochemical properties, interactions with Pd and their role in the selective hydrogenation of nitrobenzophenone

Nitrogen-doped carbon nanotubes (N-CNTs) containing 63%, 73% and 80% pyrrolic-N were synthesized and used to evaluate the influence of pyrrolic nitrogen on the physicochemical properties and catalytic activity of Pd supported on N-CNTs (Pd/N-CNTs). Micrographs of Pd/N-CNTs showed that Pd was located along the defect sites of N-CNTs indicating strong Pd-support interactions. X-ray photoelectron spectroscopy revealed that the abundance of Pd0 decreased while that of Pd2+ increased as the quantity of pyrrolic nitrogen increased. The Pd2+ species were formed as Pd–N coordination complexes, which stabilized Pd2+ nanoparticles. Selective hydrogenation of nitrobenzophenone to aminobenzophenone or p-benzylaniline was used to evaluate the catalytic performance of catalysts. Pd/N-CNTs exhibited a higher selectivity towards aminobenzophenone than Pd on carbon nanotubes and Pd on activated carbon. The enhanced selectivity towards nitro-reduction alone, observed with Pd/N-CNTs was attributed to the promoting effect of pyrrolic-N. Hence, Pd/N-CNTs are promising catalysts for the selective reduction of nitro arenes.

Ionic self-assembly of porphyrin nanostructures on the surface of charge-altered track-etched membranes

Track-etched polymer membranes are typically used as templates in the synthesis of various nanowires or nanotubes arrays. The unique advantages of track-etched membranes, such as uniform pore structure, excellent porosity, easily tailored pore sizes, and a well characterized surface chemistry, may find use in self-assembly strategies where colloidal nanostructures can be tethered to a suitable substrate to produce devices of interest. Meso-tetrakis(4-phenylsulfonicacid)porphyrin dihydrochloride and Sn(IV) tetrakis(4-pyridyl)porphyrin were used to synthesize ionic self-assembled porphyrin nanorods. The track-etched membranes surface charge was changed from negative to positive using polyethyleneimine. The porphyrin nanorods were either filtered through or self-assembled onto the surface of track-etched membranes. Comparisons were made with track-etched membranes modified with, and without, polyethyleneimine. Assembly of the porphyrin nanotubes only occurred on the surface of positively charged track-etched membranes, and filtration of the porphyrin nanorods produced a mesh-like structure on the surface of the membrane irrespective of the track-etched membrane pore diameter. In each case the characteristic absorbance profiles of the porphyrin nanorods was maintained. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and UV-vis spectroscopy were used to characterize the various systems.

Hall Measurements on Carbon Nanotube Paper Modified With Electroless Deposited Platinum

Carbon nanotube paper, sometimes referred to as bucky paper, is a random arrangement of carbon nanotubes meshed into a single robust structure, which can be manipulated with relative ease. Multi-walled carbon nanotubes were used to make the nanotube paper, and were subsequently modified with platinum using an electroless deposition method based on substrate enhanced electroless deposition. This involves the use of a sacrificial metal substrate that undergoes electro-dissolution while the platinum metal deposits out of solution onto the nanotube paper via a galvanic displacement reaction. The samples were characterized using SEM/EDS, and Hall-effect measurements. The SEM/EDS analysis clearly revealed deposits of platinum (Pt) distributed over the nanotube paper surface, and the qualitative elemental analysis revealed co-deposition of other elements from the metal substrates used. When stainless steel was used as sacrificial metal a large degree of Pt contamination with various other metals was observed. Whereas when pure sacrificial metals were used bimetallic Pt clusters resulted. The co-deposition of a bimetallic system upon carbon nanotubes was a function of the metal type and the time of exposure. Hall-effect measurements revealed some interesting fluctuations in sheet carrier density and the dominant carrier switched from N- to P-type when Pt was deposited onto the nanotube paper. Perspectives on the use of the nanotube paper as a replacement to traditional carbon cloth in water electrolysis systems are also discussed.

Bulk Heterojunction Solar Cell with Nitrogen-Doped Carbon Nanotubes in the Active Layer: Effect of Nanocomposite Synthesis Technique on Photovoltaic Properties

Nanocomposites of poly(3-hexylthiophene) (P3HT) and nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized by two methods; specifically, direct solution mixing and in situ polymerization. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray dispersive spectroscopy, UV-Vis spectrophotometry, photoluminescence spectrophotometry (PL), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis, and dispersive surface energy analysis. The nanocomposites were used in the active layer of a bulk heterojunction organic solar cell with the composition ITO/PEDOT:PSS/P3HT:N-CNTS:PCBM/LiF/Al. TEM and SEM analysis showed that the polymer successfully wrapped the N-CNTs. FTIR results indicated good π-π interaction within the nanocomposite synthesized by in situ polymerization as opposed to samples made by direct solution mixing. Dispersive surface energies of the N-CNTs and nanocomposites supported the fact that polymer covered the N-CNTs well. J-V analysis show that good devices were formed from the two nanocomposites, however, the in situ polymerization nanocomposite showed better photovoltaic characteristics.

Mechanochemical synthesis and spectroscopic properties of 1,1′-ferrocenyldiacrylonitriles: the effect of para-substituents

An efficient and simple solvent-free mechanochemical approach for the synthesis of 1,1′-ferrocenyldiacrylonitriles was achieved by grinding together 1,1′-ferrocenedicarboxaldehyde (1) and phenylacetonitriles. A range of 1,1′-ferrocenyldiacrylonitriles and ferrocenylacrylonitriles (2–7) were synthesized within short reaction times, with water as the only by-product. In a similar manner, grinding together ferrocenemonocarboxaldehyde (8) and phenylenediacetonitrile yielded phenylene-3,3′-bis-(ferrocenyl)diacrylonitrile (9) and 3-ferrocenyl-2-(acetonitrophenyl)acrylonitrile (10). The yield and selectivity towards formation of ferrocenyldiacrylonitriles was strongly influenced by the electronegativity of the para-substituent on the phenyl ring of phenylacetonitriles. The compounds were characterized using NMR, IR, and UV–visible spectroscopy and HR-MS. Cyclic voltammetry measurements of selected compounds highlighted the role of ligands in tuning the electrochemical properties of 1,1′-ferrocenyldiacrylonitriles. X-ray crystallographic analysis highlighted the effect of the electronegativity of the para-substituent on the conformation of cyclopentadienyl rings attached to a ferrocenyl moiety. Graphical Abstract Mechanochemical synthesis of ferrocenylacrylonitriles.

Organic solar cells with boron- or nitrogen-doped carbon nanotubes in the P3HT: PCBM photoactive layer

Either boron- or nitrogen-doped carbon nanotubes (B- or N-CNTs) were incorporated in bulk heterojunction organic solar cells photoactive layer composed of poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The physical and chemical properties were investigated using different spectroscopic techniques. The cell performance was followed from their current-voltage (J-V) characteristics. Recombination dynamics of the photo-generated free charge carriers were investigated using micro- to milliseconds transient absorption spectroscopy (TAS). Transmission electron microscopy (TEM) images revealed the presence of cone structures and bamboo compartments in B-CNTs and N-CNTs, respectively. X-ray photoelectron spectroscopy (XPS) revealed very little boron was substituted in the carbon network and presence of pyrrolic, pyridinic, and quaternary species of nitrogen in N-CNTs. J-V characteristics were found to be similar for the devices with B- and N-CNTs even though boron- and nitrogen-doped CNTs are known to have different properties, that is, p-type and n-type, respectively. TAS results showed that all devices had long lived free charge carriers but the devices with B- or N-CNTs had low power conservation efficiency and voltage.

Gold nanoparticles for the quantification of very low levels of poly-diallyldimethylammonium chloride in river water

We present a colorimetric method based on gold nanoparticle aggregation to detect and quantify poly-diallyldimethylammonium chloride (poly-DADMAC), a common water treatment polyelectrolyte, in river water. The protocol developed has an excellent linear range between 10 and 100 μg L−1 (R = 0.99), with a lower limit of detection of 0.54 μg L−1 and a lower limit of quantification of 1.5 μg L−1. The method has excellent intermediate precision (0.1–0.7%), relatively quick analysis times, requires no extraction or derivatization methods, and is robust and rugged. Results of spiked river water samples collected from the Umgeni River located in the province of KwaZulu-Natal, South Africa show that the method can detect low levels of poly-DADMAC in environmental matrices.

Synthesis highly active platinum tri-metallic electrocatalysts using "one-step" organometallic chemical vapour deposition technique for methanol oxidation process

A simple solvent free method for the synthesis of tri-metallic platinum electrocatalysts on carbon nanotubes is presented. By investigating the platinum alloy electrocatalysts, it was showed that the additional metals of platinum alloys could reduce the metal particle sizes and produce larger chemical-active surface area, as well as the higher methanol oxidation activity of the catalysts. The organometallic chemical vapour deposition method was successfully applied to produce multiple samples of PtRuFe, PtRuCu and PtRuV. The electrocatalysts were characterized by ICP, XRD, HRTEM and the catalytic activity was determined by cyclic voltammetry (CV).

Synthesis, Characterization, and Application of TiO2 Nanoparticles – Effect of pH Adjusted Solvent

Abstract TiO2 nanoparticles were synthesized via the sol-gel method by varying the pH of the solvent used in the synthesis. The aim of the pH variation was to study its effect on the surface energy amongst other characteristics, and photocatalytic properties. The sol-gel method was adopted in the synthesis of TiO2 nanoparticles and calcined in air at 400 °C at 2 °C/min. The as-prepared materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), N2 sorption, Raman spectroscopy, fluorescence spectrometry, and electron spin resonance spectroscopy (ESR), surface energy analyser (SEA), vibrating sample magnetometer (VSM). Photocatalytic properties of the materials were evaluated by monitoring the decoloration of model dye, methylene blue (MB) under natural sunlight conditions. The as-prepared materials existed in the anatase phase with polycrystalline and paramagnetic properties. The amount of surface defects of the as-prepared materials correlated well with the crystal size. The highest dispersive surface energy, 89.17 mJ/m2 exhibited by TB400, and the least dispersive energy of 49.67 mJ/m2 by TN400 are attributed to their microporosity. The acid - base numbers show that the materials are amphoteric with more of the basic sites. The values of the acidity-basicity ratio confirm the effect of pH in the synthesis of TiO2. The photocatalytic activities of the as-prepared materials were in the order of TB400 > TN400 > TA400, attributed to their characteristic crystal sizes, and surface defects.