Jason Tam

Recent Advances in Superhydrophobic Electrodeposits

In this review, we present an extensive summary of research on superhydrophobic electrodeposits reported in the literature over the past decade. As a synthesis technique, electrodeposition is a simple and scalable process to produce non-wetting metal surfaces. There are three main categories of superhydrophobic surfaces made by electrodeposition: (i) electrodeposits that are inherently non-wetting due to hierarchical roughness generated from the process; (ii) electrodeposits with plated surface roughness that are further modified with low surface energy material; (iii) composite electrodeposits with co-deposited inert and hydrophobic particles. A recently developed strategy to improve the durability during the application of superhydrophobic electrodeposits by controlling the microstructure of the metal matrix and the co-deposition of hydrophobic ceramic particles will also be addressed.

Technospheric Mining of Rare Earth Elements from Bauxite Residue (Red Mud): Process Optimization, Kinetic Investigation, and Microwave Pretreatment

Some rare earth elements (REEs) are classified under critical materials, i.e., essential in use and subject to supply risk, due to their increasing demand, monopolistic supply, and environmentally unsustainable and expensive mining practices. To tackle the REE supply challenge, new initiatives have been started focusing on their extraction from alternative secondary resources. This study puts the emphasis on technospheric mining of REEs from bauxite residue (red mud) produced by the aluminum industry. Characterization results showed the bauxite residue sample contains about 0.03 wt% REEs. Systematic leaching experiments showed that concentrated HNO3 is the most effective lixiviant. However, because of the process complexities, H2SO4 was selected as the lixiviant. To further enhance the leaching efficiency, a novel process based on microwave pretreatment was employed. Results indicated that microwave pretreatment creates cracks and pores in the particles, enabling the lixiviant to diffuse further into the particles, bringing more REEs into solution, yielding of 64.2% and 78.7% for Sc and Nd, respectively, which are higher than the maximum obtained when HNO3 was used. This novel process of “H2SO4 leaching-coupled with-microwave pretreatment” proves to be a promising technique that can help realize the technological potential of REE recovery from secondary resources, particularly bauxite residue.

Crystallographic orientation–surface energy–wetting property relationships of rare earth oxides

Controlling the wetting property of ceramics, which is characterized by their water contact angles (WCAs), is of great interest because of their better thermal and chemical robustness compared with polymer materials. Among many ceramics, rare earth oxides (REOs) have attracted attention because of their high WCA (∼115°). Although several non-wetting mechanisms of REOs have been proposed thus far, the intrinsic mechanism has not been clarified yet due to the lack of information on crystallographic orientation–surface energy (SE)–WCA relationships. Here we report the WCA of (001), (110), and (111) oriented REO epitaxial films, which have different surface energies. We found that the WCA of fresh REO epitaxial film surfaces, which were prepared using a pulsed laser deposition technique, strongly depends on the crystallographic orientations, WCA(111) > WCA(110) > WCA(001), which reflects the differences in surface energy; SE(111) < SE(110) < SE(001). Moreover, we found that the WCA on REOs increases rapidly and converges to about 80° upon exposure to ambient air, regardless of the crystallographic orientation, likely due to surface adsorption of airborne carbon species. The present finding of ‘There is a strong correlation between the crystallographic orientation, wetting property and the surface energy’ is of great importance for the understanding of the wetting properties of ceramics.

Microwave Treatment for Extraction of Rare Earth Elements from Phosphogypsum

Many advanced technologies in modern society require the use of rare earth elements (REEs). Since these technologies are dominating the world, the demand for REEs is increasing fast. Therefore, finding new sources for them is highly of interest. One of the secondary sources for REEs is phosphogypsum (PG) that is a by-product generated by phosphoric acid production. This research builds upon our previous studies investigating the hydrometallurgical recovery of REEs from PG. Here, we investigate the effect of microwaving the PG sample before leaching in acid. Microwave radiation results in the dielectric heating of water molecules in the PG crystals and vaporization, causing the formation of breaks and pores in these particles as the vapor escapes. The lixivant would then be able to penetrate and diffuse further into the PG particles, bringing more REEs into solution. Our results show that REEs leaching efficiency increases when microwave treatment is used.

Multifunctional iron oxide–carbon hybrid microrods

In this work, iron oxide microrods (MRs) with different crystal phases were successfully fabricated by a facile solvothermal method and sequential annealing processes. It was found that the carbon content remained in the structure when annealing at low temperature (150 °C). The carbon in the MRs contributed to the higher dye adsorption and drug loading capabilities of the MRs. The Fe3O4–C sample showed superior adsorption for both a cationic dye (methylene blue) and an anionic dye (methyl orange) with an equilibrium adsorption capability of 11.7 mg g−1 and 20.8 mg g−1, respectively. When applied as a drug carrier for a tissue plasminogen activator, the mass loading ratio of the MRs was as high as 12.9% for chemical loading and 7.8% for physical loading. With the high dye adsorption/drug loading ratio, such magnetic structures show promise for use in water treatment and advanced medical applications.