Ratna Balgis

Self-Organized Macroporous Carbon Structure Derived from Phenolic Resin via Spray Pyrolysis for High-Performance Electrocatalyst

The synthesis and evaluation of porous carbon derived from phenolic resin using a fast and facile spray pyrolysis method has been studied for use as a new electrocatalyst support material. By adding polystyrene latex nanoparticles as a template to the phenolic resin precursor, self-organized macroporous carbon structure was first developed. The mass ratio of phenolic resin to PSL at 0.625 gave the optimum porous morphology. Pt nanoparticles (∼20 wt %) were grown on the carbon surface using a standard industrial impregnation method. Well-dispersed Pt nanoparticles of average size 3.91 nm were observed on the surface of porous carbon particles. The high catalytic performance of porous Pt/C electrocatalyst was confirmed by the high mass activity and electrochemically active surface area, which were 450.81 mA mg(-1)-Pt and 81.78 m(2) g(-1)-Pt, respectively. The porous Pt/C catalyst obtains two times higher mass activity than that of the commercial Pt/C catalyst and performs excellent durability under acid conditions.

Aerosol synthesis of self-organized nanostructured hollow and porous carbon particles using a dual polymer system.

A facile method for designing and synthesizing nanostructured carbon particles via ultrasonic spray pyrolysis of a self-organized dual polymer system comprising phenolic resin and charged polystyrene latex is reported. The method produces either hollow carbon particles, whose CO2 adsorption capacity is 3.0 mmol g(-1), or porous carbon particles whose CO2 adsorption capacity is 4.8 mmol g(-1), although the two particle types had similar diameters of about 360 nm. We investigate how the zeta potential of the polystyrene latex particles, and the resulting electrostatic interaction with the negatively charged phenolic resin, influences the particle morphology, pore structure, and CO2 adsorption capacity.

Hollow Silica as an Optically Transparent and Thermally Insulating Polymer Additive

We present an improved synthesis route to hollow silica particles starting from tetramethyl orthosilicate (TMOS) instead of the traditionally used ethyl ester. The silica was first deposited onto polystyrene (PS) particles that were later removed. The here introduced, apparently minor modification in synthesis, however, allowed for a very high purity material. The improved, low density hollow silica particles were successfully implemented into polymer films and permitted maintaining optical transparency while significantly improving the heat barrier properties of the composite. Mechanistic investigations revealed the dominant role of here used methanol as a cosolvent and its role in controlling the hydrolysis rate of the silicic ester, and subsequent formation of hollow silica particles. Systematic experiments using various reaction parameters revealed a transition between regions of inhomogeneous material production at fast hydrolysis rate and reliable silica deposition on the surface of PS as a core-shell structured particle. The shell-thickness was controlled from 6.2 to 17.4 nm by increasing TMOS concentration and the diameter from 95 to 430 nm through use of the different sizes of PS particles. Hollow silica particle with the shell-thickness about 6.2 nm displayed a high light transmittance intensity up to 95% at 680 nm (length of light path ∼ 1 cm). Polyethersulfone (PES)/hollow silica composite films (35 ± 5 μm thick) exhibited a much lower thermal conductivity (0.03 ± 0.005 W m·K(-1)) than pure polymer films. This indicates that the prepared hollow silica is able to be used for cost and energy effective optical devices requiring thermal insulation.

Direct synthesis of carbon quantum dots in aqueous polymer solution: one-pot reaction and preparation of transparent UV-blocking films

Carbon quantum dots (CQDs) were characterized and their synthesis optimized extensively over recent years. It is becoming more and more important to develop synthesis solutions for CQDs applications to allow simple and cheap applications with composite materials. Here, we present a one-pot CQDs reaction in an aqueous polyvinyl alcohol (PVA) solution and the synthesis of transparent UV protection films. The synthesis solution was tuned in a way that transparent UV-protection films cast from unpurified CQDs–PVA solutions could be obtained without the need of yield consuming purification steps. Measuring the impact of varying PVA, branched polyethylene imine (b-PEI), and citric acid (CA) concentrations on the solutions and films UV/Vis transmission and absorbance allowed elucidating important factors influencing the solution to film property transition. Applying CQDs–PVA films on commercially available PET bottle films resulted in high transparency of the composite film in the visible range (>80%) and UV absorption of over 90%. Lastly, our CQDs–PVA film performed stable UV-blocking and did not show any bleaching effects over several days of UV-exposure.

Highly conductive nano-sized Magnéli phases titanium oxide (TiO x )

Despite the strong recent revival of Magnéli phase TiOx as a promising conductive material, synthesis of Magnéli phase TiOx nanoparticles has been a challenge because of the heavy sintering nature of TiO2 at elevated temperatures. We have successfully synthesized chain-structured Magnéli phases TiOx with diameters under 30 nm using a thermal-induced plasma process. The synthesized nanoparticles consisted of a mixture of several Magnéli phases. A post-synthesis heat-treatment was performed to reduce the electrical resistivity without changing the particle morphology. The resistivity of the heat-treated particle was as low as 0.04 Ω.cm, with a specific surface area of 52.9 m2 g−1. The effects of heat-treatment on changes in the crystal structure and their correlation with the electron conductivity are discussed based on transmission electron microscopy images, X-ray diffraction spectra, and X-ray adsorption fine structure spectra. Electrochemical characterization using cyclic voltammetry and potentiodynamic scan shows a remarkable electrochemical stability in a strongly oxidizing environment.

Tunable Synthesis of Mesoporous Silica Particles with Unique Radially Oriented Pore Structures from Tetramethyl Orthosilicate via Oil–Water Emulsion Process

Numerous studies of the synthesis of mesoporous silica (MPS) particles with tailored properties have been published. Among those studies, tetraethyl orthosilicate (TEOS) is commonly used as a silica source, but tetramethyl orthosilicate (TMOS) is rarely used because its reaction is fast and difficult to control. In this study, MPS particles were synthesized via one-step controlled polymerization of styrene and hydrolysis of TMOS, followed by the addition of hexadecyltrimethylammonium bromide (CTAB) and n-octane. The MPS particles obtained from TMOS generally have small inner pores, but the MPS particles obtained in this study had a unique radially oriented structure, a high surface area up to 800 m2 g-1, and large pores, of size 20 nm. The content of styrene in the emulsion system played a key role in increasing pore sizes of the MPS particles. A plausible mechanism for particle formation based on the phase behavior and type of the emulsion system is proposed. For further research, this material is expected to be useful for various applications, such as in drug delivery, filtration, and catalyst supports.

Synthesis of Dual-Size Cellulose–Polyvinylpyrrolidone Nanofiber Composites via One-Step Electrospinning Method for High-Performance Air Filter

Dual-size nanofibers consisting of a random mixture of nano- and submicron-size nanofibers are promising structures for specific applications such as air filters because of their increased specific surface area and low pressure drop. Synthesis of dual-size nanofibers using one-step electrospinning was reported here for the first time. The formation of well-mixed nano- and submicron-size cellulose-polyvinylpyrrolidone nanofiber composites was accomplished utilizing the physical properties of TEMPO-oxidized cellulose nanofibers (i.e., high thixotropy and high magnitude of zeta potential) and tuning the charge of the polymer jet, which influences the formation and shape of Taylor cone, and Coulombic explosion. The dual-size nanofibers were then spun on the surface of a HEPA filter to obtain a multilayer air filter. Aerosol filtration measurements show that this multilayer air filter has an incredibly high performance, shown by the high quality factor (Qf), 0.117 Pa-1, which is 10 times the Qf of commercial HEPA filters.

Synthesis of nitrogen-functionalized macroporous carbon particles via spray pyrolysis of melamine-resin

In this study, we developed the first synthesis of macroporous carbon particles with high nitrogen content from a melamine resin via spray pyrolysis. A dual-polymer precursor consisting of melamine resin and a polystyrene latex (PSL) template was used to control the carbon particle morphology. The pore size and porous structure were adjusted by changing the PSL particle size and the PSL/melamine resin ratio, respectively. A PSL/melamine resin ratio of 1.6 : 1 gave the best morphology. Thermal decomposition and carbonization of the melamine resin were performed for several seconds in a tubular furnace. The nitrogen content of the particles obtained at carbonization temperatures between 600 and 1000 °C ranged from 5.44% to 39.2%. The nitrogen content was approximately two to 10 times higher than those achieved using a hydrothermal route. The thermal decomposition was homogeneous and all reactions were performed in droplets, which acted as a micro-reactor system; therefore, we were able to clarify the mechanisms of melamine resin decomposition and particle structuration.

Enhanced Electrocatalytic Activity of Pt/3D Hierarchical Bimodal Macroporous Carbon Nanospheres

Proton exchange membrane fuel cells require electrocatalysts with a high platinum (Pt) loading, large active surface area, and favorable hydrodynamic profile for practical applications. Here, we report the design of three-dimensional hierarchical bimodal macroporous carbon nanospheres with an interconnected pore system, which are applied as an electrocatalyst support. Carbon-supported Pt (Pt/C) catalysts were prepared by aerosol spray pyrolysis followed by microwave chemical deposition. The hierarchical porous structures not only increased the dispersion of Pt nanoparticles but also improved catalytic performance. A hierarchical bimodal macroporous Pt/C catalyst with a mixture of 30 and 120 nm size pores showed the best performance. The electrochemical surface area and mass activity values of this support were 96 m2 g-1-Pt and 378 mA mg-1-Pt, respectively at a Pt loading of 15 wt %.

Selective Low-Energy Carbon Dioxide Adsorption Using Monodisperse Nitrogen-Rich Hollow Carbon Submicron Spheres

Monodisperse, nitrogen-doped hollow carbon spheres of submicron size were synthesized using hexamethoxymethylmelamine as both a carbon and nitrogen source in a short (1 h) microwave-assisted synthesis. After carbonization at 550 °C, porous carbon spheres with a remarkably high nitrogen content of 37.1% were obtained, which consisting mainly of highly basic pyridinic moieties. The synthesized hollow spheres exhibited high selectivity for carbon dioxide (CO2) over nitrogen and oxygen gases, with a capture capacity up to 1.56 mmol CO2 g-1. The low adsorption enthalpy of the synthesized hollow carbon spheres permits good adsorbent regeneration. Evaluation of the feasibility of scaling up shows their potential for large-scale applications.