Abstract
Surface-modified ZnAl layered double hydroxides (LDHs) were prepared by reaction of AgNO3, with both ZnAlCl (LDH1) and ZnAlCO3 exchanged on the surface with chloride anions (LDH3). In this way, AgCl nanoparticles with crystalline domains ranging from 40 to 100 nm were grown on the LDH surface. An additional sample was prepared by partial reduction of silver to obtain Ag@AgCl-LDH (LDH2). The composites were tested as catalysts in Rhodamine B (RhB) degradation, wherein LDH2 showed complete cleavage of RhB after 45 min of irradiation versus 70 min needed in the presence of AgCl. This time decreased to 35 min for LDH1 and 15 min for LDH3, underlining the role of the AgCl dimensions and anion in the interlayer region. Studies on the reactive species involved in the degradation process revealed that, for all catalysts, O2·− was the main active species, while, to some extent, holes contribute to the activity of the LDH3. Finally, the composites showed high bactericidal activity, under irradiation, against Escherichia coli, comparable with that of Gentamicin, the positive control. A synergic effect of silver released from the composites and the production of reactive oxygen species was considered.
Highlights
Environmental pollution, with particular attention to water contamination, is a global problem that has led research towards the development of eco-sustainable technologies for environmental remediation
layered double hydroxides (LDHs) containing different anions, analyzed by field emission scanning electron microscopy (FE-scanning electron microscope (SEM)), exhibit different morphologies: ZnAlCO3 is constituted of hexagonal microcrystals assembled to form a sand-rose morphology with a main dimension of about 2 μm, while ZnAlCl consists of flat hexagonal microcrystals of diameter 2–5 μm and thickness of 200–300 nm
ZnAlCl and ZnAlCO3 were used as support for AgCl NPs and the composites obtained were tested as catalysts in the photodegradation of Rhodamine B (RhB)
Summary
Environmental pollution, with particular attention to water contamination, is a global problem that has led research towards the development of eco-sustainable technologies for environmental remediation. LDHs have a general formula [M(II)1−x M(III)x (OH)2 ](An− )x/n ·H2 O, where M(II) (M = Mg, Zn, Cu, Ni, Co, etc.) and M(III) (M = Al, Ga, Cr, Mn, In, Fe, etc) are divalent and trivalent metals; x is the molar fraction of the trivalent metal (mol M(III)/(mol M(III) + mol(M(II)), which ranges between 0.2 and 0.4 and determines the charge density of the lamellae, while An− is the counter anion located in the interlayer gallery [21] In this context, the preparation of composites constituted by layered double hydroxides and silver/silver halides (Ag/AgX, X = Br, Cl, I) has been explored by Fan et al [22]. The anti-bacterial activity of the composites against Escherichia coli was investigated under irradiation and dark conditions, which showed that the light enhanced the ability of the composites to kill bacteria
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