ABSTRACT
In this paper, we study artificial opals as a promising material platform for terahertz (THz) optics. Materials were synthesized using self-assembly of porous SiO2 nanoparticles and annealing at different temperatures to further tune their optical properties. Two distinct approaches for the fabrication of bulk THz optics from these novel materials were considered. First, THz cylindrical lenses of identical geometry but different refractive indices and focal lengths were produced using standard mechanical processing of opals, in order to highlight their compatibility with conventional technologies of bulk optics fabrication. Second, a THz axicone was made via direct sedimentation of aqueous colloidal suspension of SiO2 nanoparticles in the mold of geometry inverse to that of a desired optical shape, followed by annealing and polishing. The second approach has an advantage of being considerably less labor intensive, while capable of obtaining optical elements of complex geometries. Thus fabricated bulk THz optical elements were studied experimentally using continuous-wave THz imaging, and the results were compared with 2D and 3D numerical predictions based on the finite-difference time-domain and finite-element frequency-domain methods. Our findings highlight technological robustness of the developed THz optical material platform and, thus, open the door for creating a variety of bulk THz optical elements of complex shapes and widely-tunable optical performance.
ABSTRACT
Researchers have focused their attention on environment-friendly adsorption materials to solve the energy shortage problem and guarantee the sustainable development of human society. For that matter, pomelo peel, which is a low-cost and universal biomass waste, can be used as an effective carbon source with a large specific surface area. In this paper, a novel composite adsorbent, consisting of a three-dimensional honeycomb-like porous carbon material and MnO2 nanowires (HLPC/MnO2), has been successfully synthesized using alkaline activation followed by a carbonization procedure at high temperatures and in situ growth of MnO2 nanowires. The as-prepared composite was characterized using XRD, FT-IR, XPS, SEM, TEM and BET. The surface area of the HLPC reached 1147.41 m2 g-1. The results of the adsorption experiments show that the highest adsorption value of the HLPC/MnO2 composite was 238.09 mg-U per g-adsorbent at pH 5. The thermodynamic and kinetic parameters demonstrate that the removal process correlates well with a Langmuir adsorption isotherm model and pseudo-second-order kinetic model. Thus, the HLPC/MnO2 composite is an excellent adsorbent for removing uranium(vi) ions from aqueous solutions.
ABSTRACT
A novel rod-like, dual-shell structural adsorbent of polypyrrole/cobalt ferrite/multiwalled carbon nanotubes (PPy/CoFe2O4/MWCNTs) was successfully synthesized by a hydrothermal method, which could easily separate uranium(vi) ions with an external magnetic field. The structure and morphology of PPy/CoFe2O4/MWCNTs were characterized by VSM, XRD, XPS TEM and FT-IR. The results proved that the dual-shell structure was obtained in which a shell of cobalt ferrite and polypyrrole formed around the MWCNTs core. In batch adsorption experiments, including pH, equilibrium time and temperature on uranium adsorption, were investigated. The main results show that the PPy/CoFe2O4/MWCNTs composite has a higher affinity towards the uptake of uranium(vi) from aqueous solutions. The highest adsorption capacity reached was 148.8 mg U per g at pH 7. A kinetic analysis showed that the adsorption process was best described by a pseudo-second-order kinetic model. The uranium sorption equilibrium data correlated well with the Langmuir sorption isotherm model in the thermodynamic analysis. 0.5 mol per L NaHCO3 was used as the desorbent and good adsorption properties were shown after the desorption procedures were repeated three times. Thus, PPy/CoFe2O4/MWCNTs was an excellent adsorbent for removing uranium(vi) ions.
ABSTRACT
The efficient development of selective materials for the recovery of uranium from nuclear waste and seawater is necessary for their potential application in nuclear fuel and the mitigation of nuclear pollution. In this work, a graphene oxide/amidoxime hydrogel (AGH) exhibits a promising adsorption performance for uranium from various aqueous solutions, including simulated seawater. We show high adsorption capacities (Qm = 398.4 mg g(-1)) and high % removals at ppm or ppb levels in aqueous solutions for uranium species. In the presence of high concentrations of competitive ions such as Mg(2+), Ca(2+), Ba(2+) and Sr(2+), AGH displays an enhanced selectivity for uranium. For low uranium concentrations in simulated seawater, AGH binds uranium efficiently and selectively. The results presented here reveal that the AGH is a potential adsorbent for remediating nuclear industrial effluent and adsorbing uranium from seawater.
ABSTRACT
Carbon inverse opals (C-IOP) were noncovalently modified with tetraphenylmethylenediphospine dioxide (TPMDPDO). The distribution of TPMDPDO between C-IOP and aqueous HNO3 solutions has been studied. The effect of HNO3 concentration in the aqueous phase and that of the TPMDPDO concentration in the sorbent phase on the adsorption of microquantities of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, U, and Th nitrates from HNO3 solutions by C-IOP modified with TPMDPDO is considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanide(III) adsorption from moderate-concentration HNO3 solutions decreases with increasing element atomic number.
ABSTRACT
The formation of silica nano- and microparticles has been studied during growth by the modified Stöber-Fink-Bohn (SFB) method. It has been experimentally found that the density and fractal structure of particles vary with size as they grow from 70 to 2200 nm. We propose a model of particle structure which is a dense primary particle core and is composed of concentric secondary particle shells terminating in dense primary particle layers.
ABSTRACT
The synthesis, morphology, structural and optical characteristics of SiC/C nanocomposites with an inverse opal lattice have been investigated. The samples were prepared by thermochemical treatment of opal matrices filled with carbon compounds which was followed by silicon dioxide dissolution. The samples were studied by electron microscopy, x-ray diffraction, photoluminescence, IR and Raman scattering spectroscopy. The electron microscopy data revealed a highly porous periodic structure which was a three-dimensional replica of the voids of the initial opal lattice. The hexagonal silicon carbide was found to be non-uniformly distributed throughout the volume, its greater part located in the surface layer up to 50 µm deep. The data of x-ray diffraction, IR and Raman scattering spectroscopy enabled us to assume that the composite had hexagonal diamond fragments. The photoluminescence and optical reflection spectra of the composites have been measured.
