Search

Hierarchical porous iron and nitrogen co-doped carbon (Fe-N/C) materials have been considered as an appealing non-noble metal-based catalyst in oxygen reduction reactions (ORR). However, the conductivity loss caused by the scattering of electrons on pores and defects markedly limits their catalytic activity, which attracted seldom attention in this area. Herein, a novel crystalline carbon modified hierarchical porous Fe-N/C electrocatalyst with enhanced electronic conductivity is designed and prepared via a two-step calcination-catalysis process. The resistivity of hierarchical porous Fe-N/C is decreased from 2.123 Ω cm to 0.479 Ω cm after crystalline carbon introduction. The electrocatalyst annealed at 800 °C (Fe-N/C-800) exhibits a superior activity with the half-wave potential (E1/2) of 0.89 V, which outperforms the commercial carbon-supported platinum (Pt/C) catalyst (0.85 V). The strategy of crystalline carbon modification provides a fresh approach to improve the electronic conductivity of porous carbon-based materials.

Developing highly active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is critical to large-scale applications of electrochemical water splitting. In the present work, a novel porous NiO/NiCo2O4 heterostructure is constructed by two-stage calcination of nickel-cobalt bimetallic hydroxide precursors prepared using a microwave-assisted hydrothermal method, in which abundant interfaces are constituted. The NiO phase stabilized in NiCo2O4 matrix is the nanometer scale (ca. 13 nm). The porous nanoscale NiO/NiCo2O4 heterostructure shows a 10 mA cm−2 current density under the overpotential of 264 mV which outperforms the noble catalyst RuO2. It is demonstrated that the highly active Ni3+ species generated by the oxidation of nanometer scale NiO surface are responsible for enhanced OER. Additionally, DFT calculations certify that the heterostructure interfaces promote the chemisorption of OH intermediates. This strategy of increasing the intrinsic activity and improving the chemisorption abilities for oxygen-containing intermediates by constructing nanoscale heterostructure electrocatalysts provides a feasible method to accelerate the reaction rate of OER.

Graphene promoted triphasic N/Ti3+-TiO2 (GNTT) heterostructures with different weight addition ratios of graphene have been assembled by a facile in-situ hydrothermal treatment of TiN and graphene oxide. The obtained GNTT photocatalysts are characterized by a collection of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and photoluminescence (PL), etc. It is demonstrated that graphene modified N/Ti3+ codoped TiO2 with ternary phases mixture of brookite, anatase and rutile can be obtained. Furthermore, the GNTT heterostructure photocatalysts exhibit an enhanced photoactivity for photocatalytic degradation of methyl blue, levofloxacin, and rhodamine B as compared with TiO2, N-doped TiO2, and N/Ti3+ codoped TiO2 (NTT). The reason for the improved photoactivity can be listed as follows: i) N and Ti3+ doping can severally form N2p impurity level above valance band (VB) and local states below the conduction band (CB) of TiO2, which contribute to the visible light response of TiO2; ii) the ternary heterophase junction can efficiently transfer and separate photogenerated electron-hole pairs; iii) graphene acts as an electron reservoir to trap and transport the electrons photogenerated from TiO2. The synergistic effect of these factors accounts for the photoactivity advancement of GNTT photocatalysts. This study develops a novel approach to improve the visible light utilization of TiO2 and facilitates their applications in the environment and energy issues.

Carbon-incorporated TiO 2 microspheres (CTMs), produced by a flame assisted hydrolysis method, were successfully decorated with Cu 2 O nanoparticles via a chemical bath deposition process. A red shift of absorption edge and enhanced visible light absorption were observed for the resulted Cu 2 O/CTMs composites compared with bare TiO 2 and CTMs. Their effective visible-light-driven photocatalytic activity and the effect of deposition amount of Cu 2 O on the photocatalytic properties were determined by the degradation of methylene blue. The highest degradation rate was achieved for Cu 2 O/CTMs composite (29.2%) compared to CTMs (18.5%) and bare TiO 2 (7.3%) under visible light illumination for 80 min. The improved photoactivity can be ascribed to the integrative synergistic effect of carbon and Cu 2 O on TiO 2 . This work develops a rapid and facile approach for the fabrication of Cu 2 O decorated carbon-incorporated TiO 2 microspheres composites and demonstrates it is an efficient route to improve the photocatalytic activity of TiO 2 .

A ternary composite of Cu2O, graphene and rutile TiO2 nanorods was prepared using Cu(CH3COO)2·H2O, graphene oxide and TiCl4 as the starting materials and its enhanced photocatalytic performance was demonstrated. Graphene/TiO2 nanorod composites (GT) were obtained by a simple hydrothermal method and then, Cu2O was coupled onto the surface of graphene/rutile TiO2 to form Cu2O/graphene/rutile TiO2 nanorod (CGT) composites via a chemical bath deposition process. The as-prepared sample was characterized by X-ray diffraction (XRD), emission field scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), specific surface area analyzer (BET), Raman spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). It is found that the introduction of graphene and Cu2O has little effect on the morphology of TiO2 nanorods with average dimensions of 140 nm (length) × 30 nm (diameter) (L/D ratio ≈5). A red shift of light absorption edge and more absorption in the visible light region were observed for the resulted ternary samples compared with TiO2 and graphene/TiO2 composites. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation, which showed 2.8 times corresponding enhancement of the degradation efficiency for the ternary composites compared with TiO2. This work provides a new strategy to improve the visible light response of TiO2 and facilitate its application in environmental remediation.

Chemically bonded graphene/TiO2 nanorod hybrid composites with superior dispersity were synthesized by a one-step in situ hydrothermal method using graphene oxide (GO) and TiO2 (P25) as the starting materials. The as-prepared samples were characterized by XRD, XPS, TEM, FE-SEM, EDX, Raman, N2 adsorption, and UV–vis DRS techniques. Enhanced light absorption and a red shift of absorption edge were observed for the composites in the ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). Their effective photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation. An enhancement of photocatalytic performance was observed over graphene/TiO2 nanorod hybrid composite photocatalysts, as 3.7 times larger than that of pristine TiO2 nanorods. This work demonstrated that the synthesis of TiO2 nanorods and simultaneous conversion of GO to graphene “without using reducing agents” had shown to be a rapid, direct and clean approach to fabricate chemically bonded graphene/TiO2 nanorod hybrid composites with enhanced photocatalytic performance.

The insufficient separation of photogenerated charge carriers and faint CO2 capture remains the major obstacles for photocatalytic conversion of CO2 into solar fuel. Rational design of semiconductor photocatalysts with unique structures may be promising to break this bottleneck. Herein, bismuth rich Bi4O5B2 hollow microspheres are designed as a robust photocatalyst for efficient CO2 reduction. Thanks to the bismuth rich strategy, the highly dispersed band structure and the elevated conduction band (CB) potential facilitate the charge transfer and photoreduction ability. Meanwhile, hollow structure provides the large specific area and creates a resonance in its interior to enhance the CO2 adsorption and activation. Benefiting from the collaborative promotion effect, the local charge arrangement and electronic structure are tuned so as to an exceptional efficiency of photocatalytic CO2 conversion into CO (3.16 μmol g−1 h−1) and CH4 (0.5 μmol g−1 h−1) is attained over hollow Bi4O5Br2, which is superior to that of solid Bi4O5Br2 and BiOBr, as well as other reported Bi-based photocatalysts. This work paves new opportunities for exploring high-efficiency CO2 photoreduction catalysts.