Darren Delai Sun

Self-Etching Reconstruction of Hierarchically Mesoporous F-TiO2 Hollow Microspherical Photocatalyst for Concurrent Membrane Water Purifications

We report a large-scale self-etching approach for the synthesis of monodispersed mesoporous F-TiO2 hollow microspheres. The self-etching derived from HF was elucidated by the morphology, chemical composition, and crystal size evolutions from solid to hollow microspheres with the increase in the concentration of H2SO4. The resulting TiO2 hollow microspheres exhibited ease for the concurrent membrane filtration and photocatalysis, providing high potential for engineering application in advanced water treatment, for not only increasing water production but also improving water quality.

Nano Gives the Answer: Breaking the Bottleneck of Internal Concentration Polarization with a Nanofiber Composite Forward Osmosis Membrane for a High Water Production Rate

Clean water shortage is one of the biggest global crises. [ 1 ] Thus clean water production and regeneration have become the main concerns. Among a variety of technologies, forward osmosis (FO) is a well-recognized osmotic process for producing clean water because of the low energy input, [ 2 ] as shown in Figure S1 (Supporting Information). Driven by osmotic pressure gradient ( Δ π ) across a semipermeable FO membrane, water diffuses naturally through the membrane, leaving impurities behind. This process has great potential for various applications including wastewater reclamation, [ 3 ] seawater desalination, [ 4 ] and energy production. [ 5 ]

Graphene oxide–CdS composite with high photocatalytic degradation and disinfection activities under visible light irradiation

Graphene oxide (GO)-CdS composites were synthesized via a novel two-phase mixing method successfully. CdS nanoparticles were uniformly self-assembled on GO sheets at water/toluene interface. The photocatalytic degradation (photodegradation) and disinfection activities of GO-CdS composites were investigated thoroughly. The results show that GO-CdS composites exhibit higher efficiency in photodegradation of various water pollutants than pure CdS nanoparticles under visible light irradiation. In addition, the interactions between GO sheets and CdS nanoparticles inhibit the photo-corrosion of CdS and leaching of Cd(2+). Only 3.5 wt% Cd(2+) of GO-CdS was leached out after photodegradation, while 38.6 wt% Cd(2+) of CdS was lost into aqueous solution. Furthermore, the disinfection activity of GO-CdS composites was investigated for the first time. Nearly 100% of both Gram-negative Escherichia coli (E. coli) and Gram-positive Bacillus subtilis (B. subtilis) were killed within 25 min under visible light irradiation. The excellent performances of GO-CdS composites can be attributed to that (1) effective charge transfer from CdS to GO reduces the recombination rate of photo-generated electron-hole pairs; (2) uniform deposition of CdS on GO sheets eliminates aggregation of CdS nanoparticles; and (3) the strong interactions between GO and CdS enhancing the durability of GO-CdS composites. Finally, the mechanism behind these excellent performances was verified by transient photocurrent measurement and further confirmed by ESR technique as well as employing a radical scavenging species - dimethyl sulfoxide (DMSO).

Graphene oxide enwrapped Ag3PO4 composite: towards a highly efficient and stable visible-light-induced photocatalyst for water purification.

A novel graphene oxide (GO) enwrapped Ag3PO4 (GO–Ag3PO4) composite as a visible-light-induced photocatalyst has been fabricated through an ion-exchange method of CH3COOAg and Na2HPO4 in the presence of GO sheets. Scanning electron microscope and X-ray diffraction analysis confirmed that Ag3PO4 particles have been enwrapped by GO sheets. The UV-vis spectra curve of the GO–Ag3PO4 composite showed strong absorbance in the visible light regions. The photocatalytic activity of the composite was evaluated by the degradation of organic dye (AO7) and phenol under visible-light irradiation. The results indicated that this novel GO–Ag3PO4 composite exhibited significantly higher photocatalytic activities and improved stability under visible-light irradiation, compared with bare Ag3PO4. Moreover, the GO–Ag3PO4 composite showed both excellent intrinsic antibacterial and visible-light-induced photocatalytic disinfection activities toward E. coli cells. The possible mechanism for the enhanced photocatalytic properties and antibacterial activity of the GO–Ag3PO4 composite was also discussed. Our finding paves a way to design highly efficient and stable visible-light-induced photocatalysts for the removal of organic pollutants and pathogenic bacteria for water purification.

Concurrent filtration and solar photocatalytic disinfection/degradation using high-performance Ag/TiO2 nanofiber membrane.

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.

High quality graphene oxide-CdS-Pt nanocomposites for efficient photocatalytic hydrogen evolution†

Graphene oxide–CdS–Pt (GO–CdS–Pt) nanocomposites with different amounts of Pt nanoparticles were successfully synthesized via the formic acid reduction process followed by a two-phase mixing method. The morphology, crystal phase and optical properties of obtained composites were well characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectroscopy, Fourier transform IR spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic activity of GO–CdS–Pt composites for hydrogen generation was investigated. The results show that the GO–CdS–Pt composite containing 0.5 at% of Pt exhibits the highest hydrogen evolution rate of 123 mL h−1 g−1 with strong photostability, which is about 2.5 times higher than that of GO–CdS and 10.3 times higher than that of CdS. The increased photocatalytic hydrogen generation efficiency is attributed to the effective charge separation and decreased anti-recombination with the addition of GO and Pt, as well as the low overpotential of Pt for water splitting. Our findings pave a way to design multi-component graphene-based composites for highly efficient H2 generation and other applications.

Facile synthesis of monodispersed silver nanoparticles on graphene oxide sheets with enhanced antibacterial activity

Graphene oxide–Ag nanoparticle (GO–Ag) composites were synthesized through a facile two-phase (toluene–water) process. Transmission Electron Microscopy and X-ray diffraction analysis revealed that the Ag nanoparticles anchored on GO sheets were spherical in shape and highly monodispersed with uniform size of 6 nm. The antibacterial activity of GO–Ag composites was investigated against gram-negative bacteria Escherichia coli (E. coli) and showed a remarkably enhanced antibacterial activity compared with the original Ag nanoparticles, suggesting that the as-prepared nanocomposites may be used as effective antibacterial materials.

Novel-structured electrospun TiO2/CuO composite nanofibers for high efficient photocatalytic cogeneration of clean water and energy from dye wastewater.

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.

Highly Efficient and Flexible Electrospun Carbon–Silica Nanofibrous Membrane for Ultrafast Gravity-Driven Oil–Water Separation

A novel free-standing and flexible electrospun carbon-silica composite nanofibrous membrane is newly introduced. The characterization results suggest that the electrospun composite nanofibers are constructed by carbon chains interpenetrated through a linear network of 3-dimensional SiO2. Thermogravimetric analysis indicates that the presence of insulating silica further improve the thermal resistance of the membrane. Additionally, the mechanical strength test shows that the membranes toughness and flexibility can be enhanced if the concentration of SiO2 is maintained below 2.7 wt %. Thermal and chemical stability test show that the membranes wettability properties can be sustained at an elevated temperature up to 300 °C and no discernible change in wettability was observed under highly acidic and basic conditions. After surface-coating with silicone oil for 30 mins, the composite membrane exhibits ultra-hydrophobic and superoleophilic properties with water and oil contact angles being 144.2 ± 1.2° and 0°, respectively. The enhanced flexibility and selective wetting property enables the membrane to serve as an effective substrate for separating free oil from water. Lab-scale oil-water separation test indicates that the membrane possesses excellent oil-water separation efficiency. In addition, its inherent property of high porosity allows oil-water separation to be performed in a gravity-driven process with high-flux. We anticipate that this study will open up a new avenue for fabrication of free-standing carbonaceous composite membrane with tunable flexibility for energy efficient and high-throughput production of clean water.

Hierarchically multifunctional TiO2 nano-thorn membrane for water purification

A novel TiO(2) nano-thorn membrane was assembled for concurrent filtration and photocatalytic oxidization to remove pollutants in water. This membrane has hierarchical porous and multifunctional properties, which provide these advantages: (1) producing water with high quality; (2) increasing water flux; and (3) eliminating membrane fouling.