Composite membranes were successfully prepared using a phase-inversion method. The X-ray powder diffraction (XRD) and energy dispersive X-ray (EDX) profiles has confirmed formation of 4.8 wt % Ag/poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP), 3 wt % Ag-MWCNTs/PVDF-HFP (EDX surface composition of Ag nanoparticles) and 1.5 wt % MWCNTs/PVDF-HFP composite membranes. The MWCNTs crystallites are mainly encapsulated by a layer of PVDF-HFP, as evidenced by disappearance of graphitic peak. The scanning electron microscopy (SEM) images have depicted the formation of microporous structure, with few MWCNTs on the surface and strongly interacting with PVDF-HFP as demonstrated by thermogravimetric analysis (TGA), XRD and Fourier transform infrared (FTIR) data. The data indicated an increase in porosity, swellability and water content of the PVDF-HFP membrane with the addition of MWCNTs and/or Ag nanoparticles, showing an improved hydrophilicity. The 1.5 wt % MWCNTs/PVDF-HFP composite membrane showed good desalination and fouling resistance rates, which correlates with a low water contact angle. The combined effects of Ag nanoparticles and MWCNTs do not promote fouling resistance of PVDF-HFP membranes, as shown during NaCl microfiltration (this is linked with high water contact angle as compared to that of MWCNTs/PVDF-HFP composite). Both 1.5 wt % MWCNTs/PVDF-HFP and 3 wt % Ag-MWCNTs/PVDF-HFP composite membranes prevented the bacteria passing through the membrane (100% bacterial load reduction). The surface of 3 wt % Ag-MWCNTs/PVDF-HFP showed good bactericidal and non-leaching properties of the dopant materials (MWCNTs and Ag), as evidenced by bacterial growth on the edges of the membranes.

Silver doped multi-walled carbon nanotube/β-cyclodextrin (1% Ag-MWCNTs/β-CD) nanocomposite was prepared by reductive pre-treatment of Ag+ on MWCNTs, followed by binding with β-CD. Crystalline structure, morphology and crystallite size estimation were carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The interaction between Escherichia coli (E. coli), ATCC 25922 bacteria and 1% Ag doped MWCNTs/β-CD nanocomposite was investigated by FE-SEM. The antibacterial activity of the nanocomposite was studied by monitoring the absorbance of contaminated water using a UV-vis spectrophotometer. The nanocomposites caused a growth delay in the growth rate of E. coli bacteria. The structural analysis of the bacteria by FE-SEM showed clusters of nanocomposite anchored to the bacterial cell wall during the initial stages of interaction. Results also indicate that treated bacteria show significant damage on the outer membranes, which were recognised by the formation of ‘pits’. The study shows that 1% Ag-MWCNTs/β-CD nanocomposite is bactericidal.

In this work, nanocomposite membranes were prepared using silver nanoparticles (Ag) attached to poly(amidoamine) dendrimer (P)-functionalised multi-walled carbon nanotubes (CNTs) blended with poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) polymeric membranes (i.e., AgP-CNT/PVDF-HFP) via the phase inversion method. The nanocomposites were characterised and analysed via transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), thermal gravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis. The TEM and EDX analyses confirmed the presence of Ag nanoparticles on the nanocomposites, while the SEM and BET data showed the spongy morphology of the nanocomposite membranes with improved surface areas. The sample analysis of surface water collected from the Sekhukhune district, Limpopo Province, South Africa indicated that the water could not be used for human consumption without being treated. The nanocomposite membranes significantly reduced the physicochemical parameters of the sampled water, such as turbidity, TSS, TDS and carbonate hardness, to 4 NTU, 7 mg/L, 7.69 mg/L and 5.9 mg/L, respectively. Significant improvements in microbial load (0 CFU/mL) and BOD (3.0 mg/L) reduction were noted after membrane treatment. Furthermore, toxic heavy metals such as chromium, cadmium and nickel were remarkably reduced to 0.0138, 0.0012 and 0.015 mg/L, respectively. The results clearly suggest that the AgP-CNT/PVDF-HFP nanocomposite membrane can be used for surface water treatment.

The as-prepared (Co₃O₄) and hydrazine-treated (Co₃O₄(H)) cobalt catalysts were prepared using the precipitation method and evaluated at a temperature range of 40–220 °C for preferential oxidation (PROX) of CO in excess hydrogen. An improved surface reducibility with smaller crystallite size was noted on hydrazine-treated cobalt species (i.e., Co₃O₄(H) catalyst), which indicates some surface transformation. This finding correlates with the surface roughness formation (as depicted by scanning electron microscope (SEM) and transmission electron microscope (TEM) data), which was further confirmed by an increase in the Brunauer–Emmett–Teller (BET) surface area. The mesoporous structure of the Co₃O₄(H) catalyst remained intact, as compared to that of the Co₃O₄ catalyst. Interestingly, the in situ treatment of the standalone Co₃O₄(H) catalyst decreased the maximum CO conversion temperature (T_100%) from 160 °C (over Co₃O₄) to 100 °C, with good selectivity. The Co₃O₄(H) catalyst showed good stability, with approximately 85% CO conversion at 100 °C for 21 h, as compared to a faster deactivation of the Co₃O₄ catalyst. However, the Co₃O₄(H) catalyst was unstable in both CO₂ and the moisture environment. Based on the evaluation of spent hydrazine-treated (CoO(H)) cobalt catalyst, the high PROX activity is associated with the formation of Co³⁺ species as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and temperature-programmed reduction (TPR) data.

The existence of pesticides in water at ultra-trace levels necessitates the use of a suitable pre-concentration method for their detection. The objective of this study was to develop an ultra-synthetic adsorbent to extract chlorpyrifos (CPF) and imazalil (IMA) pesticides in water. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy confirm that both oxidised and isophorone diamine multiwalled carbon nanotubes (IPD-MWCNTs) were successfully prepared with an intact structure; which was further confirmed by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The Brunauer–Emmet–Teller (BET) showed a high surface area of both oxidised and IPD-MWCNTs, which is linked to the formation of additional active sites. TGA further showed that the nanocomposites were highly stable within the pesticides quantification operating temperature. CPF and IMA were recovered using a low dosage of IPD-MWCNTs adsorbent (0.030 g) and eluted by a combined solvent (ethanol and chloroform (50:50, v/v)). The adsorbent was reusable over seven repeated cycles, with an acceptable percentage relative standard deviation (%RSD) ranging from 3 to 8%. The IPD-MWCNTs adsorption sites are highly stable and cannot be easily fouled, as compared to that of oxidised MWCNTs. Lower limits of detection (LOD) and quantification (LOQ) for CPF (0.026 and 0.078 µg.L⁻¹) and IMA (0.033 and 0.100 µg.L⁻¹) were achieved. Better recoveries for both analytes at low and high concentrations (as well as in real water samples) were obtained by IPD-MWCNTs whereas a conventional adsorbent (i.e. polymeric reverse phase) can only achieve better recoveries at high concentrations.