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Monolayer gold could exhibit properties of benefit to various applications, but has been challenging to synthesize. Now, the exfoliation of two-dimensional single-atom-thick gold layers - termed goldene - is achieved through wet-chemically etching away Ti3C2 from Ti3AuC2, a nanolaminated MAX-phase. Goldene shows lattice contraction and an increase in the gold 4f binding energy compared with the bulk., Funding Agencies|MIRAI2.0 Joint seed funding

Thermal treatments can have detrimental effects on the photocatalytic hydrogen (H2) evolution performance and impact the formation mechanism of the active state of surface-supported co-catalysts. In this work, a range of Ni-based co-catalysts is investigated immobilized on TiO2, evaluated their H2 evolution rates in situ over 21 h, and analyzed the samples at various stages with a comprehensive set of spectroscopic and microscopy techniques. It is found that achieving the optimal hydrogen evolution (HER) performance requires the right Ni0:Ni2+ ratio, rather than only Ni0, and that Ni needs to be weakly adsorbed on the TiO2 surface to create a dynamic state. Under these conditions, Ni can undergo an efficient redox shuttle, involving the transformation of Ni2+ to Ni0 and back after releasing the accumulated electrons for H+ reduction (i.e., Ni2+ <-> Ni0). Yet, when the calcination temperature of the Ni/TiO2 photocatalysts increases, resulting in stronger coordination/adsorption of Ni on TiO2, this process is gradually inhibited, which ultimately leads to decreased HER performances. This work emphasizes the significance and influence of thermal treatments on the Ni active state formation - a process that can be relevant to other HER co-catalysts. This research underscores the impact of thermal treatment on the formation of Nis active state for hydrogen evolution reaction (HER) . For optimal performance, Ni should weakly adsorb onto the substrate, efficiently shuttling between Ni2+ and Ni0 and reversing after H+ reduction (Ni2+ <-> Ni0). However, raising the calcination temperature strengthens Ni coordination/adsorption on the substrate, gradually inhibiting this process and reducing HER performances.image, Funding Agencies|TU Wien Bibliothek; FWF [P32801-N]; FFG "HARD2D" [879844]

The design of active and selective co-catalysts constitutes one of the major challenges in developing heterogeneous photocatalysts for energy conversion applications. This work provides a comprehensive insight into thermally induced bottom-up generation and transformation of a series of promising Cu-based co-catalysts. We demonstrate that the volcano-type HER profile as a function of calcination temperature is independent of the type of the Cu precursor but is affected by changes in oxidation state and location of the copper species. Supported by DFT modeling, our data suggest that low temperature (<200 degrees C) treatments facilitate electronic communication between the Cu species and TiO2, which allows for a more efficient charge utilization and maximum HER rates. In contrast, higher temperatures (>200 degrees C) do not affect the Cu oxidation state, but induce a gradual, temperature-dependent surface-to-bulk diffusion of Cu, which results in interstitial, tetra-coordinated Cu+ species. The disappearance of Cu from the surface and the introduction of new defect states is associated with a drop in HER performance. This work examines electronic and structural effects that are in control of the photocatalytic activity and can be transferred to other systems for further advancing photocatalysis., Funding Agencies|SSF Foundation [EM16-0004]; Austrian Science Fund (FWF)Austrian Science Fund (FWF) [P32801]; TU-D doctoral college (TU Wien); TU Wien Bibliothek

Photocatalysis on semiconductor metal oxide surfaces has attracted considerable attention as a sustainable environmentally friendly method for water/air purification and hydrogen production by water splitting. Among semiconducting metal oxides TiO2 has been intensively investigated as a promising photocatalyst candidate. However, despite many efforts, its photocatalytic activity is far from a practical level mainly due to inefficient charge carrier separation and resulting charge carrier recombination. An advantageous strategy to address this issue is the development of heterostructures by coupling to a metal to form a Schottky junction or to metal oxides to create a p-n junction at their interface in order to prevent the recombination by vectorial charge carrier separation at these energy junctions. On the other hand it was revealed over the past decade that crystal facets play a decisive role in trapping of charge carriers and thus photocatalytic redox reactions. Thus, selective deposition of metal or metal oxides onto specific facets would enhance the photocatalytic activity by improving charge separation. To achieve higher activities, two methods, the supercritical fluid chemical deposition route and the photodeposition method, were investigated to deposit selectively p-type NiO onto specific facets of ntype TiO2 single crystalline nanoparticles to establish a p-n junction. The resulting NiO/TiO2 nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 sorption measurements, UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The heterojunction photocatalysts showed higher photocatalytic efficiency than pure TiO2 for the decomposition of organic dyes. Particularly, 0.1-0.25 wt % of NiO was the optimal loading amount, showing the highest activity. To elucidate the role of crystal facets o

Thermally induced intercalation of noble metals into non-van der Waals ceramic compounds presents a method to produce a new class of layered materials. We recently demonstrated an exchange reaction of Au with A layers of MAX phase carbides with plentiful combinations of A and M elements. Here, we report the first substitution of Al with Au in a Ti2AlN MAX phase nitride at an elevated temperature without destroying the original layered structure. These results bolster the generalization of the Au intercalation for the A elements in MAX phases with diverse combinations of M, A, and X elements. Furthermore, we propose crucial factors to achieve the exchange reaction: there should be a chemical potential for the A element to dissolve in or react with noble metals to intercalate; the noble metals should be inert to the initial metal carbides/nitrides; and it is necessary to choose the reaction temperature that allows balanced interdiffusion of the noble metals and A elements., Funding Agencies|Swedish Research CouncilSwedish Research Council [2017-03909, 642-2013-8020]; Knut and Alice Wallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM16-0004]