Zhanhu Guo | University of Tennessee Knoxville (original) (raw)

Papers by Zhanhu Guo

Advanced Powder Technology, 2013

This article provides an overview of current research activities on the synthesis and application... more This article provides an overview of current research activities on the synthesis and applications of magnetic nanocomposites, especially highlights their potential environmental remediations such as heavy metal (Cr, As, Pd, Hg) removal. After a brief introduction of the emergency situation of heavy metal pollution all over the world and current techniques designed to deal with these situations, different synthetic methods to fabricate various types of magnetic nanocomposites will be reviewed. The focus is to reveal the advantages of magnetic nanocomposites as an efficient adsorbent which is able to reduce the heavy metal concentrations well below the EPA requirement. At the same time, the conventional process can be redesigned to be an economic and energetic one without using extra energy to recycle the adsorbent, which is desired for future. This review mainly deals with the heavy metal removal using magnetic nanocomposites, the adsorption behaviors of heavy metal ions on the surface of novel adsorbents are well investigated including the concentration effect of both contaminants and adsorbents, adsorption kinetics, solution pH effect with regards to real application.

Engineered Science

A comprehensive overview of the up-to-date research activities targeting electromagnetic interfer... more A comprehensive overview of the up-to-date research activities targeting electromagnetic interference (EMI) shielding is provided, focusing on the multifunctional polymer nanocomposites (PNCs) reinforced with a variety of conductive fillers. The unique dielectric, magnetic and other physicochemical properties derived from certain morphology-, composition-, and loading-controlled nanostructures for EMI shielding behaviors are elaborated. The conductive fillers including three different categories: carbon, metals, and conductive polymers in the EMI shielding PNCs are discussed together with their synergistic effects on enhancing the EMI shielding property. The enhanced electromagnetic interference shielding effectiveness and mechanisms are discussed with detailed examples and are envisioned to provide rational design of next generation lightweight EMI shielding materials.

Engineered Science

Polymer-based dielectric materials have attracted increasing attention owing to their huge potent... more Polymer-based dielectric materials have attracted increasing attention owing to their huge potential applications in modern electronic devices. The dielectric behaviors of polymer composites are greatly determined by the distribution of fillers, thus the clarification of the relationship between the dielectric properties of the composites and the spatial distribution of fillers would be highly favorable for designing novel high-performance dielectrics. Herein, the dielectric performances of ternary composites consisting of barium titanate (BT), carbon nanotube (CNT) and poly(vinylidene fluoride) (PVDF) were investigated. For comparison, the dielectric properties of trilayer 3 composites were also studied. The ternary composites exhibited an ultra-high dielectric constant of 7×10 @10 kHz, but a high loss tangent of 25 @10 kHz. For the trilayer composites, the BT/PVDF outer layers could restrain the development of leakage current, leading to low loss tangent (0.03 @10 kHz) and high breakdown strength. Meanwhile, the trilayer composites also achieved a high dielectric constant of 95 @10 kHz owing to the considerably enhanced polarizations at the filler/matrix and layer/layer interfaces. This research provides important sights into the relationship between the dielectric properties of the composites and the spatial distributions of fillers, which will strongly boost the exploration of high-performance dielectrics.

Nanofibrillated cellulose (NFC) is highly regarded as a popular new material due to its impressiv... more Nanofibrillated cellulose (NFC) is highly regarded as a popular new material due to its impressive mechanical properties, great potential for functionalization, easy accessibility, and environmental sustainability as precursors. The immobilization of nanoparticles in an NFC network is an effective way to fabricate transparent functionalized nanopaper. In this work, a uniform, flexible, magnetic nanopaper is prepared by the immobilization of Fe 3 O 4 nanoparticles in an NFC network in an aqueous medium. The resulting transparent magnetic nanopaper (TMNP) possesses excellent transparency and magnetic properties combined with outstanding mechanical performance and flexibility. The combination of these characteristics makes TMNP an excellent candidate for magneto-optical applications.

Four Al 2 O 3 nanostructures (i.e. nanofiber, nanoplatelet, nanorod and nanoflake) have been succ... more Four Al 2 O 3 nanostructures (i.e. nanofiber, nanoplatelet, nanorod and nanoflake) have been successfully synthesized via hydrothermal procedures followed by a dehydration process. Subsequently, polyaniline (PANI) nanocomposites incorporating these four Al 2 O 3 nanostructures have been fabricated using a surface initialized polymerization (SIP) method. Both TEM and SEM are used to characterize the morphologies of the Al 2 O 3 nanostructures and PANI/Al 2 O 3 nanocomposites. X-Ray diffraction results reveal that the morphology of the nanofiller has a significant effect on the crystallization behavior of the PANI during polymerization. The electrical conductivity and dielectric permittivity of these nanocomposites are strongly related to both the morphology of the filler and the dispersion quality. Temperature-dependent-conductivity measurements from 50-290 K show that the electron transportation of the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH is well correlated to the dielectric response of these nanocomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results reveal an enhanced thermal stability of the PANI/Al 2 O 3 nanocomposites as compared to that of pure PANI due to the strong interaction between the nanofillers and polymer matrix. The mechanism of the SIP method is also elaborated in this work.

Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO 3) nanoparticles (NPs) and n... more Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO 3) nanoparticles (NPs) and nanorods (NRs) are fabricated via a facile surface-initiated-polymerization (SIP) method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations reveal the uniform coating of polymer on the filler surface and a good dispersion of the nanofillers within the polymer matrix. Unique negative permittivity is observed in pure PANI and its nanocomposites. The switching frequency (frequency where real permittivity switches from negative to positive) can be easily tuned by changing the particle loading and filler morphology. Conductivity measurements are performed from 50$290 K, and results show that the electron transportation in the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH well explains the dielectric response of the metacomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposites with the addition of nanofillers as compared to that of pure PANI.

A waste-free process to recycle Fe@Fe 2 O 3 /polypropylene (PP) polymer nanocomposites (PNCs) is ... more A waste-free process to recycle Fe@Fe 2 O 3 /polypropylene (PP) polymer nanocomposites (PNCs) is introduced to synthesize magnetic carbon nanocomposites (MCNCs) and simultaneously produce useful chemical species which can be utilized as a feedstock in petrochemical industry. The magnetic nanoparticles (NPs) are found to have an effective catalytic activity on the pyrolysis of PP. The PNCs (with a NP loading of 20.0 wt%) undergo a complete degradation with 2 h pyrolysis at 500 uC in a H 2 / Ar atmosphere and the degradation components exhibit a distribution of species with different numbers of carbon, while only 40% of pure PP is decomposed after applying the same pyrolytic conditions. The coked solid waste from the conventional process has been utilized as a carbon source to form a protective carbon shell surrounding the magnetic NPs. The magnetic carbon nanocomposites (MCNCs) pyrolyzed from PNCs containing 20.0 wt% NPs demonstrate extremely fast Cr(VI) removal from wastewater with the almost complete removal of Cr(VI) within 10 min. The pH effect on the Cr(VI) removal efficiency is investigated with a preferable value of 1-3. The adsorbent exhibits much higher adsorption capacity in acidic solutions than that in alkali solutions. The large saturation magnetization (32.5 emu g 21) of these novel magnetic carbon nanocomposites allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from the liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The significantly reduced treatment time required to remove the Cr(VI) makes these MCNCs promising for the efficient removal of the heavy metals from wastewater. Kinetic investigation reveals the pseudo-second-order adsorption of Cr(VI) on these novel magnetic carbon nanocomposite adsorbents.

J. Mater. Chem. A, 2015

For the first time, the exciting reaction between the bio-inspired dopamine and the epoxy functio... more For the first time, the exciting reaction between the bio-inspired dopamine and the epoxy functional poly(ethylene oxide) (PEO) at elevated temperatures was found and utilized for fabricating dopamine/ poly(ethylene oxide) (PEO) network membranes for sustainable gas separation. The gas transport properties of the synthesized novel membrane were investigated aiming at energy (H 2 ) purification and CO 2 capture. The membrane was confirmed to be CO 2 selective and exhibited relatively high selectivity especially for CO 2 /N 2 separation. Importantly, the flexible incorporation of low-molecular-weight poly(ethylene glycol) dimethyl ether (PEGDME) into the swollen network membrane greatly improved the gas transport performance and the CO 2 permeability was increased by 550%. Furthermore, the temperature and upstream pressure dependence of our developed membranes have been examined in detail. Surprisingly, the plasticization phenomena in the membranes at higher upstream pressure can be harnessed to enhance the gas transport performance by increasing both the CO 2 permeability and the CO 2 /other tested gas selectivity mainly due to the network structure and CO 2 -philic character. This report will expedite the rapid discovery of new materials derived from bio-inspired dopamine for possibly solving energy and environmental issues. † Electronic supplementary information (ESI) available: Digital photographs of PEO-526 treated at various stages. (a) Original PEO-526, (b) treatment at 80 C for 6 hours, and (c and d) treatment at 160 C for 2 hours. Digital photographs of the DA/PEO mixture treated (a) at 120 C for 6 hours and (b) at 160 C for 2 hours. Calculated activation energy of D-PEO and D-PEO-I. Gas permeability of D-PEO and D-PEO-I compared with other PEO-based membranes. Gas diffusivity and solubility of D-PEO-I compared with LCM. See

Applied Surface Science, 2015

ABSTRACT The interactions between poly(acrylic acid) (PAA) and alumina have been widely investiga... more ABSTRACT The interactions between poly(acrylic acid) (PAA) and alumina have been widely investigated. In this study, the pattern of small molecular weight PAA (MW 3000) interaction with γ-alumina has been dissected. The alumina/PAA hybrids were prepared at pH 4.0, 5.5, and 7.0, respectively. Nitrogen absorption–desorption analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis were conducted to illustrate the characteristics of the hybrids. At pH 4.0, the coiled PAA conformation yielded polymer adsorption primarily on alumina outer surface. At higher pH values, the more stretched PAA molecules were able to infiltrate inside the alumina pores. The phenomenon is explained by the polymer chain reptation motion model. Coiled polymer chains are not oriented enough to penetrate the oxide pore channels. In contrary, stretched polymer chains are more likely to move along the pore channels.

... Gülhan GÜNGÖR & Meral KARAKIŞLA* ... Int., 39: 153-1159 (1996). [11] Karakışla, M., S... more ... Gülhan GÜNGÖR & Meral KARAKIŞLA* ... Int., 39: 153-1159 (1996). [11] Karakışla, M., Saçak, M., Erdem, E. And Akbulut, U., “Synthesis and characterization of malonic acid-doped polyaniline”, J. Appl.Electrochem., 27: 309-316 (1997). [12] Wei, Y., Sun,Y., Tang, X., J. Phys. ...

Advanced Powder Technology, 2013

This article provides an overview of current research activities on the synthesis and application... more This article provides an overview of current research activities on the synthesis and applications of magnetic nanocomposites, especially highlights their potential environmental remediations such as heavy metal (Cr, As, Pd, Hg) removal. After a brief introduction of the emergency situation of heavy metal pollution all over the world and current techniques designed to deal with these situations, different synthetic methods to fabricate various types of magnetic nanocomposites will be reviewed. The focus is to reveal the advantages of magnetic nanocomposites as an efficient adsorbent which is able to reduce the heavy metal concentrations well below the EPA requirement. At the same time, the conventional process can be redesigned to be an economic and energetic one without using extra energy to recycle the adsorbent, which is desired for future. This review mainly deals with the heavy metal removal using magnetic nanocomposites, the adsorption behaviors of heavy metal ions on the surface of novel adsorbents are well investigated including the concentration effect of both contaminants and adsorbents, adsorption kinetics, solution pH effect with regards to real application.

Engineered Science

A comprehensive overview of the up-to-date research activities targeting electromagnetic interfer... more A comprehensive overview of the up-to-date research activities targeting electromagnetic interference (EMI) shielding is provided, focusing on the multifunctional polymer nanocomposites (PNCs) reinforced with a variety of conductive fillers. The unique dielectric, magnetic and other physicochemical properties derived from certain morphology-, composition-, and loading-controlled nanostructures for EMI shielding behaviors are elaborated. The conductive fillers including three different categories: carbon, metals, and conductive polymers in the EMI shielding PNCs are discussed together with their synergistic effects on enhancing the EMI shielding property. The enhanced electromagnetic interference shielding effectiveness and mechanisms are discussed with detailed examples and are envisioned to provide rational design of next generation lightweight EMI shielding materials.

Engineered Science

Polymer-based dielectric materials have attracted increasing attention owing to their huge potent... more Polymer-based dielectric materials have attracted increasing attention owing to their huge potential applications in modern electronic devices. The dielectric behaviors of polymer composites are greatly determined by the distribution of fillers, thus the clarification of the relationship between the dielectric properties of the composites and the spatial distribution of fillers would be highly favorable for designing novel high-performance dielectrics. Herein, the dielectric performances of ternary composites consisting of barium titanate (BT), carbon nanotube (CNT) and poly(vinylidene fluoride) (PVDF) were investigated. For comparison, the dielectric properties of trilayer 3 composites were also studied. The ternary composites exhibited an ultra-high dielectric constant of 7×10 @10 kHz, but a high loss tangent of 25 @10 kHz. For the trilayer composites, the BT/PVDF outer layers could restrain the development of leakage current, leading to low loss tangent (0.03 @10 kHz) and high breakdown strength. Meanwhile, the trilayer composites also achieved a high dielectric constant of 95 @10 kHz owing to the considerably enhanced polarizations at the filler/matrix and layer/layer interfaces. This research provides important sights into the relationship between the dielectric properties of the composites and the spatial distributions of fillers, which will strongly boost the exploration of high-performance dielectrics.

Nanofibrillated cellulose (NFC) is highly regarded as a popular new material due to its impressiv... more Nanofibrillated cellulose (NFC) is highly regarded as a popular new material due to its impressive mechanical properties, great potential for functionalization, easy accessibility, and environmental sustainability as precursors. The immobilization of nanoparticles in an NFC network is an effective way to fabricate transparent functionalized nanopaper. In this work, a uniform, flexible, magnetic nanopaper is prepared by the immobilization of Fe 3 O 4 nanoparticles in an NFC network in an aqueous medium. The resulting transparent magnetic nanopaper (TMNP) possesses excellent transparency and magnetic properties combined with outstanding mechanical performance and flexibility. The combination of these characteristics makes TMNP an excellent candidate for magneto-optical applications.

Four Al 2 O 3 nanostructures (i.e. nanofiber, nanoplatelet, nanorod and nanoflake) have been succ... more Four Al 2 O 3 nanostructures (i.e. nanofiber, nanoplatelet, nanorod and nanoflake) have been successfully synthesized via hydrothermal procedures followed by a dehydration process. Subsequently, polyaniline (PANI) nanocomposites incorporating these four Al 2 O 3 nanostructures have been fabricated using a surface initialized polymerization (SIP) method. Both TEM and SEM are used to characterize the morphologies of the Al 2 O 3 nanostructures and PANI/Al 2 O 3 nanocomposites. X-Ray diffraction results reveal that the morphology of the nanofiller has a significant effect on the crystallization behavior of the PANI during polymerization. The electrical conductivity and dielectric permittivity of these nanocomposites are strongly related to both the morphology of the filler and the dispersion quality. Temperature-dependent-conductivity measurements from 50-290 K show that the electron transportation of the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH is well correlated to the dielectric response of these nanocomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results reveal an enhanced thermal stability of the PANI/Al 2 O 3 nanocomposites as compared to that of pure PANI due to the strong interaction between the nanofillers and polymer matrix. The mechanism of the SIP method is also elaborated in this work.

Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO 3) nanoparticles (NPs) and n... more Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO 3) nanoparticles (NPs) and nanorods (NRs) are fabricated via a facile surface-initiated-polymerization (SIP) method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations reveal the uniform coating of polymer on the filler surface and a good dispersion of the nanofillers within the polymer matrix. Unique negative permittivity is observed in pure PANI and its nanocomposites. The switching frequency (frequency where real permittivity switches from negative to positive) can be easily tuned by changing the particle loading and filler morphology. Conductivity measurements are performed from 50$290 K, and results show that the electron transportation in the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH well explains the dielectric response of the metacomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposites with the addition of nanofillers as compared to that of pure PANI.

A waste-free process to recycle Fe@Fe 2 O 3 /polypropylene (PP) polymer nanocomposites (PNCs) is ... more A waste-free process to recycle Fe@Fe 2 O 3 /polypropylene (PP) polymer nanocomposites (PNCs) is introduced to synthesize magnetic carbon nanocomposites (MCNCs) and simultaneously produce useful chemical species which can be utilized as a feedstock in petrochemical industry. The magnetic nanoparticles (NPs) are found to have an effective catalytic activity on the pyrolysis of PP. The PNCs (with a NP loading of 20.0 wt%) undergo a complete degradation with 2 h pyrolysis at 500 uC in a H 2 / Ar atmosphere and the degradation components exhibit a distribution of species with different numbers of carbon, while only 40% of pure PP is decomposed after applying the same pyrolytic conditions. The coked solid waste from the conventional process has been utilized as a carbon source to form a protective carbon shell surrounding the magnetic NPs. The magnetic carbon nanocomposites (MCNCs) pyrolyzed from PNCs containing 20.0 wt% NPs demonstrate extremely fast Cr(VI) removal from wastewater with the almost complete removal of Cr(VI) within 10 min. The pH effect on the Cr(VI) removal efficiency is investigated with a preferable value of 1-3. The adsorbent exhibits much higher adsorption capacity in acidic solutions than that in alkali solutions. The large saturation magnetization (32.5 emu g 21) of these novel magnetic carbon nanocomposites allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from the liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The significantly reduced treatment time required to remove the Cr(VI) makes these MCNCs promising for the efficient removal of the heavy metals from wastewater. Kinetic investigation reveals the pseudo-second-order adsorption of Cr(VI) on these novel magnetic carbon nanocomposite adsorbents.

J. Mater. Chem. A, 2015

For the first time, the exciting reaction between the bio-inspired dopamine and the epoxy functio... more For the first time, the exciting reaction between the bio-inspired dopamine and the epoxy functional poly(ethylene oxide) (PEO) at elevated temperatures was found and utilized for fabricating dopamine/ poly(ethylene oxide) (PEO) network membranes for sustainable gas separation. The gas transport properties of the synthesized novel membrane were investigated aiming at energy (H 2 ) purification and CO 2 capture. The membrane was confirmed to be CO 2 selective and exhibited relatively high selectivity especially for CO 2 /N 2 separation. Importantly, the flexible incorporation of low-molecular-weight poly(ethylene glycol) dimethyl ether (PEGDME) into the swollen network membrane greatly improved the gas transport performance and the CO 2 permeability was increased by 550%. Furthermore, the temperature and upstream pressure dependence of our developed membranes have been examined in detail. Surprisingly, the plasticization phenomena in the membranes at higher upstream pressure can be harnessed to enhance the gas transport performance by increasing both the CO 2 permeability and the CO 2 /other tested gas selectivity mainly due to the network structure and CO 2 -philic character. This report will expedite the rapid discovery of new materials derived from bio-inspired dopamine for possibly solving energy and environmental issues. † Electronic supplementary information (ESI) available: Digital photographs of PEO-526 treated at various stages. (a) Original PEO-526, (b) treatment at 80 C for 6 hours, and (c and d) treatment at 160 C for 2 hours. Digital photographs of the DA/PEO mixture treated (a) at 120 C for 6 hours and (b) at 160 C for 2 hours. Calculated activation energy of D-PEO and D-PEO-I. Gas permeability of D-PEO and D-PEO-I compared with other PEO-based membranes. Gas diffusivity and solubility of D-PEO-I compared with LCM. See

Applied Surface Science, 2015

ABSTRACT The interactions between poly(acrylic acid) (PAA) and alumina have been widely investiga... more ABSTRACT The interactions between poly(acrylic acid) (PAA) and alumina have been widely investigated. In this study, the pattern of small molecular weight PAA (MW 3000) interaction with γ-alumina has been dissected. The alumina/PAA hybrids were prepared at pH 4.0, 5.5, and 7.0, respectively. Nitrogen absorption–desorption analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis were conducted to illustrate the characteristics of the hybrids. At pH 4.0, the coiled PAA conformation yielded polymer adsorption primarily on alumina outer surface. At higher pH values, the more stretched PAA molecules were able to infiltrate inside the alumina pores. The phenomenon is explained by the polymer chain reptation motion model. Coiled polymer chains are not oriented enough to penetrate the oxide pore channels. In contrary, stretched polymer chains are more likely to move along the pore channels.

... Gülhan GÜNGÖR & Meral KARAKIŞLA* ... Int., 39: 153-1159 (1996). [11] Karakışla, M., S... more ... Gülhan GÜNGÖR & Meral KARAKIŞLA* ... Int., 39: 153-1159 (1996). [11] Karakışla, M., Saçak, M., Erdem, E. And Akbulut, U., “Synthesis and characterization of malonic acid-doped polyaniline”, J. Appl.Electrochem., 27: 309-316 (1997). [12] Wei, Y., Sun,Y., Tang, X., J. Phys. ...