Qinhui Zhang

Synthesis of Ag@AgBr/AgCl heterostructured nanocashews with enhanced photocatalytic performance via anion exchange

Heterostructured Ag@AgBr/AgCl nanocashews have been synthesized by an anion-exchange reaction between AgCl nanocubes and Br− ions followed by photoreduction. Compared to polyhedral Ag@AgBr nanoparticles, the obtained nanostructures exhibit enhanced photocatalytic activity towards decomposition of organic pollutants, i.e., rhodamine-B (RhB). For example, only 2 min is taken to completely decompose RhB molecules with the assistance of these novel heterostructured nanoparticles under visible light irradiation. Furthermore, the as-synthesized nanocatalyst can be reused 20 times without losing activity, showing its high stability. Interestingly, the novel heterostructured Ag@AgBr/AgCl nanophotocatalyst also shows efficient visible light conversion of CO2 to energetic fuels, e.g. methanol/ethanol. Therefore, the present route opens an avenue to achieve highly efficient visible-light-driven nanophotocatalysts for applications in environmental remediation and resourceful use of CO2.

Plasmonic silver incorporated silver halides for efficient photocatalysis

The development of visible-light-responsive photocatalysts is a promising challenge in the management of environmental pollution. Silver–silver halide nano-photocatalysts have received intensive attention due to their excellent photocatalytic performance in recent years, where silver nanoparticles/nanoclusters demonstrate plasmonic enhanced light absorption efficiency and have been considered as an important component in various functional photocatalytic nanocomposite materials, serving for harvesting visible light. This review provides an overall survey on the state-of-the-art silver–silver halide-based photocatalysts, fundamental understanding of their plasmonically induced photo-reactions and their major environmental applications. We first discuss the basic concepts of localized surface plasmon resonance, and outline the general mechanism of silver–silver halide-based photocatalysis. We then discuss the latest progress in the design and fabrication of silver halide based photocatalysis using various strategies. Next, we highlight some selected examples to demonstrate the new applications of silver/silver halide nano-photocatalysts. Eventually, we provide an outlook of the present challenges and some perspectives of new directions in this interesting and emerging research area.

Syntheses and structures of lithium zirconates for high-temperature CO2 absorption

The sorption and further application of CO2 is a highlight in the field of environmental protection and sustainable development. Lithium-containing zirconates (LixZryOz) are promising materials for high-temperature chemisorption of CO2 and have attracted tremendous interest. This review presents discussion on the recent status of LixZryOz based CO2 sorbents at high temperature. Special attention is focused on the solid state chemistry, synthetic strategies, high-temperature CO2 capture–regeneration properties and possible sorption mechanisms for LixZryOz with different Li/Zr ratios, including Li2ZrO3, Li6Zr2O7, Li8ZrO6, and Li2ZrO3 doping with alkali metals.

Plasmonic enhancement of photocatalysis over Ag incorporated AgI hollow nanostructures

Hollow-structured polyhedral nanostructures of AgI nanoboxes and cube-tetrapod Ag/AgI cages have been fabricated through the controlled reaction of I− ions with nanocubes and cube-tetrapods of AgCl based on the principle of the Kirkendall effect. The Ag0 nanodomains in the source nanoparticles of AgCl:Ag are preserved in the final hollow Ag/AgI cages during the chemical conversion of AgCl to AgI. The obtained hollow cube-tetrapod Ag/AgI nanostructures exhibited enhanced light absorption in the visible region and photocatalytic performance towards hydrogen evolution from water reduction and decomposition of organic pollutants, owing to the contribution of the surface plasmon resonance (SPR) effect of silver nanoparticles (nanodomains). The present versatile route can be generalized to the preparation of other inorganic functional materials with hollow interiors for different applications.

Graphene oxide coupled AgBr nanosheets: an efficient dual-functional visible-light-responsive nanophotocatalyst with enhanced performance

A facile 2-dimensional coupling of AgBr nanosheets with graphene oxide (GO) sheet has been developed to fabricate an efficient dual-functional visible-light-responsive GO@AgBr nanophotocatalyst. Compared to bare AgBr nanosheets, the as-obtained GO@AgBr nanocomposite exhibits enhanced photocatalytic activity towards degradation of rhodamine-B (RhB) and evolution of H2 from aqueous-methanol solution. The RhB molecules can be decomposed completely within 4 min under visible light irradiation and the catalyst can be reused 10 times without losing activity. A possible mechanism for the highly efficient photocatalyst is proposed, implying GO serves as electron acceptor to facilitate the charge transfer and suppress the recombination of electron–hole pairs. This work provides a convenient means for the exploration of highly efficient and stable GO-based composite photocatalysts.

Converting AgCl nanocubes to silver nanowires through a glycerol-mediated solution route

Silver nanowires have been synthesized from AgCl nanocubes through a glycerol-mediated solution method with the assistance of a polymer surfactant (PVP). The influencing factors such as reaction time, PVP and temperature on the quality and quantity of the product were investigated through monitoring the reaction process using electronic microscopy. The results indicate that appropriate temperature and time are crucial to produce nanowires, whereas PVP concentration influences the diameter and length of the nanowires. The possible mechanism is proposed. The investigations of silver sources show that AgCl nanocubes are proper feedstock to acquire silver nanowires. This paper provides a new way to produce silver nanowires from insoluble salts.

Catalytic hydrothermal liquefaction of Euglena sp. microalgae over zeolite catalysts for the production of bio-oil

In this paper, Euglena sp. microalgae with low lipid and high ash contents were successfully converted into bio-oil with/without catalysts through hydrothermal liquefaction (HTL) at 280 °C and a reaction time of 30 min. The introduction of acidic microporous zeolite catalysts (HZSM-22, HZSM-5, H beta, MCM-22, and SAPO-11) with high hydrothermal stability further improved the bio-oil quality in situ. Various methods, including elemental analysis, high heat value (HHV), and gas chromatography (GC)-mass spectrometry (MS), were used to analyze the physicochemical properties of the obtained bio-oil. Results indicated that catalyst addition could enhance C and H contents, reduce O and N contents, and also improve HHV (the maximum value of 37.08 MJ kg−1 was obtained for the H beta catalyst). GC-MS revealed that the bio-oil obtained by direct HTL contained relatively high amounts of N-containing compounds (30.87%) and acid compounds (16.44%). Meanwhile, the catalysts introduced in situ not only lowered the contents of nitrogen and acids to some extent, but also simultaneously increased the hydrocarbon content. This result was most pronounced over the H beta catalyst, which reduced the nitrogen content to 16.68% and decreased the acid content to 9.50%. The hydrocarbon content increased to 43.43%. Ultimately, a reasonable reaction network for Euglena sp. HTL was proposed and provides a basis for the processs further industrialization.

Oil-soluble Ni-Mo sulfide nanoparticles and their hydrogenation catalytic properties

Oil-soluble bimetallic Ni-Mo sulfide nanoparticles (NiMoS) with narrow size distribution were successfully synthesized through a composite-surfactants-assisted-solvothermal process. The surface functionality and lipophilicity of the Ni-Mo sulfides were shown by transmission electronic microscopy, Fourier transform infrared and ultraviolet spectroscopy. The as-prepared Ni-Mo sulfides supported on activated carbon (NiMoS/AC) exhibited enhanced catalytic activity towards naphthalene hydrogenation instead of cracking. For comparison, CoMoS/AC and MoS2/AC catalysts were also prepared through similar procedures, and it was found that their catalytic performance decreased in the order of NiMoS/AC>CoMoS/AC>MoS2/AC. Furthermore, the activity of the bimetallic NiMoS nanocatalyst can be effectively tuned via variation of the atomic ratio of Ni/(Ni+Mo).

Study of the coordinative nature of alkylaluminum modified Phillips CrOx/SiO2 catalyst by multinucleai solid-state NMR

Solid-state nuclear magnetic resonance spectroscopy was used to investigate the coordinative states of surface Al species on various alkylaluminum-modified Phillips CrOx/SiO2 catalysts. The alkylaluminum-modified Phillips CrOx/SiO2 catalysts were examined via ethylene homopolymerization. 1H and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra clearly demonstrated that the existing states of surface Al species in alkylaluminum-modified catalysts strongly depended on the type of alkylaluminum cocatalyst, concentration of alkylaluminum and the calcination temperature. 1H MAS NMR spectra of alkylaluminum-modified Phillips CrOx/SiO2 catalysts, calcined at two different temperatures, exhibited similar trends in peak shift. 1H spectra showed that with an increase of Al/Cr ratio and calcination temperature, the main peak shifted to high field, indicating that the dominant surface proton species changed from hydroxyl to ethoxyl and ethyl groups. 27Al MAS NMR spectra showed the presence of three different coordination states (6-, 5-, and 4-coordinated Al species) in the alkylaluminum-modified Phillips catalysts. In comparison of different alkylaluminum cocatalysts, it was found that the reactivity of alkylaluminum modified Phillips catalyst decreased in the order of TEA>DEAH>DEAE. The amount of 4-coordinated Al species of Phillips catalysts modified by TEA, DEAE and DEAH also decreased in the order of TEA>DEAH>DEAE, indicating that the presence of 4-coordinated Al species is related to the polymerization activity.