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Polymers have been considered as promising photocatalysts for energy conversion and environmental remediation, because of their inherent advantages such as adjustable optical and electronic properties as well as abundant active sites. However, it is difficult for polymers without effective design to achieve ideal photocatalytic performance. Compared with bulk polymers, polymer nanosheets obtained by exfoliation have the thickness of single or multiple atomic layers, which possess numerous unique advantages, such as more accessible active sites, shorter carrier transport distances, a prolonged lifetime of photogenerated carriers and the atomic level regulation of the backbone. Therefore extensive efforts have been focused on photocatalysts based on polymer nanosheets, and remarkable progress has been reported. In this review, the principles of photocatalytic water splitting, pollutant degradation and CO2 reduction are briefly introduced. And then recent advances in polymer nanosheets (conjugated microporous polymers, covalent organic frameworks, conjugated triazine frameworks and carbon nitrides) and their heterojunctions in the above-mentioned fields are highlighted. Specifically, the effects of the modification strategy on their light absorption ability, carrier migration, and photocatalytic activity are discussed. Finally, the important challenges and potential opportunities for developing polymer nanosheets and their heterojunctions as high-performance photocatalysts are envisaged. The insights exhibited in this review can provide a useful guidance for the design and development of polymer nanosheet based photocatalysts. [ABSTRACT FROM AUTHOR]

Construction of a heterojunction between quantum dots and TiO2 nanowire arrays via electrostatic self-assembly is rarely reported. In this work, mercury lamp irradiation was used to change the surface potential of WO3 quantum dots and TiO2 nanowire arrays, resulting in WO3 quantum dots tightly attached on the surface of TiO2 nanowire through electrostatic self-assembly. Photoelectrochemical measurements showed that the WO3 quantum dots formed a type II heterojunction with the TiO2 nanowire arrays rather than serving as carrier-trapping sites. In the self-assembly system, the TiO2 nanowire arrays provide a charge-transfer channel for the WO3 quantum dots, greatly improving the contribution of the WO3 quantum dots to the photocurrent. Quantitative calculations showed that the improvement of the bulk carrier-separation efficiency was the reason for the enhanced photoelectrochemical performance of the self-assembled system. The photocurrent density of the optical self-assembled system at 1.23 V (vs. RHE) was ∼5.5 times as high as that of the TiO2 nanowire arrays. More importantly, the self-assembled system exhibited excellent photoelectrochemical stability. [ABSTRACT FROM AUTHOR]

g-C3N4-loaded carbon nanofibers (CNCNF) were obtained via electrostatic spinning and high temperature calcination. Highly crystalline g-C3N4 can be obtained at 800 °C due to the protection of carbon nanofibers. Benefiting from the high conductivity of carbon nanofibers and the high carrier separation efficiency of g-C3N4, CNCNF shows a significantly enhanced photocatalytic hydrogen production activity (7.7-fold more than pristine g-C3N4), also, the mechanism of photocatalytic performance enhancement is discussed. [ABSTRACT FROM AUTHOR]

The surface grafting of electro‐negative cyano groups on polymer carbon nitrides (PCNs) is an effective way to tail their electronic structure. Despite the significant progress in the synthesis of cyano group‐enriched PCN, developing a simple and efficient method remains challenging. Here, a facile strategy was developed for fabricating surface cyano‐rich PCN (PCN‐DM) with a porous structure via chemical vapor modification using diaminomaleonitrile. The cyano groups of diaminomaleonitrile substituted the amino groups on PCN surface via a deamination. The hydrogen production rate of the PCN‐DM was approximately 17 times higher than that of pristine PCN. This significant increase in photocatalytic performance could be assigned to the fusion of cyano groups in the surface of PCN, forming new gap states that broadened the visible‐light harvesting and accelerated charge separation for photoredox reactions. This study unveils a promising approach for incorporating functional units in the design of novel photocatalysts for efficient hydrogen production. [ABSTRACT FROM AUTHOR]

Broad-spectrum heterogeneous 1 T/2H MoSe2 homojunction nanosheets were prepared using single-step solvothermal process. The 1 T and 2H phase ratios in the homojunction could be controlled by adjusting the amount of NaBH4. Moreover, the presence of 1 T phase in the 1 T/2H MoSe2 increased the absorption ability of MoSe2 and accelerated electron transport, which greatly enhances the photocatalytic degradation activity under broad-spectrum range. Radical trapping experiments indicated that ·OH and ·O2− radicals are the main active species of methylene blue degradation. Combined with the results of photocatalytic activity and band structure, the photocatalytic mechanism of the 1 T/2H MoSe2 was proposed. [ABSTRACT FROM AUTHOR]

Stable and efficient photoelectrochemical water splitting has been achieved using a BaTaO2N photoanode decorated with CoO microflowers. The CoO microflowers effectively collect holes from BaTaO2N which kinetically protects BaTaO2N against photocorrosion. A Faraday efficiency of almost unity (99.2%) has been recorded for O2 evolution reactions. The tips of the CoO microflowers are the most active sites for water oxidation reactions. [ABSTRACT FROM AUTHOR]

Although BaNbO2N has visible light absorption as far as 740 nm, its photocatalytic activity is generally very poor under ordinary conditions, being incommensurate to its light absorption properties. In this work, we introduce Ca into the B site of BaNbO2N to form a complex perovskite BaNb1−x/3Cax/3O2+yN1−y (0 ≤ x, y ≤ 1). The presence of Ca in BaNbO2N has great impact on a number of important properties such as band gap value, nitrogen content, surface hydrophilicity, and defects levels. In particular, defects such as Nb4+ species are effectively suppressed in Ca‐modified BaNbO2N. More importantly, photocatalytic activity of BaNbO2N for water oxidation reactions is substantially improved after Ca modifications. Compared with pristine BaNbO2N, more than twofold enhancement in photocatalytic oxygen evolution is observed for BaNb0.8Ca0.2O2+yN1−y (x = 0.6). Such improvements probably stem from the suppression of Nb4+ species in the structure as well as enhanced surface hydrophilicity after Ca modification. The facile approach by incorporating alkaline earth cations into crystal structure can be well extended to other perovskite oxynitrides whose photocatalytic activity is subject to those defective species. [ABSTRACT FROM AUTHOR]