RESUMO
It is highly desirable to explore functionalized polymer semiconductor/g-C3N4 heterojunction photocatalysts with the tight interfacial connection for promoting the photogenerated electron-hole pair separation, improving the hydrophilicity, extending the visible light response and achieving the efficient visible light-driven H2 evolution. Herein, we synthesized novel poly[9,9-bis(3-ethyl phosphate propyl)fluorene-alt-benzothiadiazole] (PPFBT) with a phosphate ester on every repeating unit by the Suzuki polymerization and then fabricated PPFBT/hydroxylated g-C3N4 (PPFBT/CN-OH) heterojunctions via a surface hydroxyl-induced assembly process. The ratio-optimized 5PPFBT/CN-OH shows the hydrogen evolution activity of 2662.4 µmol·g-1·h-1, an 11.1-time enhancement compared to CN-OH. The improved photocatalytic activity is mainly attributed to the enhanced electron-hole pair separation due to the tight interfacial connection by hydrogen bond (P=O H-O) and N S interactions between PPFBT and CN-OH. It is verified that abundant phosphate ester groups of PPFBT improve the hydrophilicity and form coordination bonds with platinum (P=O:Pt) as a cocatalyst to facilitate water splitting for H2 evolution. It is also confirmed that the enhanced electron-hole pair separation is mainly dependent on the excited high-energy level electron transfer from CN-OH to PPFBT. This work provides a rational molecular design strategy for constructing efficient functionalized polymer semiconductor/g-C3N4 heterojunctions for sunlight-driven H2 evolution.
RESUMO
It is highly desirable to enhance the photogenerated charge separation of g-C3N4 by constructing efficient heterojunctions, especially with an additional organic constitution for solar-hydrogen conversion. Herein, g-C3N4 nanosheets have been modified controllably with nano-sized poly(3-thiophenecarboxylic acid) (PTA) through in situ photopolymerization and then coordinated with Fe(III) via the -COOH groups of modified PTA, forming an interface of tightly contacted nanoheterojunctions between the Fe(III)-coordinated PTA and g-C3N4. The resulting ratio-optimized nanoheterojunction displays a ~4.6-fold enhancement of the visible-light photocatalytic H2 evolution activity compared to bare g-C3N4. Based on the surface photovoltage spectra, measurements of the amount of â¢OH produced, photoluminescence (PL) spectra, photoelectrochemical curves, and single-wavelength photocurrent action spectra, it was confirmed that the improved photoactivity of g-C3N4 is attributed to the significantly promoted charge separation by the transfer of high-energy electrons from the lowest unoccupied molecular orbital (LUMO) of g-C3N4 to the modified PTA via the formed tight interface, dependent on the hydrogen bond interaction between the -COOH of PTA and the -NH2 of g-C3N4, and the continuous transfer to the coordinated Fe(III) with -OH favorable for connection with Pt as the cocatalyst. This study demonstrates a feasible strategy for solar-light-driven energy production over the large family of g-C3N4 heterojunction photocatalysts with exceptional visible-light activities.
RESUMO
It is highly desired to explore closely contacted polymer semiconductor/g-C3N4 heterojunction photocatalysts with promoted photogenerated-carrier separation and extended visible-light response for efficient visible-light-driven H2 production. Here, we first synthesized the nitro-terminated oligothiophene (OTh) by the controlled copolymerization of thiophene and 2-nitrothiophene monomers, then constructed the nitro-terminated oligothiophene/crystallinity-improved g-C3N4 (OTh/g-C3N4) heterojunctions by a grinding-induced combination strategy. The ratio-optimized 20OTh5/g-C3N4 shows highly efficient H2 production activity up to 3.63 mmol h-1 g-1 under visible-light irradiation, with â¼25.9-time enhancement compared to that of g-C3N4. As verified by time-resolved photoluminescence spectra, surface photovoltage spectra, and the fluorescence spectra related to â¢OH amounts, the improved photocatalytic activity is due to the promoted photogenerated-carrier transfer and separation in the heterojunctions and the expanded visible-light response. It is also confirmed that the controlled OTh chain length, improved g-C3N4 crystallinity, and tight interface contact dependent on the hydrogen bonds and N···S interactions between OTh and g-C3N4 are reasonable for enhanced photogenerated-carrier separation with the electron transfer from OTh to g-C3N4. This work illustrates a feasible strategy to construct efficient polymer semiconductor/g-C3N4 heterojunction photocatalysts for solar-light-driven H2 production.
RESUMO
Ti3C2Tx-MXenes have extremely promising applications in electrochemistry, but the development of Ti3C2Tx is limited due to severe self-stacking problem. Here, we introduced oxygen vacancy-enriched molybdenum trioxide (MoO3-x) with pseudocapacitive properties as the intercalator of Ti3C2Tx and PEDOT with high electronic conductivity as the co-intercalator and conductive binder of Ti3C2Tx to synthesize Ti3C2Tx/MoO3-x/PEDOT:PSS (TMP) free-standing films by vacuum-assisted filtration and H2SO4 soaking. The tightly intercalated free-standing film structure can effectively improve the self-stacking phenomenon of Ti3C2Tx, expose more active sites and facilitate electron/ion transport, thus making TMP show excellent electrochemical performance. The volumetric and gravimetric capacitance of optimized TMP-2 can reach 1898.5 F cm-3 and 523.0 F g-1 at 1 A g-1 with a rate performance of 90.5% at the current density from 1 A g-1 to 20 A g-1, which is significantly better than those of MXene-based composites reported in the literature. The directly-assembled TMP-2//TMP-2 flexible solid-state supercapacitor displays high energy/power output performances (25.1 W h L-1 at 6383.1 W L-1, 6.9 W h kg-1 at 1758.4 W kg-1) and there is no obvious change after 100 cycles at a bending angle of 180°. As a result, the tightly intercalated TMP-2 free-standing film with high volumetric/gravimetric capacitances is a promising material for flexible energy storage devices.