As a key to realize the chemical looping air separation (CLAS) process, CuO is a good oxygen carrier candidate because of its high oxygen transport capacity and excellent thermodynamic characteristics. However, it is hampered by easy deactivation during redox cycles. In this work, a Cu−Zr oxygen carrier is developed via a metal−organic framework (MOF) self-templated method to realize high redox reactivity and favorable thermal stability for the CLAS process. The physicochemistry property and reduction kinetics are investigated through isothermal redox cycles, material characterizations, and reduction kinetic modeling. Compared to the coprecipitated oxygen carrier (Copr.), the MOF-derived oxygen carrier (MOF-D) obtains a 35% faster average reaction rate at the temperature interval of 800−900 °C, especially a 60% reduction rate increase at 850 °C. This enhanced reaction rate is mainly ascribed to the lower intrinsic activation energy (126.3 kJ•mol −1 for MOF-D vs 157.3 kJ•mol −1 for Copr.) rather than the amount of active oxygen species. The oxygen-releasing mechanisms for the MOF-derived and coprecipitated oxygen carriers follow the nucleation and nuclei growth model with a transition of one-dimensional growth to two-dimensional nucleation at two temperature ranges (800−825 and 850−900 °C). This study offers a new route to develop an efficient oxygen carrier for the CLAS process.

The characteristics of the materials used in early buildings in China have led to a large proportion of discarded red bricks among the construction waste generated by demolishing abandoned buildings. The application of red brick aggregate with a particle size ≤5 mm and red brick powder with particle size 0.125~0.75 mm (referred to as recycled brick powder) was studied in this study after the crushing of waste red brick in road structures. The research results will provide a theoretical basis for the whole-grain recycling of waste red brick aggregate. The aggregate of red brick with a particle size smaller than 2 mm was mixed with different amounts of cement soil and fiber to prepare a cement-stable binder for the sub-base material. The recycled brick powder of 0.125~0.75 mm was used to replace the quartz sand with different substitution rates. As pavement materials, different amounts of fiber were used to prepare fiber-reinforced recycled-brick-powder cementitious composites. The optimal mixing ratio of the two materials was evaluated from the mechanical properties. The results showed that the optimal mixing ratio of the cement-stable binder was as follows: waste-red-brick-aggregate content was 50%, cement content was 4%, and fiber content was 0.2%. The optimum ratio of fiber-reinforced recycled-brick-powder cementitious composites was determined to be as follows: the replacement rate of recycled brick powder is 25%, and the content of PVA fiber is 1%. The regression analysis was used to fit the equations between the fiber content and the 7d unconfined compressive strength and the tensile strength of the cement-stabilized binder for different red-brick-aggregate admixtures at 4% cement content. A scanning electron microscope was used to observe the failure modes of the fiber. The influence of failure modes, such as pulling out, fracture, and plastic deformation, on the mechanical properties was expounded.

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