Hongwei Bai - Academia.edu (original) (raw)

Papers by Hongwei Bai

Polymers

To address the worldwide oil and water separation issue, a novel approach was inspired by natural... more To address the worldwide oil and water separation issue, a novel approach was inspired by natural phenomena to synthesize superhydrophilic and underwater superoleophobic organic/inorganic nanofibrous membranes via a scale up fabrication approach. The synthesized membranes possess a delicate organic core of PVDF-HFP and an inorganic shell of a CuO nanosheet structure, which endows super-flexible properties owing to the merits of PVDF-HFP backbones, and superhydrophilic functions contributed by the extremely rough surface of a CuO nanosheet anchored on flexible PVDF-HFP. Such an organic core and inorganic shell architecture not only functionalizes membrane performance in terms of antifouling, high flux, and low energy consumption, but also extends the lifespan by enhancing its mechanical strength and alkaline resistance to broaden its applicability. The resultant membrane exhibits good oil/water separation efficiency higher than 99.7%, as well as excellent anti-fouling properties for ...

Environmental science & technology, Jan 6, 2018

Wastewaters with high concentrations of organic pollutants pose a great challenge for membrane fi... more Wastewaters with high concentrations of organic pollutants pose a great challenge for membrane filtration due to their severe fouling propensity. In this study, a hydrogel forward osmosis (FO) membrane is explored for treating wastewaters of high concentration organic pollutants. This FO membrane has an ultrathin hydrogel selective layer, which is highly hydrophilic (water contact angle as low as 18°) and smooth (surface roughness <5 nm). Investigated with typical organic foulants (protein, alginate, humic acid, and oil) of high concentration (2000-20 000 mg/L), this hydrogel FO membrane exhibits remarkably superior antifouling capability, with its water flux decline ratio lower than a quarter that of commercial FO membrane under identical experimental conditions. The foulants on hydrogel membrane surface can be easily removed by simple physical cleaning without any chemical usage. At the same time, this hydrogel FO membrane achieves ∼2 times higher separation efficiency than com...

Scientific Reports, 2016

Surfactant stabilized oil-in-water nanoemulsions pose a severe threat to both the environment and... more Surfactant stabilized oil-in-water nanoemulsions pose a severe threat to both the environment and human health. Recent development of membrane filtration technology has enabled efficient oil removal from oil/water nanoemulsion, however, the concurrent removal of surfactant and oil remains unsolved because the existing filtration membranes still suffer from low surfactant removal rate and serious surfactant-induced fouling issue. In this study, to realize the concurrent removal of surfactant and oil from nanoemulsion, a novel hierarchically-structured membrane is designed with a nanostructured selective layer on top of a microstructured support layer. The physical and chemical properties of the overall membrane, including wettability, surface roughness, electric charge, thickness and structures, are delicately tailored through a nano-engineered fabrication process, that is, graphene oxide (GO) nanosheet assisted phase inversion coupled with surface functionalization. Compared with the membrane fabricated by conventional phase inversion, this novel membrane has four times higher water flux, significantly higher rejections of both oil (~99.9%) and surfactant (as high as 93.5%), and two thirds lower fouling ratio when treating surfactant stabilized oil-in-water nanoemulsion. Due to its excellent performances and facile fabrication process, this nano-engineered membrane is expected to have wide practical applications in the oil/water separation fields of environmental protection and water purification. Surfactant-stabilized oil/water nanoemulsions (typical droplet size: 20~200 nm) are widely encountered in various industries including oil refinery, pharmaceutical, cosmetics, food, etc 1-9. To kinetically stabilize nanoemulsion, surfactant is added with considerable amount in oil/water nanoemulsions 10-12. These oil/water nanoemulsions have aroused growing environmental and health concerns because of (1) the persistent stability and high transportability of nanosized oil droplet in environment 13-16 , and (2) the severe eco-toxicity of surfactant due to its strong bio-reactivity 17-19. The complete separation of oil/water nanoemulsion remains an extreme challenge due to the coexistence of nanometer-sized oil droplets and tiny surfactant molecules (typical surfactant micelle radius: < 10 nm, Table S1) 13,20. Traditional technologies, such as gravity separation, air flotation, skimming, centrifuge, etc. are incapable of removing emulsified oil and surfactant from nanoemulsion 21,22. Membrane technology, which functions primarily on the principle of size exclusion 23 , is the most promising technology to address the challenge of complete separation of nanoemulsion. Recently, membrane development has significantly advanced in terms of separating oil from nanoemulsion 24-27. On one hand, the study from Solomon et al. employed a hydrophobic membrane to separate water-in-oil nanoemulsion, by allowing oil to pass through membrane while repelling water 24. But there exist intrinsic problems for hydrophobic membrane: (1) low flux subject to the high permeate (oil) viscosity, according to Hagen-Poiseuille equation 28 , and (2) severe oil-fouling resulted from the hydrophobicity of membrane material 29,30. On the other hand, some studies employed a hydrophilic membrane to separate oil-in-water

Applied Catalysis B Environmental, 2011

Here we present a simple two-phase assembling method to produce high-quality graphene oxide-TiO 2... more Here we present a simple two-phase assembling method to produce high-quality graphene oxide-TiO 2 nanorod composites (GO-TiO 2 NRCs) on gram scale. TiO 2 nanorods dispersed in toluene are synthesized from a facile two-phase hydrothermal method. The effective attachment of TiO 2 nanorods on the whole GO sheets at the water-toluene interface is confirmed by Transmission Electron Microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The as-synthesized TiO 2 nanorods show a slightly higher efficiency in the photocatalytic degradation of C. I. Acid Orange 7 (AO7) irradiated under UV light (λ=254 nm) and higher antibacterial activity under simulated sunlight than that of TiO 2 nanoparticles with the same diameter. After combined with graphene oxide (GO), the GO-TiO 2 NRCs show much higher photocatalytic activities than that of TiO 2 nanorods alone and the GO-TiO 2 nanoparticle composites (GO-TiO 2 NPCs). The ratio of TiO 2 and GO has no evident effect on the photocatalytic activity of GO-TiO 2 NRCs when all the TiO 2 nanorods are anchored on the GO sheets. The higher photocatalytic activity of GO-TiO 2 NRCs is ascribed to the anti-charge recombination and the more (101) facets. Considering the superior photocatalytic activity of GO-TiO 2 Keywords：Graphene oxide, TiO 2 , Nanorod, Composites, Gram-scale, Two-phase NRCs and the fact that they can been easily mass-produced, we expect this material may find important applications in environmental engineering and other fields.

Http Dx Doi Org 10 1080 01496395 2012 694005, 2013

ABSTRACT Here, hierarchical ZnO nanoflake spheres were hydrothermally synthesized at a large scal... more ABSTRACT Here, hierarchical ZnO nanoflake spheres were hydrothermally synthesized at a large scale. These hierarchical ZnO nanoflake spheres were well characterized and successfully assembled on a piece of polymer membrane surface to form a multifunctional membrane with a “win-win” aim to realize the mitigation of membrane fouling and reuse of catalysts. This newly developed membrane demonstrated the removal ability of high pollutants via filtration, photodegradation of pollutants, and antibacterial growth under visible light irradiation. At the same time, this novel membrane holds the potential to produce clean water at a constant high flux.

Scientific reports, Jan 29, 2015

Managing the wastewater discharged from oil and shale gas fields is a big challenge, because this... more Managing the wastewater discharged from oil and shale gas fields is a big challenge, because this kind of wastewater is normally polluted by high contents of both oils and salts. Conventional pressure-driven membranes experience little success for treating this wastewater because of either severe membrane fouling or incapability of desalination. In this study, we designed a new nanocomposite forward osmosis (FO) membrane for accomplishing simultaneous oil/water separation and desalination. This nanocomposite FO membrane is composed of an oil-repelling and salt-rejecting hydrogel selective layer on top of a graphene oxide (GO) nanosheets infused polymeric support layer. The hydrogel selective layer demonstrates strong underwater oleophobicity that leads to superior anti-fouling capability under various oil/water emulsions, and the infused GO in support layer can significantly mitigate internal concentration polarization (ICP) through reducing FO membrane structural parameter by as mu...

Separation and Purification Technology, 2015

International Journal of Photoenergy, 2012

Solar visible light is a source of clean and cheap energy. Herein, a new kind of hierarchical CuO... more Solar visible light is a source of clean and cheap energy. Herein, a new kind of hierarchical CuO/ZnO nanomaterial was synthesized using a facile process. Characterized by FESEM, TEM, XRD, XPS, and so forth, this CuO/ZnO naomaterial shows a special hierarchical nanostructure with CuO nanoparticles grown on ZnO nanorods. By assembling the hierarchical CuO/ZnO nanomaterials on a piece of commercial glassfiber membrane, a novel hierarchical CuO/ZnO membrane was fabricated. This CuO/ZnO membrane demonstrated excellent environmental applications, such as improved photodegradation of contaminants and antibacterial activity, under the irradiation of visible light. Compared with pure ZnO nanorod membrane, the improved photodegradation and antibacterial capacities of this hierarchical CuO/ZnO membrane result from the special hierarchical nanostructure of CuO/ZnO nanomaterials, which could enhance light utilization rate, enlarge specific surface area, and retard the recombination of electrons...

RSC Advances, 2013

ABSTRACT Many capping agents like citrate, PVP (polyvinylpyrrolidone) and PEG (polyethylene glyco... more ABSTRACT Many capping agents like citrate, PVP (polyvinylpyrrolidone) and PEG (polyethylene glycol) have been applied for stabilizing silver nanoparticles (AgNPs) in waters, and other work has also been conducted to investigate the influences of physicochemical properties of aqueous solutions on the important aspects of AgNPs behaviours. Herein, we successfully synthesized graphene oxide (GO)-AgNPs composite and investigated its stability in natural reservoir water (NRW) for the first time. The effects of physicochemical properties like pH, electrolytes, humic acid (HA) and bacteria in solutions were addressed. What's more, the stability of GO-AgNPs composite in NRW was studied over a period of 7 days with natural light exposure and compared to the stability of commercial citrate capped AgNPs (citrate-AgNPs). Using transmission electron microscopy, surface plasmon resonance (SPR) spectra and ζ-potentials measurements, we explained the mechanisms behind the stability of GO-AgNPs composite and the aggregation of citrate-AgNPs. We demonstrated that physicochemical properties like pH, electrolytes, HA and bacteria exhibit negligible effects on the GO-AgNPs composite which has good stability in NRW without Ag release. As GO is a widely used carbon based material, GO-AgNPs composite is of great significance in broadening the applications of AgNPs in water purification and many others fields.

ChemPlusChem, 2012

ABSTRACT Inspired by the highly efficient hierarchical structure of plants that use natural light... more ABSTRACT Inspired by the highly efficient hierarchical structure of plants that use natural light, the hierarchical “forest-like” TiO2 nanofiber/ZnO nanorod/CuO nanoparticle ternary material 2 is synthesized by a stepwise process: electrospinning of TiO2 nanofibers, hydrothermal growth of ZnO nanorods, and photodeposition of CuO nanoparticles. Material 2 has a higher photodegradation rate of acid orange (AO 7) and stronger antibacterial capability under irradiation with solar light in comparison to that of the hierarchical “tree-like” TiO2 nanofiber/ZnO nanorod material 1 and one dimensional as-spun TiO2 nanofibers. These enhancements result from the unique hierarchical forest- and tree-like features of materials 1 and 2, which enhance the light absorption capability, increase the specific surface area for mass transfer and bacteria attachment, create more reaction sites, and retard the recombination of photogenerated electrons and holes. A proportional relationship was found between the photocatalytic activity and the hierarchy of the materials. The sizes of the hierarchical nanostructured materials are in the micron range, which provides the opportunity for using these materials in engineering applications.

Journal of Membrane Science, 2015

ABSTRACT Heterojunctioned architectures were facilely fabricated using hydrothermally treated ele... more ABSTRACT Heterojunctioned architectures were facilely fabricated using hydrothermally treated electrospun TiO2 nanofibers in an alkaline Sr(NO3)(2) precursor solution in an electronic oven. TiO2 on the fiber surface was partially dissolved into Ti4+ to react with Sr2+ in favor of the nucleation of SrTiO3 on TiO2 nanofibers, and thus a heterojunction was formed between SrTiO3 and TiO2, which will benefit the improvement of photocatalytic activity. And then a multifunctional membrane was created by functionalizing the surface of commercial cellulose acetate (CA) membrane with heterojunctioned SrTiO3/TiO2 nanofibers. This newly structured membrane exhibited excellent water purification performances in a concurrent photocatalytic membrane filtration system under the irradiation of UV light, because it is able to integrate the advantages of photocatalysis and membrane filtration while minimizes their disadvantages. The high water purification performances in terms of high photodegradation ability and high permeate flux are attributed to the high photocatalytic activity of heterojunctioned SrTiO3/TiO2 nanofibers architectures and their structured porous functional layer favorable for fast water pass through.

Water Science & Technology: Water Supply, 2009

TiO2 photocatalytic oxidation was combined with microfiltration (MF) (PCOMF) to remove humic acid... more TiO2 photocatalytic oxidation was combined with microfiltration (MF) (PCOMF) to remove humic acid (HA) in waters through investigating the flux performance, TOC, UV254 and UV436 removal efficiency, the fouled membrane surfaces by SEM. The results demonstrated that the combined PCOMF process showed a high removal efficiency of UV254 and UV436 of HA (close to 100%). The removal efficiency of TOC was about 84.34% indicating that most of HA was mineralized into water and carbon. The SEM images witnessed that the fouling on the membrane surfaces contaminated by PCO effluents after UV254 and UV365 light irradiation was mainly attributed to cake layer, which was reversible due to the increase of aggregated particles size consisting of HA and TiO2. Eventually, the combined PCOMF process displayed an improved effect on HA removal and fouling control to a certain level.

Energy, 2014

ABSTRACT We facilely fabricate hierarchical 3D microspheres consisting of 2D V2O5 (vanadium pento... more ABSTRACT We facilely fabricate hierarchical 3D microspheres consisting of 2D V2O5 (vanadium pentoxide) nanosheets by a low temperature hydrothermal method and use it to structure hierarchical 3D micro-/nano-LIBs (lithium ion batteries) cathode. This is a template-free and facile method easy for scale-up production of hierarchical 3D micro-/nano-structured V2O5 spheres beneficial for high performance LIBs applications. Such a facile method resulted hierarchical 3D micro-/nano-V2O5 possess many unique features good for LIBs: (1) 2D V2O5 nanosheets facilitate the Li+ diffusions and electron transports; (2) hierarchical 3D micro-/nano-cathode structure built up by V2O5 nanosheet spheres will lead to the close and sufficient contact between electrolytes and activate materials and at the same time will create buffer volume to accommodate the volume change during discharging/charging process; and (3) micro-scale V2O5 spheres are easy to result in high cell packing density beneficial for high power battery. As revealed by the experimental results, the micro-/nano-V2O5 electrode demonstrates high initial discharge and charge capacities with no irreversible loss, high rate capacities at different currents and long-lasting lifespan. The high-energy and high-power performances of the micro-/nano-V2O5 electrode is ascribed to the unique hierarchical micro-/nano-structure merits of V2O5 spheres as abovementioned. In view of the advantages of facile fabrication method and unique features of 3D micro-/nano-V2O5 spheres for high power and high energy LIB battery, it is of great significance to beneficially broaden the applications of high-energy and high-power LIBs with creating novel hierarchical micro-/nano-structured V2O5 cathode materials.

Environmental science & technology, Jan 28, 2015

A green approach was successfully developed to reap three environmental benefits simultaneously: ... more A green approach was successfully developed to reap three environmental benefits simultaneously: (1) clean water production, (2) hydrogen (H2) generation, and (3) well-dispersed in situ Cu(2+) recovery for direct TiO2-CuO composite reclamation, by exploiting the synergistic integration of photocatalytic reaction of Cu-EDTA and one-dimensional (1D) ultralong and ultrathin TiO2 nanofibers. In this light-initiated system, Cu-EDTA was oxidized by TiO2 thus releasing Cu(2+) which was reduced and recovered through uniform adsorption onto the long and porous TiO2 surface. A win-win platform was thus attained, on which Cu was recovered while providing active sites for H2 generation via photoreduction of H2O and enhancing photo-oxidation of remaining intermediate oxidation byproducts. Experimental results showed a H2 generation rate of 251 μmol/h concomitantly with TOC reduction. The used TiO2 nanofibers deposited with Cu were reclaimed directly as the TiO2-CuO composite after a facile heat ...

Water Science & Technology: Water Supply, 2011

Hybrid UV/TiO2 photocatalytic oxidation (PCO) and ultrafiltration (UF) process (PCO-UF) were used... more Hybrid UV/TiO2 photocatalytic oxidation (PCO) and ultrafiltration (UF) process (PCO-UF) were used to remove humic acid (HA) and control membrane fouling. The PCO-UF process showed advantages in terms of higher removal rate of HA, higher permeate flux and less membrane fouling over UF alone and PCO alone on HA removal and membrane fouling control. Membrane material and pH of feed water were shown to be the influence on the performance of PCO-UF process. It was observed that higher pH of HA feed water and a hydrophobic membrane lead to better removal of HA with relatively higher permeate flux. The experimental results in this study demonstrated that 100 kDa ultraflic UF membrane and pH 9 of HA feed water would be the optimal choice for HA removal in the combined PCO-UF process.

Water Research, 2013

Please cite this article in press as: Bai, H., et al., Hierarchical 3D dendritic TiO 2 nanosphere... more Please cite this article in press as: Bai, H., et al., Hierarchical 3D dendritic TiO 2 nanospheres building with ultralong 1D nanoribbon/wires for high performance concurrent photocatalytic membrane water purification, Water Research (2013), http:// dx.

Water Research, 2013

It is still a challenge to photocatalytically cogenerate clean water and energy from dye wastewat... more It is still a challenge to photocatalytically cogenerate clean water and energy from dye wastewater owing to the relatively low photocatalytic efficiency of photocatalysts. In this study, novel-structured TiO2/CuO composite nanofibers were successfully fabricated via facile electrospinning. For the first time, the TiO2/CuO composite nanofibers demonstrated multifunctional ability for concurrent photocatalytic organic degradation and H2 generation from dye wastewater. The enhanced photocatalytic activity of TiO2/CuO composite nanofibers was ascribed to its excellent synergy of physicochemical properties: 1) mesoporosity and large specific surface area for efficient substrate adsorption, mass transfer and light harvesting; 2) red-shift of the absorbance spectra for enhanced light utilization; 3) long nanofibrous structure for efficient charge transfer and ease of recovery, 4) TiO2/CuO heterojunctions which enhance the separation of electrons and holes and 5) presence of CuO which serve as co-catalyst for the H2 production. The TiO2/CuO composite nanofibers also exhibited rapid settleability by gravity and uncompromised reusability. Thus, the as-synthesized TiO2/CuO composite nanofibers represent a promising candidate for highly efficient concurrent photocatalytic organic degradation and clean energy production from dye wastewater.

Water Research, 2012

A facile polyol synthesis was used for the deposition of Ag nanoparticles on electrospun TiO2 nan... more A facile polyol synthesis was used for the deposition of Ag nanoparticles on electrospun TiO2 nanofibers for the subsequent fabrication of Ag/TiO2 nanofiber membrane. The permeate flux of the Ag/TiO2 nanofiber membrane was remarkably high compared to commercial P25 deposited membrane. The Ag/TiO2 nanofiber membrane achieved 99.9% bacteria inactivation and 80.0% dye degradation under solar irradiation within 30 min. The Ag/TiO2 nanofiber membrane also showed excellent antibacterial capability without solar irradiation. Considering the excellent intrinsic antibacterial activity and high-performance photocatalytic disinfection/degradation under solar irradiation, this novel membrane proved to have promising applications in water purification industry.

Separation Science and Technology, 2013

Separation and Purification Technology, 2013

ABSTRACT A general method for the fabrication of flexible, multifunctional and hierarchically-nan... more ABSTRACT A general method for the fabrication of flexible, multifunctional and hierarchically-nanostructured membranes was reported. As an example, the as-prepared TiO2 nanorod self-supporting membrane shows excellent advantages, when it is used in concurrent filtration and degradation of the pollutants in waters, including high mechanical flexibility, high permeate flux, high photocatalytic activity and no membrane fouling problem, which indicate its great potential for sustainable environmental applications. And this general method also was successfully demonstrated with a ZnO nanoflake self-supporting membrane, which also have great potential in environmental and energy applications.

Polymers

Environmental science & technology, Jan 6, 2018

Scientific Reports, 2016

Applied Catalysis B Environmental, 2011

Http Dx Doi Org 10 1080 01496395 2012 694005, 2013

Scientific reports, Jan 29, 2015

Separation and Purification Technology, 2015

International Journal of Photoenergy, 2012

RSC Advances, 2013

ChemPlusChem, 2012

Journal of Membrane Science, 2015

Water Science & Technology: Water Supply, 2009

Energy, 2014

Environmental science & technology, Jan 28, 2015

Water Science & Technology: Water Supply, 2011

Water Research, 2013

Water Research, 2012

Separation Science and Technology, 2013

Separation and Purification Technology, 2013