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[Display omitted] • A Ti-Al-C MAX phase (Ti 3 AlC 2) is used to recover gold from acidic solutions. • High gold extraction capacity (>6000 mg/g) is achieved at pH < 1. • High selectivity for gold is observed in the presence of interfering metal ions. • Gold recovery is likely to proceed via a reduction reaction similar to cementation. • High purity gold (92 mass%) is recovered without any posttreatment. Given the scarcity of natural gold sources and associated mining challenges, the recovery of gold from secondary sources, such as electronic equipment waste (e-waste), becomes imperative. E-waste is typically treated with aqua regia to obtain highly acidic gold-containing solutions, which are subsequently processed by various methods to recover gold. Gold recovery materials offer numerous benefits but often exhibit insufficient selectivity, efficiency, and cost-effectiveness. To address this problem, we herein used a nonmodified pristine Ti-Al-C MAX phase (Ti 3 AlC 2) to realize the one-pot room-temperature recovery of gold from highly acidic solutions (pH < 1) in the form of easily collectable bulky ball-shaped Au0 aggregates. High gold selectivity (K d = 2.03 × 106 mL/g) and extraction efficiency (∼99 %) were observed even in the presence of interfering metal ions (Pd2+, Pt4+, Co2+, Ni2+, Cu2+, Zn2+), and the maximum gold extraction capacity (>6000 mg/g) surpassed that of previously reported gold recovery materials. The recovered gold was highly pure (>90 mass%) and contained minimal amounts of the original MAX phase, which obviated the need for intensive postpurification. The results of instrumental analyses suggested that gold recovery relied on electron transfer, similar to cementation, and primarily involved the reduction of solution-phase Au3+ to Au0 via electron transfer from the Ti and Al of Ti 3 AlC 2. Thus, our work demonstrates the significant potential of pristine Ti 3 AlC 2 for the energy-efficient recovery of gold from highly acidic solutions and paves the way for the efficient valorization of e-waste. [ABSTRACT FROM AUTHOR]

• HTiNbO 5 nanosheets are prepared with a facile hydrothermal method in acid solution. • Using this method, preparation time is reduced from several days to 12 h. • Both acid type and starting KTiNbO 5 are keys to this preparation. • The prepared HTiNbO 5 nanosheets show good photocatalytic activity. Due to the rich chemistry, HTiNbO 5 nanosheets are interesting candidates in many applications but the long preparation time limits their uses. Here, we report a novel fast, and facile preparation of HTiNbO 5 nanosheets by hydrothermal treatment of KTiNbO 5 with acid solution. Investigation on various acids shows that the acid strength and structure determine the product. The bulky structure of citric acid promotes the exfoliation and stabilizes the nanosheets, preventing the decomposition. Nature of KTiNbO 5 is also important as only KTiNbO 5 prepared from molten salt, but not solid-state reaction, gives pure nanosheets. The obtained nanosheets have good crystallinity and photocatalytic activity. Therefore, this novel one-step hydrothermal preparation would play a role in realizing applications of HTiNbO 5 nanosheets and might benefit the exfoliation of other layered oxides. [ABSTRACT FROM AUTHOR]