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.

Pharmaceutical contaminants such as tetracycline pose an increasing threat to aquatic ecosystems and human health as a result of their persistence in water sources and their contribution to antibiotic resistance. This study developed chitosan nanocomposites by incorporating functionalised and nitrogen-doped multi-walled carbon nanotubes (FMWCNTs and NMWCNTs) for the removal of tetracycline pharmaceutical contaminants from water. The composites were characterised with FTIR, SEM, XRD, BET, UV–Vis, and TGA under various conditions (pH, adsorbent dosage, concentration, contact time, and temperature). Optimal tetracycline removal (85%) was achieved with pH 6, 2 g/L adsorbent dose, 10 ppm concentration, and 30 min contact time. The FMWCNT–chitosan composite could be recycled five times with an adsorption loss of only 2%. The FMWCNT–chitosan composite showed the good adsorption efficiency of 82% in the presence of counter ions and 70% in a binary system. The adsorption process followed the Langmuir isotherm (263 mg/g), indicative of monolayer adsorption and pseudo-second-order kinetics. Among the nanocomposites prepared, the FMWCNT–chitosan composite showed the highest performance, removing more than 85% of tetracycline from water samples.

Humic acid (HA) is abundant in soil and aquatic systems and can hinder wastewater treatment by affecting the removal of heavy metals and other contaminants. Herein, this study presents chitosan-zirconia (CTS-ZrO2) composites doped with functionalized multi-walled carbon nanotubes (f-MWCNTs) for HA adsorption. The composites were characterized using TGA, BET, EDX, XRD, FTIR and SEM. Batch experiments assessed the effects of pH (2-8), adsorbent dosage (1-5 g L-1), initial HA concentration (10-50 mg L-1), contact time (5-240 min), temperature (25-40 ºC), ionic strength, reusability and binary systems. The CT-ZrO2-f-MWCNTs composite exhibited a maximum adsorption capacity of 32.89 mg g-1 at pH 3, dosage of 2 g L-1, initial HA concentration of 10 mg L-1 and 25 ºC, achieving 99.04% removal within 30 min. The adsorbent remained effective after five cycles and isotherm studies indicated that adsorption followed the Langmuir Type II model, suggesting multilayer adsorption.