Chongbin Wang

Fabrication of hybrid membranes by incorporating acid–base pair functionalized hollow mesoporous silica for enhanced proton conductivity

Hollow mesoporous silica microspheres with a uniform pore size and a large surface area are synthesized and functionalized by three kinds of amino acids with different acid–base pairs, including sulfonic acid–amino groups (HMS-Cys), phosphoric acid–amino groups (HMS-Phos) and carboxylic acid–amino groups (HMS-Asp). The incorporation of these microspheres into a Nafion matrix enhances the water uptake and adjusts the organic–inorganic interface and hydrophilic ionic domains inside the membranes. Microspheres with a hollow mesoporous structure endow the membranes with strong water retention ability. The proton conductivities of hybrid membranes are more than 8 times higher than that of recast Nafion at 40 °C and 20% RH after 90 min of testing. The acid–base pairs within the membranes work as proton donors and acceptors, and the retained water molecules are used as hydrogen-bonded bridges, which reduce the energy barrier for proton conduction. At the filler content of 4 wt%, the HMS-Cys embedded membrane shows the highest proton conductivity of 1.19 × 10−1 S cm−1 (30 °C, 100% RH). In addition, hybrid membranes incorporated with amino acid functionalized HMS show small reliance on humidity. The proton conductivities of all the hybrid membranes are ∼5.29–11.1 times higher than that of the recast Nafion under 26.1% RH and 80 °C.

Synthesis and characterization of g-C3N4 nanosheet modified polyamide nanofiltration membranes with good permeation and antifouling properties

The incorporation of nano materials into a polyamide (PA) active layer of nanofiltration membranes has become a main choice for the improvement of membrane performance. In this paper, g-C3N4 nanosheets (CNs) were introduced to aqueous solution for the modification of a PA active layer via an interfacial polymerization reaction between piperazine and trimesoyl chloride monomers. FT-IR and XRD analysis confirmed the presence of CNs on the surface of nanofiltration membranes. SEM images indicated the formation of an active layer on the top of the polyethersulfone (PES) substrate and a good dispersion of CNs. AFM images proved that the surface roughness was increased after the incorporation of CNs. The contact angle measurement demonstrated that the surface hydrophilicity of the CN modified PA (PA/CNs) membrane was promoted. Thermal stability and surface charge of the membranes were investigated by TGA and zeta potential analysis, respectively. Compared with a pristine PA membrane, for the membrane containing CNs (0.0025 wt% in aqueous solution) a distinct increase of water flux from 20.9 L m−2 h−1 to 37.6 L m−2 h−1 at 2 bar was observed, while salt rejection of Na2SO4 was maintained above 84.0%. Whats more, the anti-fouling properties of the PA/CNs membrane were investigated by using bovine serum albumin and humic acid aqueous solutions, and the results confirmed that the incorporation of CNs into PA membranes could improve antifouling performance.

Third- and high-order nonlinear optical properties of an intramolecular charge-transfer compound

An oligo(phenylenevinylene) bridged intramolecular charge-transfer (ICT) compound, (TCNQ)2OPV3, has been synthesized and its third- and fifth-order nonlinear optical refraction indexes have been determined by measurement with the 4f system with a phase-object, under near-infrared excitation.

Enhanced proton conductivity of proton exchange membranes by incorporating phosphorylated hollow titania spheres

Phosphorylated hollow titania spheres (PHTS) with a superior water retention property are synthesized via a soft-template method and introduced into a sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate SPEEK/PHTS hybrid membranes. The incorporation of PHTS renders hybrid membranes with higher water uptake but lower swelling degree. The increased water retention capacity and additional proton transfer sites in the organic–inorganic interfacial zones lead to an enhancement in membrane proton conductivity. The highest proton conductivity (σ) of 0.228 S cm−1 at 70 °C under 100% RH for the hybrid membrane with 20 wt% of PHTS is achieved, which is two orders of magnitude higher than the pristine SPEEK membrane. Moreover, the PHTS fillers also prolong the tortuous pathways for methanol transport, conferring the hybrid membranes lower methanol permeability (P) in the range of 3.8–4.4 × 10−7 cm2 s−1. The maximum selectivity (σ/P) of as-prepared hybrid membranes is 2.09 × 105 S s cm−3, twice higher than a pristine SPEEK membrane.

Phosphorylated graphene monoliths with high mixed proton/electron conductivity

A mixed ionic–electronic conductor (MIEC) plays a crucial role in electrochemical technologies relevant to energy conversion and storage. The existing composite materials often suffer from poor mixed conducting performance due to the distinct phase boundaries and random distributions of the transport channels. Herein, we propose the concept for the fabrication of a single-phase MIEC using two-dimensional (2D) building blocks-phosphorylated graphene nanosheets, which are assembled into three-dimensional (3D) interconnected networks with long-range ordered nanochannels. Attributed to the sufficient proton carriers (phosphate groups) confined in electron-conductive nanochannels and the integration of conductive pathways, simultaneously enhanced proton conductivity (0.13 S cm−1) and electron conductivity (0.265 S cm−1) are achieved at 98% RH and 35 °C, surpassing the current performance of all graphene-based MIECs. This approach may pave the way for designing MIECs with high mixed conduction by utilizing the unique properties of 2D materials, beyond the limitations of pure proton-conducting/electron-conducting materials.

One-pot synthesis of silica–titania binary nanoparticles with acid–base pairs via biomimetic mineralization to fabricate highly proton-conductive membranes

Simultaneous manipulation of vehicle-type and Grotthuss-type proton conduction within proton exchange membranes (PEMs) to induce satisfactory proton conductivity is crucial and challenging for promising environmentally friendly devices such as PEM fuel cells. In this study, a facile one-pot biomimetic mineralization approach is proposed for the construction of binary SiO2–TiO2 nanoparticles with a tunable ratio of silica to titania. Then the nanoparticles are functionalized by acid–base pairs and introduced into a Nafion matrix to fabricate novel hybrid membranes. The interaction between functional groups on SiO2–TiO2 binary nanoparticles and the polymer endows the hybrid membrane with good interfacial compatibility and enhanced dimensional stability. The incorporation of acid–base pairs reduces the activation energy for proton transfer; as a result, the hybrid membrane exhibits the highest proton conductivity of 1.37 × 10−2 S cm−1 at 26.1% RH and 80 °C, which is two orders of magnitude higher than that of recast Nafion. Compared with recast Nafion, a 51.3% increase in maximum power density is achieved for the Nafion/Si1–Ti2-160 hybrid membrane at 60 °C.