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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]

In this research, we successfully produced hierarchical porous activated carbon from biowaste employing one-step KOH activation and applied as ultrahigh-performance supercapacitor electrode materials. The coconut shell-derived activated carbon (CSAC) features a hierarchical porous structure in a honeycomb-like morphology, leading to a high specific surface area (2228 m2 g−1) as well as a significant pore volume (1.07 cm3 g−1). The initial test with the CSAC electrode, conducted in a 6 M KOH loaded symmetric supercapacitor, demonstrated an ultrahigh capacitance of 367 F g−1 at a current density of 0.2 A g−1 together with 92.09% retention after 10,000 cycles at 10 A g−1. More impressively, the zinc–ion hybrid supercapacitor using CSAC as a cathode achieves a high-rate capability (153 mAh g−1 at 0.2 A g−1 and 75 mAh g−1 at 10 A g−1), high energy density (134.9 Wh kg−1 at 175 W kg−1), as well as exceptional cycling stability (93.81% capacity retention after 10,000 cycles at 10 A g−1). Such work thus illuminates a new pathway for converting biowaste-derived carbons into materials for ultrahigh-performance energy storge applications. [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]

Black core-shelled anatase titania were successfully prepared using a simple one-step synthetic method by calcining colloid titania precursor in N 2 flow under atmospheric pressure. The physicochemical properties of the as-prepared samples were characterized by various techniques such as X-ray diffraction, high resolution transmission electron microcopy, etc. The samples demonstrate a unique core-shelled structure and electron paramagnetic resonance spectra reveal the presence of high concentration of Ti 3+ and oxygen vacancies at the surface, which accounts for their black appearance. A possible mechanism for the formation of such core–shell structure is proposed based on the results (X-ray photoelectron spectra, etc) of products prepared under different ration between urea and hydrochloric acid. Ethanol absolute is found to have critical effect in preventing phase transition of titania (from anatase to rutile) upon elevated temperatures. The black appearance of the sample powder (high visible light absorption) as well as slow electron/hole recombination rate after introducing oxygen vacancies/N species signify the core-shelled anatase titania as an efficient visible light active photocatalyst. [ABSTRACT FROM AUTHOR]

Black and yellow anatase TiO2 doped with hydrogen and nitrogen elements annealed under a N2/Ar/air atmosphere are produced. More interestingly, one kind of black TiO2 has excellent performance for degradation of methylene blue under visible-light irradiation but photodegradation of the other is quite limited. [ABSTRACT FROM AUTHOR]

Surface defects have a significant effect on the photocatalytic reaction of Bi 4 Ti 3 O 12 , but the mechanism is unclear. In addition, when surface defects and highly exposed facets exist at the same time, which factor plays the main role in photocatalytic activity is also controversial. Herein, it is found that Bi 4 Ti 3 O 12 with adjustable concentrations of surface defects and percentage of exposed {001} facets can be prepared by using titania of different crystal types and sizes as raw materials, which is extremely beneficial for exploring the above problems. The photocatalytic activity of Bi 4 Ti 3 O 12 nanosheets with surface defects and exposed {001} facets was the same as that of Bi 4 Ti 3 O 12 nanosheets with surface defects alone (about 72.5% of photodegradation levofloxacin under 10 min of simulated sunlight irradiation). Based on the experimental results and density functional theory calculations, the influence mechanism of surface defects was deeply studied. The surface defects resulting from partial exfoliation of the external (Bi 2 O 2)2+ layers changed band structure of Bi 4 Ti 3 O 12. More importantly, surface defects with high concentration became hole trapping sites, which was conducive to the faster participation of holes in the photocatalytic oxidation process. [Display omitted] • Bi 4 Ti 3 O 12 with surface defects and exposed {001} facets was prepared. • The surface defects resulted from partial exfoliation of (Bi 2 O 2)2+ layers. • The enhanced photocatalytic performance was determined by the surface defects. • Surface defects with high concentration served as hole trapping sites. [ABSTRACT FROM AUTHOR]

• IPN of resorcinol formaldehyde-zinc tartrate and poly(styrene-maleic anhydride) (RF-Zn/PSMA) was prepared. • Three-dimensional hierarchical porous carbon (THPC) was firstly carbonized from IPN of RF-Zn/PSMA. • Specific surface area and pore structure of carbon can be tuned by controlling the synthesis process of IPN. • THPC exhibited a high specific capacitance, energy outputs and long cycle life. [Display omitted] Herein, we propose a three-dimensional hierarchical porous carbon (THPC) derived from interpenetrating polymer networks (IPNs) of resorcinol formaldehyde-zinc tartrate and poly(styrene-maleic anhydride) (RF-Zn/PSMA), which was prepared via a gel swelling method. The three-dimensional hierarchical and interconnected pore structure involving micro-, meso- and macropores benefits from the synergistic pore-forming effect of PSMA pyrolysis and zinc tartrate decomposition during carbonization process. A high specific surface area of 742 m2 g−1 together with a cheese-like morphology was found for obtained THPC, exhibiting a high specific capacitance of 235 F g−1 at 1 A g−1 in 6 M KOH. THPC assembled symmetrical supercapacitor using 6 M KOH and 1 M Na 2 SO 4 as electrolytes deliver energy outputs of 6.47 and 15.3 Wh kg−1 at 100 and 180 W kg−1, respectively. More attractively, the assembled supercapacitor based on the THPC achieves a high energy outputs of 50.45 Wh kg−1 at 350 W kg−1 in EMIMBF 4 under wide potential window of 3.5 V, indicating its practical application prospect. Our findings open up new playgrounds for the design and electrochemical application of hierarchical porous carbon using IPNs as precursor. [ABSTRACT FROM AUTHOR]

Construction of a heterojunction between quantum dots and TiO 2 nanowire arrays via electrostatic self-assembly is rarely reported. In this work, mercury lamp irradiation was used to change the surface potential of WO 3 quantum dots and TiO 2 nanowire arrays, resulting in WO 3 quantum dots tightly attached on the surface of TiO 2 nanowire through electrostatic self-assembly. Photoelectrochemical measurements showed that the WO 3 quantum dots formed a type II heterojunction with the TiO 2 nanowire arrays rather than serving as carrier-trapping sites. In the self-assembly system, the TiO 2 nanowire arrays provide a charge-transfer channel for the WO 3 quantum dots, greatly improving the contribution of the WO 3 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 TiO 2 nanowire arrays. More importantly, the self-assembled system exhibited excellent photoelectrochemical stability.

Photodeposition of dual-cocatalysts Pt-Cr or Rh-Cr on the surface of ZnIn 2 S 4 is used to achieve overall water splitting. Compared with the hybrid loading of the Pt element and Cr element, the formation of the Rh-S bond results in space separation of the Rh element and Cr element. The Rh-S bond and space separation of cocatalysts promote the transfer of bulk carriers to the surface and inhibit self-corrosion.

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., (© 2022 Wiley-VCH GmbH.)

Normal MoS 2 exhibits a low photocatalytic performance for H 2 production owing to the deficiency of the active sites and the poor electrical conductance. In this work, MoS 2 anchored on the surface of the carbon nanofibers was designed to enhance the activity of the exposed edge and the electrical conductivity at the same time. The oxidation of the surface Mo atoms increases the activity of the exposed edge of the MoS 2 . The introduction of carbon nanofibers facilitates the effective transportation of the electron-hole pairs by enhancing the electrical conductivity. As a result, the introduction of carbon nanofibers and Mo 6+ can facilitate the electron-hole pair separation to enhance the photocatalytic hydrogen evolution reaction (HER) performance (to eight fold more than normal MoS 2 )., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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.

Pt and RhO x cocatalysts are selectively deposited at inner and outer surface of ZnTiO 3- x N y hollow nanospheres, respectively. The resulting photocatalytic systems exhibit promising activity for photocatalytic overall water splitting with stoichiometric H 2 /O 2 ratio under simulated solar insolation. Selective deposition of Pt and RhO x cocatalysts at different surfaces not only mitigates back reactions of the products but also induces strong potential gradient within nanospheres that promotes efficient dissociation and fast migration of photocarriers to the surface., (© 2021 Wiley-VCH GmbH.)

Ultrathin nitrogen-doped perovskite nanosheets LaTa 2 O 6.77 N 0.15 - have been fabricated by exfoliating Dion-Jacobson-type layered perovskite RbLaTa 2 O 6.77 N 0.15 . These nanosheets demonstrate superior photocatalytic activities for water splitting into hydrogen and oxygen and remain active with photon wavelengths as far as 600 nm. Their apparent quantum efficiency under visible-light illumination (λ ≥ 420 nm) approaches 1.29% and 3.27% for photocatalytic hydrogen and oxygen production, being almost 4-fold and 8-fold higher than bulk RbLaTa 2 O 6.77 N 0.15 . Their outstanding performance likely stems from their tiny thickness (single perovskite slab) that essentially removes bulk charge diffusion steps and extends the lifetime of photogenerated charges. Theoretical calculations reveal a peculiar 2D charge transportation phenomenon in RbLaTa 2 O 6.77 N 0.15 ; thus, exfoliating RbLaTa 2 O 6.77 N 0.15 into LaTa 2 O 6.77 N 0.15 - nanosheets has limited impact on charge transportation properties but significantly enhances the surface areas which contributes to more reaction sites.

A gray TiO₂/SrTiO₃ composite nanocrystalline sensor with narrow band-gap was successfully prepared through a facile wet chemical method. The precursor was calcined in N₂ flow under atmospheric pressure and thereafter, a humidity sensor based on the composite was fabricated. The sensor showed high resistive sensitivity and varied by more than four orders of magnitude with an increase in relative humidity (RH) from 11% to 95%. The response and recovery time were about 3.1 s and 76 s, respectively with maximum hysteresis at 1% RH. In comparison with pure SrTiO₃ and black TiO₂, the gray composite based device exhibits a higher sensitivity. These results demonstrate the potential of gray TiO₂/SrTiO₃ for humidity sensing applications., Competing Interests: The authors declare no conflict of interest.