Xavier Yangkou Mbianda

Nanosponge cyclodextrin polyurethanes and their modification with nanomaterials for the removal of pollutants from waste water: A review

Water is a worldwide vital resource for sustaining life and due to the pollution of water by different classes of pollutants (inorganic, organic and pathogens), many ongoing studies in water purification remain a critical issue to governments, scientists and industries. The challenge is to develop a water purification technology which will be effective at removing these contaminants simultaneously and reducing their concentrations to ultra low levels from waste water. This review article serves to give an overview on cyclodextrin nanosponge adsorbents which have already been used for water treatment. The modification of these cyclodextrin nanosponges with existing adsorbent nanomaterials (carbon nanotubes, TiO2 and silver nanoparticles) and the factors affecting the adsorption capacity of these nanosorbents are discussed. The nanotoxicity of these engineered nanosorbents material is also addressed since nanotoxicity is a major concern to human health and environment.

Kinetic release studies of nitrogen-containing bisphosphonate from gum acacia crosslinked hydrogels

Natural polymer hydrogels are useful for controlling release of drugs. In this study, hydrogels containing gum acacia were synthesized by free-radical polymerization of acrylamide with gum acacia. The effect of gum acacia in the hydrogels on the release mechanism of nitrogen-containing bisphosphonate (BP) was studied at pH 1.2 and 7.4. The hydrogels exhibited high swelling ratios at pH 7.4 and low swelling ratios at pH 1.2. The release study was performed using UV-Visible spectroscopy via complex formation with Fe(III) ions. At pH 1.2, the release profile was found to be anomalous while at pH 7.4, the release kinetic of BP was a perfect zero-order release mechanism. The hydrogels were found to be pH-sensitive and the release profiles of the BP were found to be influenced by the degree of crosslinking of the hydrogel network with gum acacia. The preliminary results suggest that these hydrogels are promising devices for controlled delivery of bisphosphonate to the gastrointestinal region.

Phosphorylated multiwalled carbon nanotube-cyclodextrin polymer: Synthesis, characterisation and potential application in water purification

Multiwalled carbon nanotubes were synthesised by the nebulised spray pyrolysis method and purified to remove amorphous carbon and fullerenes. The purified multiwalled carbon nanotubes were oxidised using a 3:1 H2SO4/HNO3 mixture to introduce carboxylic groups and to a smaller extent hydroxyl groups on the walls of the carbon nanotubes. Subsequently, the oxidised carbon nanotubes were chlorinated using oxalyl chloride to generate acyl chloride groups through which phosphorylation took place. 4-Aminophenyl methylphosphonate was attached to the multiwalled carbon nanotubes via an amidation reaction. FT-IR and XPS confirmed the presence of PO, PO and PCP functional groups in the phosphorylated carbon nanotubes. Polymerisation of the phosphorylated carbon nanotubes with cyclodextrins was achieved using hexamethylene diisocyanate as a bifunctional linker. Surface morphology of the polymer was investigated by SEM while FT-IR was used to confirm the polymerisation reaction. Moreover, the thermal stability of the polymer was probed using TGA while BET was employed to determine the surface area and pore volume of the polymer. Furthermore, the polymer was tested for the removal of cobalt and 4-chlorophenol from synthetic aqueous solutions of the pollutants. The polymer displayed potential as an adsorbent for both cobalt and 4-chlorophenol.

Photocatalytic degradation of the diazo dye naphthol blue black in water using MWCNT/Gd,N,S-TiO2 nanocomposites under simulated solar light.

A simple sol-gel method was employed to prepare gadolinium, nitrogen and sulphur tridoped titania decorated on oxidised multiwalled carbon nanotubes (MWCNT/Gd,N,S-TiO2), using titanium (IV) butoxide and thiourea as titanium and nitrogen and sulphur source, respectively. Samples of varying gadolinium loadings (0.2%, 0.6%, 1.0% and 3.0% Gd3+) relative to titania were prepared to investigate the effect of gadolinium loading and the amounts of carbon nanotubes, nitrogen and sulphur were kept constant for all the samples. Furthermore, the prepared nanocomposites were evaluated for the degradation of naphthol blue black (NBB) in water under simulated solar light irradiation. Higher degradation efficiency (95.7%) was recorded for the MWCNT/Gd,N,S-TiO2 (0.6% Gd) nanocomposites. The higher photocatalytic activity is attributed to the combined effect of improved visible light absorption and charge separation due to the synergistic effect of Gd, MWCNTs, N, S and TiO2. Total organic carbon (TOC) analysis revealed a higher degree of complete mineralisation of naphthol blue black (78.0% TOC removal) which minimises the possible formation of toxic degradation by-products such as the aromatic amines. The MWCNT/Gd,N,S-TiO2 (0.6% Gd) was fairly stable and could be re-used for five times, reaching a maximum degradation efficiency of 91.8% after the five cycles.

Epichlorohydrin crosslinked carboxymethyl cellulose-ethylenediamine imprinted polymer for the selective uptake of Cr(VI)

A new ion-imprinted polymer (IIP) was synthesized from sodium carboxymethyl cellulose and used for the adsorption of hexavalent chromium from aqueous solution. Epichlorohydrin was used to stabilize the polymer before ethylenediamine (EDA) ligand and Cr(VI) were introduced. The obtained IIP was characterized with FTIR, XPS, TGA,13C NMR, SEM, EDX, BET and zeta sizer. The kinetics of adsorption followed a pseudo-second-order model while the Langmuir adsorption isotherm provided the best fit with a maximum adsorption capacity of 177.62mg/g at 25°C. The Langmuir adsorption capacity for the non-imprinted polymer (NIP) at 25°C was 149.93mg/g. Thermodynamic parameters indicated an endothermic process and spontaneous adsorption of Cr (VI) on the polymers. IIP adsorbent was successfully recycled 5 times using 0.1M NaOH as a leachate; 98% Cr(VI) was desorbed during the last adsorption-desorption cycle.

Synthesis and characterization of water-soluble polyaspartamides containing platinum(II) complex and bisphosphonate as potential antimalarial drug

Polyaspartamides conjugates and co-conjugates containing platinum(II) complex and bisphosphonate were synthesized by stepwise reaction of polysuccinimide with selected primary amines. The first step was achieved by aminolytic ring opening of polysuccinimide and afforded conjugates containing bisphosphonate and dihydroxylato ligand for platinum chelation. In the second step conjugates were chelated to platinum(II) complex. These conjugates and co-conjugates were characterized by proton and phosphorus nuclear magnetic resonance (1H and 31P NMR), Fourier transform spectroscopy (FTIR), scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDX). The mass percentage incorporation of platinum in the co-conjugates was determined by ICP-OES and was found to be between 1.9 and 3.7 percent, while the mass percentage incorporation of bisphosphonate in the conjugates and co-conjugates was found to be between 2.5 and 3.1 percent by NMR. The preliminary pharmacological evaluation performed on co-conjugates 4, 5 and 6 revealed that co-conjugate 6 exhibited enhanced antimalarial activity than chloroquine, while co-conjugates 4 and 5 were less active.

Synthesis and Characterization of a Novel Bio Nanosponge Filter (pMWCNT-CD/TiO 2 -Ag) as Potential Adsorbent for Water Purification

This study reports the synthesis and characterization of a novel bio nanosponge filter for applications in water treatment. Firstly the oxidized multiwalled carbon nanotubes (MWCNTs) were chlorinated using oxalyl chloride and then phosphorylated via an amidation reaction. The phosphorylated carbon nanotube (pMWCNT) obtained was polymerized with β-cyclodextrin (βCD) using hexamethylene diisocyanate (HMDI) as a linker. The resulting polymer (pMWCNT-βCD) was decorated by a sol-gel method with TiO2 and Ag nanoparticles to obtain a biopolymer nanocomposite, pMWCNT-βCD/TiO2-Ag. For a better evaluation of the target material, CD polymer and pMWCNT-CD polymer were also synthesized for comparison purposes. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs and the polymerization reaction. Laser Raman spectroscopy analysis showed the presence of MWCNT, CD and the anatase crystalline form of TiO2 in the nanocomposite. Preliminary adsorption studies were also conducted in order to test the capability of the new bio nanosponge filter to remove metal ions pollutants from synthetic wastewater solutions.

Synthesis, characterization and the release kinetics of antiproliferative agents from polyamidoamine conjugates.

Abstract Polyamidoamine conjugates containing curcumin and bisphosphonate were synthesized via a one-pot aqueous phase Michael addition reaction. In the design of the conjugate, bisphosphonate formed an integral part of the polymer carrier backbone. Curcumin was incorporated onto the polyamidoamine backbone via piperazine linker. The conjugates were characterized by Fourier transform spectroscopy, energy-dispersive X-ray analysis, atomic force spectroscopy and nuclear magnetic resonance spectroscopy and it confirmed the successful incorporation of the antiproliferative agents onto the carriers. The weight percentage incorporation of bisphosphonate to the carriers was found to be between 2.56% and 3.34%. The in vitro release studies of curcumin from the polyamidoamine conjugate were performed in dialysis bag at selected pH values. The release of curcumin was significantly slower at pH 7.4 when compared to pH 5.8. The release profiles indicate that the conjugates are more stable at pH 7.4 and are potential sustained drug-delivery systems for combination therapy.

STRUCTURAL, SPECTROSCOPIC AND REACTIVITY STUDIES ON PHOSPHORIC AMIDES

A series of non-cyclic, cyclic and bicyclic phosphotriamidates has been sythesized and their structure, NMR spectroscopic characteristics and their chemical reactivity are discussed.

Recovery of gold from mining solutions using Au(III)-imprinted polymeric resins with pyridine, ethylenediamine and aminothiophosphate functionalities

ABSTRACT New Au(III)-ion-imprinted polymers (Au(III)-IIPs) with pyridine (4-VP), ethylenediamine (EDA) or aminothiophosphate (ADT) functionalities were prepared and employed in recovering Au(III) ions from aqueous media. These polymers demonstrated good adsorption capability for Au(III) ions owing to their faster kinetics adsorption, higher capacity and good recyclability. The Au(III) ions kinetic data fitted well to pseudo-second-order rate equation. The equilibrium data were best described by the Langmuir isotherm, with the maximum adsorption capacity of 418.41, 393.70 and 189.75 mg g–1 for IIPs with 4-VP, EDA and ADT, respectively. The IIPs displayed excellent recognition towards Au(III) in its binary systems with Pb(II), Ni(II), Cu(II), Mn(II) and Fe(III), Pt(IV) and Pd(II). The suitability of the developed IIPs for selective recovery of Au(III) in real leach liquor samples and acid mine drainage spiked with standards was successfully demonstrated.