Synthesis of polyoxometalates for detailed solution reactivity studies

PhD ThesisNon-aqueous methodologies provide an opportunity to access a range of polyoxometalates that may not be stable in H2O and enable mechanistic studies into hydrolytic and protonation behaviours, which are fundamental to polyoxometalate chemistry. 17O-enriched (TBA)6[NaPW11O39] was prepared via an efficient non-aqueous route and shown to be a suitable precursor to [(L)MPW11O39]n- (M = Sn2+, Pb2+, Bi3+, Sb3+, Sn4+, Ti4+) for detailed systematic studies. Reactions were monitored by 31P NMR while products were characterised by FT-IR, multinuclear NMR (1H, 13C, 17O, 31P, 119Sn, 183W and 207Pb), solid state NMR, ESI-MS, CHN microanalysis, UV-Vis and/or single crystal XRD. Using this approach, the readily-hydrolysable tin derivatives, (TBA)4[(CH3O)SnPW11O39] and (TBA)8[(μ-O)(SnPW11O39)2] were prepared for the first time and the previously reported (TBA)4[(HO)TiPW11O39] was shown to be stable in DMSO for up to 3 months possibly due to interaction between HO- and DMSO. As a result of the more ionic character of Sn—OCH3 bond compared with Ti—OCH3, (TBA)4[(CH3O)SnPW11O39] was observed to hydrolyse faster than (TBA)4[(CH3O)TiPW11O39] whereas (TBA)4[ClTiPW11O39] with a large excess of H2O hydrolysed more readily than (TBA)4[ClSnPW11O39]. Although (TBA)4[(HO)TiPW11O39] underwent condensation to (TBA)8[(μ-O)(TiPW11O39)2] easily in acetonitrile at room temperature, this reaction only occured for (TBA)4[(HO)SnPW11O39] at elevated temperature (~120oC) in the presence of a water-scavenging agent such as N, N’-dicyclohexylcarbodiimide (DCC). These experimental observations were consistent with DFT calculations on the energetics of the hydrolysis and condensation of (TBA)4[(CH3O)SnPW11O39] and (TBA)4[(CH3O)TiPW11O39]. Protonation studies on the 17O-enriched POMs provided insights into protonation of the MOW sites in (TBA)4[(CH3O)TiPW11O39], (TBA)4[ClMIVPW11O39] (M = Sn, Ti), (TBA)5[MIIPW11O39] (M = Sn, Pb) and (TBA)4[MIIIPW11O39] (M = Sb, Bi) and protonation at both TiOW and TiOTi sites in (TBA)8[(μ-O)(TiPW11O39)2] whilst reactions between (TBA)8[(μ-O)(TiPW11O39)2] and electrophiles indicated possible formation of adducts. Treatment of (TBA)4[(L)SnPW11O39] (L = Cl, HO) with NaBH4 resulted in reduction of the tin heteroatom only whereas reaction between (TBA)5[SnIIPW11O39] and halogens (Br2 and I2) or the molybdate (TBA)3[PMo12O40] showed oxidation of tin (II). Electrochemical studies in acetonitrile revealed no redox processes associated with the heterometals in (TBA)4[(L)SnIVPW11O39] and (TBA)5[PbIIPW11O39] while redox waves assigned to Sn2+/Sn4+ were observed for Abstract ii (TBA)5[SnIIPW11O39] within the potential range studied. Finally, attempts to prepare Lindqvist-type derivatives, [(L)MW5O18]n- (M = Co2+, Mo2+, Sn2+, Pb2+, Fe2+, Cu2+, Cr3+, Sb3+, Bi3+) from a tungstate precursor prepared by hydrolysis of a 3:2 mixture of (TBA)2WO4 and WO(OMe)4 provided evidence that only in certain cases were the required heterometalates formed. Acetonitrile hydrolysis was observed under reaction conditions and the acetamide adduct (TBA)3[{CH3C(O)NH2}CoW5O17(OMe)] was characterised crystallographically. An attempt to prepare [(L)MoIIW5O18]4- produced the crystallographically characterised, one-electron reduced (TBA)3[W6O19].Niger Delta Development Commission (NDDC):, Sokoto State University: COST Action CM1203: The Royal Society of Chemistry

Immobilization of Polyoxometalate-Ionic Liquid on Coconut Shell Nanoporous Carbon Support: An Improved Material for Water Purification

Access to clean water by all is one of the UN Sustainable Development Goals. To achieve this, there is need to prepare sustainable materials for efficient water purification. This research aims to immobilize the Polyoxomatelate-Ionic Liquid (POM-IL), {[CH3(CH2)6]4N}7[α-PW11O39] on nanoporous carbon (NC) prepared from coconut shell to form an advanced material (POM-IL@NC) for effective removal of multiple contaminants from polluted water. The POM-IL@NC material was characterized by Fourier Transform-Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) Analysis and Brunauer-Emmett-Teller (BET) method. The material was then tested respectively for the removal of copper and lead using Atomic Absorption Spectroscopy (AAS) and methylene blue using Ultraviolet-Visible (UV-Vis) Spectroscopy from simulated polluted waters via adsorption. The material was further subjected to antimicrobial analysis. The results showed that the POM-IL@NC material performed better than the pristine NC in the removal of copper, lead and methylene blue from the contaminated water. The POM-IL@NC also exhibited significant improvement in antimicrobial activity than NC against Escherichia coli and Staphylococcus aureus. This shows that the new material could effectively be applied for multiple contaminants treatment of polluted water

Nanoporous carbon from waste egg shells modified with copper-nanoparticles – An Efficient material for removal of microbial contaminants from polluted water

The paper examines the efficiency of nanoporous carbon modified with copper nanoparticles (nC@CuNPs) for the removal of microbial contaminants from polluted waters. The modified material was prepared by wet impregnation of the unmodified carbon material in a solution of as-prepared Cu-nanoparticles. The materials were characterized by UV-Visible Spectroscopy, Fourier Transform-Infrared (FTIR) Spectroscopy, and Thermogravimetric Analysis. The materials were then investigated for their ability to remove copper and lead using Atomic Absorption Spectroscopy (AAS), methylene blue using Ultraviolet-Visible (UV-Vis) Spectroscopy and microbial contaminants from simulated polluted water. The results showed that in addition to retaining its heavy metals (Cu and Pb), and methylene blue removal capacity, the modified material, nC@CuNPs was efficient in removing microbial contaminants (E. coli and Salmonella) from the polluted water. The study provides an avenue for the provision of easy access to a range of such water purification materials to the increasing world population and contributes towards meeting the United Nationals Sustainable Development Goals (UN SDGs)