scholarly journals Direction-Dependent Properties in Inverted Carbon Nitride Colloidal Glasses with Gradient Porosity

2021 ◽  
Author(s):  
Jochen Bahner ◽  
Lukas Dobler ◽  
Marvin Frisch ◽  
Lars Vogelsang ◽  
Helmut Cölfen ◽  
...  
Keyword(s):  
Band Gap ◽  
Carbon Nitride ◽  
Analytical Ultracentrifugation ◽  
Glass Structure ◽  
Dense Packing ◽  
Gradient Material ◽  
Wall Material ◽  
Structural Colors ◽  
Functional Gradient Material ◽  
Colloidal Glasses

It is well known that the step from a dense packing of colloidal beads to the inverted systems was important for the optimization of photonic crystal properties. Inverted opals made of high-refractive index semiconductors have attracted great attention due to their supreme optical features such as the occurrence of a photonic band-gap and because of an astonishing behavior in photocatalysis or for photovoltaics caused by so-called slow photons. It is much less known that photonic glasses, despite being disordered, exhibit unique optical properties too like random lasing or high-contrast structural colors. In analogy to opals and inverted opals, one can expect that inverted colloidal glasses may lead to an amplification of photonic properties as well or even to the emergence of unexpected features. An inverted photonic glass is characterized by a dense packing of monodisperse voids with colloidal dimensions without any long-range order. The preparation of inverse photonic glasses has rarely been reported by now and cases for materials composed of a semiconductor as a pore-wall material are unknown. The synthesis of porous carbon nitride (C<sub>3</sub>N<sub>4</sub>) with inverted colloidal glass structure is demonstrated here using a template approach. The formation of the template with glass-like order is achieved by analytical ultracentrifugation (AUZ) of size-selected silica colloids, followed by infiltration of a precursor sol, transformation to carbon nitride and the final removal of the template. The use of AUZ is particularly important because it even allows to use a mixture of differently sized template particles, which are gradually fractionated. Monoliths with optimized morphological features exhibiting a gradient porosity and highly accessible pores are obtained. The result are materials with a graded structure. What makes such functional gradient material interesting is, a dependence of the optical features on the position can be expected. In addition, the method presented here allows to synthesize materials with adjustable composition ranging from carbon over nitrogen-doped carbon to C<sub>3</sub>N<sub>4</sub> with either graphitic or polymeric structure. Therefore, the optical band gap is highly adjustable and tunable with regards to the photonic properties, as confirmed by optical absorption and photoluminescence measurements.

scholarly journals Direction-Dependent Properties in Inverted Carbon Nitride Colloidal Glasses with Gradient Porosity

2021 ◽  
Author(s):  
Jochen Bahner ◽  
Lukas Dobler ◽  
Marvin Frisch ◽  
Lars Vogelsang ◽  
Helmut Cölfen ◽  
...  
Keyword(s):  
Band Gap ◽  
Carbon Nitride ◽  
Analytical Ultracentrifugation ◽  
Glass Structure ◽  
Dense Packing ◽  
Gradient Material ◽  
Wall Material ◽  
Structural Colors ◽  
Functional Gradient Material ◽  
Colloidal Glasses

It is well known that the step from a dense packing of colloidal beads to the inverted systems was important for the optimization of photonic crystal properties. Inverted opals made of high-refractive index semiconductors have attracted great attention due to their supreme optical features such as the occurrence of a photonic band-gap and because of an astonishing behavior in photocatalysis or for photovoltaics caused by so-called slow photons. It is much less known that photonic glasses, despite being disordered, exhibit unique optical properties too like random lasing or high-contrast structural colors. In analogy to opals and inverted opals, one can expect that inverted colloidal glasses may lead to an amplification of photonic properties as well or even to the emergence of unexpected features. An inverted photonic glass is characterized by a dense packing of monodisperse voids with colloidal dimensions without any long-range order. The preparation of inverse photonic glasses has rarely been reported by now and cases for materials composed of a semiconductor as a pore-wall material are unknown. The synthesis of porous carbon nitride (C<sub>3</sub>N<sub>4</sub>) with inverted colloidal glass structure is demonstrated here using a template approach. The formation of the template with glass-like order is achieved by analytical ultracentrifugation (AUZ) of size-selected silica colloids, followed by infiltration of a precursor sol, transformation to carbon nitride and the final removal of the template. The use of AUZ is particularly important because it even allows to use a mixture of differently sized template particles, which are gradually fractionated. Monoliths with optimized morphological features exhibiting a gradient porosity and highly accessible pores are obtained. The result are materials with a graded structure. What makes such functional gradient material interesting is, a dependence of the optical features on the position can be expected. In addition, the method presented here allows to synthesize materials with adjustable composition ranging from carbon over nitrogen-doped carbon to C<sub>3</sub>N<sub>4</sub> with either graphitic or polymeric structure. Therefore, the optical band gap is highly adjustable and tunable with regards to the photonic properties, as confirmed by optical absorption and photoluminescence measurements.

scholarly journals Prediction of Band Gap Energy of Doped Graphitic Carbon Nitride Using Genetic Algorithm-Based Support Vector Regression and Extreme Learning Machine

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 411
Author(s):  
Taoreed O. Owolabi ◽  
Mohd Amiruddin Abd Rahman
Keyword(s):  
Genetic Algorithm ◽  
Visible Light ◽  
Band Gap ◽  
Carbon Nitride ◽  
Activation Function ◽  
Graphitic Carbon ◽  
Graphitic Carbon Nitride ◽  
Support Vector ◽  
Learning Machine ◽  
Photocatalytic Applications

Graphitic carbon nitride is a stable and distinct two dimensional carbon-based polymeric semiconductor with remarkable potentials in organic pollutants degradation, chemical sensors, the reduction of CO2, water splitting and other photocatalytic applications. Efficient utilization of this material is hampered by the nature of its band gap and the rapid recombination of electron-hole pairs. Heteroatom incorporation due to doping alters the symmetry of the semiconductor and has been among the adopted strategies to tailor the band gap for enhancing the visible-light harvesting capacity of the material. Electron modulation and enhancement of reaction active sites due to doping as evident from the change in specific surface area of doped graphitic carbon nitride is employed in this work for modeling the associated band gap using hybrid genetic algorithm-based support vector regression (GSVR) and extreme learning machine (ELM). The developed GSVR performs better than ELM-SINE (with sine activation function), ELM-TRANBAS (with triangular basis activation function) and ELM-SIG (with sigmoid activation function) model with performance enhancement of 69.92%, 73.59% and 73.67%, respectively, on the basis of root mean square error as a measure of performance. The four developed models are also compared using correlation coefficient and mean absolute error while the developed GSVR demonstrates a high degree of precision and robustness. The excellent generalization and predictive strength of the developed models would ultimately facilitate quick determination of the band gap of doped graphitic carbon nitride and enhance its visible-light harvesting capacity for various photocatalytic applications.

Development of Modelling Methods for Materials to be Used as Bone Substitutes

2007 ◽  
Vol 361-363 ◽  
pp. 903-906 ◽  
Author(s):  
R. Gabbrielli ◽  
I.G. Turner ◽  
Chris R. Bowen
Keyword(s):  
Mechanical Strength ◽  
Volume Fraction ◽  
Bone Substitutes ◽  
Gradient Material ◽  
Periodic Surfaces ◽  
Triply Periodic ◽  
Functional Gradient Material ◽  
Spatial Periodicity ◽  
Bearing Materials ◽  
Modelling Methods

The demand in the medical industry for load bearing materials is ever increasing. The techniques currently used for the manufacture of such materials are not optimized in terms of porosity and mechanical strength. This study adopts a microstructural shape design approach to the production of open porous materials, which utilizes spatial periodicity as a simple way to generate the models. A set of triply periodic surfaces expressed via trigonometric functions in the implicit form are presented. A geometric description of the topology of the microstructure is necessary when macroscopic properties such as mechanical strength, stiffness and isotropy are required to be optimised for a given value of volume fraction. A distinction between the families of structures produced is made on the basis of topology. The models generated have been used successfully to manufacture both a range of structures with different volume fractions of pores and samples of functional gradient material using rapid prototyping.

scholarly journals ON THE LOSS OF STABILITY OF A TWO-LAYERED PLATE MADE OF A FUNCTIONAL-GRADIENT MATERIAL WITH A NON-UNIFORM FIELD OF PRE-STRESSES

2019 ◽  
Vol 81 (4) ◽  
pp. 513-520
Author(s):  
V.V. Eremeev
Keyword(s):  
Constitutive Relation ◽  
Linear Instability ◽  
Functionally Graded ◽  
Initial Stresses ◽  
Gradient Material ◽  
Internal Stresses ◽  
Uniform Field ◽  
Loss Of Stability ◽  
Material Inhomogeneity ◽  
Functional Gradient Material

In the framework of three-dimensional nonlinear elasticity we consider linear instability of a composite plate made of functionally graded material and having initial stresses. The plae consists of two layers which were obtained as a result of flattening of an annual sector of an elastic cylinder. This deformation results in appearance of internal stresses. Thus, the plate becomes initially stressed. The initial stresses depend on the thickness coordinate, so we get inhomogeneous stress field. We have two types of inhomogeneities, the first is the inhomogeneity of the initial stresses whereas the second is the material inhomogeneity.We use the incompressible neo-Hookean material model as a constitutive relation. Despite of relatively simple form this model describes properly severe deformations of some rubber-like materials. For incompressible materials the flattening constitutes one of the so-called universal deformations, that is such deformation which is independent on the choice of constitutive relation. The material inhomogeneity is described through a dependence of the shear modulus on the thickness coordinate. Such inhomogeneity could be related to the manufacturing of the material or to further treatment. The stability was analysed using the linearization approach. We superimpose infinitesimal deformations on the finite initial one. The linearized boundary-value problem was derived and its nontrivial solutions were obtained. The solution was obtained in series of trigonometric functions. This helps to automatically satisfy a part of boundary conditions. We consider the influence of the inhomogeneity and initial stresses. We show that the initial stresses may significantly change critical deformations. For example, the loss of stability is possible due to initial stresses only.

scholarly journals Optimized Synthesis Temperature and Time to Obtain Crystalline Carbon Nitride with Enhanced Photocatalytic Activity for Phenol Degradation

2020 ◽  
Vol 20 (6) ◽  
pp. 1392
Author(s):  
Leny Yuliati ◽  
Mohd Hayrie Mohd Hatta ◽  
Siew Ling Lee ◽  
Hendrik Oktendy Lintang
Keyword(s):  
Photocatalytic Activity ◽  
Specific Surface ◽  
Band Gap ◽  
Surface Area ◽  
Carbon Nitride ◽  
Phenol Degradation ◽  
Synthesis Temperature ◽  
Band Gap Energy ◽  
Synthesis Time ◽  
Gap Energy

In this work, the crystalline carbon nitride photocatalysts were synthesized by an ionothermal technique with varied synthesis temperature of 500, 550, and 600 °C, and synthesis time of 2, 4, and 6 h. Fourier transform infrared spectra showed the successful formation of the prepared carbon nitrides from their characteristic vibration peaks. X-ray diffraction patterns suggested that the same phase of poly(triazine imide) and heptazine could be observed, but with different crystallinity. The optical properties showed that different temperatures and synthesis time resulted in the different band gap energy (2.72–3.02 eV) as well as the specific surface area (24–73 m2 g–1). The transmission electron microscopy image revealed that the crystalline carbon nitride has a near-hexagonal prismatic crystallite size of about 50 nm. Analysis by high-performance liquid chromatography showed that the best photocatalytic activity for phenol degradation under solar light simulator was obtained on the crystalline carbon nitride prepared at the 550 °C for 4 h, which would be due to the high crystallinity, suitable low band gap energy (2.82 eV), and large specific surface area (73 m2 g–1). Controlling both the temperature and synthesis time is shown to be important to obtain the best physicochemical properties leading to high activity.

Band gap-tunable potassium doped graphitic carbon nitride with enhanced mineralization ability

2015 ◽  
Vol 44 (3) ◽  
pp. 1084-1092 ◽  
Author(s):  
Shaozheng Hu ◽  
Fayun Li ◽  
Zhiping Fan ◽  
Fei Wang ◽  
Yanfeng Zhao ◽  
...  
Keyword(s):  
Optical Properties ◽  
Photocatalytic Degradation ◽  
Crystal Lattice ◽  
Band Gap ◽  
Carbon Nitride ◽  
Graphitic Carbon ◽  
Graphitic Carbon Nitride ◽  
Structural And Optical Properties

Potassium doped into the g-C3N4 crystal lattice can tune the positions of the CB and VB potentials, influence the structural and optical properties and thus improve the photocatalytic degradation and mineralization ability.

scholarly journals Buckling of a composite bar made of a functional-gradient material with an inhomogeneous pre-stress field

2018 ◽  
Vol 226 ◽  
pp. 01014
Author(s):  
Vadim V. Eremeev ◽  
Denis V. Ivashchenko
Keyword(s):  
Stress Field ◽  
Circular Cylinder ◽  
Nonlinear Elasticity ◽  
Linear Instability ◽  
Initial Stresses ◽  
Gradient Material ◽  
Material Inhomogeneity ◽  
Functional Gradient ◽  
Functional Gradient Material ◽  
Graded Material

Within the 3D nonlinear elasticity we discuss the linear instability of a composite bar made of a functially graded material and having initial stresses. The bar consists of two layers which are inflated for a annular wedge of a circular cylinder. We present the linearized boundary0value problem and obtain its non-trivial solutions. The influence of the material inhomogeneity and the initial stresses are discussed.

Hydrothermal Synthesis of Band Gap-Tunable Oxygen-Doped g-C3N4 with Outstanding “Two-Channel” Photocatalytic H2O2 Production Ability Assisted by Dissolution–Precipitation Process

NANO ◽  
2019 ◽  
Vol 14 (02) ◽  
pp. 1950023 ◽  
Author(s):  
Hui Wang ◽  
Yuanhao Guan ◽  
Shaozheng Hu ◽  
Yanbo Pei ◽  
Wentao Ma ◽  
...  
Keyword(s):  
Band Gap ◽  
Carbon Nitride ◽  
Separation Efficiency ◽  
Electrochemical Impedance ◽  
Band Gap Energy ◽  
Precipitation Process ◽  
H2o2 Production ◽  
Impedance Spectra ◽  
Electrochemical Impedance Spectra ◽  
Photogenerated Electrons

Here, band gap-tunable oxygen-doped graphitic carbon nitride (g-C3N4) with outstanding “two-channel” photocatalytic H2O2 production ability was prepared via hydrothermal treatment assisted by dissolution–precipitation process. XRD, N2 adsorption, UV–Vis, Fourier-transform infrared spectra, SEM, electrochemical impedance spectra, XPS and photoluminescence were used to characterize the obtained catalysts. The photocatalytic H2O2 production ability of as-prepared catalyst was investigated. The results show that oxygen doping not only changes the morphology of catalyst, decreases the band gap energy and promotes the separation efficiency of photogenerated electrons and holes, but also tunes the CB and VB potentials. As-prepared oxygen-doped g-C3N4 displays a H2O2 concentration of 3.8[Formula: see text]mmol[Formula: see text]L[Formula: see text], more than 7.6 times higher than that of neat g-C3N4. Because of the shift of CB and VB potentials, not only the CB electrons of oxygen-doped g-C3N4 reduce O2 to form H2O2, but also the VB holes can oxidize OH− to form [Formula: see text]OH, which subsequently react with each other to form H2O2. Such “two-channel pathway” causes the remarkably promoted H2O2 production ability.

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