A low-cost semiconductor-based photocatalyst using visible light energy has attracted increasing interest for energy generation and environmental remediation. Herein, plasmonic Bi metal was deposited in situ in g-C3N4@Bi2WO6 microspheres via a hydrothermal method. As an electron-conduction bridge, metallic Bi was inserted as the interlayer between g-C3N4 and the surface of Bi2WO6 microspheres to enhance visible light absorption due to the surface plasmon resonance (SPR) effect and facilitate efficient electron-carrier separation. Different characterization techniques, including XRD, SEM, TEM, UV–vis, XPS, photoluminescence, and photocurrent generation, were employed to investigate the morphology and optical properties of the as-prepared samples. The results indicated that the g-C3N4(20%)@Bi@Bi2WO6 microsphere sample exhibited an extraordinary enhanced photocatalytic activity, higher than those of the g-C3N4, Bi2WO6, and g-C3N4(20%)@Bi2WO6 samples. It implies that the heterostructured combination of g-C3N4, metallic Bi, and Bi2WO6 microspheres provided synergistic photocatalytic activity via an efficient electron transfer process. On the basis of the results, a possible photocatalytic mechanism of the as-prepared samples was proposed. The present study demonstrated the feasibility of utilizing low-cost metallic Bi as a substitute for noble metals to design a doped photocatalysis composite with enhanced photocatalytic performance.Keywords: Bi2WO6 microspheres; charge separation; g-C3N4; plasmonic Bi metal; SPR effect;

•A novel atomic scale g-C3N4/Bi2WO6 heterojunction (UTCB) was synthesized by a simple and efficient way.•Effective charge transfer across substantial heterojunction interface.•The large specific area of the ultrathin heterojunction providing more active sites.•Higher photocatalytic efficiency toward ibuprofen.•Four photodegradation pathways of ibuprofen under visible light irradiation were proposed.Although photocatalytic degradation is an ideal strategy for cleaning environmental pollution, it remains challenging to construct a highly efficient photocatalytic system by steering the charge flow in a precise manner. In this study, a novel atomic scale g-C3N4/Bi2WO6 heterojunction (UTCB) constructed by ultrathin g-C3N4 nanosheets (ug-CN) and monolayer Bi2WO6 nanosheets (m-BWO) was successfully prepared by hydrothermal reaction. The UTCB heterojunctions were characterized by various techniques including XRD, TEM, AFM, BET measurements, UV–vis spectrometry, and XPS. The results indicated that UTCB heterojunctions were assembly of m-BWO on ug-CN and presented high separation efficiency of photogenerated carriers. Under visible light irradiation, the optimum molar ratio of ug-CN/m-BWO (1:4, UTCB-25) reached almost 96.1% removal efficiency of IBF within 1 h, which was about 2.7 times as that of pure m-BWO. The photocatalytic mechanisms of UTCB-25 were revealed, suggesting that the synergistic effect of UTCB-25 heterojunction with strong interfacial interaction promoted the photoinduced charge separation. According to the LC–MS/MS, five photodegradation pathways of IBF under visible light irradiation were proposed. This study could open new opportunities for the rational design and a better understanding of atomic scale two dimensions/two dimensions (2D/2D) heterojunctions in environmental or other applications.Download high-res image (163KB)Download full-size image

The photocatalytic degradation of norfloxacin by bismuth tungstate (Bi2WO6) with different hierarchical architectures was investigated under visible light irradiation. Bi2WO6 was prepared by hydrothermal method with the reaction solution pH ranging from 4 to11. The relatively ultrathin Bi2WO6 nanoflakes prepared at pH 4 showed excellent adsorption and photodegradation efficiency towards norfloxacin. The characterization results showed that Bi2WO6 prepared at pH 4 had a larger specific area and faster photo-generated carrier separation rate. The decay rate reached the maximum in weak alkaline reaction solution, which could be attributed to the presence of moderate OH− anions. The present study demonstrated that the smaller size of Bi2WO6 could be an efficient photocatalyst on the degradation of norfloxacin in the aquatic environment.

Noble metal nanoparticles (NPs) applied in heterogeneous catalysis have attracted considerable attention due to their highly efficient catalytic performance. Pd/Au bimetallic NPs were successfully decorated on the ultrathin graphitic carbon nitride nanosheets (g-C3N4-N) by a facile one-pot deposition reduction method. The obtained results show that Pd/Au NPs with average diameter around 8 nm are homogeneously dispersed on the surface of unmodified g-C3N4-N. The obtained materials were characterized via transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). In addition, considering the large surface area and special π-bonded planar structure, the unique ultrathin g-C3N4-N behave as an excellent carrier and stabilizer in this synthesis. The as-synthesized Pd/Au bimetallic nanohybrids show superior catalytic performance and stability for reduction of p-nitrophenol (p-NP), which is better than either of pure Pd or Au nanohybrids. Besides, the catalytic activities of Pd/Au@g-C3N4-N nanohybrids were found to be controlled by altering the Pd versus Au mass ratio in the preparation process.Download high-res image (71KB)Download full-size image

In this work, to gain insight into the mechanism of p-nitrophenol (PNP) removal using the reactivity of a biochar supported nanoscale zerovalent iron composite (nZVI/biochar) and nanoscale zero valent iron (nZVI) under anaerobic or aerobic conditions, batch experiments and models were conducted. The PNP removal rate in the more acidic solutions was higher, while it was significantly suppressed at higher pH, especially at pH 9.0. The peak value of the apparent rate constants suggests that the reactivity of nZVI/biochar could be much stronger than that of nZVI under the same aeration conditions. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using nZVI/biochar or nZVI. The reaction constants obtained through a Langmuir–Hinshelwood mechanism under different aeration conditions followed the trend nZVI/biochar (N2) > nZVI/biochar (air) > nZVI (N2) > nZVI (air), indicating that nZVI/biochar under anaerobic conditions exhibits enhanced activity for the degradation of PNP. The nZVI/biochar under anaerobic conditions has the lowest Arrhenius activation energy of PNP degradation–adsorption, suggesting that the surface interaction of eliminating PNP has a low energy barrier. In addition, TOC removal under anaerobic conditions was negligible compared with that under the aerobic system and the total number of iron ions leaching at solution pH 3.0 in the nZVI/biochar or nZVI system under air aeration conditions was much higher than that under nitrogen aeration conditions. The profiles of the intermediates formed during the PNP degradation indicated that in the anaerobic environment, reduction was the predominant step in the removal process, while the degradation of PNP could be regarded as a combination of oxidation and reduction in an aerobic environment.

Aiming at developing a safe and efficient alternative to traditional drinking water disinfection, this work successfully synthesized a novel antibacterial material with high surface area, ultra large pore size and tunable loading of immobilized lysozyme. The immobilized enzymes exhibit high antibacterial efficacy without forming carcinogenic disinfection byproducts. Critical immobilization parameters were optimized to keep the activity of the immobilized enzyme at a high level. The immobilization of lysozymes on 3DOm COOH could be confirmed by the characterizations of transmission electron microscopy, X-ray diffraction and Zeta-Potential. In addition, the structural stability of lysozymes on 3DOm COOH were studied by Fourier transform infrared spectroscopy. The antibacterial performance of 3DOm COOH-Lyz were specifically investigated based on the disinfection efficacy of Staphylococcus aureus in water. The results revealed that the immobilization capacity and relative activity of immobilized lysozyme were 814 mg/g carrier and 80%, respectively, under the optimal immobilization conditions. And the antibacterial material with the initial mass ratio of lysozyme and 3DOm COOH as 3:1 exhibited maximum bacteria removal efficiency (98.1%) at pH 5. Moreover, the reusability test indicated that 3DOm COOH-Lyz has certain operational stability, and remains 82% bacterial removal efficiency even in the fifth cycle, which provides a promising application for safe and efficient drinking water disinfection in small-scale and emergency water treatment.Download high-res image (142KB)Download full-size image

•Phosphorus doped porous ultrathin g-C3N4 nanosheets (PCN-S) was prepared successfully.•P doping can greatly broaden the visible light response region of PCN-S.•Porous and ultrathin structure can increase the specific surface area of PCN-S.•PCN-S presents enhanced redox ability for the simultaneous removal of Cr(VI) and 2,4-DCP.•The synergistic effect of Cr(VI) and 2,4-DCP has been systematic studied.Carbon nitride (g-C3N4) has attracted great attention for its wide applications in hydrogen evolution and photocatalytic degradation. In this study, phosphorus doped porous ultrathin carbon nitride nanosheets (PCN-S) were prepared successfully via the element doping and thermal exfoliation method. The prepared PCN-S was characterized by XRD, SEM, TEM, N2-adsorption-desorption measurement, FT-IR, XPS, UV–vis diffuse reflectance spectra, photoluminescence (PL), photocurrent response (I-t) and EIS. The results show that PCN-S owns regular crystal structure of g-C3N4, large specific surface areas and nanosheet structure with lots of in-plane pores on its surface, excellent chemical stability, and broad light response to the whole visible light region, which was attributed to the doping of phosphorus element. Under visible light irradiation, the photocatalytic reduction of Cr(VI) over different samples indicated that the P doping and porous nanosheet structure play an important role for the enhanced performance of PCN-S. The reason was that P element doping can broaden the visible light response region, and large specific surface areas from the porous nanosheet structure can provide quantities of active sites for the photocatalytic reaction. Then the detailed study on the PCN-S for simultaneous photocatalytic reduction of Cr(VI) and oxidation of 2,4-diclorophenol (2,4-DCP) was conducted. The experiments results show that low pH value and enough dissolved oxygen were found to promote Cr(VI) reduction and 2,4-DCP oxidation. The detailed photocatalytic mechanism was proposed. The strategies used in this study could provide new insight into the design of g-C3N4 based materials with high photocatalytic activity, and present potential for the treatment of Cr(VI)/2,4-DCP or other mixed pollutants in wastewater.Download high-res image (201KB)Download full-size image

•NPG combined with GR–5DNAzyme and AQDS created simple detection strategy.•An anionic intercalator was used as indicator for lead ions detection.•The mechanism of the GR–5DNAzyme–based electrochemical sensor was revealed.•The sensor showed a promising potential for the detecting of Pb2+ in real sample.A label–free electrochemical sensor, based on a classic lead ions (Pb2+)–dependent GR–5DNAzyme as the catalytic unit, disodium–anthraquinone–2,6–disulfonate (AQDS) as DNA intercalator, and nanoporous gold (NPG) for signal amplification, was designed for sensitive and selective detection of Pb2+. Firstly, NPG modified electrode surface were employed as a platform for the immobilization of thiolated probe DNA, and then, hybridized with DNAzyme catalytic beacons. The Pb2+–induced catalytic reaction makes the substrate strand break at the cleavage sitGe irreversibly, which disturbs the formation of DNA strands. AQDS served as an indicator that intercalated into the base–pairing regions of DNAzyme, resulting in a strong electrochemical signal. In the presence of Pb2+, the complementary regions were reduced, due to the fracture of the DNA strand, resulting in the release of AQDS. And a decreased current was obtained, corresponding to Pb2+ concentration. Taking advantage of the amplification effect of NPG electrode for increasing the reaction sites of thiol modified capture probe, the proposed electrochemical biosensor could detect Pb2+ quantitatively, in the range of 1–120 nM, with a limit of detection as low as 0.02 nM, which is much lower than the maximum contamination level for Pb2+ in drinking water defined by the U.S. Environmental Protection Agency. The electrochemical sensor was also used to detect Pb2+ from real water samples, and the results showed excellent agreement with the values determined by inductively coupled plasma mass spectroscopy. This biosensor showed a promising potential for on–site detecting Pb2+ in aqueous environment.

The utilization of solar energy based on semiconductor photocatalysts for pollutant removal and environmental remediation has become a research hot spot and attracted great attention. In this study, a novel ternary BiVO4/Ag/Cu2O nanocomposite has been successfully synthesized via simple wet impregnation of Cu2O particles coupled with a subsequent photo-reduction pathway for the deposition of metallic Ag on the surface of BiVO4. The resulting BiVO4/Ag/Cu2O photocatalyst was used for the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). Results showed that the coating contents of the Cu2O and Ag particles presented a great effect on the eventual photocatalytic activity of the photocatalysts, and the optimum coating contents of Cu2O and Ag were obtained with their mass ratios of 3% and 2%, respectively. Under optimum conditions, nearly 91.22% TC removal efficiency was obtained based on ternary BiVO4/Ag/Cu2O nanocomposites, higher than that of pure BiVO4 (42.9%) and binary BiVO4/Cu2O (65.17%) and BiVO4/Ag (72.63%) nanocomposites. Meanwhile, the enhanced total organic carbon (TOC) removal efficiency also indicated the excellent photocatalytic degradation ability of the BiVO4/Ag/Cu2O nanocomposites. As for their practical application, the effects of initial TC concentration, various supporting electrolytes and different irradiation conditions were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs) was used to show the by-products of TC molecule degradation. Cycling experiments indicated the high stability of the as-prepared photocatalysts. Furthermore, the results obtained from radical trapping experiments and ESR measurements suggested that the photocatalytic degradation of TC in the BiVO4/Ag/Cu2O based photocatalytic system was the joint action of the photogenerated holes (h+), superoxide radical (˙O2−) and hydroxyl radical (˙OH). The enhanced photocatalytic activity of BiVO4/Ag/Cu2O was attributed to the synergistic effect of Cu2O, Ag and BiVO4, especially the surface plasmon resonance effect and the established local electric field brought about by metallic Ag. Additionally, to deeply understand the reaction mechanism, a dual Z-scheme charge transfer pathway has been proposed.

Palladium/iron (Pd/Fe) bimetallic nanoparticles were embedded within phosphorus-doped ordered mesoporous carbons (Pd/NZVI@P) with high dechlorination activity for 2,4-dichlorophenol (2,4-DCP). The Pd/Fe bimetal nanoparticles of about 15 nm diameter embedded in phosphorus-doped ordered mesoporous carbons (P-OMCs) were homogeneously distributed. The high dechlorination activity was mainly attributed to the homogeneous distribution of Pd/Fe bimetal nanoparticles, which were characterized by transmission electron microscopy (TEM) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) with image mapping. Dechlorination kinetics indicated that the dechlorination rates of 2,4-DCP increased with the increasing of Pd content. The use of P-OMCs as supporting materials to embed enough Pd/Fe bimetal nanoparticles kept the nanoparticles highly active and stable. Besides, solution pH had a significant effect on the dechlorination of 2,4-DCP and the passivation of the Pd/NZVI@P samples. The effects of the number and position of chlorine atoms for different chlorophenols (CPs) on the dechlorination activity were also revealed; the result indicated that the dechlorination of CPs by catalytic reduction preferentially begins from the para-position of the ring, and more chlorine atoms of CPs are favorable for the occurrence of the dechlorination reaction. This study demonstrated that P-OMC is a promising supporting material for the preparation of some effective composite metals for the catalytic dechlorination of CPs.

Iron nanoparticle-doped magnetic ordered mesoporous carbon (Fe/OMC) was prepared by co-impregnation and carbothermal reduction methods, and used for highly effective adsorption and degradation of bisphenol A (BPA). Several techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption isotherms were applied to characterize the prepared composites. Batch experiments were conducted to explore the decontamination performance, and the results showed that the removal capacity can reach an equilibrium value of 311 mg g−1 at an initial BPA concentration of 200 mg L−1. Kinetic study showed that it agreed well with the pseudo-second-order model (R2 = 0.999). In addition, the Langmuir and Freundlich models were used to describe the removal process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the existence of Fe0 nanoparticles in the obtained composites. The mechanism of interaction between Fe/OMC and BPA was investigated by Fourier transform infrared spectrometry (FTIR), XRD and XPS analyses. Furthermore, thermodynamics studies were carried out and the exhausted composites could be regenerated with ethanol and easily separated with a magnet.

•CdS and Cu2S quantum dots were doped on TiO2 branched nanorod arrays successfully.•The utilization efficiency of light has been significantly improved.•The formed heterostructure increased the separate efficiency of electron–hole pairs.•The whole performance of the PEC water splitting system has been improved.This paper described a facile method for the design and utilization of three-dimensional TiO2 branched nanorod arrays with CdS and Cu2S quantum dots co-sensitized photoelectrode for photoelectrochemical water splitting. CdS and Cu2S quantum dots were attached on the surface of TiO2 BNRs by successive ionic layer adsorption and reaction (SILAR). The morphology and element composition of the fabricated samples were characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and the optical features were measured by UV–vis diffuse reflection spectroscopy (UV–vis DRS) and photocurrent density–voltage (I–V) curves. The photocurrent value can be significantly enhanced due to the introduction of CdS and Cu2S quantum dots on the TiO2 BNRs surface. The 9 cycles of CdS and 6 cycles of Cu2S presented the best performance and reached a high photocurrent density to 13.65 mA at 0 V versus Ag/AgCl and hydrogen generation efficiency of 7.74% at −0.467 V versus Ag/AgCl. This enhancement can be attributed to the improved light absorption and the heterojunction formed between CdS and Cu2S, which can greatly promote the introduction and transportation of the photo electrons. This work provided a facile way for the synthesis of high performance photoelectrode for photoelectrochemical water splitting.Download high-res image (381KB)Download full-size image

•OMC–GNPs was synthesized and then applied to improve DNA sensing efficiency.•Label free impedimetric sensing system was developed for the determination of Pb2+.•The mechanism of the DNAzyme-based electrochemical sensor was revealed.•This method could be extended for the analysis of various metal ions–DNAzymes.A novel label-free impedimetric sensing system based on DNAzyme and ordered mesoporous carbon–gold nanoparticle (OMC–GNPs) for the determination of Pb2+ concentration was developed in the present study. Firstly, gold nanoparticles deposited on the modified electrode surface were employed as a platform for the immobilization of thiolated probe DNA, and then hybridized with DNAzyme catalytic beacons. Subsequently, in the presence of Pb2+, the DNAzyme could be activated to cleave the substrate strand into two DNA fragments, which causes differences in the electrical properties of the film. Randles equivalent circuit was employed to evaluate the electrochemical impedance spectroscopy (EIS) result. The charge transfer resistance (RCT) value for the [Fe(CN)6]3−/4− redox indicator was remarkably decline after hybridization with Pb2+. The difference in RCT values before and after hybridization with Pb2+ showed a linear relation with the concentration of the Pb2+ in a range of 5×10−10–5×10−5 M, with a detection limit of 2×10−10 M (S/N=3). Furthermore, with the application of Pb2+ dependent 8-17DNAzyme, the proposed sensing system exhibited high selectivity without using any labeled probes. This biosensor demonstrated a promising potential for Pb2+ detection in real sample.

•Incorporating DNAzymes/DNA and nanomaterials greatly improves sensor performance.•Recent progress in various sensing configuration and mechanisms of the nano-biosensors.•More indepth study on DNA structure change and metal ion selectivity is required.Heavy metal pollution is one of the most serious concerns to human health because these substances are toxic and retained by the ecological system. Many efforts have been taken over the past few years for the detection of heavy metal ions in the environment. Incorporation of DNAzymes/DNA molecules (including T–T or C–C mismatches and G-quadruplexes) and nanomaterials into sensors can lead to significant improvement in the performance of sensors in terms of sensitivity, selectivity, multiplexed detection capability and portability. This review presents a recent advance in biosensors based on DNAzymes/DNA molecules functionalized nanostructures for heavy metal detection. Furthermore, advances in biosensing devices/chip based on this method for the detection of metal ions are summarized. This paper highlights the strategies for design of heavy metal biosensors benefiting from the use of DNAzymes/DNA molecules and nanomaterials.

•A Z-scheme Ag2CrO4/g-C3N4-N photocatalyst was prepared successfully;.•The high surface areas of the g-C3N4-N can prevent the aggregation of Ag2CrO4 nanoparticles;.•The synergistic effect between Ag2CrO4 and g-C3N4-N promoted the separation of charges;.•Enhanced photocatalysis was achieved via Z-scheme Ag2CrO4/g-C3N4-N photocatalysts.Graphite-like carbon nitride (g-C3N4) and silver-based compounds have attracted considerable attentions due to their excellent optical characteristic and photocatalytic performance. In this work, Z-scheme silver chromate-g-C3N4 nanosheets photocatalysts were prepared by binding growth of Ag2CrO4 nanoparticles on the surface of g-C3N4 nanosheets (g-C3N4-N) via a facile precipitation method. The morphologies, structure, specific surface area and optical property of the prepared photocatalysts were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-vis DRS) and photoluminescence (PL) spectra. The photocatalytic performances of the prepared Ag2CrO4/g-C3N4-N were evaluated by photodegradation of methyl orange (MO) and rhodamine B (RhB) under visible light irradiation (λ > 400 nm). The experiment results indicated that Ag2CrO4/g-C3N4-N composites presented enhanced photocatalytic activity and stability in the degradation of the dye contaminants in aqueous solution. The optimal composites with the mass ratio of Ag2CrO4 to g-C3N4-N as 50% (CNA-50) showed the highest photocatalytic activity for MO degradation, which is 5.9 and 10.8 times than those of pure Ag2CrO4 and pure g-C3N4-N, respectively. The formation of Ag2CrO4/g-C3N4-N Z-scheme heterojunction contributed to the improved photodegradation efficiency, which can not only promote the separation and transportation efficiencies of the photogenerated electron-hole pairs, but also present strong redox ability. And meanwhile the excellent transportation efficiency of the photogenerated electrons from Ag2CrO4 to g-C3N4-N greatly hindered the photocorrosion of Ag2CrO4 nanoparticles. This work provides a new understanding into the mechanism of the g-C3N4-N based composite and gives a new insight into the design and fabrication of Z-scheme photocatalysts.

A highly efficient method for removal of p-nitrophenol and its conversion p-aminophenol from water was proposed using a novel catalyst–adsorbent composite of gold nanoparticles supported on functionalized mesoporous carbon (Au@CMK-3-O). The immobilized gold nanoparticles presented excellent catalytic ability to converse p-nitrophenol into p-aminophenol with the help of sodium borohydride, and the oxidized mesoporous carbon (CMK-3-O) serving as both carrier and adsorbent also exhibited high efficiency to remove p-aminophenol. The morphology and structure of the composite were characterized via SEM, TEM, FTIR and XPS analysis. Moreover, the mechanism of reaction process and the parameters of kinetics and thermodynamics were investigated. The activation energy was figured as 86.8 kJ mol−1 for the adsorption and reduction of p-nitrophenol to p-aminophenol. The thermodynamic analysis based on the rate constants evaluated by pseudo-first-order model reveals that the adsorption–reduction process is an endothermic procedure with the rise of randomness. The anti-oxidation and regeneration study indicates that Au@CMK-3-O can be reused for 6 times with more than 90% conversion efficiency and keep high activity after exposing in air for 1 month, which possesses great prospects in application of nitroaromatic pollutant removal.

An electrochemical sensor was developed for attomolar Hg2+ detection. Three single-stranded DNA probes were rationally designed for selective and sensitive detection of the target, which combined T-Hg2+-T coordination chemistry and the characteristic of convenient modification of electrochemical signal indicator. Graphene and nanoAu were successively electrodeposited on a glass carbon electrode surface to improve the electrode conductivity and functionalize with the 10-mer thymine-rich DNA probe (P1). NanoAu carriers functionalized with 29-mer guanine-rich DNA probe (P3) labeled methyl blue (MB-nanoAu-P 3s) were used to further strengthen signal response. In the presence of Hg2+, a T-T mismatched dsDNA would occur between P1 and a 22-mer thymine-rich DNA probe (P2) on the electrode surface due to T-Hg2+-T coordination chemistry. Followed by adding the MB-nanoAu-P 3s for hybridization with P2, square wave voltammetry was executed. Under optimal conditions, Hg2+ could be detected in the range from 1.0 aM to 100 nM with a detection limit of 0.001 aM. Selectivity measurements reveal that the sensor is specific for Hg2+ even with interference by high concentrations of other metal ions. Three different environmental samples were analyzed by the sensor and the results were compared with that from an atomic fluorescence spectrometry. The developed sensor was demonstrated to achieve excellent detectability. It may be applied to development of ultrasensitive detection strategies.

This study demonstrates a novel biosensor for silver(I) ion detection based on nanoporous gold (NPG) and duplex-like DNA scaffolds with anionic intercalator. The hairpin structure was formed initially through hybridization with the unlabeled probe (S1 + S2 + S3). In the presence of Ag+, the structure of immobilized DNA changed to duplex-like structure, and formed a C–Ag+–C complex at electrode surface. The response current of the modified electrode after immersing in the disodium anthraquinone-2,6-disulfonate (AQDS) as the signal agent was changed. And an increased current was obtained, corresponding to Ag+ concentration. NPG provided faster electron transfer and an excellent platform for DNA immobilization. Under optimal conditions, silver(I) ion could be detected in the range from 1 × 10−10 M to 1 × 10−6 M, and the lower detection limit of the biosensor for Ag+ is 4.8 × 10−11 M with good specificity. The results showed that this novel approach provided a reliable method for the quantification of Ag+ with sensitivity and specificity, which was potential for practical applications.

Mesoporous carbon nitride was synthesized and then applied to construct biosensor.Using enzyme-scaffolded-gold nanoclusters to construct this biosensor.The mechanism for the biosensor was revealed.The proposed approach would be attractive for the analysis of MnP genes.This work has demonstrated an amplified and selective detection platform using enzyme-scaffolded-gold nanoclusters as signal label, coupling with mesoporous carbon nitride (MCN) and gold nanoparticles (GNPs) modified glassy carbon electrode (GCE). Streptavidin-horseradish peroxidase (SA-HRP) has been integrated with gold nanoclusters (GNCs) as scaffold using a simple, fast and non-toxic method. The mechanisms of enzymatic amplification, redox cycling and signal amplification by this biosensor were discussed in detail. GNCs might perform important roles as electrocatalyst as well as electron transducer in these processes. The concentrations of reagents and the reaction times of these reagents were optimized to improve the analytical performances. Under the optimized condition, the signal response to enzyme-scaffolded-gold nanoclusters catalyzed reaction was linearly related to the natural logarithm of the target nucleic acid concentration in the range from 10−17 M to 10–9 M with a correlation coefficient of 0.9946, and the detection limit was 8.0×10−18 M (S/N=3). Besides, synthesized oligonucleotide as well as Phanerochaete chrysosporium MnP fragments amplified using polymerase chain reaction and digested by restriction endonucleases were tested. Furthermore, this biosensor exhibited good precision, stability, sensitivity, and selectivity, and discriminated satisfactorily against mismatched nucleic acid samples of similar lengths.

This study demonstrates a new, unlabeled immobilized DNA-based biosensor with ordered mesoporous carbon nitride material (MCN) for the detection of Ag+ by electrochemical impedance spectroscopy (EIS) with [Fe(CN)6]4−/3− as the redox couple. The unlabeled immobilized DNA initially formed the hairpin-like structure through hybridization with the probe, and then changed to duplex-like structure upon interaction with Ag+ in solution to form a C–Ag+–C complex at electrode surface. As a result, the interfacial charge-transfer resistance of the electrode towards the [Fe(CN)6]4−/3− redox couple was changed. Thus, a declined charge transfer resistance (Rct) was obtained, corresponding to Ag+ concentration. MCN provide an excellent platform for DNA immobilization and faster electron transfer. Impedance data were analyzed with the help of Randles equivalent circuit. The lower detection limit of the biosensor for Ag+ is 5 × 10−11 M with good specificity. All results showed that this novel approach provides a reliable method for Ag+ detection with sensitivity and specificity, potentially useful for practical applications. Moreover, other DNA detection methods for more heavy metals may be obtained from this idea and applied in the environmental field.

Magnetic mesoporous carbon incorporated with polyaniline (PANI–Fe/OMC) is developed for enhanced adsorption and reduction of toxic Cr(VI) to non-toxic Cr(III). Several physicochemical techniques including TEM, FTIR and XPS analyses confirmed that magnetic iron nanoparticles and amino groups have been successfully bound on the mesoporous matrix. The adsorption capacity of the functionalized material is two- and ten-fold that of the magnetic mesoporous carbon (Fe/OMC) and pristine mesoporous silicon (SBA-15), respectively. Solution pH exhibited a remarkable impact on the Cr(VI) adsorption and the maximum uptake amount (172.33 mg g−1) occurred at pH 2.0. The good fitting of adsorption process using pseudo-second-order and Langmuir models indicated the chemisorption process of Cr(VI) removal. The regeneration study revealed that PANI–Fe/OMC can be reused without loss of their activity in repetitive adsorption tests. Moreover, the resultant adsorbent can be effectively applied in actual wastewater treatment due to the excellent removal performance in fixed-bed column and real water samples. The interaction between Cr(VI) and PANI–Fe/OMC was investigated by FTIR and XPS analyses. The results indicate that the amino groups on the surface of PANI–Fe/OMC are involved in Cr(VI) uptake, and simultaneously some toxic Cr(VI) are reduced to non-toxic Cr(III) during the removal process.

Mercury, one of the most widespread highly toxic heavy metals, has severe detrimental effects on human health and the environment. It is significant to develop a sensitive and reliable method of accurately detecting trace levels of mercuric ions in environmental media to meet the ever-increasing demands of ongoing environmental monitoring programs. A three-dimensional mercuric ion sensor was constructed using mercury-specific oligonucleotides, gold nanoclusters, and an anionic intercalator. Due to the steric reaction field in the electrode surface microenvironment formed by the gold nanoclusters, the sensor could spatially capture mercuric ions with electroactive indication to realize trace mercury measurements with high sensitivity; the sensor exhibited strong environmental adaptability, high selectivity, and other advantages. Under optimal conditions, mercuric ions could be detected in the range from 0.05 to 350 nM, and the detection limit was 0.01 nM. The mercuric ion sensor was compared with atomic fluorescence spectrometry to analyze municipal wastewater and river water samples. In addition, the sensor performance was also analyzed according to derived formulae. This accurate method has the potential to be deployed in the field for measurements of mercury in environmental media.

A biosensor based on tyrosinase immobilized with ordered mesoporous carbon–Au (OMC–Au), L-lysine membrane and Au nanoparticles (tyrosinase/OMC–Au/L-lysine/Au) was combined with artificial neural networks (ANNs) for the simultaneous determination of catechol (CC) and hydroquinone (HQ) in compost bioremediation of municipal solid waste. The good performance of biosensor provided the potential applicability for the simultaneous identification and quantification of catechol and hydroquinone in real samples, and the combination with ANNs offered a good chemometric tool for data analysis in respect to the dynamic, nonlinear, and uncertain characteristics of the complex composting system. Good prediction ability was attained after the ANNs model optimization, and the direct detection range for catechol and hydroquinone were directly analyzed by the ANNs model and varied between 1.0 × 10−7 and 1.1 × 10−4 M, significantly extended compared to the linear model (4.0 × 10−7 to 8.0 × 10−5 M). Finally, the performance of the ANNs model was compared with the linear regression model. The results demonstrate that the prediction results by the ANNs model are more precise than those by the linear regression, and the latter was far from accurate at high levels of catechol and hydroquinone beyond the linear range. All the results show that the combination of the biosensor and ANNs is a rapid and sensitive method in the quantitative study of composting system.

•Mesoporous carbon nitride (MCN) was synthesized, and then applied to construct the biosensor with the immobilized enzyme firstly.•Fabrication process, characterizations, and sensing mechanism (the lower detection limit, different linear range and sensitivity) of the enzyme-based biosensor based on MCN are revealed.•Searching for the interference effect between catechol and phenol, and other interferent especially hydroquinone firstly.•The enzyme-based biosensor has potential applications in detecting catechol and phenol in compost extracts.Herein, we reported here a promising biosensor by taking advantage of the unique ordered mesoporous carbon nitride material (MCN) to convert the recognition information into a detectable signal with enzyme firstly, which could realize the sensitive, especially, selective detection of catechol and phenol in compost bioremediation samples. The mechanism including the MCN based on electrochemical, biosensor assembly, enzyme immobilization, and enzyme kinetics (elucidating the lower detection limit, different linear range and sensitivity) was discussed in detail. Under optimal conditions, GCE/MCN/Tyr biosensor was evaluated by chronoamperometry measurements and the reduction current of phenol and catechol was proportional to their concentration in the range of 5.00×10−8–9.50×10−6 M and 5.00×10−8–1.25×10−5 M with a correlation coefficient of 0.9991 and 0.9881, respectively. The detection limits of catechol and phenol were 10.24 nM and 15.00 nM (S/N=3), respectively. Besides, the data obtained from interference experiments indicated that the biosensor had good specificity. All the results showed that this material is suitable for load enzyme and applied to the biosensor due to the proposed biosensor exhibited improved analytical performances in terms of the detection limit and specificity, provided a powerful tool for rapid, sensitive, especially, selective monitoring of catechol and phenol simultaneously. Moreover, the obtained results may open the way to other MCN–enzyme applications in the environmental field.

A novel biosensor was developed based on tyrosinase immobilization with ordered mesoporous carbon–Au (OMC–Au), L-lysine membrane and Au nanoparticles on a glassy carbon electrode (GCE). It was applied for the simultaneous determination of dihydroxybenzene isomers using differential pulse voltammetry (DPV). The tyrosinase/OMC–Au/L-lysine/Au film was characterized by scanning electron microscopy (SEM) and impedance spectra. Under optimized conditions, the DPV study results for two isomers, hydroquinone (HQ, 1,4-dihydroxybenzene) and catechol (CC, 1,2-dihydroxybenzene) showed low peak potentials, and the peak-to-peak difference was about 135.85 mV, which ensured the anti-interference ability of the biosensor and made simultaneous detection of dihydroxybenzene isomers possible in real samples. DPV peak currents increased linearly with concentration over the range of 4.0 × 10−7 to 8.0 × 10−5 M, and the detection limits of hydroquinone and catechol were 5 × 10−8 M and 2.5 × 10−8 M (S/N = 3), respectively. The tyrosinase biosensor exhibited good repeatability and stability. In addition, the response mechanism of enzyme catalysed redox on the OMC–Au/L-lysine/Au film modified electrode based on electrochemical study was discussed. The proposed method could be extended for the development of other enzyme-based biosensors.

A magnetic separation and detection method for a target sequence of a gene encoding cellulase using biocompatible core–shell nanoparticle probes was developed. An aminated capture probe was conjugated with biocompatible Fe3O4–SiO2–Au core–shell nanoparticles. The target probe and signal probe were hybridized with the capture probe on the surface of the inorganic DNA carrier, which resulted in core–shell nanoparticle probes. In the presence of an external magnetic field, it is convenient and time-saving to realize the detection of the cellulase gene in Trichoderma reesei (T. reesei) by liquid fermentation and subsequent magnetic separation. Quantitative PCR (Q-PCR) was performed to give absolute quantification of the concentration of the target nucleic acid, and the Q-PCR result was compared to that of the electrochemical method. The optimized experimental conditions were studied to maximize the hybridization efficiency and detection sensitivity. The amperometric current response was linearly related to the common logarithm of the target nucleic acid concentration in the range of 1.0 × 10−13 to 1.0 × 10−9 M, with a detection limit of 1.2 × 10−14 M.

We have developed an optical assay for NADH (Dihydronicotinamide adenine dinucleotide) based on the catalytic growth of gold–silver core–shell nanoparticles (Au–Ag–CSNPs). The nanoparticles were immobilized on pretreated glass slide and are shown to catalyze the NADH-mediated reduction of Ag(I) ions in the presence of 1,4-benzoquinone and cetyltrimethyl ammonium ion. This leads to the formation of Au–Ag–CSNPs on the glass. The absorption peak of the Au–Ag–CSNPs at 415 nm increases with the concentration of NADH in the solution used, and this can be measured by UV–vis photometry. High-resolution scanning electron microscopy analysis of the morphology of the surface of the Au–Ag–CSNPs before and after the catalytic reaction revealed a growth of their diameter. Under optimal conditions, NADH can be determined in the concentration range from 0.2 to 3.2 mM, and the detection limit is 15.6 μM. The sensor has good precision and good storage stability, simple in operation, and can be fabricated at low costs, which made it suitable for the determination of NADH in complex biological systems and in related degradation processes of contaminants.Graphical abstractHighlights► We developed an optical NADH sensor by biocatalytic growth of Au–Ag nanoparticles. ► Au seeds-catalyzed NADH-mediated reduction of Ag+ enables particle growth on chip. ► SEM of sensor morphology before and after reaction revealed a diameter increase. ► Absorption peak of growing particles at 415 nm increases with NADH concentration. ► It was precise, fast, good in storage stability and anti-interference ability.

This research investigated the adsorption of zinc and lead from binary metal solution with tunable selectivity. A nano adsorbent was prepared by introducing imine groups onto the surface of stability enhanced magnetic nanoparticles and then characterized by TEM and FTIR. Binary metal components adsorption was carried out in different concentration of metal and EDTA solution. Due to the interaction between metals and adsorbent in the presence of EDTA, the selective adsorption of zinc and lead could be achieved with 100% selectivity. To only remove zinc from binary metals, the solution condition was [EDTA]/[M2+] = 0.7 with pH of 6, and its saturated adsorption capacity was 1.25 mmol/g. For selective adsorption of lead, an equilibrium adsorption capacity of 0.81 mmol/g was obtained under the condition of [EDTA]/[M2+] = 0.7 and pH of 2. The exhausted adsorbent could be regenerated by simple acid or alkali wash, and high purity lead and zinc salt solutions were recovered and concentrated.

•The Fe@Fe2O3 nanobunches (NBZI) presents high removal capacity of arsenic in acid wastewater.•Aerobic NBZI system possesses better stability in acid wastewater than anoxic system.•NBZI possesses strong ability to stabilize arsenic in sediment.•Removal pathways of arsenic under aerobic or anoxic conditions were proposed.High concentration of arsenic in acid wastewater and polluted river sediment caused by metallurgical industry has presented a great environmental challenge for decades. Nanoscale zero valent iron (nZVI) can detoxify arsenic-bearing wastewater and groundwater, but the low adsorption capacity and rapid passivation restrict its large-scale application. This study proposed a highly efficient arsenic treatment nanotechnology, using the core-shell Fe@Fe2O3 nanobunches (NBZI) for removal of arsenic in acid wastewater with cyclic stability and transformation of arsenic speciation in sediment. The adsorption capacity of As(III) by NBZI was 60 times as high as that of nanoscale zero valent iron (nZVI) at neutral pH. Characterization of the prepared materials after reaction revealed that the contents of As(III) and As(V) were 65% and 35% under aerobic conditions, respectively, which is the evidence of oxidation included in the reaction process apart from adsorption and co-precipitation. The presence of oxygen was proved to improve the adsorption ability of the prepared NBZI towards As(III) with the removal efficiency increasing from 68% to 92%. In order to further enhance the performance of NBZI-2 in the absence of oxygen, a new Fenton-Like system of NBZI/H2O2 to remove arsenic under the anoxic condition was also proposed. Furthermore, the removal efficiency of arsenic in acid wastewater remained to be 78% after 9 times of cycling. Meanwhile, most of the mobile fraction of arsenic in river sediment was transformed into residues after NBZI treatment for 20 days. The reaction mechanism between NBZI and arsenic was discussed in detail at last, indicating great potential of NBZI for the treatment of arsenic in wastewater and sediment.Download high-res image (269KB)Download full-size image

•SPAN nanofibers and OMC modified electrode showed good conductivity and stability.•An Hg2+ biosensor with good regenerability was constructed based on the electrode.•The proposed Hg2+ biosensor exhibited a wide linear range and low detection limit.•The biosensor was used to analyze Hg2+ in lake sediment pore water and tap water.In this paper, a reusable electrochemical biosensor was developed for highly sensitive detection of mercury ions (Hg2+) using an anionic intercalator, which was based on Hg2+-induced conformational change of a thymine-rich, single-stranded DNA (ssDNA) supported on the platform of ordered mesoporous carbon (OMC) and self-doped polyaniline (SPAN) nanofibers. In the presence of Hg2+, the mercury-specific oligonucleotides were induced and folded into hairpin structure through mismatched thymine-Hg2+-thymine (T-Hg2+-T) base pairs from random coils. Then, the indicators intercalated into the hairpin structure and increased electric signal. OMC and SPAN nanofibers possessed excellent electrical conductivity which synergistically accelerated electron transfer and greatly improved the efficiency of electrochemical reaction at the electrode interface. Meanwhile, SPAN nanofibers strongly adhered to the electrode surface and attached rod-like OMC homogeneously and firmly, which provided a stable platform for DNA immobilization. Under the optimal conditions, the detection limit (LOD) for Hg2+ was 0.6 fM (S/N = 3). Furthermore, the biosensor could be easily regenerated by cysteine for cyclic utilization. Some environmental samples including lake sediment pore water and tap water were analyzed by the developed biosensor, the relatively satisfactory results indicated that it provided a green and promising strategy for detection of trace Hg2+ in the practical application.Download high-res image (158KB)Download full-size image

A magnetic separation and detection method for a target sequence of a gene encoding cellulase using biocompatible core–shell nanoparticle probes was developed. An aminated capture probe was conjugated with biocompatible Fe3O4–SiO2–Au core–shell nanoparticles. The target probe and signal probe were hybridized with the capture probe on the surface of the inorganic DNA carrier, which resulted in core–shell nanoparticle probes. In the presence of an external magnetic field, it is convenient and time-saving to realize the detection of the cellulase gene in Trichoderma reesei (T. reesei) by liquid fermentation and subsequent magnetic separation. Quantitative PCR (Q-PCR) was performed to give absolute quantification of the concentration of the target nucleic acid, and the Q-PCR result was compared to that of the electrochemical method. The optimized experimental conditions were studied to maximize the hybridization efficiency and detection sensitivity. The amperometric current response was linearly related to the common logarithm of the target nucleic acid concentration in the range of 1.0 × 10−13 to 1.0 × 10−9 M, with a detection limit of 1.2 × 10−14 M.

The utilization of solar energy based on semiconductor photocatalysts for pollutant removal and environmental remediation has become a research hot spot and attracted great attention. In this study, a novel ternary BiVO4/Ag/Cu2O nanocomposite has been successfully synthesized via simple wet impregnation of Cu2O particles coupled with a subsequent photo-reduction pathway for the deposition of metallic Ag on the surface of BiVO4. The resulting BiVO4/Ag/Cu2O photocatalyst was used for the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). Results showed that the coating contents of the Cu2O and Ag particles presented a great effect on the eventual photocatalytic activity of the photocatalysts, and the optimum coating contents of Cu2O and Ag were obtained with their mass ratios of 3% and 2%, respectively. Under optimum conditions, nearly 91.22% TC removal efficiency was obtained based on ternary BiVO4/Ag/Cu2O nanocomposites, higher than that of pure BiVO4 (42.9%) and binary BiVO4/Cu2O (65.17%) and BiVO4/Ag (72.63%) nanocomposites. Meanwhile, the enhanced total organic carbon (TOC) removal efficiency also indicated the excellent photocatalytic degradation ability of the BiVO4/Ag/Cu2O nanocomposites. As for their practical application, the effects of initial TC concentration, various supporting electrolytes and different irradiation conditions were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs) was used to show the by-products of TC molecule degradation. Cycling experiments indicated the high stability of the as-prepared photocatalysts. Furthermore, the results obtained from radical trapping experiments and ESR measurements suggested that the photocatalytic degradation of TC in the BiVO4/Ag/Cu2O based photocatalytic system was the joint action of the photogenerated holes (h+), superoxide radical (˙O2−) and hydroxyl radical (˙OH). The enhanced photocatalytic activity of BiVO4/Ag/Cu2O was attributed to the synergistic effect of Cu2O, Ag and BiVO4, especially the surface plasmon resonance effect and the established local electric field brought about by metallic Ag. Additionally, to deeply understand the reaction mechanism, a dual Z-scheme charge transfer pathway has been proposed.

Palladium/iron (Pd/Fe) bimetallic nanoparticles were embedded within phosphorus-doped ordered mesoporous carbons (Pd/NZVI@P) with high dechlorination activity for 2,4-dichlorophenol (2,4-DCP). The Pd/Fe bimetal nanoparticles of about 15 nm diameter embedded in phosphorus-doped ordered mesoporous carbons (P-OMCs) were homogeneously distributed. The high dechlorination activity was mainly attributed to the homogeneous distribution of Pd/Fe bimetal nanoparticles, which were characterized by transmission electron microscopy (TEM) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) with image mapping. Dechlorination kinetics indicated that the dechlorination rates of 2,4-DCP increased with the increasing of Pd content. The use of P-OMCs as supporting materials to embed enough Pd/Fe bimetal nanoparticles kept the nanoparticles highly active and stable. Besides, solution pH had a significant effect on the dechlorination of 2,4-DCP and the passivation of the Pd/NZVI@P samples. The effects of the number and position of chlorine atoms for different chlorophenols (CPs) on the dechlorination activity were also revealed; the result indicated that the dechlorination of CPs by catalytic reduction preferentially begins from the para-position of the ring, and more chlorine atoms of CPs are favorable for the occurrence of the dechlorination reaction. This study demonstrated that P-OMC is a promising supporting material for the preparation of some effective composite metals for the catalytic dechlorination of CPs.

A biosensor based on tyrosinase immobilized with ordered mesoporous carbon–Au (OMC–Au), L-lysine membrane and Au nanoparticles (tyrosinase/OMC–Au/L-lysine/Au) was combined with artificial neural networks (ANNs) for the simultaneous determination of catechol (CC) and hydroquinone (HQ) in compost bioremediation of municipal solid waste. The good performance of biosensor provided the potential applicability for the simultaneous identification and quantification of catechol and hydroquinone in real samples, and the combination with ANNs offered a good chemometric tool for data analysis in respect to the dynamic, nonlinear, and uncertain characteristics of the complex composting system. Good prediction ability was attained after the ANNs model optimization, and the direct detection range for catechol and hydroquinone were directly analyzed by the ANNs model and varied between 1.0 × 10−7 and 1.1 × 10−4 M, significantly extended compared to the linear model (4.0 × 10−7 to 8.0 × 10−5 M). Finally, the performance of the ANNs model was compared with the linear regression model. The results demonstrate that the prediction results by the ANNs model are more precise than those by the linear regression, and the latter was far from accurate at high levels of catechol and hydroquinone beyond the linear range. All the results show that the combination of the biosensor and ANNs is a rapid and sensitive method in the quantitative study of composting system.