Ultrafast excited‐state decay and intrinsic charge carrier recombination restrain the photoactivity enhancement for solar‐to‐H2 production. Here, a CdS‐fullerene/graphene (CdS‐F/G) photocatalyst is ...synthesized for enhancing visible‐light‐driven hydrogen generation from earth‐abundant water. The CdS‐F/G shows ultrafast interfacial electrons/holes transfer and holes self‐trapping process in photocatalysis. The in‐situ dynamic study from transient absorption spectroscopy reveals the sub‐microsecond‐lived excited states (≈172.6 ns), interfacial electron transfer (≈30.3 ps), and hole trapping (≈44.0 ps) in the CdS‐F/G photocatalyst. The efficient active species transportation and prolonged lifetime significantly enhance the charge separation state survival, increasing the photoactivity and photostability. Consequently, visible‐light activity enhancement (>400%) of H2 evolution reaction (HER) is obtained at the CdS‐F/G photocatalyst with high stability (>36 h). The 127.2 µmol h−1 g−1 performance corresponding to a quantum efficiency of 7.24% at 420 nm is not only higher than the case of pristine CdS (29.2 µmol h−1 g−1) but also much higher than that of CdS‐Pt photocatalyst (73.8 µmol h−1 g−1). The cost‐effective CdS‐F/G photocatalyst exhibits a great potential for sustainable and high‐efficiency photocatalytic water splitting into clean energy carriers. Moreover, the optimized electronic structure associated with interfacial electrons/holes transfer and holes self‐trapping promotes overall water splitting for H2 and O2 generation.
Fullerene–graphene (F/G) boosts the excited state survival to sub‐microsecond and overall improves the photocatalytic activity/stability of CdS. The lower Fermi level of F/G enables it to collect charge carriers from the CdS photocatalyst for highly efficient interfacial electrons/holes transport and H2 production. As a result, the enhanced H2 production rate demonstrates a great potential to replace noble metal (Pt) for solar‐to‐H2 conversion.
The overall water splitting efficiency is mainly restricted by the slow kinetics of oxygen evolution. Therefore, it is essential to develop active oxygen evolution catalysts. In this context, we ...designed and synthesized a tungsten oxide catalyst with oxygen vacancies for photocatalytic oxygen evolution, which exhibited a higher oxygen evolution rate of 683 μmol h−1 g−1 than that of pure WO3 (159 μmol h−1 g−1). Subsequent studies through transient absorption spectroscopy found that the oxygen vacancies can produce electron trapping states to inhibit the direct recombination of photogenerated carriers. Additionally, a Pt cocatalyst can promote electron trap states to participate in the reaction to improve the photocatalytic performance further. This work uses femtosecond transient absorption spectroscopy to explain the photocatalytic oxygen evolution mechanism of inorganic materials and provides new insights into the design of high‐efficiency water‐splitting catalysts.
In photocatalytic oxygen evolution, some excited electrons can be trapped more easily to form trapped state electrons due to the presence of oxygen vacancies in Ov‐WO3‐600. This process can partially inhibit direct recombination and prolong the lifetime of photogenerated charges. In addition, photodeposited Pt can serve as an active site to capture the trapped state electrons to react with electron sacrificial agents.
Efficient photocatalytic solar-to-H2 conversion is pivotal to zero-carbon energy supply. Graphitic carbon nitride (g-C3N4) is a promising visible-light photocatalyst but suffers from intrinsic ...electron–hole recombination and deep-charge trapping, limiting its efficiency. Here, we show a synergistic strategy of porosity, vacancy and shallow(trapping)-state engineering to enrich catalytic sites and promote the lifetime of active electrons by thermochemical treatment and phosphorus-interstitial-doping. The latter enhances the electron delocalization in the π-conjugate polymeric structure. The optimized photocatalyst shows a ∼800% increase in H2 generation (6323 μmol h−1 g−1) and an about 5-fold increase in quantum efficiency (QE420 nm = 5.08%). The superior performance is attributed to the long-lived shallow charge trapping, as a result of proton-feeding to the coordinated phosphorus site during the photocatalytic reaction, which enhances the photogenerated carrier lifetime and positively optimizes the band structure of the catalyst. Femtosecond transient absorption spectroscopy reveals a doubling lifetime of shallow-trapped charges (∼405.5 ps), favoring high mobility for electron-involved photocatalytic H2 generation. This work provides a new mechanism for improving charge carrier dynamics and photocatalytic performance.
Exploring TiO2‐photocatalysts for sunlight conversion has high demand in artificial photosynthesis. In this work, edge‐enriched ultrathin molybdenum disulfide (MoS2) flakes are uniformly embedded ...into the bulk of yolk‐shell TiO2 as a cocatalyst to accelerate photogenerated‐electron transfer from the bulk to the surface of TiO2. The as‐formed MoS2/TiO2 (0.14 wt%) hybrids exhibit a high hydrogen evolution rate (HER) of 2443 µmol g−1 h−1, about 1000% and 470% of that of pristine TiO2 (247 µmol g−1 h−1) and bulk MoS2 decorated TiO2 (513 µmol g−1 h−1). Such a greatly enhanced HER is attributed to the exposed catalytic edges of the ultrathin MoS2 flakes with a robust chemical linkage (TiS bond), providing rapid charge transfer channels between TiO2 and MoS2. The catalytic stability is promoted by the antiaggregation of the highly dispersed MoS2 flakes in the bulk of yolk‐shell TiO2. The exponential fitted decay kinetics of time‐resolved photoluminescence (ns‐PL) spectra illustrates that embedding ultrathin MoS2 flakes in TiO2 effectively decreases the average lifetime of PL in the MoS2/TiO2 hybrids (τave = 4.55 ns), faster than that of pristine TiO2 (≈7.17 ns) and the bulk MoS2/TiO2 (≈6.13 ns), allowing a superior charge separation and charge trapping process for reducing water.
Chemical bonding of ultrathin MoS2 flakes mediates the electron transfer channel from the bulk to the surface of crystal TiO2. Embedded ultrathin MoS2 effectively suppresses charge trapping and shows excellent photoactivity and high stability with the increasing exposed catalytically edges. The transient fluorescence kinetics confirms the prolonged lifetime of photogenerated active electrons in an MoS2/TiO2 composite.
Undesired photoelectronic dormancy through active species decay is adverse to photoactivity enhancement. An insufficient extrinsic driving force leads to ultrafast deep charge trapping and ...photoactive species depopulation in carbon nitride (g‐C3N4). Excitation of shallow trapping in g‐C3N4 with long‐lived excited states opens up the possibility of pursuing high‐efficiency photocatalysis. Herein, a near‐field‐assisted model is constructed consisting of an In2O3‐cube/g‐C3N4 heterojunction associated with ultrafast photodynamic coupling. This In2O3‐cube‐induced near‐field assistance system provides catalytic “hot areas”, efficiently enhances the lifetimes of excited states and shallow trapping in g‐C3N4 and this favors an increased active species density. Optical simulations combined with time‐resolved transient absorption spectroscopy shows there is a built‐in charge transfer and the active species lifetimes are longer in the In2O3‐cube/g‐C3N4 hybrid. Besides these properties, the estimated overpotential and interfacial kinetics of the In2O3‐cube/g‐C3N4 hybrid co‐promotes the liquid phase reaction and also helps in boosting the photocatalytic performance. The photocatalytic results exhibit a tremendous improvement (34‐fold) for visible‐light‐driven hydrogen production. Near‐field‐assisted long‐lived active species and the influences of trap states is a novel finding for enhancing (g‐C3N4)‐based photocatalytic performance.
A near‐field‐assisted model containing an In2O3‐cube/g‐C3N4 heterojunction that can assist with ultrafast photodynamic coupling is constructed. Near‐field assistance is found to enhance long‐lived shallow charge trapping in g‐C3N4 so as to favor generating an increased photoactive species population. A mechanism for the photophysical and photochemical routes is deduced from time‐resolved spectroscopy combined with results from optical simulations.
Non‐alternant topologies have attracted considerable attention due to their unique physiochemical characteristics in recent years. Here, three novel topological nanographenes molecular models of ...nitrogen‐doped Stone–Thrower–Wales (S–T–W) defects were achieved through intramolecular direct arylation. Their chemical structures were unambiguously elucidated by single‐crystal analysis. Among them, threefold intramolecular direct arylation compound (C42H21N) is the largest nanographene bearing a N‐doped non‐alternant topology to date, in which the non‐benzenoid rings account for 83 % of the total molecular skeleton. The absorption maxima of this compound was located in the near‐infrared region with a long tail up to 900 nm, which was much longer than those reported for similarly sized N‐doped nanographene with six‐membered rings (C40H15N). In addition, the electronic energy gaps of these series compounds clearly decreased with the introduction of non‐alternant topologies (from 2.27 eV to 1.50 eV). It is noteworthy that C42H21N possesses such a low energy gap (Egopt=1.40 eV; Egcv=1.50 eV), yet is highly stable under ambient conditions. Our work reported herein demonstrates that the non‐alternant topology could significantly influence the electronic configurations of nanocarbons, where the introduction of a non‐alternanting topology may be an effective way to narrow the energy gap without extending the molecular π‐conjugation.
Saddle‐shaped nanographenes containing N‐doped Stone‐Thrower‐Wales topological defects have been synthesized that possess much narrower energy gaps than similar‐sized N‐doped nanographenes with six‐membered rings. This work indicates that the introduction of non‐alternant topologies is an efficient way to narrow the energy gap without extending the molecular size.
Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited-state intramolecular motions. Although AIE has attracted increasing attention due to the ...significant applications in biomedical and optoelectronics, an in-depth understanding of the excited-state intramolecular motion has yet to be fully developed. Here we found the non-aromatic annulene derivative of cyclooctatetrathiophene shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism is investigated through photoluminescence spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism as well as by pressure-dependent fluorescent spectra etc., which indicate that the aromaticity reversal from ground state to the excited state serves as a driving force for inducing the excited-state intramolecular vibration, leading to the AIE phenomenon. Therefore, aromaticity reversal is demonstrated as a reliable strategy to develop vibrational AIE systems. This work also provides a new viewpoint to understand the excited-state intramolecular motion behavior of lumiongens.
Understanding the structural features and the dynamics and properties of charge carriers in photocatalysts is critical to develop them for practical applications. Photocatalytic H2 production on ...molybdenum sulfide/cadmium sulfide (MoS2/CdS) nanorods in the presence of lactic acid under visible light (λ > 420 nm) was investigated. The optimized MoS2/CdS photocatalysts with 1.52 wt% MoS2 showed the highest rate of 154.748 μmol h−1 mg−1, which is 5 times faster than that of bare CdS nanorods. Experimental results from HR-TEM, UV-vis, and photoelectrochemical measurements suggest that an intimate contact interface, extended light response range, effective separation of the photogenerated charge carriers and high photocurrent density on the MoS2 modification contributed to the photocatalytic enhancement of the MoS2/CdS photocatalysts. Electrochemical measurements indicate that MoS2 is an efficient H2 evolution co-catalyst, which is attributed to the promotion of the photocatalytic activity. Femtosecond transient absorption (fs-TA) spectroscopy was performed to investigate the dynamics of the charge carriers that led to hydrogen production by these composites. The results reveal that the enhanced hole trapping process and effective electrons transfer (within 14.8 ps) from CdS to MoS2 in MoS2/CdS composites can promote their photocatalytic activity dramatically.
A particular challenge in the design of organic photosensitizers (PSs) with donor–acceptor (D‐A) structures is that it is based on trial and error rather than specific rules. Now these challenges are ...addressed by proposing two efficient strategies to enhance the photosensitization efficiency: polymerization‐facilitated photosensitization and the D‐A even–odd effect. Conjugated polymers have been found to exhibit a higher 1O2 generation efficiency than their small molecular counterparts. Furthermore, PSs with A‐D‐A structures show enhanced photosensitization efficiency over those with D‐A‐D structures. Theoretical calculations suggest an enhanced intersystem crossing (ISC) efficiency by these strategies. Both in vitro and in vivo experiments demonstrate that the resulting materials can be used as photosensitizers in image‐guided photodynamic anticancer therapy. These guidelines are applicable to other polymers and small molecules to lead to the development of new PSs.
Conjugated polymers have a higher 1O2 generation efficiency than their small molecular counterparts. Photosensitizers with A‐D‐A structures are better than D‐A‐D structures. Both in vitro and in vivo experiments show that the resulting materials can be used as photosensitizers in image‐guided photodynamic anticancer therapy. D=donor, A=acceptor.
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