Yajun Zhou

Brand new P-doped g-C3N4: enhanced photocatalytic activity for H2 evolution and Rhodamine B degradation under visible light

P-doped g-C3N4 has been successfully synthesized using hexachlorocyclotriphosphazene, a low cost and environmentally benign compound, as phosphorus source, and guanidiniumhydrochloride as g-C3N4 precursor, via a thermally induced copolymerization route. The obtained P-doped g-C3N4 showed excellent photocatalytic performance both in the photoreduction of H2O to produce H2 and the photodegradation of Rhodamine B (RhB). H2 evolution rate on modified g-C3N4 reached 50.6 μmol h−1, which is 2.9 times higher than that of the pure g-C3N4. RhB (10 mg L−1) was completely photodegraded within 10 min. The structure and texture properties of the P-doped g-C3N4 have been investigated in detail by XRD, FTIR, TEM, EDS and STEM. With the results of XPS and 31P NMR, a possible existing form of P atom in the framework g-C3N4 has been put forward. The introduction of a P atom significantly changes the electronic property of g-C3N4 and suppresses the recombination of photogenerated charge carriers, thus improving its photocatalytic performance.

Highly selective CO2 photoreduction to CO over g-C3N4/Bi2WO6 composites under visible light

CO2 is highly stable and therefore extremely difficult to be reduced at room temperature even by photocatalysis. Herein, a series of g-C3N4/Bi2WO6 composites have been synthesized through a facile in situ hydrothermal approach, which demonstrated greatly enhanced response to visible light, and consequently a remarkably enhanced CO2 selective photoreduction to CO. The g-C3N4 content and synthesis parameters of these composites have been tuned to obtain the optimized photocatalytic activity with a peak CO production rate of 5.19 μmol g−1 h−1 under visible light irradiation at room temperature, which was 22 and 6.4 times that on pure g-C3N4 and Bi2WO6, respectively. Based on the matched band energy potentials between g-C3N4 and Bi2WO6 in the synthesized composites, a possible Z-scheme mechanism, which features a significantly promoted separation of photo-generated carriers under visible light irradiation by the composites, has been proposed to account for the distinctive CO2 photoreduction performance.

A post-grafting strategy to modify g-C3N4 with aromatic heterocycles for enhanced photocatalytic activity

A novel and facile post-grafting strategy, instead of conventional copolymerization, via a Schiff base chemical reaction between aldehyde and –NH2 groups has been developed to construct aromatic heterocycle-grafted graphitic carbon nitride (g-C3N4) photocatalysts for the first time. The high-resolution N 1s XPS spectrum and the CO2 TPD analysis confirmed the successful introduction of heterocycles and the reduced structural defects (unreacted –NH2 groups during the copolymerization modification of g-C3N4). The post-grafting of aromatic rings into the g-C3N4 network did not disrupt the original framework of g-C3N4, but effectively expanded its π-delocalized system, enlarged its surface area and promoted the separation and transfer of photo-excited charge carriers. As a result, the obtained copolymer composites exhibit significantly enhanced visible-light photocatalytic activity for H2 evolution over pristine g-C3N4. This strategy is general and can be used to graft large numbers of aromatic rings of different molecular structures onto g-C3N4.

A Redox‐anchoring Approach to Well‐dispersed MoCx/C Nanocomposite for Efficient Electrocatalytic Hydrogen Evolution

Here we report a redox-anchoring strategy for synthesizing a non-noble metal carbide (MoCx ) nanocomposite electrocatalyst for water electrolysis in acidic media, using glucose and ammonium heptamolybdate as carbon and Mo precursors, respectively, without the need of gaseous carbon sources such as CH4 . Specifically, the aldehyde groups of glucose are capable of reducing Mo6+ to Mo4+ (MoO2 ), and thus molybdenum species can be well anchored by a redox reaction onto a carbon matrix to prevent the aggregation of MoCx nanoparticles during the following carbonization process. The morphology and chemical composition of the electrocatalysts were well characterized by BSE-SEM, TEM, XRD and XPS. The obtained MoCx -2 sample showed a reasonably high hydrogen evolution reaction (HER) activity and excellent stability in an acidic electrolyte, and its overpotential required for a current density output of 20 mA cm-2 is as low as 193 mV. Such a prominent performance is ascribed to the excellent dispersity and nano-size, and the large reactive surface area of MoCx particles. This work may open a new way to the design and fabrication of other non-noble metal carbide nanocatalysts for various electrochemical applications.

Pt/MnO2 nanosheets: facile synthesis and highly efficient catalyst for ethylene oxidation at low temperature

Transition metal oxides (TMOs) have been playing an indispensible role in the catalysis of redox reactions. In particular, two dimensional TMOs expose their surface/edge sites to a large extent, which brings unique catalytic features such as greatly enhanced catalytic activities. Here a series of MnO2 nanosheets have been facilely synthesized by a simple redox reaction between KMnO4 and 2-(N-morpholino)ethane sulfonic acid (MES) at room temperature. Among the obtained MnO2 samples, MnO2-48 h showed the highest performance in removing C2H4 resulting from its highest concentration of surface active oxygen species. To further improve the oxidation activity of the catalyst, a small amount of Pt nanoparticles (NPs) was subsequently loaded on MnO2 nanosheets (Pt/MnO2) by a colloidal deposition method. The Pt/MnO2 demonstrated enhanced catalytic performance and maintained complete removal of 20 ppm C2H4 at 50 °C for at least 12 h, which can be attributed to the large amount of adsorbed oxygen species and synergetic catalytic effect between Pt and the MnO2 support.

A unique route to fabricate mesoporous carbon with abundant ferric species as a heterogeneous Fenton catalyst under neutral conditions

The incorporation of large amounts of metal oxide species into mesoporous carbon without pore blockage is still a challenge. Herein, a unique approach combining physical vapor infiltration (PVI) with hard-templating replication, has been developed to prepare mesoporous carbon immobilized with abundant and highly dispersed ferric species using ferrocene as a single source for both carbon and iron. As a heterogeneous Fenton catalyst, the as-synthesized mesoporous carbon Fe/mC-450-H, which was obtained at 450 °C in an H2 atmosphere, can efficiently adsorb and degrade methylene blue (MB) at neutral pH values with H2O2.

Ni-assisted low-temperature synthesis of MoCx with enhanced HER activity

Here we report a novel one-pot approach to synthesize MoCx catalysts at much lowered temperature for hydrogen evolution reaction (HER) in acidic solution. A room-temperature co-precipitation reaction among Ni2+ , MoO42- and 2-methylimidazole in an aqueous solution produced a Mo-Ni-imidazole complex, which was used as the precursor to fabricate MoCx . The morphological and chemical properties of the obtained MoCx affected by calcination and other additive metal sources (like Fe, Co, Cu) were investigated in detail. We demonstrated that Ni-Mo alloying took place prior to MoCx formation during heating, which catalyzed the crystallization of MoCx at relatively low temperature. The MoCx /Ni-650 catalyst exhibited a quite low overpotential of 172 mV at 20 mA cm-2 . The high performance originates from the synergistic effect between MoCx and Ni-Mo alloy, high ratio of Mo3+ /Mo2+ , as well as high electrochemically active surface area and low charge-transfer resistance. This work would open a new way to the design and fabrication of other transition-metal carbide catalysts.

α-Ferrous oxalate dihydrate: a simple coordination polymer featuring photocatalytic and photo-initiated Fenton oxidations

As a kind of efficient photocatalyst, coordination polymers (CPs) have gained much attention in recent years. However, their safety issue and time-consuming synthesis impede their practical application. Here in this paper we first demonstrate the facile synthesis and photocatalytic degradation performance of 1D α-ferrous oxalate dihydrate (α-FOD), which is one of the simplest CPs. A unique two-pathway photocatalytic mechanism which combines traditional photocatalytic and photo-initiated Fenton oxidations has been proposed. The excellent photocatalytic performance and cost-effective fabrication make α-FOD a new promising candidate for the photocatalytic degradation of organic pollutants in practical applications.摘要最近, 配位聚合物作为一种引人注目的光催化剂已经引起了很多研究者的兴趣. 但是危险耗时的制备方法使它的应用受到了限制. 本文采用便捷的制备方法合成了一种简单的线性配位聚合物 “二水合草酸亚铁”, 并证实了其光催化降解染料的活性和能力. 同时, 我们提出了一种独特的结合了传统光催化氧化和光Fenton氧化的双途径催化氧化机理. 二水合草酸亚铁优异的光催化性能及其经济简单的合成方法, 使其有望成为一种有效的降解有机染料的光催化剂.