Heterogeneous photocatalysis is a type of Advanced Oxidative Process that has been
highlighted by the use of semiconductors that can be excited by visible radiation, generating
radicals that will participate in the photocatalytic mechanism in the degradation of various
contaminants in aqueous medium. In this work, composites formed by two semiconductors,
silver phosphate (Ag3PO4) and zinc sulfide (ZnS) were synthesized and applied to the
degradation of Rhodamine B (RhB) dye. Ag3PO4/ZnS composites with different ZnS mass
proportions (1%, 5%, 10%) were synthesized in order to improve their photocatalytic
performance compared to pure materials. After the synthesis, all samples were structurally
characterized by X-ray diffraction and Fourier transform infrared spectroscopy, which
confirmed the formation of Ag3PO4/ZnS composites. The Rietveld refinement of the samples
showed a good fit between the profile observed experimentally and the profile calculated, with
low deviation of the statistical parameters. The UV–Vis diffuse reflectance spectroscopy
revealed a band gap of 3.82 eV for ZnS and 2.44 eV for Ag3PO4, while the composites showed
a decrease in the band gap compared to the Ag3PO4. The morphology of the composites was
obtained by scanning electron microscopy showing irregular spherical microparticles (Ag3PO4)
of approximately 200nm, and flower-like microparticles (ZnS) of 4-5μm. The photocatalytic
efficiency of the samples was evaluated under visible radiation for the degradation of the RhB
dye. The ZnS sample was not efficient under the conditions studied, while the composite
containing 5% of ZnS (Ag/Zn5%) and the Ag3PO4 degraded 93% and 75% at 15 minutes,
respectively. In the study of pH variation, both Ag3PO4 and Ag/Zn5% presented showed better
results in natural pH of the RhB solution. The lowest dose of catalyst (30mg) for the Ag3PO4
and Ag/Zn5% samples showed better photocatalytic activity in the degradation of RhB. In
addition, the photocatalytic mechanisms of all samples were investigated using different types
of oxidant-species scavengers. For Ag3PO4, the holes play a main role in degradation of the
RhB, while for the Ag/Zn5% composite, both holes and superoxide radicals played a significant
role in dye degradation. The Ag/Zn5% showed an improvement in stability in comparison to
pure Ag3PO4; however, was not possible to completely solve the photocorrosion process.
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