The research theme focuses on the pursuit of a sustainable environment via environmental chemistry and environmental chemical engineering. Advance toward Cool Earth and Clean Earth goals with waste reuse, recycling, and management as core concepts. In the goal of Cool Earth, mineral carbonation technology with the use of industrial wastes has been developed for CO2 sequestration and utilization. In the goal of Clean Earth, the recycled or synthesized material from waste or wastewater is developed and used in many applications. In addition to the above-mentioned research directions, other research topics such as metal recycling of waste materials, wastewater treatment technologies, and circular economy concepts are also being investigated.

• CO2 mineralization from alkaline waste for CO2 capture and utilization. [click]

Mitigation and alleviation of climate change is an urgent issue.  CO2 emissions accounted for approximately 3/4 of GHG emissions is prime target to treat this topic in this century. On the other hand, alkaline waste produced from several industries is severe problem as well. Mineral carbonation of alkaline waste for CO2 utilization is one of promising options.  The CO2 flue gas will be sequestered as stable carbonates and considered for further applications.

• The concept of CO2 capture and utilization: CCU without CO2 purification and pressurization (Ho et al., 2019); Role of mineral carbonation: case study of Taiwan (Ho et al. 2022)

• Direct aqueous carbonation of alkaline wastes under low-energy input: Concrete fines (Ho et al., 2020, 2021), coal fly ash (Ho et al., 2021), and steel slag (Ho et al., 2022).

• Circular indirect carbonation with electrochemical technologies. (Ho et al., 2022)

• Mineral carbonation with seawater (Ho & Iizuka, 2023).

• Metal recycling from waste via hydrometallurgical technology. [click]

Metal circulation from waste is an increasingly important issue at present. Due to limited metal resources and more and more generated waste, such as industrial waste and commercial waste, in order to avoid excessive development of limited resources and negative impact of waste, hydrometallurgical technology is promoted to recycle the metals from waste.

• Valuable metal recycling from Lithium ion batteries (LIBs) via hydrometallurgical technology. (Chen & Ho, 2018a, 2018b, Chen et al., 2018) 

• Tantalum Recovery from Epoxy-Coated Solid Electrolyte Tantalum Capacitors. (Chen et al., 2019) 

• Waste material recycling and utilization for the circular economy.

To achieve an actual sustainable society, the circular economy should be developed. The waste materials are processed to be recycled and used for several ways and the comprehensive concept of circular economy based on environmental, material and chemical engineering design approach is important. 

• Waste LIBs treatment.  (National patents: Chen et al., 2018a, 2018b, 2020)

• Chemical recycling and use of concrete waste. (Ho et al., 2021)

• Concept of cement and concrete industries for carbon recycling and mineral carbon capture and utilization. (Izumi et al., 2021)

• Wastewater treatment.

• Removal of toxic elements: arsenic, fluoride (Iizuka et al., 2022), iron, zinc.

• Development of alternative materials derived from wastes: concrete sludge-derived materials (Iizuka et al., 2022), concrete fines (Ho et al.,2023)

• Electrochemical methods. (Iizuk et al., 2023)