Band gap tunable hybrid organic−inorganic lead halide perovskites (APbX 3 , A = CH 3 NH 3 + and NH 2 CHNH 2 + , and X = Cl, Br, or I) have attracted significant attention in optoelectronic-and photovoltaic-related fields on account of their outstanding optoelectronic properties. Single crystals of hybrid perovskites, such as CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 , were certified to be advantageous over thin films as photodetectors. However, their resistance toward heat and moisture hinders their future development. Fully inorganic perovskite CsPbBr 3 stands a chance to fill the gap as a novel photodetector with perovskite structure. We revealed the growth of CsPbBr 3 single crystal was of a 2D nucleation mechanism. Similarities of d values and octahedra arrangements along [101] and [020] orientations restricted single-crystal growth. Under optimized conditions, orthorhombic CsPbBr 3 single crystals with (101) crystallographic facets were grown by using methyl alcohol as antisolvent from saturated DMSO solution. The optoelectronic properties of the single crystal were explored through a metal− semiconductor−metal photodetector device. Meanwhile, their steady and transient performances were also investigated. A highest responsivity of 0.028 A/W and a response time of <100 ms were achieved.

The big challenging issues in photocatalytic H 2 evolution are efficient separation of the photoinduced carriers, the stability of the catalyst, enhancing quantum efficiency, and requiring photoinduced electrons to enrich on photocatalysts' surface. Herein, Ti 3 C 2 MXene quantum dots (QDs) possess the activity of Pt as a co-catalyst in promoting the photocatalytic H 2 evolution to form heterostructures with g-C 3 N 4 nanosheets (NSs) (denoted g-C 3 N 4 @Ti 3 C 2 QDs). The photocatalytic H 2 evolution rate of g-C 3 N 4 @Ti 3 C 2 QD composites with an optimized Ti 3 C 2 QD loading amounts (100 mL) is nearly 26, 3 and 10 times higher than pristine g-C 3 N 4 NSs, Pt/g-C 3 N 4 , and Ti 3 C 2 MXene sheet/g-C 3 N 4 , respectively. The Ti 3 C 2 QDs increase the specific surface area of g-C 3 N 4 and boost the density of the active site. Besides, metallic Ti 3 C 2 QDs possess excellent electronic conductivity, causing the improvement of carrier transfer efficiency. KEYWORDS: photocatalytic H 2 production, Ti 3 C 2 MXene quantum dots, g-C 3 N 4 nanosheets, co-catalysts

The commercial Haber-Bosch process for NH3 production not only requires large amounts of energy and hydrogen supply but also generates tremendous greenhouse CO2 emission. To mitigate energy and environmental challenges, renewable ammonia production technologies based on electrochemical and photochemical methods, in particular, photocatalytic nitrogen fixation in aqueous phase for ammonia production is highly desired. In the present work, single-atom Pt anchored at the −N3 sites of stable and ultrathin covalent triazine framework (CTF) nanosheets have been successfully synthesized (Pt-SACs/CTF). The well-defined coordination structure of Pt–N3 sites in the Pt-SACs/CTF catalyst have been characterized using HAADF-STEM and EXAFS, as well as ab initio molecular dynamics simulations. The ammonia production rate over the as-synthesized Pt-SACs/CTF catalyst is 171.40 μmol g–1 h–1 in the absence of sacrificial agent. On the basis of density functional theory calculations, it has been found that the alternating mechanism is energetically more favorable than the distal mechanism over the well-defined Pt–N3 sites. The significance of the present work is to demonstrate that the single-atom metal catalysts are anchored at the two-dimensional stable CTF nanosheets for photocatalytic nitrogen fixation to ammonia.

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