Investigations on electrical conductivity and dielectric properties of graphene oxide nanosheets synthetized from modified Hummer’s method

Biochar with enhanced performance prepared based on "graphite-structure regulation" conjecture designed to effectively control water pollution

In this work, corn straw was used as raw material, Hummers method and activation were used to adjust the graphite structure in biochar, and preparing straw based biochar (H-BCS) with ultra-high specific surface area (3441.80 m2/g), highly total pore volume (1.9859 cm3/g), and further enhanced physicochemical properties. Compared with untreated straw biochar (BCS), the specific surface area and total pore volume of H-BCS were increased by 47.24 % and 55.85 %, respectively. H-BCS showed good removal ability in subsequent experiments by using chloramphenicol (CP), hexavalent chromium (Cr6+), and crystal violet (CV) as adsorption models. In addition, the adsorption capacities of H-BCS (CP: 1396.30 mg/g, Cr6+: 218.40 mg/g, and CV: 1246.24 mg/g) are not only higher than most adsorbents, even after undergoing 5 cycles of regeneration, its adsorption capacity remains above 80 %, indicating significant potential for practical applications. In addition, we also speculated and analyzed the conjecture about the "graphite-structure regulation" during the preparation process, and finally discussed the possible mechanism during the adsorption processes. We hope this work could provide a new strategy to solve the restriction of biochar performance by further exploring the regulation of graphite structure in carbon materials.

Application of graphene oxide in tumor targeting and tumor therapy

Graphene oxide (GO), as a kind of two-dimensional sp2 carbon nanomaterials, has attracted great attention in many fields in the past decade. Due to its unique physical and chemical properties, GO is showing great promise in the field of biomedicine. For GO, all the atoms on its surface are exposed to the surface with ultra-high specific surface area, and a variety of groups on the surface, such as carboxyl, hydroxyl and epoxy groups, can effectively bind/load various biomolecules. Due to the availability of these groups, GO also possesses excellent hydrophilicity and biocompatibility for the modification of the desired biocompatible molecules or polymers on the surface of GO. The nano-network structure and hydrophobicity of GO enable it to load a large number of hydrophobic drugs containing benzene rings and it has been widely used as a multi-functional nano-carrier for chemotherapeutic drug or gene delivery. This review article will give an in-depth overview of the synthesis methods of GO, the advantages and disadvantages of GO used in nano-drug delivery system, the research progress of GO as a stimulus-responsive nano-drug carrier, and the application of these intelligent systems in cancer treatment.

Hydrothermal synthesis of polyaniline nanospheres coupled with graphene oxide for enhanced specific capacitance performances

Polyaniline is one of the most common electrode materials for supercapacitors. The morphology of polyaniline directly affects the properties of polyaniline. In this paper, a new method for preparing hollow polyaniline nanospheres is described. Polyaniline-S with solid and hollow structures are successfully synthesized by the hydrothermal method, through varying the amounts of the catalyst and oxidant. The prepared hollow nanospheres have uniform particle size, a smooth surface, and uniform wall thickness. The hollow structure provides rapid permeability to the material, facilitating the transfer and transport of charges and ions in the electrolyte, and it can also act as an ion storage tank to increase the accumulation of ions inside. The specific capacitance of polyaniline-S is high at 235 F g-1 at 0.5 A g-1. To reduce the aggregation of polyaniline-S and improve the electrochemical activity, polyaniline-S, and graphene oxide are composited using the interfacial electrostatic interaction. The content of graphene oxide has a significant influence on the electrochemical performance of the composites. The specific capacitance of the polyaniline-S/ graphene oxide composite with a 10% loading amount of graphene oxide reaches 535 F g-1 at 0.5 A g-1, increase of nearly 128% compared to representing a significant polyaniline-S. The specific capacitance retention rate is 93.6% after 10,000 cycles.

Structural Control and Electrical Behavior of Thermally Reduced Graphene Oxide Samples Assisted with Malonic Acid and Phosphorus Pentoxide

We present a detailed study of the structural and electrical changes occurring in two graphene oxide (GO) samples during thermal reduction in the presence of malonic acid (MA) (5 and 10 wt%) and P2O5 additives. The morphology and de-oxidation efficiency of reduced GO (rGO) samples are characterized by Fourier transform infrared, X-ray photoelectron, energy-dispersive X-ray, Raman spectroscopies, transmission electron and scanning electron microscopies, X-ray diffraction (XRD), and electrical conductivity measurements. Results show that MA and P2O5 additives are responsible for the recovery of π-conjugation in rGO as the XRD pattern presents peaks corresponding to (002) graphitic-lattice planes, suggesting the formation of the sp2-like carbon structure. Raman spectra show disorders in graphene sheets. Elemental analysis shows that the proposed reduction method in the presence of additives also suggests the simultaneous insertion of phosphorus with a relatively high content (0.3–2.3 at%) in rGO. Electrical conductivity measurements show that higher amounts of additives used in the GO reduction more effectively improve electron mobility in rGO samples, as they possess the highest electrical conductivity. Moreover, the relatively high conductivity at low bulk density indicates that prepared rGO samples could be applied as metal-free and non-expensive carbon-based electrodes for supercapacitors and (bio)sensors.

Graphene-Modified Co-B-P Catalysts for Hydrogen Generation from Sodium Borohydride Hydrolysis

Sodium borohydride (NaBH₄) is considered a good candidate for hydrogen generation from hydrolysis because of its high hydrogen storage capacity (10.8 wt%) and environmentally friendly hydrolysis products. However, due to its sluggish hydrogen generation (HG) rate in the water, it usually needs an efficient catalyst to enhance the HG rate. In this work, graphene oxide (GO)-modified Co-B-P catalysts were obtained using a chemical in situ reduction method. The structure and composition of the as-prepared catalysts were characterized, and the catalytic performance for NaBH₄ hydrolysis was measured as well. The results show that the as-prepared catalyst with a GO content of 75 mg (Co-B-P/75rGO) exhibited an optimal catalytic efficiency with an HG rate of 12087.8 mL min^-1 g^-1 at 25 °C, far better than majority of the findings that have been reported. The catalyst had a good stability with 88.9% of the initial catalytic efficiency following 10 cycles. In addition, Co-, B-, and P-modified graphene showed a synergistic effect improving the kinetics and thermodynamics of NaBH₄ hydrolysis with a lower activation energy of 28.64 kJ mol^-1. These results reveal that the GO-modified Co-B-P catalyst has good potential for borohydride hydrolysis applications.

Increased structural defects of graphene oxide compromised reductive capacity of ZVI towards hexavalent chromium

Graphene oxide (GO) was treated with irradiation beams to understand the defective degree of carbon structure of GO in relation to electron transfer property of impregnated zerovalent iron (ZVI). The GO-supported ZVI (ZVI/GO) was synthesized and then characterized by an X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The results showed that the oxygen-bearing functional groups, oxygen content and structural disorder were increased as a function of irradiation beam intensity. ZVI was dominant in the composites, but proportion of iron oxide increased with greater oxygen content. Batch sorption revealed that Cr(VI) removal decreased from 20.11 g kg^-1 to 2.30 g kg^-1 as solution pH rose from 3 to 9. Cr(VI) removal capacity was 26.39 g kg^-1, 23.12 g kg^-1 and 12.35 g kg^-1 for ZVI/GO₀, ZVI/GO_12.3 and ZVI/GO_36.9, respectively. The reduction capacity of sorbents followed similar trends as Cr(VI) sorption as per desorption experiment, which accounted for a major Cr(VI) detoxification mechanism by ZVI/GO composites. The electrochemical tests demonstrated that unfavorable electron transfer rate of ZVI/GO composites was aggravated by greater structural disorder of GO. Thus, higher dose of irradiations could create more disorder in graphitic carbon and promote oxidation of ZVI, which hindered Cr(VI) reduction.

Experimental Evaluation on the Catalytic Activity of a Novel CeZrK/rGO Nanocomposite for Soot Oxidation in Catalyzed Diesel Particulate Filter

A nanostructured solid solution catalyst CeZrK/rGO for soot oxidation in catalyzed diesel particulate filter was synthesized using the dipping method. The reduced graphene oxide (rGO) was used as the catalyst carrier, and CeO2, ZrO2, and K2O were mixed with the molar ratio of 5:1:1, 5:2:2 and 5:3:3, which were referred to as Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO, respectively. The structure, morphology and catalytic activity of the CeZrK/rGO nanocomposites were thoroughly investigated and the results show that the CeZrK/rGO nanocomposites have nanoscale pore structure (36.1–36.9 nm), high-dispersion quality, large specific surface area (117.2–152.4 m2/g), small crystallite size (6.7–8.3 nm), abundant oxygen vacancies and superior redox capacity. The 50% soot conversion temperatures of Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO under tight contact condition were decreased to 352 °C, 339 °C and 358 °C respectively. The high catalytic activity of CeZrK/rGO nanocomposites can be ascribed to the following factors: the doping of Zr and K ions causes the nanocrystalline phase formation in CeZrK solid solutions, reduces the crystallite size, generates abundant oxygen vacancies and improves redox capacity; the rGO as a carrier provides a large specific surface area, thereby improving the contact between soot and catalyst.