Changjing Cheng

Poly(4-styrenesulfonic acid-co-maleic acid)-sodium-modified magnetic reduced graphene oxide for enhanced adsorption performance toward cationic dyes

By combining the advantages of poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSMA) with abundant anionic functional groups (–COO− and –SO3−), graphene oxide (GO) with high specific surface area and Fe3O4 nanoparticles with excellent magnetic responsiveness, a novel type of PSSMA-modified magnetic reduced graphene oxide nanocomposite (PSSMA/M-rGO) was synthesized via a simple and facile one-step solvothermal method and used for removing cationic dyes from aqueous solutions in this study. The as-synthesized PSSMA/M-rGO was characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, X-ray diffraction, vibrating sample magnetometry, dynamic light scattering and nitrogen adsorption-desorption technique. Three typical cationic dyes, basic fuchsin (BF), crystal violet (CV) and methylene blue (MB) were used as model dye pollutants to evaluate the adsorption performance of the resultant PSSMA/M-rGO. The adsorption of three cationic dyes onto both PSSMA/M-rGO and M-rGO without PSSMA modification on the surface were systematically investigated at different experiment conditions. The results indicate that the binding of PSSMA on M-rGO can significantly enhance the adsorption capacities and removal efficiencies of the three dyes. This is due to the rich –COO− and –SO3− groups on PSSMA/M-rGO having strong electrostatic interactions with the positively charged dye molecules. The adsorption kinetics and isotherms of the three dyes onto both adsorbents demonstrate that the kinetics and equilibrium adsorptions can be well-described by pseudo-second-order kinetics and Langmuir model, respectively. Moreover, the PSSMA/M-rGO nanocomposites also demonstrate high removal efficiencies toward mixed dyes of BF, CV and MB. Such functional nanocomposites with high adsorption capacity, low production cost and excellent recyclability, are promising as candidate adsorbents for highly-efficient removal of cationic organic pollutants from aqueous solutions.

One-step synthesis of nickel cobalt sulphides particles: tuning the composition for high performance supercapacitors

NiS2–CoS2 composites with different Ni and Co molar ratios for supercapacitors (SCs) were synthesized by one-step hydrothermal co-deposition method using cheap Na2S2O3·5H2O as sulfur source. With the increase of Ni content, the composites particle size increases gradually and the hollow sphere structure becomes more obvious. The electrochemical measurements demonstrate that these composites possess a high specific capacitance (Cm) performance, good rate capability and long cycle stability. To be specific, the Cm of Ni/Co/S-1 composite is the largest, up to 954.3 F g−1 at 1 A g−1, and as high as 309.5 F g−1 even at large current density of 20 A g−1. Furthermore, the Ni/Co/S-1 maintains 99.9% of its initial Cm after 1000 cycles at 5 A g−1. Moreover, the asymmetric supercapacitors with Ni/Co/S-1 as positive electrode and active carbon as negative electrode are of prominent energy density of 29.3 W h−1 kg−1 at the power density of 0.7 kW kg−1, and superior cycling stability of 99.1% initial value retention after 1000 cycles.

Temperature-switched controlled release nanosystems based on molecular recognition and polymer phase transition

Environmental stimuli-responsive nanosystems that can release their encapsulated or loaded substances in spatial-, temporal- and dosage-controlled fashions have attracted tremendous attention, especially from the field of nanomedicine. In this work, a novel temperature-switched controlled release nanosystem based on the molecular recognition of beta-cyclodextrin (β-CD) and thermosensitivity based on the phase transition of poly(N-isopropylacrylamide) (PNIPAM) is developed. This smart nanosystem consists of magnetic Fe3O4 colloidal nanocrystal clusters (MCNCs) core grafted with linear PNIPAM chains attached to numerous β-CD units, (denoted as Fe3O4@PNG–CD). β-CD units act as containers for the loading of hydrophobic model drugs, PNIPAM chains serve as intelligent “microvalves” for controlling the release of loaded model drugs, and MCNCs core can achieve a “site-specific targeting” function. The gating mechanism involves that temperature can significantly affect the association constants of β-CD toward model drug molecules in β-CD modified PNIPAM chains. The resultant Fe3O4@PNG–CD nanoparticles have excellent thermo-reversible adsorption/desorption properties for the loaded model drug 8-anilino-1-naphthalenesulfonic acid ammonium salt (ANS), and demonstrate a positive temperature “on–off” release fashion. By simply changing the temperature, the delivery rate can be effectively controlled. At temperature above the lower critical solution temperature (LCST) of the grafted PNG–CD chains (open gate), the delivery rate of ANS is fast, but very slow at temperature below the LCST (closed gate). These multifunctional nanoparticles provide a new mode for designing and engineering intelligent controlled release nanosystems.

Thermo-responsive adsorption and separation of amino acid enantiomers using smart polymer-brush-modified magnetic nanoparticles

Multifunctional magnetic nanoparticles simultaneously possessing thermo-responsive properties and chiral recognition ability show great potential in enantiomeric separation. In this study, a novel type of multifunctional magnetic Fe3O4 nanoparticle, decorated with smart polymer brushes consisting of poly(N-isopropylacrylamide-co-glycidyl methacrylate) chains with pendent β-cyclodextrin (β-CD) units, was fabricated as a chiral nanoselector for the thermo-sensitive selective adsorption and separation of three amino acid enantiomers. These smart polymer brushes were grafted on the surface of Fe3O4 nanoparticles via a combination of surface-initiated atom transfer radical polymerization and ring-opening reaction. The pendent β-CD units can serve as smart receptors for selectively recognizing enantiomeric molecules via formation of stable host–guest inclusion complexes. The thermo-sensitive poly(N-isopropylacrylamide) chains can act as microenvironmental adjustors for tuning the inclusion constants of β-CD toward enantiomeric guest molecules. The prepared multifunctional magnetic nanoparticles exhibit excellent thermo-responsive adsorption and decomplexation performances toward amino acid enantiomers. Via simply changing the operation temperature, the decomplexation of amino acid enantiomers and regeneration of the smart chiral magnetic nanoparticles can be easily achieved. Besides, the magnetic properties of the regenerated smart nanoparticles enable easy recovery under an external magnetic field for reuse. Such multifunctional magnetic nanoparticles with highly chiral recognition capability, excellent thermo-sensitive adsorption and decomplexation properties toward amino acid enantiomers, and recyclability show great potential in chiral separations.

β-Cyclodextrin polymer brushes decorated magnetic colloidal nanocrystal clusters for the release of hydrophobic drugs

Abstractβ-Cyclodextrin (β-CD) polymern brushes decorated magnetic Fe3O4 colloidal nanocrystal clusters (Fe3O4@PG-CD) were fabricated by a combination of surface-initiated atom transfer radical polymerization on the surface of Br-anchored Fe3O4 colloidal nanocrystal clusters (Fe3O4–Br) and ring-opening reaction of epoxy groups. The resulted Fe3O4@PG-CD hybrid nanoparticles were characterized by several methods including Fourier transform infrared, transmission electron microscope, dynamic light scattering instrument, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer. Moreover, the potential of as-synthesized Fe3O4@PG-CD as a carrier of hydrophobic anticancer drug 5-fluorouracil (5-FU) was also investigated. The results showed that the prepared Fe3O4@PG-CD have core/shell structure and high saturated magnetism. 5-FU could be loaded into the Fe3O4@PG-CD via the formation of β-CD/5-FU inclusion complex. Furthermore, the Fe3O4@PG-CD displayed a high loading capacity and pH-dependent release behavior for 5-FU. The release behavior demonstrated a simple Fickian diffusion in the acidic environment (pH 2.0 and 4.0) but neither non-Fickian nor anomalous when neutral. The results reveal that this nanosystem seems to be a very promising vehicle for the hydrophobic drugs for pH-dependent controlled release.

Effect of sulfate in mineral precursor on capacitance behavior of prepared activated carbon

Analog sulfur-containing precursors (ASCPs) were employed to prepare activated carbon (AC) for supercapacitor by potassium hydroxide (KOH) chemical activation. The influence of sulfate, K2SO4, FeSO4, and CaSO4 on pore structure of resultant AC and its capacitance performance was investigated extensively. The results indicate that FeSO4 and K2SO4 in ASCPs can be involved deeply in activation reaction. K2SO4 can play a synergistic activation role in increasing porosity and capacitance performance, while FeSO4 can react with and consume a certain amount of KOH, thus decreasing the performance of AC. Compared with K2SO4 and FeSO4, CaSO4 in ASCPs has low reactivity; namely, only a small part of CaSO4 was involved in activation reaction, while most of it was transformed into CaCO3 residued in AC during washing process. Due to coexistence of CaCO3 with AC, the porosity and capacitance performance of AC were decreased obviously. Furthermore, it is noteworthy that in comparison with K+ and Ca2+, Fe2+ in ASCPs is more beneficial for transformation of inorganic sulfate into organic thioether in AC.

Sodium dodecylbenzene sulfonate-assisted synthesis of a carbon-cloth-based polyaniline flexible material for supercapacitors

Carbon-cloth-based polyaniline flexible electrode materials were fabricated by a simple chemical oxidation method with the assistance of sodium dodecylbenzene sulfonate (SDBS) at different concentrations, where SDBS acts as a surfactant and dopant to control the morphology, structure and capacitance performance of the electrode material. TGA, BET, XRD, FT-IR, UV-vis and SEM analyses showed that a suitable amount of SDBS can enhance the interchain spacing of the polyaniline and the regularity of its main-chain structure as well as helping to vary its morphology (e.g., networks, spherical, or rod-like structures) on carbon cloth. More importantly, SDBS facilitated the bonding between polyaniline and carbon cloth, leading to the formation of good three-dimensional networks and spherical and rod-like structures, respectively. The insertion/de-insertion of electrolyte ions was easier due to the unique morphology and structure of materials prepared with SDBS, and the utilization ratio of polyaniline was also higher. Cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy tests revealed that of the three composites studied (PANI/CC-0,1,2, depending on the SDBS amount), PANI/CC-1 achieved the optimal capacitance performance, i.e., a high specific capacitance (up to 537 F g−1 at the current density of 0.5 A g−1, which is 31.9% higher than that without SDBS), high capacity retention (83.4% after 1000 charge–discharge cycles, compared to 46.9% for PANI/CC-0), and high energy density (74.5 W h kg−1 at a power density of 0.25 kW kg−1) as well as the best rate capability and the lowest impedance. In summary, the addition of a suitable amount of SDBS has a positive effect on improving the capacitance performance of carbon-cloth-based polyaniline electrodes.