Electrochemical nitrogen reduction: recent progress and prospects.

Ammonia is one of the most useful chemicals for the fertilizer industry and is also promising as an important energy carrier for fuel cell application, and is currently mostly produced by the traditional Haber-Bosch process under high temperature and pressure conditions. This energy-intensive process is detrimental to the environment due to the dependence on fossil fuels and the emission of significant greenhouse gases (such as CO2). Ammonia production via the electrochemical nitrogen reduction reaction (ENRR) has been recognized as a green sustainable alternative to the Haber-Bosch process in recent years. Current ENRR research mainly focuses on the catalyst for ammonia selective production and the enhancement of faradaic efficiency at high current density; however, these have not been explored well due to the unavailability of highly efficient and cheap catalysts. Herein, this review provides information on the ENRR process along with (i) theoretical background, (ii) experimental methodology of the electrocatalytic process and (iii) computational screening of promising catalysts. The impact of active sites and defects on the activity, selectivity, and stability of the catalysts is deeply understood. Furthermore, we demonstrate the mechanistic understanding of the ENRR process on the surface of catalysts, with the aim of boosting the improvement of the ENRR activities. The ammonia detection methods are also summarized along with thorough discussion of control experiments. Finally, this review highlights prevailing problems in existing ENRR methods of ammonia production along with technical advancements proposed to address these issues and concludes with comments on opportunities and future directions of the ENRR process.

Dual labeled mesoporous silica nanospheres based electrochemical immunosensor for ultrasensitive detection of carcinoembryonic antigen.

Carcinoembryonic antigen (CEA) is a well-known cancer biomarker for the detection of several malignancies. The development of ultrasensitive CEA diagnostic tools is crucial for early detection and progression observation of tumors. Herein, a dual signal amplified sandwich-type electrochemical immunoassay was developed based on dual-labeled mesoporous silica nanospheres as a signal amplifier, combined with NiO@Au decorated graphene as a conductive layer for ultrasensitive and rapid determination of CEA. The dual-labeled mesoporous silica (DLMS) nanosphere, which was synthesized by entrapping Au nanorod (Au NR) and horseradish peroxidase (HRP) in the channels of amine-functionalized SBA-15 followed by subordinate antibody (Ab2) conjugation which was denoted as Au NR@SBA-15/Ab2-HRP. The dual signal amplification from Au NR@SBA-15 and HRP enhanced the sensitivity of the proposed immunoassay. Consequently, the developed DLMS based immunosensor displayed ultra-low limits of detection of 5.25 fg/mL and a wide range of linearity (0.1-5 pg/mL), which was extended for CEA determination in real-time samples with improved recoveries of >98%. Therefore, this dual amplification prototype would cater to the clinical requirements for the ultrasensitive detection of CEA biomarkers.

Spatial Compartmentalization of Cobalt Phosphide in P-Doped Dual Carbon Shells for Efficient Alkaline Overall Water Splitting.

Highly durable and earth-abundant bifunctional catalysts with low cell voltage are desirable for alkaline overall water splitting in the industrial fields. Herein, a novel carbon-based CoP hybrid with spatial compartmentalization of CoP nanoparticles (NPs) in P-doped dual carbon shells is achieved via a cheap Co-glycerate-template strategy. Benefitted from the uniform atomic blending of Co2+ ions in the Co-glycerate precursors, CoP NPs in situ formed in the confined space with NaH2PO2 as phosphorus source during the annealing process; meanwhile, glycerate suffered carbonization and transformed into P-doped dual carbon shells during the annealing process, including interior thin carbon coating, closely encircled CoP NP, and peripheral hollow carbon sphere loading a lot of CoP NPs. Not only does spatial compartmentalization of CoP NPs avoid the aggregation and expose more active sites but also P-doped dual carbon shells improve the conductivity and durability of the catalyst. As expected, the optimized hybrid exhibits outstanding electrocatalytic activities in alkaline media, such as hydrogen evolution reaction (HER) overpotential of 101 mV, oxygen evolution reaction (OER) overpotential of 280 mV, and a low cell voltage of 1.66 V to deliver a current density of 10 mA cm-2. Moreover, durability and stability are greatly improved under harsh electrochemical conditions. The current strategy shades new insight into the development of carbon-based transition metal phosphides (TMP) catalysts for electrocatalysis applications.

A mesoporous silver-doped TiO2-SnO2 nanocomposite on g-C3N4 nanosheets and decorated with a hierarchical core-shell metal-organic framework for simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid.

An electrochemical sensor is described for the simultaneous voltammetric determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). An indium-tin oxide (ITO) electrode was modified with a hierarchical core-shell metal-organic framework and Ag-doped mesoporous metal-oxide based hybrid nanocomposites on g-C3N4 nanosheets. The morphology, structural and chemical composition of the hybrid nanocomposite was characterized using different analytical methods. The modified ITO showed superior electrocatalytic performance towards the oxidation of AA, DA and UA due to the enhanced surface area, synergistic effects and well-organized porous assembly. Figures of merit, include (a) linear responses from 0.1 to 200 µM, 2.5 to 100 µM and 2.5 to 625 µM; (b) detection limits (at S/N = 3) of 0.02, 0.01 and 0.06 µM, and (c) well separated oxidation peaks near -50, 186 and 390 mV (vs. Ag/AgCl) for simultaneous sensing AA, DA and UA, respectively. The sensor was evaluated by analysing spiked serum samples and gave data with precision, with recoveries of >98%. Graphical abstractSchematic Representation of a Mesoporous Silver-doped TiO2-SnO2 Nanocomposite (h-ATS) on g-C3N4 Nanosheets and Decorated with a Hierarchical Core-Shell Metal-Organic Framework (NC@GC) Based Electrochemical Sensor for Simultaneous Voltammetric Detection of Ascorbic acid, Dopamine and Uric acid.

Ti3+ self-doped TiO2-x nanowires for efficient electrocatalytic N2 reduction to NH3.

Electrochemical N2 reduction is an environmentally friendly and sustainable approach for NH3 synthesis under mild conditions, while an efficient electrocatalyst is crucial for the N2 reduction reaction (NRR). Herein, we report Ti3+ self-doped TiO2-x nanowires on Ti mesh (Ti3+-TiO2-x/TM) as an efficient non-noble-metal NRR electrocatalyst with excellent selectivity. In 0.1 M Na2SO4, the Ti3+-TiO2-x/TM achieves a high faradaic efficiency of 14.62% with a NH3 yield of 3.51 × 10-11 mol s-1 cm-2 at -0.55 V vs. the reversible hydrogen electrode. Density functional theory calculations further reveal that introducing Ti3+ decreases the reaction energy barrier and increases the number of active sites on the TiO2 surface for the NRR.

Platinum-Copper Bimetallic Alloy Nanoflowers as Efficient Electrocatalyst for the Methanol Oxidation Reaction.

Special morphological noble metal-based bimetallic alloy nanostructures became popular for methanol oxidation reaction in order to reduce the high cost of the Pt catalyst and improve the catalyst activity. Herein, we developed a facile one pot hydrothermal method for the synthesis of platinum-copper bimetallic nanoflowers (Pt-Cu NFs) in the presence of hexadecyl trimethyl ammonium bromide (CTAB). The morphology, structure and composition of Pt-Cu NFs were carefully characterized and the synthesized parameters were optimized systematically by adjusting different experimental conditions. Results showed that the CTAB usage and the NaI amount were critical to the controlled synthesis of Pt-Cu NFs. The Pt-Cu NFs were high-performance electrocatalysts for the methanol oxidation reaction (MOR) with superior activity and superior stability in alkaline solution, which were far better than pure Pt nanoparticle electrocatalysts.

Biomimetic Synthesis of Polydopamine Coated ZnFe2O4 Composites as Anode Materials for Lithium-Ion Batteries.

Metal oxides as anode materials for lithium storage suffer from poor cycling stability due to their conversion mechanisms. Here, we report an efficient biomimetic method to fabricate a conformal coating of conductive polymer on ZnFe2O4 nanoparticles, which shows outstanding electrochemical performance as anode material for lithium storage. Polydopamine (PDA) film, a bionic ionic permeable film, was successfully coated on the surfaces of ZnFe2O4 particles by the self-polymerization of dopamine in the presence of an alkaline buffer solution. The thickness of PDA coating layer was tunable by controlling the reaction time, and the obtained ZnFe2O4/PDA sample with 8 nm coating layer exhibited an outstanding electrochemical performance in terms of cycling stability and rate capability. ZnFe2O4/PDA composites delivered an initial discharge capacity of 2079 mAh g-1 at 1 A g-1 and showed a minimum capacity decay after 150 cycles. Importantly, the coating layer improved the rate capability of composites compared to that of its counterpart, the bare ZnFe2O4 particle materials. The outstanding electrochemical performance was because of the buffering and protective effects of the PDA coating layer, which could be a general protection strategy for electrode materials in lithium-ion batteries.

CdS/ZnS Heterostructured Porous Composite with Enhanced Visible Light Photocatalysis.

Fabrication of semiconductor composites consisting of multicomponent or multiphase heterojunctions is a very effective strategy to design highly active photocatalyst systems. Here we present a facile design to fabricate novel CdS/ZnS heterostructured porous sheet-like nanocomposite based on a cation-exchanged hydrothermal procedure. Micro-structural analyses reveal that the product is a kind of heterostructured composite with porous structure and high crystallinity. The composite nanosheets exhibited enhanced visible-light photoactivity compared with pure ZnS or CdS. Among them, sample of Cd0.45Zn0.55S gave the highest degradation rate of about 99% under visible-light irradiation within 60 min when 10 mg of the sample was added into 50 mL of methyl orange in aqueous solution (10 mg/L). The enhanced photocatalytic activity was presumed to result from the direct photoinduced interfacial charge transfer (IFCT) from the valence band (VB) of ZnS to CdS.

Sensitive Detection of Rifampicin Based on Au-Carbon Nanocomposite.

Gold nanoparticles-supported Cabot Vulcan XC72R (Au/VXC72R) nanocomposite was synthesized by chemical reduction of gold (III) chloride with VXC72R. A novel electrochemical sensor based on the Au/VXC72R nanocomposite has been fabricated for the sensitive detection of rifampicin (RIF). Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, structure and compositions of the nanocomposite. Under the optimal conditions, the Au/VXC72R-chitosan/GCE can be used to determine RIF concentration in a linear range from 5 × 10-7 mol/L to 1 × 10-5 mol/L with the detection limit of 1.1 × 107 M (S/N = 3). The proposed approach exhibits good stability, acceptable reproducibility and applicability, which will probably bring widespread applications in quality monitoring in real samples.

Sensitive Determination of Dopamine and Paracetamol Based on Carbon Nanotubes-Supported Pd Nanoparticles.

A novel chemically modified electrode was constructed in this study based on the carbon nanotubes-supported Pd nanoparticles (Pd/CNTs). It was demonstrated that the sensor could be used for the determination of dopamine (DA) and paracetamol (PA). The measurements were carried out through application of cyclic voltammetry (CV), differential pulse voltammetry (DPV) and amperometric i-t curve. Under optimum conditions and using the amperometric i-t curve method, the modified electrode provided linear response versus dopamine concentrations in the range of 0.3 × 10-6-5.0 × 10-5 M and PA concentrations in the range of 0.2 × 10-6-6.0 × 10-5 M, respectively. The detection limits for the DA and PA were 9.1 × 10-8 M and 8.9 × 10-8 M (S/N = 3), respectively. The sensitivities for of the electrode were 0.928 and 1.532 µA µM-1 cm-1, respectively.

Low Cost and Reliable Electrochemical Sensor for Rutin Detection Based on Au Nanoparticles-Loaded ZnS Nanocomposites.

Facile preparation of electrode modified materials with low-cost nanocomposites is an important step to develop highly active electrochemical sensors for mass-market applications. Here we fabricated Au nanoparticles (AuNPs)-loaded ZnS nanocomposites for the sensitive determination of rutin due to the cooperative amplification of the conductivity and catalytic activity of AuNPs on ZnS spheres resulting from the high loading ratio of AuNPs on ZnS spheres. Under the optimal conditions, the developed sensor based on AuNPs-loaded ZnS nanocomposites exhibited excellent electrocatalytic activity towards rutin in a linear range from 1 × 10-7 mol/L to 2 × 10-5 mol/L with a limit of detection of 15.3 nM at a signal-to-noise ratio of 3. Furthermore, the proposed method gave satisfactory results for rutin determination in pharmaceutical tablets, which offer promising potential for rutin electrochemical analysis in serum monitoring or Chinese medical analysis owing to its simplicity, low cost, high sensitivity and good stability.

Facile Synthesis of Carboxylic Functionalized MFe2O4 (M = Mn, Co, Zn) Nanospheres.

A facile one-pot solvothermal method was developed for the synthesis of carboxylic functionalized MFe2O4 (M = Mn, Co, Zn) nanospheres. Field-emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectrometer, and a superconducting quantum interference device magnetometer were used to characterize the morphologies, compositions and properties of the functionalized materials. Results show that all of the products were cubic spinel structures and exhibited hierarchical sphere-like morphologies, which were composed of primary nanocrystals. The MFe2O4 present advantageous functionality and good water dispensability due to the preferential exposure of uncoordinated carboxylate groups on their respective surfaces. These properties make them ideal candidates for various important applications such as drug delivery, bioseparation, and magnetic resonance imaging.

Facile synthesis of fluorescent porous zinc sulfide nanospheres and their application for potential drug delivery and live cell imaging.

Fabrication of intrinsically fluorescent porous nanocarriers that are simultaneously stable in aqueous solutions and photostable is critical for their application in drug delivery and optical imaging but remains a challenge. In this study, fluorescent porous zinc sulfide nanospheres were synthesized by a facile gum arabic-assisted hydrothermal procedure. The morphology, composition and properties of the nanospheres have been characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, N(2) adsorption-desorption analysis, thermal gravimetric analysis, fourier transform infrared spectrograph, optical measurement, dynamic light scattering, and cytotoxicity assay. They exhibit larger surface area, excellent colloidal stability, photostable fluorescent signals, and good biocompatibility, which makes them promising hosts for drug delivery and cellular imaging. The fluorescent dye safranine-T was employed as a drug model and loaded into the porous nanospheres, which were delivered to human cervical cancer HeLa cells in vitro for live cell imaging.

Single-crystalline Bi2S3 nanobelts: hydrothermal synthesis and growth mechanism.

High-quality single-crystalline Bi2S3 nanobelts were synthesized with Bi(NO3)3 x 5H2O and thioacetamide (TAA) as the raw materials in the polyvinylpyrrolidone (PVP) aqueous solution via a facile hydrothermal route. The morphology and crystallinity of the nanobelts were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDX), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The effects of a series of reaction parameters on the morphology of Bi2S3 were studied. A plausible growth mechanism based on preferred orientation growth is proposed to address the formation of Bi2S3 nanobelts.

Structural effects of Fe3O4 nanocrystals on peroxidase-like activity.

The catalytic activity of nanocrystal catalysts depends strongly on their structures. Herein, we report three distinct structures of Fe(3)O(4) nanocrystals, cluster spheres, octahedra, and triangular plates, prepared by a similar hydrothermal procedure. Additionally, the three Fe(3)O(4) nanostructures were used as peroxidase nanomimetics and the correlation between the catalytic activities and the structures was first explored by using 3,3',5,5'-tetramethylbenzidine and H(2)O(2) as peroxidase substrates. The results showed that the peroxidase-like activities of the Fe(3)O(4) nanocrystals were structure dependent and followed the order cluster spheres>triangular plates>octahedra; this order was closely related to their preferential exposure of catalytically active iron atoms or crystal planes. Such investigation is of great significance for peroxidase nanomimetics with enhanced activity and utilization.

Characterization and cellular uptake of platinum anticancer drugs encapsulated in apoferritin.

Clinical application of platinum-based anticancer drugs is largely limited by severe general toxicity and drug resistance. Drug delivery systems with tumor-targeting potential are highly desired for improving the efficacy and applicability of these drugs. This study describes an alternative strategy for the delivery of platinum drugs (cisplatin, carboplatin and oxaliplatin) by encapsulating each of them in the cavity of apoferritin (AFt). The encapsulation was achieved through manipulating the pH-dependent unfolding-refolding process of AFt at pH 2.0 and 7.4, respectively, in saturated drug solution. UV-vis spectrometry, circular dichroism spectrometry, dynamic light scattering, and inductively coupled plasma mass spectrometry were used to characterize the AFt-drug complexes. The loading capacity of AFt varies with respective drugs and the structural integrity of the protein shell remains intact after encapsulation. In vitro assays on the rat pheochromocytoma cell line (PC12) show that AFt-cisplatin inhibits the cells in a slow but sustaining mode and the cellular uptake of platinum is enhanced by AFt. AFt-carboplatin and AFt-oxaliplatin complexes only exhibit a marginal cytotoxicity towards this cell line under similar concentrations.

Fabrication of water soluble and biocompatible CdSe nanoparticles in apoferritin with the aid of EDTA.

Apoferritin-coated photoluminescent CdSe nanoparticles generated by an EDTA-mediated in situ method are photostable, water soluble and biocompatible.

[Spectroscopic study on the effect of crystallization of the hydroxyapatite on the secondary structure of bovine serum albumin].

The effect of crystallization of hydroxyapatite on the secondary structure of bovine serum albumin (BSA) was studied by circular dichroism spectrum, Fourier transform infrared spectroscopy, derivative, deconvolution and curve-fitting techniques in the present paper. The CD results show that pure bovine serum albumin is composed of 56.8% alpha-helices, 5.8% beta-sheets, 14.1% beta-turns and 23.9% random structures, while the bovine serum albumin in the Ca10(PO4)6(OH)2/bovine serum albumin solution is composed of 25.4% alpha-helices, 25.0% beta-sheets, 20.0% beta-turns and 29.7% random structures. The results of Fourier transform infrared spectroscopy are in good agreement with those from the CD spectra. From these results it can be seen that the percentage of alpha-helix decreased, while that of the beta-sheet increased with the formation of the crystal of hydroxyapatite, and with the reaction time increasing, the percentages of alpha-helix obviously dropped and those of beta-sheet markedly rose. These results showed that alpha-helix transformed into beta-sheet. Furthermore the essence of these changes is discussed.

Fabrication of protein-conjugated silver sulfide nanorods in the bovine serum albumin solution.

Highly ordered silver sulfide nanorods conjugated with the Bovine Serum Albumin (BSA) protein have been successfully achieved at ambient temperature. Such a process is very simple and controllable, directly using silver nitrate and thioacetamide (TAA) as the reactants in the aqueous solution of BSA. The products have been characterized by XRD, HRTEM-SAED, SEM-EDS, TG-DTA, FT-IR, and CD spectroscopy. The results of the research show that the as-prepared Ag2S nanorods are monodispersed with sizes about 40 nm in diameter and 220 nm in length, and exhibit a high degree of crystallinity and good photoluminescence. Furthermore, an interesting mechanism is discussed for the formation of the Ag2S nanorods.

Effect of PbII on the secondary structure and biological activity of trypsin.

The effects of Pb(II) on the secondary structure and biological activity of trypsin have been examined by monitoring changes in its conductivity and IR and circular dichroism (CD) spectra. The results show that Pb(II) reacts with trypsin, and that the binding sites might be -OH and -NH groups in pepsin. The CD spectra indicate that interaction with Pb(II) significantly affects the secondary structure of trypsin, the beta-sheet-structure content being increased by about 42%, whilst those of alpha-helix and beta-turn structures are decreased by 13% and 21%, respectively. The results clearly demonstrate that Pb(II) affects the biological activity of trypsin by modifying its secondary structure. Most interesting is that Pb(II) up-regulates the activity of trypsin at low concentrations while down-regulating it at high concentrations.