High Surface Area Nanomaterials Research Articles

3D carbonaceous nanostructured transition metal nitride, carbonitride and carbide as polysulfide regulators for lithium-sulfur batteries

We report a general and straightforward approach to produce high surface area nanomaterials of transition metal nitride, carbonitride and carbide nanoparticles that are highly dispersed on 3D carbonaceous structure. The preparation of these novel nanomaterials involves a simple one-step heat treatment of a metal precursor and urea-derived graphitic carbon nitride mixture under argon, unlike the conventional methods of using ammonia gas to prepare nitride and high-temperature carbothermal reduction of oxide to produce carbide. With this approach, we have synthesized titanium nitride (TiN/C), vanadium carbonitride (V2CN/C) and niobium carbide-based (NbC/C) nanomaterials using alkoxide precursors. Taking advantage of their high electronic conductivity and surface properties, we have developed the nitrides and carbides as polysulfide (PS) regulators to combat the well-known problems of lithium-sulfur (Li-S) batteries (shuttle phenomena, insulating sulfur, etc.). In particular, V2CN/C nanomaterial was found to possess higher redox activity as compared to TiN/C and NbC/C based on density functional theory (DFT) calculations, polysulfide adsorption studies and various electrochemical experiments. V2CN/C also demonstrated superior performance with an initial specific capacity of 1055 mAh g−1 at 0.2 C and sulfur loading of 4.5 mg cm−2, and a practical areal capacity and capacity retention of ~ 4.2 mAh cm−2 and 89%, respectively, after 300 cycles.

(Invited) Microfabricated Chemical Sensors for Industrial, Health and Environmental Monitoring

There remains a strong need for miniaturized, low-power gas sensors that can be deployed in wireless applications for improved environmental protection, for public health, and for safe and efficient operation of many industrial processes. Leveraging the microfabrication technologies and utilizing innovations in high surface area nanomaterials are providing exciting opportunities towards low-power microchemical sensors. In this presentation, I will discuss one of the approaches we have been pursuing, which is based on a highly efficient microheater platform with fast response and recovery times. The design, fabrication and characteristics of this platform will be presented. I will also discuss the use of two-dimensional materials for gas sensing applications since they offer the highest possible surface area for gas interaction, leading to high sensitivity. Assembling these two-dimensional materials into three-dimensional assemblies, such as aerogels, provides a low-density material with large number of interconnected pores that increases the surface area available in a given footprint while maintaining the properties of the few-layer sheets. By integrating these nanomaterials with our microheater platform, we have achieved fast and sensitive detection of several health and environmental pollutants. The talk will end with current limitations and plans for future directions.

Synthesis and characterization of NiO, MoO3, and NiMoO4 nanostructures through a green, facile method and their potential use as electrocatalysts for water splitting

NiO, MoO3, and NiMoO4 nanostructures were synthesized using a solution combustion method, employing agar as an organic fuel. TGA/DSC and BET analyses showed that the synthesis of NiO and NiMoO4 involved an intense exothermic combustion reaction that resulted in high surface area nanomaterials, with large pore volume and small pore size. XRD confirmed the phase composition and crystallite size of the synthesized materials. The particle size range was 20–40 nm for NiMoO4 and NiO, and 200–350 nm for MoO3. Band gap values of 3.44, 3.13, and 3.18 eV were determined for NiO, MoO3, and NiMoO4, respectively. Raman spectroscopy provided structural information about the synthesized materials, while FTIR results revealed that agar acts as both a metal-ion chelating agent and fuel. XPS confirmed the valence states of the produced materials and purported their purity, while the zeta potential measurements underpinned the stability of the samples in aqueous media. The synthesized materials were tested as potential electrocatalysts in water electrolysis for the oxygen (OER) and the hydrogen evolution reactions (HER) in an alkaline medium. The results demonstrated that NiMoO4 exhibits an excellent electrocatalytic activity in both OER and HER.

(Invited) Microfabricated Sensors for Industrial, Health and Environmental Monitoring

Introduction There remains a strong need for miniaturized, low-power gas sensors that can be deployed in wireless applications for improved environmental protection, for public health, and for safe and efficient operation of many industrial processes. Leveraging the microfabrication technologies and utilizing innovations in high surface area nanomaterials provide exciting opportunities towards low-power microchemical sensors. Approach One approach is based on a highly efficient microheater platform (Figure 1) with fast response and recovery times. The design, fabrication, and characterization of the microheater platform is described, with polysilicon as the heater material for moderate temperature [1] and silicon carbide [2] for improved reliability at high temperature operation. A small, isolated heated area decreases the required power consumption and a closed membrane facilitates easier deposition of sensing materials.The use of two-dimensional materials is attractive for gas sensing applications since they offer the highest possible surface area for gas interaction, leading to high sensitivity. Assembling these two-dimensional materials into three dimensions, such as aerogels, provides a low-density material with large number of interconnected pores that increases the surface area available in a given footprint while maintaining the properties of the few-layer sheets. Sensing materials for combustible and toxic gas detection have been developed based on ultra-high surface area aerogels [3-6]. Results and Conclusions By integrating these nanomaterials with our microheater platform, we have achieved fast and sensitive detection of several health and environmental pollutants. For combustible gas sensing, graphene or boron nitride aerogel acts as a scaffold for catalytic platinum or palladium nanoparticles [1,3]. Bare graphene aerogel, graphene aerogel coated with single to few-layer transition metal dichalcogenide (TMDC) sheets, and TMDC aerogels are used for toxic gas detection [4-8]. The microheater platform is also used for localized growth of nanocrystalline metal oxide sensing film. The fast thermal response of the microheater leads to rapid heating of the precursor, creating a highly porous film that is beneficial for toxic gas sensing [9,10]. The talk will end with current limitations and plans for future directions.

Intrinsic photoelectrocatalytic activity in oriented, photonic TiO2 nanotubes

In this work, we grow oriented photonic TiO2 nanotubes (TNTs) with a well-established anodization method and their intrinsic catalytic and electronic properties are studied by means of (photo)electrochemical methods. The oriented photonic TNTs are assessed by the RctCdl (ΩF) product, which is a measure of the intrinsic photoelectrocatalytic activity (IPA) of the material. The RctCdl product decouples any surface area effects and it can be applied at any potential and accompanied reaction without knowing the actual electrochemically active surface area (EASA). Moreover, electrochemical impedance spectroscopy (EIS) is used in order to investigate the frequency dispersion in the single frequency Mott-Schottky (MS) measurement. The choice of frequency and the frequency dispersion in MS measurements in nanostructured and of high surface area semiconductors are rarely addressed and can result in erroneous values of two important parameters, i.e. flat band position and donor or acceptor densities. This work provides further insights into important electrochemical aspects and catalytic properties of high surface area nanomaterials for photoelectrochemical applications.

Enhanced hydrogen storage performance in Pd3Co decorated nitrogen/boron doped graphene composites

In order to harness the potential of hydrogen as an alternative energy carrier, overcoming the barrier related to its storage is of utmost importance. In this direction, it has been shown that dissociation of hydrogen molecules into atoms followed by their adsorption onto high surface area nanomaterials like reduced graphene oxide is a promising pathway. In the present study, we have exploited this pathway, commonly known as the “spillover mechanism” and achieved a hydrogen storage capacity of ∼4.6 wt% at 30 bar and 25 °C in Pd3Co decorated boron doped graphene composite. We demonstrate that optimum loading of transition metal alloy nanoparticles coupled with heteroatom (nitrogen or boron) doped graphene support is an efficient, easy and cost effective avenue towards meeting the US department of energy (DOE) targets for gravimetric hydrogen storage capacity at room temperature and moderate pressures.

Recent developments in high surface area bioelectrodes for enzymatic fuel cells

Enzymatic fuel cells (EFC) function in a similar way to low temperature proton exchange membrane fuel cells (PEMFC) but use enzymes instead of noble metals as catalysts for fuel and oxidant transformation. The need for EFCs that deliver enhanced power has resulted in high surface/volume ratio conductive materials being considered as enzyme host matrices. While the enhanced surface has effectively led to higher catalytic currents, the use of high surface area nanomaterials (HSM) has also induced new issues related to the wiring of enzymes, the role of porosity, and the effect on stability. This review discusses the most important features reported in this area over the past three years, and proposes future directions concerning EFC applications. Recent developments in high surface area bioelectrodes for enzymatic fuel cells. Available from: https://www.researchgate.net/publication/318305120_Recent_developments_in_high_surface_area_bioelectrodes_for_enzymatic_fuel_cells [accessed Jul 19, 2017].

Salt flux synthesis of single and bimetallic carbide nanowires

Metal carbide compounds have a broad range of interesting properties and are some of the hardest and highest melting point compounds known. However, their high melting points force very high reaction temperatures and thus limit the formation of high surface area nanomaterials. To avoid the extreme synthesis temperatures commonly associated with these materials, a new salt flux technique has been employed to reduce reaction temperatures and form these materials in the nanometer regime. Additionally, the use of multiwall carbon nanotubes as a reactant further reduces the diffusion distance and provides a template for the final carbide materials. The metal carbide compounds produced through this low temperature salt flux technique maintain the nanowire morphology of the carbon nanotubes but increase in size to ∼15–20 nm diameter due to the incorporation of metal in the carbon lattice. These nano-carbides not only have nanowire like shape but also have much higher surface areas than traditionally prepared metal carbides. Finally, bimetallic carbides with composition control can be produced with this method by simply using two metal precursors in the reaction. This method provides the ability to produce nano sized metal carbide materials with size, morphology, and composition control and will allow for these compounds to be synthesized and studied in a whole new size and temperature regime.

Modeling and Experimental Study of Micro Enzymatic Biofuel Cells

Miniaturized enzymatic biofuel cells (EBFCs) converting biological energy into electrical energy by using enzyme-modified electrodes are considered as a candidate to power implantable medical devices and portable electronics. In this study, modeling of the EBFC system has been conducted using finite element analysis. The design rule has been developed in the steady state and the effect of orientation of EBFC chip in blood artery has been studied. In the experimental part, 3D carbon micropillar arrays have been fabricated and different functionalization techniques on the glassy carbon surface have also been demonstrated. Moreover, high surface area nanomaterials graphene has been integrated to improve the performance of EBFCs. The amperometric response for graphene based bioelectrodes exhibited excellent electrochemical performance and the resulting EBFC generated a maximum power density of 136.3 μWcm-2 at 0.59 V, which is about 7 times of the bare carbon based EBFC.

Modeling and Experimental Study of Micro Enzymatic Biofuel Cells

Miniaturized enzymatic biofuel cells (EBFCs) converting biological energy into electrical energy by using enzyme-modified electrodes are considered as a candidate to power implantable medical devices and portable electronics. In this study, modeling of the EBFC system has been conducted using finite element analysis based on COMSOL Multiphysics 4.3a in terms of cell performance, efficiency and optimum cell configurations. Two modules have been applied to obtain the maximum theoretical cell performance of on-chip microelectrodes: 1) diffusion module to incorporate the mass transport and enzymatic kinetics; 2) conductive module to integrate concentration and potential. The design rule has been developed in the steady state. The effect of orientation of the microelectrode arrays in blood artery has been studied. In the experimental part, integration of the high surface area nanomaterials such as carbon nanotubes (CNTs) and graphene could be one of the effective solutions to further improve the performance of current EBFCs. The EBFC systems employing 3D carbon micropillar arrays integrated with different nanomaterials, such as graphene, reduced graphene oxide (rGO) and rGO/CNTs composite have been investigated. The fabrication process of this micro-system combined top-down carbon microelectromechanical system (C-MEMS) technology to fabricate the 3D micropillar arrays platform and bottom-up electrophoretic deposition (EPD) to deposit various carbon based nanomaterials onto the 3D micropillar arrays. The materials characterization, electrochemical characterization and device evaluation have been conducted. Upon comparison among bioelectrodes integrated with different nanomaterials, the amperometric response of the rGO/CNTs based bioelectrodes exhibited the best electrochemical performance and the as-resulted 3D micro EBFC generated a maximum power density of 196.04 µWcm-2 at 0.61 V. In addition, modeling of the rGO/CNTs EBFC system based on finite element analysis has also been conducted to predict the theoretical cell performance. The power density of actual device has been noted to be 71.1% of the modeling result.

Non-covalent functionalization of high-surface area nanomaterials: a new class of sorbent materials

A non-covalent approach to functionalizing nanostructured materials with high-specificity ligands yields effective sorbents for capture of trace metal ions from water.

Nanobiosensors: the future for diagnosis of disease?

Nanobiosensors: the future for diagnosis of disease? Shalini Prasad Department of Bioengineering, University of Texas, Dallas, TX, USA Abstract: Nanotechnology is having a profound impact on the development of a new class of biosensors known as nanobiosensors. Nanobiosensors commonly comprise a biological recognition molecule immobilized onto the surface of a signal transducer. The reaction between the biorecognition molecule and the analyte is a heterogeneous reaction and therefore the design of the biosensing interface is important in determining the performance of the nanobiosensor. Nanobiosensors are being widely used for molecular detection of biomarkers associated with diagnosis of disease. The application of new nanomaterials in biosensing has influenced biosensing research. The use of high surface area nanomaterials has been important in producing nanobiosensors with greater sensitivity and shorter response times. This review summarizes the advances in disease diagnostics, primarily through the detection of molecular biomarkers, such as proteins and nucleic acids mediated by use of nanobiosensors. Keywords: nanomaterial, biosensors, disease diagnosis, biomimetic, macromolecular crowding, performance metrics

Nanostructured F doped IrO2 electro-catalyst powders for PEM based water electrolysis

Fluorine doped iridium oxide (IrO2:F) powders with varying F content ranging from 0 to 20 wt.% has been synthesized by using a modification of the Adams fusion method. The precursors (IrCl4 and NH4F) are mixed with NaNO3 and heated to elevated temperatures to form high surface area nanomaterials as electro-catalysts for PEM based water electrolysis. The catalysts were then coated on a porous Ti substrate and have been studied for the oxygen evolution reaction in PEM based water electrolysis. The IrO2:F with an optimum composition of IrO2:10 wt.% F shows remarkably superior electrochemical activity and chemical stability compared to pure IrO2. The results have also been supported via kinetic studies by conducting rotating disk electrode (RDE) experiments. The RDE studies confirm that the electro-catalysts follow the two electron transfer reaction for electrolysis with calculated activation energy of ∼25 kJ mol−1. Single full cell tests conducted also validate the superior electrochemical activity of the 10 wt.% F doped IrO2.

Nanobiomaterials and Nanoanalysis: Opportunities for Improving the Science to Benefit Biomedical Technologies

AbstractNanomaterials advocated for biomedical applications must exhibit well‐controlled surface properties to achieve optimum performance in complex biological or physiological fluids. Dispersed materials with extremely high specific surface areas require as extensive characterization as their macroscale biomaterials analogues. However, current literature is replete with many examples of nanophase materials, most notably nanoparticles, with little emphasis placed on reporting rigorous surface analysis or characterization, or in formal implementation of surface property standards needed to validate structure‐property relationships for biomedical applications. Correlations of nanophase surface properties with their stability, toxicity and biodistributions are essential for in vivo applications. Surface contamination is likely, given their processing conditions and interfacial energies. Leaching adventitious adsorbates from high surface area nanomaterials is a possible toxicity mechanism. Polydimethylsiloxane (PDMS), long known as a ubiquitous contaminant in clean room conditions, chemical synthesis and microfabrication, remains a likely culprit in nanosystems fabrication, especially in synthesis, soft lithography and contact molding methods. New standards and expectations for analyzing the interfacial properties of nanoparticles and nano‐fabricated technologies are required. Surface science analytical rigor similar to that applied to biomedical devices, nanophases in microelectronics and heterogeneous catalysts should serve as a model for nanomaterials characterization in biomedical technologies.

Self-Assembly of Virus-Structured High Surface Area Nanomaterials and Their Application as Battery Electrodes

High area nickel and cobalt surfaces were assembled using modified Tobacco mosaic virus (TMV) templates. Rod-shaped TMV templates (300 x 18 nm) engineered to encode unique cysteine residues were self-assembled onto gold patterned surfaces in a vertically oriented fashion, producing a >10-fold increase in surface area. Electroless deposition of ionic metals onto surface-assembled virus templates produced uniform metal coatings up to 40 nm in thickness. Within a nickel-zinc battery system, the incorporation of virus-assembled electrode surfaces more than doubled the total electrode capacity. When combined, these findings demonstrate that surface-assembled virus templates provide a robust platform for the fabrication of oriented high surface area materials.