CN Morphology Research Articles

Maximizing charge dynamics in ZnIn2S4/CN Van der Waals heterojunction for optimal hydrogen production from photoreforming of glucose

Biomass photoreforming stands out as a promising avenue for green hydrogen, leveraging solar energy for the generation and transformation of clean and renewable energy resources. The pursuit of efficient photocatalysts is motivated by the unsatisfied hydrogen evolution performance arising from the complex and stubborn structure of biomass. Herein, we loaded 2-dimensional (2D) ZnIn2S4 onto 2D carbon nitride nanosheets, resulting in the formation of Van der Waals (VDW) heterojunctions (ZIS/CN). Band structure and morphology of CN were rationally tailored through precursor engineering to effectively magnify interfacial internal electric field and minimize diffusion pathway within the VDW heterostructure, realizing optimal charge dynamics in ZIS/DCN. As a result, intensified H2 generation was achieved, which was 350 times higher than pure DCN and outperformed ZIS at the same unit mass. This work offers design principles for VDW heterostructured photocatalysts and accelerates the transition towards a more sustainable manner in biomass reforming.

Doping of graphitic carbon nitride with oxygen by means of cyanuric acid: Properties and photocatalytic applications

Bare and oxygen doped graphitic carbon nitride were synthetized by the thermal polymerization of melamine (CN-M) and the mechanical mixtures of melamine and cyanuric acid, respectively, at 550 °C for 4 h. The ratios of melamine and cyanuric acid were 1:0.5, 1:1 and 1:2 (CN-MCA1, CN-MCA2 and CN-MCA3). The content of oxygen increased from 1.88 wt% (CN-M) to 3.93 wt% (CN-MCA3) and the specific surface area increased from 14 to 41 m2 g−1. The prepared CN materials were characterized by the elemental analysis, UV-Vis diffuse reflectance, X-ray diffraction, Fourier transform infrared spectrometry, the physisorption of nitrogen, scanning electron and high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, the determination of zeta potentials, and the Mott-Schottky method.The addition of cyanuric acid led to partial changes in the CN morphology, as documented by occurrence of CN tubes, increase in the specific surface area and was a source of additional -O- and -OH moieties which modified the CN surface in addition to the spontaneous oxygenation observed in CN-M. The above effects positively influenced photocatalytic activity of the CN materials as demonstrated using Rhodamine B (RhB) and the Ofloxacin antibiotics. The photocatalytic decomposition of Ofloxacin was more efficient than that of RhB and differed in kinetics (first-order vs. zero-order reaction). The reusability and stability of the CN materials was verified by repeating batch photocatalytic decompositions of Ofloxacin experiments for five times.

Application of Nanoroll-Type Ag/g-C<sub>3</sub>N<sub>4</sub> for Selective Conversion of Toxic Nitrobenzene to Industrially-Valuable Aminobenzene

Silver nanoparticles were loaded onto g-C3N4 (CN) with a nanoroll-type morphology (Ag/CN) synthesized using a co-polymerization method for highly selective conversion of toxic nitrobenzene to industrially-valuable aminobenzene. Scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) images of Ag/CN revealed the generation of the nanoroll-type morphology of CN. Additionally, HRTEM analysis provided direct evidence of the generation of a Schottky barrier between Ag and CN in the Ag/CN nanohybrid. Photoluminescence analysis and photocurrent measurements suggested that the introduction of Ag into CN could minimize charge recombination rates, enhancing the mobility of electrons and holes to the surface of the photocatalyst. Compared to pristine CN, Ag/CN displayed much higher ability in the photocatalytic reduction of nitrobenzene to aminobenzene, underscoring the importance of Ag deposition on CN. The enhanced photocatalytic performance and photocurrent generation were primarily ascribed to the Schottky junction formed at the Ag/CN interface, greater visible-light absorption efficiency, and improved charge separation associated with the nanoroll morphology of CN. Ag would act as an electron sink/trapping center, enhancing the charge separation, and also serve as a good co-catalyst. Overall, the synergistic effects of these features of Ag/CN improved the photocatalytic conversion of nitrobenzene to aminobenzene.

The ALMA Lupus protoplanetary disk survey: evidence for compact gas disks and molecular rings from CN

Context. The cyanide radical CN is abundant in protoplanetary disks, with line fluxes often comparable to those of 13CO. It is known to be sensitive to UV irradiation of the upper disk atmosphere, with models predicting ring-shaped emission. Aims. We seek to characterize the CN emission from 94 Class-II disks in the Lupus star-forming region, compare it to observations in other regions, and interpret our observations with a grid of models. The CN emission morphology is discussed for two primordial disks, Sz 71 and Sz 98, and is modeled in more detail. Methods. ALMA observed CN N = 3−2 in Lupus disks down to sensitivities better than previous surveys. Models constructed with the physico-chemical code DALI are used to study the integrated fluxes of the disks and resolved emission of CN in disks without (dust) substructures. Results. CN N = 3−2 is bright, and detected in 38% of sources, but its disk-integrated flux is not strongly correlated to either 13CO or continuum flux. Compared to pre-ALMA single-dish surveys, no significant difference in the CN flux distributions in Lupus and Taurus–Auriga is found, although ρ Ophiuchus disks may be fainter on average. We find ring-shaped CN emission with peak radii of ~50 AU in two resolved disks. Conclusions. A large fraction of sources are faint in CN; only exponential gas surface density cutoffs at Rc ≤ 15 AU can reconcile observations with models. This is the first observational evidence of such a compact gas disk population in Lupus. Absolute intensities and the emission morphology of CN are reproduced by DALI models without the need for any continuum substructure; they are unrelated to the CO snowline location. The observations presented here, together with the modeling of these rings, provide a new probe of the structure and conditions in disks, and particularly their incident UV radiation field, if disk size is determined from the data.

In Situ Construction of Globe‐like Carbon Nitride as a Self‐Cocatalyst Modified Tree‐like Carbon Nitride for Drastic Improvement in Visible‐Light Photocatalytic Hydrogen Evolution

AbstractPhotogenerated carriers possess high recombination efficiency in carbon–nitrogen materials, which results in lower photocatalytic H2 evolution activity. By reviewing the literature, it was concluded that relying only on a structure‐controlled technique was insufficient to reduce the combination of photogenerated carriers without introducing a foreign material or element. Hence, bulk‐like g‐C3N4 [CN (B)], globe/strip‐like g‐C3N4 [CN (G/S)], and globe/tree‐like g‐C3N4 [CN (G/T)] were in situ obtained through a facile calcination method. Similar to platinum (Pt) as a cocatalyst, globe‐like carbon nitride as a self‐cocatalyst was found to improve the separation efficiency of photogenerated carriers effectively. Interestingly, the hollow‐tree‐branch morphology of CN (G/T) effectively transmitted photogenerated holes, which thereby enhanced the photocatalytic H2 evolution activity. The H2 production rates of CN (G/S) and CN (G/T) were almost 10.7 and 18.3 times greater, respectively, than that of CN (B) without the addition of Pt as a cocatalyst. Notably, CN (G/S) and CN (G/T) displayed considerable rates of H2 production in water relative to that shown by CN (B) (no activity) without the use of any sacrificial agent and by using Pt as a cocatalyst. CN (G/T) showed outstanding long‐term stability, as evidenced by seven cycle tests performed over 28 h. The charge separation and transfer process of the compounds were verified by photoluminescence (PL), time‐resolved PL spectroscopy, and photocurrent measurements.

TRAPPIST photometry and imaging monitoring of comet C/2013 R1 (Lovejoy): Implications for the origin of daughter species

We report the results of the narrow band photometry and imaging monitoring of comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla observatory). We gathered around 400 images over 8 months pre- and post-perihelion between September 12, 2013 and July 6, 2014. We followed the evolution of the OH, NH, CN, C3 , and C2 production rates computed with the Haser model as well as the evolution of the dust production. All five gas species display an asymmetry about perihelion, the rate of brightening being steeper than the rate of fading. The study of the coma morphology reveals gas and dust jets which indicate one or several active zone(s) on the nucleus. The dust, C2 , and C3 morphologies present some similarities while the CN morphology is different. OH and NH are enhanced in the tail direction. The study of the evolution of the comet activity shows that the OH, NH, and C2 production rates evolution with the heliocentric distance is correlated to the dust evolution. The CN and, to a lesser extent, the C3 do not display such a correlation with the dust. These evidences and the comparison with parent species production rates indicate that C2 and C3 on one side and OH and NH on the other side could be -at least partially- released from organic-rich grains and icy grains. On the contrary, all evidences point to HCN being the main parent of CN in this comet.

The highly unusual outgassing of Comet 103P/Hartley 2 from narrowband photometry and imaging of the coma

We report on photometry and imaging of Comet 103P/Hartley 2 obtained at Lowell Observatory from 1991 through 2011. We acquired photoelectric photometry on two nights in 1991, four nights in 1997/1998, and 13 nights in 2010/2011. We observed a strong secular decrease in water and all other observed species production in 2010/2011 from the 1991 and 1997/1998 levels. We see evidence for a strong asymmetry with respect to perihelion in the production rates of our usual bandpasses, with peak production occurring ∼10days post-perihelion and production rates considerably higher post-perihelion. The composition was “typical,” in agreement with the findings of other investigators. We obtained imaging on 39 nights from 2010 July until 2011 January. We find that, after accounting for their varying parentage and lifetimes, the C2 and C3 coma morphology resemble the CN morphology we reported previously. These species exhibited an hourglass shape in October and November, and the morphology changed with rotation and evolved over time. The OH and NH coma morphology showed hints of an hourglass shape near the nucleus, but was also enhanced in the anti-sunward hemisphere. This tailward brightness enhancement did not vary significantly with rotation and evolved with the viewing geometry. We conclude that all five gas species likely originate from the same source regions on the nucleus, but that OH and NH were derived from small grains of water and ammonia ice that survived long enough to be affected by radiation pressure and driven in the anti-sunward direction. We detected the faint, sunward facing dust jet reported by other authors, and did not detect a corresponding gas feature. This jet varied little during a night but exhibited some variations from night to night, suggesting it is located near the total angular momentum vector. Overall, our imaging results support the conclusions of other authors that Hartley 2’s “hyperactivity” is caused by icy particles of various sizes that are lifted off the surface and break up in the coma to greatly increase the effective active surface area.

CN MORPHOLOGY STUDIES OF COMET 103P/HARTLEY 2

We report on narrowband CN imaging of Comet 103P/Hartley 2 obtained at Lowell Observatory on 39 nights from 2010 July until 2011 January. We observed two features, one generally to the north and the other generally to the south. The CN morphology varied during the apparition: no morphology was seen in July; in August and September the northern feature dominated and appeared as a mostly face-on spiral; in October, November, and December the northern and southern features were roughly equal in brightness and looked like more side-on corkscrews; in January the southern feature was dominant but the morphology was indistinct due to very low signal. The morphology changed smoothly during each night and similar morphology was seen from night to night. However, the morphology did not exactly repeat each rotation cycle, suggesting that there is a small non-principal axis rotation. Based on the repetition of the morphology, we find evidence that the fundamental rotation period was increasing: 16.7 hr from August 13-17, 17.2 hr from September 10-13, 18.2 hr from October 12-19, and 18.7 hr from October 31-November 7. We conducted Monte Carlo jet modeling to constrain the pole orientation and locations of the active regions based on the observed morphology. Our preliminary, self-consistent pole solution has an obliquity of 10 deg relative to the comet's orbital plane (i.e., it is centered near RA = 257 deg and Dec=+67 deg with an uncertainty around this position of about 15 deg) and has two mid-latitude sources, one in each hemisphere.

Fe-based catalysts from Mg/Fe layered double hydroxides for preparation of N-doped carbon nanotubes

The N-doped carbon nanotubes (CN x) were prepared by catalytic chemical vapor deposition of ethylenediamine with a series of Mg/Fe layered double hydroxides (LDHs) as catalyst precursors. The catalytic actived Fe particles were obtained by calcination of LDHs containing Fe 3+ ions followed by reduction. The purification of CN x was carried out using a diluted nitric acid. The obtained products were characterized by X-ray diffraction, inductively coupled plasma spectrum, transmission electron microscope, X-ray photoelectron spectroscopy and Raman spectroscopy. The growth temperature has a distinct effect on the morphology and structure of CN x. Enhancing the growth temperature from 550 °C to 750 °C, the morphology of CN x changes from straight to bamboo-like and to bell-like, whereas the N-doped level decreases from 8.8 to 5.7 at.%. The content of Fe in precursors has little effect on the morphology of CN x, but it affects the N-doped level and structure. These results indicate that the morphology and structure of CN x are related to the synthetic parameters, like the growth temperature and composition of catalyst.

Catalytic synthesis of nitrogen-doped multi-walled carbon nanotubes using layered double hydroxides as catalyst precursors

The nitrogen (N)-doped carbon (CNx) nanotubes were synthesized by pyrolysis of ethylenediamine with Ni1·07Mg1·01AlO3·58, Ni1·99Mg0·29AlO3·78, and Ni2·31Mg0·08AlO3·89 mixed oxides as catalysts at 650°C. Those mixed oxides were obtained by calcination of corresponding layered double hydroxide precursors (LDHs). Structure and composition of LDHs and mixed oxides were characterized by X-ray diffraction (XRD) and Inductively coupled plasma spectrum. X-ray photoelectron spectroscopy and transmission electron microscope were used to characterize the N content, proportion of pyridine-like N structure and morphology of CN x nanotubes. The results showed that the tubes grown with Ni2·31Mg0·08AlO3·89 as catalysts had more obvious bamboo-like structure, larger diameter than those grown with Ni1·07Mg1·01AlO3·58 and Ni1·99Mg0·29AlO3·78. The N content and proportion of graphitic-like N structures increased with the content of Ni2+ increasing in LDH precursors. The morphology, N content and pyridine-like N structures for CN x nanotubes can be controlled to a certain extent by varying the content of Ni2+ in LDH precursors.

Cyanogen Jets and the Rotation State of Comet Machholz (C/2004 Q2)

Extensive observations of Comet Machholz (C/2004 Q2) from 2005 February, March, and April were used to derive a number of the properties of the comet's nucleus. Images were obtained using narrowband comet filters to isolate the CN morphology. The images revealed two jets that pointed in roughly opposite directions relative to the nucleus and changed on hourly timescales. The morphology repeated itself in a periodic manner, and this fact was used to determine a rotation period for the nucleus of 17.60 ± 0.05 hr. The morphology was also used to estimate a pole orientation of R.A. = 50°, decl. = +35°, and the jet source locations were found to be on opposite hemispheres at mid-latitudes. The longitudes are also about 180° apart, although this is not well constrained. The CN features were measured to be moving at about 0.8 km s-1, which is close to the canonical value typically quoted for gas outflow. Future modeling of the CN features will be used to improve and extend these results.

Structural and bonding properties of carbon nitride films prepared by dc magnetron sputtering

Amorphous carbon nitride (CN x ) films have been deposited onto Si(100) substrates by reactive sputtering of a graphite target in a pure N 2 ambient. A modified cylindrical DC magnetron plasma was used as a sputter deposition source and the effects of substrate DC self-bias voltage caused by RF bias on film properties were investigated. X-ray photoelectron spectroscopy (XPS) spectra of N 1s and C 1s electron confirmed the existence of multiple bonding states for carbon and nitrogen (sp 2 and sp 3) in the film. Fourier transform infrared (FTIR) spectroscopy studies showed a systematic variation in spectra by a DC self-bias voltage. Raman spectra revealed two peaks corresponding to G band (1580 cm −1) and D band (1370 cm −1). The ratio of integrated intensities of D and G band ( I D/ I G) increased with DC self-bias voltage, suggesting increased disorder by the ion bombardment on growing film. Variation in the morphology of CN x films deposited at different bias voltage was examined by scanning electron microscopy (SEM).