Development and Characterization of Clay–Nanocomposites for Water Purification

Abstract

In this work we propose a facile method of preparing cost-effective clay-metaloxide/metal (CuO/Ag and ZnO/Ag) composite pellets for an efficient water purification technique. Clay, with intrinsic antibacterial activity, served as a membrane support for different metaloxide/Ag nanoparticles (NPs) concentrations (2.5, 5 and 10 wt.%), as the active fillers. The effect of time (24 and 48 h) on the bactericidal activity of these pellets was also monitored. The clay–nanocomposite pellets were characterized using: X-ray diffraction, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible (UV–Vis) spectrophotometry and nitrogen desorption analysis. The antibacterial activity performance was tested using E. coli and S. aureus strains of ATCC25922 and ATCC25923, respectively, in two aqueous media (nutrient broth and nutrient-free) by the colony-forming unit method. The results showed that the clay-CuO/Ag composite with a bandgap (1.24 eV) exhibited overall best performance under all conditions and time factors of ~100% efficiency in nutrient-free medium for all concentrations and times and 20–40% efficiency in nutrient broth for 24 h. The clay-ZnO/Ag with a bandgap of 2.88 eV showed no bactericidal activity in both media, except for that with 10 wt.% ZnO/Ag which showed 100% efficiency in nutrient-free medium after 24 h. All the synthesized composites showed 100% bactericidal efficiency in nutrient free medium after 48 h. These results indicate that, the clay/metaloxide/Ag could serve as efficient water purification technique, with a potential for large-scale commercialization.

Expanded clay aggregates multi-functionality for water purification: Disinfection and adsorption studies

“…It was also observed that the adsorbents were not consumed after six cycles of filtration although there was a decrease in flow rate (not part of the present studies). Similar disinfection assay was published by Asamoah et al (2020) using clay-metaloxide/metal composite pellets. We postulate that the high disinfection result might have arisen from bacterial cell wall that possessed amphoteric properties due to the presence of cationic and anionic groups, surface charge and modification of the adsorbent (Londono & Williams, 2016).…”

Antibacterial Activity of Solvothermal Obtained ZnO Nanoparticles with Different Morphology and Photocatalytic Activity against a Dye Mixture: Methylene Blue, Rhodamine B and Methyl Orange

“…The emission peak near band edge (NBE) is usually located in UV domain, most often in the interval 380–400 nm, and is the result of exciton recombination [ 48 , 49 , 50 ]. When the nanoparticles have multiple surface defects that can block the recombination process by trapping the free electrons, the NBE will usually have lower intensity when compared with the visible emission bands [ 51 , 52 ].…”

Influence of the Alcohols on the ZnO Synthesis and Its Properties: The Photocatalytic and Antimicrobial Activities

“…The green emission from 2.42 eV (513 nm) and further is generated mainly by VO and VO+ defects [3,105,107,109,110]. The strongest emission intensity is observed for the ZnO_C4 sample, indicating a higher density of surface defects.…”

“…The UV emission is generally placed around 390-400 nm, the near-band-edge (NBE) location, and is generated by the free exciton recombination (recombination of the electron and hole pair that was previously generated by the absorption of a photon). The presence of various surface defects that can trap the free electrons and block the recombination are the cause of the decreased intensity of this band vs. the visible emission bands [105][106][107]. The visible emission of the ZnO nanoparticles, or deep-level emission (DLE), is assigned to the electronic levels generated inside the band-gap by the defects like oxygen vacancies (V O ), zinc vacancies (V Zn ), oxygen anti-sites (O Zn ), oxygen interstitials (O i ), or zinc interstitials (Zn i ), the relative energetic position of them inside the band-gap being reported in literature [3,108].…”