Кафедра биофизики

Titanium dioxide (TiO₂) is regarded as an important prototype photocatalytic material for several decades. The charge carrier kinetics determines the photocatalytic properties of TiO₂ materials; this is found to be greatly dependent on electronic structures. It has been revealed that the intrinsic intermediate gap states (intrinsic GSs) play a significant role in charge carrier kinetics that drive the photocatalytic processes of TiO₂ materials, which are not well summarized until now. Motivated by this thought, the purpose of this review focuses on physiochemical science of the intrinsic GSs of TiO₂ materials and their important role in charge carrier kinetics. We first give a summary on the chemical resources of the intrinsic GSs in TiO₂ and their physiochemical nature. Their general energy distribution, charge carrier population, and the associated thermodynamic properties are also elaborated from an overall viewpoint. We further carefully summarise and compare the experimental studies on the energy and the density distribution of the intrinsic GSs and discuss the associated chemical resources and charge carrier localizations. Trapping is the dominant function of intrinsic GSs in the charge carrier kinetics of TiO₂ materials. The significant effect of trapping on the transport, recombination, and interfacial transfer of charge carriers are also comprehensive summarized. Furthermore, the effects of charge carrier kinetics on photocatalytic performances are also discussed to some extents. Because of the importance of intrinsic GSs in modulating charge carrier kinetics, it is expected to increase the photocatalytic activity by engineering the intrinsic GSs, not only for TiO₂ materials, but also for the other semiconductor photocatalysts.

Carbon dioxide (CO₂) is regarded as a main contributor to the greenhouse effect. As a potential strategy to mitigate its negative impacts, the reduction of CO₂ is environmentally critical, economically meaningful and scientifically challenging. Being both thermodynamically and kinetically unfavored, CO₂ reduction requires catalysts as a crucial component irrespective of the reaction modes, be it electrocatalytic, photoelectrocatalytic or photocatalytic. In an effort to systematically review the types of catalysts that have been studied for CO₂ reduction, we categorize them into two major groups: those being activated by external sources and those being photoexcited and activated themselves. Attention is focused on the detailed mechanisms for each group by which the reduction of CO₂ proceeds, yielding a summary of the guiding principles for catalyst designs. This review highlights the importance of mechanistic studies, which permits us to discuss our perspectives on potential directions of catalyst investigation for future catalytic CO₂ reduction research.

Photochemistry based on acenes and their derivatives is one of the emerging research areas in the field of polycyclic aromatic hydrocarbons (PAHs). However, due to the increased reactivity of larger acenes towards light and singlet oxygen, it is difficult to precisely control their photochemical reactions. Therefore, the unexpected reactivity of acene-based molecules brings about two challenging topics: how to design stable acenes and how to utilize the photochemistry to design new acene-based functional materials. In this review, we first focus on the mechanism of photochemistry of acenes to theoretically understand how these reactions could have happened. Next, we will give a summary on both acene-based photocyclization and photooxidation reactions.

To relieve the growing pressure originated from the energy shortage and environmental issues, solar-energy conversion into chemical or electrical energy has undergone an unprecedented development as a promising strategy in recent years. Indium sulfide (In₂S₃), an efficient visible-light harvester, has been extensively investigated in the field of photoconversion, owing to the fascinating merits including superior photo-absorption coefficient, photoelectric sensitivity, favorable carrier mobility, moderate band gap, excellent stability, and low toxicity. To take full advantage of these properties and further expand beyond the existing short board like low quantum efficiency, various In₂S₃-based functional nanostructures like nanoparticles, nanotubes, atomic two-dimensional sheets, and nanosheets-assembled complexes have been developed. Meanwhile, pleasurable characters of In₂S₃ have been modulated via defective engineering, doping, and hybridization (with inorganic materials or bio-molecules). Gratifyingly, In₂S₃-based photocatalytic, photoelectrocatalytic and photovoltaic systems have made significant impact on the field of energy and environmental issues. Therefore, this review provides an overview of crystal and morphologic structures of pristine In₂S₃ as well as many outstanding properties. Moreover, the pristine In₂S₃ and its derivatives with diverse synthesis routes are systematically summarized. Further, the advancement of In₂S₃-based photocatalytic, photoelectrocatalytic and photovoltaic systems, especially in environmental decontamination, artificial photosynthesis for renewable fuels and solar cells, are highlighted in detail. Ultimately, we conclude with a summary and propose some invigorating perspectives on the challenges from atomic (or macroscopical) structure modulation in material nature, photochemical behavior understanding to solar photovoltaic applications at the forefront of this research platform.

Due to the defect structure, suitable band gap, photoelectric sensitivity and low toxicity, state-of-the-art accomplishments of In₂S₃-based photocatalysis and photovoltaics have been achieved for solar-energy conversion and utilization. A broad photoconversion field of photochemically environmental decontamination, artificial photosynthesis for renewable fuels, and solar cells makes sense for energy and environmental issues.

Photoelectrocatalysis studies have emerged tremendous knowledge and experience, which has led to discovery of a number of active materials. Due to complexity of the processes involved, however, development of suitable semiconductor and catalyst for the photoelectrocatalysis still requires a try-and-error approach as different parameters are coherently varied to determine overall performance. This contribution provides insight into the key optoelectronic properties of the semiconductors, such as absorption coefficient, dielectric constant, effective masses, exciton binding energy, and band positions. The combined assessment from theoretical and experimental points of view is reviewed, which may help thorough understanding of the semiconductors and the way to reliably characterize them, and in turn to develop improved photoelectrocatalytic materials.

Photocatalytic reactions are governed by photogenerated charge carriers upon band gap excitation. Therefore, for better understanding of the mechanism, the dynamics of photocarriers should be studied. One of the attractive materials is TiO₂, which has been extensively investigated in the field of photocatalysis. This review article summarizes our recent works of time-resolved visible to mid-IR absorption measurements to elucidate the difference of anatase, rutile, and brookite TiO₂ powders. The distinctive photocatalytic activities of these polymorphs are determined by the electron-trapping processes at the defects on powders. Powders are rich in defects and these defects capture photogenerated electrons. The depth of the trap is crystal phase dependent, and they are estimated to be < 0.1 eV, ∼0.4 eV and ∼0.9 eV for anatase, brookite, and rutile, respectively. Electron trapping reduces probability to meet with holes and then elongate the lifetime of holes. Therefore, it works negatively for the reaction of electrons but positively works for the reaction of holes. In the steady-state reactions, both electrons and holes should be consumed. Hence, the balance between the positive and negative effects of defects determines the distinctive photocatalytic activities of anatase, rutile, and brookite TiO₂ powders.

Fluorescent carbon dots (C-dots) are new class of nanomaterials with widespread applications in optoelectronics, bio-imaging, catalysis, and sensing. The origin of photoluminescence of carbon dots is a debatable issue which is pretend to depend on the chemical structures such as graphitic conjugated core, molecular fluorophores and the surface defect states found to be dependent on the method of preparation. In this review, we have illustrated the important issues and challenges of the luminescent carbon dots and their potential applications. Graphitic conjugated core containing carbon dots is being synthesized usually from bulk materials like graphite, graphene and graphene oxide which exhibit size dependent photoluminescence behaviour due to quantum confinement. On the other hand, carbon dots synthesized from small molecules exhibit excitation dependent emission due to the presence of surface energy trap states which can be tuned by surface modification. Again, presence of both conjugated core and surface defect generates dual emission property. It is evident that various molecular fluorophores are produced inside carbon dots during low temperature synthesis. Hetero-atom doping is another strategy to tune the photoluminescence properties of carbon dots. Red emitting carbon dots are found to be suitable for bio-imaging applications after surface modification. Again, high quantum yield and solar light absorbing carbon dots are required for light harvesting and optoelectronic applications. Surface modified carbon dots are found to be appropriate for sensing applications. Analysis reveals that carbon dots based hybrid systems provide good applicability towards construction of solar cell devices because of their efficient charge separation.

Chemical Structure monitors the photoluminescence properties of carbon dots

The emergence of cuprous oxide (Cu₂O) as a visible light active semiconductor for photocatalytic and photoelectrochemical applications has elevated significantly over the past decade. With photocorrosion identified as a severe issue for Cu₂O, its photoactivity has been greatly restricted. Given that Cu₂O redox potentials are located in between its band gap, the possible occurrence of self-photoreduction or self-oxidation upon illumination is inevitable. Various efforts have been directed to implement effective strategies in enhancing the photostability of Cu₂O. In particular, most of the studies focused on improving the charge transfer from Cu₂O to reactants or co-catalyst to avoid accumulation of charge within the particles. This review presents recent research progresses for the development of strategies to suppress Cu₂O photocorrosion in regards to its intrinsic properties and charge kinetics. It is shown that effective transport of electrons or holes out of Cu₂O photocatalyst by engineering its crystal structure, tuning its reaction environment or depositing secondary elements could effectively inhibit Cu₂O from experiencing self-photodecomposition. Understanding of the charge dynamics with respect to its photocorrosion is pivotal to optimize the design of Cu₂O photocatalyst for enhanced performance in the future.

Highly anisotropic 2D nanosheets of inorganic solids with nanometer-level thickness attract a great deal of research activity because of their unique merits in exploring novel high performance photocatalysts applicable for environmental purification and production of renewable clean energy. The 2D inorganic nanosheets possess many valuable properties such as tailorable band structures and chemical compositions, large surface areas, well-defined defect-free surface structure, and tunable electrical conductivities. Due to these unique advantages of 2D inorganic nanosheets, these materials can be used as promising building blocks for hybrid-type photocatalysts with optimized band structures, expanded surface areas, improved charge separation behaviors, and enhanced reaction kinetics. Of prime importance is that unusually strong electronic coupling can occur between very thin 2D inorganic nanosheets and hybridized nanospecies, leading to the synergistic optimization of electronic and optical properties, and thus the remarkable enhancement of photocatalytic activity. Depending on the type of component nanosheets, diverse examples of inorganic nanosheet-based photocatalysts are presented along with the in-depth discussion about critical roles of inorganic nanosheet in these hybrid photocatalysts. Future perspectives in the researches for 2D inorganic nanosheet-based photocatalysts are discussed to offer useful directions for designing and synthesizing novel high performance photocatalysts applicable for renewable energy production and environmental purification.