Narrow Results

Ultrafine nanoparticles owing to their increased surface to volume ratio, coupled with the ability to tune their surface properties through molecular modification have made them ideal for their detection and remediation of broad range of environmental contaminants. Arsenic contamination has become a worldwide epidemic and remediation of this problem needs the development of technology with improved materials and systems with high efficiency. In the present study, we have demonstrated a simple and efficient method using surface functionalized ultrafine iron oxide nanoparticles for absolute removal of arsenic from arsenic treated water with low contact time period and low adsorbent dose. The efficiency of arsenic removal has been drastically improved by considering nanoparticles of size 10 nm and subsequent surface engineering of the nanoparticles resulting more adsorption sites being exposed to arsenic. The mechanism for adsorption was identified through electron microscopic and spectroscopic studies. The adsorption equilibrium data were well fitted to Freundlich isotherm.

A biomimetic and facile approach for integrating Fe₃O₄ and Au with polydopamine (PDA) was proposed to construct gold-coated Fe₃O₄ nanoparticles (Fe₃O₄@Au–PDA) with a core–shell structure by coupling in situ reduction with a seed-mediated method in aqueous solution at room temperature. The morphology, structure and composition of the core–shell structured Fe₃O₄@Au–PDA nanoparticles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS). The formation process of Au shell was assessed using a UV-Vis spectrophotometer. More importantly, according to investigating changes in PDA molecules by Fourier transform infrared spectroscopy (FTIR) and in preparation process of the zeta-potential data of nanoparticles, the mechanism of core–shell structure formation was proposed. Firstly, PDA-coated Fe₃O₄ are obtained using dopamine (DA) self-polymerization to form thin and surface-adherent PDA films onto the surface of a Fe₃O₄ "core". Then, Au seeds are attached on the surface of PDA-coated Fe₃O₄ via electrostatic interaction in order to serve as nucleation centers catalyzing the reduction of Au³⁺ to Au⁰ by the catechol groups in PDA. Accompanied by the deposition of Au, PDA films transfer from the surface of Fe₃O₄ to that of Au as stabilizing agent. In order to confirm the reasonableness of this mechanism, two verification experiments were conducted. The presence of PDA on the surface of Fe₃O₄@Au–PDA nanoparticles was confirmed by the finding that glycine or ethylenediamine could be grafted onto Fe₃O₄@Au–PDA nanoparticles through Schiff base reaction. In addition, Fe₃O₄@Au–DA nanoparticles, in which DA was substituted for PDA, were prepared using the same method as that for Fe₃O₄@Au–PDA nanoparticles and characterized by UV-Vis, TEM and FTIR. The results validated that DA possesses multiple functions of attaching Au seeds as well as acting as both reductant and stabilizing agent, the same functions as those of PDA.

The composite $\alpha$-FeOOH nanorods/Ag₃PO₄ photocatalyst has been successfully fabricated through a facile hydrothermal process combined with a successive in situ precipitation technique. The SEM and TEM images show that Ag₃PO₄ particles have been successfully loaded on the surface of FeOOH nanorods. The photocatalytic activities of the $\alpha$-FeOOH/Ag₃PO₄ composite were investigated for their efficiency on the degradation of Rhodamine B (RhB) under ultra-violet light and visible light irradiation, and the results showed that the $\alpha$-FeOOH/Ag₃PO₄ composite possessed remarkable photocatalytic activities. The enhanced photocatalytic activity can be attributed to the strong absorption in visible light and the effective separation of photogenerated hole–electron pairs between Ag₃PO₄ and $\alpha$-FeOOH.

Nitrogen-doped graphene (NG) was generated by hydrothermal method, using GO as the raw material and formamide as the reducing-doping source. The composite material was characterized by Fourier transform infrared (FTIR) spectrum, X-ray diffraction (XRD) spectrum, X-ray photoelectron spectroscopy (XPS). The results showed that Nitrogen was successfully doped in the graphene. Through regulating the reaction temperature, time and the ratio of graphite oxide and formamide, the different nitrogen contents were obtained, the highest nitrogen content was 5.67%. NG was also synthesized by urea or ammonia, characterizing by XPS. The characterization results showed that for taking urea and ammonia as nitrogen source, pyrrolic-N was the main form of nitrogen existing, taking formamide as a nitrogen, pyridinic-N was the main form of nitrogen existing. Based on these experimental results by different nitrogen source, the N-doped graphene mechanism was interpreted.

Reduced graphene oxide-SnSe (rGO-SnSe) nanohybrids were synthesized with a solution chemical reaction at room temperature. The nanohybrids were characterized by various techniques for their microstructural and photocatalytic activities in photodegradation of alkaline dye malachite green in the water. The effects of rGO/SnSe ratio, initial solution pH, and H₂O₂ concentration on the photodegradation efficiency were studied. The SnSe nanocrystallines with nanoscale size and narrow bandgap were formed and uniformly adhered on the rGO surface. Raman analysis confirmed the reduction of GO. The experimental results indicated that the nanohybrids showed excellent sunlight-excited photocatalytic activity in degrading malachite green in the water. Significantly, the nanohybrids showed remarkable photo-Fenton-like catalytic activity. The photodegradation rates of the hybrids were greater than that of SnSe nanoparticles, increased with increasing rGO/SnSe ratio, and related to operation parameters. High photocatalytic activities were ascribed to the efficiency interface effect that was confirmed by the calculations of band energy level and photoconductivity. The TOC measurement further verified the photodegradation results. The nanoparticles and nanohybrids also showed excellent reusability.

Novel n-SrTiO₃/p-BiOI heterojunction composites were successfully fabricated by loading SrTiO₃ particles onto the surface of BiOI nanoflakes via a two-step method. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), energy-disperse X-ray spectroscopy (EDS), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS) and electrochemical measurements. The results show that the n-SrTiO₃/p-BiOI heterojunction composites are composed of perovskite structure SrTiO₃ and tetragonal phase BiOI. The composites exhibit excellent photocatalytic performance for the degradation of crystal violet (CV) solution under simulated solar light irradiation, which is superior to that of pristine BiOI and SrTiO₃. The 30wt.%SrTiO₃/BiOI composite is found to be the optimal composite, over which the dye degradation reaches 92.5% for 30min of photocatalysis. The photocatalytic activity of the 30wt.%SrTiO₃/BiOI composite is found to be 3.94 times and 28.2 times higher than that of bare BiOI and SrTiO₃, respectively. The reactive species trapping experiments suggest that $•{\mathrm{\text{O}}}_2^{-}$ and holes are the main active species responsible for the CV degradation. In addition, the electrochemical measurements elucidate the effective separation of photoinduced electron–hole pairs. Moreover, on the basis of experimental and theoretical results, a possible mechanism for the enhanced photocatalytic performance of the SrTiO₃/BiOI heterojunction composites is also proposed.

Nucleate pool boiling heat transfer experiments have been conducted to nanofluids on a horizontal cylinder tube under atmospheric pressure. The nanofluids are prepared by dispersing Al₂O₃ nanoparticles into distilled water at concentrations of 0.001, 0.01, 0.1, 1 and 2wt.% with or without sodium, 4-dodecylbenzenesulfonate (SDBS). The experimental results showed that: nanofluids at lower concentrations (0.001wt.% to 1wt.%) can obviously enhance the pool boiling heat transfer performance, but signs of deterioration can be observed at higher concentration (2wt.%). The presence of SDBS can obviously enhance the pool boiling heat transfer performance, and with the presence of SDBS, a maximum enhancement ratio of BHTC of 69.88%, and a maximum decrease ratio of super heat of 41.12% can be found in Group NS5 and NS4, respectively. The tube diameter and wall thickness of heating surface are the influential factors for boiling heat transfer coefficient. Besides, we find that Rohsenow formula failed to predict the characteristics of nanofluids. The mechanism study shows that: the decrease of surface tension, which leads to the decrease of bubble departure diameter, and the presence of agglomerates in nanofluids are the reasons for the enhanced pool boiling heat transfer performance. At higher concentration, particle deposition will lead to the decrease of distribution density of the vaporization core, and as a result of that, the boiling heat transfer performance will deteriorate.

Doping Ag-enhanced and glutathione-stabilized Au nanoclusters (GSH–Ag/AuNCs) were prepared by the one-step ultraviolet radiation combined with microwave heating method. The effects of the molar ratio of Au–Ag and different types of energy suppliers on the fluorescent performance of GSH–Ag/AuNCs were studied in detail. After that, a new ratio fluorescent probe (RF-probe) based on the mixing of GSH–Ag/AuNCs with carbon dots (CDs) was designed for sensitive and selective determination of copper gluconate (CG) and cupric sulfate (CS). For the CDs–GSH–Ag/AuNCs RF-probe, the fluorescence (FL) of CDs (at 440nm) and that of alloy nanoclusters (NCs) (at 605nm) were, respectively, unaffected and strongly quenched in the presence of CG/CS at ${\lambda }_{\mathrm{\text{ex}}}=370$nm coming from the dynamic quenching process. Corresponding linear ranges and limit of detection (LOD) of the RF-probe for the CG/CS assay were estimated to be 0.17–6.20/0.17–5.62$\mu$mol/L and 16.80/15.95nmol/L, respectively. Furthermore, the proposed RF-probe was successfully used for the assays of CG in CG tablets and CG additive, and CS in infant formula and CS additive, respectively.

AgBr/zeolite photocatalysts with different mass ratios were synthesized by depositing AgBr on the surface of 4A zeolite via the one-step precipitation method. AgBr/zeolite with mass ratios of 1:1 exhibited the highest photocatalytic activity, resulting in the complete degradation of the methyl orange (MO) dye under visible-light irradiation for 30min. The photocatalysts were characterized by N₂ adsorption–desorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The AgBr particles around 4A zeolite were smaller than pure AgBr. The specific surface area of 1:1 AgBr/zeolite was much larger than that of pure AgBr, which indicates that 1:1 AgBr/zeolite possessed more active sites. The photocatalytic stability of 1:1 AgBr/zeolite was investigated, and MO degradation rate of 90.4% was achieved after five cycling runs. The trapping experiments showed that hydroxyl radical ($\cdot$OH), superoxide radical ($\cdot {\text{O}}_2^{-}$), and hole (h⁺) were the reactive species responsible for removing MO, and h⁺ played a key role in MO removal. A possible reaction mechanism in AgBr/zeolite photocatalytic system for MO degradation was proposed.