Retraction Note: Modified of CaO-Nanoparticle Synthesized from Waste Oyster Shells with Tin Tailings as a Renewable Catalyst for Biodiesel Production from Waste Cooking Oil as a Feedstock(Chemistry Africa, (2022), 6, (1025–1035), 10.1007/s42250-022-00541-y)

The Editor-in-Chief has retracted this article. After publication, a number of concerns were brought to the publisher by a third party. • Figure 1 appears to overlap with two articles previously published by one or more of the same authors, figure 2 of [1] and figure 7 of [2], and figure 1 of one paper published subsequently by a shared author [3]. • Figure 9a appears to overlap with figure 9d of a now retracted article by the same authors [4]. • One curve in Figure 8 appears to partially overlap with one of the curves in Figure 2 in [5]. The Author has not provided a sufficient response to concerns or the raw data upon request. The Editor has lost confidence in the data and conclusions of this article. Author Victor Sunday Aigbodion has not responded to correspondence from the publisher regarding this retraction.