We developed a new chemical strategy to enhance the stability of lead selenide nanocrystals (PbSe NCs) against oxidation through the surface passivation by P-O- moieties. In the synthesis of PbSe NCs, tris(diethylamino)phosphine (TDP) selenide (Se) was used as a Se precursor, and the resulting PbSe NCs withstood long-term air exposure while showing nearly no sign of oxidation. Nuclear magnetic resonance (NMR) spectroscopy reveals that TDP derivatives passivate the surface of PbSe NC. Through a series of ligand cleavage reactions, we found that the TDP derivatives are bound on NC surface through the P-O- moiety. Based on such understanding, it turned out that direct addition of various PAs during the synthesis of PbSe NCs also results in the NCs whose absorption spectrum remains nearly intact after air exposure for weeks. The P-O- moieties render the NCs stable in the operation of field effect transistors, suggesting that our findings can enable the use of air stable PbSe NCs in wider array of optoelectronic applications.

Growth of monodisperse indium phosphide (InP) quantum dots (QDs) represents a pressing demand in display applications, as size uniformity is related to color purity in display products. Here, we report the colloidal synthesis of InP QDs in the presence of Zn precursors in which size uniformity is markedly enhanced as compared to the case of InP QDs synthesized without Zn precursors. Nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and mass spectrometry analyses on aliquots taken during the synthesis allow us to monitor the appearance of metal− phosphorus complex intermediates in the growth of InP QDs. In the presence of zinc carboxylate, intermediate species containing Zn−P bonding appears. The Zn−P intermediate complex with P(SiMe 3 ) 3 exhibits lower reactivity than that of the In−P complex, which is corroborated by our prediction based on density functional theory and electrostatic potential charge analysis. The formation of a stable Zn−P intermediate complex results in lower reactivity, which enables slow growth of QDs and lowers the extreme reactivity of P(SiMe 3 ) 3 , hence monodisperse QDs. Insights from experimental and theoretical studies advance mechanistic understanding and control of nucleation and growth of InP QDs, which are key to the preparation of monodisperse InP-based QDs in meeting the demand of the display market.

We report the photocatalytic conversion of CO2 to CH4 using CuPt alloy nanoclusters anchored on TiO2. As the size of CuPt alloy nanoclusters decreases, the photocatalytic activity improves significantly. Small CuPt nanoclusters strongly bind CO2 intermediates and have a stronger interaction with the TiO2 support, which also contributes to an increased CH4 generation rate. The alloying and size effects prove to be the key to efficient CO2 reduction, highlighting a strategic platform for the design of photocatalysts for CO2 conversion.

We examine the effects of chlorine-passivation of Cd surface atoms on photocatalytic H 2 O reduction by CdSe NCs. Transient absorption spectroscopy reveals that Cl passivation removes electron trap states in CdSe NCs, which is also reflected in an increase of photoluminescence quantum yield, e.g., from 9 to 22% after the Cl treatment. Size-tunable energy states in CdSe NCs enable the systematic investigation of surface defects and their effect on the photocatalytic hydrogen generation rate. It turns out that, depending on band-edge energy levels, the surface trap states may enhance or inhibit photocatalysis. Cl-treated CdSe NCs larger than 2.7 nm show a higher hydrogen evolution rate than untreated CdSe NCs of the same size as Cl treatment removes trap states with energy below the H 2 O reduction potential. In contrast, the same Cl treatment does not increase the photocatalytic rate of CdSe NCs smaller than 2.7 nm because both the conduction band edge and trap states are above the water reduction potential. The size-dependence of the effect of Cl treatment suggests that electron trap states in CdSe may promote photocatalytic activity by enhancing charge separation.

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