Guoqiang Liu

Electrostatic Self-Assembly of Au Nanoparticles onto Thermosensitive Magnetic Core-Shell Microgels for Thermally Tunable and Magnetically Recyclable Catalysis

A facile route to fabricate a nanocomposite of Fe3O4@poly[N-isopropylacrylamide (NIPAM)-co-2-(dimethylamino)ethyl methacrylate (DMAEMA)]@Au (Fe3O4@PND@Au) is developed for magnetically recyclable and thermally tunable catalysis. The negatively charged Au nanoparticles with an average diameter of 10 nm are homogeneously loaded onto positively charged thermoresponsive magnetic core-shell microgels of Fe3O4@poly(NIPAM-co-DMAEMA) (Fe3O4@PND) through electrostatic self-assembly. This type of attachment offers perspectives for using charged polymeric shell on a broad variety of nanoparticles to immobilize the opposite-charged nanoparticles. The thermosensitive PND shell with swollen or collapsed properties can be as a retractable Au carrier, thereby tuning the aggregation or dispersion of Au nanoparticles, which leads to an increase or decrease of catalytic activity. Therefore, the catalytic activity of Fe3O4@PND@Au can be modulated by the volume transition of thermosensitive microgel shells. Importantly, the mode of tuning the aggregation or dispersion of Au nanoparticles using a thermosensitive carrier offers a novel strategy to adjust and control the catalytic activity, which is completely different with the traditional regulation mode of controlling the diffusion of reactants toward the catalytic Au core using the thermosensitive poly(N-isopropylacrylamide) network as a nanogate. Concurrent with the thermally tunable catalysis, the magnetic susceptibility of magnetic cores enables the Fe3O4@PND@Au nanocomposites to be capable of serving as smart nanoreactors for thermally tunable and magnetically recyclable catalysis.

Core–Shell–Corona-Structured Polyelectrolyte Brushes-Grafting Magnetic Nanoparticles for Water Harvesting

A novel superhydrophilic material, charged polymer brushes-grafted magnetic core-shell-corona composite nanoparticles (Fe3O4@SiO2@PSPMA), was developed to harvest water through the hydration effect. Because of both the strong hydration capability and the good swelling performance, the negatively charged polymer brushes, PSPMA brushes, endow the composite nanoparticles with superhydrophilicity and a good water-absorbing performance like a sponge, while the magnetic Fe3O4 cores allow easy separation of Fe3O4@SiO2@PSPMA nanoparticles with absorbed water from oil/water mixture under an external magnetic field. The functional particles have the capability of harvesting water droplets whether floating on an oil surface or in the oil. This water-absorbing material uses selective wettability to harvest water and achieve oil-water separation and may be useful in finding novel approaches for recycling water from sewage and removing water in the petroleum industry.

S,N-Containing Co-MOF derived Co9S8@S,N-doped carbon materials as efficient oxygen electrocatalysts and supercapacitor electrode materials

Controllable synthesis of metal–organic framework (MOF) materials with tunable morphologies, sizes, compositions and pore structures is critically important for MOF materials and their pyrolysis derivatives’ applications in environmental and energy fields. Here we report the synthesis of Co-MOF crystals with controllable morphologies, sizes and S/N ratios in water/NaOH and ethylene glycol/NaOH systems using thiophene-2,5-dicarboxylate (Tdc) and 4,4′-bipyridine (Bpy) as S, N dual organic ligands by a “pillar-layer” assembly method. Water and ethylene glycol with different viscosities result in various crystallization processes of [Co(Tdc)(Bpy)]n crystals in the corresponding reaction system, thus respectively obtaining three-dimensional (3D) Co-MOF ([Co(Tdc)(Bpy)]n) bulk and cuboid structures in water/NaOH and ethylene glycol/NaOH reaction systems. The as-prepared Co-MOF crystals in two different reaction systems were further pyrolytically treated at 800 °C in a N2 atmosphere to obtain Co9S8@S,N-doped carbon materials with different surface areas, pore distributions and S/N doping ratios. As electrocatalysts, the Co9S8@S,N-doped carbon cuboid (Co9S8@SNCC) obtained in the ethylene glycol/NaOH system demonstrates superior bifunctional electrocatalytic activities toward both oxygen reduction and evolution reactions resulting from Co9S8 and S, N doping in the carbon structure providing catalytic active sites, better than that of Co9S8@S,N-doped carbon bulk (Co9S8@SNCB) obtained in the water/NaOH system and comparable to commercial Pt/C and RuO2 catalysts. Owing to its high surface area and porous structure, Co9S8@SNCC also exhibits great potential as the electrode material for application in supercapacitors, with high performance and recycling stability.

Hairy Polyelectrolyte Brushes-Grafted Thermosensitive Microgels as Artificial Synovial Fluid for Simultaneous Biomimetic Lubrication and Arthritis Treatment

We report the fabrication of poly(3-sulfopropyl methacrylate potassium salt) (PSPMK) brushes grafted poly(N-isopropylacrylamide) (PNIPAAm) microgels and their potential as artificial synovial fluid for biomimetic aqueous lubrication and arthritis treatment. The negatively charged PSPMK brushes and thermosensitive PNIPAAm microgels play water-based hydration lubrication and temperature-triggered drug release, respectively. Under soft friction pairs, an ultralow coefficient of friction was achieved, while the hairy thermosensitive microgels showed a desirable temperature-triggered drugs release performance. Such a soft charged hairy microgel offers great possibility for designing intelligent synovial fluid. What is more, the combination of lubrication and drug loading capabilities enables the large clinical potential of novel soft hairy nanoparticles as synthetic joint lubricant fluid in arthritis treatment.

Charged Polymer Brushes-Grafted Hollow Silica Nanoparticles as a Novel Promising Material for Simultaneous Joint Lubrication and Treatment

The fabrication of core/shell charged polymer brushes-grafted hollow silica nanoparticles (PSPMA-g-HSNPs) is reported. Because of the excellent hydration capability of the shells consisting of charged polymer brushes, the functional nanoparticles can achieve a good lubricating effect in aqueous media via hydration lubrication mechanism. The mesoporous hollow silica cores endow the nanoparticles with drug loading-release capability. Aspirin, as a useful drug for treating arthritis, was employed to carry out in vitro drug loading and release studies. It is clear that brushes-modified hollow silica exhibited long-term drug release performance. The combination of lubrication and drug loading capabilities results in the great clinical potential of new multifunctional nanoparticles as injectable joint lubricant fluid in arthritis treatment.

Tuning the Tribological Property with Thermal Sensitive Microgels for Aqueous Lubrication

Thermoresponsive microgels, poly(N-isopropylacrylamide)-graft-poly(ethylene glycol) (PNIPAAm-g-PEG), were synthesized via emulsifier-free emulsion polymerization and the tribological property as water lubricating additive was studied. The microgels had good thermoresponsive collapse/swelling performance with lower critical solution temperature (LCST) ca. 38.4 °C. The rheological characterization and tribological tests showed that the microgels had a good lubricating performance in aqueous lubrication through interfacial physisorption and hydration lubrication, but the friction coefficient was impacted by temperature (below and above LCST). The tunable thermosensitive tribological property was attributed to the hydrophobic interaction and the enhanced interfacial absorption, which were both triggered by the elevated temperature. Furthermore, in order to avoid the water erosion in aqueous lubrication, the microgels were used together with 1H-benzotriazoles (BTA). Because of the good antifriction and anticorrosion property of BTA and the interplay between microgels and BTA, the microgels/BTA exhibited a synergistic effect in aqueous lubrication and the tribological property was more sensitive around the LCST. The present work is beneficial to understanding the tribological property of responsive microgels in aqueous lubrication and provides a novel approach for achieving low-friction through soft matters.

Photothermally actuated interfacial hydration for fast friction switch on hydrophilic polymer brush modified PDMS sheet incorporated with Fe3O4 nanoparticles

A near-infrared light triggered fast interfacial friction switch was achieved with polyelectrolyte brush grafted PDMS embedded with Fe3O4 nanoparticles, where the in situ heating up of the photothermal Fe3O4 nanoparticles in the polymer matrix changes the interface humidity and thereafter alters the hydration level of the interfacial polymer brushes.

Shrimp-shell derived carbon nanodots as precursors to fabricate Fe,N-doped porous graphitic carbon electrocatalysts for efficient oxygen reduction in zinc–air batteries

In this work, shrimp-shell derived N-doped carbon nanodots (N-CNs) as carbon and nitrogen sources are assembled into particle-like aggregates by a simple polymerization reaction of pyrrole in the presence of Fe3+ to form Fe containing N-CN/polypyrrole (PPY) composites (Fe–N-CN/PPy). The resulting composites are thermally treated by a facile pyrolysis approach under a N2 atmosphere to obtain an Fe,N-doped porous graphitic carbon (Fe-N-PGC) material. The results demonstrate that the pyrolytically converted carbon material at 800 °C (Fe-N-PGC-800) exhibits an approximately mesoporous structure with a pore size distribution centered at ∼1.97 nm and ∼2.8 nm and a surface area of 806.7 m2 g−1. As an electrocatalyst for oxygen reduction reaction (ORR) in alkaline media, Fe-N-PGC-800 shows superior ORR catalytic activity with an onset potential of −0.017 V and a limiting current density of 5.42 mA cm−2 (at −0.4 V, vs. Ag/AgCl), which is superior to that of commercial Pt/C catalysts (onset potential of −0.018 V and a limiting current density of 5.21 mA cm−2 at −0.4 V, vs. Ag/AgCl). Additionally, Fe-N-PGC-800 also exhibits good ORR activity in acidic media with an onset potential of 0.53 V and a limiting current density of 5.58 mA cm−2 (at 0.1 V, vs. Ag/AgCl), comparable to that of most reported Fe-based N-doped carbon electrocatalysts. An air cathode made from Fe-N-PGC-800 shows high performance and superior cycling durability in zinc–air batteries (gravimetric energy density of 752 Wh kg−1), comparable to that of commercial Pt/C-based batteries (gravimetric energy density of 774 Wh kg−1). This work demonstrates the feasibility of utilizing biomass as a starting material to fabricate Fe,N-doped carbon materials as high performance ORR electrocatalysts for practical application in ORR-relevant energy devices.

Electrocatalytic oxidation of benzyl alcohol for simultaneously promoting H2 evolution by a Co0.83Ni0.17/activated carbon electrocatalyst

Electrocatalytic water splitting as an environmentally friendly method to produce clean H2 has attracted wide attention. However, efficient improvement of the performance of the oxidation half-reaction during water splitting, thus enhancing H2 evolution efficiency, has become an urgent issue. Herein, non-precious metal Co0.83Ni0.17 alloy nanoparticles on activated carbon (Co0.83Ni0.17/AC) have been successfully fabricated by a simple thermal-treatment method. The resulting Co0.83Ni0.17/AC with a dominant alloy particle size of 45 nm exhibits a microporous and mesoporous structure with a surface area of 159.2 m2 g−1. As an electrocatalyst, the as-prepared Co0.83Ni0.17/AC demonstrates bifunctional electrocatalytic activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, delivering overpotentials of 193 and 325 mV at 10 mA cm−2, respectively. Importantly, it is found that the electrocatalytic oxidation of benzyl alcohol to benzoic acid on Co0.83Ni0.17/AC is more favourable than the OER process, with almost 224 mV less overpotential at 10 mA cm−2 and 96% faradaic efficiency at 1.425 V vs. RHE (passing charge amount of ∼40C). As a simultaneous anode and cathode electrocatalyst for water splitting, Co0.83Ni0.17/AC displays a H2 generation rate of 8.98 μmol min−1 in 1.0 M KOH solution containing 10 mM benzyl alcohol, almost 1.4 times that obtained by an OER-introduced water splitting system, with near 98% faradaic efficiency for H2. This work would be helpful to develop low-cost and abundant bifunctional electrocatalysts for electrocatalytic organic synthesis and simultaneously improving H2 generation from water splitting.

Efficiently electrocatalytic oxidation of benzyl alcohol for energy- saved zinc-air battery using a multifunctional nickel–cobalt alloy electrocatalyst

We investigate the possibility of utilizing benzyl alcohol oxidation reaction to replace sluggish oxygen evolution reaction (OER) for the charging process in a rechargeable zinc-air battery, catalyzed by NiCo alloy nanoparticles supported on activated carbon (NiCo/AC) with the multifunctional electrocatalytic activities of the oxygen reduction, oxygen evolution and benzyl alcohol oxidation reactions. As an electrocatalyst for the oxygen reduction reaction (OER), NiCo/AC exhibits superior catalytic activity with an onset potential of 0.85u202fV (vs. RHE), a half-wave potential of 0.74u202fV (vs. RHE) and a large limiting current density of 4.65u202fmAu202fcm-2 at 0.2u202fV (vs. RHE). Moreover, NiCo/AC also demonstrates the electrocatalytic oxidation activities toward water and benzyl alcohol, moreover, the benzyl alcohol oxidation reaction is more thermodynamically and kinetically favourable with 254u202fmV smaller overpotential than water oxidation at 10u202fmAu202fcm-2. Owing to these advantages, NiCo/AC as air cathode material is assembled into a home-made rechargeable zinc-air battery, resulting an almost 200u202fmV lower charging voltage at the current density of 50u202fmAu202fcm-2 in the presence of 0.1u202fM benzyl alcohol compared to the battery without benzyl alcohol, consequently obtaining 10.5% energy saving at the charging current density of 50u202fmAu202fcm-2 with high durability.