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Understanding the charge reactions at the semiconductor/cocatalyst interface is of great interest for boosting photoelectrochemical water splitting since the charge transfer to water molecules is the sluggish one. Besides the dopants, porosity, or ion-penetration of the cocatalyst, the crystallinity of the cocatalyst may also influence the charge reactions at the interface. Herein, we prepared amorphous LaNiOx and crystalline La-doped NiO (c-LaNiOx) cocatalysts through photochemical decomposition and ion-exchange of Ni(OH)2 precipitation, respectively. Both lanthanum nickel oxides (LaNiOx) showed considerable improvement of hematite photoanodes. By using electrochemical impedance measurements, we confirmed that the catalyst could store photogenerated charges with reduced transfer resistance and passivate the surface state, resulting in the overall charge transfer rate enhancement. This study may lead to a chance to uncover the kinetic bottleneck with an efficient cocatalyst in well-controlled crystallinity in the future. [ABSTRACT FROM AUTHOR]

Robust, metal-free, macroscopic 3D porous CN/CE hybrid photocatalyst was fabricated by the co-assembly of g-C 3 N 4 and cellulose substrate, in which such an interconnected porous network facilitates mass transport, strong adsorption and multireflection of incident light. Consequently, the CN/CE hybrid photocatalyst exhibited both an excellent adsorption capacity and improved photocatalytic activity toward methylene blue degradation with degradation rate of 99.8%. • Robust, metal-free, 3D porous g-C 3 N 4 /cellulose hybrid photocatalyst was fabricated. • Highly porous network facilitates mass transport, adsorption and light multireflection. • Syncretic interface between g-C 3 N 4 and cellulose increases photoelectrons transfer. • Methylene blue removal ratio over the CN/CE hybrid photocatalyst reaches up to 99.8%. • The CN/CE hybrid photocatalyst exhibits mechanical stability and high reusability. Robust, metal-free, macroscopic 3D porous g-C 3 N 4 /cellulose (CN/CE) hybrid photocatalyst was successfully fabricated by the co-assembly of g-C 3 N 4 and cellulose substrate. The morphology, structure, mechanical property, optical and electrochemical performances, and photocatalytic activity of the CN/CE were investigated in detail. The obtained CN/CE hybrid photocatalyst possessed homogeneous 3D interconnected network structure, excellent mechanical strength and considerable recyclability. Also, the CN/CE hybrid photocatalyst exhibited both an excellent adsorption capacity and improved photocatalytic activity toward methylene blue (MB) degradation with degradation rate of 99.8%, much higher than that of pure g-C 3 N 4 (54.2%). The enhanced photocatalytic performance of CN/CE derived from the synergistic effects of homogeneous 3D interconnected network structure and syncretic interfaces between g-C 3 N 4 and cellulose, facilitating mass transport, light absorption and reactant adsorption, as well as the transfer of the photogenerated electrons. Moreover, the CN/CE hybrid photocatalyst indicated a high reusability and stability without significant reduction in its efficiency with nearly 96% of MB degradation after four cycles. This work not only demonstrated the importance of homogeneous interconnected network structure to prepare highly effective photocatalyst, but also provided a new insight into the approach for design and utilization of stable and recyclable metal-free photocatalyst for visible light derived contaminant degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-organic polymers (MOPs) can enhance the photoelectrochemical (PEC) water oxidation performance of BiVO 4 photoanodes, but their PEC mechanisms have yet to be comprehended. In this work, we constructed an active and stable composite photoelectrode by overlaying a uniform MOP on the BiVO 4 surface using Fe2+ as the metal ions and 2,5-dihydroxyterephthalic acid (DHTA) as ligand. Such modification on the BiVO 4 surface yielded a core-shell structure that could effectively enhance the PEC water oxidation activity of the BiVO 4 photoanode. Our intensity-modulated photocurrent spectroscopy analysis revealed that the MOP overlayer could concurrently reduce the surface charge recombination rate constant (k sr) and enhance the charge transfer rate constant (k tr), thus accelerating water oxidation activity. These phenomena can be ascribed to the passivation of the surface that inhibits the recombination of the charge carrier and the MOP catalytic layer that improves the hole transfer. Our rate law analysis also demonstrated that the MOP coverage shifted the reaction order of the BiVO 4 photoanode from the third-order to the first-order, resulting in a more favorable rate-determining step where only one hole accumulation is required to overcome water oxidation. This work provides new insights into the reaction mechanism of MOP-modified semiconductor photoanodes. [ABSTRACT FROM AUTHOR]

Multiple-step mechanisms have been extensively proposed in many electrocatalytic and/or photocatalytic oxygen evolution reactions. But the surface charge reaction is less studied quantitatively. More difficultly, the verification methods for new multiple-step photocatalytic reactions are rarely found, which could be one of the main reasons for the insufficient reaction mechanism study. In this work, we aim to elucidate the rate-law relationship of the multiple-charge reactions, which is derived based on the microkinetics calculation on the photophysical redox reactions using pre-equilibrium approximation and steady-state approximation. The numerical analysis demonstrates that an nth-order feature could be observed when the nth-step is a rate-determined step in a multiple-step reaction. Likely, the 4th-order charge transfer could be possibly found for oxygen evolution reaction, suggesting the analytical methods and results could further boost the fundamental studies in photocatalysts and multiple-step reactions. [ABSTRACT FROM AUTHOR]

Photoenzymatic catalysis is an efficient strategy for selectively converting CO 2 into valuable chemicals. However, the sluggish reaction kinetics, resulting from low visible light utilization and rapid recombination of photogenerated carriers, severely inhibit the yields of target products. Herein, we present a novel artificial photosynthesis platform of 2D/2D MXene/crystalline COF-367 heterostructure for efficient conversion of CO 2 into HCOOH. This platform is extremely sensitive to solar light (λ ≤ 750 nm), with rapid charge separation and transfer due to the well-designed abundant ultrathin 2D/2D hetero-interfaces. Remarkably, Ti 3 C 2 /COF-367 achieves an impressive yield of 83.38% for coenzyme NADH regeneration with absence of electron mediator. Furthermore, it demonstrates a cascade ultra-high production rate of HCOOH at 1.88 mmol g−1 h−1 with almost 100 % selectivity. This work represents the first example of MXene to promote charge transfer in COFs-based photoenzymatic synergistic catalytic system, and provides insights into the development of organic/inorganic hybrids for CO 2 photoreduction. [Display omitted] • First example of MXene to promote charge transfer in COFs-based photoenzymatic catalytic system. • Ultrathin highly crystalline imine-linked COF-367 nanosheets were synthesized. • Abundant ultrathin 2D/2D hetero-interfaces for rapid charge separation/transfer. • Impressive NADH regeneration yield of 83.38% without electron mediator. • Ultra-high HCOOH production rate of 1.88 mmol g−1 h−1 with high selectivity. [ABSTRACT FROM AUTHOR]

Although hybrid solar cells take advantages of both inorganic and organic semiconductors for high performance, there have not been comparably photoelectric conversion efficiencies as expected from this kind of solar cells till now. The photoelectric response behavior of inorganic/organic hybrid solar cells has been explained on the theory of inorganic solar cells, but the distinctive wavelength dependent photoelectric character of organic semiconductors has not been well considered. In this work, Ag 2 S/organic bulk heterojunction solar cell devices were designed and fabricated in-situ on indium tin oxide (ITO) based on the direct metal surface elemental reaction (DMSER) method, to understand the corresponding photoinduced charge carrier dynamics under different wavelength light. The commonly used small molecule Spiro-OMeTAD and polymeric PTB7-Th were selected as the organic components of the fabricated solar cells. In Ag 2 S/Spiro-OMeTAD, Ag 2 S donated the charge carriers and controlled the photoinduced charge carrier dynamics of the devices at both 355 nm and 532 nm lights. Under 532 nm light, the PTB7-Th acted as hole transport materials (HTM) rather than charge carrier donor. These results indicated that hybrid thin films without wavelength dependent charge carrier dynamics is preferred for high performance solar cells. [ABSTRACT FROM AUTHOR]

An ultrathin layered 2D/2D van der Waals heterojunction of ReS 2 /high-crystalline g-C 3 N 4 is reported to significantly improve photocatalytic H 2 production attribute to its efficient charge transport, strong visible light harvesting, and suppressed recombination of photogenerated carriers. [Display omitted] • Ultrathin layered 2D/2D van der Waals heterojunction of ReS 2 /high-crystalline g-C 3 N 4. • Efficient charge transport of highly crystalline g-C 3 N 4 by eliminating deep defects. • Strong visible light harvesting, and excellent conductivity of ReS 2 nanoflakes. • Synergistic effect of rapid charge separation and transfer in 2D/2D heterojunction. • Superior photocatalytic H 2 -evolution efficiency of 3.46 mmol g−1h−1. Fabricating efficient nanocatalysts with excellent visible light response, coupled with rapid charge separation and transfer efficiency is still the most challenge for solar-driven hydrogen (H 2) evolution. Herein, an ultrathin layered 2D/2D van der Waals heterojunction of ReS 2 /high-crystalline g-C 3 N 4 (CCN) is constructed for the first time to significantly boost photocatalytic H 2 production. The as-prepared optimized 15% ReS 2 /CCN exhibits the highest H 2 -evolution rate of 3.46 mmol g−1h−1 under visible light irradiation, a 2.7 fold enhancements over that of pristine CCN and is also much higher than ReS 2 alone. The excellent photocatalytic performance of ReS 2 /CCN is mainly attributed to the efficient charge transport of highly crystalline CCN by eliminating deep defects, the strong visible light harvesting of ReS 2 nanoflakes, as well as the synergistic effect of an ultrathin layered 2D/2D heterojunction to rapidly enable charge-separation while inhibiting the charge recombination. This work provides an efficient photocatalyst for H 2 energy production, and sheds light on fundamental insight to a rational design of photo/electro nanocatalysts or heterojunction materials toward highly efficient photocatalyst. [ABSTRACT FROM AUTHOR]

A superior ultra-thin g-C 3 N 4 material is screened for efficient photocatalytic in- situ H 2 O 2 production to remove antibiotics via a cascade reaction, which is attributed to its special surface electronic structure, rapid charge transfer efficiency and nearly two-electron (2e-) oxygen reduction reaction (ORR) process. [Display omitted] • Efficient strategy of photocatalytic in- situ H 2 O 2 production to remove antibiotics. • A superior ultra-thin g-C 3 N 4 nanosheets is screened for H 2 O 2 production. • Unpaired electron of g-C 3 N 4 is an important factor affecting performance. • The maximum H 2 O 2 production rate of pure g-C 3 N 4 arrives 665.4 μmol h−1 g−1. Photocatalytic in- situ hydrogen peroxide (H 2 O 2) preparation for cascade reactions is a novel and promising application strategy, especially for environmental remediation. Graphitic carbon nitride (g-C 3 N 4) has been proven to be one of the most effective catalysts. However, the H 2 O 2 yields on g-C 3 N 4 materials fabricated by different precursors varied greatly, so that the reasons need to be explored urgently for the later using. In this work, a series of different ultra-thin g-C 3 N 4 nanosheets catalysts are synthesized, on which the H 2 O 2 generation and tetracycline removal abilities are evaluated comprehensively. Among these, the g-C 3 N 4 nanosheets prepared by dicyandiamide (DCN) is demonstrated the excellent one with the maximum H 2 O 2 production efficiency of 665.4 μmol h−1 g−1, and its apparent quantum yield (AQY) arrives to 9.3% when illuminated at 400 nm. The superior photocatalytic performance of DCN is attributed to its nearly two-electron (2e-) oxygen reduction reaction (ORR) process, numerous unpaired electrons, suitable band structure, rapid charge separation and transfer efficiency. This work provides an effective strategy for wastewater purification without adding H 2 O 2 , which has screened an excellent ultra-thin g-C 3 N 4 catalyst, for the further photocatalysis research. [ABSTRACT FROM AUTHOR]