Two-Dimensional Nanomaterials and Their Composites for Electrochemical Detection of Toxic Mercury Ions in Water

The presence of trace amounts of mercury ion (Hg2+) in drinking water has a detrimental effect on human health. The development of an electrochemical sensor for Hg2+ detection is still challenging to obtain ultra-trace sensitivity, excellent selectivity, wide Linear Detection Ranges (LDRs), and ultra-low detection limit. This work presents an electrochemical sensor based on two-dimensional nanomaterials and their composites for the enhanced sensing of Hg2+ in water. Graphene oxide (GO)-silver nanowires (AgNWs) composite and metallic 1T phase tungsten disulfide (WS2) microflowers were utilized for the fabrication of electrochemical sensors using drop-casting. Under the optimized experimental conditions, the GO-AgNWs composite modified sensor showed a high sensitivity of ~ 0.29 μA/nM and linear response in the range of 1-70 nM toward Hg2+, whereas 1T-WS2 microflowers modified sensor showed excellent sensitivities of ~ 15.9 μA/μM, 2.54 μA/μM, 13.84 μA/μM, and 0.04646 μA/μM toward Hg2+ with LDRs of 1- 90 nM, 0.1-0.4 μM, 0.5-1.0 μM, and 0.1-1.0 mM, respectively. An ultra-low detection limit of 0.1 nM and 0.0798 nM or 79.8 pM toward Hg2+ was obtained by GO-AgNWs composite and 1T-WS2 modified sensors, which are well below the guideline value recommended by the World Health Organization and the United States Environmental Protection Agency. The sensors exhibited excellent selectivity for Hg2+ against other heavy metal ions including Cu2+, Fe3+, Ni2+, Pb2+, Cr3+, K+, Na+, Ag+, Sn2+, and Cd2+. The thus obtained excellent sensitivity and selectivity with wide LDRs and ultra-low detection limits can be attributed to the synergistic effect of GO and conductive AgNWs, high conductivity, large surface area microflower structured 1T-WS2, and the complexation of Hg2+ ions with sulfur (S2-) and GO. In addition to good repeatability, reproducibility, and stability, these sensors showed practical feasibility of Hg2+ detection in tap water suggesting a promising device for real applications

Characterization and Applications of Metal Ferrite Nanocomposites

This Special Issue focuses on ferrite-based nanomaterial synthesis and characterization including (i) Synthesis, (ii) Advanced chemical and physical characterization of structure and properties, (iii) Magnetic behaviour, (iv) Computational and theoretical studies of reaction mechanisms, kinetics, and thermodynamics, (v) Applications of nanomaterials in environmental, biological, catalytic, medical, cultural heritage, food, geochemical, polymer, and materials science. Additionally, the effect of reaction time, reaction temperature, and oleic acid concentration on the properties of CoFe2O4 nanoparticles was investigated. In this Special Issue, the effect of SiO2 embedding on the production of single-phase ferrites, as well as on the structure, morphology and magnetic properties of (Zn0.6Mn0.4Fe2O4)δ(SiO2)100−δ (δ = 0–100%) NPs, synthesized by the sol–gel method and annealed at different temperatures, is analysed. The obtained results indicated that the preparation route strongly influences the particle sizes and, implicitly, the magnetic behaviour of the NPs. The Zn0.6Mn0.4Fe2O4 embedded in SiO2 exhibits superparamagnetic-like behaviour, whereas the unembedded Zn0.6Mn0.4Fe2O4 behaves similar to a high-quality ferrimagnet. This Special Issue also includes the study on Bi2Cu(C2O4)4·0.25H2O synthesis by thermolysis, followed by its integration within a CuBi/carbon nanofiber (CNF) paste electrode and its application in electrochemical detection of amoxicillin (AMX) in aqueous solution. By adding a concentration step in the detection protocol, selective and simultaneous detection of AMX in a multi-component matrix is also possible

Synthesis and Characterization of Transition Metal Oxide and Dichalcogenide Nanomaterials for Energy and Environmental Applications

Transition metal oxides (TMOs) and transition metal dichalcogenides (TMDs) have gained immense interest recently for energy and environmental applications due to their exceptional structural, electronic, and optical properties. For example, titanium dioxide (TiO2) as one of the TMO photocatalysts has been widely studied due to its stability, non-toxicity, wide availability, and high efficiency. However, its wide bandgap significantly limits its use under visible light or solar light. Recent studies also show that semiconducting TMDs could be used as potential supercapacitor electrode materials and platinum (Pt)-free electrocatalysts for economical utilization of renewable energy, because the high cost and scarcity of Pt have impeded the large-scale commercialization of many green technologies. In this dissertation study, various novel TMO and TMD nanomaterials are designed and synthesized, and their catalytic performance is further investigated. First, a facile route for the controllable synthesis of modified TiO2 is designed to improve its photocatalytic efficiency under the visible/solar light. The resulting Ti3+-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4), showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti4+ on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributing to the high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti3+-doped TiO2 under visible-light can be tuned. The band gap of Ti3+-doped TiO2 based on the Kubelka-Munk function is 3.1 eV, which is smaller than that of pristine TiO2 (3.28 eV), confirming that adding NaBH4 as a reductant causes the absorption edge of TiO2 to shift to a lower energy region. After 20 min of simulated sunlight irradiation of photocatalytic reactions for the degradation of methylene blue (MB) aqueous solution, nearly 97.2% of MB was degraded by the sample TiO2-4 (reduced by 12 g of NaBH4 in the hydrothermal reaction), compared with the degradation efficiency of the pristine TiO2 (23.5%). The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials with enhanced visible light absorption, narrowed band gap, and improved photocatalytic activity. Second, cobalt sulfide-based (CoSx) nanostructures as one of the TMDs are competitive candidates for fabrication of supercapacitor electrodes due to their high specific surface area, high electrical conductivity, and redox-active structures. However, CoSx materials still suffer from relatively low specific capacitances, degradation of performance over long cycling duration, and tedious synthesis and assembly methods. Hence, metallic vertically-aligned cobalt pyrite (CoS2) nanowires (NWs) are prepared directly on current collecting electrodes, e.g., carbon cloth or graphite disc, for high-performance supercapacitors. These vertically-aligned CoS2 NWs have a variety of advantages for supercapacitor applications. Because the metallic CoS2 NWs are synthesized directly on the current collector, the good electrical connection enables efficient charge transfer between the active CoS2 materials and the current collector. In addition, the open spaces between the vertical NWs lead to a large accessible surface area and afford rapid mass transport. Moreover, the robust CoS2 NW structure results in high stability of the active materials during long-term operation. Electrochemical characterization reveals that the CoS2 NWs enable a large specific capacitance (828.2 F/g at a scan rate of 0.01 V/s) and excellent long-term cycling stability (0-2.5% capacity loss after 4,250 cycles at 5 A/g) for pseudocapacitors. This example of vertically-aligned metallic CoS2 NWs for supercapacitor applications expands the opportunities for transition metal sulfide-based nanostructures in emerging energy storage applications. Third, to combine the advantages of TMOs and TMDs, an aerosol processing method is developed for the facile and green synthesis of reduced graphene oxide (rGO)/tungsten disulfide (WS2)/tungsten trioxide (WO3) ternary nanohybrids, because both TMOs and TMDs are promising candidates for platinum-free electrocatalysts in renewable energy applications. The resulting hybrid material has a spherical structure constructed of crumpled graphene and WS2/WO3 nanorods. The crumpled graphene/WS2/WO3 (CGTH) catalyst showed a superior electrocatalytic activity in the hydrogen evolution reaction (HER), with a Tafel slope of 37 mV/dec and an onset potential of 96 mV. Compared with reported MoS2/WS2-based electrocatalysts, this hybrid material shows one of the highest catalytic activities in HER. The environmentally-friendly synthesis and outstanding performance suggest a great potential of CGTH for noble metal-free electrocatalysts in water splitting. Next, in order to improve the specific capacity of lithium-ion batteries (LIBs)/ potassium-ion batteries (PIBs) and relieve volume expansion of nanoparticles to fulfill the urgent need of reliable energy storage applications, TMD nanomaterials especially MoS2 quantum dots (QDs) have been considered promising anode materials for LIBs owing to their higher theoretical capacity and better rate capability compared with commercial graphite anodes. An exfoliated mesoporous MoS2 QDs-graphite composite anode was designed and investigated. The MoS2 QDs are located in the void spaces between graphite particles, thereby preventing the graphite particles from losing electrical contact with the current collector and enhancing the cycling performance of the MoS2/graphite composite anode. The optimized MoS2 QDs with graphite composites displayed good charge/discharge characteristics and the capacity maintained at 449.8 mAh g-1 after 300 charge/discharge cycles for LIBs. And the MoS2 QDs for PIB cells exhibited a stable capacity of approximately 409 mAh g-1 for 17 cycles. Finally, metal-organic frameworks (MOFs) have attracted substantial research attention owing to their tunable pore size, high pore volume, high specific surface area, and highly ordered crystalline porous networks. Previous studies have mostly focused on sensing, drug delivery, batteries, and selective catalysis; however, their application as photocatalysts has not been thoroughly reported. It is well known that bulk MoS2 is unsuitable for photocatalytic applications due to the insufficient reduction and oxidation ability for the photocatalysis. However, exfoliated MoS2 exhibits a direct band gap of 2.8 eV resulting from quantum confinement, which enables it to possess suitable band positions and to retain good visible-light absorption ability. As a result, it is considered to be a promising candidate for photocatalytic applications. Encapsulating exfoliated MoS2 into MOF exhibits enhanced absorption in the visible light range compared with pure MOF and the highest hydrogen production rate could reach 68.4 μmol h-1g-1, which is much higher than that on pure MOF. With suitable band structure and improved light-harvesting ability, exfoliated MoS2@MOF can be a potential photocatalyst for hydrogen production. This dissertation study suggests that modified TiO2 and exfoliated MoS2@MOF can be efficient photocatalysts with enhanced visible light absorption ability; metallic CoS2 NWs could be active materials with a large specific capacitance and excellent stability; reduced graphene oxide (rGO)/tungsten disulfide (WS2)/tungsten trioxide (WO3) as a ternary nanohybrid offers advantages of TMOs and TMDs, making it an outstanding noble-metal free electrocatalyst in water splitting; and MoS2 QDs with relieved volume expansion are promising anode materials for LIBs/PIBs. The study provides a scientific foundation to design and discover low-cost, efficient and stable TMOs and TMDs candidates for suitable energy and environmental applications

Magnetic nanoparticles: From Design and Synthesis to Real World Applications

The increasing number of scientific publications focusing on magnetic materials indicates growing interest in the broader scientific community. Substantial progress was made in the synthesis of magnetic materials of desired size, morphology, chemical composition, and surface chemistry. Physical and chemical stability of magnetic materials is acquired by the coating. Moreover, surface layers of polymers, silica, biomolecules, etc. can be designed to obtain affinity to target molecules. The combination of the ability to respond to the external magnetic field and the rich possibilities of coatings makes magnetic materials universal tool for magnetic separations of small molecules, biomolecules and cells. In the biomedical field, magnetic particles and magnetic composites are utilized as the drug carriers, as contrast agents for magnetic resonance imaging (MRI), and in magnetic hyperthermia. However, the multifunctional magnetic particles enabling the diagnosis and therapy at the same time are emerging. The presented review article summarizes the findings regarding the design and synthesis of magnetic materials focused on biomedical applications. We highlight the utilization of magnetic materials in separation/preconcentration of various molecules and cells, and their use in diagnosis and therapy

Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field

Exclusive Papers of the Editorial Board Members (EBMs) of the Materials Chemistry Section of Molecules

The book is intended to collect the recent contributions (either research or review papers) to the development of the “Materials Chemistry” research fields by the Editorial Board Members of the Materials Chemistry Section of Molecules. The aim is to present the recent progress in the fields and to highlight the key role of Materials Chemistry in a multidisciplinary research context

Synthesis, Characterisation and Application of RU(II) and OS(II) Complexes and Porous Framework Materials.

Nowadays, cancer diseases have a massive global impact on our health services, economies, and resources. Cancer research has undoubtedly become one of the most important pursuits of modern science due to high mortality rates. Cancer is caused by malfunctioning cells, which cause them to divide rapidly, grow to abnormal sizes, and infiltrate neighbouring organs, eventually leading to death. Due to abnormal resistance of cancerous cells to naturally released apoptotic signals, three main treatment strategies for cancer are initiated: surgical removal of the tumour, chemical intrusion into the cancer cells, and chemotherap

Novel Graphene Oxide Based Nanocomposites: Synthesis and Application Towards Adsorptive Removal of Toxic Inorganic/Organic Pollutants from Aqueous Media

In this doctoral work, we have synthesized a series of GO based composite nanoadsorbents such as MgO-MgFe2O4 decorated GO (MgO-MgFe2O4/GO), amine functionalized GO mounted with ZnO-ZnFe2O4 (NH2-GO/ZnO-ZnFe2O4), AlOOH-FeOOH nanorods functionalized GO (GO/AlOOH-FeOOH) and GO/g-C3N4 decorated with Fe3O4 (GO/g-C3N4-Fe3O4) nanomaterials by using hydrothermal method. Then the prepared GO based metal oxide nanocomposites were used as novel adsorbent for adsorption study of inorganic pollutants such as fluoride ions (F-), hexavalent chromium (Cr(VI)), arsenate (As(V)) and organic pollutants like methylene blue (MB) dye, tetracycline (TC) antibiotic from water. The formation, composition, bonding, crystalline phase, surface morphology, size, and surface area of these prepared nanocomposites were analyzed by XRD, FTIR, Raman, XPS, FESEM, HRTEM, and BET analytical techniques. Batch adsorption experiments were carried out under various conditions including pH, time, concentration, adsorbent dose and temperature. The synthesized MgO-MgFe2O4/GO magnetic nanocomposite was used as adsorbent for removal of F- ions from water. The maximum adsorption capacity for F- ions removal is found to be 34 mg/g, which is higher as comparable to MgO-Fe2O3 nanocomposite. The amine functionalized GO decorated with ZnO-ZnFe2O4 (NH2-GO/ZnO-ZnFe2O4) nanocomposite material was used for remediation of Cr (VI) from water. It was observed that introduction of NH2 groups to GO/ZnO-ZnFe2O4 nanocomposite play a very important role for remediation of hexavalent chromium with a maximum uptake capacity of 109.89 mg/g. Apart from this we have also prepared GO/AlOOH-FeOOH composite nanomaterials by one step hydrothermal method and have used for decontamination of arsenate (As(V)) ions from water. Experimental finding reveals that the prepared GO based nanocomposite material is highly efficient for remediation of As(V) ions from water. Furthermore, we have also synthesized GO/g-C3N4 (graphitic carbon nitride) 2D layered composite materials decorated with Fe3O4 nanoparticles and have used for removal of methylene blue (MB) dye and tetracycline (TC) antibiotic from aqueous media. It was found that the adsorption of TC and MB was pH dependent and maximum adsorption capacities of 120 and 220 mg/g were achieved for TC and MB respectively. All the prepared GO based nanoadsorbents were regenerated and reused up to 5 successive cycles without major loss in their sorption capacity. From the obtained experimental results, plausible adsorption mechanism has been proposed for all adsorption process

Rational Design of Non-precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

This reprinted edition of the Special Issue entitled “Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes” covers some of the recent advances in relation to the fabrication and fine-tuning of metal oxide catalysts by means of advanced synthetic and/or promotional routes. It consists of fourteen high-quality papers on various aspects of catalysis, related to the rational design and fine-tuning strategies during some of the most relevant applications in heterogeneous catalysis, such as N2O decomposition, the dry reforming of methane (DRM), methane combustion and partial oxidation, and selective catalytic reduction (SCR), among others