Hui Tong Chua

Microfluidic size selective growth of palladium nano-particles on carbon nano-onions

Size selective growth of palladium nano-particles 2-7 nm in diameter on the surface of carbon nano-onions (CNOs) (derived from catalytic cracking of methane) in water involves pretreating the CNOs with p-phosphonic acid calix[8]arene then H(2)PdCl(4) followed by dynamic thin film processing under hydrogen in a vortex fluidic device.

Shear flow assisted decoration of carbon nano-onions with platinum nanoparticles

Aqueous based controlled decoration of platinum nanoparticles on plasma treated carbon nano-onions (CNOs) occurs within the shear flow generated by a vortex fluidic device (VFD), using ascorbic acid as the reducing agent, with the electrocatalytic potential of the resulting Pt-NPs@CNOs nano-composites demonstrated.

High-yield synthesis of silicon carbide nanowires by solar and lamp ablation

We report a reasonably high yield (~50%) synthesis of silicon carbide (SiC) nanowires from silicon oxides and carbon in vacuum, by novel solar and lamp photothermal ablation methods that obviate the need for catalysis, and allow relatively short reaction times (~10 min) in a nominally one-step process that does not involve toxic reagents. The one-dimensional core/shell β-SiC/SiOx nanostructures-characterized by SEM, TEM, HRTEM, SAED, XRD and EDS-are typically several microns long, with core and outer diameters of about 10 and 30 nm, respectively. HRTEM revealed additional distinctive nanoscale structures that also shed light on the formation pathways.

Generating Hydrogen Gas from Methane with Carbon Captured as Pure Spheroidal Nanomaterials

Energy production by using hydrogen gas as a feedstock is considered to be one of the keys to creating clean energy, with the proviso that the gas is generated in a sustainable way with no emissions. A simple, self-sustaining process generating hydrogen gas from methane using inexpensive stainless steel wire-mesh catalysts at elevated temperatures (800 °C) is reported. A theoretical analysis of the production of electricity by this process revealed peak chain energy efficiencies up to 21% (emission free) when using a percentage of the produced hydrogen (approximately 40% of purified yield) as the heat source. In addition, a practical method has been developed to purify the carbon byproduct, affording essentially pure highly graphitic spheroidal carbon for advanced materials applications.

Methane desorption and adsorption measurements on activated carbon in 281–343 K and pressures to 1.2 MPa

The desorption characteristics of methane from a Maxsorb II specimen of activated carbon were measured over the temperature range of 281–343xa0K and at pressures up to 1.2xa0MPa. The technique of measuring the dead volume in the measurement system using helium calibration has also been perfected. The desorption data were fitted to two isotherm models proposed by Tóth and Dubinin–Astakhov with an accuracy better than 0.004xa0gxa0g−1. The data are compared with those from adsorption and correlations are developed by combining the adsorption and desorption data. The Henry’s law coefficients and their relations with extrapolated isosteric heat of adsorption at saturation are analyzed.

Facile synthesis of electrochemically active Pt nanoparticle decorated carbon nano onions

Well dispersed platinum nanoparticles 1–5 nm (average 2 nm) in diameter on carbon nano onions (CNOs) are accessible using a simple and scalable one-step batch method. This technique involves pre-treatment of acid digested CNOs with H2PtCl6 prior to reduction using hydrogen at ambient conditions, with the composite material being electrochemically active. The effect of different Pt loading, surface treatment, and the processing temperature on the dispersion of platinum nanoparticles on the CNOs has been studied in detail.

Deep geothermal: The ‘Moon Landing’ mission in the unconventional energy and minerals space

Deep geothermal from the hot crystalline basement has remained an unsolved frontier for the geothermal industry for the past 30 years. This poses the challenge for developing a new unconventional geomechanics approach to stimulate such reservoirs. While a number of new unconventional brittle techniques are still available to improve stimulation on short time scales, the astonishing richness of failure modes of longer time scales in hot rocks has so far been overlooked. These failure modes represent a series of microscopic processes: brittle microfracturing prevails at low temperatures and fairly high deviatoric stresses, while upon increasing temperature and decreasing applied stress or longer time scales, the failure modes switch to transgranular and intergranular creep fractures. Accordingly, fluids play an active role and create their own pathways through facilitating shear localization by a process of time-dependent dissolution and precipitation creep, rather than being a passive constituent by simply following brittle fractures that are generated inside a shear zone caused by other localization mechanisms. We lay out a new theoretical approach for the design of new strategies to utilize, enhance and maintain the natural permeability in the deeper and hotter domain of geothermal reservoirs. The advantage of the approach is that, rather than engineering an entirely new EGS reservoir, we acknowledge a suite of creep-assisted geological processes that are driven by the current tectonic stress field. Such processes are particularly supported by higher temperatures potentially allowing in the future to target commercially viable combinations of temperatures and flow rates.

Entropic Bounds for Multi-Scale and Multi-Physics Coupling in Earth Sciences

The ability to understand and predict how thermal, hydrological,mechanical and chemical (THMC) processes interact is fundamental to many research initiatives and industrial applications. We present (1) a new Thermal– Hydrological–Mechanical–Chemical (THMC) coupling formulation, based on non-equilibrium thermodynamics; (2) show how THMC feedback is incorporated in the thermodynamic approach; (3) suggest a unifying thermodynamic framework for multi-scaling; and (4) formulate a new rationale for assessing upper and lower bounds of dissipation for THMC processes. The technique is based on deducing time and length scales suitable for separating processes using a macroscopic finite time thermodynamic approach. We show that if the time and length scales are suitably chosen, the calculation of entropic bounds can be used to describe three different types of material and process uncertainties: geometric uncertainties,stemming from the microstructure; process uncertainty, stemming from the correct derivation of the constitutive behavior; and uncertainties in time evolution, stemming from the path dependence of the time integration of the irreversible entropy production. Although the approach is specifically formulated here for THMC coupling we suggest that it has a much broader applicability. In a general sense it consists of finding the entropic bounds of the dissipation defined by the product of thermodynamic force times thermodynamic flux which in material sciences corresponds to generalized stress and generalized strain rates, respectively.

Methane Catalytic Cracking to Make COx Free Hydrogen and Carbons (Nanotubes, Microfibers, Microballs)

The catalytic cracking of methane to produce COx free hydrogen and a spectrum of advanced carbon nano materials was studied. Over several genres of catalysts by cracking of undiluted methane we produced hydrogen and highly graphitic carbon nanotubes (single-, thin- and multi-walled), straight microfibers, nano onions over the solid oxides solution, perovskite structured mixed oxides and mesoporous supported catalysts. The influences of reaction temperature on the methane conversion over various catalysts were investigated. The yields of carbon materials were monitored during the cracking running and the results indicated that these series of catalysts are promising for the commercialization of carbon nanotubes, microfibers and microballs.

Waste Heat Performance Ratio

While the multi-effect distillation desalination industry has made definite strides in terms of improving efficiency, the potential of low-grade heat sources and renewable energies remain overlooked. Although the basic principle remains the same, the nature of sensible heat sources requires different optimization approaches than conventional steam-driven systems. In this chapter we hold that the conventional performance measure is incongruent with such applications and posit a new benchmark.