Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO S-Scheme Heterojunctions for Photochemical and Photo-/Electrochemical Hydrogen Production

Te-MoTe2-MoSe2/ZnO S-scheme heterojunctions are engineered to ascertain the advanced redox ability in sustainable HER operations. Photo-physical studies have established the steady state transfer of photo-induced charge carriers whereas an improved transfer dynamics realized by state-of-art ultrafast transient absorption and irradiated-XPS analysis of optimized 5wt% Te-MoTe2-MoSe2/ZnO heterostructure. 2.5, 5, and 7.5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ, 5MTMZ and 7.5MTMZ) exhibited 2.8, 3.3, and 3.1-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09%, 41.42% and 38.79% at HER rate of 4.45, 5.25, and 4.92 mmol/gcat/h, respectively. Electrochemical water splitting experiments manifest subdued 583 and 566 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mA cm-2 current density for HER, and 961 and 793 mV for OER, respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step is evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

Verifying the Charge-Transfer Mechanism in S-Scheme Heterojunctions Using Femtosecond Transient Absorption Spectroscopy

The S-scheme heterojunction is flourishing in photocatalysis because it concurrently realizes separated charge carriers and sufficient redox ability. Steady-state charge transfer has been confirmed by other methods. However, an essential part, the transfer dynamics in S-scheme heterojunctions, is still missing. To compensate, a series of cadmium sulfide/pyrene-alt-difluorinated benzothiadiazole heterojunctions were constructed and the photophysical processes were investigated with femtosecond transient absorption spectroscopy. Encouragingly, an interfacial charge-transfer signal was detected in the spectra of the heterojunction, which provides solid evidence for S-scheme charge transfer to complement the results from well-established methods. Furthermore, the lifetime for interfacial charge transfer was calculated to be ca. 78.6 ps. Moreover, the S-scheme heterojunction photocatalysts exhibit higher photocatalytic conversion of 1,2-diols and H₂ production rates than bare cadmium sulfide.

Deciphering the Relaxation Mechanism of Red-Emitting Carbon Dots Using Ultrafast Spectroscopy and Global Target Analysis

Red-emitting carbon dots (C-dots) have tremendous potential for bioimaging and optoelectronic applications. Here, we investigated the structural modification of red-emitting C-dots due to boron doping and their ultrafast relaxation dynamics. It is evident from the X-ray photoelectron spectroscopy study that the relative percentage of pyrridinic nitrogen is increased at the expense of amino nitrogen and graphitic nitrogen in B-doped C-dots. Transient absorption spectroscopy and global target analysis reveal the formation of an additional excited-state level that takes away a significant amount of the excited-state population after boron doping. This new excited state slows the initial relaxation process toward the emissive state from 317 to 750 fs and increases the overall lifetime from 1.03 to 1.45 ns in B-doped C-dots.

Side-Chain Type Polysulfates: Their Synthesis, AIE Properties and Applications for p-Nitrophenol Detection in Water

Two small molecular monomers, ph-TPE and ph-TPE-CN, and their homopolymers Poly (ph-TPE) and Poly (ph-TPE-CN) containing tetra phenylethylene and sulfate structures, were synthesized by a sulfur (VI) fluorine exchange click reaction (SuFEx) and radical polymerization. All the monomers and polymers exhibit a typical aggregation-induced emission (AIE) effect both in the solid state and aggregated state. Moreover, based on the intermolecular charge transfer (ICT) effect between the tetra phenylethylene chromophore and p-nitrophenol, both polymers could be used for the selective detection of p-nitrophenol. The detection limit and reactivity coefficient of Poly (ph-TPE) are 0.081 μM and 5.15×10⁴  M^-1 , respectively, whereas the detection limit and reactivity coefficient of Poly (ph-TPE-CN) are 0.077 μM and 1.81×10⁴  M^-1 , respectively. This can be attributed to the greater sensitivity of Poly (ph-TPE-CN) to p-nitrophenol than that of Poly (ph-TPE). This work provides a new methodology for the preparation and broadening application of side-chain type AIE-active polysulfate fluorescent probes.