Jiangyao Chen

Enhanced visible-light-driven photocatalytic inactivation of Escherichia coli using g-C3N4/TiO2 hybrid photocatalyst synthesized using a hydrothermal-calcination approach

Biohazards are widely present in wastewater, and contaminated water can arouse various waterborne diseases. Therefore, effectively removing biohazards from water is a worldwide need. In this study, a novel visible-light-driven (VLD) graphitic carbon nitride (g-C3N4)/TiO2 hybrid photocatalyst with high photocatalytic bacterial inactivation activity was successfully synthesized using a facile hydrothermal-calcination approach. The optimum synthesized hybrid photocatalyst is composed of micron-sized TiO2 spheres (average diameter: ca. 2 μm) and wrapped with lamellar g-C3N4 (thickness: ca. 2 nm), with narrowing bandgap (ca. 2.48 eV), leading to a significant improvement of visible light (VL) absorption and effective separation of photo-generated electron-hole pairs. This greatly enhances VL photocatalytic inactivation activity towards bacteria in water. Using this hybrid photocatalyst, 10(7) cfu mL(-1) of Escherichia coli K-12 could be completely inactivated within 180 min under VL irradiation. SEM images indicate that bacterial cells were greatly damaged, leading to a severe leakage of intracellular components during photocatalytic inactivation processes. The study concludes that bacterial cell destruction and water disinfection can be achieved using this newly fabricated VLD hybrid photocatalyst.

Synthesis and Characterization of Novel Plasmonic Ag/AgX-CNTs (X = Cl, Br, I) Nanocomposite Photocatalysts and Synergetic Degradation of Organic Pollutant under Visible Light

A series of novel well-defined Ag/AgX (X = Cl, Br, I) loaded carbon nanotubes (CNTs) composite photocatalysts (Ag/AgX-CNTs) were fabricated for the first time via a facile ultrasonic assistant deposition-precipitation method at the room temperature (25 ± 1 °C). X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption analysis, scanning electron microscopy, and ultraviolet-visible light absorption spectra analysis were used to characterize the structure, morphology, and optical properties of the as-prepared photocatalysts. Results confirmed the existence of the direct interfacial contact between Ag/AgX nanoparticles and CNTs, and Ag/AgX-CNTs nanocomposites exhibit superior absorbance in the visible light (VL) region owing to the surface plasmon resonance (SPR) of Ag nanoparticles. The fabricated composite photocatalysts were employed to remove 2,4,6-tribromophenol (TBP) in aqueous phase. A remarkably enhanced VL photocatalytic degradation efficiency of Ag/AgX-CNTs nanocomposites was observed when compared to that of pure AgX or CNTs. The photocatalytic activity enhancement of Ag/AgX-CNTs was due to the effective electron transfer from photoexcited AgX and plasmon-excited Ag(0) nanoparticles to CNTs. This can effectively decrease the recombination of electron-hole pairs, lead to a prolonged lifetime of the photoholes that promotes the degradation efficiency.

Synthesis of Carbon Nanotube Anatase TiO2 Sub-micrometer-sized Sphere Composite Photocatalyst for Synergistic Degradation of Gaseous Styrene

The carbon nanotube (CNT)-sub-micrometer-sized anatase TiO₂ sphere composite photocatalysts were synthesized by a facile one-step hydrothermal method using titanium tetrafluoride as titanium source and CNTs as structure regulator. Various technologies including X-ray diffraction, UV-visible absorption spectra, N₂ adsorption-desorption, scanning electron microscopy, and transmission electron microscopy were employed to characterize the structure properties of the prepared composite photocatalysts. The results indicated that the composite photocatalysts consisted of CNTs wrapping around the sub-micrometer-sized anatase TiO₂ spheres with controllable crystal facets and that the aggregated particles with average diameter ranged from 200 to 600 nm. The fabricated composite photocatalysts were used to degrade gaseous styrene in this work. As expected, a synergistic effect that remarkably enhancing the photocatalytic degradation efficiency of gaseous styrene by the prepared composite photocatalysts was observed in comparison with that the degradation efficiency using pure anatase TiO₂ and the adsorption of CNTs. Similar results were also confirmed in the decolorization of liquid methyl orange. Further investigation demonstrated that the synergistic effect in the photocatalytic activity was related to the structure of the sub-micrometer-sized anatase TiO₂ spheres and the significant roles of CNTs in the composite photocatalysts. By controlling the content of CNTs, the content of TiO₂ or the temperature during the hydrothermal synthesis process, anatase TiO₂ spheres with controllable crystallite size and dominant crystal facets such as {001}, {101}, or polycrystalline could be obtained, which was beneficial for the increase in the synergistic effect and further enhancement of the photocatalytic efficiencies.

Adsorption and degradation of model volatile organic compounds by a combined titania-montmorillonite-silica photocatalyst

A series of adsorptive photocatalysts, combined titania-montmorillonite-silica were synthesized. The resultant photocatalysts consisted of more and more spherically agglomerated TiO(2) particles with increasing of TiO(2) content, and anatase was the only crystalline phase with nano-scale TiO(2) particles. With increasing of the cation exchange capacity to TiO(2) molar ratio, specific surface area and pore volume increased very slightly. In a fluidized bed photocatalytic reactor by choosing toluene, ethyl acetate and ethanethiol as model pollutants, all catalysts had relatively high adsorption capacities and preferred to adsorb higher polarity pollutants. Langmuir isotherm model better described equilibrium data compared to Freundlich model. Competitive adsorptions were observed for the mixed pollutants on the catalysts, leading to decrease adsorption capacity for each pollutant. The combined titania-montmorillonite-silica photocatalyst exhibited excellent photocatalytic removal ability to model pollutants of various components. Almost 100% of degradation efficiency was achieved within 120 min for each pollutant with about 500 ppb initial concentration, though the efficiencies of multi-component compounds slightly decreased. All photocatalytic reactions followed the Langmuir-Hinshelwood model. Degradation rate constants of multi-component systems were lower than those for single systems, following the order of toluene

Pollution profiles and health risk assessment of VOCs emitted during e-waste dismantling processes associated with different dismantling methods

Pollution profiles of typical volatile organic compounds (VOCs) emitted during dismantling of various printed circuit board assemblies (PCBAs) of e-wastes using different methods were comparatively investigated in the real e-waste dismantling workshops in South China in April 2013. Similar pollution profiles and concentrations of VOCs were observed between dismantling mobile phone and hard disk PCBAs by using electric blowers and between dismantling television and power supplier PCBAs using electric heating furnaces. Aromatic hydrocarbons (accounting for >60% of the sum of VOCs) were the dominant group during using electric blowers, while aromatic (accounting for >44% of the sum of VOCs) and halogenated hydrocarbons (accounting for >48% of the sum of VOCs) were the two dominant groups which contributed equally using electric heating furnaces. However, the distribution profiles of VOCs emitted during dismantling of televisions, hard disks and micro motors using rotary incinerators varied greatly, though aromatic hydrocarbons were still the dominant group. The combustion of e-wastes led to the most severe contamination of VOCs, with total VOCs (3.3×10(4) μg m(-3)) using rotary incinerators about 190, 180, 139, and 40 times higher than those using mechanical cutting, electric soldering iron, electric blower, and electric heating furnace, respectively. Both cancer and non-cancer risks existed for workers due to exposure to on-site emitted VOCs in all workshops especially in those using rotary incinerators according to the USEPA methodology, whereas only cancer risks existed in rotary incinerator workshops according to the American Conference of Industrial Hygienists methodology.

Pollution profiles, health risk of VOCs and biohazards emitted from municipal solid waste transfer station and elimination by an integrated biological-photocatalytic flow system: A pilot-scale investigation

Volatile organic compounds (VOCs) and biohazards air pollution in municipal solid waste transfer station were investigated. As compressor working, the concentrations of almost all quantified 14 VOCs (0.32-306.03 μg m(-3)) were much higher than those as compressor off (0-13.31 μg m(-3)). Comparatively, only 3 VOCs with extremely low concentrations could be detected at control area. Total microorganism was 7567 CFU m(-3) as compressor working, which was 1.14 and 6.22 times higher than that of compressor off and control area, respectively. Bacteria were the most abundant microorganism at all three sampling places. At pilot-scale, during whole 60-day treatment, for VOCs, the average removal efficiencies were over 92% after biotrickling filter-photocatalytic (BTF-PC) treatment. Although non-cancer and cancer risks of some VOCs were over the concern level before treatment, almost all VOCs were removed substantially and both potential risks were below the concern after BTF-PC treatment. Additionally, biohazard concentrations decreased dramatically and air quality was purified from polluted to cleanness after PC treatment. All results demonstrated that the integrated technology possessed high removal capacity and long stability for the removal of VOCs and biohazards at a pilot scale.

VOCs elimination and health risk reduction in e-waste dismantling workshop using integrated techniques of electrostatic precipitation with advanced oxidation technologies

Volatile organic compounds (VOCs) emitted during the electronic waste dismantling process (EWDP) were treated at a pilot scale, using integrated electrostatic precipitation (EP)-advanced oxidation technologies (AOTs, subsequent photocatalysis (PC) and ozonation). Although no obvious alteration was seen in VOC concentration and composition, EP technology removed 47.2% of total suspended particles, greatly reducing the negative effect of particles on subsequent AOTs. After the AOT treatment, average removal efficiencies of 95.7%, 95.4%, 87.4%, and 97.5% were achieved for aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, as well as nitrogen- and oxygen-containing compounds, respectively, over 60-day treatment period. Furthermore, high elimination capacities were also seen using hybrid technique of PC with ozonation; this was due to the PC units high loading rates and excellent pre-treatment abilities, and the ozonation units high elimination capacity. In addition, the non-cancer and cancer risks, as well as the occupational exposure cancer risk, for workers exposed to emitted VOCs in workshop were reduced dramatically after the integrated technique treatment. Results demonstrated that the integrated technique led to highly efficient and stable VOC removal from EWDP emissions at a pilot scale. This study points to an efficient approach for atmospheric purification and improving human health in e-waste recycling regions.

Vapor-phase hydrothermal synthesis of rutile TiO2 nanostructured film with exposed pyramid-shaped (1 1 1) surface and superiorly photoelectrocatalytic performance

Rutile TiO2 nanostructured film with exposed pyramid-shaped (111) surface was successfully fabricated using metal titanium foil as substrate through a facile vapor-phase hydrothermal method. The fabricated rutile TiO2 film was composed of vertically aligned rod-like structures with diameters ranged from 400 to 700 nm and thickness of ca. 2.0 μm. The obtained rutile TiO2 film as photoanode exhibited excellent photoelectrocatalytic activity toward water oxidation and rhodamine B decolorization under UV illumination, which was more than 3.5 and 1.2 times of that obtained by highly ordered anatase TiO2 nanotube array film photoanode under the same experimental conditions, respectively. The excellent photoelectrocatalytic performance of the rutile TiO2 film photoanode could be due to the superior photoelectron transfer property and the high oxidative capability of {111} crystal facets. The superior photoelectron transfer capability of the photoanodes was manifested by the inherent resistance (R0) of the photoanodes using a simple photoelectrochemical method. The calculated R0 values were 50.5 and 86.2 Ω for the rutile TiO2 nanostructured film and anatase TiO2 nanotube array film, respectively. Lower R0 value of the rutile TiO2 photoanode indicated a superior photoelectron transfer capability owing to good single crystal property of the rod-like rutile nanostructure. Almost identical valence band level (1.94 eV) of the rutile TiO2 nanostructured film and anatase TiO2 nanotube array film (meaning a similar oxidation capability) further confirmed the significant role of photoelectron transfer capability and exposed high-energy {111} crystal facets for improved photoelectrocatalytic performance of the rutile TiO2 nanostructured film photoanode.

Enhanced visible-light photocatalytic activity to volatile organic compounds degradation and deactivation resistance mechanism of titania confined inside a metal-organic framework

Poor visible-light-driven activity and deactivation property as well as wide band gap of the most common TiO2 photocatalyst significantly limits its practical application in volatile organic compounds (VOCs) purification. In this study, tiny TiO2 nanoparticles incorporated into a typical metal-organic framework (MOF), NH2-UiO-66, with controllable TiO2 content and size, were synthesized based on the hard-soft acid-base (HSAB) principle and applied to VOCs purification. Compared to bare TiO2, the TiO2@NH2-UiO-66 composites could extend the optical absorption to the visible light range and accelerate the photogenerated electrons-holes separation, due to the excellent interface contact between TiO2 and NH2-UiO-66. Moreover, the abundant interconnected 3D cavities of the outer MOF allowed for VOCs to easily diffuse into the pores, producing a concentration microenvironment around the encapsulated TiO2. The TiO2@NH2-UiO-66 composites exhibited a markedly improved photocatalytic efficiency and a good resistance to deactivation during the photocatalytic degradation of gaseous styrene under visible light illumination, which were associated with the synergetic effects between the TiO2 and MOF. The TiO2@NH2-UiO-66 with 5 wt% TiO2 could efficiently mineralize styrene to CO2 to some extent companying with the removal ratio >99% within 600 min, whereas the removal efficiency over the bare TiO2 only 32.5%.

Cutting down on the ozone and SOA formation as well as health risks of VOCs emitted from e-waste dismantlement by integration technique

Elimination of volatile organic compounds (VOCs) in the e-waste dismantling industry by an integration technique of spray tower-electrostatic precipitation-photocatalysis was conducted to investigate its application possibility for reducing formation of O3 and secondary organic aerosols (SOAs) as well as exposure risk. Results revealed the average 5.4 × 102 μg m-3 of VOCs with the top two groups being aromatic hydrocarbons (AHs, 55.93%) and halogenated hydrocarbons (HHs, 33.33%), contributing to 1.3 × 103 and 3.0 × 104 μg m-3 of the O3 and SOA (OFP and SOAFP) formation potential, respectively. Furthermore, 86.47% of OFP and 99.87% of SOAFP were ascribed to AHs, in which toluene ranked first (35.30% and 48.07%). The highest removal efficiency (76.92%) for VOCs by the integrated technique resulted in excellent prevention efficiencies of OFP (71.54%) and SOAFP (80.62%). Occupational cancer risk assessment found that HHs (62.63%) and AHs (36.93%) were the top two contributors. After the treatment by the integrated technique, 55.44% of the total risk index was reduced with the accumulation of few low-concentrated and more toxic AHs (e.g. 6.6 μg m-3 benzene on average). All results suggest that controlling AH and HH emissions from the e-waste dismantling source could efficiently prevent atmospheric secondary pollution and human exposure risk to industrial emission.