The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in ...constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.
This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum ...dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π–π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graphene and graphene oxide.
A Nano zerovalent iron nanoparticles graphene composite (G-nZVI) was prepared via a sodium borohydride reduction of graphene oxide and iron chloride under an argon atmosphere. Powder X-ray ...diffraction patterns showed the formation of the magnetic graphene/nanoscale-zerovalent-iron (G-nZVI) composites and bare nanoscale-zerovalent-iron (nZVI) particles. TEM analysis shows the formation of ∼10 nm particles. Adsorption experiments show a maximum Pb(II) adsorption capacity for the G-nZVI composite with 6 wt% graphene oxide loading. Additionally the effects of pH, temperature, contact time, ionic strength and initial metal ion concentration on Pb(II) ion removal were studied. X-ray photoelectron spectroscopy analysis after adsorption results confirmed the composite's ability to adsorb and immobilize lead more efficiently in its zerovalent and bivalent forms, as compared to bare iron nanoparticles. The adsorption of Pb(II) ions fit a pseudo-second-order kinetic model, and adsorption isotherms can be described using the Freundlich equations. G-nZVI shows great potential as an efficient adsorbent for lead immobilization from water, as it exhibits stability, reducing power, a large surface area, and magnetic separation.
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•This work details the magnetic separation of lead ions from contaminated water.•The absorbant is a novel water dispersible magnetic graphene composite.•The magnetic graphene absorbant can be prepared via a chemical route.•The absorbant immobilizes zero- and bi-valent lead forms in contaminated water.
This review deals with wide-ranging environmental studies of graphene-based materials on the adsorption of hazardous materials and photocatalytic degradation of pollutants for water remediation and ...the physisorption, chemisorption, reactive adsorption, and separation for gas storage. The environmental and biological toxicity of graphene, which is an important issue if graphene composites are to be applied in environmental remediation, is also addressed.
A polyindole-reduced graphene oxide (PIG) hybrid was synthesized by reducing graphene oxide sheets in the presence of polyindole. We have shown PIG as a material for capturing carbon dioxide (CO2). ...The PIG hybrid was chemically activated at temperatures of 400-800 °C, which resulted in nitrogen (N)-doped graphene sheets. The N-doped graphene sheets are microporous with an adsorption pore size of 0.6 nm for CO2 and show a maximum (Brunauer, Emmet and Teller) surface area of 936 m(2) g(-1). The hybrid activated at 600 °C (PIG6) possesses a surface area of 534 m(2) g(-1) and a micropore volume of 0.29 cm(3) g(-1). PIG6 shows a maximum CO2 adsorption capacity of 3.0 mmol g(-1) at 25 °C and 1 atm. This high CO2 uptake is due to the highly microporous character of the material and its N content. The material retains its original adsorption capacity on recycling even after 10 cycles (within experimental error). PIG6 also shows high adsorption selectivity ratios for CO2 over N2, CH4 and H2 of 23, 4 and 85 at 25 °C, respectively.
Graphene sheets decorated with SnO(2) nanoparticles (RGO-SnO(2)) were prepared via a redox reaction between graphene oxide (GO) and SnCl(2). Graphene oxide (GO) was reduced to graphene (RGO) and ...Sn(2+) was oxidized to SnO(2) during the redox reaction, leading to a homogeneous distribution of SnO(2) nanoparticles on RGO sheets. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show uniform distribution of the nanoparticles on the RGO surface and high-resolution transmission electron microscopy (HRTEM) shows an average particle size of 3-5 nm. The RGO-SnO(2) composite showed an enhanced photocatalytic degradation activity for the organic dye methylene blue under sunlight compared to bare SnO(2) nanoparticles. This result leads us to believe that the RGO-SnO(2) composite could be used in catalytic photodegradation of other organic dyes.
Nanosize platinum clusters with small diameters of 2-4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not ...yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA-graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA-graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA-graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries.
An activated carbon material derived from waste coffee grounds is shown to be an effective and stable medium for methane storage. The sample activated at 900 °C displays a surface area of 1040.3 m(2) ...g(-1) and a micropore volume of 0.574 cm(3) g(-1) and exhibits a stable CH4 adsorption capacity of ∼4.2 mmol g(-1) at 3.0 MPa and a temperature range of 298 ± 10 K. The same material exhibits an impressive hydrogen storage capacity of 1.75 wt% as well at 77 K and 100 kPa. Here, we also propose a mechanism for the formation of activated carbon from spent coffee grounds. At low temperatures, the material has two distinct types with low and high surface areas; however, activation at elevated temperatures drives off the low surface area carbon, leaving behind the porous high surface area activated carbon.
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•The moisture stability was boosted by REM incorporation, AM exchange and pre-adsorbed NH3.•The protective mechanism differences were systematically and explicitly revealed.•Better ...water-resistant Cu-SAPO-34 was obtained by the optimized combination strategy.
The low-temperature hydrothermal instability of Cu-SAPO-34 is an unresolved issue, thus jeopardizing its commercial application in NH3-SCR due to severe structural damage and loss of activity. Herein, we reported that efficient strategies i.e., rare earth metal (REM, denotes Ce, La, and Sm) incorporation, alkali metal (AM, denotes Na, K, and Cs) exchange, and NH3 pre-adsorption were utilized to boost the moisture stability of Cu-SAPO-34 through various protective mechanisms. Our extensive characterizations revealed that AM ions readily exchanged with the susceptive Si–O(H)–Al bonds and ZCu(OH) sites, and at the same time left a majority of undamaged Z2Cu sites providing optimal protective effect in the entire temperature window studied here. On the other hand, REM co-cations only guarded Si–O(H)–Al bonds and Z2Cu sites but not the ZCu(OH) sites, this resulted in a poor protective effect in the low-temperature region. By contrast, chemisorbed NH3 only partially prevented Si–O(H)–Al and ZCu(OH) sites from hydrolysis, explaining why this protective effect was superior to REM in the low-temperature region but inferior to REM in the high-temperature region. These different protective mechanisms were explicitly revealed and were used in combination for the first time showing that the hydrothermal stability of Cu-SAPO-34 could be tuned precisely, the mechanistic guidance given here will surely be useful in developing more durable SCR catalysts.
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