Optimizing the band structure of sponge-like S-doped poly(heptazine imide) with quantum confinement effect towards boosting visible-light photocatalytic H2 generation.

Simultaneously manipulating the nanostructure and band structure of semiconductors for boosting the photocatalytic performance of photocatalyts is highly desirable. Herein, a series of hierarchical sponge-like S-doped poly(heptazine imide) (HS-SPHI) assembled by ultrathin nanosheets were successfully fabricated via a facile bottom-up supramolecular preassembly approach using melamine (MA) and trithiocyanuric acid (TTCA) as precursors. Benefiting from the synergistic effect of the S-doping and their unique hierarchical porous structure coupled with quantum confinement effect, the as-obtained HS-SPHIs are endowed with extended visible-light response, improved charge separation efficiency, enlarged specific surface area, and enhanced thermodynamic driving force for water reduction. As a result, all the HS-SPHIs exhibit remarkable boosting visible-light (>420 nm) photocatalytic H2evolution (PHE). The maximum PHE rate achieved by HS-SPHI-650 can be up to 3584.2 µmol g-1h-1, with an apparent quantum efficiency (AQE) of 14.67 % at 420 nm, which is about 22.4 times than that of pristine bulk g-C3N4 (B-GCN). We believe that this work will provide a significant strategy for optimizing the band structure of PCN in order to improve its photocatalytic performance.

Partially cross-linked carbon nitride with unimpeded charge transfer between different chains for boosting photocatalytic hydrogen production.

A heptazine-based, partially cross-linked carbon nitride (PC-CN) was successfully prepared via a solid-chloride-salt-assisted polycondensation method. The cross-linking favors the charge transport between different chains, thus dramatically boosting the photocatalytic hydrogen evolution activity of PC-CN, up to 29.3 times that of traditional 1D-CN.

Template-free preparation of carbon nitride hollow spheres with adjustable sizes for photocatalytic hydrogen generation.

Carbon nitride hollow spheres (CNHS) with adjustable sizes were successfully fabricated via a template-free supramolecular pre-assembly strategy, in which melamine-cyanuric acid (MCA) hollow spheres were constructed through hydrogen bonds. A feasible formation mechanism was proposed, which coupled an inside-out Ostwald ripening with the supramolecular pre-assembly process. Interestingly, the sizes of MCA could be manipulated by changing the pre-assembly temperature. Consequently, the sizes of CNHS were adjustable. The optimal CNHS exhibited excellent photocatalytic hydrogen evolution rate (98.6 µmol/h) in the visible-light region, which was approximately 11 times higher than that of bulk carbon nitride calcined by melamine. The significantly improved performance was due to the contributions including: the unique architectures with remarkable light absorption ability, high electrical conductivity, relatively narrowed band gap, fast charge separation. This work provides a facile template-free supramolecular pre-assembly strategy to fabricate carbon nitride hollow spheres with adjustable sizes for the first time.

A facile one-step synthesis of ZnO quantum dots modified poly(triazine imide) nanosheets for enhanced hydrogen evolution under visible light.

A heterojunction of crystalline poly(triazine imide) (PTI) nanosheets and ZnO quantum dots (QDs) (∼3 nm) was synthesized by a one-step ionothermal condensation of cyanamide. The resulting PTI/ZnO-QDs heterostructure exhibits a significantly enhanced H2 evolution to 63 times that of pure PTI and 3.4 times that of graphitic carbon nitride (g-C3N4) under visible light.

TiO2 nanoparticles-functionalized N-doped graphene with superior interfacial contact and enhanced charge separation for photocatalytic hydrogen generation.

Titanium dioxide (TiO2) nanoparticles-functionalized N-doped graphene (NGR) composites (NGR/TiO2) were prepared through solvothermal treatment approach using exfoliated NGR and tetrabutyl titanate as the staring materials. The composites were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectra, photoelectrochemical, and electrochemical measurements. Nitrogen doping provides favorable nucleation and anchor sites for TiO2 nanocrystals formation on NGR sheets, helping to form an intimate interfacial contact between NGR and TiO2 nanoparticles. Moreover, NGR has higher electrical conductivity than the reduced graphene oxide (RGO) due to the recovery of the sp(2) graphite network and decrease of defects, resulting in more effective charge transfer and charge separation in the NGR/TiO2 composite. NGR/TiO2 nanocomposite demonstrated a higher photocatalytic activity for hydrogen production as compared to its counterpart, TiO2-functionalized RGO composite (RGO/TiO2). This work provides new insights to design new more efficient graphene-based nanocomposite photocatalysts for solar energy conversion.

Synergistic contributions by decreasing overpotential and enhancing charge-transfer in α-Fe2O3/Mn3O4/graphene catalysts with heterostructures for photocatalytic water oxidation.

A novel nanocomposite consisting of α-Fe2O3, Mn3O4 and reduced graphene oxide (r-GO) has been facilely synthesized through a two-step method: solvothermal reaction for Mn3O4-modified α-Fe2O3 (α-Fe2O3/Mn3O4) and self-assembly process for combining α-Fe2O3/Mn3O4 with r-GO (α-Fe2O3/Mn3O4/r-GO). The morphology and structure of the nanocomposite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that rod-like hematite was modified by Mn3O4 and dispersed on the surface of r-GO. Raman and Fourier transform infrared spectra (FTIR) showed superior interfacial contacts between α-Fe2O3/Mn3O4 and r-GO. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) and photoelectrochemical characterization revealed a high light-harvesting efficiency, a lowered overpotential for water oxidation and an excellent charge transfer performance of α-Fe2O3/Mn3O4/r-GO nanocomposite with heterostructures. The photocatalytic oxygen evolution from the optimized photocatalyst was up to 1406.2 µmol g(-1) in 10 h of UV-vis light irradiation and the quantum yield was ca. 4.35% at 365 nm. Our investigation suggests that constructing a catalyst with heterostructures is a promising method to enhance photocatalytic activity.

RuO2/TiSi2/graphene composite for enhanced photocatalytic hydrogen generation under visible light irradiation.

A novel composite composed of TiSi(2), graphene and RuO(2) nanoparticles was fabricated by a one-pot deposition method using reduced graphene oxide (RGO) as a supporting matrix and RuCl(3) as the RuO(2) precursor. The resulting RuO(2)/TiSi(2)/RGO composite was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectra, photoelectrical response and electrochemical impedance spectra. The results indicated that the three components in the composite were effectively contacted, thus facilitating the photogenerated charges transfer and separation through multiple routes. By using the composite as a photocatalyst for visible-light water splitting the average hydrogen production rate could reach 97.5 µmol h(-1) g(-1), which is higher than that from RuO(2)/TiSi(2) and pure TiSi(2) systems under the same conditions.

Photocatalytic hydrogen evolution based on efficient energy and electron transfers in donor-bridge-acceptor multibranched-porphyrin-functionalized platinum nanocomposites.

Two donor-bridge-acceptor conjugates (5,10,15,20-tetrakis[4-(N,N-diphenylaminobenzoate)phenyl] porphyrin (TPPZ) and 5,10,15,20-tetrakis[4-(N,N-diphenylaminostyryl)phenyl] porphyrin (TPPX)) were covalently linked to triphenylamine (TPA) at the meso-position of porphyrin ring. The triphenylamine entities were expected to act as energy donors and the porphyrins to act as an energy acceptor. In this paper, we report on the synthesis of these multibranched-porphyrin-functionalized Pt nanocomposites. The conjugates used here not only served as a stabilizer to prevent agglomeration of Pt nanoparticles, but also as a light-harvesting photosensitizer. The occurrence of photoinduced electron-transfer processes was confirmed by time-resolved fluorescence and photoelectrochemical spectral measurements. The different efficiencies for energy and electron transfer in the two multibranched porphyrins and the functionalized Pt nanocomposites were attributed to diverse covalent linkages. Moreover, in the reduction of water to produce H(2), the photocatalytic activity of the Pt nanocomposite functionalized by TPPX, in which the triphenylamine and porphyrin moieties are bonded through an ethylene bridge, was much higher than that of the platinum nanocomposite functionalized by TPPZ, in which the two moieties are bonded through an ester. This investigation demonstrates the fundamental advantages of constructing donor-bridge-acceptor conjugates as highly efficient photosensitizers based on efficient energy and electron transfer.