Unexpected Intrinsic Catalytic Function of Porous Boron Nitride Nanorods for Highly Efficient Peroxymonosulfate Activation in Water Treatment.

Porous boron nitride (BN) nanorods, which were synthesized via a one-stage pyrolysis, exhibited excellent catalytic performance for organics' degradation via peroxymonosulfate (PMS) activation. The origin of the unexpected catalytic function of porous BN nanorods was proposed, in which non-radical oxidation driven by the defects on porous BN dominated the sulfamethoxazole degradation via the generation of singlet oxygen (1O2). The adsorption energy between PMS and BN was calculated via density functional theory (DFT), and the PMS activation kinetics were further investigated using an electrochemical methodology. The evolution of 1O2 was verified by electron spin resonance (ESR) and chemical scavenging experiments. The observed non-radical oxidation presented a high robustness in different water matrices, combined with a series of much less toxic intermediates. The used BN was easily regenerated by heating in air, in which the B-O bond was fully recovered. These findings provide new insights for BN as a non-metal catalyst for organics' degradation via PMS activation, in both theoretical and practical prospects.

Highly Robust Interfacially Polymerized PA Layer on Thermally Responsive Semi-IPN Hydrogel: Toward On-Demand Tuning of Porosity and Surface Charge.

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel-liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc.

BiOClBr-coated fabrics with enhanced antimicrobial properties under ambient light.

This study demonstrates the fabrication of ambient light enabled antimicrobial functional fabrics by coating flower-like bismuth oxyhalide i.e. BiOCl0.875Br0.125, with the use of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) as binders for improved coating robustness and durability. The uniformity of the microparticles was ensured with simultaneous probe sonication during the stages of crystal nucleation and growth. The polymeric binders not only strongly anchor the particle on the fabric, but also serve as an ultra-thin protective layer on the BiOClBr that mitigates bismuth leaching. The efficacy of inhibiting bacteria was investigated over the BiOClBr-coated fabrics i.e. cotton and polyester, and the results showed that the coated fabrics could effectively inhibit both Gram-positive and Gram-negative bacteria, i.e. S. aureus and E. coli. In comparison with fabrics coated with other photocatalytic materials including bismuth oxide (Bi2O3) and zinc oxide (ZnO), an exceptionally better antimicrobial efficacy was observed for BiOClBr-coated fabrics. The BiOClBr-coated cotton showed ∼5.0 and ∼6.8 times higher disinfection efficacy towards E. coli compared to that of ZnO and Bi2O3-coated cotton with the same particle weight percentage, respectively. Further elucidation of the probable mechanism by BiOClBr-coated fabrics is related to the excess amount of reactive oxygen species (ROS). Overall, BiOClBr has been shown to be a promising material to fabricate cost-effective antimicrobial functional surfaces for both environmental and biomedical applications e.g. protective laboratory and factory clothing.

In Situ Formation of 3D Conductive and Cell-Laden Graphene Hydrogel for Electrically Regulating Cellular Behavior.

Electroconductive and injectable hydrogels are attracting increasing attention owing to the needs of electrically induced regulation of cell behavior, tissue engineering of electroactive tissues, and achieving minimum invasiveness during tissue repair. In this study, a novel in situ formed 3D conductive and cell-laden hydrogel is developed, which can be broadly used in bioprinting, tissue engineering, neuroengineering etc. An instantaneous, uniform spatial distribution and encapsulation of cells can be achieved as a result of hydrogen bonding induced hydrogel formation. Particularly, the cell-laden hydrogel can be easily obtained by simply mixing and shaking the polydopamine (PDA) functionalized rGO (rGO-PDA) with polyvinyl alcohol (PVA) solution containing cells. Graphene oxide is reduced and functionalized by dopamine to restore the electrical conductivity, while simultaneously enhancing both hydrophilicity and biocompatibility of reduced graphene oxide. In vitro culture of PC12 cells within the cell-laden hydrogel demonstrates its biocompatibility, noncytotoxicity as well as the ability to support long-term cell growth and proliferation. Enhanced neuronal differentiation is also observed, both with and without electrical stimulation. Overall, this 3D conductive, cell-laden hydrogel holds great promise as potential platform for tissue engineering of electroactive tissues.

Design Rationale for Stimuli-Responsive, Semi-interpenetrating Polymer Network Hydrogels-A Quantitative Approach.

Stimuli-responsive semi-interpenetrating polymer network (semi-IPN) hydrogels form an important class of polymers for their tunable properties via molecular design. They are widely investigated for a diverse range of applications including drug delivery, sensors, actuators, and osmotic agents. However, in-depth studies on some of the critical design principles affecting diffusion/leaching of linear polymer from semi-IPN hydrogels are lacking. Herein, for the first time, by preparing a series of model semi-IPN hydrogels based on thermally responsive poly (N-isopropyl acrylamide) (PNIPAM) network and linear poly(sodium acrylate) (PSA), a systematic and quantitative study concerning linear polymer chain retention and swelling/deswelling kinetics is reported. The study shows that PSA retention is significantly affected not only by PSA molecular weight and concentration, but also by polymerization temperature, which could be linked to homogeneity and internal morphology of the hydrogel. Surprisingly, there is no obvious influence of crosslinking density of PNIPAM network toward PSA retention, while faster swelling and deswelling at higher crosslinking density are observed in terms of swelling rate constant and deswelling activation energy. These findings offer new insights on the factors affecting structural and physicochemical properties of such semi-IPN hydrogels, which should in turn serve as a general guideline for materials design.

Salt Template Assisted BN Scaffold Fabrication toward Highly Thermally Conductive Epoxy Composites.

With the trend of device miniaturization and higher integration, polymer composites with high thermal conductivity are highly desirable for efficient removal of accumulated heat to maintain high performance of electronics. In this work, epoxy composites embedded with three-dimensional hexagonal boron nitride (BN) scaffold were fabricated. The BN-poly(vinylidene difluoride) (PVDF) scaffold was prepared by the salt template method using PVDF as the adhesive, while the corresponding epoxy composite was manufactured with vacuum-assisted impregnation. The epoxy/BN-PVDF composite exhibits high thermal conductivity with low loading of BN. The thermal conductivity of epoxy/BN-PVDF composite achieved 1.227 W/(m K) with 21 wt % BN, contributed by the constructed BN pathway held together by PVDF adhesive. In addition, PVDF could be further converted into carbon by thermal treatment, further enhancing the thermal conductivity of epoxy/BN-C composites through alleviating the phonon scattering at the interfaces, eventually obtaining thermal conductivity of 1.466 W/(m K). This type of epoxy-based composite with high thermal conductivity is promising to be used as thermal management materials in advanced electronic devices.

Insights into the speciation of heavy metals during pyrolysis of industrial sludge.

The purpose of this study was to determine the mechanisms in heavy metals immobilisation during pyrolysis of industrial sludge (IS). Pyrolysis was conducted in a fixed-bed unit at the temperature range between 400 and 800°C. Conventional and advanced analytical techniques were employed to assess the influencing parameters on the transformation of heavy metals during pyrolysis process. The examined heavy metals (i.e. Mn, Ni, Cu, Zn, Cd, and Pb) were effectively immobilised in the char derived at ≤600°C. In contrast, for the char derived at ≥700°C, Mn, Cu, and Zn leaching efficiencies were significantly increased. According to BCR sequential extraction procedure (SEP) results, pyrolysis of IS conducted at ≤600°C transformed heavy metals into stable fractions (i.e. associated with Fe-Mn nodules, and organics and sulphides), while Mn, Cu, and Zn bound in these fractions decomposed into easily soluble forms at higher temperatures. Advanced analytical characterisation (XRD, EDX, XPS, and FTIR) of the derived char and anion concentrations in the leachate have demonstrated that the increase in metal leaching was probably due to the formation of metal halides.

Bioinspired reinforcement of cyclosiloxane hybrid polymer.

Structural analysis showed that cyclosiloxane hybrid polymer (CHP) is a collection of nano-sized nacre-like structures in random orientations. Inspired by the reinforcement of nacre-like materials, basal-functionalized graphene (GO-AA) was inserted between CHP layers, acting as 'double-sided tape' to improve the mechanical properties. The resulting GO-AA/CHP nanocomposites showed a 156% improvement in toughness with only a 0.08 wt% loading of GO-AA, and a 25% improvement in thermal conductivity with a 0.10 wt% loading of GO-AA. The proposed 'double-sided tape' effect was also used to explain the highly efficient enhancement in thermal conductivity. This research promotes the application of CHP in harsher environments, demonstrates its prospects in thermal management areas, and contributes to nature-inspired materials design.

An eco-friendly approach for heavy metal adsorbent regeneration using CO2-responsive molecular octopus.

Perennial problems of adsorption in wastewater treatment include adsorbent recycling, generation of waste sludge and secondary pollution because harmful concentrated acids, bases or strong chelators are often used for adsorbent regeneration and adsorbate recovery. We report, for the first time, an eco-friendly regeneration concept demonstrated with a CO2-responsive octopus-like polymeric adsorbent. Various heavy metals can be scavenged at very high Qe by such adsorbent through coordination. Most importantly, the rapid and complete regeneration of the adsorbent and recovery of the heavy metal ions can be readily achieved by CO2 bubbling within a few minutes under mild conditions, i.e., room temperature and atmospheric pressure. The adsorbent can then be restored to its adsorptive state and reused upon removal of CO2 by simply bubbling another gas. This eco-friendly, effective, ultra-fast and repeatable CO2-triggered regeneration process using CO2-responsive adsorbent with versatile structure, morphology or form can be incorporated into a sustainable closed-loop wastewater treatment process to solve the perennial problems.

A Dual-Responsive Nanocomposite toward Climate-Adaptable Solar Modulation for Energy-Saving Smart Windows.

In this work, a novel fully autonomous photothermotropic material made by hybridization of the poly(N-isopropylacrylamide) (PNIPAM) hydrogel and antimony-tin oxide (ATO) is presented. In this photothermotropic system, the near-infrared (NIR)-absorbing ATO acts as nanoheater to induce the optical switching of the hydrogel. Such a new passive smart window is characterized by excellent NIR shielding, a photothermally activated switching mechanism, enhanced response speed, and solar modulation ability. Systems with 0, 5, 10, and 15 atom % Sb-doped ATO in PNIPAM were investigated, and it was found that a PNIPAM/ATO nanocomposite is able to be photothermally activated. The 10 atom % Sb-doped PNIPAM/ATO exhibits the best response speed and solar modulation ability. Different film thicknesses and ATO contents will affect the response rate and solar modulation ability. Structural stability tests at 15 cycles under continuous exposure to solar irradiation at 1 sun intensity demonstrated the performance stability of such a photothermotropic system. We conclude that such a novel photothermotropic hybrid can be used as a new generation of autonomous passive smart windows for climate-adaptable solar modulation.

Novel low temperature synthesis route for functional Au/ZnFe mixed oxide nanohybrids.

ZnFe layered double hydroxide (LDH) was synthesized through which the [AuCl4](-) anions were directly intercalated in situ. Low temperature calcination converts the [AuCl4](-) intercalated LDH into an intimately mixed ZnFe metal oxides containing favorably dispersed Au nanoparticles. The unique microstructure exhibited substantially improved photocatalytic activity by more than 40 times compared to the baseline material intercalated with [CO3](2-). Such improvement is unprecedented among noble metal decorated photocatalyst materials and is elucidated based on the mechanisms of morphology evolution.

H2O-EG-assisted synthesis of uniform urchinlike rutile TiO2 with superior lithium storage properties.

A facile green method to synthesize uniform nanostructured urchinlike rutile TiO2 is demonstrated. Titanium trichloride was selected as the TiO2 precursor, and a mixed solvent containing H2O and ethylene glycol was used. By using this binary medium, the nucleation and crystal growth of rutile TiO2 can be regulated, giving rise to very uniform urchinlike structures with tailorable sizes. As confirmed by the SEM and TEM analysis, large particles with dense aggregation of needle-like building blocks or small ones with loosely packed subunits could be obtained at different reaction conditions. The as-prepared samples were applied as the anode material for lithium-ion batteries, and they were shown to have superior properties with a high reversible capacity of 140 mA h g(-1) at a high current rate of 10 C for up to 300 cycles, which is almost unmatched by other rutile TiO2-based electrodes. A stable capacity of 88 mA h g(-1) can also be delivered at an extremely high rate of 50 C, suggesting the great potential of the as-prepared product for high-rate lithium-ion batteries.

Superabsorbent cryogels decorated with silver nanoparticles as a novel water technology for point-of-use disinfection.

This paper reports the preparation of poly(sodium acrylate) (PSA) cryogels decorated with silver nanoparticles (AgNPs) for point-of-use (POU) water disinfection. The PSA/Ag cryogels combine the high porosity, excellent mechanical and water absorption properties of cryogels, and uniform dispersion of fine AgNPs on the cryogel pore surface for rapid disinfection with minimal Ag release (<100 µg L(-1)). They were used in a process that employed their ability to absorb water, which subsequently could be released via application of mild pressure. Their antibacterial performance was evaluated based on the disinfection efficacies of E. coli and B. subtilis . The PSA/Ag cryogels had excellent disinfection efficacies showing close to a 3 log reduction of viable bacteria after a brief 15 s contact time. They were highly reusable as there was no significant difference in the disinfection efficacies over five cycles of operation. The biocidal action of the PSA/Ag cryogels is believed to be dominated by surface-controlled mechanisms that are dependent on direct contact of the interface of PSA/Ag cryogels with the bacterial cells. The PSA/Ag cryogels are thought to offer a simpler approach for drinking water disinfection in disaster relief applications.

Colloidal CuInSe2 nanocrystals: from gradient stoichiometry toward homogeneous alloyed structure mediated by conducting polymer P3HT.

We report, for the first time, the synthesis of colloidal copper indium selenide (CuInSe2) nanocrystals (NCs) possessing a gradient stoichiometry that is potentially tunable by the presence of a conducting polymer, i.e., poly(3-hexyl thiophene) (P3HT) in the synthesis medium. Dibenzyl ether (DBE) was used as a reaction medium, whereas copper acetylacetonate (Cu(acac)2), indium acetylacetonate (In(acac)3), and selenium powder were used as Cu, In, and Se sources, respectively. The Se precursor was tri-n-octylphosphine selenide (TOP-Se). Without the presence of P3HT, the resulting NCs consist of a p-type (Cu(1+) rich) core and an n-type (In(3+) rich) shell. Such a gradient stoichiometry was moderated to be substantially more homogeneous because the presence of P3HT is believed to have significantly reduced the reactivity difference between Cu(acac)2 and In(acac)3, as well as and their respective monomers. Furthermore, the P3HT also acts as a surface coordination species, contributing to the readily preparation of conducting polymer-NCs hybrids by a single-step synthesis. The understandings of this work can serve as a guide for design and synthesis of conducting polymer-NCs hybrids based on various ternary or quaternary compound semiconductors with different core-shell composition gradient.

Stability studies of CdSe nanocrystals in an aqueous environment.

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH-) while photo-generated holes oxidize CdSe to Cd2+ and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH=10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).

Inkjet printing of multi-walled carbon nanotube/polymer composite thin film for interconnection.

In this paper, multi-walled carbon nanotube (MWCNT) ink was selectively patterned by inkjet printing on substrates to form conductive traces and electrodes for interconnection application. MWCNT was firstly functionalized using concentrated acid and dispersed in deionized water to form a colloidal solution. Various concentrations of MWCNT were formulated to test the stability of the solution. The printability of the MWCNT ink was examined against printing temperature, ink concentration and ink droplet pitch. Rheological properties of the ink were determined by rheometer and sessile drop method. The electrical conductivity of the MWCNT pattern was measured against multiple printing of MWCNT on the same pattern (up to 10 layers). While single layer printing pattern exhibited highest resistance, the CNT entangled together and formed a random network with more printed layers has higher conductivity. The electrical properties of the printed film was compared to a composite ink of CNT and conducting polymer (CNT ink was mixed with conductive polymer solution, Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) (PEDOT:PSS)). Scanning electron microscopy (SEM) was used to observe the surface structure and atomic force microscopy (AFM) was used to study the morphology of the printed film under different conditions.

Fabrication of lab-on chip platforms by hot embossing and photo patterning.

In this paper, we review the approaches developed in our laboratory to fabricate polymer-based microfluidic devices to suit a range of applications in bio- or chemical analysis. Thermoplastic materials such as polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are used to fabricate microfluidic devices via hot embossing. To emboss microchannels, we use hard stamps fabricated in silicon or soft stamps molded on poly(dimethylsiloxane) (PDMS). Hard stamps are fabricated on silicon wafers through photolithography and deep reactive ion etching (DRIE). Soft stamps are fabricated by casting PDMS prepolymer on silicon molds. To enclose the fluidic channels, direct fusion bonding was found to produce the highest bond strength with minimal structural deformation. One-step photolithographic methods have also been explored to produce via photochemical patterning microfluidic structures in photocurable materials. We use the photocurable capabilities of a PDMS copolymer, which incorporates a methacrylate crosslinker. Microfluidic channels are produced via one step-photopatterning processes by crosslinking the prepolymer mixture through a photomask. The smaller feature size attainable was 100 microm. Structures with higher spatial resolution are fabricated through a photoimprinting process whereby a mold is pressed against the precured mixture during UV crosslinking exposure. The application of the fabricated fluidic devices in electrophoretic ion analysis is also presented.