Search Results (15)

The efficiency of CO₂ photoreduction is often limited by the low reactivity of CO₂ molecules and the rapid recombination of photogenerated charge carriers in most of the photocatalysts developed so far. In this study, we report a newly developed p-type Bi₂Te₃/SrTiO₃ (pBT/STO) nanocomposite for efficient CO₂ photoreduction. Upon light irradiation, the thermoelectric pBT with a strong light absorption capacity generates the photothermal effect favoring the activation of CO₂ molecules. Meanwhile, a temperature gradient formed in pBT induces a thermoelectric field via the Seebeck effect, which promotes the charge carriers’ separation/transfer. In addition, the excellent electric conductivity and large work function render pBT an efficient cocatalyst for further improving the charge carriers’ separation/transfer. Owing to the synergistic photothermoelectric (PTE) effect on activation of CO₂ molecules and promotion of charge separation/transfer, the efficiency of CO₂ photoreduction over pBT/STO is significantly enhanced. We achieve the highest CO evolution rate of 28.0 μmol·g_cat⁻¹·h⁻¹ over the optimal pBT(3)/STO, which is 12.8 times that of pure STO. This work suggests that a thermoelectric material and a semiconductor can be incorporated into a nanocomposite system for efficient CO₂ reduction via the synergistic photothermoelectric effect on activating the CO₂ molecules and promoting the charge carriers’ separation/transfer. Full article

This work reports the investigations of the electric potential impacts on the mechanical buckling of the piezoelectric nanocomposite doubly curved shallow shells reinforced by functionally gradient graphene platelets (FGGPLs). A four-variable shear deformation shell theory is utilized to describe the components of displacement. The present nanocomposite shells are presumed to be rested on an elastic foundation and subject to electric potential and in-plane compressive loads. These shells are composed of several bonded layers. Each layer is composed of piezoelectric materials strengthened by uniformly distributed GPLs. The Halpin–Tsai model is employed to calculate the Young’s modulus of each layer, whereas Poisson’s ratio, mass density, and piezoelectric coefficients are evaluated based on the mixture rule. The graphene components are graded from one layer to another according to four different piecewise laws. The stability differential equations are deduced based on the principle of virtual work. To test the validity of this work, the current mechanical buckling load is analogized with that available in the literature. Several parametric investigations have been performed to demonstrate the effects of the shell geometry elastic foundation stiffness, GPL volume fraction, and external electric voltage on the mechanical buckling load of the GPLs/piezoelectric nanocomposite doubly curved shallow shells. It is found that the buckling load of GPLs/piezoelectric nanocomposite doubly curved shallow shells without elastic foundations is reduced by increasing the external electric voltage. Moreover, by increasing the elastic foundation stiffness, the shell strength is enhanced, leading to an increase in the critical buckling load. Full article

In this paper, a machine-learning model is utilized to estimate the temperature-dependent moduli of neat, thermally reduced graphene and covalently functionalized graphene/epoxy nanocomposites. In addition, the governed mathematical expressions have been used to solve the buckling problem of beams fabricated from such nanocomposites in the presence of a thermal gradient. In order to do so, an energy-based method including the shear deformable beam hypothesis is used. The beam structure is rested on the Winkler–Pasternak substrate. The reported verifications demonstrate the impressive precision of the presented ML model, as well as the buckling response of the under-study structures. Finally, in the framework of some numerical case studies, the impact of several parameters on the buckling of nanocomposite beams is depicted. The results of this study delineate that temperature has a vital role in the determination of the critical buckling load that the nanocomposite structures can endure. Full article

The activation of carbon dioxide (CO₂) molecules and separation/transfer of photoinduced charge carriers are two crucial factors influencing the efficiency of CO₂ photoreduction. Herein, we report a p-type Bi₂Te₃/commercial TiO₂ (pBT/P25) nanocomposite for enhanced CO₂ photoreduction. Upon light irradiation, a temperature gradient formed in pBT induces the Seebeck effect to build a thermoelectric field, which promotes the charge carriers’ separation/transfer. Additionally, pBT with a strong light absorption capacity generates the photothermal effect favoring the activation of CO₂ molecules. In addition, the excellent electric conductivity and large work function render pBT an efficient cocatalyst for further improving the charge carriers’ separation/transfer. Owing to the synergistic enhancement effect of pBT on the activation of CO₂ molecules and promotion of charge separation/transfer, we achieved the highest CO evolution rate over pBT(2)/P25 of 19.2 μmol·g_cat⁻¹·h⁻¹, which was approximately 5.5 times that of bare P25. This work suggests that a thermoelectric material/semiconductor nanocomposite could be developed as an efficient photo-thermo-electro-chemical conversion system for enhanced CO₂ reduction via promoting the charge carriers’ separation/transfer. Full article

Membrane reactors (MR) with an appropriate catalyst are considered to be an innovative and intensified technology for converting a fuel into the hydrogen-rich gas with the simultaneous recovery of high-quality hydrogen. Characteristics of an asymmetric membrane disk module consisting of a gas-tight nanocomposite functional coating (Ni + Cu/Nd_5.5WO_11.25-δ mixed proton-electron conducting nanocomposite) deposited on a gas-permeable functionally graded substrate has previously been extensively studied at lab-scale using MRs, containing the catalyst in a packed bed and in the form of a monolith. The catalytic monolith consisted of a FeCrAl substrate with a washcoat and an Ni + Ru/Pr_0.35Ce_0.35Zr_0.35O₂ active component. It has been shown that the driving potential for hydrogen permeation across the same membrane in a monolithic catalyst –assisted MR is greater compared to the packed bed catalyst. This paper presents results of the study where a one-dimensional isothermal model was used to interrelate catalytic and permeation phenomena in a MR with ethanol steam reforming over the monolith, operating at atmospheric pressure and in the temperature range of 700–900 °C. The developed mathematical reaction–transport model for the constituent layers of the catalyst-asymmetric membrane assembly together with a Sieverts’ equation for the functional dense layer, taking also into account the effect of boundary layers, was implemented in a COMSOL Multiphysics environment. Good agreement with the experimental data of the lab-scale MR with reasonable parameters values is provided. In numerical experiments, concentration profiles along the reactor axis were obtained, showing the effect of the emerging concentration gradient in the boundary layer adjacent to the membrane. Studies have shown that a MR with a catalytic monolith along with appropriate organization of a stagnant feed flow between the monolith and the membrane surface may enhance production and flux of hydrogen, as well as the efficiency characteristics of the reactor compared to a reactor with packed beds. Full article

Well-defined Zn₂GeO₄/g-C₃N₄ nanocomposites with a band alignment of type-I were prepared by the ultrasound-assisted solvent method, starting from g-C₃N₄ nanosheets and incorporating 0, 10, 20, and 40 wt% of Zn₂GeO₄. In this study, we have investigated in-depth the photoluminescence emission and photocatalytic activity of these nanocomposites. Our experimental results showed that an increased mass ratio of Zn₂GeO₄ to g-C₃N₄ can significantly improve their photoluminescence and photocatalytic responses. Additionally, we have noted that the broadband photoluminescence (PL) emission for these nanocomposites reveals three electronic transitions; the first two well-defined transitions (at ca. 450 nm and 488 nm) can be attributed to π*→ lone pair (LP) and π*→π transitions of g-C₃N₄, while the single shoulder at ca. 532 nm is due to the oxygen vacancy (Vo) as well as the hybridization of 4s and 4p orbital states in the Zn and Ge belonging to Zn₂GeO₄. These experimental findings are also supported by theoretical calculations performed under periodic conditions based on the density functional theory (DFT) fragment. The theoretical findings for these nanocomposites suggest a possible strain-induced increase in the Zn-O bond length, as well as a shortening of the Ge-O bond of both tetrahedral [ZnO₄] and [GeO₄] clusters, respectively. Thus, this disordered structure promotes local polarization and a charge gradient in the Zn₂GeO₄/g-C₃N₄ interface that enable an efficient separation and transfer of the photoexcited charges. Finally, theoretical results show a good correlation with our experimental data. Full article

To improve the structural stiffness, strength and reduce the weight of nanoplate structure, functionally graded (FG) graphene-reinforced nanocomposite (GRNC) laminated plates are exploited in this paper. The bending and buckling behaviors of FG-GRNC laminated nanoplates are investigated by using novel quasi-3D hyperbolic higher order shear deformation plate theory in conjunction with modified continuum nonlocal strain gradient theory, which considered both length and material scale parameters. The modified model of Halpin–Tsai is employed to calculate the effective Young’s modulus of the GRNC plate along the thickness direction, and Poisson’s ratio and mass density are computed by using the rule of mixture. An analytical approach of the Galerkin method is developed to solve governing equilibrium equations of the GRNC nanoplate and obtain closed-form solutions for bending deflection, stress distributions and critical buckling loads. A detailed parametric analysis is carried out to highlight influences of length scale parameter (nonlocal), material scale parameter (gradient), distribution pattern, the GPL weight fraction, thickness stretching, geometry and size of GPLs, geometry of the plate and the total number of layers on the stresses, deformation and critical buckling loads. Some details are studied exclusively for the first time, such as stresses and nonlocality effect. Full article

Reverse electrodialysis (RED) generates power directly by transforming salinity gradient into electrical energy. The ion transport properties of the ion-exchange membranes need to be investigated deeply to improve the limiting efficiencies of the RED. The interaction between “counterions” and “ionic species” in the membrane requires a fundamental understanding of the phase separation process. Here, we report on sulfonated poly(vinylidene fluoride-co-hexafluoropropylene)/graphitic carbon nitride nanocomposites for RED application. We demonstrate that the rearrangement of the hydrophilic and hydrophobic domains in the semicrystalline polymer at a nanoscale level improves ion conduction. The rearrangement of the ionic species in polymer and “the functionalized nanosheet with ionic species” enhances the proton conduction in the hybrid membrane without a change in the structural integrity of the membrane. A detailed discussion has been provided on the membrane nanostructure, chemical configuration, structural robustness, surface morphology, and ion transport properties of the prepared hybrid membrane. Furthermore, the RED device was fabricated by combining synthesized cation exchange membrane with commercially available anion exchange membrane, NEOSEPTA, and a maximum power density of 0.2 W m⁻² was successfully achieved under varying flow rates at the ambient condition. Full article

This work studies the dynamic response of Bernoulli–Euler multilayered polymer functionally graded carbon nanotubes-reinforced composite nano-beams subjected to hygro-thermal environments. The governing equations were derived by employing Hamilton’s principle on the basis of the local/nonlocal stress gradient theory of elasticity (L/NStressG). A Wolfram language code in Mathematica was written to carry out a parametric investigation on the influence of different parameters on their dynamic response, such as the nonlocal parameter, the gradient length parameter, the mixture parameter and the hygro-thermal loadings and the total volume fraction of CNTs for different functionally graded distribution schemes. It is shown how the proposed approach is able to capture the dynamic behavior of multilayered polymer FG-CNTRC nano-beams under hygro-thermal environments. Full article

This work aims at analyzing elastic wave characteristics in a polymeric nanocomposite curved beam reinforced by graphene nanoplatelets (GNPs). GNPs are adopted as a nanofiller inside the matrix to enhance the effective properties, which are approximated through Halpin-Tasi model and a modified rule of mixture. A higher-order shear deformation theory accounting for thickness stretching and the general strain gradient model to have both nonlocality and strain gradient size-dependency phenomena are adopted to model the nanobeam. A virtual work of Hamilton statement is utilized to get the governing motion equations and is solved in conjunction with the harmonic solution procedure. A comparative study shows the effects of small-scale coefficients, opening angle, weight fraction, the total number of layers in GNPs, and wave numbers on the propagation of waves in reinforced nanocomposite curved beams. This work is also developed for two different distribution of GNPs in a polymeric matrix, namely uniformly distribution and functionally graded one. Full article

With their hierarchical architectures incorporating gradients in composition, porosity, and orientation, natural materials have evolved optimized balance of mechanical properties. Deciphered from the structure of bamboo, we prepared cellular solids with convex and/or concave porosity gradient and investigated their static mechanical and impact properties. Non-monotonous porosity dependences of tensile, crush, and impact strength were related to the shape of porosity gradient rather than to the properties of the wall material alone. Our results provide experimental evidence, that novel mechanically robust low density additively fabricated cellular nano-composites with convex porosity gradient satisfy the structural requirements of lightweight engineering parts. Moreover, novel functions, such as reduced flammability or electrical conductivity, can easily be introduced by selecting the type and spatial organization of nanoparticles and cellular structure of the cellular micro-particles (CMPs). Full article

A novel functionally graded (FG) polymer-based nanocomposite reinforced by graphene nanoplatelets is proposed based on a new distribution law, which is constructed by the error function and contains a gradient index. The variation of the gradient index can result in a continuous variation of the weight fraction of graphene nanoplatelets (GPLs), which forms a sandwich structure with graded mechanical properties. The modified Halpin–Tsai micromechanics model is used to evaluate the effective Young’s modulus of the novel functionally graded graphene nanoplatelets reinforced composites (FG-GPLRCs). The bending and elastic vibration behaviors of the novel nanocomposite beams are investigated. An improved third order shear deformation theory (TSDT), which is proven to have a higher accuracy, is implemented to derive the governing equations related to the bending and vibrations. The Chebyshev–Ritz method is applied to describe various boundary conditions of the beams. The bending displacement, stress state, and vibration frequency of the proposed FG polymer-based nanocomposite beams under uniformly distributed loads are provided in detail. The numerical results show that the proposed distributions of GPL nanofillers can lead to a more effective pattern of improving the mechanical properties of GPL-reinforced composites than the common ones. Full article

Although new drug delivery systems have been intensely developed in the past decade, no significant increase in the efficiency of drug delivery by nanostructure carriers has been achieved. The reasons are the lack of information about acute toxicity, the influence of the submicron size of the carrier and difficulties with the study of biodistribution in vivo. Here we propose, for the first time in vivo, new nanocomposite submicron carriers made of bovine serum albumin (BSA) and tannic acid (TA) and containing magnetite nanoparticles with sufficient content for navigation in a magnetic field gradient on mice. We examined the efficacy of these submicron carriers as a delivery vehicle in combination with magnetite nanoparticles which were systemically administered intravenously. In addition, the systemic toxicity of this carrier for intravenous administration was explicitly studied. The results showed that (BSA/TA) carriers in the given doses were hemocompatible and didn’t cause any adverse effect on the respiratory system, kidney or liver functions. A combination of gradient-magnetic-field controllable biodistribution of submicron carriers with fluorescence tomography/MRI imaging in vivo provides a new opportunity to improve drug delivery efficiency. Full article

Quantum-mechanical calculations are applied to examine magnetic and electronic properties of phases appearing in binary Fe-Al-based nanocomposites. The calculations are carried out using the Vienna Ab-initio Simulation Package which implements density functional theory and generalized gradient approximation. The focus is on a disordered solid solution with 18.75 at. % Al in body-centered-cubic ferromagnetic iron, so-called $\alpha$ -phase, and an ordered intermetallic compound Fe ${}_3$ Al with the D0 ${}_3$ structure. In order to reveal the impact of the actual atomic distribution in the disordered Fe-Al $\alpha$ -phase three different special quasi-random structures with or without the 1st and/or 2nd nearest-neighbor Al-Al pairs are used. According to our calculations, energy decreases when eliminating the 1st and 2nd nearest neighbor Al-Al pairs. On the other hand, the local magnetic moments of the Fe atoms decrease with Al concentration in the 1st coordination sphere and increase if the concentration of Al atoms increases in the 2nd one. Furthermore, when simulating Fe-Al/Fe ${}_3$ Al nanocomposites (superlattices), changes of local magnetic moments of the Fe atoms up to 0.5 ${\mathsf{\mu }}_{\mathrm{B}}$ are predicted. These changes very sensitively depend on both the distribution of atoms and the crystallographic orientation of the interfaces. Full article

Magnetically-actuated functional gradient nanocomposites can be locally modulated to generate unprecedented mechanical gradients that can be applied to various interfaces and surfaces through following the design principles of natural biological materials. However, a key question is how to modulate the concentration of magnetic particles using an external magnetic field. Here, we propose a model to obtain the gradient concentration distribution of magnetic particles and mechanical gradients. The results show that three states exist when the magnetic force changes in the z direction, including the unchanging state, the stable gradient state, and the over-accumulation state, which are consistent with experiment results. If both radial and axial magnetic forces are present, the inhomogeneity of magnetic–particle distribution in two dimensions was found to break the functional gradient. Furthermore, the size effects of a functional gradient sample were studied, which indicated that adjusting the magnetic force and diffusion constant would enable larger nanocomposites samples to generate functional gradients. Full article