Guocheng Huang

Porous Fluorinated SnO2 Hollow Nanospheres: Transformative Self-assembly and Photocatalytic Inactivation of Bacteria

Highly porous surface fluorinated SnO2 hollow nanospheres (SnO2(F) HNS) were produced in high yield by a hydrothermal treatment of stannous fluoride in the presence of hydrogen peroxide. Two important processes in terms of oriented self-assembly and in situ self-transformation were highlighted for the formation of as-prepared SnO2(F) HNS, which were largely relying on the directing effects of selected specific chemical species in the present synthesis system. Significantly, these SnO2(F) HNS showed considerable activity in photocatalytic inactivation of a surface negatively charged bacterium, Escherichia coli K-12, in aqueous saline solution. The dominant reactive species involved in the inactivation process were also identified.

Visible-light-driven photocatalytic inactivation of Escherichia coli by magnetic Fe2O3–AgBr

Bacterial inactivation by magnetic photocatalyst receives increasing interests for the ease recovery and reuse of photocatalysts. This study investigated bacterial inactivation by a magnetic photocatalysts, Fe2O3-AgBr, under the irradiation of a commercially available light emitting diode lamp. The effects of different factors on the inactivation of Escherichia coli were also evaluated, in term of the efficiency in inactivation. The results showed that Fe2O3-AgBr was able to inactivate both Gram negative (E. coli) and Gram positive (Staphylococcus aureus) bacteria. Bacterial inactivation by Fe2O3-AgBr was more favorable under high temperature and alkaline pH. Presence of Ca(2+) promoted the bacterial inactivation while the presence of [Formula: see text] was inhibitory. The mechanisms of photocatalytic bacterial inactivation were systemically studied and the effects of the presence of various specific reactive species scavengers and argon suggest that Fe2O3-AgBr inactivate bacterial cells by the oxidation of H2O2 generated from the photo-generated electron and direct oxidation of photo-generated hole. The detection of different reactive species further supported the proposed mechanisms. The results provide information for the evaluation of bacterial inactivation performance of Fe2O3-AgBr under different conditions. More importantly, bacterial inactivation for five consecutive cycles demonstrated Fe2O3-AgBr exhibited highly stable bactericidal activity and suggest that the magnetic Fe2O3-AgBr has great potential for water disinfection.

Visible-light-driven photocatalytic bacterial inactivation and the mechanism of zinc oxysulfide under LED light irradiation

Zinc oxysulfide (ZnO0.6S0.4) nanoparticles, prepared via a coprecipitation–calcination method, were used as an effective visible-light-driven (VLD) photocatalyst for the inactivation of a typical Gram-negative bacterium, Escherichia coli K-12 for the first time. An energy-saving white light emitting diode (LED) lamp was employed as the visible light (VL) source. Compared to the only UV-responsive pure ZnO and ZnS, the light active region of ZnO0.6S0.4 was expanded as far as 550 nm in the VL region. Significantly, the obtained ZnO0.6S0.4 nanoparticles showed considerable VLD photocatalytic bacterial inactivation activity under white LED irradiation. The mechanism of inactivation was investigated in-depth. Photogenerated holes (h+) and hydrogen peroxide (H2O2) were predominantly responsible for the bacterial inactivation. Moreover, H2O2 was evidenced to be derived only from electrons in the conduction band of ZnO0.6S0.4 in the present photocatalytic system. The integrated damage from the direct oxidation effect of the h+ and continuous accumulation of H2O2 resulted in a high bacterial inactivation efficiency of ZnO0.6S0.4 nanoparticles under visible white LED lamp irradiation. The destruction process of bacterial cells by the ZnO0.6S0.4 photocatalyst was also monitored. This was shown to begin with an attack of the cell membrane and then end in the release of intracellular components.

Role of in Situ Resultant H2O2 in the Visible-Light-Driven Photocatalytic Inactivation of E. coli Using Natural Sphalerite: A Genetic Study

This study investigated how a natural sphalerite (NS) photocatalyst, under visible light irradiation, supports photocatalytic bacterial inactivation. This was done by comparing parent E. coli BW25113, and its two isogenic single-gene knock-out mutants, E. coli JW0797-1 (dps(-) mutant) and JW1721-1 (katE(-) mutant), where both dps and KatE genes are likely related to H2O2 production. NS could inactivate approximately 5-, 7- and 7-log of E. coli BW25113, JW0797-1, and JW1721-1 within 6 h irradiation, respectively. The two isogenic mutants were more susceptible to photocatalysis than the parental strain because of their lack of a defense system against H2O2 oxidative stress. The ability of in situ resultant H2O2 to serve as a defense against photocatalytic inactivation was also confirmed using scavenging experiments and partition system experiments. Studying catalase activity further revealed that in situ H2O2 played an important role in these inactivation processes. The destruction of bacterial cells from the cell envelope to the intracellular components was also observed using field emission-scanning electron microscopy. Moreover, FT-IR was used to monitor bacterial cell decomposition, key functional group evolution, and bacterial cell structures. This is the first study to investigate the photocatalytic inactivation mechanism of E. coli using single-gene deletion mutants under visible light irradiation.

Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants

ABSTRACT The dual roles of capsular extracellular polymeric substances (EPS) in the photocatalytic inactivation of bacteria were demonstrated in a TiO2-UVA system, by comparing wild-type Escherichia coli strain BW25113 and isogenic mutants with upregulated and downregulated production of capsular EPS. In a partition system in which direct contact between bacterial cells and TiO2 particles was inhibited, an increase in the amount of EPS was associated with increased bacterial resistance to photocatalytic inactivation. In contrast, when bacterial cells were in direct contact with TiO2 particles, an increase in the amount of capsular EPS decreased cell viability during photocatalytic treatment. Taken together, these results suggest that although capsular EPS can protect bacterial cells by consuming photogenerated reactive species, it also facilitates photocatalytic inactivation of bacteria by promoting the adhesion of TiO2 particles to the cell surface. Fluorescence microscopy and scanning electron microscopy analyses further confirmed that high capsular EPS density led to more TiO2 particles attaching to cells and forming bacterium-TiO2 aggregates. Calculations of interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, suggested that the presence of capsular EPS enhances the attachment of TiO2 particles to bacterial cells via acid-base interactions. Consideration of these mechanisms is critical for understanding bacterium-nanoparticle interactions and the photocatalytic inactivation of bacteria.

Noble-metal loading reverses temperature dependent photocatalytic hydrogen generation in methanol–water solutions

Co-catalysts and sacrificing reagents are important components in artificial photocatalytic processes. Here we demonstrate that noble-metal loading reverses the temperature dependent photocatalytic activity trends of photocatalytic hydrogen (H2) generation with methanol as a sacrificing reagent. This finding suggested that visible and infrared light can enhance photocatalytic H2 generation via a heat effect over noble-metal/photocatalysts.

Simultaneous nutrient removal, optimised CO2 mitigation and biofuel feedstock production by Chlorogonium sp. grown in secondary treated non-sterile saline sewage effluent

The phycoremediation process has great potential for effectively addressing environmental pollution. To explore the capabilities of simultaneous algal nutrient removal, CO2 mitigation and biofuel feedstock production from spent water resources, a Chlorogonium sp. isolated from a tilapia pond in Hong Kong was grown in non-sterile saline sewage effluent for a bioremediation study. With high removal efficiencies of NH3-N (88.35±14.39%), NO3(-)-N (85.39±14.96%), TN (93.34±6.47%) and PO4(3-)-P (91.80±17.44%), Chlorogonium sp. achieved a CO2 consumption rate of 58.96 mg L(-1) d(-1), which was optimised by the response surface methodology. Under optimised conditions, the lipid content of the algal biomass reached 24.26±2.67%. Overall, the isolated Chlorogonium sp. showed promising potential in the simultaneous purification of saline sewage effluent in terms of tertiary treatment and CO2 sequestration while delivering feedstock for potential biofuel production in a waste-recycling manner.

Investigation of drinking water bacterial community through high-throughput sequencing

and chloraminated distributed water. The major species of the Delivery of safe and pathogen-free drinking water is crucial to public health. However, there exist challenges to the maintenance of the sterility of drinking water throughout the drinking water distribution systems (DWDS). Microbial growth in DWDS, such as growth of opportunistic pathogenic microorganisms, can lead to severe health problems in consumers (Berry et al., 2006; Brettar and Hofle, 2006; Lu et al., 2014; Zhang et al., 2015). Therefore, the impact of different factors on the drinking water biofilm bacterial community in DWDS merits investigation to provide information and insight into the development of effective control measures (Fig. 1). In the past, culture-based methods or direct counting methods have been the major strategies for the investigation of themicrobial community (Liu et al., 2013). Lehtola et al. (2004) investigated the biofilm bacterial community on different pipe materials (copper and plastic) by various methods such as heterotrophic plate count, lipid biomarker, and fluorescence staining. The results showed that biofilm formationwas slower in copper pipes than in plastic pipes. Moreover, pipe materials also influenced the microbial and Gram-negative bacteria community structure in biofilms and drinking water. A recent studyalso confirmed thatmicrobial communitywas affected by pipematerials (Liu et al., 2014). However, thesemethods have a limitation in identifying different bacterial cells in the sample.

Corrigendum to “Interaction between bacterial cell membranes and nano-TiO2 revealed by two-dimensional FTIR correlation spectroscopy using bacterial ghost as a model cell envelope” [Water Res. 118 (2017) 104–113]

The authors regret to inform that there are few typological errors in the above-cited paper. The corrections are given below. (1) The last second sentence in Abstract. “Additionally, the asynchronous map of 2D-FTIR-COS indicated a sequential order of functionalities bonded to TiO2 nanoparticles with the order of: COO-> aromatic C=C stretching > C=O, ketone > N-H, amide II.” (2) Section 3.2 (p. 108) “The signs of the cross peaks (Table 1) indicate that sequential order of the bonding affinities of these bands with TiO2 nanoparticles follow the order: COO-→ aromatic C=C stretching → C=O, ketone → N-H, amide II.” (3) Section 4.1 (p. 111) “Additionally, the asynchronous map of 2D-FTIR-COS indicates the propensities of functionalities bonded to TiO2 nanoparticle followed as: COO− > aromatic C=C stretching > C=O, ketone > N-H, amide II.” (4) The second bullet point in the Conclusions. “The asynchronous map of 2D-FTIR-COS suggested a sequential order of functionalities bonded to TiO2 nanoparticles with the order from high to low: COO-> aromatic C=C stretching > C=O, ketone > N-H, amide II.”