Latest ArticlesIt is generally recognized that the formation and accumulation of iron oxides on the surface of zero-valent iron (Fe0) resulting in significant decrease of contaminant degradation rates during the long-term reactions. However, in this study, we found that the removal efficiencies of p-nitrophenol (PNP) by micro zero-valent iron (mFe0) could maintain at the satisfactory level in the process of continuous reactions (20 cycles). The removal rate constant (0.1779 min-1) of the 5th cycle was 6.74 times higher than that of the 1st reaction (0.0264 min-1), even the 20th cycle (0.0371 min-1) was higher than that of the 1st reaction. Interestingly, almost no dissolved iron was detected in the solution, and the total iron concentrations decreased dramatically with the process of continuous reactions. The results of scanning electron microscope and energy dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD) revealed that the structure and composition of corrosion products change from amorphous to highly crystal with the increase of the number of cycles. The corrosion products were mainly magnetite (Fe3O4) and a small part of maghemite (γ-Fe2O3), which were in the form of microspheres on the surface of mFe0. The formation of surface oxidation shell hindered the release of Fe2+. X-ray photoelectron spectroscopy (XPS) results illustrated that partial Fe3O4 could be converted into γ-Fe2O3. Electrochemical analysis proved that the electron transfer rate of mFe0 increased with the formation of the oxides shell. However, the consumption of iron core and thicker oxide film weakened the electron transfer rate. Besides, the quenching experiments indicated that the reaction activity of mFe0 could be enhanced with the addition of scavengers. This study deepened the understanding of the structural transformation and radical production of mFe0 in continuous reactions.
Electrochemical analysis is a promising technique for detecting biotoxic and non-biodegradable heavy metals. This article proposes a novel composite electrode based on a polyaniline (PANi) framework doped with bismuth nanoparticle@graphene oxide multi-walled carbon nanotubes (Bi NPs@GO-MWCNTs) for the simultaneous detection of multiple heavy metal ions. Composite electrodes are prepared on screen-printed electrodes (SPCEs) using an efficient dispensing technique. We used a SM200SX-3A dispenser to load a laboratory-specific ink with optimized viscosity and adhesion to draw a pattern on the work area. The SPCE was used as substrate to facilitate cost-effective and more convenient real-time detection technology. Electrochemical techniques, such as cyclic voltammetry and differential pulse voltammetry, were used to demonstrate the sensing capabilities of the proposed sensor. The sensitivity, limit of detection, and linear range of the PANi-Bi NPs@GO-MWCNT electrode are 2.57×102 μA L μmol-1 cm-2, 0.01 nmol/L, and 0.01 nmol/L–5 mmol/L and 0.15×10-1 μA L μmol-1 cm-2, 0.5 nmol/L, and 0.5 nmol/L–5 mmol/L for mercury ion (Hg(Ⅱ)) and copper ion (Cu(Ⅱ)) detection, respectively. In addition, the electrode exhibits a good selectivity and repeatability for Hg(Ⅱ) and Cu(Ⅱ) sensing when tested in a complex heavy metal ion solution. The constructed electrode system exhibits a detection performance superior to similar methods and also increases the types of heavy metal ions that can be detected. Therefore, the proposed device can be used as an efficient sensor for the detection of multiple heavy metal ions in complex environments.
In this paper, a novel mesoporous silica gel evenly doped by Prussian blue nanoparticles (PBMSG) was successfully synthesized by using N, N-dimethylamide as template with a large Barrett-Emmett-Teller (BET) surface area of 505 m2/g and an average pore size of 2.9 nm. The static adsorption experiments showed that the equilibration time of PBMSG for Cs+ was about 30 min. The adsorption isotherm of PBMSG for Cs+ accorded with Langmuir model and the theoretical maximum adsorption capacity was 80.0±2.9 mg/g. When the initial concentration of Cs+ was 1.00 mg/L, the adsorption partition coefficient Kd could reach 3.5×104 mL/g After adsorption, Cs+ could be eluted by dilute hydrochloric acid (pH 2) with an efficiency of 89.8%, while no K+, Fe3+, Fe2+ was eluted. PBMSG exhibited good selectivity toward Cs+ and Rb+. In the presence of high concentration of K+, the selective adsorption of PBMSG could change the mass ratio of K+, Rb+ and Cs+ from 96.63:0.83:1.00–1.12:0.73:1.00. The separation of Cs+ and Rb+ from K+ with similar concentration (100 mg/g) was realized by column experiment. This indicated that PBMSG was suitable for rapid recovery of low concentration of rubidium and cesium from complex matrixes, such as wastewater and salt lake brine, etc.
Multiple pollutants including pathogenic microorganism contaminations and emerging organic contaminations (EOCs) have shown a growing threat to the environment, especially the natural waters. However, the control and removal of pathogenic microorganism contaminations and EOCs have been greatly limited since limited knowledge of their environmental behaviors. Thus, a novel and efficient photocatalyst Ag2O/BiOBr heterojunction was synthesized and used for removal of multiple pollutants including Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), tetracycline and acetaminophen under visible light. The results showed that there were valid electron transfer pathways between BiOBr and Ag2O, the main electron transfer direction was the BiOBr to Ag2O. Photo-generated electrons were stored in Ag2O and thus separation efficiency between holes and photo-generated electrons was obviously enhanced. Active oxygen species were highly produced and eventually end up with the high efficiency of removal of multiple pollutants. For Ag2O/BiOBr with Ag2O content at 3% (the best performance) under visible light, log decrease of E. coli was 7.16 (removal efficiency was 100%) in 120 min, log decrease of S. aureus was 7.23 (removal efficiency was 100%) in 160 min, C/C0 of tetracycline was 0.06 in 180 min, C/C0 of acetaminophen was 0.17 in 180 min. This work could provide a promising candidate in the actual contaminated natural waters for cleaning multiple pollutants.
Electrochemical detection is an efficient method for the detection of Bisphenol A (BPA). Herein, a sensitive photo-electrochemical sensor based on two-dimensional (2D) TiO2 (001) nanosheets was fabricated and then used for BPA electrochemical detection. Upon light irradiation, the 2D TiO2 (001) nanosheets electrode provided a lower detection limit of BPA detection compared with an ambient electrochemical determination. The low detection limit is ~5.37 nmol/L (S/N=3). Furthermore, profiting from the photoelectric characteristics, the 2D TiO2 (001) nanosheets electrode exhibits a nice regeneration property. After 45 min of light irradiation, the electrochemical signal was regenerated from 14.7% to 82.9% of the original signal at the 6th cycle. This is attributed to the non-selective ·OH mediation produced by the 2D TiO2 (001) nanosheets mineralizing anodic polymeric products and resuming surface reactive sites. This investigation indicates that photo-assistance is an efficient method to improve the electrochemical sensor for detecting BPA in water environments.
This study demonstrated interesting ultrafast activation of molecular O2 by copper oxide (CuO) particles and very rapid elimination of aqueous 2, 4-dichlorophenol (2, 4-DCP) within reaction time of 30 s. Electron paramagnetic resonance (EPR) characterization indicated that ·OH, Cu3+, 1O2 and O2·- were generated in the CuO/O2 systems, wherein O2·- would be the main reactive species responsible for 2, 4-DCP degradation. It was further found that the catalytic ability of CuO for O2 activation was highly size dependent and nano-CuO was far reactive than micro-CuO. H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analyses revealed that both the quantity and the reactivity of the surface reaction sites (surface Cu+ and O2) could determine the catalytic ability of CuO affecting efficient Cu+-based molecular oxygen activation. Moreover, the O2 activation ability of CuO would depend on not only the dimension, but also crystalline factors, for example, the exposed facets.
The high cost and low reserves of noble metals greatly hinder their practical applications in new energy production and conversion. The exploration of cost-effective alternative electrocatalysts with the ability to drive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is extremely significant to promote overall water splitting. Herein, ultrathin CoSe2/CNTs nanocomposites have been synthesized by a facile two-step method, where the ultrathin Co-MOF (metal organic-framework) decorated with cable-like carbon nanotubes (CNTs) (Co-MOF/CNTs) was initially fabricated, and followed a low-temperature selenization process. The ultrathin CoSe2 nanosheets as well as the superior conductivity of CNTs synergistically resulted in abundant active sites and enhanced conductivity to boost the electrocatalytic activity. The as-prepared CoSe2/CNTs electrocatalysts exhibited an overpotential of 190 mV and 300 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA/cm2 for the HER and OER in alkaline solution, respectively, and demonstrated superior durability. Furthermore, the as-prepared bifunctional CoSe2/CNTs electrocatalysts can act as cathode and anode in an electrolyzer, showing a cell voltage of 1.75 V at 10 mA/cm2 for overall water splitting.
This study aimed to construct a photoelectrocatalytic (PEC) reaction system based on the self-made reduced TiO2 NTAs (r-TNAs) photoanode and activated carbon/Polytetrafluoroethylene (AC/PTFE) cathode. It would be observed clearly that the degradation rate constant of carbamazepine (CBZ) over r-TNAs(photoanode)-AC/PTFE(cathode) PEC system (0.04961 min-1) was even higher than that of r-TNAs(photoanode)-Pt(cathode) PEC system (0.04602 min-1) with the assistance of visible light irradiation and +0.4 V external potential. Besides, in order to obtain optimized conditions, the influence of key parameters such as pH value, electric current density and electrolyte concentration were studied. Most importantly, photoelectrochemical (PECH) properties, reactive oxide species contribution, ·OH formation rate and CBZ degradation pathway were determined. The results illustrated that the excellent PEC degradation performance depended on the excellent photocatalytic property of r-TNAs photoanode and electron transfer property of photoelectrodes in r-TNAs(photoanode)-AC/PTFE(cathode) PEC system. Therefore, the study demonstrated that the r-TNAs(photoanode)-AC/PTFE(cathode) PEC system could be expected to replace metal-catalyzed cathodes depending on its excellent PEC performance activity and low cost as well as the reaction system possessed objective and practical application prospect.
In this work, the reduction of mercury ions (Hg2+) to elemental mercury (Hg0) was easily achieved using highly reductive carbon dots (r-CDs), which synthesized from sucrose by a simple and cost-effective method. After a careful mechanistic study, the reduction was probably accomplished with the large numbers of electrons contained in r-CDs rather than the oxidation of its functional groups. Additionally, a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed that the r-CDs were nontoxic to wildlife and human beings. Consequently, the r-CDs were used as an alternative to toxic reductants (SnCl2 or NaBH4) for the sensitive and in situ determination of mercury by cold vapor generation (CVG) coupled to a miniature point discharge optical emission spectrometer (μPD-OES). Limit of detection of 0.05 μg/L was obtained for Hg2+, with relative standard deviation (RSD) less than 5.4% at a concentration of 5 μg/L. The accuracy of r-CDs induced CVG-μPD-OES was validated by the determination of mercury in a certified reference material (DOLT-5, dogfish liver) and five natural water samples collected from different rivers and lakes in Chengdu City. Since r-CDs are nontoxic and prepared from abundant and inexpensive sucrose, the r-CDs induced CVG-μPD-OES retains the great potential for the inexpensive and environmentally friendly field analysis of mercury in natural water. The accuracy of the proposed method was validated by the analysis of a certified reference material and several water samples with satisfactory results.
The removal efficiency of pollutants in Fe(0) electrocoagulation (EC) has been associated closely with the speciation of generated Fe(II)/Fe(III) oxides during this process, which is very complicated and can be affected by various factors. In this work, in-situ Raman, X-ray diffraction and some other techniques have been used to study the speciation of Fe under different conditions and to establish a relationship between Fe speciation and Sb(V) removal efficiency. Results indicated that concentration of dissolved oxygen (DO) is a key factor influencing Fe(0) EC. It was found that green rusts (GRs) were formed and were then transformed into magnetite at lower DO concentration, and Sb(V) removal efficiency reached 99.9% after 30 min of EC. In contrast, γ-FeOOH was formed at high DO concentration, and the removal efficiency of Sb(V) after 30 min of EC was only 72.8%. In the presence of sulfite and phosphate with low concentrations, GRs can be stabilized and benefit the removal of Sb(V). We believe this work will provide some new insights on the mechanism of Fe(0) EC and the effective removal of other pollutants during Fe(0) EC process.
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