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We demonstrate a pH-mediated fine-tuning method for the transmittance and optical properties of graphene oxide membranes (GOMs) which are assembled at liquid/air interface starting from graphene oxide (GO) hydrosols. The transmittance of GOM continuously decreases with the increase of the pH value of the parent hydrosol. The size and surface chemistry of GO nanosheets are discussed to how to influence the transmittance of GO hydrosol and the optical properties of the resulting membrane since a size classification occurs in acidic condition and a deoxygenate reaction is initiated by basic environment. This study indicates an easy strategy for precisely adjusting the optical properties of graphene-based membrane, which is very important for developing novel optical devices.

Multi-walled carbon nanotubes have been synthesized through the solid-phase transformation of metal-containing glass-like carbon nanoparticles by heating at temperatures of 800–1000 °C. From microscopic observations on the morphologies and structures of the nanotubes and various intermediate objects, it is shown that the transformation occurs by nanoparticles first assembling into wire-like nanostructures, and then transforming into nanotubes via particle–particle coalescence and structural crystallization.

Carbon-encapsulated Fe nanoparticles with size between 5 and 20 nm were synthesized via a picric acid-detonation-induced pyrolysis of ferrocene, which is characterized by a self-heating and extremely fast process. The nanoparticles exhibit well-constructed core–shell structures, with bcc-Fe cores and graphitic shells. The graphitic shells can protect effectively the cores against the attack of HNO3 solution. The formation of the core–shell nanoparticles can be selectively controlled by adjusting the composition of the picric acid-ferrocene mixture, which determines C/Fe atomic ratio of the reaction system. The core–shell nanoparticles are preferably formed at low C/Fe atomic ratios, while tubular structures are formed at high C/Fe ratio. The possible pathway for the carbonencapsulated Fe nanoparticles formation is discussed briefly. 2004 Elsevier Ltd. All rights reserved.

Multi-walled carbon nanotubes (CNTs) have been efficiently synthesized by a self-heating detonation process, operated at low loading densities of picric acid (PA), which acts as the explosive to provide needed high temperatures and parts of carbon sources. Paraffin or benzene provides additional carbon source for tube assembling and hydrogen source to capture oxygen in PA to form H2O and thus to survive some carbon species from oxidation. Cobalt nanoparticles, in situ formed from a detonation-assisted decomposition and reduction of cobalt acetate, show good catalytic activity for nanotube nucleation and growth and for disproportionation reaction of CO generated from the PA detonation. The nanotubes and catalyst particles are characterized by SEM, TEM, EDX, SAED, XRD, and Raman spectroscopy techniques. Some tubes are well crystallized but others have lots of structural defects, especially for the tubes with thin walls and bamboo-like shapes. The catalyst particles show conical shapes and exhibit a fcc crystalline structure of parent cobalt. These data also experimentally show that tube growth is at a very high rate and suggest that it is possible for a large-scale synthesis of CNTs under high-density and high-pressure conditions. � 2003 Elsevier Ltd. All rights reserved.

Fe–C hybrid xerogels were prepared by mixing an aqueous pitch (AP) sol with an iron nitrate solution. The explosion behaviors of the hybrid xerogels and the related reactions were studied by explosion experiments, thermogravimetry (TG) and differential scanning calorimetry (DSC). The results show that the presence of iron nitrate significantly promotes the explosion of the AP. The structures of the explosion products were studied by transmission electron microscopy (TEM), which showed iron–carbon nano-materials of particle sizes of 5–50 nm. Furthermore, nano-particles of iron carbide encapsulated by carbon shells were found. The encapsulation effectively prevents the reductive iron species from oxidation by air. It was also found that the formation of the encapsulation structure is greatly dependent on the explosion conditions.

Fe7C3 nanocrystals encapsulated in carbon nanoparticles, with sizes ranging from 10 to 40 nm, were synthesized via the explosion of a hybrid xerogel containing oxidized pitch and iron nitrate. Explosion of the hybrid xerogel was induced by heat treatment. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were employed to determine the structure of the nanoparticles in the explosion product. The results show that the Fe7C3 nanocrystals are nested inside amorphous carbon shells that protect them from oxidation by air.

Graphene was synthesized by the detonation-assisted reduction of graphite oxide (GO) prepared by the modified Hummers method. Nitrogen-doped reduced GO (N-RGO) was obtained through an in situ nitrogen-doping during detonation. The morphology, elemental composition and structure of the N-RGO were characterized by TEM, SEM, IR, XPS, XRD and Raman spectroscopy. The catalytic activity of the N-RGO as a fuel cell electrode for the oxygen reduction reaction (ORR) was investigated by a rotating ring disk electrode technique. Results showed that the GO was exfoliated and reduced to few layer graphene by the detonation. The oxygen-containing species of GO were reduced and the C/O molar ratio was increased to 26.2, which is much higher than for RGO. Nitrogen, as high as 2.11 at.%, was incorporated into the graphene structure. The diffusion-limited current for ORR increased from 0.24 mA for RGO to 0.49 mA for N-RGO, indicating a higher catalytic activity of N-RGO for ORR than that of RGO.

High yield carbon nanowires were fabricated by a detonation-assisted chemical vapor deposition approach,using low activity iron-nickel as catalyst or a cobalt catalyst to freeze the growth process of carbon nanotubes. TEM observations indicated that the two kinds of carbon nanowires had rough surfaces. Compared with the nanowires obtained from the iron-nickel catalyst,the products obtained from the cobalt catalyst had uniform diameter and were less coalesced. The difference should be associated with the activity of the metal catalysts. Methylene blue degradation experiments showed that the latter carbon nanowires can enhance the photocatalysis activity of ZnS nanocrystals.

The nucleation and growth of carbon nanotubes (CNTs) using chemical vapor deposition with a metal-carbon catalyst have been studied experimentally and theoretically. Results suggest that the nucleation and growth of multiwalled CNTs are not due to the metal alone, but that carbon nuclei (once formed) also contribute to radial and axial growth. Metal particles mainly promote the nucleation and growth of the innermost carbon shell (s), and catalyze the ordering of the carbon atoms to form graphene structures. The intrinsic difference between multiwalled CNT formation and single-walled CNT formation seems to be associated with a self-catalytic function of carbon nuclei.