Nitrogen doped carbon materials, as the most promising non-metal electrocatalyst for oxygen reduction reaction (ORR), have attracted great attention because of their catalytic activities approaching to that of commercial Pt/C, good ethanol tolerance, low price and chemical stability. Here, we demonstrate the conjugated polymer-mediated synthesis of a series of nitrogen doped carbon nanoribbons (NDCNRs) through direct carbonization of polyaniline-polypyrrole (PANI-PPy) nanofibers with different monomer ratios. It is important to point out that ammonium fluoride (NH4F) applied in the carbonization process benefits for the production of more defect sites, higher surface area as well as electrochemically active surface area, and the morphology conversion from nanofibers into nanoribbons, though F element doping is not detected in the F-NDCNRs. With optimized monomer ratio (aniline:pyrrole = 1:3), the as-obtained F-NDCNRs(1:3), with higher content of graphitic-N, graphitic-N/pyridinic-N ratio and defect density, provide admirable ORR catalytic performance with an onset potential of 0.976 V vs RHE and a half-wave potential of 0.864 V vs RHE. This study provides new insights into the synthesis of efficient metal-free nitrogen doping carbon materials for ORR applications.Download high-res image (203KB)Download full-size image

Molecularly grafted carbon nitride (CN) nanosheets, matching well with the emission energy of upconversion phosphors (UCPs), were acquired for the first time. As a result of energy gap engineering, the assembled composites successfully realized the full use of visible-NIR light and afforded much higher activity than any CN- or UCP-based photocatalyst ever reported.

The usage of noble metal catalysts for oxygen reduction reaction (ORR) can be minimized by supporting them on porous carbon. Herein, a simple and industrially scalable approach for preparation of porous carbon supports is developed by directly pyrolyzing microporous organic polymers (MOPs). The rigid aromatic building blocks in MOPs function as self-templates to retain the high surface area and regular pore distribution during carbonization to the formation of high quality microporous carbon framework. The electrochemical performance of Pd catalysts supporting on MOPs-derived carbons is evaluated and compared with commercial products, indicating the superiority of MOPs as carbon precursor. Significant difference in ORR activity is observed among three types of MOPs due to the impact of framework and heteroatom. The highest performance of Pd/CKN catalyst is attributed to heteroatom-induced altering of electronic structures besides the stable skeleton.

As a promising photocatalyst, the large bandgap (3.2 eV) of anatase TiO2 seriously limits its light absorption of the UV portion of the solar spectrum, making it less applicable in industrial fields. A popular approach for enhancing visible light activity by narrowing the bandgap is doping, however, the dopant-induced defect states in the TiO2 lattice may act as recombination centers for the photogenerated charge carriers. Here we report a facile soft-chemical route to engineer the surface properties of TiO2 crystals using ethanol as the sole organic solvent. The individual TiO2 nanocrystals synthesized in the first step, possessing high affinity with ethanol molecules, tend to assemble together by interfacial Ti–Ti bonding during the following ethanol evaporation induced self-assembly process. Formation of Ti–Ti bonds at the interface simultaneously brings about the decrease of surface oxygen atoms in the TiO2 structural unit, which dramatically alters the electronic structure and extends the light absorption to ∼550 nm. Such a dopant-/additive-free TiO2 assembly exhibits considerable photocatalytic activity under visible light due to its narrower bandgap than individual nanocrystals. Further, an electron paramagnetic resonance measurement is used to confirm the capability of generating reactive ˙OH radicals on the surface of assembled TiO2 under visible-light irradiation.

Anatase TiO2 nanosheets supported on reduced graphene oxide (RGO) were synthesized via a one-step, solvothermal method. During the solvothermal step, graphene oxide (GO) was reduced to RGO, and, subsequently, anatase TiO2 with 73.7% exposed {001} facets was grown in situ on the surfaces of the RGO nanosheets. Compared with pure TiO2, the RGO/TiO2 hybrid nanocomposite had improved photoactivity as a result of effective photoinduced electron transfer from TiO2 to the RGO acceptor through interfacial interactions. Trapping tests showed that the oxidation of dye molecules proceeded for about 22% through the reaction with •OH radicals, and the remaining 78% occurred via direct interactions with holes. The holes left in TiO2 crystals were the main reason for the enhanced photocatalytic properties of the RGO/TiO2 composite. This paper not only reports the fabrication of highly active photocatalysts but also gives deeper insight into the photocatalytic mechanism of carbon/TiO2 composites.Keywords: photocatalytic mechanism; RGO/TiO2 hybrid nanocomposites; TiO2 {001} facets;

Nano-sized anatase TiO2 with exposed {001} facets was synthesized from lamellar protonated titanate precursor. Owing to small size (ca. 11 nm) and high surface area (155 m2 g−1), the crystals with 26.1% {001} facets exhibited markedly superior photoactivity to reference ca. 76 nm anatase TiO2 nanosheets with 88.4% {001} facets.

Herein we obtain a novel incorporating style of polyaniline (PANI)/TiO2 composites (Ns) via a designed two-step route. In comparison with conventional incorporating style (Cs), one-dimensional (1D) PANI is introduced in the step of TiO2 crystal growth instead of after crystallization. During the hydrothermal process, 1D PANI can act as an effective template to stabilize TiO2 particles at nanoscale through interfacial chemical bonds. In this way, the transition of some newly formed anatase crystals to rutile phase is partly suppressed. Also, the as-prepared composites show obvious light response in a wide range of 230–900 nm due to the sensitizing effect of PANI. Ns exhibit the improved visible photocatalytic property with scarce decrease of UV photoactivity. Overall, this work would provide new insights into the fabrication of conducting polymer/semiconductor composites with desired nanostructure as high performance photocatalysts and would facilitate their applications in environmental purification and solar energy conversion.Graphical abstractHighlights► New strategy for synthesis of polyaniline/TiO2 composites with desired structure. ► Polyaniline acts as an effective template in TiO2 system besides sensitizer. ► Composites possess high visible activity and similar UV activity compared to TiO2.

A WO3/TiO2 composite is constructed with the ability to degrade organic molecules under visible irradiation, which is newly explored by UV pre-irradiation. The long lasting visible-light photoactivity and the consecutive photocatalytic process will benefit the efficient use of solar energy.

Mixed surfactant solution, containing cetyltrimethyl ammonium bromide (CTAB) and sodium dodecylbenzyl sulfonate (SDBS), is used to prepare polyaniline (PANI) with soft 1D structure and high electrical conductivity. The mixed surfactants in the reaction play double roles of soft templates and dispersion reagents. The influence of CTAB–SDBS ratio on the morphology and conductive property of PANI is investigated. Through varying the proportion of surfactants, uniformly branched nanofibers with higher aspect ratio and good dispersion are obtained, which possess the highest conductivity (0.102 S·cm−1). Moreover, FT-IR spectra are measured to explain the change of structure and conductivity under assistance of mixed surfactants. As a result, the mixed surfactants have significant effect on the electron density of whole structure as well as the PANI molecular orientation.The novel method for synthesis of PANI nanofiber is proposed via a synergism of anionic surfactant (SDBS) and cationic surfactant (CTAB). The proportion of mixed surfactants has significant effect on the morphology and electrical conductivity. Uniform PANI nanofibers with the highest conductivity are obtained as 2:1 of CTAB/SDBS ratio.Highlights► Novel method for synthesis of PANI nanofibers with high conductivity is proposed. ► SDBS–CTAB mixed systems play double roles of soft template and dispersion reagent. ► Morphology and conductivity can be optimized by varying CTAB/SDBS ratio.

The successful adjustment of phase composition and morphology of anatase/rutile TiO2 nanocomposites is achieved via a soft chemical strategy, which involves no templates, hydrothermal treatments, or calcinations. The process consists of a NaOH treatment of the hydrolysate of titanium tetra-n-butoxide and a subsequent acidic peptization of the H-titanate intermediate. The effects of the acid peptization time, acid volume, and the NaOH-treatment time on the properties of products are systematically investigated. For the first time, the two-way phase transition between anatase and rutile is realized through adjusting the acid peptization time, which provides a promising way to control the phase ratio in preparing TiO2 anatase/rutile composites. The mechanism of the phase transitions and crystal growth under such soft chemical processes is discussed in detail, and the evolution of the phase composition is illustrated according to dissolution−reassembly equilibrium.

A WO3/TiO2 composite is constructed with the ability to degrade organic molecules under visible irradiation, which is newly explored by UV pre-irradiation. The long lasting visible-light photoactivity and the consecutive photocatalytic process will benefit the efficient use of solar energy.

Molecularly grafted carbon nitride (CN) nanosheets, matching well with the emission energy of upconversion phosphors (UCPs), were acquired for the first time. As a result of energy gap engineering, the assembled composites successfully realized the full use of visible-NIR light and afforded much higher activity than any CN- or UCP-based photocatalyst ever reported.

Nano-sized anatase TiO2 with exposed {001} facets was synthesized from lamellar protonated titanate precursor. Owing to small size (ca. 11 nm) and high surface area (155 m2 g−1), the crystals with 26.1% {001} facets exhibited markedly superior photoactivity to reference ca. 76 nm anatase TiO2 nanosheets with 88.4% {001} facets.