Towards the Continuous Hydrothermal Synthesis of ZnO@Mg2Al-CO3 Core-Shell Composite Nanomaterials

Abstract

Core-shell Zinc Oxide/Layered Double Hydroxide (ZnO@LDH) composite nanomaterials have been produced by a one-step continuous hydrothermal synthesis process, in an attempt to further enhance the application potential of layered double hydroxide (LDH) nanomaterials. The synthesis involves two hydrothermal reactors in series with the first producing a ZnO core and the second producing the Mg2Al-CO3 shell. Crystal domain length of single phase ZnO and composite ZnO was 25 nm and 42 nm, respectively. The ZnO@LDH composite had a specific surface area of 76 m2 g−1, which was larger than ZnO or Mg2Al-CO3 when produced separately (53 m2 g−1 and 58 m2 g−1, respectively). The increased specific surface area is attributed to the structural arrangement of the Mg2Al-CO3 in the composite. Platelets are envisaged to nucleate on the core and grow outwards, thus reducing the face–face stacking that occurs in conventional Mg2Al-CO3 synthesis. The Mg/Al ratio in the single phase LDH was close to the theoretical ratio of 2, but the Mg/Al ratio in the composite was 1.27 due to the formation of Zn2Al-CO3 LDH from residual Zn2+ ions. NaOH concentration was also found to influence Mg/Al ratio, with lower NaOH resulting in a lower Mg/Al ratio. NaOH concentration also affected morphology and specific surface area, with reduced NaOH content in the second reaction stage causing a dramatic increase in specific surface area (> 250 m2 g−1). The formation of a core-shell composite material was achieved through continuous synthesis; however, the final product was not entirely ZnO@Mg2Al-CO3. The product contained a mixture of ZnO, Mg2Al-CO3, Zn2Al-CO3, and the composite material. Whilst further optimisation is required in order to remove other crystalline impurities from the synthesis, this research acts as a stepping stone towards the formation of composite materials via a one-step continuous synthesis.

Green Synthesis of Selenium and Tellurium Nanoparticles: Current Trends, Biological Properties and Biomedical Applications

“…The quantity of engineered nanoparticles (NPs) is expected to increase significantly in the years to come as they receive growing global attention due to their attractive properties, multifunctionalities, unique characteristics, and innovative applications in different industrial and scientific domains [2][3][4][5][6]. Several physical and chemical methods have been extensively explored to fabricate NPs, such as laser ablation [7,8], coprecipitation [9,10], hydrothermal route [11,12], solvothermal route [13,14], sol-gel process [15,16], polyol process [17,18], electrochemical methods [19,20], sonochemistry [21,22], and microwaveassisted methods [23,24]. However, the use of toxic chemicals and/or the generation of harmful byproducts limit their application in clinical fields.…”

Ecological synthesis of nickel–zinc–aluminium layered double hydroxides (Ni–Zn–Al LDH) in flow infrared radiated agitated tubular reactor (flow-IR-ATR)

“…Clark et al used a flow process to obtain LDH in a hydrothermal reactor. The authors obtained ZnO combined with Mg 2 AlCO 3 LDH with a yield of 3.6 dm 3 /h [17].…”