Yagang Zhang

Biomass based nitrogen-doped structure-tunable versatile porous carbon materials

Hierarchical nitrogen-doped porous carbons (HNPCs) with tunable pore structures and ultrahigh specific surface areas were designed and prepared from sustainable biomass precursor cellulose carbamate via simultaneous carbonization and activation by a facile one-pot approach. The as-synthesized HNPCs exhibited an ultrahigh specific surface area (3700 m2 g−1), a high pore volume (3.60 cm3 g−1) and a high level of nitrogen-doping (7.7%). The HNPCs were structurally tunable in terms of their pore structure and morphology by adjusting the calcination temperature. In three-electrode systems, the electrode made of HNPCs prepared at 900 °C (HNPCs-900) showed a high specific capacitance of 339 F g−1 in 6 M KOH aqueous electrolyte and 282 F g−1 in 1 M H2SO4 electrolyte at a current density of 0.5 A g−1. An outstanding rate capability (∼73% retention at a current density of 20 A g−1) and excellent cycling stability (∼95% retention after 5000 galvanostatic charge–discharge cycles at a current density of 5 A g−1) in KOH electrolyte were achieved. In two-electrode systems, the electrode made of HNPCs-900 exhibited a high specific capacitance of 289 F g−1 at 0.5 A g−1 and good rate capacity (∼72% retention at a current density of 20 A g−1) as well as cycling stability (∼92% retention at 2 A g−1) after 5000 cycles. Furthermore, the HNPCs-900 showed an unprecedented adsorption capacity for methylene blue (1551 mg g−1) which was among the few highest ever reported for dye removal. The HNPCs could be used as functional materials for energy storage and waste water treatment.

Quadruply hydrogen bonding modules as highly selective nanoscale adhesive agents.

Covalently linking DNA base analogues DAN, DeUG, or UPy to glass slides led to functional surfaces that could be glued together using a functionalized polystyrene displaying the complementary recognition unit. Nonspecific adhesion was minimized with fluorinated alkane (Teflon-like or Scotchgard-like) surfaces.

Control interfacial properties and tensile strength of glass fibre/PP composites by grafting poly(ethylene glycol) chains on glass fibre surface

To control the interphase properties of glass fibre/PP composites, poly(ethylene glycol) (PEG) chains with different average molar mass (w) were grafted onto the glass fibre surface by treating the fibres with γ-APS, HDI and PEG stepwise. The interfacial adhesion of composites was studied as a function of the w of PEG chain grafted on the glass surface. The contact angle measurement, ATR-FTIR, XPS and AFM analysis for the grafted glass fibres (GFs) proved that the PEG chains were grafted onto the GF surface successfully. The increasing roughness of the GF surface confirms that the lengths of the grafted chains grow as the w of PEG increases. The single fibre strength was measured and the data were analyzed by using the two-parameter Weibull model. The results showed that the grafting of PEG on the GF surface lead to a slightly reduced tensile strength and Weibull modulus. The tensile strength of the unidirectional GF reinforced PP composites was tested from 90° and 0° off-axis. It is found that grafting PEG chains onto the GF surface by this three-stage method is an effective means to improve the interfacial adhesion and transverse and longitudinal tensile properties of GF/PP composites. The results showed that as the w of PEG increased, the interfacial adhesion of the composites improved.

A patterned colorimetric sensor array for rapid detection of TNT at ppt level

We describe a simple photolithographic method for patterning a porous membrane to create well-defined polymer walls to improve the printability of a colorimetric sensor array. The resulting array demonstrated highly selective detection of 2,4,6-trinitrotoluene (TNT) vapour and other nitroaromatic compounds.

Solvent programmable polymers based on restricted rotation.

Solvent programmable polymers (SPPs) were developed that can modulate their recognition properties by heating in different solvents. These highly cross-linked polymer gels were able to respond to differences in solvent polarity at elevated temperatures via rotation about a C(aryl)-N(imide) bond of a carboxylic acid monomer. When heated in polar solvents such as water, the number of solvent accessible carboxylic acids in the polymers increases. When heated in nonpolar solvents such as toluene, the number of solvent accessible carboxylic acids decreases. On cooling to rt, these changes are preserved and maintained even when the polymer is removed from the solvent imprinting environment. The solvent memory is due to the reestablishment of restricted rotation around that C(aryl)-N(imide) bond, which locks the carboxylic acid recognition groups into either a solvent accessible or inaccessible orientation. The solvent programmability was also shown to be reversible. The fidelity of the SPP switching process did not decrease after five cycles of heating in polar and nonpolar solvents.

Azobenzene dye-coupled quadruply hydrogen-bonding modules as colorimetric indicators for supramolecular interactions.

Summary The facile coupling of azobenzene dyes to the quadruply hydrogen-bonding modules 2,7-diamido-1,8-naphthyridine (DAN) and 7-deazaguanine urea (DeUG) is described. The coupling of azobenzene dye 2 to mono-amido DAN units 4, 7, and 9 was effected by classic 4-(dimethylamino)pyridine (DMAP)-catalyzed peptide synthesis with N-(3-dimethylaminopropyl)-N’-ethyl carbodiimide hydrochloride (EDC) as activating agent, affording the respective amide products 5, 8, and 10 in 60–71% yield. The amide linkage was formed through either the aliphatic or aromatic ester group of 2, allowing both the flexibility and absorption maximum to be tuned. Azobenzene dye 1 was coupled to the DeUG unit 11 by Steglich esterification to afford the product amide 12 in 35% yield. Alternatively, azobenzene dye 16 underwent a room-temperature copper-catalyzed azide–alkyne Huisgen cycloaddition with DeUG alkyne 17 to give triazole 18 in 71% yield. Azobenzene coupled DAN modules 5, 8, and 10 are bright orange–red in color, and azobenzene coupled DeUG modules 12 and 18 are orange–yellow in color. Azobenzene coupled DAN and DeUG modules were successfully used as colorimetric indicators for specific DAN–DeUG and DAN–UPy (2-ureido-4(1H)-pyrimidone) quadruply hydrogen-bonding interactions.

Synthesis and application of magnetic reduced graphene oxide composites for the removal of bisphenol A in aqueous solution—a mechanistic study

Two kinds of magnetic reduced graphene oxide composites (MRGO) namely MRGO-1 and MRGO-2 with different reduction degrees are synthesized by a facile method. MRGO-2 is obtained by further reduction of MRGO-1 using hydrazine to obtain a relatively deeper reduction degree. Removal of bisphenol A (BPA) from aqueous solution using MRGO-1 and MRGO-2 is investigated. The kinetics and isotherm data of BPA absorbed by MRGO-1 and MRGO-2 are both well fitted with the pseudo-second-order kinetic model and the Langmuir isotherm, respectively. The maximum adsorption capacity of MRGO-1 and MRGO-2 for BPA obtained from the Langmuir isotherm is 92.98 mg g−1 and 71.66 mg g−1 at 288.15 K, respectively. Furthermore, the used MRGO-1 and MRGO-2 could be collected and recycled efficiently via an external magnet. The BPA adsorption capacity of the MRGO-1 still remained greater than 86% of the initial adsorption capacity after nine repeated absorption–desorption cycles. A thermodynamic study shows that the adsorption is a spontaneous and exothermic process. The maximum adsorption capacity of MRGO-1 for BPA is higher than that of MRGO-2, implying a deeper reduction process to MRGO-2 from MRGO-1 is not essential for the removal of BPA from aqueous solution. The energy is saved by omitting the deep reduction process. It is also found that if severe aggregation of graphene sheets in the deep reduction process to MRGO-2 from MRGO-1 can be alleviated, the corresponding absorption capacity of MRGO-2 for BPA may be greatly improved.

Unveiling the mechanism of electron transfer facilitated regeneration of active Fe2+ by nano-dispersed iron/graphene catalyst for phenol removal

Nano-dispersed Fe0 and Fe3O4 on reduced graphene oxide (Fe0/Fe3O4-RGO) was prepared and characterized. The prepared Fe0/Fe3O4-RGO was used as a magnetically separable Fenton-like catalyst and showed superior catalytic activity compared to Fe3O4-RGO and Fe3O4 as well as other Fenton-like catalysts for the removal of phenol. The Fe0/Fe3O4-RGO achieved 100% removal efficiency for phenol within 30 min. Free radical inhibition experiments and Electron Paramagnetic Resonance (EPR) showed that the main reactive species was ˙OH rather than FeIV. High resolution TEM results revealed that nanoscale Fe0 and Fe3O4 were uniformly dispersed and distributed on RGO without agglomeration, furnishing more active sites. The catalyst featured a unique mechanism of electron transfer-facilitated regeneration of active Fe2+ by nano-dispersed iron/graphene. RGO served as an effective mediator to facilitate the electron transfer from Fe0 to Fe3+ for the regeneration of Fe2+, which was critical in the catalytic process. This electron transfer-facilitated regeneration of active Fe2+ resulted in a reusable catalyst with high catalytic activity for the removal of phenol. The nano-dispersed Fe0/Fe3O4-RGO could be easily separated and recovered by magnetic field. The Fe0/Fe3O4-RGO catalyst was reusable and the removal efficiency of phenol after 5 catalytic cycles was as high as 93%. The Fe0/Fe3O4-RGO could be an effective Fenton-like catalyst for the treatment of waste water containing refractory phenol and phenol type pollutants.

Preparation and evaluation of molecularly imprinted polymer for selective recognition and adsorption of gossypol

Molecularly imprinted polymers (MIPs) were designed and prepared via bulk thermal polymerization with gossypol as the template molecule and dimethylaminoethyl methacrylate as the functional monomer. The morphology and microstructures of MIPs were characterized by scanning electron microscope and Brunauer‐Emmett‐Teller surface areas. Static adsorption tests were performed to evaluate adsorption behavior of gossypol by the MIPs. It was found that adsorption kinetics and adsorption isotherms data of MIPs for gossypol were fit well with the pseudo‐second‐order model and Freundlich model, respectively. Scatchard analysis showed that heterogeneous binding sites were formed in the MIPs, including lower‐affinity binding sites with the maximum adsorption of 252 mg/g and higher‐affinity binding sites with the maximum adsorption of 632 mg/g. Binding studies also revealed that MIPs had favorable selectivity towards gossypol compared with non‐imprinted polymers. Furthermore, adsorption capacity of MIPs maintained above 90% after 5 regeneration cycles, indicating MIPs were recyclable and could be used multiple times. These results demonstrated that prepared MIPs could be a promising functional material for selective adsorption of gossypol.

Characterization of molecularly imprinted polymers using a new polar solvent titration method

A new method of characterizing molecularly imprinted polymers (MIPs) was developed and tested, which provides a more accurate means of identifying and measuring the molecular imprinting effect. In the new polar solvent titration method, a series of imprinted and non‐imprinted polymers were prepared in solutions containing increasing concentrations of a polar solvent. The polar solvent additives systematically disrupted the templation and monomer aggregation processes in the prepolymerization solutions, and the extent of disruption was captured by the polymerization process. The changes in binding capacity within each series of polymers were measured, providing a quantitative assessment of the templation and monomer aggregation processes in the imprinted and non‐imprinted polymers. The new method was tested using three different diphenyl phosphate imprinted polymers made using three different urea functional monomers. Each monomer had varying efficiencies of templation and monomer aggregation. The new MIP characterization method was found to have several advantages. To independently verify the new characterization method, the MIPs were also characterized using traditional binding isotherm analyses. The two methods appeared to give consistent conclusions. First, the polar solvent titration method is less susceptible to false positives in identifying the imprinting effect. Second, the method is able to differentiate and quantify changes in binding capacity, as measured at a fixed guest and polymer concentration, arising from templation or monomer aggregation processes in the prepolymerization solution. Third, the method was also easy to carry out, taking advantage of the ease of preparing MIPs. Copyright