•Simultaneous bacteria inactivation and heavy metal ions removal was investigated.•Nano-MgO exhibited high efficiencies for E. coli inactivation and Cd2+ removal.•ROS production and direct interaction between MgO and E. coli are two main factors.•Cd2+ existed in the system accelerated E. coli inactivation by nano-MgO.In this study, highly active MgO nanoparticles synthesized via sol–gel and calcination processes were used for the simultaneous bacterial disinfection and heavy metal ions removal from aqueous solution. Compared with commercial MgO, the synthesized MgO nanoparticles exhibited high efficiencies for both Escherichia coli (E. coli) inactivation and heavy metal ions (Cd2+ and Pb2+) removal. Surprisingly, the bacterial inactivation activity of MgO nanoparticles was improved in the presence of Cd2+ in the system. Partition experiments for bacterial inactivation, reactive oxygen species (ROS) detection and characterizations of the products adsorbed on MgO were used to further investigate the antibacterial mechanism of MgO nanoparticles in the absence and presence of Cd2+. It can be concluded that ROS production and the direct interaction between MgO and E. coli are mainly two factors for bacterial inactivation of MgO nanoparticles, which are prone to attack the cell membrane. When the cell membrane was damaged, heavy metal ions entered easily into bacterial cell and thus accelerated bacterial inactivation. The results in this study indicated that nanosized MgO could be a promising candidate for the treatment of wastewater contaminated by bacteria and heavy metals, due to its facile preparation, low cost, environmentally friendly characteristic and high removal efficiencies.

•ZnO0.6S0.4 was synthesized by simple co-precipitation and calcination method.•Photocatalytic H2 production with simultaneous pollutant degradation was achieved.•The maximum of 110% H2 promotion was obtained with optimal concentration of RV5.•Degradation intermediates of RV5 were effective to enhance H2 production.Photocatalytic hydrogen (H2) production was performed by visible-light-driven (VLD) ternary photocatalyst, zinc oxysulfide (ZnO0.6S0.4) in the presence of sulfide/sulfite (S22−/SO32−) sacrificing system, with simultaneous azo-dye Reactive Violet 5 (RV5) degradation. Enhancement in both RV5 degradation and H2 production was achieved, with the promotion of H2 production after decolorization of RV5. The effect of initial concentration of RV5 was found to be influential on the enhancement of H2 during the simultaneous processes, with a maximum of 110% increase of H2 produced. The mechanism of the simultaneous system was investigated by scavenger study and intermediate analysis, including Fourier transform-infrared (FTIR) spectroscopy and total organic carbon (TOC) analysis. It was confirmed that the partial degradation of RV5 and presence of dynamic organic intermediates contributed to the enhancement in H2 production. The present study revealed the feasibility of developing VLD photocatalysis as a sustainable and environmentally friendly technology for concurrent organic pollutant degradation with energy generation.Download high-res image (217KB)Download full-size image

•ZnO nanopowders doped with different metal ions were prepared by a sol-gel method.•Li doping promoted the grain growth and crystallization of ZnO particles.•Al and Ti doping improved the bacterial inactivation activity of ZnO nanopowders.•Al-doped ZnO exhibited the best photocatalytic activity under visible light.•Al-doped ZnO had much absorbed oxygen, narrow band gap and broad light absorption.Among metal oxide photocatalysts, zinc oxide (ZnO) has attracted extensive attention due to its advantages of low toxicity and relatively low cost of production. In this work, ZnO nanopowders doped with different metal ions (Li+, Mg2+, Al3+ and Ti4+) were synthesized by a sol-gel method. Multiple techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffused reflectance spectra (UV-vis DRS), photoluminescence (PL) spectra and Brunauer-Emmett-Teller (BET) measurements were employed to study the structures, morphologies and physicochemical properties of the photocatalysts. The influence of metal ion doping on the photocatalytic activity of ZnO was assessed by inactivating a typical Gram-negative bacterium, Escherichia coli K-12 under visible-light irradiation. It was found that Al doping and Ti doping could promote the photocatalytic bacterial inactivation activity of ZnO, while Li doping and Mg doping hindered the bacterial inactivation activity of ZnO photocatalysts. Moreover, Al-doped ZnO exhibited the best visible-light-driven (VLD) photocatalytic activity among these samples, with 7-log of E. coli K-12 cells being completely inactivated within 4 h. The large percentage of absorbed oxygen, narrow band gap and extended visible light absorption were considered to contribute to the powerful VLD photocatalytic activity of Al-doped ZnO.Download high-res image (100KB)Download full-size image

•Ag-MgO nanocomposite was firstly synthesized and used as an antibacterial agent.•Ag-MgO nanocomposite exhibited excellent antibacterial activity against E. coli.•A synergistic antibacterial effect between Ag and MgO NPs was found.•A mechanism for promoting O2− generation was proposed.Ag-MgO nanocomposite, synthesized by loading small-sized Ag nanoparticles on the surface of MgO nanoparticles, was firstly used as an effective antibacterial agent against Escherichia coli. The microstructure, morphology and composition of the nanocomposite were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray (EDX) analyzer, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and flame atomic emission spectroscopy (FAES) measurements. An interfacial interaction between Ag and MgO was confirmed by XRD and XPS analyses, which could effectively inhibit the release of silver ions (Ag+) from the nanocomposite. Antibacterial tests showed that the as-prepared Ag-MgO nanocomposite exhibited stronger antibacterial activity against Escherichia coli, compared to pure MgO and equivalent Ag nanoparticles alone, indicating a synergistic effect between Ag and MgO. Based on the results of reactive oxygen species (ROS) detection, the enhanced antibacterial activity of Ag-MgO nanocomposite was attributed to the promotion of ROS production, because Ag particles on the surface of MgO are in favor of electron transfer, which could enhance ROS production via one-electron reduction of oxygen. Taking into consideration easy preparation, low cost, low release rate of Ag+, and high antibacterial activity of Ag-MgO nanocomposite, it is a very promising candidate material for bacterial disinfection.

A simple alkali (NaOH) post-treatment approach assisted with light irradiation to in situ obtain Bi2O4 nanoparticle-decorated BiOBr nanosheets, brown BiOBr-0.01, is presented for the first time. Bi2O4 nanoparticles are formed due to a combined action of NaOH-induced dehalogenation and light triggered photogenerated hole (h+) oxidation processes on the surface of BiOBr nanosheets. Importantly, by varying the NaOH concertation in the post-treatment, the content of Bi2O4 phase in the hybrid structures can be easily tuned, and predominantly exposed highly reactive {001}-facet of BiOBr nanosheet can be well preserved. Significantly, without any foreign elements, the light absorption of as-prepared BiOBr-0.01 is extended to the near-infrared (NIR) region. In comparison with normal BiOBr, brown BiOBr-0.01 nanosheet shows superior photocatalytic activity for the dye degradation and microbial disinfection. Particularly, it exhibit excellent capability to photocatalytically reduce CO2 into CO and CH4, whereas the normal BiOBr is completely incapable for CO2 conversion under simulated sunlight irradiation. The exceptional enhancement is due to the Bi2O4 extended light absorption, efficient photogenerated e–/h+ pair separation, and the increased surface-adsorbed ability to reactants. This facile post-treatment method is promising for different bismuth-based systems and hence offers a path to a large variety of materials.

ZnO nanorods have been successfully prepared at low temperature (60 °C) in the presence of ammonia via a simple aqueous solution-based chemical approach. After calcination at 300 °C, many unique pitted structures are found on the surface of ZnO nanorods, although the shape and size of ZnO nanorods have almost no changes. Furthermore, the pit-structured ZnO nanorods exhibit higher photocatalytic activity for methylene blue photodegradation with a rate constant (k) of 0.01402 min−1, which is about 3 times more than that of uncalcined sample. The formation of the pitted structures is presumably attributed to the decomposition of a trace amount of ZnO(NH3)n complex implanted into ZnO crystals. In addition, a photocatalytic mechanism is proposed to explain the enhanced photocatalytic activity of the pit-structured ZnO nanorods.

Herein, Ag-doped magnesium oxide (MgO) nanoparticles were prepared by a citric acid-assist sol-gel method. It is evidenced that the size of MgO particles decreases after Ag doping and a small amount of Ag is doped into MgO crystal. The bacterial inactivation of as-prepared Ag-doped MgO against Escherichia coli (E. coli) suggests that Ag doping can greatly enhance the antibacterial activity of MgO nanoparticles and 1% Ag-doped MgO inactivates effectively 7-log bacterial cells within 20 min. The releases of metal ions (Ag+ and Mg2+) from Ag-doped MgO are at a very low level, which would not play the leading role in bacterial inactivation. The mechanism for the improvement of antibacterial activity of Ag-doped MgO is concluded as three aspects. Firstly, Ag doping can inhibit the grain growth of MgO nanoparticles, resulting in smaller size of MgO particles. Secondly, when Ag+ is doped into MgO matrix, more oxygen vacancies will be generated to keep an overall neutral charge. Thirdly, Ag-doped MgO has a relatively low electron-transfer resistance, which can accelerate the electron transfer within MgO crystal, in favour of the single-electron reduction of adsorbed oxygen. All these would substantially enhance ROS production and the contact interaction between bacterial cells and nanoparticles. Therefore, Ag doping can markedly promote the antibacterial activity of MgO nanoparticles.

•NZVI was modified using tetraethyl orthosilicate and hexadecyltrimethoxysilane.•HS-NZVI showed high removal ability towards Cr(VI) in water.•HS-NZVI exhibited higher stability and reusability than pure NZVI and S-NZVI.•HS-NZVI has excellent magnetic properties to facilitate separation and recycling.•The mechanism for Cr(VI) removal was adsorption, reduction and co-precipitation.In this study, a highly stable nanoscale zero-valent iron composite (HS-NZVI) was obtained via modifying nanoscale zero-valent iron (NZVI) with tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMOS), and used for Cr(VI) remediation in aqueous solution. The obtained HS-NZVI remained stable in water without being oxidized for over 12 h. After four consecutive runs, the Cr(VI) removal efficiency of HS-NZVI maintained a value of more than 82%. Moreover, the Cr(VI) removal capacity per unit weight of NZVI in HS-NZVI reached 292.8 mg/g within 60 min at the initial Cr(VI) concentration of 120 mg/L at pH 5. The Cr(VI) removal efficiency of HS-NZVI increased with decreasing solution pH, and the experimental data for Cr(VI) removal by HS-NZVI were well-described by the pseudo-first-order reaction model. Additionally, scanning electron microscope (SEM) images, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) measurements of the product after reaction revealed that the mechanism of Cr(VI) remediation by HS-NZVI mainly involved adsorption, reduction and co-precipitation. Considering the advantages of easy preparation, excellent stability and reusability, and high Cr(VI) removal capacity as well as the magnetic recovery property, HS-NZVI is expected to have notably promising applications for the remediation of Cr(VI) contaminated sites.Download high-res image (113KB)Download full-size image