Zhifeng Jiang

Modifiers-assisted formation of nickel nanoparticles and their catalytic application to p-nitrophenol reduction

Nickel nanoparticles with different sizes and morphologies were prepared with nickel chloride as the source of nickel and hydrazine hydrate as a reductant. Cetyltrimethyl ammonium bromide (CTAB), polyethylene glycol-10000 (PEG-10000), gelatin and their composites were used as modifiers in this research. The particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The effect of using single modifiers and their composites was investigated. The results revealed that the kind of modifier used had a significant effect on the morphology and size of the Ni nanostructure. The possible formation mechanism of nickel nanoparticles was also investigated. All of the formed nickel nanoparticles showed excellent catalytic activity in the reduction of p-nitrophenol compared to the commercial RANEY® Ni. The catalytic activity of nickel particles prepared in the presence of composite modifiers was higher than nano nickel catalysts prepared in the presence of single modifiers. The magnetic property, possible catalytic mechanism and the possibility of reusability were also investigated.

Constructing graphite-like carbon nitride modified hierarchical yolk–shell TiO2 spheres for water pollution treatment and hydrogen production

Graphitic carbon nitride (g-C3N4) was hybridized by hierarchical yolk–shell TiO2 spheres via a solvothermal method by mixing the as-prepared g-C3N4 with the precursor of the TiO2 yolk–shell spheres in dimethylformamide (DMF). The introduction of DMF made the TiO2 yolk–shell spheres to be dispersed well on the surface of g-C3N4, thus improving the specific surface area of the materials. The g-C3N4 has a unique two-dimensional layered structure, which is favorable for hybridizing with TiO2. The sufficient contact interface between TiO2 and g-C3N4 could be beneficial to the separation of photogenerated charges. Multiple reflections of light within the interior cavities of titania microspheres with a yolk–shell structure can increase their light absorption. The photocatalytic experimental results indicated that the as-prepared composite TiO2/g-C3N4 (TCN) showed enhanced photocatalytic activities compared with pure TiO2 and g-C3N4. A suitable combination of g-C3N4 with TiO2 produced the highest photocatalytic activity. Moreover, the photocatalytic activity of TCN with a yolk–shell structure is higher than that of TiO2/g-C3N4 without a yolk–shell structure. Based on our experimental results, a possible photocatalytic mechanism with holes and superoxide radical species as the main active species in photocatalysis was proposed. The TCN photocatalysts prepared in this case, with high photocatalytic activity and high stability, were a promising candidate for possible practical application in industrial production.

Facile route fabrication of nano-Ni core mesoporous-silica shell particles with high catalytic activity towards 4-nitrophenol reduction

A facile, environmentally friendly synthetic route was developed to prepare nano-Ni core mesoporous-silica shell particles. Ethylenediaminetetraacetic disodium salt (EDTA) was the chelating agent and thus controlled the nucleation rate of the nano-Ni core. In this work, EDTA was used to regulate the reduction rate of nickel acetate. Thereby, by varying the amount of EDTA utilized in reaction medium, the size of nano-Ni can be readily controlled in the range of 40–80 nm. The mesoporous silica shell was fabricated by the Stober method. The nano-Ni core mesoporous-silica shell particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). UV spectrophotometry (UV/vis) was used to analyse the growth mechanism of the nano-Ni cores. The as-synthesized nano-Ni core mesoporous silica shell particles were found to show a good catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol in the presence of an excess amount of NaBH4. The magnetic properties, catalytic mechanism and the possibility of reusability were also investigated.

Natural leaves-assisted synthesis of nitrogen-doped, carbon-rich nanodots-sensitized, Ag-loaded anatase TiO2 square nanosheets with dominant {001} facets and their enhanced catalytic applications

Extending the UV response of anatase TiO2 photocatalysts into the visible light range can play a pivotal role in promoting the practical applications of these catalysts. Nitrogen and carbon co-doped, silver loaded anatase TiO2 (Ag@NC–TiO2) single-crystal nanosheets dominated by {001} facets were prepared for the first time using leaves as the nitrogen and carbon source by a facile, low cost method. The size of the Ag particles on NC–TiO2 nanosheets can be tuned from 1.5 nm to 15 nm using a photo-reduction strategy. The synthesized Ag@NC–TiO2 nanosheets show higher photocatalytic activity in the photodecomposition of organic pollutants compared to NC–TiO2, TiO2 and P25 under visible light irradiation. The enhanced photocatalytic efficiency was ascribed to a synergistic effect between N, C and Ag. In addition, the formed Ag@NC–TiO2 heteronanosheets are highly dispersible in aqueous solution and are capable of efficient catalysis for the reduction of p-nitrophenol. The present synthesis gives a promising method of forming non-metal co-doped, metal nanoparticles (NPs) loaded anatase TiO2 with dominant {001} facets and for broad applications in catalysis and photocatalysis.

In situ synthesis of bimetallic Ag/Pt loaded single-crystalline anatase TiO2 hollow nano-hemispheres and their improved photocatalytic properties

Considering that the reduction of particle size can increase the number of active sites, particle size is accepted to be the key factor in the design of photocatalysts. However, serious agglomeration of nanosized particles may cause not only a decreased surface area but also increase grain boundary recombination. Forming a hollow nano-hemisphere in single crystals with reactive sites could be a good method to overcome this drawback. In this work, we report the synthesis of novel anatase TiO2 hollow nano-hemispheres by using a mixture of CH3COO− and F− as size and morphology controlling co-agents that prevent aggregation and increase the number of active sites. Furthermore, bimetallic Ag/Pt nanoparticles (NPs) are uniformly loaded on both interior and exterior of the nano-hemispheres in situ. The Ag/Pt@TiO2 NPs with improved visible-light-harvesting ability, high charge–hole mobility, and low electron–hole recombination exhibited improved photocatalytic performance in the degradation of rhodamine B/ciprofloxacin (RhB/CIP) and hydrogen generation. The results presented here give a promising way toward the development of delicate bimetal@semiconductor composites for board applications in photocatalysis.

Characterization and comparison of uniform hydrophilic/hydrophobic transparent silica aerogel beads: skeleton strength and surface modification

Silica aerogel is a good adsorbent due to the large surface area and chemical stability. However, its inherent poor mechanical properties and hydrophobicity limit applications in water treatment. To improve the adsorption performance of silica aerogel, uniform transparent hydrophilic mesoporous silica aerogel beads with highly degree of sphericity were synthesized through a facile aging immersion and ambient pressure drying route. The designed hydrophilic silica aerogel beads possessed the mesopores, mean diameter of approximately with the average pore size of 12.51 nm, the specific surface area of 582.52 m2 g−1, and the pore volume of 1.46 cm3 g−1. For comparison, hydrophilic silica aerogel beads without skeleton improvement and hydrophobic silica aerogel beads were also obtained, respectively. The synthesized novel hydrophilic silica aerogel beads displayed a significantly improved adsorption performance with a favorable dye absorption capacity, superior to that of previously synthesised silica-based aerogel beads materials. This study demonstrates a facile and low-cost route toward transparent silica aerogel beads with macroscopic beads structures, which can be used as adsorbents, catalytic supports or the template to synthesize novel functional materials requiring high transmittance, high surface area and effective mass transport.

A Hierarchical Z‑Scheme α‐Fe2O3/g‐C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction

The challenge in the artificial photosynthesis of fossil resources from CO2 by utilizing solar energy is to achieve stable photocatalysts with effective CO2 adsorption capacity and high charge-separation efficiency. A hierarchical direct Z-scheme system consisting of urchin-like hematite and carbon nitride provides an enhanced photocatalytic activity of reduction of CO2 to CO, yielding a CO evolution rate of 27.2 µmol g-1 h-1 without cocatalyst and sacrifice reagent, which is >2.2 times higher than that produced by g-C3 N4 alone (10.3 µmol g-1 h-1 ). The enhanced photocatalytic activity of the Z-scheme hybrid material can be ascribed to its unique characteristics to accelerate the reduction process, including: (i) 3D hierarchical structure of urchin-like hematite and preferable basic sites which promotes the CO2 adsorption, and (ii) the unique Z-scheme feature efficiently promotes the separation of the electron-hole pairs and enhances the reducibility of electrons in the conduction band of the g-C3 N4 . The origin of such an obvious advantage of the hierarchical Z-scheme is not only explained based on the experimental data but also investigated by modeling CO2 adsorption and CO adsorption on the three different atomic-scale surfaces via density functional theory calculation. The study creates new opportunities for hierarchical hematite and other metal-oxide-based Z-scheme system for solar fuel generation.

In situ growth of Ag/Ag2O nanoparticles on g-C3N4 by a natural carbon nanodot-assisted green method for synergistic photocatalytic activity

Novel visible-light-driven Ag/Ag2O@g-C3N4 (AAC) hybrid materials were synthesized successfully via a green, facile hydrothermal treatment approach by reducing AgNO3 using carbon nanodots as reducing agent for the first time. Natural leaves were used as precursors to prepare carbon nanodots. By adjusting the feed mass ratio of AgNO3 to carbon nanodots, the average diameter of Ag/Ag2O can be modulated from 8 to 33 nm. The effects of Ag/Ag2O deposition on the optical and photocatalytic performance of AAC in the degradation of rhodamine B (RhB) under visible light irradiation were systematically investigated. It was found that the Ag/Ag2O content greatly influences the photocatalytic activity of AAC nanocomposites. A suitable amount of Ag/Ag2O in the AAC system could obtain the best photocatalytic activity. The experimental results indicated that all the AAC nanocomposites showed higher photocatalytic activities compared with that of pure g-C3N4. The remarkable visible-light photocatalytic activity of AAC heterostructures could be attributed to their absorption in the visible region and low recombination rate of the electron–hole pairs because of the heterojunction formed between Ag2O and g-C3N4. In addition, Ag nanoparticles are believed to play an essential role in affecting the photoreactivity because they are able to trap electrons, further separate the electron–hole pairs, and prolong the life of electron–hole pairs. In other words, it can be concluded that the increased photocatalytic activity of AAC was attributed to the synergic effect between g-C3N4, Ag2O and Ag. It is believed that the present work could render useful information for steering the design and application of noble nanoparticle loaded g-C3N4-based heterojunction composites with high photocatalytic activity.

L-cysteine-assisted synthesis of hierarchical NiS2 hollow spheres supported carbon nitride as photocatalysts with enhanced lifetime

Novel hierarchical NiS2 hollow spheres modified by graphite-like carbon nitride were prepared using a facile L-cysteine-assisted solvothermal route. The NiS2/g-C3N4 composites exhibited excellent photocatalytic efficiency in rhodamine B, methyl orange and ciprofloxacin degradation as compared to single g-C3N4 and NiS2, which could be due to the synergistic effects of the unique hollow sphere-like structure, strong visible-light absorption and increased separation rate of the photoinduced electron-hole pairs at the intimate interface of heterojunctions. A suitable combination of g-C3N4 with NiS2 showed the best photocatalytic performance. In addition, an electron spin resonance and trapping experiment demonstrated that the photogenerated hydroxyl radicals and superoxide radicals were the two main photoactive species in photocatalysis. A possible photocatalytic mechanism of NiS2/g-C3N4 composites under visible light irradiation is also proposed. The strategy presented here can be extended to a general strategy for constructing 3D/2D heterostructured photocatalysts for broad applications in photocatalysis.

Fabrication of noble-metal-free NiS2/g-C3N4 hybrid photocatalysts with visible light-responsive photocatalytic activities

Nanocomposites of NiS2 with graphitic carbon nitride (NiS2/g-C3N4) have been successfully synthesized by means of a facile hydrothermal method. The photocatalytic activities of as-prepared samples were evaluated by monitoring the photodecomposition of rhodamine B under visible light irradiation. The experimental results indicated that visible light-driven NiS2/g-C3N4 composites exhibited an enhanced photocatalytic activity compared to that of pure NiS2, due to the fast generation, separation and transportation of the photogenerated carriers resulting from the addition of NiS2 nanoparticles (NPs). Interestingly, different amounts of NiS2 deposition can affect the photocatalytic activities of the NiS2/g-C3N4 composites. A suitable loading amount of NiS2 NPs presents the best photodegradation performance. The photocatalytic reaction mechanism for the improved photocatalytic performance of NiS2/g-C3N4 catalyst was proposed which was supported by PL, PEC, EIS and active species trapping results. A promising strategy presented here provides a facile route towards the development of economical, noble metal-free composites as photocatalysts for the applications in environmental remediation.