Metastable Ni(I)-TiO2-x Photocatalysts: Self-Amplifying H2 Evolution from Plain Water without Noble Metal Co-Catalyst and Sacrificial Agent.

Decoration of semiconductor photocatalysts with cocatalysts is generally done by a step-by-step assembly process. Here, we describe the self-assembling and self-activating nature of a photocatalytic system that forms under illumination of reduced anatase TiO2 nanoparticles in an aqueous Ni2+ solution. UV illumination creates in situ a Ni+/TiO2/Ti3+ photocatalyst that self-activates and, over time, produces H2 at a higher rate. In situ X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy show that key to self-assembly and self-activation is the light-induced formation of defects in the semiconductor, which enables the formation of monovalent nickel (Ni+) surface states. Metallic nickel states, i.e., Ni0, do not form under the dark (resting state) or under illumination (active state). Once the catalyst is assembled, the Ni+ surface states act as electron relay for electron transfer to form H2 from water, in the absence of sacrificial species or noble metal cocatalysts.

Magnetic Polaron States in Photoluminescent Carbon Dots Enable Hydrogen Peroxide Photoproduction.

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induces the generation of spin-separated species, including electron/hole (e- /h+ ) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e- /h+ pairs and triplet species depends on the solvent polarity, featuring a substantial stabilization of the triplet state in a non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerge from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties are dissected theoretically by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakelike model systems, revealing the importance of size dependence and interlayer effects. The formation of the spin-separated states in Asp-CDs enables the photoproduction of hydrogen peroxide (H2 O2 ) from water and water/2-propanol mixture via a water oxidation reaction.

Graphene Nanobeacons with High-Affinity Pockets for Combined, Selective, and Effective Decontamination and Reagentless Detection of Heavy Metals.

Access to clean water for drinking, sanitation, and irrigation is a major sustainable development goal of the United Nations. Thus, technologies for cleaning water and quality-monitoring must become widely accessible and of low-cost, while being effective, selective, sustainable, and eco-friendly. To meet this challenge, hetero-bifunctional nanographene fluorescent beacons with high-affinity pockets for heavy metals are developed, offering top-rated and selective adsorption for cadmium and lead, reaching 870 and 450 mg g-1 , respectively. The heterobifunctional and multidentate pockets also operate as selective gates for fluorescence signal regulation with sub-nanomolar sensitivity (0.1 and 0.2 nm for Pb2+ and Cd2+ , respectively), due to binding affinities as low as those of antigen-antibody interactions. Importantly, the acid-proof nanographenes can be fully regenerated and reused. Their broad visible-light absorption offers an additional mode for water-quality monitoring based on ultra-low cost and user-friendly reagentless paper detection with the naked-eye at a limit of detection of 1 and 10 ppb for Pb2+ and Cd2+ ions, respectively. This work shows that photoactive nanomaterials, densely-functionalized with strong, yet selective ligands for targeted contaminants, can successfully combine features such as excellent adsorption, reusability, and sensing capabilities, in a way to extend the material's applicability, its life-cycle, and value-for-money.

Optimized Pt Single Atom Harvesting on TiO2 Nanotubes-Towards a Most Efficient Photocatalyst.

In the present work the authors show that anodic TiO2 nanotubes (NT) show excellent harvesting properties for Pt single atoms (Pt SAs) from highly dilute Pt solutions. The tube walls of anodic nanotubes, after adequate annealing to anatase, provide ample of suitable trapping sites-that is, surface Ti3+ -Ov (Ov : oxygen vacancy) defects that are highly effective to extract and accumulate Pt in the form of SAs. A saturated (maximized) SA density can be achieved by an overnight immersion of a TiO2 NT layer to a H2 PtCl6 solution with a concentration that is as low as 0.01 mm Pt. Such TiO2 NTs with surface trapped Pt SAs provide a maximized high activity for photocatalytic H2 generation (reaching a turnover frequency (TOF) of 1.24 × 106 h-1 at a density of 1.4 × 105 Pt atoms µm-2 )-a higher loading with Pt nanoparticles does not further increase the photocatalytic activity. Overall, these findings show that anodic TiO2 nanotubes provide a remarkable substrate for Pt extraction and recovery from very dilute solutions that directly results in a highly efficient photocatalyst, fabricated by a simple immersion technique.

As a single atom Pd outperforms Pt as the most active co-catalyst for photocatalytic H2 evolution.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.